Wen He

Attributed to its excellent physicochemical properties, graphene (GR) has very active applications in the fields of catalysis, optoelectronic devices, and battery electrode materials. However, until now, regulating the type and density of carriers in GR is still crucial for its practical applications. Here, reduced graphene oxide (RGO)-Bi2Te3 heterojunctions doped with different contents were prepared by a simple one-step method. The Bi2Te3 materials containing different RGO were made into broadband (365–850 ​nm) photoelectrochemical-type detectors, and the effects of the doping amount of RGO on the optoelectronic behavior of the devices and the intrinsic operation mechanism of the devices were investigated in detail. The results show that the values of Iph/Idark, Ri, and D∗ of Bi2Te3/RGO heterojunction devices obtained with 1 ​mg of RGO doping are 412, 6.072 ​mA/W, and 2.406 ​× ​1010 Jones …

The hybrid 2D/3D heterostructure, which synergistically combine the high surface area and superior surface properties of 2D materials with the volumetric advantages and mechanical stability of 3D materials, offer an efficient and unique platform for electronic, optoelectronic, and energy conversion applications. Although this structure offers numerous advantages, optimizing the performance of 2D/3D heterojunction devices still faces challenges such as interface control difficulty, doping uniformity, and scalability for mass production. To simplify and effectively optimize the performance of 2D/3D heterojunction devices, this study delves into the impact of the thickness of 2D Bi 2 Se 3 films on the performance of Bi 2 Se 3/GaN heterojunction photodetectors. In thinner Bi 2 Se 3 films, a higher surface defect density increases carrier recombination efficiency, while in thicker films, an increase in internal defects impedes …

Large-scale Bi2O3/Ag/TiO2 nanotubes (BAT NTs) were successfully synthesized using ZnO nanorods template through the facile solution process at room temperature. Highly ordered BAT NTs with an average diameter of approximately 300 nm were arranged hierarchically on the overall ITO substrate. In addition, a self-powered UV photodetector (UVPD) based on BAT NTs was assembled and the photoresponse characteristics were investigated under a wide range of UV light intensity. The BAT NTs UVPD exhibits satisfactory UV photodetection performance with detectivity of 1.55 × 1010 Jones and on/off ratio exceeding 103, associated with a fast response speed of 25 ms, which is ascribed to the efficient carrier transport inspired by the 1D structure and energy band structure. In addition, BAT NTs UVPD also features excellent environmental stability and long cycling stability. Benefitting from the desirable …

Infrared detection and imaging devices have great potential in the fields of defense and security, medical monitoring, and food safety. As a novel method, photothermal assistants can expand the absorption in the case of low-angle dependence, which is one of the key factors in improving the performance of infrared detectors. Photo-heating accelerates the transfer of carrier, inducing a change in electrical conductance and exciting “hot” electrons promote a photoelectric response and extend the response photon energies well below the semiconductor band edge. However, photodetectors require cooling to prevent overheating and reduce thermal noise, thereby improving photoelectric detection. Therefore, it remains a formidable challenge to design a suitable heterojunction photodetector that can synergistically utilize optical and thermal energy. Here, a unique asymmetric Te/Bi2Te3/In2O3 heterojunction structure …

Photodetectors with a broad-band response range are widely used in many fields and are regarded as pivotal components of the modern miniaturized electronics industry. However, commercial broad-band photodetectors composed of traditional bulk semiconductor materials are still limited by complex preparation techniques, high costs, and a lack of mechanical strength and flexibility, which are difficult to satisfy the increasing demand for flexible and wearable optoelectronics. Therefore, researchers have been devoted to finding new strategies to obtain flexible, stable, and high-performance broad-band photodetectors. In this work, a novel self-assembled BiGaSeAs composite superlattice-structured nanowire was developed with a simple chemical vapor deposition method for easy fabrication. After the device assembling, the photodetector showed outstanding performance in terms of obvious Ion/Ioff (13.9), broad …

Room temperature self-powered broadband (RTSPBD) response photodetectors have received considerable attention and are also very helpful in alleviating today's energy and environmental crisis. Herein, bismuth telluride (Bi2Te3) nanosheets were successfully synthesized and assembled into an RTSPBD photodetector. The Bi2Te3 photodetector exhibits excellent response characteristics: wide spectral range, maximum responsivity (10.254 mA/W, 435 nm), photocurrent density (106 μA/cm2), Ion/Ioff (71, 365 nm, 25 mW/cm2), rise/decay time (τrise = 0.0475 s and τdecay = 0.0468 s) and cycling stability. A superior responsivity from the ultraviolet to infrared (UV-IR) region is observed, which is attributed to the fact that the narrow bandgap topological insulating state of Bi2Te3 provides a fast charge transport channel for electrons generated by the photovoltaic effect. In addition, it was found that these …

Second harmonic generation (SHG) in van der Waals (vdWs) materials has garnered significant attention due to its potential for integrated nonlinear optical and optoelectronic applications. Stacking faults in vdWs materials, a typical kind of planar defect, can introduce a new degree of freedom to modulate the crystal symmetry and resultant SHG response, however, the physical origin and tunability of stacking-fault-governed SHG in vdWs materials remain unclear. Here, taking the intrinsically centrosymmetric vdWs RhI3 as an example, we theoretically reveal the origin of stacking-fault-governed SHG response, where the SHG response comes from the energetically favorable AC- Cstacking fault of which the electrical transitions along the high symmetry paths Gamma-M and Gamma-K in the Brillion zone play the dominant role at 810 nm. Such stacking-fault-governed SHG response is further confirmed via structural characterizations and SHG measurements. Furthermore, by applying hydrostatic pressure on RhI3, the correlation between structural evolution and SHG response is revealed with SHG enhancement up to 6.9 times, where the decreased electronic transition energies and huger momentum matrix elements due to the stronger interlayer interactions upon compression magnify the SHG susceptibility. This study develops a promising foundation based on strategically designed stacking faults for pioneering new avenues in nonlinear nano-optics.

The development trend of modern electronics and optoelectronics is constantly moving towards highly integrated, comprehensive, and miniaturized devices. Vertical configuration provides an easy means to achieve higher integration density than traditional planar configuration, and possess higher carrier generation capabilities and transfer speed, which can further enhance the performance of optoelectronic devices. This technology holds tremendous potential for designing the next generation of electronic/optoelectronic devices. In this work, we developed a vertical heterojunction photodetector, which combines narrow-bandgap 2D topological insulator Bi 2 Se 3, ultra-wide-bandgap amorphous Ga 2 O 3, and high-performance p-Si substrate, achieving broad-spectrum detection from 254 to 1000 nm and significantly shortened response time due to the advantage of carrier vertical transmission. The response time …

Integrating anisotropy and nonlinearity of physical properties in 2D materials is of great importance to the progress of nanoelectronic, nanophotonic, and nano‐optoelectronic applications. In this work, Nb3SeI7, a newly discovered ternary layered material with non‐centrosymmetric lattices, is introduced, which exhibits strong second harmonic generation (SHG), in‐plane anisotropic electricity, and light absorption. Symmetry breaking of 2D Nb3SeI7 induced by the polar off‐center displacement of niobium leads to a high nonlinear optical response with a second‐order susceptibility of 6.71 pm V−1 and a high anisotropic factor of photoresponsivity up to 4.6, which are higher than most of the 2D materials. These properties of 2D Nb3SeI7 create new possibilities for chip‐integrated nonlinear optics devices and future‐proof polarization‐sensitive optoelectronic systems.

Low-frequency shear and breathing modes are important Raman signatures of two-dimensional (2D) materials, providing information on the number of layers and insights into interlayer interactions. We elucidate the nature of low-frequency modes in a 2D polar metal–2D Ga covalently bonded to a SiC substrate, using a first-principles Green’s function-based approach. The low-frequency Raman modes are dominated by surface resonance modes, consisting primarily of out-of-phase shear modes in Ga, coupled to SiC phonons. Breathing modes are strongly coupled to the substrate and do not give rise to peaks in the phonon spectra. The highest-frequency shear mode blue-shifts significantly with increasing thickness, reflecting both an increase in the number of Ga layers and an increase in the effective interlayer force constant. The surface resonance modes evolve into localized 2D Ga modes as the phonon …

A novel technique for achieving 2D metal layers-Confinement Heteroepitaxy (CHet)[1]-has recently been extended to metallic alloys [2]. We report here the structural energetics, electronic properties, and structural trends in CHet-based Indium/Gallium alloys, identifying trends that may generalize to other 2D metallic alloys that also form continuously tunable alloys. In particular, a rapid reduction in the superconducting transition temperature with increasing indium fraction appears to correlate to the depletion of carrier pockets that participate strongly in the superconductivity of pure 2D Gallium.

2D polar metals synthesized by confinement heteroepitaxy at the SiC/graphene interface are covalently bound to the SiC substrate. In this work, we elucidate the importance of the SiC substrate, and specifically the Ga/Si interface, on the low-frequency resonant Raman spectra of 2D Ga on SiC. The low-frequency Raman modes are dominated by in-plane shear modes in 2D Ga. We show that the frequency of these shear modes is modified by the presence of the substrate for few-layer Ga and that these shear modes couple strongly to the electronic states corresponding to the interface Ga and Si atoms. Consequently, resonant Raman enhancement occurs at laser incident energies that are resonant with the interband optical transitions involving these interface Ga and Si states. This resonant Raman enhancement is observed in laser-energy-dependent measurements, an experimental signature of the strong …

Chemically stable quantum‐confined 2D metals are of interest in next‐generation nanoscale quantum devices. Bottom‐up design and synthesis of such metals could enable the creation of materials with tailored, on‐demand, electronic and optical properties for applications that utilize tunable plasmonic coupling, optical nonlinearity, epsilon‐near‐zero behavior, or wavelength‐specific light trapping. In this work, it is demonstrated that the electronic, superconducting, and optical properties of air‐stable 2D metals can be controllably tuned by the formation of alloys. Environmentally robust large‐area 2D‐InxGa1−x alloys are synthesized byConfinement Heteroepitaxy (CHet). Near‐complete solid solubility is achieved with no evidence of phase segregation, and the composition is tunable over the full range of x by changing the relative elemental composition of the precursor. The optical and electronic properties directly …

The electron dynamics of atomically thin 2-D polar metal heterostructures, which consisted of a few crystalline metal atomic layers intercalated between hexagonal silicon carbide and graphene grown from the silicon carbide, were studied using nearly degenerate transient absorption spectroscopy. Optical pumping created charge carriers in both the 2-D metals and graphene components. Wavelength-dependent probing suggests that graphene-to-metal carrier transfer occurred on a sub-picosecond time scale. Following rapid (<300 fs) carrier–carrier scattering, charge carriers monitored through the metal interband transition relaxed through several consecutive cooling mechanisms that included sub-picosecond carrier–phonon scattering and dissipation to the silicon carbide substrate over tens of picoseconds. By studying 2-D In, 2-D Ga, and a Ga/In alloy, we resolved accelerated electron–phonon scattering rates …

This work is a systematic experimental and theoretical study of the in‐plane dielectric functions of 2D gallium and indium films consisting of two or three atomic metal layers confined between silicon carbide and graphene with a corresponding bonding gradient from covalent to metallic to van der Waals type. k‐space resolved free electron and bound electron contributions to the optical response are identified, with the latter pointing towards the existence of thickness dependent quantum confinement phenomena. The resonance energies in the dielectric functions and the observed epsilon near‐zero behavior in the near infrared to visible spectral range, are dependent on the number of atomic metal layers and properties of the metal involved. A model‐based spectroscopic ellipsometry approach is used to estimate the number of atomic metal layers, providing a convenient route over expensive invasive …