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- 2018
- computer statistical experiment
- statistical optimization
- resonant-tunneling diode
- negative voltage current differential resistance
- characteristics
- heterojunction
- quantum well
- resonant tunneling border
- Electronic Science and Technology
- Optoelectronic Information Science and Engineering
- Bauman Moscow State Technical University
- V.N. Karazin Kharkiv National University
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Unusual Electronic States and Superconducting Proximity Effect of Bi Films Modulated by NbSe2 Substrate
摘要： Heterostructures of two-dimensional layered materials can be functionalized with exotic phenomena that are unpresented with each constituting component. The interface effect plays a key role in determining the electronic properties of the heterostructure, whose characterization requires a correlation with the morphology with atomic-scale precision. Here, we report an investigation on the electronic properties of few-layer Bi(110) films mediated by NbSe2 substrate. By utilizing scanning tunneling microscopy and spectroscopy, we show a significant variation of the density of states at different Bi film thicknesses, resulting in an unusual superconducting proximity effect that deviates from the conventional monotonous decay behavior. Moreover, the electronic states of the Bi films are also prominently modulated by the Moiré pattern spatially. With first-principles calculations, we illuminate these findings as the results of covalent-like quasi-bonds formed at the Bi/NbSe2 interface, which profoundly alter the charge distributions in the Bi films. Our study indicates a viable way of modulating the electronic properties of ultrathin films by quasi-covalent interfacial couplings beyond conventional van der Waals interactions.
关键词： few-layers bismuth(110),two-dimensional heterostructures,thickness dependence,scanning tunneling microscopy,density functional theory calculations,covalent-like quasi-bonds,proximity effect
更新于2025-09-23 15:22:29
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Investigation of CVD graphene as-grown on Cu foil using simultaneous scanning tunneling/atomic force microscopy
摘要： Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of graphene reveal either a triangular or honeycomb pattern at the atomic scale depending on the imaging parameters. The triangular patterns at the atomic scale are particularly difficult to interpret, as the maxima in the images could be every other carbon atom in the six-fold hexagonal array or even a hollow site. Carbon sites exhibit an inequivalent electronic structure in HOPG or multilayer graphene due to the presence of a carbon atom or a hollow site underneath. In this work, we report small-amplitude, simultaneous STM/AFM imaging using a metallic (tungsten) tip, of the graphene surface as-grown by chemical vapor deposition (CVD) on Cu foils. Truly simultaneous operation is possible only with the use of small oscillation amplitudes. Under a typical STM imaging regime the force interaction is found to be repulsive. Force–distance spectroscopy revealed a maximum attractive force of about 7 nN between the tip and carbon/hollow sites. We obtained different contrast between force and STM topography images for atomic features. A honeycomb pattern showing all six carbon atoms is revealed in AFM images. In one contrast type, simultaneously acquired STM topography revealed hollow sites to be brighter. In another, a triangular array with maxima located in between the two carbon atoms was acquired in STM topography.
关键词： scanning tunneling microscopy,CVD graphene,simultaneous operation,atomic force microscopy,small amplitude
更新于2025-09-23 15:22:29
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Analysis of current transport mechanisms in sol-gel grown Si/ZnO heterojunction diodes in high temperature environment
摘要： This paper analyzes the electrical parameters of Si/ZnO heterojunction diodes in the wide temperature range, i.e. from room temperature (298 K) to 573 K to study the electrical performance of the diode in very high temperature environment. In this work, sol-gel derived nanostructured ZnO thin film was deposited directly on p-Si substrate using spin coating technique. Electrical parameters, such as rectification ratio, reverse saturation current, ideality factor, barrier height, series resistance and activation energy are derived from current-voltage characteristics of the device, measured using semiconductor parameter analyzer in the temperature range of 298 K–573 K for bias voltage of ± 5 V. The ideality factor, barrier height and series resistance is derived as 2.66, 0.789 eV and 3554 Ω respectively at 298 K, whereas at 573 K these are modified as 1.58, 1.15 eV and 801 Ω respectively. The above-mentioned results indicate the presence of spatial barrier height inhomogeneities (BHI) in high temperature environment. Hence, we have included the Gaussian distribution of spatial BHI in our analysis to calculate the effective Richardson constant (RC). Before inclusion of spatial BHI, RC was 4.026 × 10^{-6} Acm^{-2}K^{-2}. However, after inclusion of spatial BHI, RC is modified to 29.14 Acm^{-2}K^{-2}, which is nearer to the theoretical value (32 Acm^{-2}K^{-2}). Therefore, this study indicates that our as-fabricated Si/ZnO heterojunction diodes can sustain their electrical behaviour in very high temperature environment also and they are suitable for high temperature electronic and optoelectronic application.
关键词： Current-voltage characteristics,Richardson constant,Trap-assisted tunneling,Spatial barrier inhomogeneities,Heterojunction diode,Semiconductor thin film
更新于2025-09-23 15:22:29
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Image charge effect on the light emission of rutile TiO <sub/>2</sub> (110) induced by a scanning tunneling microscope
摘要： The plasmon-enhanced light emission of rutile TiO2(110) surface has been investigated by a low-temperature scanning tunneling microscope (STM). We found that the photon emission arises from the inelastic electron tunneling between the STM tip and the conduction band or defect states of TiO2(110). In contrast to the Au(111) surface, the maximum photon energy as a function of the bias voltage clearly deviates from the linear scaling behavior, suggesting the non-negligible effect of the STM tip on the band structure of TiO2. By performing differential conductance (dI/dV) measurements, it was revealed that such a deviation is not related to the tip-induced band bending, but is attributed to the image charge effect of the metal tip, which significantly shifts the band edges of the TiO2(110) towards the Femi level (EF) during the tunneling process. This work not only sheds new lights onto the understanding of plasmon-enhanced light emission of semiconductor surfaces, but also opens up a new avenue for engineering the plasmon-mediated interfacial charge transfer in molecular and semiconducting materials.
关键词： TiO2,scanning tunneling microscopy,light emission,plasmon
更新于2025-09-23 15:22:29
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[IEEE 2018 2nd International Conference on Electronics, Materials Engineering & Nano-Technology (IEMENTech) - Kolkata (2018.5.4-2018.5.5)] 2018 2nd International Conference on Electronics, Materials Engineering & Nano-Technology (IEMENTech) - Effect of Self-Consistency Technique on Current Density Profile of Resonant Tunneling Diode
摘要： This paper reveals the importance of self-consistency technique for computing current density in resonant tunneling device. AlxGa1-xAs/GaAs/AlyGa1-yAs is considered for simulation purpose, and both Schr?dinger and Poisson's equations are simultaneously solved subject to appropriate boundary conditions to obtain current density as a function of externally applied bias. Structural parameters and material compositions within type-I range are varied to get the fluctuations in current, which is otherwise absent when calculation is performed without applying self-consistency technique. Findings are significant as magnitude of current obtained is higher than that obtained when self-consistency is absent. Result has immense importance for low bias application of RTD due to the presence of peaks at particular system compositions.
关键词： Peak current density,Resonant tunneling diode,Poisson's equation,Current density,Self-consistency technique,Schrodinger's equation
更新于2025-09-23 15:22:29
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Accurate Gap Determination in Monolayer and Bilayer Graphene/h-BN Moiré Superlattices
摘要： High mobility single and few-layer graphene sheets are in many ways attractive as nanoelectronic circuit hosts but lack energy gaps, which are essential to the operation of field-effect transistors. One of the methods used to create gaps in the spectrum of graphene systems is to form long period moiré patterns by aligning the graphene and hexagonal boron nitride (h-BN) substrate lattices. Here, we use planar tunneling devices with thin h-BN barriers to obtain direct and accurate tunneling spectroscopy measurements of the energy gaps in single- and bi-layer graphene-h-BN superlattice structures at charge neutrality (first Dirac point) and at integer moiré band occupancies (second Dirac point, SDP) as a function of external electric and magnetic fields and the interface twist angle. In single-layer graphene we find, in agreement with previous work, that gaps are formed at neutrality and at the hole-doped SDP, but not at the electron-doped SDP. Both primary and secondary gaps can be determined accurately by extrapolating Landau fan patterns to zero magnetic field and are as large as ≈ 17 meV for devices in near perfect alignment. For bilayer graphene, we find that gaps occur only at charge neutrality where they can be modified by an external electric field.
关键词： graphene-h-BN moiré superlattice,Landau level tunneling spectroscopy,bilayer graphene-h-BN superstructure,high-precision measurement,graphene energy gap
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Evidence for single-electron tunneling in electron energy spectra of diamond tip field emitter
摘要： Field emission from microscale diamond tips was studied using electron energy spectroscopy. A processing at high emission currents was applied to modify the atomic surface structure of pristine diamond tips. Subsequently, staircase-like current-voltage characteristics were obtained which are typical for the single-electron tunneling occurring due to the Coulomb blockade effect in emitting carbon nanostructures formed on the surface of the diamond tips. Characteristic electron energy spectra consisted of several peaks, each corresponding to a certain charging state of the emitting nanostructure. The measured spectra were used to determine the parameters of the Coulomb blockade (e.g. charging energy) and reveal peculiar features of single-electron effects in field emission systems.
关键词： electron energy spectroscopy,Coulomb blockade,single-electron tunneling,field emission
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Thermo-enhanced field electron emission by bandto-ban tunneling from p-Si/ZnO nano-emitters
摘要： We fabricated full array of uniform individual p-Si/ZnO nano-emitters and demonstrated the strong thermo-enhanced field emission. The emission current density showed about ten-time enhancement (from 1.31 to 12.11 mA/cm2 at 60.6 MV/m) by increasing the temperature from 323 K to 623 K. The strong thermo-enhancement was proposed to be benefit from the increase of band-to-band tunneling probability at the surface portion of the p-Si/ZnO nano-junction. This work provides promising cathode for portable x-ray tubes/panel, ionization vacuum gauges and low energy electron beam lithography, in where electron-dose control at a fixed energy is needed.
关键词： p-Si/ZnO heterojunction,band-to-band tunneling,solution-phase growth,thermo-enhanced field emission,nano-template
更新于2025-09-23 15:21:21
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Monte Carlo Modeling of the Diodes with Lateral Resonant Tunneling Border
摘要： Diodes with resonant tunneling border (RTB) are studied as possible high speed and wide-band devices. The diodes represent planar two-terminal n+-n-n+-GaAs-based structures containing lateral active border as a AlGaAs/GaAs double barrier resonant tunneling structure connected to anode contact. The 2-D model of electron transport in the device is proposed. The analysis of the diodes operation was performed using ensemble Monte Carlo technique. Transfer matrix approach for simulation of tunneling transfer is applied. The influence of parameters of the diode structure such as a position of RTB, a composition of AlGaAs barriers and a material doping on current – voltage characteristics of diode has been investigated. strong influence of contact size and geometry on the diode characteristic. The aim of the work is to construct an effective numerical 2D model used to consider electron transport at high frequencies with taking into account hot-carrier effects in cases where the mean free path is comparable to the device dimensions and electron tunneling processes are in place. The basis of the proposed model is ensemble Monte Carlo method [4]. The other model elements are chosen by obtaining accurate physical results per reasonable time.
关键词： negative voltage current differential resistance,characteristics,heterojunction,quantum well,resonant tunneling border
更新于2025-09-23 15:21:21
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Nanophotonic energy storage in upconversion nanoparticles
摘要： In nanophotonic energy storage, an energy conversion model is established for intrinsic nanophotonic energy storage (NPES) effects. Here we realize that the charge inhomogeneous distribution on the surface of upconversion nanoparticles (UCNPs) would persistently exist as well as the formation and migration of surface defects states despite of the compound component ratio, even following the stringent stoichiometric ratio. Our preliminary efforts on NPES effect has recognized from the recent published work [Nature 561, 88 (2018)], which the surface quantum confinement arose because of a recently found surface vacancy induced Coulomb states (SVIC) states. Further in-depth excavation on surface charge density distributions and defect orbitals of surface localized electronics and holes have affirmatively repeated the Guerra’s theory [Nature 554, 346 (2018)] and reflected the existence of surface defect states in both stoichiometric and non-stoichiometric compounds. Therefore, beyond the experimental trail-based multi-doping chemical modifications, we proposed the surface electronic process for efficient NPES effect can be modulated by an intrinsic level-matching induced surface resonant quantum tunneling (LM-SRQT) in this work. The UCNP size-effect can be confirmed that simply might be not an influencing factor of dominating NPES effect while the surface degree of non-crystallizations indeed matters.
关键词： level-matching induced surface resonant quantum tunneling (LM-SRQT),surface vacancy induced Coulomb states (SVIC) states,nano energy,nanophotonic energy storage (NPES),electron-transfer surface mechanism
更新于2025-09-23 15:21:21