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- 2018
- computer statistical experiment
- statistical optimization
- resonant-tunneling diode
- negative voltage current differential resistance
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- Electronic Science and Technology
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- Bauman Moscow State Technical University
- V.N. Karazin Kharkiv National University
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Light from van der Waals quantum tunneling devices
摘要： The understanding of and control over light emission from quantum tunneling has challenged researchers for more than four decades due to the intricate interplay of electrical and optical properties in atomic scale volumes. Here we introduce a device architecture that allows for the disentanglement of electronic and photonic pathways—van der Waals quantum tunneling devices. The electronic properties are defined by a stack of two-dimensional atomic crystals whereas the optical properties are controlled via an external photonic architecture. In van der Waals heterostructures made of gold, hexagonal boron nitride and graphene we find that inelastic tunneling results in the emission of photons and surface plasmon polaritons. By coupling these heterostructures to optical nanocube antennas we achieve resonant enhancement of the photon emission rate in narrow frequency bands by four orders of magnitude. Our results lead the way towards a new generation of nanophotonic devices that are driven by quantum tunneling.
关键词： van der Waals heterostructures,inelastic electron tunneling,nanophotonics,light emission,quantum tunneling,optical antennas
更新于2025-09-19 17:15:36
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Atomic-Scale Characterization of Graphene p–n Junctions for Electron-Optical Applications
摘要： Graphene p-n junctions offer a potentially powerful approach towards controlling electron trajectories via collimation and focusing in ballistic solid-state devices. The ability of p-n junctions to control electron trajectories depends crucially on the doping profile and roughness of the junction. Here, we use four-probe scanning tunneling microscopy and spectroscopy (STM/STS) to characterize two state-of-the-art graphene p-n junction geometries at the atomic scale, one with CMOS polySi gates and another with naturally cleaved graphite gates. Using spectroscopic imaging, we characterize the local doping profile across and along the p-n junctions. We find that realistic junctions exhibit non-ideality both in their geometry as well as in the doping profile across the junction. We show that the geometry of the junction can be improved by using the cleaved edge of van der Waals metals such as graphite to define the junction. We quantify the geometric roughness and doping profiles of junctions experimentally and use these parameters in Nonequilibrium Green’s Function based simulations of focusing and collimation in these realistic junctions. We find that for realizing Veselago focusing, it is crucial to minimize lateral interface roughness which only natural graphite gates achieve, and to reduce junction width, in which both devices under investigation underperform. We also find that carrier collimation is currently limited by the non-linearity of the doping profile across the junction. Our work provides benchmarks of the current graphene p-n junction quality and provides guidance for future improvements.
关键词： graphene p-n junctions,collimation,Veselago lensing,scanning tunneling microscopy,solid state electron optics
更新于2025-09-19 17:15:36
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Influence of the support on stabilizing local defects in strained monolayer oxide films
摘要： Two-dimensional materials with a honeycomb lattice, such as graphene and hexagonal boron nitride, often contain local defects in which the hexagonal elements are replaced by four, five, seven, and eight-membered rings. An example is the Stone-Wales (S-W) defect, where a bond rotation causes four hexagons to be transformed into a cluster of two pentagons and two heptagons. A further series of similar defects incorporating divacancies results in larger structures of non-hexagonal elements. In this paper, we use scanning tunneling microscopy (STM) and density functional theory (DFT) modeling to investigate the structure and energetics of S-W and divacancy defects in a honeycomb (2 × 2) Ti2O3 monolayer grown on an Au(111) substrate. The epitaxial rumpled Ti2O3 monolayer is pseudomorphic and in a state of elastic compression. As a consequence, divacancy defects, which induce tension in freestanding films, relieve the compression in the epitaxial Ti2O3 monolayer and therefore have significantly lower energies when compared with their freestanding counterparts. We find that at the divacancy defect sites there is a local reduction of the charge transfer between the film and the substrate, the rumpling is reduced, and the film has an increased separation from the substrate. Our results demonstrate the capacity of the substrate to significantly influence the energetics, and hence favor vacancy-type defects, in compressively strained 2D materials. This approach could be applied more broadly, for example to tensile monolayers, where vacancy-type defects would be rare and interstitial-type defects might be favored.
关键词： elastic strain,local structural defects,monolayers,scanning tunneling microscopy (STM),density functional theory (DFT),two-dimensional materials,ultrathin oxide films
更新于2025-09-19 17:15:36
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Nanostructuring Confinement for Controllable Interfacial Charge Transfer
摘要： Carbon nanostructures supported semiconductors are common in photocatalytic and photoelectrochemical applications, as it is expected that the nanoconductors can improve the spatial separation and transport of photogenerated charge carriers. Transfer of charge carriers through the carbon-semiconductor interface is the key electronic process, which determines the role of charge separation channels, and is sensitively influenced by band structures of the semiconductor near the contacts. Usually, this electronic process suffers from excessive energy dissipation by thermionic emission, which will undesirably prevent the interfacial charge transfer and eventually aggravate the recombination of photogenerated charge carriers. Unfortunately, this critical issue has hardly been consciously considered. Here, ultrathin dopant-free tunneling interlayers coated on the surface of graphene and sandwiched between the carbon sheets and the semiconductor nanostructures are adopted as a model system to demonstrate energy saving for the interfacial charge transfer. The nanostructuring confinement of band bending within the ultrathin interlayers in contact with the graphene sheets effectively narrows the width of the potential barriers, which enables tunneling of a substantial number of photogenerated electrons to the co-catalysts without unduly consuming energy. Besides, the dopant-free tunneling interlayers simultaneously block the transferred electrons in the sandwiched graphene sheets from leakage.
关键词： nanostructuring confinement,thermionic emission,electron tunneling,charge transfer,charge transport
更新于2025-09-19 17:15:36
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AsP/InSe Van der Waals Tunneling Heterojunctions with Ultrahigh Reverse Rectification Ratio and High Photosensitivity
摘要： Van der Waals heterojunctions made of 2D materials offer competitive opportunities in designing and achieving multifunctional and high-performance electronic and optoelectronic devices. However, due to the significant reverse tunneling current in such thin p–n junctions, a low rectification ratio along with a large reverse current is often inevitable for the heterojunctions. Here, a vertically stacked van der Waals heterojunction (vdWH) tunneling device is reported consisting of black arsenic phosphorus (AsP) and indium selenide (InSe), which shows a record high reverse rectification ratio exceeding 107 along with an unusual ultralow forward current below picoampere and a high current on/off ratio over 108 simultaneously at room temperature under the proper band alignment design of both the Schottky junction and the heterojunction. Therefore, the vdWH tunneling device can function as an ultrasensitive photodetector with an ultrahigh light on/off ratio of 1 × 107, a comparable responsivity of around 1 A W?1, and a high detectivity over 1 × 1012 Jones in the visible wavelength range. Furthermore, the device exhibits a clear photovoltaic effect and shows a spectral detection capability up to 1550 nm. The work sheds light on developing future electronic and optoelectronic multifunctional devices based on the van der Waals integration of 2D materials with designed band alignment.
关键词： van der Waals heterojunctions,backward diodes,rectification,photodiodes,tunneling
更新于2025-09-19 17:15:36
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[IEEE 2018 IEEE SENSORS - New Delhi, India (2018.10.28-2018.10.31)] 2018 IEEE SENSORS - IETS in MIS Contacts: Towards a Quantum Biomimetic Electronic Nose
摘要： Inelastic electron tunneling spectroscopy (IETS) has been used to detect the vibrational modes of molecules and has been proposed as the mechanism of olfaction according to the so-called Vibration Theory. Motivated by the promise of an electronic nose that will be biomimetic - in the sense of the Vibration Theory - we demonstrate here IET spectroscopy of vibrational modes in metal-insulator-semiconductor (MIS) devices consisting of ultrathin HfO2 deposited on silicon by Atomic Layer Deposition (ALD). Low-noise IETS measurements at 10K are carried out using second harmonic detection by a standard lock-in procedure. Parallely, a filtering algorithm is applied to the measured I-V data to compute its second derivative. The IETS peaks in the filtered data and experimentally measured lock-in data are compared and are found to be in agreement with each other; as well as with other experimental vibrational energy data measured through IETS or other techniques.
关键词： smoothening algorithm,Inelastic Electron Tunneling Spectroscopy,Electronic nose
更新于2025-09-19 17:15:36
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Many-body States Description of Single-molecule Electroluminescence Driven by Scanning Tunneling Microscope
摘要： Electron transport and optical properties of a single molecule in contact with conductive materials have attracted considerable attention owing to their scientific importance and potential applications. With recent progresses of experimental techniques, especially by the virtue of scanning tunneling microscope (STM)-induced light emission, where the tunneling current of the STM is used as an atomic-scale source for induction of light emission from a single molecule, it becomes possible to investigate single-molecule properties at sub-nanometer spacial resolution. Despite extensive experimental studies, the microscopic mechanism of electronic excitation of a single molecule in STM-induced light emission is yet to be clarified. Here we present a formulation of single-molecule electroluminescence driven by electron transfer between a molecule and metal electrodes based on a many-body state representation of the molecule. The effects of intra-molecular Coulomb interaction on conductance and luminescence spectra are investigated using the nonequilibrium Hubbard Green's function technique combined with first-principles calculations. We compare simulation results with experimental data and find that the intra-molecular Coulomb interaction is crucial for reproducing recent experiments for a single phthalocyanine molecule. The developed theory provides a unified description of both electron-transport and optical properties of a single molecule in contact with metal electrodes driven out of equilibrium, and thereby it contributes to a microscopic understanding of optoelectronic conversion in single molecules on solid surfaces and in nanometer-scale junctions.
关键词： Single molecule luminescence,exciton formation,nonequilibrium Hubbard Green's function technique,time-dependent density functional theory (TDDFT),scanning tunneling microscope-induced light emission,Vibronic interaction
更新于2025-09-19 17:15:36
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RECENT ADVANCES IN ULTRAFAST TIME-RESOLVED SCANNING TUNNELING MICROSCOPY
摘要： Making smaller and faster functional devices has led to an increasing demand for a microscopic technique that allows the investigation of carrier and phonon dynamics with both high spatial and temporal resolutions. Traditional optical pump–probe methods can achieve femtosecond temporal resolution but fall short in the spatial resolution due to the diffraction limit. Scanning tunneling microscopy (STM), on the contrary, has realized atomic-scale spatial resolution relying on the high sensitivity of the tunneling current to the tip-sample distance. However, limited by the electronics bandwidth, STM can only push the temporal resolution to the microseconds scale, restricting its applications to probe various ultrafast dynamic processes. The combination of these two methods takes advantages of optical pump–probe techniques and highly localized tunneling currents of STM, providing one viable solution to track atomic-scale ultrafast dynamics in single molecules and low-dimensional materials. In this review, we will focus on several ultrafast time-resolved STM methods by coupling the tunneling junctions with pulsed electric waves, THz, near-infrared and visible laser. Their applications to probe the carrier dynamics, spin dynamics, and molecular motion will be highlighted. In the end, we will present an outlook on the challenges and new opportunities in this field.
关键词： terahertz technique,femtosecond laser,Scanning tunneling microscopy,pump-probe technique,ultrafast dynamics.
更新于2025-09-19 17:15:36
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Van der Waals broken-gap p-n heterojunction tunnel diode based on black phosphorus and rhenium disulfide
摘要： The broken-gap type-III van der Waals (vdW) heterojunction is of particular interest as there is no overlap between the energy bands of its two stacked materials. Despite several studies on straddling-gap (type-I) and staggered-gap (type-II) vdW heterojunctions, a comprehensive understanding of the current-transport and optoelectronic effects in a type-III broken-gap heterojunction remains elusive. Here, we report gate-tunable current rectifying characteristics in a black phosphorus (BP)/rhenium disulfide (ReS2) broken-gap p-n heterojunction diode. Current-transport in this heterojunction was modeled by using the Simmons approximation through direct tunneling and Fowler?Nordheim tunneling in low- and higher-bias regimes, respectively. We showed that a p-n diode based on a type-III heterojunction is mainly governed by tunneling-mediated transport, but that transport in a type-I p-n heterojunction is dominated by majority carrier diffusion in the higher-bias regime. Upon illumination with a 532-nm-wavelength laser, the BP/ReS2 broken-gap p-n heterojunction showed a photo responsivity of 8 mA/W at a laser power as high as 100 μW and photovoltaic energy conversion with an external peak quantum efficiency of 0.3%. Finally, we demonstrated a binary inverter consisting of BP p-channel and ReS2 n-channel thin film transistors for logic applications.
关键词： Rhenium disulfide,photovoltaics,quantum tunneling,broken-gap heterojunction,logic circuitry,Black phosphorous
更新于2025-09-19 17:15:36
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Nonlayered tellurene as an elemental 2D topological Insulator: experimental evidence from scanning tunneling spectroscopy
摘要： We report formation of nonlayered tellurene monolayer in its alpha-phase through an anisotropic ultrasonication method. The nonlayered tellurene has so far been predicted to exhibit a topologically insulating state of matter in two-dimensional (2D) form with an insulating interior and metallic edge-states propagating along the perimeter of the 2D objects. In this work, we report a direct evidence of elemental topological insulator behavior in the material through a localized mode of measurement, that is, scanning tunneling spectroscopic studies. We moreover deliberate on the length-scale the time-reversal symmetry-protected edge-states extend towards the interior. The metallic edge, which has been found to span over a 3 nm region, opens and widens monotonically into gapped states. The appearance of elemental 2D topological insulator phase has been explained in terms of built-in strains in the systems as viewed through a shift in Raman modes.
关键词： Scanning Tunneling Spectroscopy,Elemental 2D Topological Insulator,Nonlayered Tellurene
更新于2025-09-19 17:15:36