New Polymorphs of 2D Indium Selenide with Enhanced Electronic Properties

The 2D semiconductor indium selenide (InSe) has attracted significant interest due its unique electronic band structure, high electron mobility, and wide tunability of its band gap energy achieved by varying the layer thickness. All these features make 2D InSe a potential candidate for advanced electronic and optoelectronic applications. Here, the discovery of new polymorphs of InSe with enhanced electronic properties is reported. Using a global structure search that combines artificial swarm intelligence with first‐principles energetic calculations, polymorphs that consist of a centrosymmetric monolayer belonging to the point group D_3d are identified, distinct from well‐known polymorphs based on the D_3h monolayers that lack inversion symmetry. The new polymorphs are thermodynamically and kinetically stable, and exhibit a wider optical spectral response and larger electron mobilities compared to the known polymorphs. Opportunities to synthesize these newly discovered polymorphs and viable routes to identify them by X‐ray diffraction, Raman spectroscopy, and second harmonic generation experiments are discussed.     

Mg预处理蓝宝石衬底法制备的Zn极性ZnO外延薄膜的结构研究

通过分子束外延法在经Mg预处理的蓝宝石衬底上制备了ZnO单晶薄膜,利用高分辨透射电镜、电子全息和X射线能谱对该薄膜的结构进行了细致的研究.结果表明,在蓝宝石衬底上预沉积一层很薄的Mg层,可以生长均匀Zn极性的ZnO外延薄膜.ZnO/MgO/蓝宝石的界面非常清晰锐利,同时在界面处可以观察到大约3个原子层的MgO.预沉积的Mg薄层对随后ZnO的极性选择起了关键性作用.     

A Novel InSe-FET Biosensor based on Carrier-Scattering Regulation Derived from the DNA Probe Assembly-Determined Electrostatic Potential Distribution

Low-dimensional material field-effect transistor (FET)-based biosensors have the advantages of high sensitivity, high detection speed, small size, low cost, and excellent compatibility with integrated circuits. The sensing mechanism is extremely important in the design and fabrication of high-performance FET biosensors in practical applications. Herein, an InSe-FET biosensor is designed and its dominant sensing mechanism during detection and (mi)RNA detection performance are investigated. Finite element analysis reveals the electrostatic potential distribution in the InSe channel with DNA probe assembly showing that Coulomb scattering is the dominant sensing mechanism for carrier scattering-sensitive InSe. The simulation and experimental results indicate that carriers in InSe are extremely sensitive to the scattering of surface impurities because of their small electron mass. The firstly reported back-gate bias working mode of an InSe-FET biosensor has a linear relationship with an extra-large detectable range of 1 fM–10 nM, high specificity for identifying 1-nucleotide polymorphisms, and excellent repeatability and reusability. The detection of biomarker miRNAs in clinical serum samples and specific RNA in SARS-CoV-2 pseudovirus samples indicate promising applications of InSe-FET biosensors in critical disease screening and the fast diagnoses of infectious diseases. This study can be useful for the design and fabrication of high-performance FET biosensors.     

Temperature Dependence of Epitaxial Graphene Formation on SiC(0001)

The formation of epitaxial graphene on SiC(0001) surfaces is studied using atomic force microscopy, Auger electron spectroscopy, electron diffraction, Raman spectroscopy, and electrical measurements. Starting from hydrogen-annealed surfaces, graphene formation by vacuum annealing is observed to begin at about 1150°C, with the overall step-terrace arrangement of the surface being preserved but with significant roughness (pit formation) on the terraces. At higher temperatures near 1250°C, the step morphology changes, with the terraces becoming more compact. At 1350°C and above, the surface morphology changes into relatively large flat terraces separated by step bunches. Features believed to arise from grain boundaries in the graphene are resolved on the terraces, as are fainter features attributed to atoms at the buried graphene/SiC interface.     

Low‐Voltage Operational,Low‐Power Consuming,and High Sensitive Tactile Switch Based on 2D Layered InSe Tribotronics

Electronics based on layered indium selenide (InSe) channels exhibit promising carrier mobility and switching characteristics. Here, an InSe tribotronic transistor (denoted as w/In InSe T‐FET) obtained through the vertical combination of an In‐doped InSe transistor and triboelectric nanogenerator is demonstrated. The w/In InSe T‐FET can be operated by adjusting the distance between two triboelectrification layers, which generates a negative electrostatic potential that serves as a gate voltage to tune the charge carrier transport behavior of the InSe channel. Benefiting from the surface charging doping of the In layer, the w/In InSe T‐FET exhibits high reliability and sensitivity with a large on/off current modulation of 10⁶ under a low drain–source voltage of 0.1 V and external frictional force. To demonstrate its function as a power‐saving tactile sensor, the w/In InSe T‐FET is used to sense “INSE” in Morse code and power on a light‐emitting diode. This work reveals the promise of 2D material–based tribotronics for use in nanosensors with low power consumption as well as in intelligent systems.     

Hg1—xCdxTe表面电子的子能带结构

讨论了Hg_(1-x)Cd_xTe MIS结构N型反型层电子子能带结构的理论和实验研究结果。描述了采用电容-电压谱,回旋共振谱和磁导振荡谱定量地研究电子子能带结构的模型和方法。推导得到的子能带色散关系,朗道能级和有效g~*因子,与测得的子能带电子的回旋共振和自旋共振结果符合得很好,从而可以定量地研究由于表面电子的自旋轨道相互作用引起的零场分裂效应,朗道能级的移动、交叉,波函数的混合效应以及电致自旋分裂的色散关系。     

N型4H-SiC ECR氢等离子体处理研究

采用电子回旋共振(ECR)氢等离子体对n型4H-SiC(0001)表面进行处理,并利用原位高能电子衍射(RHEED)对处理过程进行实时监控。在200°C～700°C温度范围内获得的RHEED图像成条纹状且对比清晰,表明SiC表面原子排列规则,单晶取向性好,计算表明表面未发生重构。用X射线光电子能谱(XPS)技术对表面成分进行分析,结果显示,表面C/C-H污染物被去除、氧含量降低。     

Anomalous Low Thermal Conductivity of Atomically Thin InSe Probed by Scanning Thermal Microscopy

The ability of a material to conduct heat influences many physical phenomena, ranging from thermal management in nanoscale devices to thermoelectrics. Van der Waals 2D materials offer a versatile platform to tailor heat transfer due to their high surface-to-volume ratio and mechanical flexibility. Here, the nanoscale thermal properties of 2D indium selenide (InSe) are studied by scanning thermal microscopy. The high electrical conductivity, broad-band optical absorption, and mechanical flexibility of 2D InSe are accompanied by an anomalous low thermal conductivity (κ). This can be smaller than that of low-κ dielectrics, such as silicon oxide, and it decreases with reducing the lateral size and/or thickness of InSe. The thermal response is probed in free-standing InSe layers as well as layers supported by a substrate, revealing the role of interfacial thermal resistance, phonon scattering, and strain. These thermal properties are critical for future emerging technologies, such as field-effect transistors that require efficient heat dissipation or thermoelectric energy conversion with low-κ, high electron mobility 2D materials, such as InSe.     

Photovoltaic effect in a-Si:H/n-InSe heterostructures

Heterostructures in an a-Si:H/InSe system were grown by the deposition of a-Si:H films onto the surface (001) of InSe single-crystal wafers and also by deposition of pure indium films with their subsequent selenization, in which case InSe films were synthesized at the a-Si:H surface. The photovoltaic effect was observed and studied for both types of heterostructures. It was concluded that the heterostructures obtained may be used as wide-band photoconverters of radiation.     

InSe Schottky Diodes Based on Van Der Waals Contacts

2D semiconductors are excellent candidates for next‐generation electronics and optoelectronics thanks to their electrical properties and strong light‐matter interaction. To fabricate devices with optimal electrical properties, it is crucial to have both high‐quality semiconducting crystals and ideal contacts at metal‐semiconductor interfaces. Thanks to the mechanical exfoliation of van der Waals crystals, atomically thin high‐quality single‐crystals can easily be obtained in a laboratory. However, conventional metal deposition techniques can introduce chemical disorder and metal‐induced mid‐gap states that induce Fermi level pinning and can degrade the metal‐semiconductor interfaces, resulting in poorly performing devices. In this article, the electrical contact characteristics of Au–InSe and graphite–InSe van der Waals contacts, obtained by stacking mechanically exfoliated InSe flakes onto pre‐patterned Au or graphite electrodes without the need for lithography or metal deposition is explored. The high quality of the metal‐semiconductor interfaces obtained by van der Waals contact allows to fabricate high‐quality Schottky diodes based on the Au–InSe Schottky barrier. The experimental observation indicates that the contact barrier at the graphite–InSe interface is negligible due to the similar electron affinity of InSe and graphite, while the Au–InSe interfaces are dominated by a large Schottky barrier.     

High-Performance Near-Infrared Photodetectors Based on Surface-Doped InSe

2D InSe is one of the semimetal chalcogenides that has been recently given attention thanks to its excellent electrical properties, such as high mobility near 1000 cm² V⁻¹ s⁻¹ and moderate band gap of ≈1.26 eV suitable for IR detection. Here, high-performance visible to near-infrared (470–980 nm wavelength (λ)) photodetectors using surface-doped InSe as a channel and few-layer graphenes (FLG) as electrodes are reported, where the InSe top region is relatively p-doped using AuCl₃. The surface-doped InSe photodetectors show outstanding performance, achieving a photoresponsivity (R) of ≈19 300 A W⁻¹ and a detectivity (D*) of ≈3 × 10¹³ Jones at λ = 470 nm, and R of ≈7870 A W⁻¹ and D* of ≈1.5 × 10¹³ Jones at λ = 980 nm, superior to previously reported 2D material-based IR photodetectors operating without an applied gate bias. Surface doping using AuCl₃ renders a band bending at the junction between the InSe surface and the top FLG contact, which facilitates electron-hole pair separation and immediate photodetection. Multiple doped or undoped InSe photodetectors with different device structures are investigated, providing insight into the photodetection mechanism and optimizing performance. Encapsulation with hexagonal boron nitride dielectric also allows for 3-month stability.     

Surface charge spectroscopy—A novel surface science technique for measuring surface state distributions on semiconductors

A novel technique, surface charge spectroscopy (SCS), has been developed for measuring interface state density at a dielectric-semiconductor interface in conjunction with x-ray photoelectron spectroscopy (XPS). In this technique, a thin dielectric layer with thickness up to 15 nm, is deposited on a semiconductor substrate. The surface Fermi level (E_Fs) of the semiconductor and the surface potential of the dielectric are measured using XPS, the latter of which can be varied by charging the dielectric with electrons from a low energy electron flood gun commonly equipped inside an XPS system. The interface state distribution in the band gap of the sample is then extracted from the relationship between the E_Fs and the dielectric surface potential with a simple space-charage calculation similar to the conventional capacitance-voltage technique. Experimental data on SiO₂/Si and SiN_x/InP samples are shown in the article to illustrate the applicability of SCS.     

Realization of Quantum Hall Effect in Chemically Synthesized InSe

Recently, 2D electron gases have been observed in atomically thin semiconducting crystals, enabling the observation of rich physical phenomena at the quantum level within the ultimate thickness limit. However, the observation of 2D electron gases and subsequent quantum Hall effect require exceptionally high crystalline quality, rendering mechanical exfoliation as the only method to produce high‐quality 2D semiconductors of black phosphorus and indium selenide (InSe), which hinder large‐scale device applications. Here, the controlled one‐step synthesis of high‐quality 2D InSe thin films via chemical vapor transport method is reported. The carrier Hall mobility of hexagonal boron nitride (hBN) encapsulated InSe flakes can be up to 5000 cm² V^?1 s^?1 at 1.5 K, enabling to observe the quantum Hall effect in a synthesized van der Waals semiconductor. The existence of the quantum Hall effect in directly synthesized 2D semiconductors indicates a high quality of the chemically synthesized 2D semiconductors, which hold promise in quantum devices and applications with high mobility.     

Synthesis and photoluminescence properties of Mn-doped ZnS nanobelts

Mn-doped ZnS nanobelts have been prepared through a thermal evaporation method at 1100℃. The synthesized nanobelts are characterized with X-ray diffraction （XRD）, scanning electron microscopy （SEM）, selected area electron diffraction （SAED）, high-resolution transmission electron microscopy （HRTEM）, and photoluminescence （PL） spectroscopy. The results show that the nanobelts have an uniform single-crystal hexagonal wurtzite structure and grow along [0001 ] direction. Room-temperature photoluminescence reveals that the intrinsic PL of the nanobelts disappears and a new PL peak of the Mn-doped ZnS nanobelts emerges at 575 nm.     

Wurtzite CdS on CdTe grown by molecular beam epitaxy

Growth of single crystal wurtzite cadmium sulfide on CdTe(111)B substrates has been achieved using molecular beam epitaxy. Reflection high-energy electron diffraction (RHEED) indicates smooth surface morphology for several hundreds of nanometers after nucleation. X-ray diffraction measurements confirm the crystalline orientation to be [0001] in the growth direction. X-ray photoelectron spectroscopy (XPS) indicates mostly stoichiometric CdS layers and the existence of a reaction at the interface. Sulfur incorporation into CdTe for various S fluxes has been investigated by Auger electron spectroscopy (AES). High-resolution TEM images of the interface between such epilayers were recorded. During the growth In was used as an in-situ dopant. The concentration and uniformity of In was determined by secondary ion mass spectrometry. Indium profiles were obtained for concentrations ranging from 5 × 10¹⁷ to 1.4 × 10²¹ cm⁻³. The experimental concentration agrees well with the variation expected from the In flux.     

用脉冲激光沉积方法制备的ZnO薄膜的结构及光致发光特性

在从室温到800℃的温度范围内,用脉冲激光沉积方法在Al₂O₃（0001）衬底上制备了ZnO薄膜。采用X射线衍射仪、原子力显微镜以及荧光光谱仪分别研究了衬底温度对ZnO薄膜表面形貌、结晶质量和光致发光特性的影响。X射线衍射仪和原子力显微镜的结果表明,当衬底温度从室温升高到400℃时,ZnO薄膜的结构及结晶质量逐渐提高,而当衬底温度超过400℃时,其结构和结晶质量变差;在400℃下生长的ZnO薄膜具有最佳的表面形貌和结晶质量。室温光致发光的测量结果表明,400℃下生长的ZnO薄膜的紫外发光强度最强,且发光波长最短（386 nm）。     

Experimental studies of metal/InP interfaces formed at room temperature and 77K

Metal/InP interfaces were formed at room temperature (RT = 300K) and low temperature (LT = 77K). A high leakage current was observed for the RT processed metal/InP samples due to its low barrier height (0.35–0.55 eV). An extremely low leakage current and high barrier height (up to 0.96 eV) were achieved when Au and Pd Schottky contacts to n-InP were produced at low temperature. Photoluminescence spectroscopy, Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), and secondary ion mass spectroscopy (SIMS) were used to study the metal/InP interfaces. Photoluminescence spectra showed that there was less surface state density in LT samples. The RT processed sample showed more O and C in the surface region of an Au/InP structure than the same sample processed at LT in the AES spectra. The phosphide out-diffusion was observed in RT processed samples by ESCA. A possible P:O layer on the metal side of the LT processed sample was found by SIMS. Extensive chemical and structural analysis indicated that LT process caused the metal film to be continuous at 50 Å, much better than in standard RT processing.     

Zinc Oxide Nanorods Grown by Arc Discharge

The arc discharge method was employed to fabricate zinc oxide (ZnO) nanorods with wurtzite structure. The microstructure analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that the ZnO nanorods grew along the [0001] direction. On average, the diameter and length of the nanorods were about 40 nm (some are as thin as 5 nm) and several hundred nanometers, respectively. The photoluminescence (PL) of the nanorods showed an ultraviolet band, a violet band, and a green band. The PL mechanism was discussed with the growth process and Raman spectroscopy.     

Electron energy-loss spectroscopy study of ZnO nanobelts

Nanobelts of ZnO have well-defined shapes that are enclosed by {0001}, {0110} and {2110} facets. The nanobelts grow along [0110] and [2110] with large flat surfaces of +/-(0001) and +/-(0110), respectively. Electron energy-loss spectroscopy has been applied to study the electronic structure of ZnO nanobelts of different growth orientations. A plasmon peak observed at 13 eV is suggested to be the result of polar surface excitation. The energy-loss near-edge structure of the oxygen K and zinc L3 edges acquired from the two types of nanobelts show clear orientation dependence, and they agree well to the calculated results.     

Surface and interface properties of PdCr/SiC Schottky diode gas sensor annealed at 425°C

The surface and interface properties of Pd_0.9Cr_0.1/SiC Schottky diode gas sensors both before and after annealing are investigated using Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). At room temperature the alloy reacted with SiC and formed Pd_xSi only in a very narrow interfacial region. After annealing for 250 h at 425°C, the surface of the Schottky contact area has much less silicon and carbon contamination than that found on the surface of an annealed Pd/SiC structure. Palladium silicides (Pd_xSi) formed at a broadened interface after annealing, but a significant layer of alloy film is still free of silicon and carbon. The chromium concentration with respect to palladium is quite uniform down to the deep interface region. A stable catalytic surface and a clean layer of Pd_0.9Cr_0.1 film are likely responsible for significantly improved device sensitivity.