Current Nanoscience (v.12, #2)

Meet Our Editorial Board Member: by Simon Scheuring (135-135).

Recent Progress of Perovskite Solar Cells by Fei Zhang, Shirong Wang, Xianggao Li, Yin Xiao (137-156).
The current article reviews recent development of perovskite solar cell, highlighting operating principles, perovskite absorber, hole-transport contact, electron-selective contact and counter electrode. The existing problems of perovskite solar cells will be discussed according to the current research result, meanwhile the advances of it are also briefly summarized.

In this review paper, the background and applications of thermoelectrics are first provided. The fundamentals of thermoelectrics which involve a few central physical parameters characterizing the electrical and thermal transport properties are described. The complicit among electrical and thermal conductivity as well as Seebeck coefficient in achieving large thermoelectric figure of merit is then discussed, which suggests nanostructure engineering as an effective approach to lower the lattice thermal conductivity for improved thermoelectric properties. The concept and approach are also demonstrated and discussed with selected examples. ZnO based thermoelectric materials are emphasized, due to the merits of inexpensiveness, earth abundance, chemical and high temperature stability as well as nontoxicity. A few examples of ZnO related oxide systems are briefly reviewed and proposed as useful model systems to investigate and understand the correlations between chemical compositions, phase equilibria, microstructure and thermoelectric properties. The outlook for designing and developing thermoelectric oxides with complex nanostructure is also provided at the end.

Performance Enhancement of Nanostructure Silicon Anode for Lithium Ion Battery by Shuwei Li, Chunsong Zhao, Bo Li, Hui Wu (169-174).
With the rapid development of electronic technology and increasing demands of space and charge efficiency, the requirements including small size, light weight, high energy capacity and long cycling life for the performance of batteries are rising increasingly. Lithium-ion battery presents many advantages, such as high energy capacity (per weight and volume), long cycling life, low pollution and working voltage. With the previous literatures mentioned, Si which has the high theoretical capacity is about to become a promising and challengeable electrode material for researchers all over the world. This review outlines means of the enormous evolution of Si anodes for lithium-ion batteries.

Standard Raman spectroscopy coupled with metal nanostructures, known as surfaceenhanced Raman spectroscopy (SERS), has exhibited great potential in detecting molecules at trace levels. Translating this profound phenomenon into practical applications requires reliable and scalable approaches to manufacture SERS-active metal nanostructures, so-called SERS substrates, with well controlled quality. Following a review on the fundamental aspects of SERS, this paper summarizes a broad spectrum of nanofabrication methods that have been employed for SERS substrates and groups these nanofabrication techniques into three categories: lithography based methods, non- lithography template methods, and direct formation. It should be noted that this review focuses on on-chip SERS substrates and the colloidal nanoparticles-based SERS substrates are not in the discussion. In the end of the review, the paper also briefly discusses several commercialized SERS substrates on the market.

Wrinkles and Wrinklons in Graphene and Graphene Nanoribbons Under Strain by Julia A. Baimova, Elena A. Korznikova, Sergey V. Dmitirev, Bo Liu, Kun Zhou (184-191).
Wrinkling of thin films and membranes is frequently observed in nature. Graphene, which represents one layer of carbon atoms or thick carbon membrane have unusual mechanical and physical properties. Particularly, graphene has high stretching stiffness in combination with very low bending stiffness and its flat configuration is easily lost under external factors such as strain, temperature or segregation of other atoms. Compressive in-plane stresses applied to graphene and graphene nanoribbons lead to the wrinkles generation. Wrinklons, which are transition zones where two or more wrinkles merge into one, appear to minimize the total potential energy of a graphene under compressive stress. The mechanical and physical properties of corrugated graphene are considerably different from those of flat graphene and can be intentionally altered by controllable wrinkling. In this review, both the recent results on wrinkling of graphene and the effect of the corrugation on the graphene properties are presented together with the description of the potential applications of the corrugated structures for the production of novel bulk carbon nanomaterials.

Nanoscaled Martensitic Domains in Ferroelastic Systems: Strain Glass by Dong Wang, Xiaobing Ren, Yunzhi Wang (192-201).
Strain glass, a frozen disordered ferroelastic state characterized by randomly distributed nanoscaled, non-ergodic martensitic domains, was recently found in ferroelastic TiNi-based alloys. Point defects like anti-site defects or dopants are found essential for the formation of the strain glass, but their role has remained obscure. In this paper, phase field method is employed to simulate how point defects change a normal ferroelastic system into a strain glass and as the result to clarify the role of point defects. We found that the local symmetry-breaking caused by the anisotropic local strain field of point defects plays a central role in the formation of strain glass. Such point-defect-induced local symmetry-breaking hinders the formation of long-range strain-ordering (twinned martensite) and results in a decrease in transition temperature Tc and a reduction of ferroelastic domain size. Above a critical defect concentration, the system transforms to a frozen state of nano-sized ferroelastic domains, i.e., strain glass. In addition, our simulation shows a gradual vanishing of heat capacity peak at the transition temperature with increasing defect concentration, and it also reproduces a characteristic non-ergodic ZFC/FC behavior of the glass state, which is in good agreement with recent experimental observations. Our results also indicate that the concentration fluctuation effect of point defects cannot stabilize a strain glass to very low temperature; thus the direct interaction between the random anisotropic strain field caused by point defects and the strain order parameter of the system is crucial for the formation of strain glass.

Background: The atomic force microscope (AFM) technique has proven to be a useful and versatile tool for the surface characterization of various materials. AFM is capable of providing three dimensional representations of surfaces down to the sub-nanometer scale resolution, with even atomic resolution. The aims of this mini review are to briefly illustrate our personal experience in AFM application for characterizing plasma-treated surface growth on different substrates, such as fluorocarbon (CFx) nano-structured films, polyethylene oxide (PEO) substrates and plasma deposited acrilic acid (pdAA) coatings, and nanocomposite materials, such as polydimethylsiloxane-gold (PDMS-Au) and chitosan-Au (CTO-Au), including the characterization of nanoparticle powder.
Methods: The CFx films were obtained by plasma enhanced-chemical vapor deposition in the non-contact AFM mode and pdAA coatings by radiofrequency glow discharges fed with AA vapors and analyzed in the contact AFM mode. Coating morphology was analized by X-Ray photoelectron microscopy (XPS) and water contact angle (WCA). The AFM images of PDMS-Au and CTO-Au nanocomposites was also acquired and analyzed for their topography.
Results: The surface topography, the root-mean square (RMS) surface roughness and the mean surface height of CFx coatings plasma-polymerised on polyethyleneterephthalate (PET) substrates were evaluated by AFM as a function of the deposition time, and AFM images obtained were used to gain detailed topographical information of the single nanostructure. By comparing the AFM images of pure PDMS with those of PDMS-Au it was possible to observe the topography of nanofillers embedded in a polymeric matrix or generated on a polymeric surface and also other main differences between the two materials.
Conclusion: The AFM technique was shown to be a versatile and promising tool for the morphological characterization of growth of plasma-treated surfaces, such as CFx nano-structured films, PEO substrates and pdAA coatings, and for the topographical characterization of nanocomposite materials such as PDMs-Au and CTO-Au. Finally, AFM can be used as a simple method able to characterize the topography of as-received nanofillers, based on the attachment of the nanopowders on a bi-adhesive tape and on 3D image processing.

Drug Coated Clay Nanoparticles for Delivery of Chemotherapeutics by L. Sun, C. Boyer, R. Grimes, D.K. Mills (207-214).
Purpose: Osteosarcoma (OSA) is the most common malignancy of bone in children and adolescents. Standard treatments include adjuvant chemotherapy, radiotherapy, hormone or biological therapy, and if OSA is refractory, surgical ablation of the primary tumor. Advancements in treatment modalities have led to increased rates of 'limb-sparing' surgeries, but patients are still threatened with the risk of recurrence. New chemotherapeutic delivery systems and strategies are needed to improve treatment options and patient outcomes.
Methods: Halloysite nanotubes (HNTs) exhibit high levels of cytocompatibility and biocompatibility and have been show to be effective at sustained drug release. HNTs were coated with the polyelectrolytes (PE), polyvinylpyrrolidone and polyacrylic acid, and methotrexate (MTX) infused within the coating layers. MTX release and cytotoxicity studies were used to assess the effectiveness of the coatings in inhibiting osteosarcoma cell growth.
Results: Polyelectrolyte coatings provided sustained release of MTX and, in an in-vitro study, were show to be effective in altering osteosarcoma cell morphology and reducing the rate of cell proliferation. We further show that MTX-coated halloysite nanotubes can be added to a polymer, Nylon-6; the MTX released, and still retain its ability to inhibit osteosarcoma cell growth.
Conclusion: HNT/MTX encapsulated complexes inhibited osteosarcoma cell proliferation and show potential as a delivery vehicle for the prevention of tumor metastasis and/or tumor recurrence after surgery.

Improving the Electrical Conductivity of Multi-walled Carbon Nanotube Thin Films Using Ag-nanowires by Amir Zilaee, Mansoor Farbod, Marzieh Khademalrasool (215-219).
Background: Transparent and conductive films (TCF) are the principal core for fabricating electronic devices. The traditional TCFs, indium tin oxide (ITO) thin films have been used for such devices which have their own drawbacks. In the present study, multi-walled carbon nanotubes (MWCNTs) thin films were fabricated and their electrical conductivity was improved by adding Ag nanowires to the CNTs for the first time in literature.
Methods: The initial multi-walled carbon nanotubes with the diameters less than 10 nm and 5-15 m length were oxidized in a mixture of sulfuric and nitric acids. Silver nanowires were synthesized by solvothermal method through reducing silver nitrate with ethylene glycol (EG) in the presence of polyvinylpyrrolidone (PVP). Different solutions including 1.8, 3.5, 5.1, and 10.5 wt.% of Ag/MWCNTs were prepared and coated on a cleaned and functionalized glass substrate by spin coating technique.
Results: For low thicknesses, dc conductivity of the films was thickness-dependent but appeared to become bulk-like for film thicknesses of about 300 nm. A sheet resistance of 1006 ohm/sq with 82% transmittance at 550 nm in wavelength was attained for 5.1wt.% Ag nanowires in MWCNTs. Using the deduced data, the DC conductivity to optical conductivity ratio for a percolated network 92.4 was calculated for 5.1wt.% of Ag nanowires in MWCNTs which was much higher than 37 for the films without using Ag nanowires.
Conclusions: It was observed that the conductivity and figure of merit of different films of MWCNTs-Ag nanowires composite were improved by increasing Ag nanowires concentration. The electrical conductivity and optical transmittance were affected by different Ag wt.% and different film thicknesses. The low sheet resistance of thin conductive films was due to the increased contact areas between MWNTs and Ag nanowires on the MWNTs surfaces.

Conducting and Biopolymer Based Electrospun Nanofiber Membranes for Wound Healing Applications by Mohammad R. Karim, Abdurahman Al-Ahmari, M.A. Dar, M.O. Aijaz, M.L. Mollah, P.M. Ajayan, J.H. Yeum, Kil-Soo Kim (220-227).
Background: Electrospinning is a modest and real tactic to harvest nanofiber membranes from micrometers to nanometers scale diameters, are useful in modern nanotechnology like biomedical, filtration, defense, catalysis, sensor and energy applications. Wound healing practice is deliberated a constant morphological modification of cells with the alteration of cell exodus, adherence, etc. In this characteristic, the advance of polymeric nanofiber scaffolds with together biodegradable and electrically conducting properties would be pronounced benefits in the biomedical field. Here it has been established the conducting polymer and biopolymer based electrospun nanofiber membranes exploited on wound healing and wound-size decline in rats successfully.
Methods: Ultrafine conducting polyaniline with o-aminobenzenesulfonic acid copolymer (PAni-co-PABSA) and poly (vinyl alcohol) (PVA)/chitosan oligossacaride (COS) biopolymers based electrospun nanofiber membranes have been exploited for wound healing applications. The nanofiber membranes were assembled by spawning double full-thickness skin wounds on the dorsum of SD rats.
Results: The current study is commenced to appraise the potentials for use of PAni-co-PABSA/PVA/COS electrospun nanofibers in wound healing in rats. The nanofiber membranes cured wounds show considerable lesser provocative responses throughout the experimental period. Area of nanofiber membranes and commercial (Fucidin®) ointment treated wounds are significantly decreased equate to control cured wounds. After 15 days treatment, the histological appearance by nanofiber membranes reveal almost complete healing and intensification in collagen and granulation as compare to control one.
Conclusion: The nanofiber membranes cured wounds have ample reduced inflammatory responses throughout the experimental period. Histological appearance after two weeks of management with PAni-co-PABSA/PVA/COS nanofiber reveals almost complete healing and an increase in collagen and granulation as compare to control.

Size-Dependent Differences in Biodistribution of Titanium Dioxide Nanoparticles After Sub-Acute Intragastric Administrations to Rats by Olga D. Hendrickson, Svetlana M. Pridvorova, Anatoly V. Zherdev, Sergey G. Klochkov, Oksana V. Novikova, Elena F. Shevtsova, Sergey O. Bachurin, Boris B. Dzantiev (228-236).
Background: The human and environmental exposure to titanium dioxide is currently large-scale. Taking into account that for TiO2 the peroral route of exposure seems to be a very important route of exposure for humans, knowledge of its biodistribution and toxicity after the peroral uptake, is highly relevant for the human health risk assessment of TiO2 NPs. The present study compares the biodistribution of titanium dioxide nanoparticles of different sizes (5-10 nm and 20-25 nm) after peroral administration to rats.
Methods: For comparison of the biodistributions of titanium dioxide nanoparticles, male rats were intragastrically administered with two specimens of TiO2 nanoparticles for a 28-day period at a daily dose of 250 mg/kg of body weight. Titanium dioxide was detected in rats` organs and tissues by atomic absorption spectroscopy.
Results: The absorption from the gastrointestinal tract (GIT) and translocation into secondary organs of titanium dioxide occurred in a size-dependent manner. After administration of the smaller nanoparticles, titanium was found in the brain, lungs, heart, liver, kidneys, spleen, small intestine, testicles, and blood (0.004-0.227 µ;g/g of organ), whereas after administration of the larger nanoparticles, titanium was accumulated only in the liver, kidneys, spleen, and small intestine (0.01- 0.29 µ;g/g of organ). The amounts of the detected titanium are much smaller than the administered doses. After repeateddose exposures, no animal deaths or toxicity indications were observed.
Conclusions: The penetration of titanium dioxide nanoparticles from the GIT of rats into the bloodstream and their translocation into secondary organs are size-dependent and has no evident toxic effect.

Performance Enhancement of Patch Antenna in Terahertz Region Using Graphene by Rajni Bala, Anupma Marwaha, Sanjay Marwaha (237-243).
Background: Graphene offers a new approach to THz communications due to its ability to support the propagation of SPP waves in the THz frequency band, and that desirable feature allows miniaturization of antenna size to micrometer scale without operating the antenna at very high resonant frequencies. The aims of this paper are to introduce readers to the conventional metallic square patch antenna fed by microstrip line with quarter wave transformer is redesigned with graphene as patch on silicon dioxide substrate with optimum height of 1.8 µ;m and permittivity of εr = 4. The conductivity model of graphene is formulated with finite thickness of the patch in order to investigate the effect of substrate properties and patch dimensions on the performance of microstrip fed square patch antenna in terahertz (THz) regime.
Methods: Research and online content associated to graphene as patch conductor is reviewed, and the proposed antenna geometry is designed and optimized in finite element method (FEM) based high frequency simulator (HFSS) software. Graphene as patch conductor material on SiO2 as substrate put forward good optical distinguish making it easy to make out the graphene layer.
Results: The use of graphene patch as conducting material for antenna, due to extraordinary electromagnetic properties and functionalities would exhibit enormous potential to enhance gain, return loss, radiation efficiency, radiated power and bandwidth. The paper shows enrichment of patch antenna in terahertz region using graphene to achieve return loss of -27.57 dB with reasonably good decibel gain at 13 THz. Much improved impedance bandwidth of 12.3% is achieved in the band of operation from 12.2 - 13.8 THz.
Conclusion: To explore the feasibility of using nano-antennas to meet the challenges of providing various miniaturized portable wireless communication devices for more flexible applications communicating at faster rates. It is apparent that graphene composite is an effective alternative to metal for the antenna structure offering simplicity in design. It is evident from the various results in terms of return loss, gain, radiation efficiency and bandwidth that the graphene based antenna realizes better characteristic as compared to metallic antenna.

Enhanced Luminescence Properties of Combustion Synthesized Y2O3:Gd Nanostructure by Seyed Mahdi Rafiaei, Aejung Kim, Mohammadreza Shokouhimehr (244-249).
Background: Y2O3:Gd phosphor nanostructures were prepared homogeneously by the combustion synthesis method at 500 °C using water and urea as the solvent and fuel, respectively. The synthesized phosphors were calcined at 800 °C and 1000 °C to improve the crystallinity and remove the organic phases. The crystal structures were characterized by an X-ray diffractometer and the morphology of the synthesized nanostructures were studied using a field emission scanning electron microscope, a transmission electron microscope, a scanning transmission electron microscopy and an energy-filtered transmission electron microscopy. The crystallite size of the phosphor materials was obtained in the range of 60 nm and changed remarkably with dopant concentration and calcination process. The maximum intensity of emission can be achieved when the dopant concentration is 7%. Further gadolinium doping resulted in the decrease of luminescence properties due to concentration quenching.
Methods: Combustion synthesis method was utilized to produce the phosphor powder with the composition of Y2-2xGd2xO3. In a typical synthesis of Y2O3:1%Gd3+ phosphor nanostructure, 5 g of yttrium nitrate and 0.055 g of gadolinium nitrate were dissolved in de-ionized water and stirred for 15 minutes at room temperature in an alumina crucible. Then 2 g urea was added to the mixture as a fuel while vigorous stirring. The precursor solution was transferred into a box furnace and heated at 500 °C for five minutes. The evaporation process started and a quick spontaneous combustion process resulted in producing a foamy and low dense powder. The produced powders were calcined at 800 °C and 1000 °C for 1 h in a box furnace in order to remove the organic materials and improve the crystallinity. Results: Y2O3:Gd phosphor nanostructures were synthesized to present the enhanced emission intensity with gadolinium doping concentration adjustment of 7%. Further doping increase resulted in the decrease of luminescence properties due to concentration quenching.
Conclusion: The nanoparticles of Y2O3:xGd3+ (x=1-12%) phosphors were synthesized by a simple combustion method. The crystallite size of synthesized powders was obtained in the approximate range of 50 nm to 90 nm. It was seen that due to similar characters of Y3+ and Gd3+ ions and Y2O3 and Gd2O3, even after doping of relatively high amounts of the dopants, all the XRD spectrum are well matched with the Y2O3 (JCPDS No. 83-0927) structure. In addition, it was found that the dopant concentration affects the crystallite size and photoluminescence properties. This study results show that Y2O3 nanostructures doped with 7%Gd3+ ions have the highest emission intensity and the increase of dopant decreases the photoluminescence properties due to quenching phenomenon.

Background: Bisphenol A (BPA) is widely used in its monomeric form in the manufacture of poly carbonate plastics, epoxy resins, and flame retardant. The visible photodegradation of BPA with di-crystalline TiO2 and CNT-COCl/TiO2 nanocomposites was investigated in this study.
Methods: The di-crystalline phases of nanocomposites were observed via preparing 1 mL HNO3 of 0.4-1.0 M for synthesis. The CNT-COCl/TiO2 nanocomposites were synthesized by doping acyl chloride- grafted CNTs onto titanium tetraisopropoxide followed by a hydrothermal method. The precursor ratio of CNT-COCl to Ti was set at 1/99 (w/w).
Results: Results showed distinguish increase in red-shift effect of characteristic wavelength at higher rutile crystalline phase. It addressed that a faster degradation rate of BPA was exhibited for di-crystalline nano-composites under visible irradiation compared to that for P25. Further, the BPA degradation rate was much higher in the photocatalytc system using di-crystalline TiO2 doped with CN-COCl. Both solution pH and addition of phosphate showed significant influences on the photo-activity of CNT-COCl/TiO2. The promotional effect caused by phosphate was ascribed to a proper charge separation and high amount of hydroxide radical formation. A degradation rate of 59.5 % was found for the synthesized CNTCOCl/ TiO2 with 50% rutile crystalline phase at pH 9.0 and 10-4 M PO43-.
Conclusion: A novel CNT-COCl/TiO2 photocatalyst was successfully synthesized and characterized. The titanium photocatalysts can be successfully excited by visible irradiation via adjusting the ratio of crystalline phase. Compare with peer carbon-doping TiO2, the CNT-COCl/TiO2 fabricated in this study has superior photocatalytic activity in visible light.

A Novel Method for the Determination of Graphite Exfoliation Degree by Feifei Jia, Bingqiao Yang, Jing Su, Shaoxian Song (260-265).
Background: Various methods are used to characterize the exfoliation degree of graphite to graphene, however they fail in time-consuming and inaccuracy. The aim of this paper is to develop an accurate and easily operated technique for the determination of the exfoliation degree of graphite in liquids.
Methods: The exfoliation of graphite has been studied to relate with the change of suspension turbidities during its exfoliation into graphene. The study included a theoretical derivation based on the Rayleigh-Gans-Debye approximation and experimental approaches.
Results: The number of fresh graphene flakes formed from the exfoliation is directly proportional to the ratio of suspension turbidity before and after the graphite particles are exfoliated.
Conclusion: The exfoliation degree of graphite could be well characterized by the changes of the turbidity. This novel method would also be an effective and promising technique to determine the exfoliation degree of layered particles in liquids.

Background: The main aim of this study is to investigate the effects of electrospinning and filtration process parameters such as polymer solution concentration, the initial concentration of metal solution and the pH of solution on the adsorption of Ag and Cr.
Methods: In this investigation, firstly, nylon 66 nanofiber membranes were prepared by electrospinning of nylon 66 solution in formic acid/chloroform mixture with the average diameter of 146.68- 760.83 nm. Then, the nanofibers were functionalized with Aminopropyltriethoxysilane (APTES) that had an amine group suitable for metal adsorption due to their high adsorption affinity for heavy metal ions. Silver and chrome that are two harmful heavy metals were chosen. The cross flow recirculation filtration set-up was employed.
Results: Under optimum condition, the maximum efficiency of the absorption of silver and chrome was 99.97% and 93.06%, respectively. Filtering mechanism of the membrane were blocked the pores and the Freundlich isotherm was found to well represent the measured adsorption data based on the higher coefficient determination (R2).
Conclusion: The maximum adsorption capacity of Ag and Cr by Freundlich model was 1946.91 and 650.41 mg g-1 respectively, showing a high capacity to work.