Applied Surface Science (v.409, #C)

Influence of surface oxidation on the radiative properties of ZrB2-SiC composites by Ning Li; Pifeng Xing; Cui Li; Peng Wang; Xinxin Jin; Xinghong Zhang (1-7).
The spectral emissivities of ZrB2-20 vol.% SiC composites with various surface components of ZrB2/SiC (ZS1), silica-rich glass (ZS2) and porous zirconia (ZS3) were measured using infrared spectrometer in the wavelength range from 2.5 to 25.0 μm. The relationship between surface oxidation (associated with surface component, thickness of oxide scale, testing temperature as well as roughness) and the radiative properties of ZrB2-SiC composites were investigated systematically. Surface component affected the radiative properties of composites significantly. The total emissivity of ZS1 varied from 0.22 to 0.81 accompanied with surface oxidation in the temperature range 300–900 °C. The emissivity of ZS2 was about 1.5 times as that of ZS3 under the same testing conditions. The oxide scale on specimen surface enhanced the radiative properties especially in terms of short-wave range, and the emissivity in the long-wave range gradually increased with the thickness of oxide scale within a certain range. The influence of testing temperature and surface roughness was also investigated. The testing temperature had a little effect on radiative properties, whereas effect of surface roughness could be negligible.
Keywords: ZrB2-SiC; Emissivity; Radiative properties; Surface oxidation;

Influence of sol concentration on CdO nanostructure with gas sensing application by Jeevitesh K. Rajput; Trilok K. Pathak; Vinod Kumar; L.P. Purohit (8-16).
Display OmittedThe effect of sol concentration has been investigated on the sol-gel derived CdO nanostructures to optimize the optical and electrical properties enhancing gas sensing properties at low temperatures. X-ray diffraction patterns show that 0.5 M CdO film has cubic structure (111) preferred orientation with 34 nm particle size. Scanning electron micrographs indicated concentration dependent surface morphology. The optical band gap energy for highly transparent thin films increases from 1.9 eV to 2.34 eV as molarity was increased from 0.2 M to 1.0 M. The photoluminescence spectra of the samples have a violet to blue emission peak centred at 435 nm. J-V characteristics show that thin film of 0.5 M has conductivity 1.41 × 10−3  S/m. The sensor characteristic such as response curve, sensor response, response time and recovery time were measured for optimized thin film at different operating temperatures. The sensor response was found 20% near room temperature (32 °C) and proportional to temperature. Fastest response time 10 s and recovery time 20 s were observed near room temperature. The resistivity of sensor was found to decrease in presence of gas attribute to more charge carriers with flower like morphology. Our study is encouraging to get faster response by CdO thin films near room temperature.
Keywords: CdO; Thin film; Physical properties; Nitrogen sensing;

Effect of mesoporous structure on the Seebeck coefficient and electrical properties of SrTi0.8Nb0.2O3 by Chang-Sun Park; Min-Hee Hong; Hyung Hee Cho; Hyung-Ho Park (17-21).
Display OmittedThe porosity of mesoporous SrTi0.8Nb0.2O3 (STNO) was controlled by changing the surfactant concentration to investigate the porosity effect on the thermoelectric properties. Mesoporous structure typically induces a large decrease in the carrier mobility and a small increase in the carrier concentration owing to carrier scattering and oxygen vacancies. These changes in the carrier mobility and concentration induce a change in the thermoelectric properties by enhancing the Seebeck coefficient owing to an increase in the electrical resistivity and carrier filtering effect. Brij-S10 surfactant induces a carrier filtering effect in STNO, and so the Seebeck coefficient could be enhanced even with increasing carrier concentration. Because the Seebeck coefficient affects the power factor more strongly than the electrical resistivity does, incorporation of Brij-S10 surfactant into STNO films increases the power factor. The maximum value of the power factor, approximately 2.2 × 10−4  W/mK2 at 200 °C, was obtained at a Brij-S10 molar ratio of 0.075. From this result, we can expect the application of STNO as a thermoelectric material with an enhanced power factor through successful adoption of mesoporous structure.
Keywords: Nb doping; SrTiO3 film; Seebeck coefficient; Electrical properties; Mesoporous structure;

Display OmittedThis paper addresses the impact of electrode contaminations on the interfacial energy level alignment, the molecular conformation, orientation and surface morphology deposited organic film at organic semiconductor/noble metal interfaces by varying of film thickness from sub-monolayer to multilayer, which currently draws significant attention with regard to its application in organic electronics. The UHV clean Ag and unclean Ag were employed as substrate whereas rubrene was used as an organic semiconducting material. The photoelectron spectroscopy (XPS and UPS) was engaged to investigate the evolution of interfacial energetics; polarization dependent near edge x-ray absorption fine structure spectroscopy (NEXAFS) was employed to understand the molecular conformation as well as orientation whereas atomic force microscopy (AFM) was used to investigate the surface morphologies of the films. The adventitious contamination layer was acted as a spacer layer between clean Ag substrate surface and rubrene molecular layer. As a consequence, hole injection barrier height, interface dipole as well as molecular-conformation, molecular-orientation and surface morphology of rubrene thin films were found to depend on the cleanliness of Ag substrate. The results have important inferences about the understanding of the impact of substrate contamination on the energy level alignment, the molecular conformation as well as orientation and surface morphology of deposited rubrene thin film at rubrene/Ag interfaces and are beneficial for the improvement of the device performance.
Keywords: Rubrene/Ag interfaces; Impact of contact contamination; Clean and unclean Ag substrate surface; Energy level alignment; Molecular conformation and orientation; Surface morphology;

Platinum-nickel alloy nanoparticles supported on carbon for 3-pentanone hydrogenation by Lihua Zhu; Tuo Zheng; Changlin Yu; Jinbao Zheng; Zhenbiao Tang; Nuowei Zhang; Qing Shu; Bing H. Chen (29-34).
Display OmittedIn this work, we prepared the Ni/Ni(OH)2/C sample at room temperature by hydrazine hydrate reducing method. The galvanic replacement reaction method was applied to deposit platinum on the Ni/Ni(OH)2 nanoparticles, to prepare the PtNi/Ni(OH)2/C catalyst. The catalyst of platinum-nickel alloy nanoparticles supported on carbon (signed as PtNi/C) was obtained by the thermal treatment of PtNi/Ni(OH)2/C in flowing hydrogen at 300 °C for 2 h. The size, nanostructure, surface properties, Pt and Ni chemical states of the PtNi/C catalyst were analyzed using powder X-ray diffraction (XRD), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM), high-angle annular dark-field scanning TEM (HAADF-STEM) and elemental energy dispersive X-ray spectroscopy (EDS) line scanning, X-ray photoelectron spectroscopy (XPS) and high-sensitivity low-energy ion scattering spectroscopy (HS-LEIS) techniques. The as-synthesized PtNi/C catalyst showed enhanced catalytic performance relative to the Ni/Ni(OH)2/C, Ni/C, Pt/C and PtNi/Ni(OH)2/C catalysts for 3-pentanone hydrogenation due to electron synergistic effect between Pt and Ni species in the PtNi/C catalyst. The PtNi/C catalyst also had exceling stability, with industrial application value.
Keywords: PtNi alloy nanoparticles; 3-pentanone hydrogenation; PtNi/Ni(OH)2/C nanocatalyst; Electron synergistic effect;

Dispersion interactions have key role on the adsorption of different amino acids on the graphene and BN-nanosheet surfaces.Display OmittedThe binding properties of the adsorption of five different classes of amino acids, namely, alanine (Ala), arginine (Arg), asparagine (Asn), histidine (His) and cysteine (Cys) on the surface of the graphene (Gra) and the born-nitride (BN) nano-sheet structures were studied from molecular viewpoint using quantum mechanics methods. Density functional theory (DFT) and DFT-D3 calculations were carried out to investigate the electronic properties and the dispersion interaction of the amino acid/adsorbent complexes.Several parameters affecting the interactions between the amino acids and the adsorbent surfaces such as solvent effect, adsorption energy and separation distance were investigated. Findings show that Arg forms the most stable complexes with the graphene and the BN nano-sheet compare to the other amino acids used in this study. The observed frequency results which were related to the band gap energies were consistent with the above statement.Results exhibit that adsorption of the amino acids on the surface of the BN nano-sheet and the graphene accompanied with the release of the energy. Calculations show that there are no bonded interactions between the amino acids and adsorbent surfaces. The polarity of the BN nano-sheet provides the more affinity towards the amino acids. These results were proved by the quantum chemistry studies.
Keywords: Amino acids; Graphene; Born-nitride nano-sheet; DFT; QTAIM; HOMO-LUMO analysis;

Durable superhydrophobic paper enabled by surface sizing of starch-based composite films by Gang Chen; Penghui Zhu; Yudi Kuang; Yu Liu; Donghan Lin; Congxing Peng; Zhicheng Wen; Zhiqiang Fang (45-51).
Superhydrophobic paper with remarkable durability is of considerable interest for its practical applications. In this study, a scalable, inexpensive, and universal surface sizing technique was implemented to prepare superhydrophobic paper with enhanced durability. A thin layer of starch-based composite, acting as a bio-binder, was first coated onto the paper surface by a sophisticated manufacturing technique called surface sizing, immediately followed by a spray coating of hexamethyl disilazane treated silica nanoparticles (HMDS-SiNPs) dispersed in ethanol on the surface of the wet starch-coated sheet, and the dual layers dried at the same time. Consequently, durable superhydrophobic paper with bi-layer structure was obtained after air drying. The as-prepared superhydrophobic paper not only exhibited a self-cleaning behavior, but also presented an enhanced durability against scratching, bending/deformation, as well as moisture. The universal surface sizing of starch-based composites may pave the way for the up-scaled and cost-effective production of durable superhydrophobic paper.
Keywords: Surface sizing; Cassava starch; Superhydrophobic paper; Silica nanoparticle; Durability;

Display OmittedHighly porous carbon nanoarchitectures (HPCNs) were derived from biomass materials, namely, corn fibers (CF), corn leafs (CL), and corn cobs (CC). We surprisingly found that by a very simple activation process the CF, CL, and CC materials can be transformed into exciting two-dimensional (2D) and three-dimensional (3D) carbon nanoarchitectures with excellent physicochemical properties. FESEM and HRTEM results confirmed a three different carbon forms (such as foams-like carbon, carbon sheets with several holes and cheese-like carbon morphology) of HPCNs. Huge surface area (2394–3475 m2/g) with excellent pore properties of HPCNs was determined by BET analysis. Well condensed graphitic plans of HPCNs were confirmed by XRD, XPS and Raman analyses. As an electrode material, HPCNs demonstrated a maximum specific capacitance (Cs) of 575 F/g in 1.0 M H2SO4 with good stability over 20,000 cycles. The CC-700 °C showed a tremendous Cs of 375 F/g even at 20000th cycles. To the best of our knowledge, this is the highest Cs by the biomass derived activated carbons in aqueous electrolytes. The CC-700 °C exhibited excellent charge-discharge behavior at various current densities (0.5–10 A g−1). Notably, CC-700 °C demonstrated an excellent Cs of 207 F/g at current density of 10 A g−1. An extraordinary change–discharge behavior was noticed at low current density of 0.5 A g−1.
Keywords: Corn; Carbon nanoarchitectures; Electrode materials; Supercapacitor; Cycle stability; Charge–discharge;

Spin selection at organic spinterface by anchoring group by Zhao Zhang; Shuai Qiu; Yuan-yuan Miao; Jun-feng Ren; Chuan-kui Wang; Gui-chao Hu (60-64).
Control of organic interfacial spin polarization is crucial in organic spintronics. Based on ab initio theory, here we proposed a spin selection at organic interface via anchoring group by adsorbing an organic molecule onto Ni(111) surface. The results demonstrate that either a positive or negative interfacial spin polarization may be obtained by choosing different anchoring groups. The orbital analysis via the projected density of states shows that the interfacial spin polarization is sensitive to the hybridization of the outer orbital of the anchoring atom as well as its energy relative to the d orbital of the ferromagnetic atom. The work indicates a feasible way to realize spin selection at the organic spinterface by anchoring group.
Keywords: Organic spinterface; Spin polarization; Anchoring group;

Flotation and adsorption performance of sodium oleate(NaOl)on powellite and fluorapatite were investigated in this work through micro-flotation tests, work of adhesion calculations, molecular dynamics simulation, micro-topography studies and FTIR measurements. The micro-flotation results show a similar flotation behaviors of powellite and fluorapatite under alkaline conditions, but a considerable difference in mineral recoveries in the pH range 2–7, which demonstrates the possibilities for separating powillite from fluorapatite under acidic conditions. The great difference in mineral recovery displays a good accordance with the obvious difference in the work of adhesion of powellite and fluorapatite at NaOl dosage range of 40–80 mg/L, obtained from flotation and contact angle measurements, respectively. The more negative interaction energy (ΔE) between NaOl and powellite/water interface from molecular dynamics simulation reveals a more easily adsorption of NaOl onto powellite than onto fluorapatite, which excellently matches with the results of flotation and work of adhesion. The results of micro-topography study shows that the adsorption of NaOl on powellite is mainly ascribed to the chemisorption of oleate ions with Ca2+ on powellite lattice or the precipitation of calcium dioleate agglomerates on powellite surface when it was in the solution without or with Ca2+, respectively. The FTIR measurements further confirm the chemisorption of oleate ions with Ca2+ active sites on powellite surface.
Keywords: Powellite; Adsorption; Flotation separation; Micro-topography;

Interfacial chemistry and energy band alignment of TiAlO on 4H-SiC determined by X-ray photoelectron spectroscopy by Qian Wang; Xinhong Cheng; Li Zheng; Peiyi Ye; Menglu Li; Lingyan Shen; Jingjie Li; Dongliang Zhang; Ziyue Gu; Yuehui Yu (71-76).
Intermixing of TiO2 with Al2O3 to form TiAlO films on 4H-SiC is expected to simultaneously boost the dielectric constant and achieve sufficient conduction/valence band offsets (CBO/VBO) between dielectrics and 4H-SiC. In this work, a composite TiAlO film rather than TiO2-Al2O3 laminations is deposited on 4H-SiC by plasma enhanced atomic layer deposition (PEALD). X-ray photoelectron spectroscopy (XPS) is performed to systematically analyze the interfacial chemistry and energy band alignment between TiAlO and 4H-SiC. An interfacial layer composed of Ti, Si, O and C forms between TiAlO and 4H-SiC during PEALD process. The VBO and CBO between TiAlO and 4H-SiC are determined to be 1.45 eV and 1.10 eV, respectively, which offer competitive barrier heights (>1 eV) for both electrons and holes and make it suitable for the fabrication of 4H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs).
Keywords: TiAlO; 4H-SiC; Interfacial chemistry; Conduction band offsets; Valance band offsets;

Nitrogen doping on NiO by reactive magnetron sputtering: A new pathway to dynamically tune the optical and electrical properties by Julien Keraudy; Axel Ferrec; Mireille Richard-Plouet; Jonathan Hamon; Antoine Goullet; Pierre-Yves Jouan (77-84).
Display OmittedN-doped nickel oxide (NiO:N) thin films were deposited on glass and silicon substrates by reactive DC magnetron sputtering in Ar/O2/N2 gas atmosphere with a series of N2/O2 gas ratio ranging from 0 to 80%. X-ray diffraction measurements have revealed that the films are constituted of Ni1-xO grains and showed enhanced polycrystalline features with increasing N-doping concentration. For the first time, we report here that N-doping in the Ni-deficient NiO (Ni1-xO) film leads to a band-gap narrowing from 3.6 to 2.3 eV. X-ray photoelectron spectroscopy (XPS) measurements proved that up to 4 atomic percent (at.%) nitrogen can be incorporated at least at the surface of the NiO:N samples. In addition, XPS valence band spectra and UV–vis transmission measurements have demonstrated that the band-gap narrowing may originates from the contribution of an intermediate band (IB) ∼2.4 eV just above the valence band maximum and the up-shifting of the valence band edge (∼0.3 eV) due to the introduction of occupied N 2p states. Local I–V measurements, carried out by conductive AFM (C-AFM), have revealed that the extrinsic doping of N atoms within the oxide can be a good way to precisely control the electrical conductivity of such p-type materials.
Keywords: Nitrogen doping; Nickel oxide; Reactive sputtering; XPS; Optical band-gap; C-AFM;

Stability, electronic and thermodynamic properties of aluminene from first-principles calculations by Junhui Yuan; Niannian Yu; Kanhao Xue; Xiangshui Miao (85-90).
Display OmittedUsing first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.
Keywords: Aluminene; Two-dimensional materials; Structural stability; First-principle calculations;

Display OmittedHighly antireflective heterostructured aluminum gallium nitride (AlGaN)/GaN ultraviolet (UV) photodetectors were demonstrated using a combination of inverted pyramidal surfaces and zinc oxide nanorod arrays (i.e., antireflective surface modification) to enhance the optical sensitivity. The microfabricated hierarchical surfaces significantly reduced the average surface reflectance to less than 0.3% in the UV region and less than 1% in the visible light region, allowing near-perfect absorption of incident light regardless of the angle of incidence (5–80°). As a result, the photodetectors fabricated on highly antireflective AlGaN/GaN surfaces showed higher sensitivity and responsivity over a broad range of incidence angles compared to photodetectors on planar AlGaN/GaN surfaces, supporting the use of a hierarchically modified sensing surface for omnidirectional UV monitoring with higher sensitivity.
Keywords: Inverted pyramid; Gallium nitride; Zinc oxide nanorod; Antireflective coating; Ultraviolet photodetectors; Surface modification;

Display OmittedSilicene, the single layer of silicon atoms arranged in a honeycomb lattice, has been synthesized in recent experiments and attracted significant attentions. Silicene is promising in future nanoelectronic devices due to its outstanding electronic properties. In experiments, however, different silicene superstructures coexist on Ag(111) substrate. For the device applications, homogenous silicene sheet with large scale and high quality is highly desired. Here, for the first time, we investigate both the temperature and the coverage effects on the thermal stability of epitaxial silicene on Ag(111) surface by ab initio molecular dynamics simulations. The relationship between the stability of various silicene superstructures and the growth conditions, including temperature and coverage of silicon atoms, is revealed by plotting the chemical potential phase diagram of silicene on Ag(111) surfaces at different temperatures. Our results are helpful for understanding the observed diversity of silicene phases on Ag(111) surfaces and provide some useful guidance for the synthesis of homogenous silicene phase in experiments.
Keywords: Silicene; Temperature effect; Coverage effect; Stability; Molecular dynamics;

Porous Al-doped ZnO rods with selective adsorption properties by Bilel Chouchene; Tahar Ben Chaabane; Kevin Mozet; Emilien Girot; Serge Corbel; Lavinia Balan; Ghouti Medjahdi; Raphaël Schneider (102-110).
Display OmittedAl-doped ZnO (ZnO:Al) rods with Al doping varying from 0 to 20% were successfully prepared via a solvothermal method. ZnO:Al rods exhibit the hexagonal wurtzite crystalline structure and their length were found to decrease from 127 to 12 nm when increasing the dopant percentage from 0 to 20%. Simultaneously, their specific surface area increased from ca. 21 to 82 m2/g. ZnO:Al (20%) rods exhibit high adsorption capability towards some negatively charged dyes like Orange II, Acid red 88 or Alizarin, which was attributed to the high specific surface of ZnO:Al rods and to the defects induced by the Al doping as demonstrated by XRD and Raman spectroscopy.
Keywords: Al-doped ZnO rods; Solvothermal synthesis; Adsorption; Anionic dyes;

Investigation of the structural anisotropy in a self-assembling glycinate layer on Cu(100) by scanning tunneling microscopy and density functional theory calculations by Mikhail Kuzmin; Kimmo Lahtonen; Leena Vuori; Rocío Sánchez-de-Armas; Mika Hirsimäki; Mika Valden (111-116).
Self-assembling organic molecule-metal interfaces exhibiting free-electron like (FEL) states offers an attractive bottom-up approach to fabricating materials for molecular electronics. Accomplishing this, however, requires detailed understanding of the fundamental driving mechanisms behind the self-assembly process. For instance, it is still unresolved as to why the adsorption of glycine ([NH2(CH2)COOH]) on isotropic Cu(100) single crystal surface leads, via deprotonation and self-assembly, to a glycinate ([NH2(CH2)COO–]) layer that exhibits anisotropic FEL behavior. Here, we report on bias-dependent scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations for glycine adsorption on Cu(100) single crystal surface. We find that after physical vapor deposition (PVD) of glycine on Cu(100), glycinate self-assembles into an overlayer exhibiting c(2 × 4) and p(2 × 4) symmetries with non-identical adsorption sites. Our findings underscore the intricacy of electrical conductivity in nanomolecular organic overlayers and the critical role the structural anisotropy at molecule-metal interface plays in the fabrication of materials for molecular electronics.
Keywords: Cu(100); Glycine; Adsorption; STM; DFT; Self-assembly;

Fluorination effect of activated carbons on performance of asymmetric capacitive deionization by Hanjoo Jo; Kyung Hoon Kim; Min-Jung Jung; Jae Hyun Park; Young-Seak Lee (117-123).
Display OmittedActivated carbons (ACs) were fluorinated and fabricated into electrodes to investigate the effect of fluorination on asymmetric capacitive deionization (CDI). Fluorine functional groups were introduced on the AC surfaces via fluorination. The specific capacitance of the fluorinated AC (F―AC) electrode increased drastically from 261 to 337 F/g compared with the untreated AC (R―AC) electrode at a scan rate of 5 mV/s, despite a decrease in the specific surface area and total pore volume after fluorination. The desalination behavior of asymmetric CDI cells assembled with an R―AC electrode as the counter electrode and an F―AC electrode as the cathode (R || F-) or anode (R || F + ) was studied. For R || F-, the salt adsorption capacity and charge efficiency increased from 10.6 mg/g and 0.58–12.4 mg/g and 0.75, respectively, compared with the CDI cell assembled with identical R―AC electrodes at 1 V. This CDI cell exhibited consistently better salt adsorption capacity and charge efficiency at different applied voltages because F―AC electrodes have a cation attractive effect originating from the partially negatively charged fluorine functional groups on the AC surface. Therefore, co-ion expulsion in the F―AC electrode as the cathode is effectively diminished, leading to enhanced CDI performance.
Keywords: Fluorination; Activated carbon; Asymmetric capacitive deionization; Desalination;

Surface microstructure evolution of highly transparent and conductive Al-doped ZnO thin films and its application in CIGS solar cells by Ke Cheng; Jingjing Liu; Ranran Jin; Jingling Liu; Xinsheng Liu; Zhangbo Lu; Ya Liu; Xiaolan Liu; Zuliang Du (124-131).
Display OmittedAluminum-doped zinc oxide (AZO) has attained intensive attention as being a very good transparent conducting oxide for photovoltaic applications. In this work, AZO films have been deposited on glass substrate by radio frequency (RF) magnetron sputtering. The influences of substrate temperatures on morphological, structural, optical and electrical properties of AZO films were systematically investigated. The results indicate that all AZO films have the hexagonal structure with c-axis preferred orientation. Morphological and electrical measurements have revealed that the substrate temperatures have strong influence on the microstructure, optical and electrical properties of AZO films. The AZO film is highly transparent from ultraviolet up to near infrared range with highest average transparency exceeding 83%. The minimum resistivity is as low as 6.1 × 10−4  Ω cm. The carrier concentration and mobility are as high as 3.357 × 1020  cm−3 and 30.48 cm2/Vs, respectively. Finally, the performances of the AZO film are evaluated by its practical application in Cu(In1-xGax)Se2 (CIGS) photovoltaic device as a transparent electrode. Benefited from its highly transparent and conductive feature, the most efficient device reveals an efficiency of 7.8% with a short-circuit current density of 28.99 mA/cm2, an open-circuit voltage of 430 mV, and a fill factor of 62.44 under standard conditions.
Keywords: AZO thin films; Magnetron sputtering; Highly transparent and conductive; Substrate temperature; Surface microstructures; CIGS photovoltaic device;

A Ni–B film was grown on Ni foam to form a binder-free highly efficient electrocatalyst for hydrazine oxidation in alkaline medium. The newly-developed Ni–B/Ni foam electrocatalyst may promote the practical application of hydrazine as a viable energy carrier for fuel cells.Display OmittedHydrazine is a promising energy carrier for fuel cells owing to its combined advantages of high theoretical cell voltage, high-power density, and no greenhouse gas emission. By using an electroless plating process, we have prepared a robust Ni–B film grown on Ni foam that is highly effective for hydrazine electrooxidation in alkaline media. The effects of reaction temperature, concentrations of hydrous hydrazine and sodium hydroxide in the fuel solution on performance of hydrazine electrooxidation reaction are investigated. The mechanistic reason for the property advantage of as-prepared Ni–B/Ni foam catalyst over the relevant catalysts is discussed based on careful kinetics studies and characterization. The facile synthesis of Ni-based catalyst with high activity and good stability is of clear significance for the development of hydrous hydrazine as a viable energy carrier.
Keywords: Ni–B catalyst; Hydrazine oxidation; Fuel cells; Electrocatalysis;

Passivation properties of tunnel oxide layer in passivated contact silicon solar cells by Hyunho Kim; Soohyun Bae; Kwang-sun Ji; Soo Min Kim; Jee Woong Yang; Chang Hyun Lee; Kyung Dong Lee; Seongtak Kim; Yoonmook Kang; Hae-Seok Lee; Donghwan Kim (140-148).
Passivated contact in advanced high-efficiency silicon solar cells based on the full back surface field (BSF) is reported here in based on the application of a tunnel oxide layer that is less than 2 nm thick. The open-circuit voltage (Voc ) was significantly improved via interface passivation due to insertion of the tunnel oxide layer. During oxide layer growth, a transition region, such as a sub-oxide, was observed at a depth of about 0.75 nm in the growth interface between the silicon oxide layer and silicon substrate. The properties of the less than 2 nm thick tunnel oxide layer were primarily affected by the characteristics of the transition region. The passivation characteristics of tunnel oxide layer should depend on the physical properties of the oxide. The interface trap density Dit is an important parameter in passivation and is influenced by the stoichiometry of the oxide which in turn strongly affected by the fabrication and the post annealing conditions. During heat treatment of a-Si:H thin films (for the purpose of crystallization to form doped layers), thin film blistering occurs due to hydrogen effusion on flat substrate surfaces. To minimize this behavior, we seek to control the surface morphology and annealing profile. Also, the passivation quality of passivataed contact structure declined for the sample annealed above 900 °C. This decline was attributed not only to local disruption of the tunnel oxide layer, but also to phosphorus diffusion. The resistivity of the tunnel oxide layer declined precipitously for the sample annealed above 900 °C. On the basis of these, implied Voc over 740 mV was achieved in n-type Si wafer through the control of the oxide stoichiometry via optimizing the annealing conditions.
Keywords: Tunnel oxide; Passivated contact; Passivation; Blistering; Solar cell;

Adsorption of arginine, glycine and aspartic acid on Mg and Mg-based alloy surfaces: A first-principles study by Zhe Fang; Jianfeng Wang; Xiaofan Yang; Qiang Sun; Yu Jia; Hairong Liu; Tingfei Xi; Shaokang Guan (149-155).
Studying the adsorption behaviors of biomolecules on the surface of Mg and Mg-based alloy has a fundamental and important role for related applications in biotechnology. In the present work, we systematically investigate and compare the adsorption properties of three typical amino acids, i.e., Arg (arginine), Gly (glycine) and Asp (aspartic acid), which form RGD tripeptide, on the Mg (0 0 0 1) surface with various doping (Zn, Y, and Nd), and aim to realize proper binding between biomolecules and Mg and Mg-based biomedical materials. Our results show that flat adsorption configurations of the functional groups binding to the surfaces are favored in energy for all the three selected amino acids. In specific, for the amino acids adsorped on clean Mg (0 0 0 1) surface, the adsorption energy (E ads ) of Arg is found to be −1.67 eV for the most stable configuration, with amino and guanidyl groups binding with the surface. However, Gly (Asp) is found to binding with the surface through amino and carboxyl groups, with a −1.16 eV (−1.15 eV) binding energy. On the 2% Zn doped Mg (0 0 0 1) alloy surface (Mg–Zn (2%)), the E ads are significantly increased to be −1.91 eV, −1.32 eV and −1.35 eV for Arg, Gly and Asp, respectively. While the Mg–Y (1%) and Mg–Nd (1%) slightly weaken the adsorption of three amino acids. Moreover, we have performed detail discussions of the binding properties between amino acids and surfaces by projected density of states (PDOS) combined with charge transfer analyses. Our studies provide a comprehensive understanding on the interactions between amino acids and Mg and Mg-based alloy surfaces, with respect to facilitate the applications of Mg and Mg-based biomedical alloys in biosensing, drug delivery, biomolecule coating and other fields in biotechnology.
Keywords: Mg (0 0 0 1) surface; Mg-based biomedical alloys; Amino acids; Adsorption property; First-principles calculation;

Bi-stage time evolution of nano-morphology on inductively coupled plasma etched fused silica surface caused by surface morphological transformation by Xiaolong Jiang; Lijuan Zhang; Yang Bai; Ying Liu; Zhengkun Liu; Keqiang Qiu; Wei Liao; Chuanchao Zhang; Ke Yang; Jing Chen; Yilan Jiang; Xiaodong Yuan (156-163).
In this work, we experimentally investigate the surface nano-roughness during the inductively coupled plasma etching of fused silica, and discover a novel bi-stage time evolution of surface nano-morphology. At the beginning, the rms roughness, correlation length and nano-mound dimensions increase linearly and rapidly with etching time. At the second stage, the roughening process slows down dramatically. The switch of evolution stage synchronizes with the morphological change from dual-scale roughness comprising long wavelength underlying surface and superimposed nano-mounds to one scale of nano-mounds. A theoretical model based on surface morphological change is proposed. The key idea is that at the beginning, etched surface is dual-scale, and both larger deposition rate of etch inhibitors and better plasma etching resistance at the surface peaks than surface valleys contribute to the roughness development. After surface morphology transforming into one-scale, the difference of plasma resistance between surface peaks and valleys vanishes, thus the roughening process slows down.
Keywords: Inductively coupled plasma etching; Plasma etching; Fused silica; Roughness; Bi-stage evolution; Morphology;

A novel method was developed to deposit nanosized silver particles on multi-walled carbon nanotubes (MWCNTs). The electroless plating of silver on MWCNTs accomplished in small solution drops generated by ultrasonic spray atomization, which inhibited excessive growth of silver particles and led to much more uniform nanometer grain-sized coatings. The results showed that pretreatment was essential for silver particles to deposit on the MWCNTs, and the electrolyte concentration and reaction temperature were important parameters which had a great influence on the morphology and structure of the silver coatings. Possible mechanisms of this method are also discussed in the paper.
Keywords: Carbon nanotubes; Electroless plating of silver; Ultrasonic spray atomization;

Display OmittedIn this research, the enhancements of surface integrity and corrosion resistance of the laser cladded parts by combined hard turning with low plasticity burnishing (LPB) were presented by both potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The investigated results indicated that the corrosion resistance of the laser cladded parts could be improved by combined hard turning with LPB than by sole hard turning. An innovative model was proposed to explain the corrosion mechanism of the laser cladded parts after hybrid machining. Both surface adsorption and passive film were observed to dominate the corrosion resistance of the hybrid machined Cr–Ni alloys by laser cladding. The surface integrity led to the inhomogeneity of passive film, and then altered the corrosion resistance of the machined samples. In terms of the surface integrity factors, residual compressive stresses and surface finish were found to play more important roles in improving the corrosion resistance than the grain refinement and microhardness of the machined surface layer materials did. Based on the research results, anti-corrosion parts with laser cladded alloys could be fabricated by hybrid machining using the combination of hard turning and LPB.
Keywords: Surface integrity; Corrosion resistance; Hybrid machining; Hard turning; Low plasticity burnishing;

Molecular dynamics study of the nanosized droplet spreading: The effect of the contact line forces on the kinetic energy dissipation by Hong Min Yoon; Sasidhar Kondaraju; Jung Shin Lee; Youngho Suh; Joonho H. Lee; Joon Sang Lee (179-186).
Display OmittedRecent studies have revealed that contact line forces play an important role in the droplet spreading process. Despite their significance, the physics related to them has been studied only indirectly and the effect of contact line forces is still being disputed. We performed a molecular dynamics simulation and mimicked the droplet spreading process at the nanoscale. Based on the results of the simulation, the contact line forces were directly calculated. We found that the forces acting on the bulk and the contact line region showed different trends. Distinct positive and negative forces, contact line spreading, and friction forces were observed near the contact line. We also observed a strong dependency of the atomic kinetics in the contact line region on the variations in the contact line forces. The atoms of the liquid in the contact line region lost their kinetic energy due to the contact line friction force and became partially immobile on the solid surface. The results of the current study will be useful for understanding the role of the contact line forces on the kinetic energy dissipation in the contact line region.
Keywords: Three phase contact line; Adhesion force; Nano-scale friction; Molecular dynamics;

The highly efficient antireflective down-conversion Bi-doped Y2O3 films have been deposited on the (100) oriented Si and quartz substrates by rf reactive magnetron sputtering using a metallic target. The effects of the Bi doping concentration on the optical and structural properties of the films were studied. The Bi/Y ratio in the films varied from 0.002 to 0.02. The undoped Y2O3 films show a cubic phase crystal structure with a preferred orientation along the (222) direction. Bi doping results in the appearance of the (111) oriented monoclinic phase crystal structure. The refractive index is increased and the optical band gap is decreased as the Bi concentration in the films is increased. The bright green photoluminescence of Bi ions was observed under ultraviolet light excitation for all the Bi-doped Y2O3 films and the luminescence intensity increases as the Bi/Y ratio is increased from 0.002 to 0.02. In addition, Bi-doped Y2O3 films show a much lower optical reflectance than the undoped Y2O3 films. These results make the Bi-doped Y2O3 films a potential application not only as a spectrum converting layer but also as an antireflective layer in crystalline Si solar cells.
Keywords: Bi-doped Y2O3 film; RF reactive magnetron sputtering; Optical and structural properties; Photoluminescence; Down-conversion;

Direct observation of hopping induced spin polarization current in oxygen deficient Co-doped ZnO by Andreev reflection technique by Kung-Shang Yang; Tzu-Yu Huang; G.D. Dwivedi; Lu-Kuei Lin; Shang-Fan Lee; Shih-Jye Sun; Hsiung Chou (194-199).
Oxygen vacancy induced ferromagnetic coupling in diluted magnetic oxide (DMO) semiconductors have been reported in several studies, but technologically more crucial spin-polarized current (SPC) is still under-developed in DMOs. Few studies have claimed that VRH mechanism can originate the SPC, but, how VRH mechanism associated with percolation path, is not clearly understood. We used Point-contact Andreev reflection (PCAR) technique to probe the SPC in Co-doped ZnO (CZO) films. Since the high resistance samples cause broadening in conductance(G)-voltage(V) curves, which may result in an unreliable evaluation of spin polarization, we include two extra parameters, (i) effective temperature and (ii) spreading resistance, for the simulation to avoid the uncertainty in extracting spin polarization. The effective G-V curves and higher spin polarization can be obtained above a certain oxygen vacancy concentration. The number of completed and fragmentary percolation paths is proportional to the concentration of oxygen vacancies. For low oxygen vacancy samples, the Pb-tip has a higher probability of covering fragmentary percolation paths than the complete ones, due to its small contact size. The completed paths may remain independent of one another and get polarized in different directions, resulting in lower spin-polarization value. High oxygen vacancy samples provide a high density of completed path, most of them link to one another by crossing over, and gives rise to high spin-polarization value.
Keywords: Andreev reflection; Spin polarization;

Electronic structure and STM imaging of the KBr-InSb interface by Piotr Ciochoń; Natalia Olszowska; Jacek J. Kołodziej (200-207).
Display OmittedWe study the properties of the InSb (001) surface covered with ultrathin KBr films, with a thickness of 1–4 ML. KBr deposition does not strongly perturb the crystallographic structure of the InSb surface and the electronic structure of the substrate also remains unaffected by the overlayer. A simple model of the studied system is proposed, in which a thin KBr layer is treated as a dielectric film, modifying potential barrier for the electrons tunneling to/from the InSb substrate. Apparent step heights on the KBr film, measured using scanning tunneling microscope (STM), agree well with the predictions of the model and the atomically-resolved STM images show the structure of the InSb-KBr interface. Our results demonstrate that STM may be used as a tool for investigations of the semiconductor–insulator interfaces.
Keywords: Thin film; Indium antimonide; KBr; Scanning tunneling; Microscopy; Interface;

The relationship study between texture vibrating plate dynamic wettability and elastic wave scattering by Jing Xu; Bin Li; Chuanping Zhou; Jing Xiao; Jing Ni (208-213).
An experimental investigation of wetting behavior of liquid droplet on texture vibrating substrate and the theoretical calculations of elastic wave scattering with two holes which based on the elastodynamics, employing complex functions are investigated to study the relationship between texture vibrating plate dynamic wettability and elastic wave scattering. Experimental results show the dynamic behavior of droplet was unstable. In 0 to π/2 cycle, droplet appeared the waveform with front steep and rear gentle along the flow direction. In π/2 to π cycle, droplet appeared slightly periodic oscillation and accompanied by a certain ripple. Based on the dynamic wetting phenomenon in a single cycle, the influence of elastic wave scattering on wetting property are analyzed. Analysis has shown that the stress concentration is caused by complex elastic wave scattering. The more concentrated the stress, the more concentrated the elastic wave energy. Compared with the single hole, the variations of dynamic stress concentration factors for two holes are complex due to the influence of interaction between two holes. Droplet emerge movement is response to the local vibration. The vibration spread in elastic plate at a time of strain, this elastic force cause droplet displacement and vibration, and accompanied with energy transfer.
Keywords: Dynamic wettability; Vibrate; Metal; Elastic waves scattering; Stress concentration;

Display OmittedPartial wetting surfaces and its influence on the droplet movement of micro and nano scale being contemplated for many useful applications. The dynamics of the droplet usually analyzed with a multiphase lattice Boltzmann method (LBM). In this paper, the influence of partial wetting surface on the dynamics of droplet is systematically analyzed for various cases. Splitting of droplets due to chemical gradient of the surface is studied and analyses of splitting time for various widths of the strips for different Weber numbers are computed. With the proposed model one can tune the splitting volume and time by carefully choosing a strip width and droplet position. The droplet spreading on chemically heterogeneous surfaces shows that the spreading can be controlled not only by parameters of Weber number but also by tuning strip width ratio. The transportation of the droplet from hydrophobic surface to hydrophilic surface due to chemical gradient is simulated and analyzed using our hybrid thermodynamic-image processing technique. The results prove that with the progress of time the surface free energy decreases with increase in spreading area. Finally, the transportation of a droplet on microstructure gradient is demonstrated. The model explains the temporal behaviour of droplet during the spreading, recoiling and translation along with tracking of contact angle hysteresis phenomenon.
Keywords: Lattice Boltzmann method (LBM); Two phase flow; Partial wetting; Micro pillars;

Catalytic combustion of dimethyl ether over α-MnO2 nanostructures with different morphologies by Gao Cheng; Lin Yu; Binbin He; Ming Sun; Bentian Zhang; Wenjin Ye; Bang Lan (223-231).
Display OmittedHerein, α-MnO2 catalysts with three well-defined morphologies (nanorod, ultra-long nanowire and microsphere) were rational designed and prepared by the hydrothermal route, and their catalytic activities were evaluated for the dimethyl ether (DME) combustion. These nanostructured α-MnO2 catalysts were characterized in detail by various analytical techniques: XRD, FESEM, TEM, BET, XPS and H2-TPR. As a result, the α-MnO2 nanorod exhibited the higher catalytic activity (T 10  = 170 °C and T 90  = 238 °C at WHSV = 30,000 mL g−1  h−1) than the other two α-MnO2 samples due to its larger specific surface area, higher average oxidation state of Mn, more abundant surface lattice oxygen (Olatt) species and higher reducibility, and there was no obvious decrease after the α-MnO2 nanorod was run for 50 h. Moreover, the transient response technique revealed that the Olatt species of the α-MnO2 nanorod should be the crucial role in the deep oxidation of DME.
Keywords: α-MnO2 nanostructures; Morphology; Hydrothermal method; Dimethyl ether; Catalytic combustion;

Display OmittedRecently, the fabrication of superhydrophobic metallic surfaces by means of pulsed laser texturing has been developed. After laser texturing, samples are typically chemically coated or aged in ambient air for a relatively long time of several weeks to achieve superhydrophobicity. To accelerate the wettability transition from hydrophilicity to superhydrophobicity without the use of additional chemical treatment, a simple annealing post process has been developed. In the present work, grid patterns were first fabricated on stainless steel by a nanosecond pulsed laser, then an additional low-temperature annealing post process at 100 °C was applied. The effect of 100–500 μm step size of the textured grid upon the wettability transition time was also investigated. The proposed post process reduced the transition time from a couple of months to within several hours. All samples showed superhydrophobicity with contact angles greater than 160° and sliding angles smaller than 10° except samples with 500 μm step size, and could be applied in several potential applications such as self-cleaning and control of water adhesion.
Keywords: Superhydrophobic stainless steel surface; Nanosecond laser texturing; Low-temperature annealing; Self-cleaning; Water adhesion;

Display OmittedRecently, copper species have been extensively investigated to replace Pt as efficient co-catalysts for the evolution of H2 due to their low cost and relatively high activity. Cu nanoparticles less than 5 nm are successfully decorated on TiO2 surface in this work by an easy and mild milling process. These Cu nanoparticles are highly dispersed on TiO2 when the loading amount of Cu is no more than 10 wt%. The sizes of Cu nanoparticles can be controlled by changing the milling environment and decrease in the order of Cu-ethanol > Cu-water > Cu nanoparticles obtained through drying milling. The highest and stable hydrogen generation can be realized on Cu/TiO2 with 2.0 wt% Cu and sizes of Cu nanoparticles ranging from 2 to 4 nm, in which high and stable photocurrent confirms promoted photogenerated charge separation. Smaller Cu clusters are demonstrated to be detrimental to hydrogen evolution at same Cu content. High loading of Cu nanoparticles of 2–4 nm will benefit photogenerated electron-hole recombination and thus decrease the activity of Cu/TiO2. The results here demonstrate the key roles of Cu cluster size in addition to Cu coverage on photocatalytic activity of Cu/TiO2 composite photocatalysts.
Keywords: TiO2; Cu nanoparticles; Ball milling environment; Tuning the size; Photocurrent response; Hydrogen evolution;

Excellent photocatalytic activity and stability are achieved over Ag3PO4/MoO3 p-n heterostructure nanocatalyst, which was increased the charge separation efficiencies.Display OmittedAg3PO4/MoO3 p-n heterojunction have been successfully fabricated by using a simple in situ solvent method. SEM, TEM, XRD, XPS and electrochemical techniques were used to study the structural and electrochemical characteristics of the resulting materials. The photocatalytic activity of the obtained composite was tested by the degradation of organic dye (methylene blue) under visible-light irradiation. The photocatalytic activity of Ag3PO4/MoO3 remained 92.5% after four recycling runs, which was much higher than that of the pure Ag3PO4 (54%). The obtained results confirm that the novel Ag3PO4/MoO3 heterostructure exhibited significantly higher photocatalytic activities and improved stability compared with bare Ag3PO4. The excellent photocatalytic activity came from the effective separation of the electron-hole pairs under the effect of built-in electric field in the interfacial the of the p-n heterojunction, and then made the holes more available for dyes oxidation.
Keywords: Ag3PO4/MoO3; Visible light; p-n heterojunction;

Microwave plasma-assisted chemical vapor deposition of porous carbon film as supercapacitive electrodes by Ai-Min Wu; Chen-Chen Feng; Hao Huang; Ramon Alberto Paredes Camacho; Song Gao; Ming-Kai Lei; Guo-Zhong Cao (261-269).
Highly porous carbon film (PCF) coated on nickel foam was prepared successfully by microwave plasma-assisted chemical vapor deposition (MPCVD) with C2H2 as carbon source and Ar as discharge gas. The PCF is uniform and dense with 3D-crosslinked nanoscale network structure possessing high degree of graphitization. When used as the electrode material in an electrochemical supercapacitor, the PCF samples verify their advantageous electrical conductivity, ion contact and electrochemical stability. The test results show that the sample prepared under 1000 W microwave power has good electrochemical performance. It displays the specific capacitance of 62.75 F/g at the current density of 2.0 A/g and retains 95% of its capacitance after 10,000 cycles at the current density of 2.0 A/g. Besides, its near-rectangular shape of the cyclic voltammograms (CV) curves exhibits typical character of an electric double-layer capacitor, which owns an enhanced ionic diffusion that can fit the requirements for energy storage applications.
Keywords: Porous carbon film; Double-layer supercapacitor; Microwave plasma; Chemical vapor deposition; Supercapacitive energy storage;

Display OmittedCurrent-voltage characteristics of solar cells based on the prepared Cu(In,Ga)Se2 films without potassium and added with and 1.0 mol% potassium ions without KCN etching treatment. Inset: Photovoltaic properties of solar cells based on the prepared Cu(In,Ga)Se2 films with various potassium-ion content without KCN etching treatment.A doping process of potassium-ion was adopted as an alternative to the toxic KCN etching used for the removal of Cu2-xSe compounds. The effects of potassium-ion doping on the phase formation and photovoltaic characteristics of the solution-coated Cu(In,Ga)Se2 films was investigated. As the incorporation of potassium ions was increased from 0 mol% to 1.0 mol%, the coexistent Cu2-xSe compounds were gradually reduced and the monophasic Cu(In,Ga)Se2 films were obtained. The potassium-ion doped Cu(In,Ga)Se2 films with dense and smooth morphology improved the coverage of CdS buffer layer and suppressed the additional shunt paths. Hence, the conversion efficiency of the solar cells fabricated without KCN treatment was significantly improved from 4.70%to 11.02%. Additionally, the diode factor (A) and the saturated current (J0) were reduced due to the suppression of carrier recombination and leakage current. Further increasing the content of potassium ions to 5.0 mol%, the oversupplied potassium ions reduced the grain size and induced the carrier recombination in the obtained films, thereby resulting in the deterioration of the cell performance. This investigation demonstrates that the incorporation of potassium ions into Cu(In,Ga)Se2 films with appropriated amounts can effectively diminish the formation of Cu2-xSe compounds, thereby improving the photovoltaic performance of the fabricated Cu(In,Ga)Se2 solar cells.
Keywords: Chalcogenides; Spin coating; Thin films; Solar cell;

Comparison of solidity and fractal dimension of plasma sprayed splat with different spreading morphologies by Shu-ying Chen; Guo-zheng Ma; Hai-dou Wang; Peng-fei He; Ming Liu; Hai-jun Wang; Bin-shi Xu (277-284).
Display OmittedThe paper deals with the quantitative characterization of spreading morphologies of plasma sprayed Fe-based alloy droplets deposited on mirror polished steels with different preheated temperature. The plasma torch was utilized as heat producer. The influence of substrate temperature on the solidification mechanism of molten droplets was investigated. The image analysis method (IMA) was employed to identify single splat from the field emission scanning electron microscope (FE-SEM) morphology. The result shows that the substrate preheated temperature has a significant effect on the flattening behavior of molten droplets. With the increment of substrate temperature, the solidification mode of splat changes from flower-like and splashed splat to disk-like splat due to the modification of wettability and cooling velocity between molten droplet and substrate. Compared with area and perimeter, both fractal dimension (FD) and solidity could separately detect the solidification mode of splat to a certain extent, while the FD seems to be more excellent in characterizing irregular morphology of splat in contrast with solidity. However, the combination of FD and solidity is more efficient in classifying solidification mode of splat.
Keywords: Solidification modes; Splat morphology; Fractal; Solidity;

We designed highly aqueous dispersible CeF3:Tb@LaF3@SiO2 nanoparticles. The epitaxial growth of inert LaF3 shell and further amorphous silica, respectively, enhanced their optical and luminescence properties, which is highly usable for luminescent biolabeling, and optical bio-probe etc.Display OmittedHighly luminescent and aqueous soluble CeF3:Tb (core),CeF3:Tb@LaF3(core/shell) and CeF3:Tb@LaF3@ SiO2 (core/shell/Si) nanoparticles(NPs) with mean particle size 12 nm were prepared by co-precipitation method at low temperature. X-ray diffraction pattern verified the phase purity, high crystallinity of hexagonal structure. The TEM image and SAED pattern revealed the single phase polycrystalline nature, well-dispersed irregular shaped hexagonal structure. FTIR spectra show the characteristic infrared peaks of silica, it suggests the successful silica surface coating around the core/shell NPs. The excitation and emission intensity of core/shell NPs were remarkably increased then their counterpart core NPs. It implies that a significant amount of nonradiative transition centers existing on the surface of core NPs has been eliminated due to the formation of passivated LaF3 layer. The silica surface modification over the core/shell NPs strikingly enhanced the solubility character in an aqueous environment.
Keywords: Cerium fluoride; Core/shell; Silica shell; Absorption spectra; FTIR; Photoluminescence;

Synthesis of carbon-supported copper catalyst and its catalytic performance in methanol dehydrogenation by Ekaterina V. Shelepova; Aleksey A. Vedyagin; Ludmila Yu. Ilina; Alexander I. Nizovskii; Pavel G. Tsyrulnikov (291-295).
Display OmittedCarbon-supported copper catalyst was prepared by incipient wetness impregnation of Sibunit with an aqueous solution of copper nitrate. Copper loading was 5 wt.%. Temperature of reductive pretreatment was varied within a range of 200–400 °C. The samples were characterized by transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron and X-ray absorption spectroscopies. Catalytic activity of the samples was studied in a reaction of methanol dehydrogenation. Silica-based catalyst with similar copper loading was used as a reference. It was found that copper is distributed over the surface of support in the form of metallic and partially oxidized particles of about 12–17 nm in size. Diminished interaction of copper with support was supposed to be responsible for high catalytic activity.
Keywords: Carbon-supported catalyst; Copper; Sibunit; Methanol dehydrogenation; Methyl formate;

Display OmittedA synthetic mineral adsorbent (SMA) was prepared by mechanochemical treatments of a solid-state mixture containing illite, wollastonite, gypsum, limestone and dolomite powder at a molar ration of 1:1:1:12:3. The XRD patterns revealed that many newly-generated minerals, namely montmorillonite, laumonite and gismondine (zeolite facies), grossular, gehlenite and calcium silicate were observed in SMA residual after full hydration. The potential of SMA for the removal of Cd(II) and Pb(II) ions from aqueous solution was investigated by batch mode. The effects of pH, concentration of adsorbate, contact time, SMA concentration and temperature on adsorption performance of SMA for Cd(II) and Pb(II) over SMA were studied. The results indicate that the adsorption process was found to follow pseudo-second-order kinetic model and Freundlich isotherm model. The maximum monolayer capacity obtained from the Langmuir isotherm at 25 °C was 47.0 and 143.3 mg g−1 for Cd(II) and Pb(II) ions, respectively. The adsorbed Cd(II) and Pb(II) can hardly be recovered at pH 3.0 but can completely recovered at pH 1.0 and 0.5, respectively. Ion exchange of Cd(II) and Pb(II) for Ca2+ was found to be the principal mechanism in the removal of Cd(II) and Pb(II) from aqueous solution by SMA, followed by adsorption and precipitation. From the investigation, it is concluded that SMA could be a useful environment-friendly, inexpensive and effective tool for removal of high amounts of toxic Cd(II) and Pb(II) ions from aquatic ecosystems.
Keywords: Synthetic mineral adsorbent; Adsorption; Cadmium; Lead; Desorption; Mechanism;

The GO embedded sandwich nanoparticles are capable of serving as an ultrasensitive, highly reproducible and stable SERS platform.Display OmittedDisplay OmittedThe graphene-mediated surface enhanced Raman scattering (SERS) substrates by virtues of plasmonic metal nanostructures and graphene or its derivatives have attracted tremendous interests which are expected to make up the deficiency of traditional plasmonic metal substrates. Herein, we designed and fabricated a novel ternary Ag@GO@Au sandwich hybrid wherein the ultrathin graphene oxide (GO) films were seamlessly wrapped around the hierarchical flower-like Ag particle core and meanwhile provided two-dimensional anchoring scaffold for the coating of Au nanoparticles (NPs). The surface coverage density of loading Au NPs could be readily controlled by tuning the dosage amount of Au particle solutions. These features endowed the sandwiched structures high enrichment capability for analytes such as aromatic molecules and astonishing SERS performance. The Raman signals were enormously enhanced with an ultrasensitive detection limit of rhodamine-6G (R6G) as low as 10−13  M based on the chemical enhancement from GO and multi-dimensional plasmonic coupling between the metal nanoparticles. In addition, the GO interlayer as an isolating shell could effectively prevent the metal–molecule direct interaction and suppress the oxidation of Ag after exposure at ambient condition which enabled the substrates excellent reproducibility with less than 6% signal variations and prolonged life-time. To evaluate the feasibility and the practical application for SERS detection in real-world samples based on GO sandwiched hybrid as SERS-active substrate, three different prohibited colorants with a series of concentrations were measured with a minimum detected concentration down to 10−9  M. Furthermore, the prepared GO sandwiched nanostructures can be used to identify different types of colorants existing in red wine, implying the great potential applications for single-particle SERS sensing of biotechnology and on-site monitoring in food security.
Keywords: Graphene oxide; Sandwich nanohybrid; Multi-dimensional coupling; SERS; High stability; Selective detection;

In vitro characterization of two different atmospheric plasma jet chemical functionalizations of titanium surfaces by F. Mussano; T. Genova; E. Verga Falzacappa; P. Scopece; L. Munaron; P. Rivolo; P. Mandracci; A. Benedetti; S. Carossa; A. Patelli (314-324).
Display OmittedPlasma surface activation and plasma polymers deposition are promising technologies capable to modulate biologically relevant surface features of biomaterials. The purpose of this study was to evaluate the biological effects of two different surface modifications, i.e. amine (NH2-Ti) and carboxylic/esteric (COOH/R-Ti) functionalities obtained from 3-aminopropyltriethoxysilane (3-APTES) and methylmethacrylate (MMA) precursors, respectively, through an atmospheric plasma jet RF-APPJ portable equipment. The coatings were characterized by Scanning Electron Microscopy, FT-IR spectroscopy, XPS and surface energy calculations. Stability in water and after UV sterilization were also verified. The pre-osteoblastic murine cell line MC3T3-E1 was used to perform the in-vitro tests. The treated samples showed a higher quantity of adsorbed proteins and improved osteoblast cells adhesion on the surfaces compared to the pristine titanium, in particular the COOH/R-Ti led to a nearly two-fold improvement. Cell proliferation on coated samples was initially (at 24 h) lower than on titanium control, while, at 48 h, COOH/R-Ti reached the proliferation rate of pristine titanium. Cells grown on NH2-Ti were more tapered and elongated in shape with lower areas than on COOH/R-Ti enriched surfaces. Finally, NH2-Ti significantly enhanced osteocalcin production, starting from 14 days, while COOH/R-Ti had this effect only from 21 days. Notably, NH2-Ti was more efficient than COOH/R-Ti at 21 days. The amine functionality elicited the most relevant osteogenic effect in terms of osteocalcin expression, thus establishing an interesting correlation between early cell morphology and later differentiation stages. Taken together, these data encourage the use of the functionalization procedures here reported in further studies.
Keywords: Titanium; Surface modification; Amine functionality; Carboxylic/esteric functionality; in vitro cell model;

Crumb waste tire rubber (WTR) was pretreated by oxygen low temperature plasma (LTP) and modified by LTP polymerization process of ethanol monomer to improve the adhesion property with oil-well cement matrix and the mechanical properties of cement. The surface properties of modified crumb WTR and the mechanical properties and structures of modified oil-well cement were investigated by means of contact angle measurement, dispersion test, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), mechanics performance tests, permeability test and scanning electron microscopy (SEM). It was demonstrated that LTP treatment changed both the surface composition and roughness. The contact angle of pretreated crumb WTR dramatically fell from 122° to 34°, and sample with ethanol LPT polymer film decreased even further to 11°. The ATR-FTIR and XPS analysis results demonstrated that hydrophilic groups, such as –COOH, C–OH, and –CHO, were introduced on the WTR surface. The oxygen atomic percent increased from 8.11% to 14.50% and 24.83%. The mechanical properties, porosity and permeability of raw cement were compared to samples modified by untreated crumb WTR, pretreated crumb WTR and ethanol LTP polymerization treated crumb WTR. It was found that after 28 days, the compressive strength of the samples with the untreated crumb WTR decreased to 80% with respect to raw cement. The tensile strength and flexural strength also had a slight reduction compared with the raw cement. On the contrary, after 28 days, the tensile strength of cement modified by LTP polymerization treated WTR increased 11.03% and 13.36%, and the flexural strength increased 9.65% and 7.31%, respectively. A decrease in the compressive strength also occurred but was inconspicuous. A tight interface bonding for ethanol LTP polymerization treated WTR with cement matrix was observed via an SEM image.
Keywords: Waste tire rubber; Low temperature plasma; Plasma polymerization; Oil-well cement; Surface modification;

Interfacial kinetics in nanosized Au/Ge films: An in situ TEM study by Aleksandr P. Kryshtal; Alexey A. Minenkov; Paulo J. Ferreira (343-349).
Display OmittedWe investigate the morphology and crystalline structure of Au/Ge films in a wide range of temperatures by in situ TEM heating. Au/Ge films with Au mass thickness of 0.2–0.3 nm and Ge thickness of 5 nm were produced in vacuum by the sequential deposition of components on a carbon substrate at room temperature. It has been shown that particles with an average size of 4 nm, formed by Au film de-wetting, melt on the germanium substrate at temperatures 110–160 °C, which are below the eutectic temperature for the bulk. The effect of crystallization-induced capillary motion of liquid eutectic particles over Ge surface has been found in this work. Formation of metastable fcc phase of Ge has been observed at the liquid–germanium interface and behind the moving particle. Formation of a liquid phase with its subsequent crystallization at the metal–semiconductor interface seems to play a key role in the metal-induced crystallization effect.
Keywords: Metal-induced crystallization; Liquid film migration; Solid/liquid interface; fcc germanium; In situ transmission electron microscopy (TEM);

Display OmittedGraphene nanosheets (GNs) have been successfully synthesized by one-step carbonization and simultaneous chemical activation of polyaniline (PANI) nanofibers, with large surface area (1759.5 m2  g−1), high pore volume (1.16 cm3  g−1) and a mesopore rich structure (volume in micropore/total ratio, 2.16%). The vital (NDs) become entrapped within a carbon lattice (to form GNs). GNs could be used as an outstanding electrode material for supercapacitors in EMIMBF4 with high cycling stability (more than 73% retention of the initial capacitance after 10,000 cycles). The symmetric supercapacitor has an excellent energy density of 170.2 Wh kg−1 (25 °C) at 0.5 A g−1, with an operating cell voltage of 4.0 V. Meanwhile, oriented activation with polymers of anisotropic geometry might be regarded as a novel process to prepare GNs.
Keywords: Anisotropic geometry; KOH; Oriented activation; GNs; Ionic liquids;

Design of a novel immobilized solid acid coating and its application in Fenton-like oxidation of phenol by Jiankang Wang; Zhaohua Jiang; Yajing Wang; Qixing Xia; Zhongping Yao (358-366).
Display OmittedA novel immobilized solid acid coating on Q235 carbon steel was successfully prepared via plasma electrolytic oxidation. Sulfate functionalized Fe3O4/FeAl2O4 was confirmed by XRD, TEM and XPS analysis and surface acidic property was verified by NH3-TPD measurement. Fenton-like degradation performance was evaluated by employing phenol as target pollutant. Fast phenol degradation under the wide range of pH (pH 6–9) was accomplished within only 11 min. Without sulfate functionalization, phenol could hardly be degraded by Fenton-like oxidation which meant that after sulfate functionalization the existence of acidic microenvironment on the catalyst surface not only provided an optimal circumstance for enhanced Fenton-like reaction, but also avoided adjusting pH of the treated wastewater. A reasonable Fenton-like degradation mechanism was proposed. This paper offered a novel design thought for synthesizing excellent Fenton-like coating catalyst under circumneutral pH.
Keywords: Fenton-like; Solid acid; Degradation; Plasma electrolytic oxidation; Coating; Phenol;

Microstructure of rapidly solidified Nb-based pre-alloyed powders for additive manufacturing by Yueling Guo; Lina Jia; Bin Kong; Shengnan Zhang; Fengxiang Zhang; Hu Zhang (367-374).
Display OmittedFor powder-based additive manufacturing, sphere-shaped Nb-37Ti-13Cr-2Al-1Si pre-alloyed powders were prepared by plasma rotating electrode processing (PREP). The microstructure, surface oxidation and microhardness of the pre-alloyed powders were systematically investigated. Results showed that the main phases were Nb solid solution (Nbss) and Cr2Nb. The Cr2Nb phases were further determined using transmission electron microscopy (TEM). Fine dendrite structures were observed in the as-fabricated pre-alloyed powders, which transformed to large grains after heat treatment (HT) at 1450 °C for 3 h. With the increase of powder size, the secondary dendrite arm spacing (SDAS) increased and the microhardness (HV) decreased. A clean powder surface free of oxide particles was obtained by PREP and an oxide layer with 9.39 nm in thickness was generated on the powder surface. Compared with Cr- and Nb-oxides, more Ti-oxides were formed on outmost powder surface with a higher content of Ti (up to 47.86 at.%). The differences upon the microstructure and microhardness of the pre-alloyed powders with different sizes were discussed.
Keywords: Niobium based alloy; Powder metallurgy; Rapid solidification; Microstructure; Surface oxide;

Biocompatibility of GaSb thin films grown by RF magnetron sputtering by Naoki Nishimoto; Junko Fujihara; Katsumi Yoshino (375-380).
Display OmittedGaSb may be suitable for biological applications, such as cellular sensors and bio-medical instrumentation because of its low toxicity compared with As (III) compounds and its band gap energy. Therefore, the biocompatibility and the film properties under physiological conditions were investigated for GaSb thin films with or without a surface coating. GaSb thin films were grown on quartz substrates by RF magnetron sputtering, and then coated with (3-mercaptopropyl) trimethoxysilane (MPT). The electrical properties, surface morphology, and crystal structure of the GaSb thin film were unaffected by the MPT coating. The cell viability assay suggested that MPT-coated GaSb thin films are biocompatible. Bare GaSb was particularly unstable in pH9 buffer. Ga elution was prevented by the MPT coating, although the Ga concentration in the pH 9 buffer was higher than that in the other solutions. The surface morphology and crystal structure were not changed by exposure to the solutions, except for the pH 9 buffer, and the thin film properties of MPT-coated GaSb exposed to distilled water and H2O2 in saline were maintained. These results indicate that MPT-coated GaSb thin films are biocompatible and could be used for temporary biomedical devices.
Keywords: GaSb; Thin film; Biocompatibility; Stability; Semiconductor; Sputtering;

In this work, a dielectric barrier discharge (DBD) operated at medium to atmospheric pressure has been used for the deposition of thin polyallylamine (PAA) films on ultra-high molecular weight polyethylene (UHMWPE) substrates. The effect of treatment time (1–5 min), discharge power (5.7–24.0 W), monomer concentration (1–2 g/h) and pressure (10–100 kPa) on the films properties, aging and stability behaviors have been investigated. The used characterization techniques are X-ray photoelectron spectroscopy, water contact angle and optical reflectance spectroscopy.In this paper, it is shown that plasma treatment time does not affect the coatings chemistry; whereas plasma power, monomer concentration and pressure control the coatings properties. It is also shown that the deposition rate of the deposited films changes with varying W/FM values. At low W/FM values, high deposition rates of up to 2 nm/s are observed.Plasma treatments were also characterized by their amino efficiency ([NH2]/[C] in %) and amino selectivity ([NH2]/[N] in %). Depending on the used parameters, these varied between 12.3% and 20% and between 71.2% and 91.1%, respectively.For the aging study, coatings that preserved most of their hydrophilicity were obtained at power ≤11.3 W, monomer concentration ≥1.5 g/h and pressure ≥50 kPa.For the stability study, coatings that showed the highest [N] (%) and lowest percentage of thickness decrease were obtained at ≤2 min, 24.0 W, 1 g/h and pressure ≤50 kPa.One can therefore control the deposition rate as well as the properties, aging and stability behaviors of the deposited coating by carefully choosing the plasma parameters.
Keywords: Plasma polymerization; Dielectric barrier discharge; Allylamine; Medium to atmospheric pressure plasma; Surface analysis;

Synthesis of MoS2 ribbons and their branched structures by chemical vapor deposition in sulfur-enriched environment by Rakesh D. Mahyavanshi; Golap Kalita; Kamal P. Sharma; Masuharu Kondo; Takeshita Dewa; Toshio Kawahara; Masaki Tanemura (396-402).
Display OmittedHere, we demonstrate the synthesis of monolayer molybdenum disulfide (MoS2) ribbons and their branched structures by chemical vapor deposition (CVD) in sulfur-enriched environment. The growth of the MoS2 ribbons, triangular and other crystals significantly depends on the exposure of sulfur and concentration of molybdenum oxide (MoO3) vapor on the substrate surface. The width and length of the synthesized ribbons is around 5–10 and 50–100 μm, respectively, where the width reduces from the nucleation point toward the end of the ribbon. Unidirectional, bi and tri-directional growth of ribbons from the nucleation point with an angle of 60° and 120° were obtained attributing to crystallographic growth orientation of MoS2 crystals. The directional growth of dichalcogenides ribbons is a significant challenge, our process shows that such unidirectional and other branched structures can be achieved by controlling the stoichiometric composition of MoO3 and sulfur exposure on the substrate surface. Interestingly, all the individual and branched ribbons possess uneven abundant edge structures, where the edges are formed with angles of 60° and 120°, indicating variation in molybdenum and sulfur edge terminations. The directional growth of MoS2 ribbons with defined edge structures in particular CVD condition can open up new possibilities for electronic and electrochemical applications.
Keywords: MoS2 ribbon; Chemical vapor deposition; Directional growth; Edge terminations;

Effects of picosecond laser repetition rate on ablation of Cr12MoV cold work mold steel by Baoye Wu; Leimin Deng; Peng Liu; Fei Zhang; Jun Duan; Xiaoyan Zeng (403-412).
Display OmittedIn this paper, the effects of pulse repetition rate on ablation efficiency and quality of Cr12MoV cold work mold steel have been studied using a picosecond (ps) pulse Nd:YVO4 laser system at λ= 1064 nm. The experimental results of area ablation on target surface reveal that laser repetition rate plays a significant role in controlling ablation efficiency and quality. Increasing the laser repetition rate, while keeping a constant mean power improves the ablation efficiency and quality. For each laser mean power, there is an optimal repetition rate to achieve a higher laser ablation efficiency with low surface roughness. A high ablation efficiency of 42.29, 44.11 and 47.52 μm3/mJ, with surface roughness of 0.476, 0.463 and 0.706 μm could be achieved at laser repetition rate of 10 MHz, for laser mean power of 15, 17 and 19 W, respectively. Scanning electron microcopy images revels that the surface morphology evolves from rough with numerous craters, to flat without pores when we increased the laser repetition rate. The effects of laser repetition rate on the heat accumulation, plasma shield and ablation threshold were analyzed by numerical simulation, spectral analysis and multi-laser shot, respectively. The synergetic effects of laser repetition rate on laser ablation rate and machining quality were analyzed and discussed systemically in this paper.
Keywords: Laser repetition rate; Ablation efficiency; Surface roughness; Heat accumulation; Plasma shielding; Threshold fluence;

In this study, our main focus is to investigate the effects of F doping and post deposition annealing (air and vacuum) on the optical and electrical characteristics of tantalum doped zinc oxide films (ZnO:Ta). A cost-effective, automated jet nebulizer spray pyrolysis technique is adopted to deposit the ZnO:Ta:F films. The doping level of Ta is kept constant (1 at.%) and that of F is varied from 5 to 20 at.% in steps of 5 at.%. The electrical resistivity of the as-deposited films decreases for 10 at.% of F concentration. The resistance increases thereafter. The same trend is also observed in annealed films. The reasons for these variations are addressed based on the effective F incorporation into the ZnO lattice and annealing atmosphere with the help of XRD, FESEM, AFM and PL studies. The incorporation of the dopants was confirmed from XPS and EDX analyses and the DFT studies show that the incorporation of the dopants does not affect the stability of the ZnO lattice. Vacuum-annealed films show better electrical properties over the as-deposited and air-annealed counterparts, though their transparency is affected marginally. A minimum resistivity of 0.81 × 10−3  Ω cm and an enhanced quality factor of 2.265 × 10−4  (Ω/sq)−1 are achieved for the vacuum-annealed films having Ta + F doping levels as 1 + 10 at.%. These results make this sample a desirable candidate for transparent electrode applications.
Keywords: ZnO thin films; Annealing; Electrical transport; Transmittance; Figure of merit;

Ultra-thin ZnSe: Anisotropic and flexible crystal structure by C. Bacaksiz; R.T. Senger; H. Sahin (426-430).
By performing density functional theory-based calculations, we investigate the structural, electronic, and mechanical properties of the thinnest ever ZnSe crystal . The vibrational spectrum analysis reveals that the monolayer ZnSe is dynamically stable and has flexible nature with its soft phonon modes. In addition, a direct electronic band gap is found at the gamma point for the monolayer structure of ZnSe. We also elucidate that the monolayer ZnSe has angle dependent in-plane elastic parameters. In particular, the in-plane stiffness values are found to be 2.07 and 6.89 N/m for the arm-chair and zig-zag directions, respectively. The angle dependency is also valid for the Poisson ratio of the monolayer ZnSe. More significantly, the in-plane stiffness of the monolayer ZnSe is the one-tenth of Young modulus of bulk zb-ZnSe which indicates that the monolayer ZnSe is a quite flexible single layer crystal. With its flexible nature and in-plane anisotropic mechanical properties, the monolayer ZnSe is a good candidate for nanoscale mechanical applications.
Keywords: Ultra-thin two-dimensional density-functional-theory;

Display OmittedJanus effect has been studied for emerging materials like Janus membranes, Janus nanoparticles, etc., and the applications including fog collection, oil/water separation, CO2 removal and stabilization of multiphasic mixtures. However, the Janus effect on oil/water separation is still unclear. Herein, Janus Cu mesh decorated with Ni-NiO/Ni(OH)2 core-shell nanoparticles is synthesized via selective electrodeposition, in which we keep one side of Cu mesh (Janus A) to be superhydrophilic, while manipulate the wettability of another side (Janus B) from hydrophobic to superhydrophilic. Experimental results indicate that Cu mesh with both-side superhydrophilic shows the superior oil/water separation performance (separation efficiency >99.5%), which is mainly due to its higher water capture percentage as well as larger oil intrusion pressure. Further, we demonstrate the orientation of Janus membranes for oil/water separation, and summarize that the wettability of the upper surface plays a more important role than the lower surface to achieve remarkable performance. Our work provides a clear insight of Janus effect on oil/water separation, it is significative to design high-performance membranes for oil/water separation and many other applications.
Keywords: Janus effect; Superhydrophilic; Core-shell; Nanoparticle; Oil/water separation;

Controlled surface properties of titania nanoparticles via surface modification, flocculation from aqueous phase (a), stabilization in aqueous phase (b), extraction to organic phase (c).Display OmittedA route to produce a stable colloidal suspension is essential if mono-dispersed particles are to be successfully synthesized, isolated, and used in subsequent nanocomposite manufacture. Dispersing nanoparticles in fluids was found to be an important approach for avoiding poor dispersion characteristics. However, there is still a great tendency for colloidal nanoparticles to flocculate over time. Steric stabilization can prevent coagulation by introducing a thick adsorbed organic layer which constitutes a significant steric barrier that can prevent the particle surfaces from coming into direct contact. One of the main features of hydrothermal synthesis technique is that it offers novel approaches for sustainable nanoparticle surface modification. This manuscript reports on the sustainable steric stabilization of titanium dioxide nanoparticles. Nanoparticle surface modification was performed via two main approaches including post-synthesis and in situ surface modification. The tuneable hydrothermal conditions (i.e. temperature, pressure, flow rates, and surfactant addition) were optimized to enable controlled steric stabilization in a continuous fashion. Effective post synthesis surface modification with organic ligand (dodecenyl succinic anhydride (DDSA)) was achieved; the optimum surface coating temperature was reported to be 180–240 °C to ensure DDSA ring opening and binding to titania nanoparticles. Organic-modified titania demonstrated complete change in surface properties from hydrophilic to hydrophobic and exhibited phase transfer from the aqueous phase to the organic phase. Exclusive surface modification in the reactor was found to be an effective approach; it demonstrated surfactant loading level 2.2 times that of post synthesis surface modification. Titania was also stabilized in aqueous media using poly acrylic acid (PAA) as polar polymeric dispersant. PAA-titania nanoparticles demonstrated a durable amorphous polymeric layer of 2 nm thickness. This manuscript revealed the state of the art for the real development of stable colloidal mono-dispersed particles with controlled surface properties.
Keywords: Hydrothermal synthesis; Colloidal nanoparticles; Steric stabilization; Surface modification;