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Bismuth is considered as one of the most promising candidates to replace Pb in the organo-lead halide perovskite, a classical material for various optoelectronic applications. When utilized in a photovoltaic cell, the performance of the cell drops due to deterioration in the absorber film and the changes in its crystal structures. In this work, a small amount of dodecylammonium chloride, C12H25NH3Cl (DCl) is added into Cs3Bi2I9 (CBI), resulting in a pinhole-free high-quality perovskite (PVK) film via a single-step solution processability, also confirmed by FTIR and XPS analyses. Structural, optical, and microscopic analyses showed that the quality, surface features, and crystallinity of the CBI films are significantly improved by adding DCl. The prepared films are successfully demonstrated in a solar cell and exhibited considerably improved photovoltaic (PV) characteristics (VOC by ~47%, JSC by ~33%, FF by 13%, and PCE by 115%) over pure CBI-based devices. Moreover, the PV device retained more than 95% of its initial PCE in the ambient laboratory environment (relative humidity 55±5%). To the best of our knowledge, this is the highest PCE along with extended environmental stability reported for solution processed CBI-based perovskite solar cells.

We fabricate germanium-based blocked-impurity-band (BIB) terahertz detectors with the same planar structure but different structural parameters. The photoresponse waveband range is about 40–130 μ m. The best detectivity of these detectors reaches as high as 1.3 × 1013 Jones at 2.6 V and 4 K. The impact of the structural parameters, including the length of the absorbing layer and blocking layer (BL) on the performance of detectors, is investigated. It is concluded that there is an optimum BL length, enabling the fabricated BIB detectors to achieve the highest sensitivity. This work highlights the importance of the optimized structural parameters and their influence on the performance of the detectors.

Owing to their high efficiency and extended environmental stability, hybrid 2D/3D-perovskites (HPVKs) are gaining an increasing interest in the field of organometal halide perovskite solar cells (PSCs). In HPVKs, the 3D component acts as an active material, where its 2D-counterpart provides protection against environmental factors. Here in, we add dodecylammonium-chloride (DACl) into the precursor solution of 3D-perovskites (FAMAPbI3) to achieve HPVKs. The formation of HPVK is confirmed by XRD, optical absorption, and Fourier-transform infrared (FTIR) spectroscopies. The structural and optical analysis affirmed that in the case of HPVKs, not only the crystallinity of perovskites is improved significantly but also a variation in its structural properties and optical bandgap have occurred. It is also observed that the surface morphologies of HPVK films are considerably improved with the incorporation of DACl. A minute amount of CsI is also added into the precursor solution of HPVKs, which further assist the formation of HPVKs and consequently causes a significant increase in the carrier lifetime. Finally, a solar cell made of HPVKs shows an improved PCE than pure 3D-perovskites. All HPVKs films and solar-cells are prepared in the ambient humidity and found to be more hydrophobic and stable, not only under relative humidity >50% but also under high thermal stress of 85 ℃.

We predict an extraordinary transmission (ET) of a periodic hole structure (PHS) by simulating plasmonic properties using finite difference time-domain Solutions. The ET effect is used to modulate the photoresponse by integrating the PHS into silicon-based blocked-impurity-band (BIB) terahertz detectors. The measured photoresponses of the experimentally realized PHS + BIB detectors confirm the tunability of photoresponses. Moreover, the electromagnetic field distribution is also simulated, which reveals that the prominent modulation effect originates from a strongly confined electromagnetic field. The response away from the resonance wavelength is largely suppressed. This work demonstrates the potential of our device in multi-spectral terahertz detection.

The remarkable optoelectronic properties and considerable performance of the organo lead‐halide perovskites (PVKs) in various optoelectronic applications grasp tremendous scientific attention. However, the existence of the toxic lead in these compounds is threatening human health and remains a major concern in the way of their commercialization. To address this issue, numerous nontoxic alternatives have been reported. Among these alternatives, bismuth‐based PVKs have emerged as a promising substitute because of similar optoelectronic properties and extended environmental stability. This work communicates briefly about the possible lead‐alternatives and explores bismuth‐based perovskites comprehensively, in terms of their structures, optoelectronic properties, and applications. A brief description of lead‐toxification is provided and the possible Pb‐alternatives from the periodic table are scrutinized. Then, the classification and crystal structures of various Bi‐based perovskites are elaborated on. Detailed optoelectronic properties of Bi‐based perovskites are also described and their optoelectronic applications are abridged. The overall photovoltaic applications along with device characteristics (i.e., V OC, J SC, fill factor, FF, and power conversion efficiency, PCE), fabrication method, device architecture, and operational stability are also summarized. Finally, a conclusion is drawn where a brief outlook highlights the challenges that hamper the future progress of Bi‐based optoelectronic devices and suggestions for future directions are provided., The toxic‐lead in organometal‐halide perovskites is hindering their applications and readily needs a replacement. This work communicates briefly about the possible nontoxic lead alternatives and explores bismuth‐based perovskites comprehensively, in terms of their structures, optoelectronic properties, and applications. This work is helpful to improve the material and performance of the bismuth‐based perovskites to bring them on par with lead‐based perovskites.

Mid-infrared blocked-impurity-band (BIB) photonic detectors are developed by sulfur (S) ions implantation into germanium (Ge) crystal. The detectors demonstrate wide photoresponse spectra ranging from 2 to 10 μm with peak response at about 6 μm. We characterize photocurrent spectra of two operating modes, forward bias mode (FBM) and reverse bias mode (RBM), and find that RBM has a lower optimum bias but a bigger photocurrent. Effect of different blocking layer (BL) length on photocurrents for the two operating modes is studied. When BL length increases, the ratio of the relative photocurrent under RBM to that under FBM at respective optimum bias enlarges. The slope of the electric field profile in BL leads to the differences of optimum bias and maximum photocurrent between two modes. The electric field strength in AL under RBM strengthens as BL length increases, resulting in larger photocurrent for longer BL.

In recent years CdTe thin film solar cells (SCs) have demonstrated promising market application foreground. However, a relatively large gap between the achieved SCs efficiencies and the theoretically predicted maximum efficiency still exists. In particular, the open circuit voltage (Voc) of the CdTe thin film SCs could be further increased, which is limited by high-work-function of CdTe. In this work, p-type narrow-gap SnTe thin films are proposed as a buffer layer in the back contact of CdTe SCs. The band alignment at SnTe/CdTe interface renders a small valance band offset, which expedites hole transport from the CdTe absorber to the hole electrode and improves the Ohmic contact for CdTe. With the insertion of a SnTe single buffer layer at the back contact, a Cu-free CdTe SC has been developed, which displays the same cell efficiency as the traditional cells using CuxTe as the back contact. The Voc of cells with ZnTe: Cu/SnTe double-layer at back contact is notably higher than the CdTe SCs fabricated with CuxTe or ZnTe: Cu single-layer at the back contact. Furthermore, accretion of hole concentration is also demonstrated by the diffusion of Sn in the CdTe absorber layer. This work shows the potential to improve CdTe SCs by using a narrow-gap IV-VI compound semiconductor.

Heavy-metal-free I-III-VI2 quantum dots (QDs) have recently emerged as favorable alternatives to toxic II-VI QDs for optoelectronic and biological applications, but low fluorescence efficiency is a key issue related to the promising nanocrystals. In this work, we demonstrate big enhancement of two-photon fluorescence efficiency and low threshold two-photon pumped amplification of spontaneous emission (ASE) of Zn-processed CuInS2 (CIS) QDs for the first time. The change of two-photon process caused by Zn2+ cation exchange in CIS QDs is systematically investigated. Two-photon ASE in Zn-processed CIS QDs films is achieved with a record of low threshold fluence of 5.7μJ/cm^2. With high two-photon fluorescence quantum yields and low threshold ASE, the Zn-processed CIS QDs could become a promising candidate for two-photon bio-imaging, nonlinear optical and novel QDs laser devices.

Fluorescent semiconducting conjugated polymer nanoparticles (CPNs) are promising candidates for enhanced luminescent devices and bioimaging. The key aspect of all fluorescent materials is their high radiative yield. Combination of CPNs with metal nanoparticles (MNPs) is one of the ways to increase their fluorescent yield. Most of such combinations are introduced in the forms of sophisticated core–shells and thin films or layers. Herein, we synthesized CPNs of poly[2-methoxy,5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and silver nanoparticles (AgNPs) in aqueous solution in the form of metal–polymer nanocomplexes (MPNCs), which are not only easily achievable but also show significantly enhanced optical absorption and luminescence properties. To synthesize MPNCs, AgNPs with different molar ratios were added to a colloidal solution of CPNs. The adsorption of AgNPs on the surfaces of the CPNs was confirmed by transmission electron microscopy and UV-VIS absorption spectroscopy. Fluorescence and optical absorption spectroscopies revealed a substantial increase in the optical absorption and photoluminescence (PL) intensity of the MPNCs. It was observed that at optimum concentrations of AgNPs and CPNs in the colloidal solution of MPNCs, the PL intensity is enhanced by ∼11 fold. The increase in PL intensity is attributed to the energy transfer from AgNPs to CPNs via near-field-coupling and electric field enhancement in the nanogaps present among the adsorbed AgNPs on the surfaces of the MPNCs, which is confirmed by finite difference time domain (FDTD) simulations. Since the MPNCs as well as their ingredients were prepared in aqueous solutions, we believe that such nanocomplexes could find use not only in enhanced fluorescent devices but also in therapeutics and diagnostics.

Owing to a complex monocline structure and high-density of defects in monocrystalline GaTe, the performance of GaTe-based electronic devices is considerably compromised. Yet, the defects’ nature in GaTe could be a merit rather than a shortcoming in other realms. In our work, the density of defects in GaTe films is utilized for a facile decoration of Au nanoparticles (NPs), which allowed us to extend its application potential to the domain of surface enhanced Raman scattering (SERS) for the first time. Two-dimensional (2D) GaTe layered structures are prepared by mechanical exfoliation, and high-density Au NPs are synthesized by immersion of 2D GaTe in HAuCl4 aqueous solution. By varying the immersion time, the sizes and coverage rate of Au NPs on GaTe can be elaborately tuned. Thanks to the defect nature of GaTe, the maximum coverage amounts to 98%. The hereby achieved Au-NPs–2D-GaTe hybrid structure demonstrates outstanding properties as a superior SERS substrate for ultrasensitive detection of R6G aromat...

An analytical method for the simultaneous determination of 13 mycotoxins in feed by magnetic dispersive solid-phase extraction combined with ultra high performance liquid chromatography and tandem mass spectrometry was developed. The samples were extracted with acetonitrile/water (80:20, v/v, containing 3% acetic acid), and separated by centrifugation after salting-out, and then treated with magnetic adsorbents to remove interferences. The separation of target mycotoxins was performed on an ACQUITY UPLC HSS T3 column using a mobile phase consisting of 1 mmol/L ammonium acetate with 0.1% formic acid and methanol by gradient elution. Good linearities for the 13 mycotoxins were achieved with correlation coefficients over 0.99, and the recoveries of mycotoxins were in the range of 89.3–112.6% at spiking at levels of 5, 20 and 100 μg/kg, with relative standard deviations of 0.9–10.4%. Based on the functional magnetic materials (MDN@Fe3O4, PSA@Fe3O4, ZrO2@Fe3O4) applied in dispersive solid-phase extraction, the pretreatment process is more convenient and it is beneficial to reduce the experimental cost by reusing the recycled magnetic materials. It is a simple, rapid and environmentally friendly analytical method for the determination of mycotoxins in feed. This article is protected by copyright. All rights reserved

We fabricate Si-based blocked impurity band (BIB) terahertz detectors using p-dopant through a standard silicon device fabrication technology. Comparison of photoresponse of the detectors under alternate operating mode and conventional operation mode (COM) is made. We demonstrate that the detectors can achieve high responsivity through positive bias on the active layer side, namely, alternate operating mode (AOM). The response of the detectors terminates at wavelength of $35~\mu \text{m}$ (8.57 THz) under AOM; on the contrary, the response is cutoff at $31~\mu \text{m}$ (9.68 THz) with a positive bias on the blocking layer, namely, COM. The relative responsivity at 0.6 V under AOM is 2.3 times of that under COM. By developing an energy band model, we find that the response difference under the two modes originates from the change of band offsets. The electric field in the blocking layer under AOM is much smaller than COM and most of the voltage drops in the active layer under AOM, which leads to the bigger multiplication of the photon-generated carriers than COM. By analyzing the origination of the dark current under the AOM, a method to improve the performance of BIB detectors under AOM is proposed.

Preparation of aluminosilicate ferrierite (FER) zeolite nanosheets with controllable thickness in the presence of a sole organic ammonium is attractive, but still challenging. In this report, with the employment of N,N-diethyl-cis-2,6-dimethylpiperidinium (DMP) as both a structure directing agent and crystal growth inhibitor, aluminosilicate FER zeolite nanosheets, with a variety of crystal thicknesses, ranging from 6 to 200 nm, are successfully synthesized under hydrothermal conditions. Very interestingly, the amount of DMP in the starting gel is the key factor for crystal thickness control of aluminosilicate FER zeolite nanosheets. The obtained FER products, with different thicknesses, are well characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), N2 sorption, thermogravimetric analysis (TG), inductively coupled plasma (ICP), and magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. This simple strategy might provide a novel avenue for the synthesis of other zeolite nanosheets with controllable thickness.

Temperature dependence of molecular absorption line shape is important information for spectroscopic studies and applications. In this work, we report a comb-locked cavity ring-down spectrometer employing a cryogenic cooler to perform absorption spectroscopy measurements at temperatures between 40 K and 300 K. As a demonstration, we recorded the spectrum of the R(0) line in the (2-0) band of HD at 46 K. The temperature was also confirmed by the Doppler width of the HD line. Spectra of CH4 near 1.394 μm were also recorded in a wide temperature range of 70−300 K. Lower-state energies of methane lines were analyzed by fitting these spectra, which can be directly compared with the HITRAN and TheoReTS databases. Considerable deviations were observed, indicating the need to investigate the assignments of the methane lines in this region.

In this work, a novel heterostructure consisting of different lattice structures with zincblende ZnTe and rock-salt PbTe is proposed. The PbTe/ZnTe heterostructures are grown by molecular beam epitaxy. Type-I band alignment at the PbTe/ZnTe heterointerface is revealed by X-ray photoelectron spectroscopy. The interface of the heterostructure exhibits exotic electrical properties. The novel heterostructure is then implemented to develop high-performance mid-infrared photodetectors which demonstrate pronounced responsivity, swift response speed, and high detectivity. The new photodetectors utilize the lateral photovoltaic effect which facilitates the understanding of the novel PbTe/ZnTe heterostructures.

The research on novel terahertz (THz) devices with high performance is in rapid ascent in order to promote applications of THz technology. In this paper, we propose a broadband, optically transparent and highly flexible multispectral beam splitter based on Ag nanowires/graphene (ANWG) composite film on polyethylene terephthalate film substrates. The properties of the ANWG-based beam splitters are investigated, which exhibit a broadband THz reflectance of about 90%, a high optical transmittance of over 86% in the visible range, and excellent mechanical flexibility. The THz experimental result of the ANWG-based beam splitter is close to those of numerical simulations using a theoretical model. In comparison with conventional THz beam splitters, the ANWG-based beam splitter possesses excellent light-splitting performances for both transmitting visible light and reflecting THz radiation, and the device can significantly improve the overall performance of THz optical systems. Moreover, the device can be effectively applied in the visible/infrared imaging systems to implement multispectral imaging. Our concept provides a promising route for realizing compact hybrid optical systems, and it has great potential for commercial applications.

Blocked impurity band (BIB) detectors play an important role in astronomical detection from the mid-infrared to THz region. We demonstrated the field dependence of the photoresponse in BIB detectors using both experimental results and theoretical calculations. It was found that there is a gain operation region between the saturation voltage of the photocurrent and the breakdown voltage of the dark current. The photoconduction gain in the gain operation region is several orders of magnitude larger than that in the other voltage range. Considering the field-assisted thermal ionization process and the photon-assisted impact ionization process, the gain operation mode can be well explained. Utilizing the gain operation mode, Ge:B BIB detectors can even detect the objects with a temperature as low as 10 K. We provide a theoretical basis to optimize BIB detectors and further improve their detection performance.

An ordered metal array normally can enhance the electric field near the surface by generating strong excitation of surface plasmons (SPs), while two-dimensional materials (2DMs) can ensure efficient adsorption of the aromatic molecules. Herein, an AuNPs/GaTe/Au-hole array structure for SERS is first theoretically simulated and successively prepared experimentally. The parameters of the Au-hole array are optimized through finite-difference time-domain (FDTD) numerical simulations; including period, depth, and geometry. With Rhodamine 6G (R6G) probe molecules, the strongest Raman signal is observed at the edge of the Au-hole. The corresponding enhancement factor reached as high as 1.8 × 106, which enabled the limiting detection concentration of 10−16 M of R6G, surpassing most of the existent SERS substrates. Simulations of GaTe, AuNPs/GaTe/Au-film, and AuNPs/GaTe/Au-hole array are applied to explain the observation of SERS activity in the Au-hole array structure. Moreover, the structure exhibited good reproducibility and stability.

Owing to their extraordinary optoelectronic properties, 2D transition metal dichalcogenides (TMDs) are proved to be promising materials for photodetectors. However, they suffered from poor absorptivity due to their atomically thin profile. Herein, CuInS2 quantum dots (QDs) and plasmonic Au nanoparticles (AuNPs) were adopted to achieve a MoS2-CuInS2-AuNPs 2D–0D hybrid by simultaneous deposition of CuInS2 QDs and AuNPs on the MoS2 nanosheet. In this configuration, MoS2 is used as a high mobility carrier transport channel, while CuInS2 QDs act as an efficient light absorber, and the AuNPs serve as a light sensitizer to enhance the local electric field around MoS2 and CuInS2 QDs via surface plasmon resonance (SPR). With such synergism of CuInS2 QDs and Au NPs, the highest responsivity of 16.65 A W − 1 and D* as high as 2.27 × 10 12 Jones are achieved for the MoS2-CuInS2-AuNPs hybrid devices under 635 nm laser, which is two orders of magnitude higher than the pristine MoS2 devices and outperformed most of the other MoS2-based photodetectors. Finally, the synergistic effect of the CuInS2 QDs and Au nanoparticles is illustrated by Finite-Difference Time-domain(FDTD) simulation. The underlying synergism strategy for such a 2D–0D configuration may also be applied to other photo-electric devices.

Under UV irradiation, photo-oxidation occurs on the surface of CdSe quantum dots (QDs), thus modifying their QD optical properties. The influence of size and surface state (SS) emission on the photoluminescence (PL) evolution of CdSe QDs was investigated. Colorimetric study of the CdSe QD emission under UV irradiation indicates that the QD size and SS emission will influence the movement of chromaticity parameters. A photo-corrosion effect reduced the QD size and caused blue shift of the band edge (BE) peak. The irradiation-induced blue shift of QD emission always moves the corresponding chromaticity coordinate counterclockwise in the chromaticity diagram. For CdSe QDs with a dominant SS peak, the different evolution between BE and SS peak under UV irradiation will substantively influence the transformation of emission color: the chromaticity coordinate moved faster when PL increased than that when it decreased. Generally, the emission color of CdSe QDs with relatively large size and weak SS peaks is more stable in irradiation process.

Plasmons in metals have great impact on light emission, propagation, and detection in visible and infrared light wave frequencies. To explore plasmonic effect on the THz detection, both a backside-illuminated and a topside-illuminated blocking impurity band (BIB) THz detectors are developed and significant influence of plasmonic effect on the performance of BIB THz detectors is observed. The plasmonic effect in the heavily doped semiconductor layer of BIB THz detectors causes high reflectance of THz radiation which curtails the detection frequencies of the backside-illuminated BIB detectors. However, due to the advantages of flip-chip package and high quantum efficiency, the dark current, the responsivity, and the detectivity of the backside-illuminated detector shows superior characteristics to the topside-illuminated detector. The performance of the THz detector could be further improved with the suppression of the plasmonic effect.

An ultrasound/microwave-assisted solid–liquid–solid dispersive extraction method was developed for the determination of 16 pyrethroid insecticides in Dendrobium officinale. The extraction and purification were performed in one step. The pyrethroids were extracted with 8:2 acetone:hexane and purified with a mixture of primary secondary amine, Florisil, C18, and graphitized carbon black. The extraction temperature, extraction time, and ultrasound power were optimized. Trans-cyfluthrin-d6 was used as the internal standard to improve the accuracy. Under the optimized conditions, the recoveries of the pyrethroids were from 72.2 to 113.9% with the limits of detection between 0.29 and 9.38 µg kg−1. The optimized method was successfully used for the determination of pyrethroids in commercial D. officinale samples and may allow monitoring pyrethroids in herbal products.

Methylammonium lead iodide (MAPbI3) perovskite has emerged as a dazzling nova in the solar cell realm. However, the robustness or stability of the material exposed to different ambiences is a key issue. In this paper, resonance Raman spectroscopy is combined with surface and bulk crystal characterizations to interpret the oxygen intercalation phenomenon on the surface of MAPbI3. We observe that oxygen can intercalate into the frameworks of MAPbI3 with the assistance of laser excitation. By lowering down the pressure in the experimental chamber, the intercalated oxygen can be readily removed. X-ray photoelectron spectroscopy and X-ray diffraction characterizations suggest that Pb–O bonds are mainly formed on the surface of MAPbI3 but are constrained to avoid the formation of PbO compound. The quantum chemical calculation based on density functional theory supports the above conclusions. The understanding of oxygen intercalation in MAPbI3 shall benefit the improvement of stability of the important solar cel...

We present a three-dimensionally configured cathode with enhanced field-emission performance formed by combining carbon nanotube (CNT) emitters with a nickel foam (NiF) substrate via a conventional screen-printing technique. The CNT/NiF cathode has low turn-on electric field of 0.53 V μm−1 (with current density of 10 μA cm−2) and threshold electric field of 0.87 V μm−1 (with current density of 0.1 mA cm−2), and a very high field enhancement factor of 1.4 × 104. The porous structure of the NiF substrate can greatly improve the field-emission properties due to its large specific surface area that can accommodate more CNTs and increase the emitter density, as well as its high electrical and thermal conductivities that facilitate current transition and heat dissipation in the cathode. Most importantly, the local electric field was also enhanced by the multistage effect resulting from the rough metal surface, which furthermore leads to a high field enhancement factor. We believe that this improved field-emission performance makes such cathodes promising candidates for use in various field-emission applications.

Methylammonium lead-iodide (CH3NH3PbI3, hereafter referred to as MAPbI3) perovskite has emerged as a dazzling nova in the solar cell realm. To date, the surface physics of these materials is still puzzling, but in this work, we demonstrate that the optical dynamics in MAPbI3 is primarily determined by the surface states. Pb dangling bonds on the surface of MAPbI3 introduce shallow electronic states. The carrier localization effect for these electronic states is rather weak as the lifetimes of the carriers on the iodine-poor surface are comparative to those in the interior region of MAPbI3. In contrast, rich-iodine on the surface of MAPbI3 induces deep trap centers for the carriers, which are detrimental to long carrier diffusion lengths. It is further proved that the surface passivation, which surprisingly prolongs the carrier diffusion lengths, mainly works on the rich-iodine on the surface rather than the Pb dangling bonds. This better understanding of the surface physics could provide essential information for improving the performance of photoelectronic devices based on MAPbI3 perovskites.

A novel Fe3O4@MDN magnetic nanomaterial was successfully developed as a magnetic dispersive solid-phase extraction adsorbent for the determination of triazole pesticide residuals in honey samples by high performance liquid chromatography coupled with triple quadrupole mass spectrometry (HPLC-MS/MS). The macromolecular structure named MDN was coated on the surface of a copolymer synthesized with silyl reagents methacrylic acid-3-(trimethoxysilyl) propyl ester (MPS) and tetraethyl orthosilicate (TEOS) based on ferriferrous oxide (Fe3O4), whose characteristics were confirmed by a scanning electron microscope (SEM). The proposed magnetic dispersive solid-phase extraction (MDSPE) method provided a rapid, environmentally friendly and magnetic stuff recyclable approach for the triazole pesticide analysis. By means of optimal conditions, the recoveries of 15 triazoles (spiked at 20 μg kg−1) ranged from 90.5 to 105.9%. The method showed good linearity, sensitivity in the range of μg per kilogram and repeatability (relative standard deviation below 6.8%, n = 5). The proposed method was confirmed to be a simple, rapid and efficient method for the analysis of triazole pesticide residuals in honey samples.

Using angle-resolved photoemission spectroscopy (ARPES), we studied bulk and surface electronic band structures of narrow-gap semiconductor lead telluride (PbTe) thin films grown by molecular beam epitaxy both perpendicular and parallel to the {\Gamma}-L direction. The comparison of ARPES data with the first-principles calculation reveals the details of band structures, orbital characters, spin-orbit splitting energies, and surface states. The photon-energy-dependent spectra show the bulk character. Both the L and {\Sigma} valence bands are observed and their energy difference is determined. The spin-orbit splitting energies at L and {\Gamma} points are 0.62 eV and 0.88 eV, respectively. The surface states below and close to the valence band maximum are identified. The valence bands are composed of a mixture of Pb 6s and Te $5p_z$ orbitals with dominant in-plane even parity, which is attributed to the layered distortion in the vicinity of PbTe (111) surface. These findings provide insights into PbTe fundamental properties and shall benefit relevant thermoelectric and optoelectronic applications., Comment: 15 pages, 6 figures, 1 table

Bandgap renormalization (BGR), or bandgap narrowing effect, is one of the many-body effects predicted by many-body theory in semiconductor physics. However, pure BGR effect has never been observed experimentally although the mixed effect of BGR with lattice-heating induced bandgap narrowing was reported in GaAs and CdTe semiconductors. PbTe has a positive temperature coefficient of bandgap. Its lattice-heating induced bandgap narrowing can be eliminated so that the pure BGR effect is possibly observed. However, that has never been reported so far because the BGR effect is weak in PbTe due to its huge dielectric screening. We study the ultrafast dynamics of photo-excited carriers in PbTe films using near-infrared femtosecond-resolved transient differential transmission (TDT) spectroscopy. A complex oscillation-like damped decay dynamics is observed. A negative dip, a fingerprint signature of BGR effect, occurs immediately after the thermalization process of the photo-excited carriers. As such, we have observed a pure BGR effect in PbTe for the first time, strongly supporting the many-body theory. Meanwhile, we have also observed a dynamic transition from a transient absorption enhancement to absorption saturation, revealing the emergence of a slow lattice-heating induced bandgap widening via carrier-phonon couplings. Based on a two-temperature model, a simulation computation is carried out, supporting the lattice-heating induced bandgap widening leads to the dynamic transition. A phenomenological dynamic model is developed, including three dynamic components: the thermalization of the photo-excited carriers, recombination of the thermalized carriers and lattice-heating induced bandgap widening, and used to best fit the excitation-power dependent TDT dynamics. Time constants and strengths of the three dynamic components are obtained for different excitation powers. Time constant variation with the excitation power reveals different roles of the carrier-carrier and carrier-phonon scattering in the thermalizing process, as well as of free carrier and exciton recombination in the decaying process of hot carriers.

Graphene photo-detectors functionalized by colloidal quantum dots (cQDs) have been demonstrated to show effective photo-detection. Although the transfer of charge carriers or energy from the cQDs to graphene is not sufficiently understood, it is clear that the mechanism and efficiency of the transfer depends on the morphology of the interface between cQDs and graphene, which is determined by the shell of the cQDs in combination with its ligands. Here, we present a study of a graphene field-effect transistor (FET), which is functionalized by long-ligand CdSe/ZnS core/shell cQDs. Time-resolved photo-luminescence from the cQDs as a function of the applied gate voltage has been investigated in order to probe transfer dynamics in this system. Thereby, a clear modification of the photo-luminescence lifetime has been observed, indicating a change of the decay channels. Furthermore, we provide responsivities under a Förster-like energy transfer model as a function of the gate voltage in support of our findings. The model shows that by applying a back-gate voltage to the photo-detector, the absorption can be tuned with respect to the photo-luminescence of the cQDs. This leads to a tunable energy transfer rate across the interface of the photo-detector, which offers an opportunity to optimize the photo-detection.

This work demonstrates the surface plasmon (SP)-exciton coupling effect on the photoluminescence (PL) enhancement in CsPbBr3 nanocrystal (NC) at PMMA/Ag nanostructure (NS) in wide spectral range excitation. The spectra dependent time resolved PL measurement reveals that the emission photons are from the recombination of localized excitons and the PL enhancement can be attributed to the near-field effect, which is also supported by evidence that the enhancements are nearly the same in the whole excitation wavelength from 200 nm to 900 nm. The non-spectral dependence of the enhancement factor suggests that there is the same dynamic process of hot electrons in CsPbBr3 NC in multiphoton excitation. The hot electrons will relax into localized exciton states, and the electric field generated by SPs will enhance the radiative recombination of excitons. This work will have benefits for revealing dynamics of hot electron relaxing and interactions in multi-photon absorption, as well as the inner mechanism of SP coupling effects.

A triple-band infrared photodetector is developed by doping sulfur into germanium. The photocurrent spectrum at 20 K shows that there are three response bands at about 1.4, 1.6, and 6.5 µm, indicating the realization of triple-band detection. The triple response bands are attributed to the electronic transitions from the valence band to the conduction band at the Γ and L points, and from the impurity band to the conduction band, respectively. At 4 K, the overall blackbody detectivity is ~1.0 × 1011 cm Hz1/2/W. We provide a new route for realizing multiband infrared detectors.

Magnetic semiconductors based on two-dimensional (2D) crystals have attracted attention owing to their intrinsic ferromagnetism and have potential for spintronic devices. Here, full-potential linearized augmented plane wave plus local orbitals method is used to explore the structural, electronic, magnetic, and magneto-optical properties of CrI3 monolayer. Our first-principles calculations show that CrI3 monolayer is a ferromagnetic indirect semiconductor with spin-up and spin-down band gaps of 1.23 and 1.90 eV, respectively, and a magnetic moment of 2.93 [Formula: see text] per Cr atom. Based on the macroscopic linear response theory, we systematically study the influences of external magnetic field and out-of-plane strain on the magneto-optical Kerr effect spectra in CrI3 monolayer. The Kerr rotation of CrI3 monolayer at 1.96 eV photon energy is [Formula: see text], which is consistent with the recent experiments. We find that the Kerr rotation reaches its maximum when the external magnetic field is perpendicular to CrI3 plane, while it is almost zero on turning the magnetic field in the plane. This result as well as the sizable magnetocrystalline anisotropy energy (MAE) of 0.79 meV verifies that CrI3 monolayer has a strong magnetic anisotropy with an out-of-plane easy axis. Further, applying out-of-plane compressive and tensile strain upon CrI3 monolayer, we observe a redshift of the Kerr rotation spectra with the increase of the strain and the peak values of the Kerr rotation increase correspondingly. The rich electronic and magnetic properties, especially the magneto-optical spectra, render CrI3 monolayer a promising 2D magnetic material for applications from sensing to data storage.

In this response, we explain the points mentioned by R. Rani and R. Bhatia in their Comment for our previous paper [AIP Advances 5, 097130 (2015)], that the high value of β obtained in Song et al. [AIP Advances 5, 097130 (2015)] is misleading because it does not corroborate with the obtained Jmax, and the obtained value of Jmax is “low” in the mentioned study as compared to the reported values [J. Appl. Phys. 111, 044307 (2012) & Appl. Phys. Lett. 102, 033102 (2013)]. For the high value of β, the obtained current Jmax is corroborated but such high value is mainly due to the multistage effect when CNTs are deposited on the rough surface of reduced graphene. For the “low” Jmax, although this is true when compared with Sameera et al. [J. Appl. Phys. 111, 044307 (2012) and Appl. Phys. Lett. 102, 033102 (2013)], but we believe that our value is a generally common value when compared with other reports [Diam. Relat. Mater. 47, 1 (2014); J. Alloys Compd. 610, 659 (2014); J. Nanomater. 2013, 5239 (2013)] using the similar method as described in our paper. Therefore, the conclusions from the experimental results on field emission performance of CNT/graphene composite materials in our paper are reliable.

We have investigated a graphene field-effect transistor functionalized with quantum dots using time-resolved photoluminescence spectroscopy. Forster transfer allows the modelling of the energy transfer between dots and graphene as a function of the backgate voltage.

A core-shell structure of novel complex conjugated polymer nanoparticles (CPNs) consisting of poly(2-methoxy,5-(2'-ethylhexyloxy)-1,4-phenylenevinylene), polyethyleneimine (PEI) is developed. PEI is used to construct CPN@PEI core-shell structure through electrostatic attraction, and shell thickness can be controlled by PEI. Small Au-Ag alloy nanoparticles (ANPs) are then inserted into CPN@PEI core-shell structure to plasmonically tune luminescence properties. The coupling structure with double polymer core-shell CPN@PEI and ANPs presents unique luminescent characters, and maximum luminescence enhancement is realized when shell thickness is 8.6 nm. The strategies taking polymer as shell material in construction of core-shell complex CPNs and tuning optical properties by ANPs shall have significant values in applications of CPNs as probes and fluorescent tags in biological science.

We integrate two dimensional hole arrays (2DHAs),a plasmonic structure, into silicon based blocked impurity band (BIB) terahertz detectors. The photoresponse of the BIB device without 2DHA covers a broad spectral range from 31 μm (9.68 THz) to 15 μm (20 THz). Although 80% of the active region is covered with a metal film in the surface plasmon (SP)-enhanced device, its absolute photoresponse is 120% higher than that of the reference device at the peak wavelength. We further find that the SP-enhanced device presents about 8-fold enhancement in comparison with the reference device at λ = 30.7 μm (9.77 THz) that is beyond the SP resonance. By an energy band model and electromagnetic field simulation, we discover that the photoresponse enhancement at both the resonance wavelength and the non-resonance wavelength is related to a strong confined electromagnetic field at the interface of the 2DHAs and active region.

We report the determination of band alignment of PbTe/SnTe (111) heterojunction interfaces using X-ray photoelectron spectroscopy (XPS). Multiple core levels of Pb and Sn were utilized to determine the valence band offset (VBO) of the heterojunction. The XPS result shows a type-III band alignment with the VBO of and the conduction band offset (CBO) of . The experimental determination of the band alignment of the PbTe/SnTe heterojunction shall benefit the improvement of PbTe/SnTe-related optoelectronic and electronic devices.

Localized surface plasmon resonance coupling effects (LSPR) have attracted much attention due to their interesting properties. This Letter demonstrates significant photoluminescence (PL) enhancement in the Au NS/CH3NH3PbI3−xClx heterostructures via the LSPR coupling. The observed PL emission enhancement is mainly attributed to the hot electron energy transfer effect related to the LSPR coupling. For the energy transfer effect, photo-generated electrons will be directly extracted into Au SPs, rather than relaxed into exciton states. This energy transfer process is much faster than the diffusion and relaxation time of free electrons, and may provide new ideas on the design of high-efficiency solar cells and ultrafast response photodetectors.

We report the enhancement of the mid-infrared (MIR) luminescence intensity in a nanoscale metal/semiconductor structure by the coupling of surface plasmon polaritons (SPPs) with excitons in a narrow-gap semiconductor. The SPPs are efficiently excited by the total internal reflection photons at a metal/semiconductor interface. The intense electric field induced by SPPs, in turn, greatly changes the radiative recombination rates of the excitons generated by the pumping laser and thus the MIR luminescence intensity. The finding avails the understanding of fundamental science of SPs in narrow-gap semiconductors and the development of novel MIR devices.

A novel self-assembled hybrid nanocompound consisting of bismuth sulfide nanocrystals (Bisub2/subSsub3/subNCs) and Ag@SiOsub2/subnanoparticles (NPs) is used to study the enhancement of photoluminescence by localized surface plasmon resonance (LSPR). Ag@SiOsub2/subcore-shell NPs were prepared by deposition of silica onto the surface of Ag NPs through the sol-gel method and followed by surface modification via 3-aminopropyltriethoxysilane for the coming conjugation with Bisub2/subSsub3/subNCs. We propose the photoluminescence enhancement by the LSPR effect through adjusting the thickness of silica shell and the Ag@SiOsub2/subNP concentration. By modulating the thickness of the silica shell and the concentration of Ag NPs, the maximum enhancement of a 5.7 fold can be reached with the thickness of an SiOsub2/subshell at 22.5 nm. A clear red shift of the emission peaks in the Bisub2/subSsub3/subNCs-Ag@SiOsub2/subNPs hybrid structures is observed. Such a metal-enhanced Bisub2/subSsub3/subquantum dot (QD) fluorescence system may have promising applications in optoelectronic device.

Behavior of defects in ion-implanted semiconductors is an everlasting topic and becomes even more critical as semiconductor devices continuously shrink and ion implantation technique has been increasingly employed. High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) were employed to investigate the structural evolution of arsenic (As) implanted silicon (Si). Project range (PR) defects and end of range (EOR) dislocations are observed via HRTEM. EDX characterization proves the two types of defects are related to dopant atoms precipitations. The sizes of both PR defects and EOR dislocations enlarge at the expense of small ones with the elevation of annealing temperature. The characterizations of electrochemical capacitance–voltage and EDX conclude that the SiO2/Si interface is playing an indispensable role in the deactivation of dopant atoms during the annealing process. As atoms are detected in the As-implanted Si region near the SiO2/Si interface but not in the silica layer. Nanoparticles composed of Si atoms in the silica layer are observed in the 1150 °C-annealed samples, which proves the migration of oxygen atoms at the SiO2/Si interface.

Owing to the Auger recombination effect, multiple excitons (MEs) in semiconductor nanocrystals (NCs) are dissipated nonradiatively at the sub-nanosecond time scale, which sets a stringent limit on the time window within which one can operate with them. Here, we show that this issue can be resolved by utilizing an intrinsic energy transfer system in CdSe NCs, where MEs created in the donor quantized states can be effectively extracted to the acceptor trap states. This was evidenced by the step-like increase in the intensity and the apparent decrease in the rise time of the trap-state photoluminescence with the elevated laser excitation power. With the radiative lifetime being tens of nanoseconds for the trap states, extended storage of MEs has been achieved and marks a crucial step towards flexible manipulations of their optoelectronic properties.