Strain engineering is an effective method to tune the properties of electrons and phonons in semiconductor materials, including two-dimensional (2D) layered materials (e.g., MoS2 or graphene). External artificial stress (ExAS) or heterostructure stacking is generally required to induce strains for modulating semiconductor bandgaps and optoelectronic functions. For layered materials, the van der Waals-stacked interlayer interaction (vdW-SI) has been considered to dominate the interlayer stacking and intralayer bonding. Here, we demonstrate self-induced uniaxial strain in the MoS2 monolayer without the assistance of ExAS or heterostructure stacking processes. The uniaxial strain occurring in local monolayer regions is manifested by the Raman split of the in-plane vibration modes E2g1 and is essentially caused by local vdW-SI within the single layer MoS2 due to a unique symmetric bilayer stacking. The local stacked configuration and the self-induced uniaxial strain may provide improved understanding of the fundamental interlayer interactions and alternative routes for strain engineering of layered structures.Keywords: first-principles plane-wave calculations; MoS2; Raman; self-induced; uniaxial strain; van der Waals stacking;

We demonstrated revertible shifts of surface-dependent localized surface plasmon resonances (LSPRs) in CuS nanodisks. Oleylamine (OYA) served as a solvent and surface ligand covering on CuS nanodisks during the thermolysis of single-source precursor copper ethylxanthate (Cu(ex)2). When OYA ligand was unloaded and reloaded on the surface of CuS nanodisks, the wavelength of LSPRs blue-shifted due to more oxygen exposure and then reverted through surface repassivation. The surface-dependent shift of LSPRs was dominated by the concentration of free holes in CuS nanodisks, which was modulated by the coverage and exchange of surface ligands, and the oxygen exposure dose and time. The semiconductor nanocrystals with tunable LSPRs have great potential in advanced plasmonics.Keywords: absorption spectra; copper sulfide; free carrier; localized surface plasmon resonance; nanocrystals; surface ligand;

We describe the fabrication of radial ZnO/Au/ZnO hybrid nanorods by analogously inserting a Au nanoparticle interlayer in single-crystalline ZnO nanorods through a feasible secondary growth process. The construction features of the ZnO/Au/ZnO hybrid nanorods can be tuned by the extent of the nanoparticle coverage and the growth processes. Investigations on the photoluminescence of the hybrid nanorods have preliminarily indicated that the metal nanoparticles lead to enhanced near-band-edge (NBE) emission and suppressed deep level emission (DLE). Such alternative processes and hybrid nanostructures are potential candidates for application in plasmonics and advanced optical devices.

WO3·nH2O microcrystals with different shapes have been synthesized via a facile inorganic hydrothermal route. By controlling the amount of Na2SO4 in the precursor solution, hexagonal WO3·0.33H2O nanoplates, WO3 nanorods, and octahedron-shaped WO3·0.5H2O crystals have been obtained, highlighting the role of Na2SO4 in the growth of WO3·nH2O crystals. Based on the experimental observations, we have discussed the growth mechanisms of the WO3·nH2O crystals. The adsorption ability and photocatalytic activities of tungsten trioxide hydrates have also been investigated, and the results show that the WO3·0.33H2O nanoplates with large surface areas show the largest adsorption ability, and WO3·0.5H2O octahedral microcrystals with large bare crystal face exhibit the highest photodegradation performance in these samples, rendering their potential application in the treatment of organic pollutants.

TiO2 nanocrystal/nanotube hybrids were presented and prepared by incubating non-prefabricated TiO2 nanocrystals in anodized TiO2 nanotubes. TiO2 nanocrystals were incubated inside the nanotubes with tuning size and aggregation morphology by means of a block copolymer-assisted evaporation induced self-assembly (EISA) process. Compared with that of the bare TiO2 nanotubes, a ∼44% increase of the concentration of dye absorbed in the TiO2 nano-hybrids was estimated from the absorption spectra. The nanostructure hybrids increased internal surface area, and were used to optimize TiO2-based photo-electrochemical conversion. The contrast of light conversion efficiency revealed an improvement from 0.75% to 1.87% when the TiO2 nano-hybrids were used as photoanodes instead of the bare nanotube arrays.Graphical abstractTiO2 nanocrystal/nanotube hybrids fabricated by incubating non-prefabricated TiO2 nanocrystals in TiO2 nanotubes for optimizing light-harvesting.Highlights► To combine nanocrystals and nanotubes aims to optimize light harvesting and electron transport in photo-electrochemical conversion. ► An alternative method was established to achieve nano-hybrids including nanocrystals and nanotubes. ► TiO2 nanocrystals were incubated inside TiO2 nanotubes by means of a wet-chemical and block copolymer-assisted assembly process. ► Such nano-hybrids have been preliminarily used and confirmed in harvesting more light and then improving light conversion efficiency. ► These will open up alternative pathways for the structure manipulations and optimizations for nanostructure-based photovoltaics and photocatalysis.

Damage buildup in 80 keV Be-implanted InAs0.93Sb0.07 epitaxial layer grown by liquid epitaxy growth (LPE) with the implantation fluences ranging from 1 × 1013 to 4 × 1015 cm−2 have been detailedly investigated by high resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). The implantation-induced nonlinear maximum perpendicular strain εm as a function of the Be fluence was deduced. Microstructural variation created by damage buildup was analyzed. The characteristics of annealing on the lattice damage were also studied. The created damages can be recovered by rapid thermal annealing at 500 °C for samples with the fluence below 1.0 × 1015 cm−2, but nano-sized residual damages still existed when the fluence reaches 4.0 × 1015 cm−2 due to the poor recrystallization of the small disorder region.

WO3 nanocrystals have been prepared by a sol–gel route and characterized by X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy. The experimental results show that WO3 nanocrystals have a high crystallographic quality and a good dispersivity. The particles’ sizes are in the range of 25–100 nm. The fabricated WO3 nanocrystal-based sensors have an excellent sensitivity and selectivity to acetone, and display a rapid response and recovery characteristics. The developed sensors exhibit a detection limit down to 0.05 ppm at 300 °C, rendering a promising application in noninvasive diagnosis of diabetes. The response mechanism of the WO3 nanocrystal sensor to low concentration of acetone has been discussed based on the depletion layer model.

We describe a flexible and competent solution for fabrication of non-prefabricated nanocrystal mesoporous TiO2-based photoanodes whose thicknesses are tunable from several hundreds of nanometers up to 12.4 μm. The combination of rapid thermal process and layer-by-layer spin-coating is successfully used to manipulate the structure and morphology of non-prefabricated nanocrystal mesoporous TiO2 films. The photovoltaic performances of mesoporous TiO2-based dye-sensitized solar cells depended on the thickness and the annealing temperature of mesoporous photoanodes. We systematically investigated and noted that the non-prefabricated nanocrystal mesoporous TiO2 films ∼6.3 μm thick annealed at 500 °C displayed better features in the short-circuit current density and overall conversion efficiency of mesoporous TiO2-based dye-sensitized solar cells.Keywords: dye-sensitized solar cells; layer-by-layer coating; mesoporous structure; non-prefabricated nanocrystal photoanode; rapid thermal process; TiO2

CdS thin films were deposited from different cadmium salts by using acidic chemical bath deposition (CBD) process. Quality characterizations were performed using different methods such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL). The crystal quality of CdS thin films was improved after CdCl2 thermal annealing at 380 °C. A compact structure of CdS thin films can be obtained by using CdCl2 in comparison with the other cadmium salts. Although a Cd/S molar ratio of ∼1 was used in our experiments, strong PL signals confirmed the high quality of CdS thin films.Research highlights▶ N-type semiconducting CdS thin films have been widely used as a window layer in the solar cells. CdS thin films prepared by chemical bath deposition (CBD) have been used in CdTe and CIGS based solar cells. Among existing techniques, CBD was simple and inexpensive to deposit CdS thin films for mass production. Typically, the CBD process for CdS films is carried out in an alkaline aqueous solution comprised of thiourea and ammonia. Recently, CBD process in acidic solutions has been developed and used for the optimization of CdS thin films. However, the effects of the variables for the acidic CBD, especially, the dependence on cadmium salts, have not been investigated systematically. In this paper, we studied the growth process, structure, morphology and optical properties of CdS thin films deposited using different cadmium salts, which is helpful for the optimization of growth condition for high quality CdS thin films used in solar cells. Acidic CBD-CdS thin films were prepared by using different cadmium salts. A post-annealing process at 380 °C was used to improve crystal quality. The CdS-Ci thin films have the highest deposition rate than other films obtained by different solution, which is due to an easier releasing rate for Cd(CH3COO)2 than the CdCl2 and CdSO4 solutions. CdS-Cli thin films have a relatively larger band gaps and better qualities. Strong PL spectra at room temperature confirm the good quality of the CdS thin films.

We report temperature-dependent optical transmission studies on Pb1−xMnxSe films grown on Zn0.04Cd0.96Te substrates by molecular beam epitaxy. The measurements were carried out from liquid nitrogen temperature to room temperature and in the frequency range of 400–4000 cm−1. The transition energy Eg of 0.215 eV, damping parameter Γ of 4.1 meV, refractive index of 5.0, and Urbach bandtail parameter Eu of ∼8 meV were determined by fitting the experimental transmission spectra for Pb1−xMnxSe at, for instance, x = 0.038 and 85 K. Other parameters, such as absorption coefficient α, the oscillator strength A, and the background dielectric constant ɛ∞ were also obtained. Temperature dependences of Γ and Eu indicate stronger carrier–phonon interactions in the Pb1−xMnxSe films.

Ordered mesoporous titania (MT) thin films have been grown on Si and indium tin oxides (ITO) substrates by evaporation-induced self-assembly (EISA) technique. The films have honeycomb-like structures and are consisted of anatase nanocrystallites, as evidenced from Raman spectra and high resolution transmission electron microscopy. The band-gap energies of the mesoporous titania thin films are larger than that of bulk TiO2 and are tunable through controlling film processing. Refractive index and extinction coefficient of the mesoporous titania thin films were determined using spectroscopic ellipsometry and were found to depend on the film thickness.

We describe a hot soap method for assembling CdSe nanoparticles inside the channels of mesoporous SBA-15 materials. X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), UV–vis absorption spectra, and fluorescence spectra have been successfully used to characterize the structure and the optical properties of the mesoporous materials. EDS analysis carried out on the pores of composite mesoporous silica shows strong Cd and Se signals, confirming the formation of CdSe nanoparticles inside the SBA-15 pores. TEM image shows that the CdSe nanoparticles are about 4–5 nm in sizes and uniformly dispersed inside the pores of mesoporous silica. In the UV–vis absorption spectra of the CdSe nanoparticles inside the SBA-15 hosts, a significant blue shift is detected and attributed to the confinement of channels of SBA-15.

•InAsSb films with different carrier concentration were obtained by LPE.•The complete optical absorption spectra of InAsSb films were obtained.•The Eg of InAsSb film was obtained by fitting the intrinsic absorption region.•The Eo value decreases with decrease of film carrier concentration.InAs1−xSbx films with x = 0.06 were grown on InAs (1 0 0) substrates by liquid phase epitaxy (LPE). Different purification procedures were applied to get InAsSb samples with different carrier concentration. The complete optical absorption spectra including absorption edge and intrinsic absorption region of InAsSb samples were extracted from the room temperature transmission spectra. The energy band gaps of InAsSb samples were obtained by fitting the intrinsic absorption spectra, giving rise to the values of 303.4–305.1 meV. The reciprocal slope (Eo) of the absorption edge related to the carrier concentration was also determined. The Eo value decreases with decrease of InAsSb epilayer carrier concentration.

High quality InAs0.85Sb0.15 film has been successfully grown on (1 0 0) InAs substrate by liquid phase epitaxy using InAs0.93Sb0.07 buffer layer. The microstructure and morphologies of the film were characterized by high-resolution X-ray diffraction, scanning electronic microscopy, optical microscopy, atomic force microscopy, and high-resolution transmission electron microscopy. These results show that the high quality film with mirror-like surface was obtained. The optical properties were investigated by photoluminescence and the Raman spectra. The peak position of photoluminescence spectrum for the film is about 0.35 eV at 77 K. In addition to the reported single-mode phonon behavior, the local vibration mode associated with Sb atoms was also observed in the Raman spectra.Highlights► InAs0.85Sb0.15 film has been grown by liquid phase epitaxy in simpler way. ► The microstructure and morphologies of the film were characterized. ► Quality of the film was improved due to lower growth temperature and buffer layer. ► The Raman local vibration mode associated with Sb atoms was firstly observed.

•High-purity InAs0.94Sb0.06 films were obtained by liquid phase epitaxy.•Prolonging hydrogen baking time was used to reduce the impurities in the film.•Adding Gd to the growth melt was also applied to purify the film.•Electrical properties of purified film were improved significantly.High-purity InAs1−xSbx films with x=0.06 were successfully grown on InAs (100) substrates by liquid phase epitaxy (LPE). Procedures were applied to purify InAs1-xSbx precursor material, which included prolonging baking time in hydrogen and adding rare-earth element gadolinium (Gd) to the growth melt. Electrical transport properties of InAs1-xSbx film were investigated by Hall measurements in the condition of the conductive InAs substrate being removed completely by chemical mechanical polishing (CMP) to eliminate its influence on the measurements. Hall measurement results show carrier concentration and mobility of our InAs1-xSbx samples are superior to the other reported values when a combinational purification procedure is applied.

•The growth temperature of GaAs1−xSbx epilayers is lower than that of other reports.•All samples exhibit bright PL emissions at room temperature.•The bandgap Eg was obtained from PL and transmission spectra.A series of GaAs1−xSbx epilayers have been successfully grown on GaAs (1 0 0) substrates by liquid phase epitaxy (LPE) technique at about 550 °C. Samples with different antimony (Sb) contents have been analyzed by high-resolution X-ray diffraction (HRXRD) measurement, which confirms the incorporation of Sb in the epilayers. Room temperature optical properties of GaAs1−xSbx epilayers were performed by photoluminescence (PL) and transmission spectra.

The InAsSb epilayers with a cutoff wavelength of 11.5 μm were successfully grown on highly lattice-mismatched semi-insulating (1 0 0) GaAs substrate by the modified liquid phase epitaxy (LPE) technique. Fourier transform infrared (FTIR) transmission spectrum revealed a strong band gap narrowing for this alloy. The electrical properties were investigated by the Van der Pauw measurements at 300 and 77 K. InAsSb epilayers showed high Hall mobilities being 11,800 cm2/V s at room temperature (RT). After an annealing treament for 10 h, the electron mobility at 77 K were improved from 1730 cm2/V s (prior to annealing) to 13,470 cm2/V s. Wet etching was used to display the surface etch pits prior to and after annealing treatment, showing that the mobility improvement was due to the reduction of the etch pits density.