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Two-dimensional van der Waals heterostructures (vdWHs) with tunable band alignment have the potential to be benignant in the development of minimal multi-functional and controllable electronics, but they have received little attention thus far. It is crucial to characterize and control the band alignment in semiconducting vdWHs, which determines the electronic and optoelectronic properties. The future success of optoelectronic devices will require improved electronic property control techniques, such as using an external electric field or strain engineering, to change the electronic structures directly. Herein, we review heterostructures fabricated as transition metal dichalcogenides (TMDCs) as one of their constituent monolayers with other notable 2D materials that can transfer from type-II to type-III (type-IIItype-II) band alignment when a biaxial strain or electric field is applied.

Magnetic nanostructured materials have found numerous biomedical applications. However, the influence of a magnetic field on the inhibition of pathogenic microorganisms has been poorly explored. Zinc and Iron nano-structured oxides have been widely used due to their biocompatibility and their excellent optoelectronic and magnetic properties. Nevertheless, little effort has been devoted to demonstrate their antibacterial activity at doses that are not harmful to mammalians. In this work, ZnO, Fe3O4 (MNPs) and ZnO@Fe3O4 (NCs) were synthesized and fully characterized. The materials exhibit good antibacterial activity to inhibit the growth of Staphylococcus aureus (S. aureus) and Helicobacter pylori (H. pylori) both, as planktonic cells and as biofilms structures at low doses. The photocatalytic activity of the materials (NCs) was demonstrated when radiated suspensions of NCs and microorganisms (MOs) exhibited higher inhibition growth of MOs in comparison to non-radiated assays. The materials show better antibacterial activity for biofilm growth inhibition in comparison to commercially available antibiotics. Magnetic antimicrobial films were fabricated by in situ deposition of MNPs in Arabic gum (AG) solution. The films exert enhanced antibacterial activity against S. aureus growth due to Fe3+lixiviation and magnetic disruption. Regarding the biocompatibility of the materials, ZnO modifies significantly biochemical parameters in Wistar rats after acute administration. Our results show that the composite ZnO@Fe3O4 at low doses: (a) exerts an optimum inhibition on the biofilm formation of microorganisms due to its synergetic activity of lixiviation of ions and oxidative activity; (b) good biocompatibility of the composite with living cells. These properties suit ZnO@Fe3O4 as potential candidates for the development of new anti-biofilm formulation.

We report on the preparation and optimization of low temperature (

Color-tunable semiconductor quantum dots (QDs) are highly attractive for a wide range of applications including imaging, sensing, and lighting. Herein, we reported a facile synthesis of copper-doped zinc sulfide quantum dots (ZnS:Cu QDs) with tunable emission colors, using a microwave-assisted one-pot reaction. 3-mercaptopropionic acid (MPA) was used as a stabilizer agent and sulfide source for the formation of ZnS:Cu QDs. The photoluminescence of ZnS:Cu QDs showed a clear red-shift as increasing Cu concentration, which can be controlled by microwave irradiation time. As increasing the irradiation time, the emission color (peak) of ZnS:Cu QDs changed from blue (500 nm) to green (540 nm), yellow (580 nm), and to orange-red (595 nm). The obtained ZnS:Cu QDs were highly luminescent, as evidenced by their high quantum yields. The potential utility of ZnS:Cu QDs as a novel lighting source was demonstrated in a near-UV chip-based white light-emitting diode.

Antimony sulfide (Sb2S3) has been employed for materials of the potential anode in sodium-ion batteries (SIBs) because it possesses a high theoretical capacity. However, volume variations coupled with sluggish diffusion kinetics cause rapid capacity degradation and cyclic instability during the sodiation/desodiation process. Here, we introduce a simple strategy to develop nitrogen-doped carbon-encapsulated antimony sulfide nanowire (Sb2S3@N-C) composites for the anode in SIBs. The resulting composites display excellent electrochemical characteristics with remarkable rate capability, ultrahigh capacity, and excellent stability derived from the synergistic effect between a one-dimensional Sb2S3 nanowire and a nitrogen-doped carbon, thus demonstrating the Sb2S3@N-C composites as a material with potential characteristics for the anode in next-generation storage devices. Electrochemical analysis reveals that pseudocapacitive behavior dominates the overall electrochemical process of the Sb2S3@N-C composites, which is responsible for the fast capacitive charge storage. The authors acknowledge support from the Cultivation Project of National Engineering Technology Center (Grant 2017B090903008), National Natural Science Foundation of China Program (Grant 51602111), Special Fund Project of Science and Technology Application in Guangdong (Grant 2017B020240002), Basic Research Project of Knowledge Innovation Program of Shenzhen City (Grant JCYJ20160229165250876), and Xijiang R&D Team.

Cancer treatment by magnetic hyperthermia offers numerous advantages, but for practical applications many variables still need to be adjusted before developing a controlled and reproducible cancer treatment that is bio-compatible (non-damaging) to healthy cells. In this work, Fe3O4 and CoFe2O4 were synthesized and systematically studied for the development of efficient therapeutic agents for applications in hyperthermia. The biocompatibility of the materials was further evaluated using HepG2 cells as biological model. Colorimetric and microscopic techniques were used to evaluate the interaction of magnetic nano-materials (MNMs) and HepG2 cells. Finally, the behavior of MNMs was evaluated under the influence of an alternating magnetic field (AMF), observing a more efficient temperature increment for CoFe2O4, a desirable behavior for biomedical applications since lower doses and shorter expositions to alternating magnetic field might be required.

Novel hybrid architectures based on ZnO nanostructures supported on reduced graphene oxide films are reported by a facile two-step aqueous electrochemical approach. Graphene oxide (GO) obtained by oxidizing graphite with either H2SO4:H3PO4 mix or H2SO4 was subjected to electrochemical reduction (ErGO) by constant potential and sweeping potential methods and further employed as seeding layer for electrodeposition of ZnO nanorods. The results showed the GO reduction rate was markedly influenced by oxygen content while Infrared spectroscopy indicated the sweeping potential was effective in removing the carbonyl and alkoxy groups but also as more defect-inducing reduction approach than constant potential, according to the Raman measurements. The subsequent electroreduction of ErGO during the electrodeposition of ZnO resulted in interfacial interaction between the seed layer and ZnO nanorods. H2SO4:H3PO4 mix induced a less disrupted graphitic plane in GO which proved beneficial for the growth of higher density ZnO nanorods with improved crystalline quality. By controlling the chemical introduction/electroreduction conditions for oxygen groups in GO materials, the interfacial interaction with ZnO nanorods and their properties could be tailored in order to obtain high performance nanoplatforms.

Bismuth chalcogenides are promising materials for thermoelectric (TE) application due to their high power factor (product of the square of the Seebeck coefficient and electrical conductivity). However, their high thermal conductivity is an issue of concern. Single doping has proven to be useful in improving TE performance in recent years. Here, it is shown that dual isovalent doping shows the synergistic effect of thermal conductivity reduction and electron density control. The insertion of large atoms in the layered Bi2Te3 structure distorts the crystal lattice and contributes significantly to phonon scattering. The ultralow thermal conductivity (KT = 0.35 W m−1 K−1 at 473 K) compensates for the low power factor and thus enhances TE performance. The density functional theory electronic structure calculation results reveal deep defects states in the valence band, which influences the electronic transport properties of the system. Therefore, the dual dopants (indium and antimony) show a coupled effect of improvement in the density of state near the Fermi level and reduction in the conduction band minimum, thus enhancing electron density. Numerically, it is demonstrated that the dual doping favors acoustic phonon scattering and thus drastically reduces the thermal conductivity.

Nowadays, air pollution has become a global menace being responsible of a significant increase on the morbidity and mortality of human beings. In view of this, sustainable and efficient technologies for air purification are being sought. Air purification by photocatalytic treatment has received a lot of attention due to the unspecific and high oxidation capacity of the catalyst; however still some variables must be optimized to assure practical applications. In this work, visible light active TiO2–Cu2+@perlite and Ag@TiO2–Cu2+/perlite supported materials were fabricated. TiO2–Cu2+ (2 at. %) were synthesized using a sol-gel procedure followed of the impregnation of the support by immersion. For Ag@TiO2–Cu2+, silver deposition was conducted by chemical reduction using sodium citrate and sodium borohydride. The materials (powders and supported materials) were characterized by Scanning Electron Microscopy (SEM) to demonstrate their small size and adherence to the substrate. A prototype of a photocatalytic air purifier was built. The efficacy of the prototype was evaluated for the disinfection of indoor air (dentistry clinics). The photo-catalyst was activated using visible and UVA low-cost high-energy LEDs. The antibacterial activity of the air filter was evaluated. Ag@TiO2–Cu2+ exerts better air disinfection activity at lower doses in comparison to TiO2–Cu2+. Bacterial growth inhibitions up to 99% were achieved for both, Gram-negative and Gram-positive bacteria. The incorporation of Ag and Cu to TiO2 improves the antibacterial activity of the materials due to enhanced photocatalytic activity and the synergic activity of TiO2 and dopant elements (Ag, Cu) to inhibit microorganism’s growth.

Emerging photonic, sensing, and quantum applications require high fields and tight localization but low power consumption. Spatial, spectral, and magnitude control of electromagnetic fields is of key importance for enabling experiments in atomic, molecular, and optical physics. We introduce the concept of zero-admittance domains as a mechanism for tailoring giant optical fields bound within or on the surface of dielectric media. The described mechanism permits the creation of highly localized fields of extreme amplitudes simultaneously for incident photons of multiple wavelengths and incidence angles but arbitrary polarization states. No material constraints are placed upon the bounding media. Both intrinsic and extrinsic potential practical limitations of the predicted field enhancement are analyzed and applications relevant to optical sensors and microsources are briefly discussed.

We investigate the low-cost, earth-abundant and air-stable inorganic absorber Sb2S3 that can be processed in the air for organic–inorganic hybrid solar cell applications. To this end, we deposited thin layers of Sb2S3 with thicknesses of 45.0 ± 5, 60.0 ± 7, 80.0 ± 8, 100.0 ± 10 and 120 ± 24 nm by a thermal evaporation method. The absorber Sb2S3 and the hole transporting layer P3HT were annealed under atmospheric conditions at temperatures of 320 and 150 °C for 30 and 10 min in air, respectively, to prepare glass/ITO/TiO2/Sb2S3/P3HT/Ag heterojunction solar cells. We noticed that the values of Jsc, Voc, FF and η were changed with the thickness variation. It is interesting that the best device condition was obtained for a thickness of 100 ± 10 nm achieving an efficiency of 1.94% which was the highest efficiency among the flat structure devices. SEM, XRD, Raman and TEM studies showed that the annealed films were polycrystalline in nature. Further characterization was carried out of the best device by spectroscopic ellipsometry, UV-vis, QE, XPS and UPS. In addition, important electronic and optical properties of Sb2S3 were investigated based on first principles density functional theory (DFT) with generalized gradient approximation (GGA). The obtained experimental values of n, k, e1 and e2 are close to the theoretical results.

sp–d exchange interaction was used to narrow the room-temperature band gap of zinc oxide films prepared by sol–gel method. Zinc oxide was doped with manganese ions by adding manganese chloride to the precursor and post-annealing in hydrogen. Films with different concentrations of manganese were prepared. Exchange interaction was established between the manganese ions in the lattice by introducing oxygen vacancies. The magnetic moment was found to increase with the concentration of manganese. For low concentrations of manganese, the band gap of the doped semiconductor was found to be wider than that of undoped ZnO films, in agreement with Vegard’s law. High concentrations of dopant resulted in a narrowing of the band gap. We ascribe the narrowing of the band gap to conduction band-edge Zeeman shifting. 12 at.% Mn was successfully substituted in ZnO films deposited by sol–gel method. Exchange interaction was established between the Mn ions through the mediation of oxygen vacancies. A narrowing of the band gap of ZnO was achieved by Zeeman shifting of the bottom of the conduction band.

We report a facile, one-pot hydrothermal strategy to prepare self-assembled three-dimensional mesoporous ZnFe2O4 submicron-sized spheres wrapped in graphene sheets as high-performance anode material for lithium ion batteries. The mesoporous submicron-sized spheres are composed of numerous nanoparticles where the void spaces between the neighboring nanoparticles provide a cushion to alleviate volume variation issues during the conversion/alloying process and also provide large contact areas with the electrolyte to facilitate lithium ion diffusion and electron transport during cycling. The synergistic effects between ZnFe2O4 submicron-sized spheres and graphene sheets are another positive effect to enhance the electrochemical performance. The electrochemical characterization of ZnFe2O4-graphene composites exhibits a high specific capacity of 1182 mAh g−1 cycling at a specific current of 100 mA g−1, and significantly enhanced rate capability and cycling stability after long-term testing resulting from their unique structure features.

Antimony sulfide can be used as a promising anode material for lithium ion batteries due to its high theoretical specific capacity derived from sequential conversion and alloying lithium insertion reactions. However, the volume variation during the lithiation/delithiation process leads to capacity fading and cyclic instability. We report a facile, one-pot hydrothermal strategy to prepare Sb2S3 nanorods wrapped in graphene sheets that are promising anode materials for lithium ion batteries. The graphene sheets serve a dual function: as heterogeneous nucleation centers in the formation process of Sb2S3 nanorods, and as a structural buffer to accommodate the volume variation during the cycling process. The resulting composites exhibit excellent electrochemical performance with a highly reversible specific capacity of ∼910 mA h g-1, cycling at 100 mA g-1, as well as good rate capability and cyclic stability derived from their unique structural features.

Bismuth sulfide (Bi2S3) is considered as a promising anode material for lithium ion batteries (LIBs) owing to its high theoretical specific capacity and intriguing reaction mechanism. However, capacity fading and cycling instability due to volume variation during the lithiation/delithiation process still remain a great challenge. Herein, we proposed a simple glucose assisted hydrothermal strategy and followed a post-treatment process to prepare hierarchical sulfur-doped carbon Bi2S3 (Bi2S3@SC) hollow nanotubes that self-assembled into sulfur-doped amorphous carbon coated Bi2S3 nanocrystals as building blocks. Glucose plays a decisive role in the formation process of Bi2S3 nanocrystals and subsequent self-assembly, forming Bi2S3@SC hollow nanotubes. The polysaccharide shell formed on the surface of Bi2S3 nanocrystals during the hydrothermal process was transformed into the sulphur-doped amorphous carbon layer after the post-treatment process. Electrochemical tests reveal that the resulting composites exhibit excellent electrochemical performance with a highly reversible cycling capacity of ∼950 mA h g−1 at a current density of 100 mA g−1, as well as a good rate capability and significantly enhanced cycling stability derived from their unique structural features, thus demonstrating the potential of Bi2S3@SC hollow nanotubes as high performance anode materials for LIBs. The analysis of electrochemical kinetics confirmed that the pseudocapacitive behavior dominates the overall storage process of Bi2S3@SC hollow nanotubes. MOE (Min. of Education, S’pore)

In this study, we have developed a facile method for preparation of highly fluorescent Au nanoclusters (AuNCs) using 11-mercaptoundecanoic acid (MUA) as both the reducing and stabilizing agent. The as-prepared MUA functionalized AuNCs (MUA-AuNCs) have good water solubility, excellent photostability, and strong fluorescence emission at 610 nm with a quantum yield of 7.28% in water. The fluorescence of MUA-AuNCs was first quenched by copper ions through electron transfer, subsequently caused obvious restoration by competitive effect after adding penicillamine, making it a potential fluorescent sensor for penicillamine with a detection limit of 0.08 μM. Furthermore, the newly designed fluorescence "on-off-on" assay was explored for the measurement of penicillamine in complex real water and urine samples with satisfactory results.

Bejaoui, A. et al., We report on the investigation by spectroscopic ellipsometry of films containing Cd1 − xHgxTe alloy quantum dots (QDs). The alloy QDs were fabricated from colloidal CdTe QDs grown by an aqueous synthesis process followed by an ion-exchange step in which Hg2+ ions progressively replace Cd2+. For ellipsometric studies, several films were prepared on glass substrates using layer-by-layer (LBL) deposition. The contribution of the QDs to the measured ellipsometric spectra is extracted from a multi-sample, transmission and multi- angle-of-incidence ellipsometric data analysis fitted using standard multilayer and effective medium models that include surface roughness effects, modeled by an effective medium approximation. The relationship of the dielectric function of the QDs retrieved from these studies to that of the corresponding II–VI bulk material counterparts is presented and discussed., The authors acknowledge financial support from the RGC/CSIC Joint Research Scheme with Refs. S-HK001/12 (RGC) and 2011HK0016 (CSIC). MIA, MG, MCQ and ARG thank the Spanish Ministry of Economy and Competitiveness for funding through grant MAT2015-70850-P, and the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496). JAZ acknowledges partial support from Project CityU 122812 from the Research Grants Council of Hong Kong. SVK and ALR acknowledge support from the Research Grants Council of Hong Kong (project CityU 11302114), and from the CityU Research Project 9610350.

We present a simple polymer-pyrolysis assisted method to prepare vanadium trioxide and carbon nanocomposites as an advanced anode material for lithium-ion batteries. The as-prepared material deliver a superior battery performance with highly retained capacity of ∼780 mAh g − 1 over 100 cycles at a current density of 200 mA g − 1 , showing excellent cyclic stability, and good rate capability. The improved electrochemical performance of vanadium trioxide and carbon nanocomposites electrode makes it promising as a suitable anode material for practical battery applications.

Multifunctional, Fe-doped indium tin oxide (ITO) nanostructured films were grown by pulsed laser deposition on sapphire substrates. The films showed low resistivity and n-type conductivity with a carrier density as high as $3\times 10^{21}~{\rm cm}^{-3}$ . A magnetic moment at room temperature larger than those of any iron oxides was measured in films with Fe doping as low as 2%. We ascribe it to the formation of bound polarons. A strong green photoemission at room temperature was observed, which we ascribe to quantum confinement effect. The coexistence of ferromagnetism and luminescence in the visible range makes our films of potential for magneto-optoelectronic applications.

We report a scalable strategy to synthesize Fe3O4/graphene nanocomposites as a high-performance anode material for lithium ion batteries. In this study, ferric citrate is used as precursor to prepare Fe3O4 nanoparticles without introducing additional reducing agent; furthermore and show that such Fe3O4 nanoparticles can be anchored on graphene sheets which attributed to multifunctional group effect of citrate. Electrochemical characterization of the Fe3O4/graphene nanocomposites exhibit large reversible capacity (∼1347 mA h g−1 at a current density of 0.2 C up to 100 cycles, and subsequent capacity of ∼619 mA h g−1 at a current density of 2 C up to 200 cycles), as well as high coulombic efficiency (∼97%), excellent rate capability, and good cyclic stability. High resolution transmission electron microscopy confirms that Fe3O4 nanoparticles, with a size of ∼4–16 nm are densely anchored on thin graphene sheets, resulting in large synergetic effects between Fe3O4 nanoparticles and graphene sheets with high electrochemical performance.

The electrical and optical properties of cadmium oxide indicate that thin films of the material could be good transparent electrodes for high-efficiency multijunction solar cells, though its complex dielectric function depends drastically on carrier concentration. This comprehensive study correlates CdO's optical gap, free-carrier absorption, refractive index, high-frequency dielectric constant, and electron effective mass with dopant concentration and species. These results are crucial for engineering optoelectronic devices based on this transparent conducting oxide.

Periodically structured Fe2O3 films are successfully fabricated by anodizing Fe foils using sinusoidally modulated current waveforms. The fabricated Fe2O3 films possess nanopores and long-range structural periodicities which can be conveniently adjusted by tuning the anodization parameters. Strong optical response and vivid film color were readily observed on the fabricated Fe2O3 films. Keywords: Fe2O3, Periodic structure, Anodization, Optical sensing

Porous SnO{sub 2} nanotubes have been synthesized by a rapid microwave-assisted hydrothermal process followed by annealing in air. The detailed morphological and structural studies indicate that the SnO{sub 2} tubes typically have diameters from 200 to 400 nm, lengths from 0.5 to 1.5 {mu}m and wall thicknesses from 50 to 100 nm. The SnO{sub 2} nanotubes are self-assembled by interconnected nanocrystals with sizes {approx}8 nm resulting in a specific surface area of {approx}54 m{sup 2} g{sup -1}. The pristine SnO{sub 2} nanotubes are used to fabricate lithium half cells to evaluate their lithium ion storage properties. The porous SnO{sub 2} nanotubes are characteristic with high lithium ion storage capacity, that is found to be 1258, 951, 757, 603, 458, and 288 mAh g{sup -1}, at 0.1, 0.2, 0.5, 1, 2, and 4C, respectively. The enhanced electrochemical properties of the SnO{sub 2} nanotubes can be ascribed to their unique geometry and porous structures. - Graphical abstract: Porous SnO{sub 2} nanotubes are synthesized by a fast microwave-assisted hydrothermal process and exhibit high lithium ion storage properties due to their unique geometry and porous characteristics. Highlights: Black-Right-Pointing-Pointer A microwave-assisted hydrothermal method was used to prepare porous SnO{sub 2} nanotubes. Black-Right-Pointing-Pointer The porous SnO{submore » 2} nanotubes have abundant mesopores on their tube walls. Black-Right-Pointing-Pointer The porous SnO{sub 2} nanotubes possess high lithium ion storage properties. Black-Right-Pointing-Pointer Our results may promote the development of high-performance anode materials.« less

Reports on electroluminescence (EL) in solid-state, nanomaterial-based devices emitting in the lower wavelength range of the visible spectrum are limited, and the emission stability of these devices is rarely reported. We have fabricated light-emitting devices (LEDs) based on integration of n-ZnO nanorods and p-GaN films, which emit in the violet to near-ultraviolet (NUV) region. We also present data on the stability of EL in fabricated devices. Vertical arrays on ZnO nanorods, with estimated ZnO nanorod density ~108 cm−2, were grown on p-GaN films with typical length of ~4 μm and width of ~120 nm. The NUV LEDs show low turn-on voltage (~3.0 V), small reverse saturation current (~10 μA), and more than two orders of magnitude rectification ratio, all of which indicates a good-quality p–n junction at the p-GaN/n-ZnO nanorod interface. The EL spectra of LEDs present an emission band centered at ~403 nm. Gaussian fitting of the EL peak revealed three emission peaks at 378 nm, 405 nm, and 431 nm with dominant emission in the NUV region. Significantly, the fabricated NUV LEDs present stable and repeatable EL characteristics, as revealed by bias-stress stability tests. The good electrical properties and stable EL performance make these nanostructure-based NUV LEDs potential candidates for mass production of next-generation lighting devices.

We present a two-step method to optimize the nanoporous characteristics of TiO2 samples thus enabling a higher charge and discharge capacity and a larger rate capability compared to dense TiO2 materials. We use a simple sol–gel process to fabricate spherical titanium glycolates precursors followed by subsequent hydrothermal or annealing treatments resulting, respectively, in highly porous or dense TiO2 nanospheres. These processes enable control of the grain size, pore structure, and specific surface area of the TiO2. The fabricated TiO2 nanostructures have been subsequently used to assemble lithium-ion batteries. Galvanostatic discharge–charge tests indicate that the porous TiO2 nanospheres possess high and stable reversible capacity of 229, 133, and 56 mAh g−1 at 0.06, 0.6 and 6 C, respectively; whereas the corresponding values for dense TiO2 nanospheres are 217, 45, and ∼1 mAh g−1. Such considerable improvement of the electrochemical activity is attributed to the porous TiO2 nanostructures, and subsequent change in diffusion length, and enables the possibility to optimize the high rate capability in TiO2-based lithium-ion batteries.

In this paper, optical properties of cubic boron nitride (cBN) in forms of films, powders and monocrystals are studied in vibrational spectral regions. For cBN single crystals, the reststrahlen peak reflectivity of about 95% has been obtained. The second-order Raman scattering spectra induced by visible light excitation is also presented. The infrared two-phonon absorption bands are suggested as additional fingerprints for identification of the cBN nature.

Zinc oxide (ZnO) nanowire synthesized from direct Zinc (Zn) vapor transport in O2 environment has been studied. The results show that the first step is the formation of ZnO film on the substrate. Then anisotropic abnormal grain growth in the form of ZnO platelets takes place. Subsequently, single-crystalline ZnO platelets grow in [0001] direction to form whiskers. During whisker growth, transformation from layer-by-layer growth to simultaneous multilayer growth occurs when the two-dimensional (2D) Ehrlich–Schwoebel (ES) barrier at the ZnO island edge is sufficiently large and the monolayer island diameter is smaller than the island spacing. As multilayered islands grows far away from the base, isotropic mass diffusion (spherical diffusion) will gradually displace anisotropic diffusion (linear diffusion), which contributes to the formation of pyramid on the top plane of the whisker. When the pyramid contains enough atomic layers, the 2D ES barrier transits to 3-dimensional ES barrier, which contributes to repeated nucleation and growth of multilayered islands or pyramids on the old pyramids. The pyramids play a critical role to taper the whisker to nanorod with a diameter less than 100 nm. The nanorod then grows to nanowire via repeated growth of epitaxial hexagonal-pyramid shape-like islands on the (0001)-plane with $$ \left\{ {11\overline{2} 3} \right\} $$ facets as the slope planes. During coarsening, the breakage of step motion of $$ \left\{ {11\overline{2} 3} \right\} $$ facets and the appearance of $$ \left\{ {11\overline{2} 0} \right\} $$ facets on the base of pyramids may result from the step bunching of {0001} facets, which is consistent with the existence of “2D” Ehrlich–Schwoebel barrier on the edge of (0001) facets.

We present evidence of amplified emission mediated by surface plasmon polaritons (SPPs) from a CdS0.2Se0.8 nanoribbon (NR) supported on a gold-coated silicon substrate. Room temperature amplified emission is observed from the nanoribbon above excitation irradiances ~25 W/cm2 when it is supported on the gold coated silicon substrate. The nanoribbon is shown to act as a resonator cavity, leading to amplification of discrete wavelengths in the emission spectrum. Evidence for the formation of SPP waves between the gold-coated substrate and the nanoribbon is shown and the resulting wavenumber increase allows for the matching of theoretical resonance wavelengths with those observed experimentally.

We investigated the properties of 7 different titanium dioxide nanostructures with different crystal structures (3 anatase, 2 rutile, and 2 mixed anatase--rutile phase). Nanoparticle samples and mesoporous sphere samples were investigated. Even for the same crystal structure, significant variations in performance were observed for anatase titania samples, while 2 rutile samples exhibited similar performance inferior to anatase-based anodes. Mixed-phase samples also exhibited lower specific capacity compared to the best performing anatase samples, and in this case a significant difference in performance was observed between nanoparticles and mesoporous spheres.

Nanocantilever arrays were formed on the edges of the +/- (0001) planes of pre-synthesized ZnS nanoribbons via catalyst-assisted post-annealing treatment on Si substrate at 600 degrees C. Similar nanostructures could also be generated when ZnS nanoribbons were annealed by mixing with Si or SiO powder. The formation of nanocantilever arrays is associated with orientation-dependent chemical etching of the +/- (0001) polar surfaces of ZnS nanoribbons. The ability of increasing structural complexity beyond the one-step "thermal evaporation and condensation" synthesis provides a new dimension to the rational design of building blocks for nanodevices.

Boron nitride (BN) films with high cubic content were deposited using pulsed dc sputtering of a B4C target and rf biasing of the substrate. The film deposition was characterized using ultraviolet-extended real-time spectroscopic ellipsometry (UV-RTSE). A three-layer optical model with constrained evolution of the layer thicknesses was used to characterize the growth of the BN films on c-Si substrates. This model was chosen for consistency with previous research and includes (i) an initial hexagonal BN (hBN) layer; (ii) a hexagonal+cubic BN (hBN+cBN) mixed-phase transition layer; and (iii) a topmost cBN layer. The evolution of the layer thicknesses was obtained as a function of the substrate bias (Vavg) used to deposit the BN films under static conditions. These results showed a minimum in the thicknesses of the hBN and mixed-phase layers, thus identifying an optimum Vavg for cBN nucleation and growth from the hBN phase under the deposition conditions used here. Complementary ex situ infrared transmission ...

A recently developed real time spectroscopic ellipsometer with an ultraviolet-extended spectral range (1.5–6.5 eV) has been applied to investigate the sputter deposition of BN films with high cBN content. Based on the optical contrast between the two phases (sp2 and sp3 bonded BN) above 4.5 eV, it has been possible to characterize the growth of these films using a two-layer isotropic optical model. In this model, the innermost layer represents the combined contribution from the sp2 bonded material (aBN and hBN) denoted collectively as hBN, whereas the outermost layer represents the contribution of the predominantly sp3 bonded material denoted as cBN. The BN films were grown on crystalline silicon substrates using two processes: (i) r.f. magnetron sputtering of a BN target with pulsed d.c. substrate biasing; and (ii) pulsed d.c. sputtering of a B4C target with r.f. substrate biasing. In both cases, the thickness evolution of the hBN and cBN layers as well as their dielectric functions over the extended spectral range have been determined. The cBN content deduced from the two-layer analysis is in good agreement with estimates from ex situ infrared transmission spectroscopy.

The electronic structure and optical properties of a series of iso-electronic and iso-structural CdS $_{x}Se_{1−x}$ solid solution nanostructures have been investigated using X-ray absorption near edge structure, extended X-ray absorption fine structure, and X-ray excited optical luminescence at various absorption edges of Cd, S, and Se. It is found that the system exhibits compositions, with variable local structure in-between that of CdS and CdSe accompanied by tunable optical band gap between that of CdS and CdSe. Theoretical calculation using density functional theory has been carried out to elucidate the observations. It is also found that luminescence induced by X-ray excitation shows new optical channels not observed previously with laser excitation. The implications of these observations are discussed.

The thin film of Sb2Se3 was deposited by thermal evaporation method and the film was annealed in N2 flow in a three zone furnace at a temperature of 290oC for 30 min. The structural properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy, respectively. It is seen that the as-deposited film is amorphous and the annealed film is polycrystalline in nature. The surface of Sb2Se3 film is oxidized with a thickness of 1.15 nm investigated by X-ray photolecetron spectroscopy (XPS) measurement. Spectroscopic ellipsometry (SE) and UV-vis spectroscopy measurements were carried out to study the optical properties of Sb2Se3 film. In addition, the first principles calculations were applied to study the electronic and optical properties of Sb2Se3. From the theoretical calculation it is seen that Sb2Se3 is intrinsically an indirect band gap semiconductor. Importantly, the experimental band gap is in good agreement with the theoretical band gap. Furthermore, the experimental values of n,k,varepsilon1, and varepsilon2 are much closer to the theoretical results. However, the obtained large dielectric constants and refractive index values suggest that exciton binding energy in Sb2Se3 should be relatively small and an antireflective coating is recommended to enhance the light absorption of Sb2Se3 for thin film solar cells application. DOI: 10.21883/FTP.2017.12.45184.8396

Vertically aligned single crystalline ZnO nanorod arrays, approximately 3 μm in length and 50-450 nm in diameter are grown by a simple solution approach on a Zn foil substrate. CdS and CdSe colloidal quantum dots are assembled onto ZnO nanorods array using water-soluble nanocrystals capped as-synthesized with a short-chain bifuncional linker thioglycolic acid. The solar cells co-sensitized with both CdS and CdSe quantum dots demonstrate superior efficiency compared with the cells using only one type of quantum dots. A thin Al2O3 layer deposited prior to quantum dot anchoring successfully acts as a barrier inhibiting electron recombination at the Zn/ZnO/electrolyte interface, resulting in power conversion efficiency of approximately 1% with an improved fill factor of 0.55. The in situ growth of ZnO nanorod arrays in a solution containing CdSe quantum dots provides better contact between two materials resulting in enhanced open circuit voltage.

Development of a high quality but low cost insulating layer is important for its application in photovoltaic cells. In this work, solution processable graphene oxide (GO) thin films were first utilized as an insulating layer to construct MIS silicon solar cells. The efficient water-soluble GO nano-sheets with controlled thickness produced a good contact with the hydrophilic silicon surfaces. The average open circuit voltage (VOC) of the GO incorporated MIS silicon solar cell was increased by 0.2 V, while their power conversion efficiency (PCE) was demonstrated as 88% higher than that of the corresponding Schottky solar cells. The improvement of the device performance in the GO-based MIS silicon solar cell is attributed to the increased built-in potential as well as the reduced interface defect, resulting in reduced carrier recombination. The ability to establish a low-cost and solution-processable insulating layer will open the door for wide application in photovoltaic and other optoelectronic devices.

We fabricated ordered hexagonal-packed vertical silicon nanowire (SiNW) arrays with varying diameters of 450–900 nm and varying lengths of 0.54–7.3 μm, and studied their Raman enhancement properties. We found the Raman enhancement per unit volume (REV) increased with decreasing wire diameters and oscillated with wire length, and the REV of seven 450-nm-diameter, 3-μm-long SiNWs was about twice that of a single SiNW having the same size. The differences were attributed to the vertical finite-length cylinder structures of the SiNW array, as supported by finite-difference-time-domain simulation results based on the helical resonant surface wave model.