Applied Surface Science (v.334, #C)

Preface by Jeff Th.M. De Hosson; Nasar Ali; Giuseppe Fierro; Mahmood Aliofkhazraei; Mircea Chipara (1).

Electronic and vibrational properties of graphene monolayers with iron adatoms: A density functional theory study by Nicholas Dimakis; Nestor E. Navarro; Julian Velazquez; Andres Salgado (2-6).
Periodic density functional calculations on graphene monolayers with and without an iron adatom have been used to elucidate iron-graphene adsorption and its effects on graphene electronic and vibrational properties. Density-of-states calculations and charge density contour plots reveal charge transfer from the iron s orbitals to the d orbitals, in agreement with past reports. Adsorbed iron atoms covalently bind to the graphene substrate, verified by the strong hybridization of iron d-states with the graphene bands in the energy region just below the Fermi level. This adsorption is weak and compared to the well-analyzed CO adsorption on Pt: It is indicated by its small adsorption energy and the minimal change of the substrate geometry due to the presence of the iron adatoms. Graphene vibrational spectra are analyzed though a systematic variation of the graphene supercell size. The shifts of graphene most prominent infrared active vibrational modes due to iron adsorption are explored using normal mode eigenvectors.
Keywords: Density functional theory; Graphene; Adsorption; Vibrational spectra; Infrared intensities;

Polyaniline coating with various substrates for hexavalent chromium removal by Bin Qiu; Cuixia Xu; Dezhi Sun; Qiang Wang; Hongbo Gu; Xin Zhang; Brandon L. Weeks; Jack Hopper; Thomas C. Ho; Zhanhu Guo; Suying Wei (7-14).
Hexavalent chromium (Cr(VI)) contamination is increasingly serious in surface water and groundwater, therefore, its removal attracts increasing attention due to its highly toxic to human health. The cost effective and sustainable adsorbents are urgently needed for the remediation of Cr(VI) pollution. Polyanline (PANI), a conductive polymer, has demonstrated a great performance on Cr(VI) removal. But the recycling is the challenge for its application due to its small size. The PANI coating with various substrates is an effective approach to solve this problem. The synthesis methods and applications of the PANI coated magnetic Fe3O4, carbon fabric and cellulose composites for the Cr(VI) removal were reviewed. Finally, this review analyzed the Cr(VI) removal mechanisms by the PANI composites considering the substrate and the PANI coating.
Keywords: Polyaniline (PANI); Magnetic; Carbon fabric; Cellulose; Chromium removal;

Improved performance of silicon nanowire/cadmium telluride quantum dots/organic hybrid solar cells by Zhaoyun Ge; Ling Xu; Renqi Zhang; Zhaoguo Xue; Hongyu Wang; Jun Xu; Yao Yu; Weining Su; Zhongyuan Ma; Kunji Chen (15-18).
We fabricated silicon nanowire/cadmium telluride quantum dots (CdTe QDs)/organic hybrid solar cells and investigated their structure and electrical properties. Transmission electron microscope revealed that CdTe QDs were uniformly distributed on the surface of the silicon nanowires, which made PEDOT:PSS easily filled the space between SiNWs. The current density–voltage (JV) characteristics of hybrid solar cells were investigated both in dark and under illumination. The result shows that the performance of the hybrid solar cells with CdTe QDs layer has an obvious improvement. The optimal short-circuit current density (J sc) of solar cells with CdTe QDs layer can reach 33.5 mA/cm2. Compared with the solar cells without CdTe QDs, J sc has an increase of 15.1%. Power conversion efficiency of solar cells also increases by 28.8%. The enhanced performance of the hybrid solar cells with CdTe QDs layers are ascribed to down-shifting effect of CdTe QDs and the modification of the silicon nanowires surface with CdTe QDs. The result of our experiments suggests that hybrid solar cells with CdTe QDs modified are promising candidates for solar cell application.
Keywords: Hybrid solar cells; CdTe QDs; Down-shifting;

Structures and energetics of lithium adatom and its dimer on graphene–a DFT study by Gagandeep Kaur; Shuchi Gupta; Keya Dharamvir (19-23).
We performed a systematic density functional theory (DFT) study of the adsorption of Lithium adatom and its dimer on graphene using SIESTA package [1], in the generalized gradient approximation (GGA). The adsorption energy, geometry, charge transfer and density of states of adatom/dimer-graphene system are calculated. The calculations showed that the interaction between Li adatom and graphene is strong (∼1.07 eV) and it prefers to adsorb on H-site. Further calculations of both horizontally and vertically aligned dimers show that the adsorption is also weak for the latter orientation. The preferred orientation of each dimer was found to be parallel to graphene sheet with the two atoms of the dimer occupying adjacent H-sites on the graphene.Significant charge transfer (∼0.388e) from Li adatom to graphene will induce electric dipole moments in the adatom/graphene system. We also calculated DOS for the stable Li -graphene system. The Fermi energy is seen to lie above the Dirac point inside the conduction band indicating that appreciable electrons are transferred from the Li adatom to the graphene sheet. We also noticed that the adsorption of Li adatom/dimer on graphene causes very little distortion to the graphene lattice.
Keywords: Graphene; Adsorption; Cluster; DFT; SIESTA; GGA;

Structure and properties of nitrided surface layer produced on NiTi shape memory alloy by low temperature plasma nitriding by Elżbieta Czarnowska; Tomasz Borowski; Agnieszka Sowińska; Józef Lelątko; Justyna Oleksiak; Janusz Kamiński; Michał Tarnowski; Tadeusz Wierzchoń (24-31).
NiTi shape memory alloys are used for bone and cardiological implants. However, on account of the metallosis effect, i.e. the release of the alloy elements into surrounding tissues, they are subjected to various surface treatment processes in order to improve their corrosion resistance and biocompatibility without influencing the required shape memory properties.In this paper, the microstructure, topography and morphology of TiN surface layer on NiTi alloy, and corrosion resistance, both before and after nitriding in low-temperature plasma at 290 °C, are presented. Examinations with the use of the potentiodynamic and electrochemical impedance spectroscopy methods were carried out and show an increase of corrosion resistance in Ringer's solution after glow-discharge nitriding. This surface titanium nitride layer also improved the adhesion of platelets and the proliferation of osteoblasts, which was investigated in in vitro experiments with human cells. Experimental data revealed that nitriding NiTi shape memory alloy under low-temperature plasma improves its properties for bone implant applications.
Keywords: Nitinol; Glow discharge nitriding; Corrosion; Biocompatibility;

The inductive micro-switch can not only induce an external acceleration, but also be controlled by the external acceleration to realize a trigger action. It is an integrative device of a sensor and an actuator. However, little work has been done to develop a comprehensive model to accurately analyze the micro size effect during micro-switch contact process. So its malfunctions related to “fail-to-closure” and “transient-closure” result in low reliability and weak anti-jamming capability. A bistable inductive micro-switch is presented based on nano electro-mechanical system (NEMS) technology and micro size effect. And the sine-model is used to describe the rough contact surface of the micro-switch. Micro size forces such as the Casimir force and van der Waals (vdW) force are analyzed in detail using the principles of vacuum energy and the Wigner–Seitz micro-continuum media. The vdW force includes the repulsive force. The simulation results of the Casimir force varied with the gap are obtained, which is compared with the relative experimental result. The dynamic equation of the bistable inductive micro-switch is established. Dynamic simulation results are shown to be in agreement with experimental results. The threshold acceleration is 6.8 g, and the response time is 17.5 μs.
Keywords: Inductive micro-switch; Micro size effect; Rough surface; Casimir force; van der Waals force;

Electrical conductivity enhancement by boron-doping in diamond using first principle calculations by Mahtab Ullah; Ejaz Ahmed; Fayyaz Hussain; Anwar Manzoor Rana; Rizwan Raza (40-44).
Representation of the electrical charge distributions of boron-doped diamond.Boron doping in diamond plays a vital role in enhancing electrical conductivity of diamond by making it a semiconductor, a conductor or even a superconductor. To elucidate this fact, partial and total density of states has been determined as a function of B-content in diamond. Moreover, the orbital charge distributions, B–C bond lengths and their population have been studied for B-doping in pristine diamond thin films by applying density functional theory (DFT). These parameters have been found to be influenced by the addition of different percentages of boron atoms in diamond. The electronic density of states, B–C bond situations as well as variations in electrical conductivities of diamond films with different boron content and determination of some relationship between these parameters were the basic tasks of this study. Diamond with high boron concentration (∼5.88% B-atoms) showed maximum splitting of energy bands (caused by acceptor impurity states) at the Fermi level which resulted in the enhancement of electron/ion conductivities. Because B atoms either substitute carbon atoms and/or assemble at grain boundaries (interstitial sites) inducing impurity levels close to the top of the valence band. At very high B-concentration, impurity states combine to form an impurity band which accesses the top of the valence band yielding metal like conductivity. Moreover, bond length and charge distributions are found to decrease with increase in boron percentage in diamond. It is noted that charge distribution decreased from +1.89 to −1.90 eV whereas bond length reduced by 0.04 Å with increasing boron content in diamond films. These theoretical results support our earlier experimental findings on B-doped diamond polycrystalline films which depict that the addition of boron atoms to diamond films gives a sudden fall in resistivity even up to 105  Ω cm making it a good semiconductor for its applications in electrical devices.
Keywords: B-doped diamond films; Orbital charge distribution; TDOS; Bond population; Electrical conductivity;

Scaling of magnetotransport properties in granular Co(c  = 0.8)Bi(1 −  c) thin films by Th. Speliotis; P. Athanasopoulos; A. Melitsiotis; V.M. Papaioannou; A. Travlos; K. Misiakos; C. Christides (45-51).
A nanogranular thin film structure with concentration Co(c  = 0.8)Bi(1 −  c), and thickness about 100 nm, exhibits one order of magnitude increase of the anomalous Hall coefficient R S (with an absolute value of |R S | = 1.43 μΩ cm at 300 K), relative to that observed in pure Co thin films. This may provide evidence that a Giant Hall Effect (GHE) contribution may appear well above the percolation threshold of Co, observed at c  ≈ 0.3 in Co(c)Bi(1 −  c) composite films. Electron microscopy (transmission and scanning), X-ray diffraction, transverse and perpendicular magnetoresistance, and Hall effect resistivity loops were employed to investigate the physical origin of this effect.
Keywords: Magnetotransport properties; Semimetals; Thin films;

An epitaxial (Bi0.45La0.05Ba0.5)(Fe0.75Nb0.25)O3 (BLB-FNO) thin film was successfully grown on an Ir-buffered (0 0 1) MgO substrate by pulsed laser deposition (PLD). The “cube-on-cube” epitaxial relation, (0 0 1)[1 0 0] BLB-FNO//(0 0 1)[1 0 0] Ir//(0 0 1)[1 0 0] MgO, was confirmed by X-ray diffraction (XRD) pole figures and cross-sectional high-resolution transmission electron microscopy (HRTEM). The ferroelectric polarization switching of the BLB-FNO thin film was investigated by piezoresponse force microscopy (PFM). Its magnetic properties, such as ferromagnetic hysteresis at room temperature and possible magnetic transition at low temperature, were also evaluated. Accordingly, we successfully demonstrated that artificial A- and B-site cation engineering would allow for stable multiferroic properties at room temperature.
Keywords: Multiferroics; Epitaxial growth; Pulsed laser deposition;

Synthesis of high magnetic moment soft magnetic nanocomposite powders for RF filters and antennas by Chins Chinnasamy; Yaaqoub Malallah; Melania M. Jasinski; Afshin S. Daryoush (58-61).
Fe60Co40 alloy nanoparticles with an average particle size of 30 nm were successfully synthesized in gram scale batches using the modified polyol process. The X-ray diffraction and microstructure studies clearly show the formation of the alloy nanoparticles. The saturation magnetization for the gram scale synthesized Fe60Co40 alloy nanoparticles is in the range of 190-205 emu/g at room temperature. The as-synthesized nanoparticles were used to fabricate transmission lines on FR4 substrate to perform radio frequency (RF) characterization of the nanoparticles at ISM RF bands of interest (all in GHz range). The complex permeability extraction of composite Fe60Co40 nanoparticles were performed using perturbation technique applied to microstrip transmission lines by relative measurement of full two port scattering parameter with respect to a baseline FR4 substrate. The extracted results show attractive characteristics for small size antennas and filters.
Keywords: Nanocomposites; FeCo alloy nanocomposite; RF antenna and filters; Power electronics;

Nanocomposite layers of mineral/osteogenic growth peptide (OGP) were synthesized on calcium phosphate coated titanium substrates by immersing in calcium-phosphate buffer solution containing OGP. Peptide incorporated mineral was characterized by determining quantity loaded, effects on mineral morphology and structure. Also, the biological activity was investigated by cell adhesion, proliferation assay, and measurement of alkaline phosphatase (ALP) activity. X-ray photoelectron spectroscopy (XPS) and micro-bicinchoninic acid (BCA) assay revealed that OGP was successfully incorporated with mineral and the amount was increased with immersion time. Incorporated OGP changed the mineral morphology from sharp plate-like shape to more rounded one, and the octacalcium phosphate structure of the mineral was gradually transformed into apatite. With confocal microscopy to examine the incorporation of fluorescently labeled peptide, OGP was evenly distributed throughout mineral layers. Mineral/OGP nanocomposites promoted cell adhesion and proliferation, and also increased ALP activity of mesenchymal stem cells (MSCs). Results presented here indicated that the mineral/OGP nanocomposites formed on titanium substrates had the potential for applications in dental implants.
Keywords: Osteogenic growth peptide; Mineral; Nanocomposites; Coprecipitation; Titanium;

Reprint of “Overhanging ferroelectric nanodot arrays created by high surface energy seeds” by Jiyoon Kim; Kwang-Won Park; Jongin Hong; Kwangsoo No (69-73).
We demonstrated a facile route for the fabrication of overhanging PbTiO3 (PTO) nanodot arrays on platinized silicon substrates using PbO vapor phase reaction sputtering on micellar monolayer films of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) loaded with TiO2 sol–gel precursor. We also investigated that the high surface energy of TiO2 contributes to the formation of overhanging ferroelectric PTO nanodot arrays by means of high-resolution transmission electron microscopy. Additionally, the crystallographic orientation of the nanoseeds had a significant influence on the ferroelectric switching properties of the PTO nanodots, which were determined by piezoresponse force microscopy (PFM).
Keywords: Ferroelectrics; Nanodot; Surface energy; PbTiO3; TiO2;

Glow discharge assisted oxynitriding process of titanium for medical application by Tadeusz Wierzchoń; Elżbieta Czarnowska; Justyna Grzonka; Agnieszka Sowińska; Michał Tarnowski; Janusz Kamiński; Krzysztof Kulikowski; Tomasz Borowski; Krzysztof J. Kurzydłowski (74-79).
The plasma oxynitriding process is a prospective method of producing titanium oxides as an integral part of a diffusive nitrided surface layer on titanium implants. This hybrid process, which combines glow discharge assisted nitriding and oxidizing, permits producing TiO2  + Ti2N + αTi(N)-type diffusive surface layers. The oxynitrided surface layers improve the corrosion and wear resistance of the substrate material. Additionally, the nanocrystalline titanium oxide TiO2 (rutile) improves the biological properties of titanium and its alloys when in contact with blood, whereas the TiN + Ti2N + αTi(N) zone eliminates the effect of metalosis.
Keywords: Glow discharge assisted nitriding and oxidizing; Titanium; Surface layer; Microstructure; Corrosion and wear resistance; Platelets adhesion;

Nanocrystalline Sn–Ni/MWCNT composite was prepared by ultrasonic-pulse electrodeposition on a copper substrate in a pyrophosphate bath at different duty cycles. Surface morphology of produced Sn–Ni/MWCNT composites were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) was conducted to understand the elemental surface composition of composites. X-ray diffraction analysis (XRD) was carried out to investigate structure of Sn–Ni/MWCNT composites. The electrochemical performance of Sn–Ni/MWCNT composite electrodes were investigated by charge/discharge tests and cyclic voltammetric experiments. The cells discharge capacities were determined by cyclic testing by a battery tester at a constant current in voltage range between 0.02 V and 1.5 V. The duty cycle was shown to be a crucial factor to improve Sn–Ni/MWCNT composite anodes for cyclability and reversible capacity.
Keywords: Li batteries; Electro co-deposition; Sn–Ni/MWCNT nanocomposite; Pulse electroplating; Duty cycle;

Fabrication and simulation of single crystal p-type Si nanowire using SOI technology by Arash Dehzangi; Farhad Larki; Mahmud G. Naseri; Manizheh Navasery; Burhanuddin Y. Majlis; Mohd F. Razip Wee; M.K. Halimah; Md. Shabiul Islam; Sawal H. Md Ali; Elias Saion (87-93).
Si nanowires (SiNWs) as building blocks for nanostructured materials and nanoelectronics have attracted much attention due to their major role in device fabrication. In the present work a top-down fabrication approach as atomic force microscope (AFM) nanolithography was performed on Si on insulator (SOI) substrate to fabricate a single crystal p-type SiNW. To draw oxide patterns on top of the SOI substrate local anodic oxidation was carried out by AFM in contact mode. After the oxidation procedure, an optimized solution of 30 wt.% KOH with 10 vol.% IPA for wet etching at 63 °C was applied to extract the nanostructure. The fabricated SiNW had 70–85 nm full width at half maximum width, 90 nm thickness and 4 μm length. The SiNW was simulated using Sentaurus 3D software with the exact same size of the fabricated device. I–V characterization of the SiNW was measured and compared with simulation results. Using simulation results variation of carrier's concentrations, valence band edge energy and recombination generation rate for different applied voltage were investigated.
Keywords: Single crystal silicon nanowire; Atomic force microscope nanolithography; Silicon on insulator; KOH wet etching;

In this study, nickel plated silicon powders were produced using an electroless deposition process. The nickel content on the surface of silicon powders was changed by using different concentrations of NiCl2 in the plating bath. The surface morphology of the produced Ni plated composite powders was characterized using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) was used to determine the elemental surface composition of the composites. X-ray diffraction (XRD) analysis was performed to investigate the structure of the nickel plated silicon powders. Electrochemical cycling test of the nickel plated silicon electrodes were performed at a constant current of 100 mA/g in CR2016 test cells. In order to investigate electrochemical reactions of the nickel plated silicon powders with electrolyte, cyclic voltammetry test was performed at a scan rate of 0.1 mV/s. Among the used concentrations, the nickel plated silicon electrode produced using 40 g/L NiCl2 had a 246 mAh/g discharge capacity after 30 cycles.
Keywords: Li ion batteries; Silicon electrode; Nickel plating; Discharge capacity; Electrochemical performance;

Flow boiling heat transfer enhancement on copper surface using Fe doped Al2O3–TiO2 composite coatings by Sujith Kumar C.S.; Suresh S.; Aneesh C.R.; Santhosh Kumar M.C.; Praveen A.S.; Raji K. (102-109).
In the present work, flow boiling experiments were conducted to study the effect of spray pyrolyzed Fe doped Al2O3–TiO2 composite coatings over the copper heater blocks on critical heat flux (CHF) and boiling heat transfer coefficient. Heat transfer studies were conducted in a mini-channel of overall dimension 30 mm × 20 mm × 0.4 mm using de-mineralized water as the working fluid. Each coated sample was tested for two mass fluxes to explore the heat transfer performance. The effect of Fe addition on wettability and porosity of the coated surfaces were measured using the static contact angle metre and the atomic force microscope (AFM), and their effect on flow boiling heat transfer were investigated. A significant enhancement in CHF and boiling heat transfer coefficient were observed on all coated samples compared to sand blasted copper surface. A maximum enhancement of 52.39% and 44.11% in the CHF and heat transfer coefficient were observed for 7.2% Fe doped TiO2–Al2O3 for a mass flux of 88 kg/m2  s.
Keywords: Minichannel; Flow boiling heat transfer; Critical heat Flux; Spray pyrolyzed alumina coating; Fe doped Al2O3–TiO2 composite; Hydrophilicity;

Extended short-wavelength spectral response of organic/(silver nanoparticles/Si nanoholes nanocomposite films) hybrid solar cells due to localized surface plasmon resonance by Zhixin Liu; Ling Xu; Wengping Zhang; Zhaoyun Ge; Jun Xu; Weining Su; Yao Yu; Zhongyuan Ma; Kunji Chen (110-114).
In this letter, we investigated spectral and opto-electronic conversion properties of the inorganic/organic hybrid cells by using silver nanoparticles (AgNPs)/Si nanoholes (SiNHs) nanocomposite films, which were fabricated by the modified metal-assisted electroless etching (EE) method. It was found that the optical absorption spectra of the films with AgNPs demonstrate a clear peak and show the enhancement of total absorption at the short wavelength. The results of current–voltage (IV) measurements show that solar cells with AgNPs exhibit an increase of the power conversion efficiency by a factor of 2–3, in comparison with those of the samples without AgNPs. Moreover, higher external quantum efficiency (EQE) values in AgNPs-decorated solar cells were confirmed in the short-wavelength spectral region (400–700 nm), which were essential to achieve high-performance photovoltaic cells. We thought these were mainly attributed to the localized surface plasmon resonance (LSPR) effects and increased light scattering of AgNPs.
Keywords: AgNPs/SiNHs nanocomposite films; Hybrid solar cell; EQE; LSPR;

Nanostructured silicon synthesis by surface modification of commercial micro-powder silicon was investigated in order to reduce the maximum volume change over cycle. The surface of micro-powder silicon was modified using an Ag metal-assisted chemical etching technique to produce nanostructured material in the form of bundle-type silicon nanorods. The volume change of the electrode using the nanostructured silicon during cycle was investigated using an in-situ dilatometer. Our result shows that nanostructured silicon synthesized using this method showed a self-relaxant characteristic as an anode material for lithium ion battery application. Moreover, binder selection plays a role in enhancing self-relaxant properties during delithiation via strong hydrogen interaction on the surface of the silicon material. The nanostructured silicon was then coated with carbon from propylene gas and showed higher capacity retention with the use of polyacrylic acid (PAA) binder. While the nano-size of the pore diameter control may significantly affect the capacity fading of nanostructured silicon, it can be mitigated via carbon coating, probably due to the prevention of Li ion penetration into 10 nano-meter sized pores.
Keywords: Bundle-type silicon nanorods (BSNR); In-situ dilatometer; Metal-assisted chemical etching; Nanostructured silicon; Self-relaxant; Volume expansion;

Preparation of nano-patterned Si structures for hetero-junction solar cells by Peng Lu; Jun Xu; Yunqing Cao; Jingwei Lai; Ling Xu; Kunji Chen (123-128).
The 220 nm and 300 nm periodically nano-patterned Si structures with low aspect ratio were fabricated by nano-sphere lithography technique. A good anti-reflection properties in a broadband spectral range (300–1200 nm) was exhibited due to the gradually changing refractive index of the formed Si nanostructures. After deposition of the intrinsic and phosphorous-doped (P-doped) amorphous Si (a-Si) film, the weighted mean reflection of the 220 nm and 300 nm periodic nanostructures was further reduced to 3.30% and 2.96%, respectively. Due to the enhanced light absorption, both the IQE and EQE of the nano-patterned cells were improved in a wide spectral range. For the 300 nm periodically nano-patterned prototype hetero-junction solar cell, the short circuit current density was increased to 34.5 mA/cm2, which was obviously improved compared with 26.8 mA/cm2 for the flat cell.
Keywords: Si nanostructures; Light trapping; Photovoltaic;

Annealing effect in structural and electrical properties of sputtered Mo thin film by P. Chelvanathan; Z. Zakaria; Y. Yusoff; M. Akhtaruzzaman; M.M. Alam; M.A. Alghoul; K. Sopian; N. Amin (129-137).
In this study, the effects of vacuum annealing on the structural and electrical properties of DC-sputtered molybdenum (Mo) thin films have been investigated. Mo thin films were deposited by DC sputtering and subsequently subjected to vacuum annealing in a tube furnace from 350 to 500 °C. Films that were deposited with different temperatures showed good adhesion with soda lime glass substrate after “tape testing”. X-ray diffraction (XRD) spectra have indicated existence of (1 1 0) and (2 1 1) orientations. However, I(1 1 0)/I(2 1 1) peak intensity ratio decreased for all vacuum annealed Mo films compared to as-sputtered films indicating change of preferential orientation. This suggests vacuum annealing can be employed to tailor the Mo thin film atomic packing density of the plane parallel to the substrate. SEM images of surface morphology clearly show compact and dense triangular like grains for as-sputtered film, while annealed films at 350 °C, 400 °C and 450 °C indicate rice-like grains. Stony grains with less uniformity were detected for films annealed for 500 °C. Meanwhile, electrical resistivity is insensitive to the vacuum annealing condition as all films showed more or less same resistivity in the range of 3 × 10−5–6 × 10−5  Ω cm.
Keywords: Thin films; Mo; Sputtering growth; Annealing; Structural properties;

Growth and characterization of RF-sputtered ZnS thin film deposited at various substrate temperatures for photovoltaic application by P. Chelvanathan; Y. Yusoff; F. Haque; M. Akhtaruzzaman; M.M. Alam; Z.A. Alothman; M.J. Rashid; K. Sopian; N. Amin (138-144).
RF-sputtered ZnS thin film was grown under various substrate temperatures with the aim of investigating its effects on the structural, surface morphology and optical properties. Investigated substrate temperature in this study was in the range of 25 °C–300 °C and the structural and optical properties were investigated in order to elucidate the changes induced by the varying thermal energy during the growth process. Structural determination by XRD method indicates all sputtered films have cubic structure with (1 1 1) as the preferential orientation. However, higher substrate temperature up to 200 °C increases the film's crystallinity and grain size evident by the increase in peak intensity. Slight peak shift indicates ZnS lattice undergoes strain relaxation process mediated through the increase in the lattice constant from 5.32 Å to 5.40 Å. SEM image of surface morphology clearly shows the evolution of grain growth in which sputtered film at 200 °C has the largest grains with distinct grain boundaries. Calculation from the obtained transmission spectra indicates optical band gap is in the range of 3.6–3.9 eV. Theoretical analysis in terms of lattice parameter between ZnS with several upcoming photovoltaic absorber layers shows that lattice matched ZnS buffer layer can be grown by varying the substrate temperature.
Keywords: Thin films; ZnS; Sputtering growth; Structural properties; Optical properties;

Structural and photovoltaic characteristics of hierarchical ZnO nanostructures electrodes by Muhammad Saleem; L. Fang; Saleem F. Shaukat; M. Ashfaq Ahmad; Rizwan Raza; Majid Niaz Akhtar; Ayesha Jamil; Samia Aslam; Ghazanfar Abbas (145-150).
Structural and photovoltaic characteristics of hierarchical ZnO nanostructures solar cell have been studied in relation to growth reaction temperature. It is found that the hierarchical ZnO nanostructures network to act not only as large surface area substrates but also as a transport medium for electrons injected from the dye molecules. The incident photon-to-current conversion efficiency is decreased by increasing the growth reaction temperature of ZnO electrodes. The best conversion efficiency of a 0.25 cm2 cell is measured to be 1.24% under 100 mW cm−2 irradiation.
Keywords: Hierarchical ZnO nanostructures; Structural properties; Photovoltaic properties;

This study investigated the photocatalytic behavior of nanocrystalline TiO2 deposited on Ag-doped long-lasting phosphor (CaAl2O4:Eu2+,Nd3+). The CaAl2O4:Eu2+,Nd3+ phosphor powders were prepared via conventional sintering using CaCO3, Al2O3, Eu2O3, and Nd2O3 as raw materials according to the appropriate molar ratios. Silver nanoparticles were loaded on the phosphor by mixing with an aqueous Ag-dispersion solution. Nanocrystalline TiO2 was deposited on Ag-doped CaAl2O4:Eu2+,Nd3+ powders via low-pressure chemical vapor deposition (LPCVD). The TiO2 coated on the phosphor was actively photo-reactive under irradiation with visible light and showed much faster benzene degradation than pure TiO2, which is almost non-reactive. The coupling of TiO2 with phosphor may result in an energy band bending in the junction region, which then induces the TiO2 crystal at the interface to be photo-reactive under irradiation with visible light. In addition, the intermetallic compound of CaTiO3 that formed at the interface between TiO2 and the CaAl2O4:(Eu2+,Nd3+) phosphor results in the formation of oxygen vacancies and additional electrons that promote the photodecomposition of benzene gas. The addition of Ag nanoparticles enhanced the photocatalytic reactivity of the TiO2/CaAl2O4:Eu2+,Nd3+ phosphor. TiO2 on the Ag-doped phosphor presented a higher benzene gas decomposition rate than the TiO2 did on the phosphor without Ag-doping under both irradiation with ultraviolet and visible light.
Keywords: Photocatalyst; TiO2; Ag-doping; Long-lasting phosphor; CaAl2O4:Eu2+,Nd3+;

Investigating the influence of effective parameters on molecular characteristics of bovine serum albumin nanoparticles by S.S. Rohiwal; R.K. Satvekar; A.P. Tiwari; A.V. Raut; S.G. Kumbhar; S.H. Pawar (157-164).
The physiochemical properties of nanoparticles provide the basic aspects about the conformational transitions which could have a strong bearing on the bioavailability for bioactive molecules such as peptides and hormones.The protein nanoparticles formulation is a challenging task as they are prone to undergo conformational transitions while processing which may affect bioavailability for bioactive compounds. Herein, a modified desolvation method is employed to prepare Bovine Serum Albumin nanoparticles, with controllable particle size ranging from 100 to 300 nm and low polydispersity index. The factors influencing the size and structure of BSA NPs viz. protein concentration, pH and the conditions for purification are well investigated. The structure of BSA NPs is altered due to processing, and may affect the effective binding ability with drugs and bioactive compounds. With that aims, investigations of molecular characteristics of BSA NPs are carried out in detail by using spectroscopic techniques. UV–visible absorption and Fourier Transform Infrared demonstrate the alteration in protein structure of BSA NPs whereas the FT-Raman spectroscopy investigates changes in the secondary and tertiary structures of the protein. The conformational changes of BSA NPs are observed by change in fluorescence intensity and emission maximum wavelength of tryptophan residue by fluorescence spectroscopy. The field emission scanning electron and atomic force microscopy micrographs confirm the size and semi-spherical morphology of the BSA NPs. The effect of concentration and pH on particle size distribution is studied by particle size analyzer.
Keywords: BSA NPs; Conformational change; Spectroscopic method; Particle size analysis; Zeta potential;

We used piezoresponse force microscopy (PFM) to investigate local domain relaxation behavior of overhanging PbTiO3 (PTO) nanodot arrays on platinized silicon substrates, which were prepared by using PbO vapor phase reaction sputtering on micellar monolayer films of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) loaded with TiO2 sol–gel precursor. The overhanging PTO nanodot arrays (92% at a temperature of 100 °C for 365 min) showed better ferroelectric retention than the PTO thin films (80% at the same condition). The enhanced polarization states and the absence of depolarization field due to homogeneous electric field inside the overhanging nanodot allowed for the remarkable durability of designated ferroelectric polarization.
Keywords: Ferroelectrics; Retention; Lead titanate; Piezoresponse force microscopy; Nanodot;

Analysis of carrier transport in photovoltaic structures of P3HT with CdSe nanocrystals by V. Kažukauskas; E. Couderc; A. Sakavičius; A. Nekrošius; V. Vertelis; P. Reiss; D. Djurado; J. Faure-Vincent (169-173).
Hybrid photovoltaic structures made of P3HT and branched CdSe nanocrystals (NCs) with 50–90 wt% ratio were investigated. Charge Extraction by Linearly Increasing Voltage (CELIV) mobility and temperature dependent (photo-)conductivity measurements were used to analyze the charge transport. The samples with 50 wt% were photosensitive, but just a minor PV effect was observed. The photovoltaic phenomenon was pronounced in the samples containing 75 wt% or more of NCs. The Open Circuit Voltages up to 1 V were obtained. The recombination of the generated carriers was fast and could be a limiting factor of the cell current. Carrier mobility was up to (3–4) × 10−4  cm2/V s. From the fitting of mobility data the best carrier transport conditions were found in the samples with 75 wt% and 83 wt% of NCs.
Keywords: P3HT; CdSe; Nanocrystals; Hybrid solar cells; Mobility; Charge transport;

We present a morphology study on laser ablation produced metal nanoparticles (NPs) deposited on carbon nanotube (CNT) substrates. We analyzed the coating geometry and topography by processing AFM and SEM images. Our results show that Ag NPs aggregate together to form large agglomerates, that Ti NPs are well dispersed on the substrate surface forming a quasi-continuous layer, and that Co, Ni, and Al NPs coat quite uniformly CNTs and locally grow in a layer like fashion. We interpret the coating and clustering geometries in terms of cohesion, surface, and interfacial energies and diffusion barriers. Fractal analysis of composites morphology suggests the formation of structures with a smoother topography relative to pure carbon nanotubes for reactive metal nanoparticles.
Keywords: Carbon nanotubes; Metal nanoparticles; Hybrid materials; Wetting; Coating; Fractal analysis;

Comparative study on the annealing types on the properties of Cu2ZnSnS4 thin films and their application to solar cells by Chang Woo Hong; Seung Wook Shin; K.V. Gurav; S.A. Vanalakar; Soo Jung Yeo; Han Seung Yang; Jae Ho Yun; Jin Hyeok Kim (180-184).
Comparative studies on the properties of Cu2ZnSnS4 (CZTS) thin films and performance of CZTS thin film solar cells (TFSCs) prepared by different sulfurization types such as commerical furnace (CF) and rapid thermal annealing (RTA) systems have been investigated. The CZTS thin film prepared using CF showed the dense microstructure with many voids and secondary phases, while that prepared using RTA showed the dense microstructure without void and with some secondary phases. The RTA annealed CZTS TFSC have shown better performance than that prepared using CF. The best performance of CZTS TFSC using RTA was 1.9% efficiency (V oc: 505 mV, Jsc: 7.5 mA/cm2 and FF: 50.2%).
Keywords: Cu 2 ZnSnS4(CZTS); Sulfurization; Commercial furnace; Rapid thermal annealing; Thin film solar cells;

Nano-structured carbon materials for improved biosensing applications by J. Razumiene; I. Sakinyte; J. Barkauskas; R. Baronas (185-191).
A set of oxidized graphite samples have been newly synthesized using different protocols. Atomic force microscopy, Raman spectroscopy, thermal gravimetric analysis and Brunauer–Emmett–Teller analysis revealed the changes in structure and functionalities of obtained graphite oxidation products (GOPs) compared to pristine graphite. The substances have been tested as electrode materials applicable for bioelectrocatalytic systems using pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH). The application of GOPs allowed achieving the direct electron transfer (DET) from active site of PQQ-GDH to the electrode surface. Needless of additional electron transfer (ET) mediating compounds highly improved features of the biosensors. The efficiency of the biosensors has been evaluated for all types of biosensors varied from 32 μA/cm2 to 64 μA/cm2 using as electrode materials GOP1 and thermally reduced graphite oxide (TRGO), respectively. TRGO containing function groups (according TGA, ∼6% of the weight loss) and smallest particles (average diameter was ∼11 nm and the average height was ∼0.5 nm) exhibited the higher efficiency for ET acceleration in the biosensor acting on principle of DET.
Keywords: Graphite oxidation products; Surface function groups; Bioelectrocatalysis; Direct electron transfer; PQQ-GDH;

Pulsed electrodeposition of Cu2ZnSnS4 thin films: Effect of pulse potentials by K.V. Gurav; Y.K. Kim; S.W. Shin; M.P. Suryawanshi; N.L. Tarwal; U.V. Ghorpade; S.M. Pawar; S.A. Vanalakar; I.Y. Kim; J.H. Yun; P.S. Patil; J.H. Kim (192-196).
Cu2ZnSnS4 (CZTS) thin films are electrodeposited on Mo substrate using pulsed electrodeposition (PED) at different pulse potentials. The pulse potential (V1) is varied from 0 V/SCE to −0.9 V/SCE and V2 fixed at −1.1 V/SCE. The effects of pulse potentials on the properties of CZTS thin films are investigated. Formation of secondary phases along with CZTS phase is evident for films deposited at low pulse potentials. The secondary phases seem to be reduced with increase in pulse potentials. The morphology of CZTS films is systematically evolved from agglomerated grains to compact one with increase in pulse potentials. The film deposited using optimized pulse potentials (V1 – −0.9 V/SCE and V2 – −1.1 V/SCE) exhibit prominent CZTS phase with nearly stoichiometric composition and has compact morphology with optical band gap energy of 1.46 eV.
Keywords: Cu2ZnSnS4 (CZTS) thin films; Pulsed electrodeposition; Thin film solar cells (TFSCs);

Fabrication and current–voltage characteristics of NiOx/ZnO based MIIM tunnel diode by Aparajita Singh; Rudraskandan Ratnadurai; Rajesh Kumar; Subramanian Krishnan; Yusuf Emirov; Shekhar Bhansali (197-204).
Enhanced asymmetric and non-linear characteristics of Ni–NiOx based MIM diode has been reported by the addition of a second insulator layer ZnO to form MIIM configuration. These properties are required for applications like energy-harvesting devices, terahertz electronics, macro electronics, etc. In this work, single insulator layer Ni–NiOx–Cr and double insulator Ni–NiOx–ZnO–Cr tunnel diodes were fabricated and their I–V characteristics were studied. A significant increase by one order of magnitude in asymmetry has been observed in case of bilayer NiOx/ZnO dielectric configuration at low voltages. The sensitivity of the NiOx and NiOx/ZnO dielectric configuration in MIM stack was 11 V−1 and 16 V−1. The improved performance of the bilayer insulator diode is due to the second insulator which enables resonant tunneling or step-tunneling. Resonant tunneling was found to be dominant through trap assisted tunneling in the NiOx/ZnO diode.
Keywords: MIM diode; MIIM diode; Resonant tunneling; Trap assisted tunneling;

Spatially selective Er/Yb-doped CaF2 crystal formation by CO2 laser exposure by Dong-Seon Kim; Jin-Ho Lee; Ki-Soo Lim (205-209).
We report the glass–ceramic precipitation on the oxyfluoride glass surface by spatially selective annealing with a CO2 laser and a heat gun exposure. X-ray diffraction analysis showed the formation of major CaF2 and miner Ca2SiO4 nanoparticles. We observed ∼100 nm nanoparticle aggregation by tunneling electron microscopy and element distribution in glass and crystal phases. Spatial distribution of glass ceramics near the glass surface was probed by confocal fluorescence microscope by using much enhanced emission from the Er ions in the laser-treated area. Strong emissions at 365 nm excitation and visible up-conversion emissions at 980 nm excitation also indicated well incorporation of Er and Yb ions into a crystalline environment.
Keywords: CaF2; Nanocrystals; Glass–ceramics; CO2 laser; Er; Upconversion;

Growth evolution of self-textured ZnO films deposited by magnetron sputtering at low temperatures by J.R.R. Bortoleto; M. Chaves; A.M. Rosa; E.P. da Silva; S.F. Durrant; L.D. Trino; P.N. Lisboa-Filho (210-215).
In this work, the evolution of the surface morphology of ZnO thin films deposited by reactive RF magnetron sputtering has been investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD). All AFM images of the films were analyzed using scaling concepts. To study the growth evolution, different ZnO films with thicknesses of up to 1270 nm were deposited at temperatures of 100 and 250 °C. For the films grown at 100 °C, AFM data show that the lateral length ξ evolves continuously while the temporal evolution of the root mean square roughness σ presents two distinct regimes. Early during the depositions, the morphology of the ZnO films is mainly characterized by granular structures. Beyond thickness of about 600 nm, pyramid-like structures with {214} crystallographic facets start to develop. For the films grown at 250 °C, however, only one growth regime was observed and for the thicker films, the surface morphology consisted of polygonal structures. For the films grown at 100 °C, the growth exponents, β, and the exponent defining the evolution of the characteristic wavelength of the surface, p, were β 1  = 0.70 ± 0.02 and β 2  = 0.26 ± 0.2; and p  = 0.2 ± 0.04. For the films grown at 250 °C, the exponent values were β  = 0.78 ± 0.02 and p  = 0.32 ± 0.05. These values of the exponents indicate the occurrence of surface mechanisms, such as shadowing and surface diffusion, as well as facet stabilization at 100 °C. For the films grown at 250 °C, however, structural misorientation during growth also plays an important role.
Keywords: Surface texturing; ZnO thin films; Magnetron sputtering; Low temperature; Growth evolution;

Photoluminescence quenching of Zirconia nanoparticle by surface modification by Gaganpreet K. Sidhu; Ajeet K. Kaushik; Sweta Rana; Shekhar Bhansali; Rajesh Kumar (216-221).
Zirconia nanoparticles (ZrO2-NPs) of size ∼10 nm have been synthesized using hydrothermal method. ZrO2-NPs annealed at high temperature (400–850 °C) exhibits a better crystallinity along with phase transformation. The PL intensity of ZrO2-NPs found to be annealing temperature dependent due to the change in crystallinity and surface defects. The ZrO2-NPs have also been synthesized in the presence of surfactants i.e. sodium dodecyl sulfate (SDS). The presence and interaction of ZrO2-NPs with surfactant has been verified using FTIR study. Optical studies showed significant reduction in PL intensity of ZrO2-NPs on surface modification. The decrease in PL intensity has been attributed to the passivation of ZrO2-NPs surface defects by surfactant molecules. The outcomes of the study pave the way to explore these ZrO2-NPs for optical sensors.
Keywords: Nanoscience; Zirconia; Surface modification; Optical sensor;

Combined effect of nitrogen doping and nanosteps on microcrystalline diamond films for improvement of field emission by U.A. Mengui; R.A. Campos; K.A. Alves; E.F. Antunes; M.H.M.O. Hamanaka; E.J. Corat; M.R. Baldan (222-226).
Nitrogen-doped microcrystalline diamond (N-MCD) films were grown on Si substrates using a hot filament reactor with methanol solution of urea as N source. Electrostatic self-assembly seeding of nanocrystalline diamond were used to obtain continuous and uniform films. Simultaneous changes in grains morphology and work function of diamond by nitrogen doping decreased the threshold field and the angular coefficient of Fowler–Nordhein plots. The field emission properties of our N-MCD films are comparable to carbon nanotube films.
Keywords: Microcrystalline diamond; Hot filament; Urea; Nitrogen doping; Field emission;

Electrospun Polyurethane based nanofibrous membranes were fabricated from the solutions prepared with various volume ratios of N,N-dimethylformamide (DMF) and Tetrahydrofuran (THF). Properties of the blended solutions were analyzed in terms of viscosity and conductivity. The morphology of nanofibrous membranes were observed by SEM analysis. Experimental results revealed that the morphologies of polyurethane nanofiber membranes have been changed significantly with the solvent selection and mixing ratios of the solvents for the electrospinning. Diameter of the nanofibers was recorded in the range between 277 nm and 556 nm, respectively. Tensile strength and elongation measurements confirmed that mechanical characteristics of the nanofibrous membranes were strongly influenced by the fiber morphology and the uniformity.
Keywords: Polyurethane; Electrospinning; Nanofiber; Solvent; DMF; THF;