Photoluminescence Peak Intensity Research Articles

Wavelength-tunable photoluminescence of CsPbBr3 microcrystal via in situ halogen doping

Lead halide perovskite semiconductors have received significant attention in recent years as promising candidates for optoelectronic applications. Their controllable bandgap in nanostructures (nanocrystals, nanowires) has been widely and successfully investigated. Intentionally manipulating the atomic behavior with dopants in their macroscopic structure with high quality and stability is still challenging. We studied the crystal structure and photoluminescence (PL) behavior of the anion (Cl) doped CsPbBr3 microcrystals. The doped microcrystal with a low doping concentration has shown a large wavelength-tunable PL emission from 535 nm to 457 nm. Two separate emission peaks (blue and green) are carefully studied in the excitation power dependent PL spectra. The doping and excitation endow the perovskite microcrystal adjustable PL emission band and peak intensities, which may serve as a new degree of manipulation freedom in the color-tunable display and functional optoelectronics.

InGaAs/AlGaAs MQWs grown by MBE: Optimizing GaAs insertion layer thickness to enhance interface quality and luminescent property

The refinement of interface structure in InGaAs/AlGaAs multiple quantum wells (MQWs) through molecular beam epitaxy (MBE) is crucial for enhancing their luminescence performance. The influencing mechanisms of the GaAs insertion layer (ISL) thicknesses on the interface structure and luminescence properties of InGaAs/AlGaAs MQWs were investigated by varying the GaAs ISL thickness variations and optimizing growth parameters. In our designed InGaAs/AlGaAs MQWs structures, GaAs ISL with thickness variables of 0 nm, 0.5 nm, 1 nm, 2 nm, and 4 nm were inserted between the interfaces of the InGaAs well layer and the AlGaAs barrier layer. Through experimental characterizations. The introduction of the GaAs ISL resulted in a gradual transition of the MQWs surface morphology from a three-dimensional (3D) island structure to a typical step-flow surface morphology, leading to the reduction in surface roughness and enhancement of hetero-interfaces quality. Moreover, the GaAs ISL with thickness exceeding 2 nm effectively inhibited the segregation of indium atoms, promoting the ordering of interface alloys and decreasing the polarization degrees from 3.76 % to 2.09 %. Temperature-dependent PL measurements indicated that the GaAs ISL could reduce interface defects and the density of non-radiative recombination centers, thereby enhancing the radiative recombination efficiency of MQWs and ultimately increasing the peak intensity of photoluminescence by 3.4 times. This work is significance for understanding the luminescent properties of InGaAs/AlGaAs MQWs, which provides reference highly efficient optoelectronic devices development.

Size Control and Photoluminescence Characteristics of InSb Quantum Dots on GaSb Substrates Grown by Molecular Beam Epitaxy

InSb self‐assembled quantum dots (QDs) have the possibility to increase the luminescence intensity of light‐emitting diodes operating in the midinfrared region. As a first step toward the midinfrared luminescence, the single‐layer InSb QDs are grown on GaSb (100) substrates by molecular beam epitaxy and the effects of V/III ratio and InSb coverage on size and density of InSb QDs and photoluminescence (PL) characteristics are investigated. As the V/III ratio increases, the distribution of QD height broadens and goes from monomodal to multimodal. The increase in the number of large QDs and their multimodal distribution are thought to be due to the ripening process. The PL intensity is maximum at a V/III ratio of 2 with PL wavelength of 1.76 μm. As the InSb coverage increases at a V/III ratio of 2, QD size and density increase while maintaining a monomodal distribution in QD size. However, the PL peak intensity decreases with increasing InSb coverage due to the increase of nonradiative QDs. The highest PL peak intensity at an InSb coverage of 2.0 monolayer and a V/III ratio of 2 with PL wavelength of 1.69 μm are obtained. The present single‐layer InSb QD shows the emission in the near‐infrared region.

High temperature synthesis, surface characterization, and photoluminescence property of boron carbon nitride

The present study demonstrates the synthesis of boron carbon nitride (BCN) by molten salt method which utilizes melamine (source of carbon and nitrogen), boric acid (source of boron) and potassium chloride as the salt. The synthesis is performed at 915 °C for 4 h under N2-atmosphere. The synthesized material is further acid-treated. The physicochemical characterization data for as-synthesized and acid-treated materials confirm successful synthesis of BCN. SEM and AFM data display that synthesized BCN pre and post acid-treatment exhibit sheet-type morphology. Thermogravimetric analysis data confirm that the acid-treated material is thermally stable up to 800 °C, with only 2 % mass-loss is observed till 800 °C. Water contact angle measurement study demonstrates that acid-treatment significantly improves the surface hydrophilicity. Additionally, the low photoluminescence peak intensity of the acid-treated material indicates low electron-hole pair recombination rate. The synthesized material may be useful for the photocatalytic degradation of potentially toxic chemicals from water.

Disentangling doping and strain effects at defects of grown MoS2 monolayers with nano-optical spectroscopy.

The role of defects in two-dimensional semiconductors and how they affect the intrinsic properties of these materials have been a widely researched topic over the past few decades. Optical characterization techniques such as photoluminescence and Raman spectroscopies are important tools to probe the physical properties of semiconductors and the impact of defects. However, confocal optical techniques present a spatial resolution limitation lying in a μm-scale, which can be overcome by the use of near-field optical measurements. Here, we use tip-enhanced photoluminescence and Raman spectroscopies to unveil the nanoscale optical properties of grown MoS2 monolayers, revealing that the impact of doping and strain can be disentangled by the combination of both techniques. A noticeable enhancement of the exciton peak intensity corresponding to trion emission quenching is observed at narrow regions down to a width of 47 nm at grain boundaries related to doping effects. Besides, localized strain fields inside the sample lead to non-uniformities in the intensity and energy position of photoluminescence peaks. Finally, two distinct MoS2 samples present different nano-optical responses at their edges associated with opposite strains. The edge of the first sample shows a photoluminescence intensity enhancement and energy blueshift corresponding to a frequency blueshift for E2g and 2LA Raman modes. In contrast, the other sample displays a photoluminescence energy redshift and frequency red shifts for E2g and 2LA Raman modes at their edges. Our work highlights the potential of combining tip-enhanced photoluminescence and Raman spectroscopies to probe localized strain fields and doping effects related to defects in two-dimensional materials.

Controlling photoluminescence of silicon quantum dots using pristine-nanostates formation

This study investigates the effective control of photoluminescence (PL) of silicon nanocrystals (Si–NCs) embedded in a SiO2 matrix, with a specific focus on tuning the luminescent wavelength profile and intensity for silicon-based optoelectronic applications. By manipulating the composition ratio (x) of SiOx, the well-known simultaneous changes in PL peak position and intensity were observed after annealing. To preserve the desired wavelength characteristics and enhance the luminesce intensity, we propose a novel approach to generate pristine nanostates (PNs) for Si-NC formation using proton irradiation (PI). The application of proton irradiation was found to be successful in significantly increasing PL intensity while strongly suppressing the peak position shifts. Through extensive spectroscopic analysis including PL, X-ray photoelectron spectroscopy, and absorption spectroscopy, we investigate specific defect states in the SiOx matrix, and identified as PNs. We interpret that these PNs consist of self-trapped exciton, E′ center, non-bridging oxygen hole center, and oxygen-deficiency center states. In the as-grown sample, the PNs promote appropriate phase separation and play a significant role in stabilizing the structure during the subsequent annealing processes. This study elucidates the Si-NC formation mechanism by enhancing O-diffusion-induced phase separation, a process accelerated in SiOx with controlled PNs. The proposed PI-induced PNs offer a novel pathway for developing Si-based optoelectronic devices with desired characteristics in the operating wavelength range. These findings open up promising possibilities for advanced silicon-based optoelectronic applications.

Multi-colour emission from ZnO[SO4]:Eu2+ nanophosphors: Effects of SO42- and Eu2+ doping concentration

Blue-emitting ZnO-SO4:Eu2+ powder phosphors were synthesized via solid state reaction method. Based on the X-ray diffraction (XRD) data, hexagonal wurtzite structures of ZnO were formed. Further structural elucidation via Raman spectroscopy showed a peak at 439 cm−1 associated with E2hgh optical mode that is a distinctive characteristic band of hexagonal wurtzite ZnO phase. The ZnO powders were composed of distorted spherical nanoparticles, which were agglomerated together as confirmed from scanning electron microscopy images. After incorporation of SO42- and Eu2+ into the ZnO lattices sites, the particle shapes became irregular. When excited at 351 nm with Xenon lamp, our samples emitted UV and blue-green visible light associated, respectively, with excitonic recombination and intrinsic structural lattice defects in ZnO. Both the photoluminescence (PL) peak intensity and positions of these emissions were influenced by SO42- and Eu2+ ions. The blue emission was dependent on the Eu2+ content with the largest intensity measured from the sample doped with 1.0 mol% of Eu2+ ions. Mechanisms of energy transfer and concentration quenching effect are discussed.

Correlative Spatial Mapping of Optoelectronic Properties in Large Area 2D MoS2 Phototransistors

Abstract2D materials‐based device performance is significantly affected by film non‐uniformity, especially for large area devices. Here, it investigates the dependence of large area 2D MoS2 phototransistor performance on film morphology through correlative mapping. Monolayer MoS2 films are quazi‐epitaxially synthesized on C‐plane sapphire (Al2O3 ) substrates by chemical vapor deposition, and the growth time and molybdenum trioxide MoO3 precursor volume are varied to obtain variations in film morphology. Raman, photoluminescence, transmittance, and photocurrent maps are generated and compared with each other to obtain a holistic understanding of large area 2D optoelectronic device performance. For example, it shows that the photoluminescence peak shift and intensity can be used to investigate strain and other defects across multiple film morphologies, giving insight into their effects on the photogenerated current in these devices. It also combines photocurrent and absorption maps to generate large area high‐resolution external quantum efficiency and internal quantum efficiency maps for the devices. This study demonstrates the benefit of correlative mapping in the understanding and advancement of large area 2D material‐based electronic and optoelectronic devices.

Photoluminescence Property of Cu(In,Ga)S2 Quantum Dots Depending on Their Composition and Nanostructure

Multinary quantum dots (QDs) composed of less toxic elements, such as CuInS2 and AgInS2, have been intensively investigated for the application to highly efficient solar energy conversion systems and novel luminescent devices, because their electronic energy structure and optical properties can be controlled by the size and chemical composition of QDs. Recently we have successfully prepared alloy QDs composed of Ag–In–Ga–S and Ag–In–Ga–Se semiconductors, the Eg of which was tunable in the visible and near-IR wavelength regions, respectively [1, 2]. These QDs exhibited a narrow PL peak assignable to the band-edge emission and their peak wavelengths were widely tunable by changing their Eg. However, there have been few investigations to prepare Cu-based multinary QDs with a narrow PL peak. Thus, in this study, we prepare spherical QDs composed of less-toxic Cu–In–Ga–S (CIGS) alloy semiconductor and investigate their composition-dependent optical properties.The synthesis of CIGS QDs was carried out by our previous heating-up method with a slight modification [1]. Powders of Cu(OAc)2, In(acac)3, Ga(acac)3, elemental sulfur were dispersed in a mixture solution of oleylamine and dodecanethiol, followed by the heat treatment at 300 oC. The resulting solution was subjected to centrifugation to remove large precipitates, and QDs were isolated from the supernatant by adding methanol as a non-solvent. Thus-obtained QDs were used as a core to prepare cores-shell-structured particles, in which the surface of CIGS core was coated by thin shell composed of ZnS or GaSx.The chemical composition of obtained QDs was controlled by the fractions of individual metal salts used as precursors. The Cu/(In+Ga) and In/(In+Ga) of obtained QDs roughly agreed with those used in preparation. The obtained QDs were spherical and their average diameter decreased from 5.4 nm to 3.4 nm with an increase in the In fraction. The absorption spectra of CIGS QDs were varied depending on both the fractions of Cu and In. The onset wavelength of QDs was blue-shifted from 840 nm to 540 nm with a decrease in the Cu/(In+Ga) in preparation from 0.7 to 0.1 when the QDs were prepared with the fixed ratio of In/(In+Ga)= 0.7. On the other hand, the QDs exhibited a blue shift of absorption onset from ca. 750 nm to 480 nm with a decrease in In/(In+Ga) ratio from 1.0 to 0 under the fixed Cu fraction in preparation, Cu/(In+Ga)= 0.3. The obtained Eg monotonously decreased from 2.77 eV to 1.74 eV with an increase in In/(In+Ga) ratio from 0 to 1.0, and these values were larger than those of corresponding bulk semiconductors due to the quantum size effect. From the ionization energy of the QDs evaluated from the onset energy of the photoelectron yield spectra in air, we determined the electronic energy structure of CIGS QDs. With a decrease in the Eg of QDs, the conduction band minimum level shifted to a lower level from ca. –2.3 eV to –3.4 eV, while the valence band maximum level was almost constant to ca. 5.1–5.2 eV.Surface coating of CIGS QDs with other semiconductor shells increased the photoluminescence (PL) intensity. The ZnS shell coating to form CIGS@ZnS core-shell QDs produced a PL peak at 649 nm (FWHM: 0.47 eV), being much broader than that of CIGS cores (FWHM: 0.23 eV) because of alloying at the interface between ZnS shell and CIGS core, though the PL quantum yield (QY) increased to 30% from 8%. In contrast, the GaSx coating on CIGS QD surface enlarged the intensity of PL peak without changing its peak width: CIGS@GaSx QDs exhibited a narrow PL peak (FWHM: 0.20 eV) at 671 nm, being comparable to the PL peak of CIGS QDs (the peak wavelength of 675 nm and the FWHM of 0.23 eV). The PL QY was also increased to 27% from 8% by the GaSx coating on CIGS QDs. The tunabilities of electronic energy structure and PL property of CIGS QDs are useful for constructing efficient light energy conversion systems and luminescent devices.[1] T. Kameyama, et al., ACS Applied. Mater. Interfaces 2018, 10, 42844-42855.[2] T. Kameyama, et al., ACS Appl. Nano Mater. 2020, 3, 3275-3287.

Harvesting strong photoluminescence of physical vapor deposited GeSn with record high deposition temperature

In this work, strong photoluminescence (PL) from physical vapor deposited GeSn on Ge-buffered Si is harvested by pursuing high deposition temperature. High-quality Ge0.938Sn0.062 films are obtained through sputtering epitaxy at a record high temperature of 405 °C. The PL peak intensity of the sputtering-grown GeSn is enhanced by 21 times compared to that of GeSn with similar Sn content grown by molecular beam epitaxy at 150 °C. The PL intensity ratio between the sputtering-grown GeSn and Ge virtual substrate reaches a value of 18. Power-dependent and temperature-dependent PL characterizations demonstrate that band-to-band recombination dominates in the sputtering-grown GeSn film. The results indicate that high-temperature sputtering epitaxy, which has the merit of low cost and high-productivity potential, is promising for preparing high-quality GeSn films for optoelectronic applications.

Plasmon-enhanced photoluminescence and Raman spectroscopy of silver nanoparticles grown by solid state dewetting

The growth of the metallic nanoparticles (NPs) on the solid substrate with the desired shape and size is a critical issue for application of these NPs in solid-state devices. Solid state dewetting (SSD) technique is simple, low cost and can be used to fabricate the metallic NPs with control on the shape and size on different substrates. In this work, silver NPs (Ag NPs) were grown on corning glass substrate by SSD of silver precursor thin film deposited at different substrate temperatures by RF sputtering. The influence of the substrate temperature on the growth of Ag NPs and their several properties like localized surface plasmon resonance (LSPR), photoluminescence (PL), and Raman spectroscopy is studied. The size of the NPs was found to vary from 25 nm to 70 nm with the variation in substrate temperature from room temperature (RT) to . For the RT films, the LSPR peak position of Ag NPs is around 474 nm. A red shift in LSPR peak for films deposited at higher temperature is observed due to change in the particle size and interparticle separation. Photoluminescence spectra suggests the presence of two photoluminescence bands at 436 and 474 nm corresponding to Ag NPs radiative interband transition and LSPR band. An intense Raman peak was observed at 1587 cm−1. Enhancement in PL peak intensity and Raman peak intensity is found to be in accordance with the LSPR of Ag NPs.

Improved Thermoelectric Figure of Merit in Polyol Method-Prepared Cu1–xBixS (x ≤ 0.06) Nanosheets

The first thermoelectric (TE) properties of simple polyol method-synthesized Cu1–xBixS (x = 0, 0.02, 0.04, 0.06) nanosheets are reported here. Various characterizations like Rietveld-refined X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray (EDAX) data analysis confirm their single-phase nature of hexagonal crystal structure with space group P63/mmc, stoichiometric nature, valence states of the elements, and nominal elemental composition. Field emission scanning electron microscopy (FESEM) images show nanosheets (NSs) with an average thickness of 27 nm. The doping of Bi atoms in the CuS lattice has been evident from the systematic increase in its crystallite size, optical band gaps, photoluminescence peak intensities, Seebeck coefficients, resistivity, thermoelectric power factors (PFs), and thermoelectric figure of merits (ZTs) with increasing x. The selected area electron diffraction (SAED) pattern confirms that nanosheets are single crystalline in nature. Fourier transform infrared (FTIR) data confirms the absorption bands of the sulfides. The value of the Seebeck coefficient increases with increasing x without deteriorating the electrical conductivity too much due to the energy-dependent scattering of the carriers at the interfaces and the modulation doping. An enhancement of 231% in the thermoelectric power factor and a 6-fold increase in ZT, both at 300 K for x = 0.06 compared to x = 0, are found that show interesting outcomes for these toxic- and rare-earth element-free TE materials.

Brightness and Lifetime Improved Light-Emitting Diodes from Sr-Doped Quasi-Two-Dimensional Perovskite Layers

Green Perovskite Light-Emitting Diodes (PeLEDs) have attracted wide attention for full spectrum displays. However, the inferior film morphology and luminescence property of quasi-two-dimensional (quasi-2D) perovskite layers limit the photoelectric property of the PeLEDs. In this paper, the effect of strontium (Sr) doped in quasi-2D perovskite layers is investigated to obtain a high-quality active layer. The morphologies and optical properties of Sr-doped quasi-2D perovskite films with different concentrations are studied. With the addition of strontium, more low-dimensional-layer perovskite phases (n = 2 and n = 3) appear in quasi-2D perovskite films, providing efficient intraband carrier funneling pathway and facilitating radiative recombination. The photoluminescence (PL) peak intensity of optimized Sr-doped quasi-2D perovskite layers increases 50% compared with the non-strontium counterpart. Moreover, green PeLEDs based on a Sr-doped quasi-2D perovskite layer reach a maximum luminance (L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> ) of 2943.77 cd/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is three times of the control device. The electroluminescence (EL) peaks of Maximum External Quantum Efficiency (MEQE) and Lmax of Sr-doped PeLEDs exhibite a slight shift, indicating the excellent stability and performance of Sr-doped devices. The optimized device can continuously operate for 360 s at MEQE driving voltage, resulting in a half-lifetime of ~60 s, which is 3-fold greater than that of the control PeLEDs.

The Effect of Nitridation on Sputtering AlN on Composited Patterned Sapphire Substrate.

Here, we report on the epitaxial growth of GaN on patterned SiO2-covered cone-shaped patterned sapphire surfaces (PSS). Physical vapor deposition (PVD) AlN films were used as buffers deposited on the SiO2-PSS substrates. The gallium nitride (GaN) growth on these substrates at different alternating radio frequency (RF) power and nitridation times was monitored with sequences of scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging results. The SEM and AFM show the detail of the crystalline process from different angles. Our findings show that the growth mode varies according to the deposition condition of the AlN films. We demonstrate a particular case where a low critical alternating current (AC) power is just able to break SiO2 covalent bonds, enabling the growth of GaN on the sides of the patterns. Furthermore, we show that by using the appropriate nitridation condition, the photoluminescence (PL) integral and peak intensities of the blue light epi-layer were enhanced by more than 5% and 15%, respectively. It means the external quantum efficiency (EQE) of epitaxial structures is promoted. The screw dislocation density was reduced by 65% according to the X-ray diffraction (XRD) spectra.

Formation mechanism and regulation of silicon vacancy centers in polycrystalline diamond films

Diamond silicon vacancy centers (SiV centers) have important application prospects in quantum information technology and biomarkers. In this work, the formation mechanism and regulation method of SiV center during the growth of polycrystalline diamond on silicon substrate are studied. By changing the ratio of nitrogen content to oxygen content in the growing atmosphere of diamond, the photoluminescence intensity of SiV center can be controlled effectively, and polycrystalline diamond samples with the ratios of SiV center photoluminescence peak to diamond intrinsic peak as high as 334.46 and as low as 1.48 are prepared. It is found that nitrogen promotes the formation of SiV center in the growth process, and the inhibition of oxygen. The surface morphology and photoluminescence spectrum for each of these samples show that the photoluminescence peak intensity of SiV center is positively correlated with the grain size of diamond, and the SiV center’s photoluminescence peak in the diamond film with obvious preferred orientation of crystal plane is higher. The distribution of Si centers and SiV centers on the surface of polycrystalline diamond are further characterized and analyzed by photoluminescence, Raman surface scanning and depth scanning spectroscopy. It is found that during the growth of polycrystalline diamond, the substrate silicon diffuses first into the diamond grain and then into the crystal structure to form the SiV center. This paper provides a theoretical basis for the development and application of SiV centers in diamond.

Ni-doped hybrids of TiO2 and two-dimensional Ti3C2 MXene for enhanced photocatalytic performance

Transition metal ion doping is an effective strategy by which to enhance the photocatalytic activity of semiconductor materials. Herein, Ni-doped TiO 2 /Ti 3 C 2 photocatalysts were designed and fabricated using a simple dipping method and their catalytic performance was verified via the degradation of rhodamine B (RhB). Ni doping induces the formation of a defect energy level in TiO 2 , which shortens the transition distance of photogenerated electrons. Ti 3 C 2 acts as a hole acceptor, which is conducive to the transfer of photogenerated charge. The results show that the Ni-doped TiO 2 /Ti 3 C 2 heterojunction structure exhibits the lowest photoluminescence peak intensity, the highest instantaneous current, and excellent photocatalytic performance compared to TiO 2 /Ti 3 C 2 and TiO 2 . At optimal Ni content, the removal efficiency of RhB is 90%, around 3.7 times higher than that of pure TiO 2 . This work details the preparation of an excellent Ni-doped heterojunction structure for enhanced photocatalytic performance, demonstrating an effective strategy by which to improve the charge separation ability. • Ni-doped hybrids of TiO 2 and Ti 3 C 2 MXene structure was prepared for enhanced photocatalytic performance. • The charge separation ability of TiO 2 was enhanced due to the doping of Ni and the coupling of co-catalyst Ti 3 C 2 . • The removal efficiency of RhB by Ni–TiO 2 /Ti 3 C 2 was 3.7 times higher than that of pure TiO 2 .

Effects of High-Temperature Growth of Dislocation Filter Layers in GaAs-on-Si

GaAs-on-Si templates with two different dislocation filter layers (DFLs) were grown at 550 °C low-temperature (LT)-DFL and 660 °C high-temperature (HT)-DFL using metal organic vapor-phase epitaxy and the effects of the growth temperature were studied. The threading dislocation density (TDD) values of LT-DFL and HT-DFL were 5.2 × 107 cm−2 and 1.5 × 107 cm−2, respectively. The 1.5 × 107 cm−2 of TDD in HT-DFL is reduced by almost one order compared to the 1.2 × 108 cm−2 of that in the control sample without DFLs. The annihilation process was mainly observed in the HT-DFL by a transmission electron microscope, resulting in a lower TDD. The 500-nm-thick GaAs bulk layer and InAs QDs were regrown on GaAs-on-Si templates and the optical properties were also evaluated by photoluminescence (PL). The highest PL peak intensity of the HT-DFL indicates that less non-radiative recombination in both the GaAs bulk and QDs occurred due to the reduced TDD. The GaAs p–i–n diodes were also fabricated to analyze the bulk leakage (JB) and the surface leakage current. The JB of HT-DFL shows the lowest value of 3.625 × 10–7 A/cm−2 at applied bias voltage of 1 V, which is 20 times lower than the JB of the control sample without DFLs. This supports that the high-temperature growth of DFL can make a good performance GaAs device on Si.

Role of gas flow direction on monolayer MoS2 growth on patterned surfaces via CVD

The chemical vapor deposition (CVD) technique has been widely used to grow high quality single layer MoS2 crystals. However, there are still issues that need to be clarified in order to determine the appropriate conditions for the repeatable and scalable process. In this study, we experimentally investigated the effect of flow direction on the size distribution and optical signal of monolayer MoS2 flakes grown on microchannel arrayed surfaces. As an important parameter controlling the CVD process, the carrier gas flow was revealed to be highly sensitive to geometric orientation of the patterned surface. The flow direction parallel to the array yielded larger flakes with narrower size distribution, and enhanced photoluminescence (PL) peak intensities compared to the case with flow normal to the array while the Raman intensities for both the cases are almost the same. The size distributions were obtained as 6 ± 13 and 37 ± 4 µm for the perpendicular and parallel cases, respectively. It was also found that the PL peak intensity increased by approximately 1.5 times when switching to parallel configuration. This study presents an experimental approach to understand the influence of the precursor stream reshaped by the growth surface geometry on the structural and optical properties of monolayer MoS2, which has great potential for use in optoelectronic applications.

A Study of the Structural and Surface Morphology and Photoluminescence of Ni-Doped AlN Thin Films Grown by Co-Sputtering.

Aluminum nitride (AlN) is a semiconductor material possessing a hexagonal wurtzite crystal structure with a large band gap of 6.2 eV. AlN thin films have several potential applications and areas for study, particularly in optoelectronics. This research study focused on the preparation of Ni-doped AlN thin films by using DC and RF magnetron sputtering for optoelectronic applications. Additionally, a comparative analysis was also carried out on the as-deposited and annealed thin films. Several spectroscopy and microscopy techniques were considered for the characterization of structural (X-ray diffraction), morphological (SEM), chemical bonding (FTIR), and emission (PL spectroscopy) properties. The XRD results show that the thin films have an oriented c-axis hexagonal structure. SEM analysis validated the granular-like morphology of the deposited sample, and FTIR results confirm the presence of chemical bonding in deposited thin films. The photoluminescence (PL) emission spectra exhibit different peaks in the visible region when excited at different wavelengths. A sharp and intense photoluminescence peak was observed at 426 nm in the violet-blue region, which can be attributed to inter-band transitions due to the incorporation of Ni in AlN. Most of the peaks in the PL spectra occurred due to direct-band recombination and indirect impurity-band recombination. After annealing, the intensity of all observed peaks increases drastically due to the development of new phases, resulting in a decrease in defects and a corresponding increase in the crystallinity of the thin film. The observed structural, morphological, and photoluminescence results suggest that Ni: AlN is a promising candidate to be used in optoelectronics applications, specifically in photovoltaic devices and lasers.

Facile preparation and modification of SrTiO3 through Ni–Cd co-doping as an efficient visible-light-driven photocatalyst

Visible light-driven Ni–Cd co-doped SrTiO3 photocatalyst was prepared through a co-precipitation technique. The influence of various amounts of doped elements on the properties of the pure SrTiO3 phase has been explored. The characterization was performed employing the X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman, X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FESEM), UV–visible diffuse reflectance spectroscopy (DRS), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), and transient photocurrent experiments. By Ni–Cd co-doping, the average particle size was reduced from 100 to 65 nm, the band gap value was lowered from 3.2 to 2.78 eV, and the powder's surface area was increased by about 2.3 times compared with the pure phase. Low PL peak intensity, small EIS radius, and higher photocurrent density of the 5 wt% doped sample indicate higher charge transfer efficiency than the pure sample. The effect of different photocatalytic experiment parameters on the photodegradation performance has been studied. In this regard, a 60-min visible light irradiation time, 1 g mL−1 initial dye concentration, and 0.7 g L−1 powder dosage were found to be the best values. After 60 min of visible light irradiation, doped SrTiO3 with 5 wt% Ni–Cd thoroughly degraded methylene blue (MB) dye. Additionally, the superoxide radical and holes also play a significant role in photodegradation as determined by the scavenger trapping test. Compared with MB, the prepared sample demonstrated less degradation ability for methyl orange (MO) and Rhodamine-B (RhB) dyes.