Nanoscale Electronics Research Articles

Softening of the optical phonon by reduced interatomic bonding strength without depolarization.

Softening of the transverse optical (TO) phonon, which could trigger ferroelectric phase transition, can usually be achieved by enhancing the long-range Coulomb interaction over the short-range bonding force1, for example, by increasing the Born effective charges2. However, it suffers from depolarization effects3,4 as the induced ferroelectricity is suppressed on size reduction of the host materials towards high-density nanoscale electronics. Here, we present an alternative route to drive the TO phonon softening by showing that the abnormal soft TO phonon in rocksalt-structured ultrawide-bandgap BeO (ref. 5) is mainly induced by a substantial reduction in the short-range bonding interaction due to the Be-O bond stretching caused by an electron cloud-overlap-induced Coulomb repulsion between two adjacent oxygen ions that are arranged octahedrally around an extremely small Be ion. We further demonstrate the emergence of robust ferroelectricity in strain-induced perovskite BaZrO3 and ultrathin HfO2 and ZrO2 films6,7 grown epitaxially on lattice-mismatched SiO2/Si substrate arising from the softening of the TO phonon driven by a reduction in the short-range bonding strength of biaxial strain-induced stretching bonds. These findings shed light on developing a unified theory for ferroelectricity enhancement in ultrathin films free from depolarization fields by tailoring chemical bonds using ionic radius differences, strains, doping and lattice distortions.

Artificial synapses based on HfOx/TiOy memristor devices for neuromorphic applications

As a result of enormous progress in nanoscale electronics, interest in artificial intelligence (AI) supported systems has also increased greatly. These systems are typically designed to process computationally intensive data. Parallel processing neural network architectures are particularly noteworthy for their ability to process dense data at high speeds, making them suitable candidates for AI algorithms. Due to their ability to combine processing and memory functions in a single device, memristors offer a significant advantage over other electronic platforms in terms of area scaling efficiency and energy savings. In this study, single-layer and bilayer metal-oxide HfOxand TiOymemristor devices inspired by biological synapses were fabricated by pulsed laser and magnetron sputtering deposition techniques in high vacuum with different oxide thicknesses. The structural and electrical properties of the fabricated devices were analysed using x-ray reflectivity, x-ray photoelectron spectroscopy, and standard two-probe electrical characterization measurements. The stoichiometry and degree of oxidation of the elements in the oxide material for each thin film were determined. Moreover, the switching characteristics of the metal oxide upper layer in bilayer devices indicated its potential as a selective layer for synapse. The devices successfully maintained the previous conductivity values, and the conductivity increased after each pulse and reached its maximum value. Furthermore, the study successfully observed synaptic behaviours with long-term potentiation, long-term depression (LTD), paired-pulse facilitation, and spike-timing-dependent plasticity, showcasing potential of the devices for neuromorphic computing applications.

High Electron Mobility in Si-Doped Two-Dimensional β-Ga2O3 Tuned Using Biaxial Strain.

Two-dimensional (2D) semiconductors have attracted much attention regarding their use in flexible electronic and optoelectronic devices, but the inherent poor electron mobility in conventional 2D materials severely restricts their applications. Using first-principles calculations in conjunction with Boltzmann transport theory, we systematically investigated the Si-doped 2D β-Ga2O3 structure mediated by biaxial strain, where the structural stabilities were determined by formation energy, phonon spectrum, and ab initio molecular dynamic simulation. Initially, the band gap values of Si-doped 2D β-Ga2O3 increased slightly, followed by a rapid decrease from 2.46 eV to 1.38 eV accompanied by strain modulations from -8% compressive to +8% tensile, which can be ascribed to the bigger energy elevation of the σ* anti-bonding in the conduction band minimum than that of the π bonding in the valence band maximum. Additionally, band structure calculations resolved a direct-to-indirect transition under the tensile strains. Furthermore, a significantly high electron mobility up to 4911.18 cm2 V-1 s-1 was discovered in Si-doped 2D β-Ga2O3 as the biaxial tensile strain approached 8%, which originated mainly from the decreased quantum confinement effect on the surface. The electrical conductivity was elevated with the increase in tensile strain and the enhancement of temperature from 300 K to 800 K. Our studies demonstrate the tunable electron mobilities and band structures of Si-doped 2D β-Ga2O3 using biaxial strain and shed light on its great potential in nanoscale electronics.

Stability, electronic and magnetic properties of boronphosphide (BP) graphenylene induced by interstitial atomic doping

In the context of low-dimensional materials, incorporating foreign atoms through doping processes has the potential to modulate the properties of host materials, which is favorable for diverse functional applications. In this study, we introduce a series of six distinct B6P6X ternary graphenylene monolayers. The B6P6X is designed through interstitial X = Cl, Br, I, O, S, and Te atomic doping of pure BP graphenylene. Through spin-polarized density functional theory (DFT), we comprehensively investigate the stability, electronic, and magnetic properties of B6P6X monolayers. We demonstrate that B6P6X monolayers are mechanically, dynamically and thermally stable with ferromagnetic ground state properties. We show that the metallic features of B6P6X (X = Cl, Br, I, O, S) and half-metallic property of B6P6Te monolayers at the PBE level can be further modulated when subjected to the HSE06 level. It is revealed that the B6P6X (X = O, S) monolayers exhibit a sizeable magnetic moment and a large magnetic anisotropy energy (MAE) value with an easy out-of-plane magnetization axis. We also found an out-of-plane MAE magnetization axis for B6P6X (X = Br, I) monolayers and an in-plane easy magnetization axis for B6P6X (X = Cl, Te) monolayers. Further investigation show that the B6P6S monolayer exhibit above room-temperature TC up to 565 K. The estimated Berezinskii–Kosterlitz–Thouless transition (BKT) temperature value of B6P6Te monolayer is 254 K. Our findings show that the B6P6X monolayers, particularly doped with chalcogens are potential candidates for nanoscale electronics and spintronics applications.

Thermodynamics and electronic structure of edges in monolayer MoSi2N4

MoSi2N4 is a two-dimensional ternary nitride semiconductor that has attracted attention for its excellent mechanical and thermal properties. Theoretical studies predict that zigzag edges of this material can host magnetic edge states and Dirac fermions, but the stability of such edges has not been examined. Here, we present a density functional theory study of the electronic and thermodynamic properties of MoSi2N4 edges. We develop a (partial) ternary phase diagram that identifies a region of chemical potentials within which MoSi2N4 is stable over competing elemental or binary phases. Based on this phase diagram, we determine the thermodynamic stability of several armchair and zigzag edges and elucidate their electronic structures. Bare zigzag edges, predicted to host exotic electronic states, are found to be substantially higher in energy than armchair edges and, thus, unlikely to occur in practice. However, with hydrogen passivation, these zigzag edges can be stabilized relative to their armchair counterparts while retaining metallicity and magnetic order. Our analysis provides a solid thermodynamic basis for further exploration of MoSi2N4 in nanoscale electronics and spintronics.

DNA-Templated Nanofabrication of CdS-Au Nanoscale Schottky Contacts and Electrical Characterization.

DNA-templated nanofabrication presents an innovative approach to creating self-assembled nanoscale metal-semiconductor-based Schottky contacts, which can advance nanoelectronics. Herein, we report the successful fabrication of metal-semiconductor Schottky contacts using a DNA origami scaffold. The scaffold, consisting of DNA strands organized into a specific linear architecture, facilitates the competitive arrangement of Au and CdS nanorods, forming heterojunctions, and addresses previous limitations in low electrical conductance making DNA-templated electronics with semiconductor nanomaterials. Electroless gold plating extends the Au nanorods and makes the necessary electrical contacts. Tungsten electrical connection lines are further created by electron beam-induced deposition. Electrical characterization reveals nonlinear Schottky barrier behavior, with electrical conductance ranging from 0.5 × 10-4 to 1.7 × 10-4 S. The conductance of these DNA-templated junctions is several million times higher than with our prior Schottky contacts. Our research establishes an innovative self-assembly approach with applicable metal and semiconductor materials for making highly conductive nanoscale Schottky contacts, paving the way for the future development of DNA-based nanoscale electronics.

Chirality-Induced Spin Selectivity in Composite Materials: A Device Perspective.

ConspectusMagnetism is an area of immense fundamental and technological importance. At the atomic level, magnetism originates from electron "spin". The field of nanospintronics (or nanoscale spin-based electronics) aims to control spins in nanoscale systems, which has resulted in astronomical improvement in data storage and magnetic field sensing technologies over the past few decades, recognized by the 2007 Nobel Prize in Physics. Spins in nanoscale solid-state devices can also act as quantum bits or qubits for emerging quantum technologies, such as quantum computing and quantum sensing.Due to the fundamental connection between magnetism and spins, ferromagnets play a key role in many solid-state spintronic devices. This is because at the Fermi level, electron density of states is spin-polarized, which permits ferromagnets to act as electrical injectors and detectors of spins. Ferromagnets, however, have limitations in terms of low spin polarization at the Fermi level, stray magnetic fields, crosstalk, and thermal instability at the nanoscale. Therefore, new physics and new materials are needed to propel spintronic and quantum device technologies to the true atomic limit. Emerging new phenomena such as chirality induced spin selectivity or CISS, in which an intriguing correlation between carrier spin and medium chirality is observed, could therefore be instrumental in nanospintronics. This effect could allow molecular-scale, chirality controlled spin injection and detection without the need for any ferromagnet, thus opening a fundamentally new direction for device spintronics.While CISS finds a myriad of applications in diverse areas such as chiral separation, recognition, detection, and asymmetric catalysis, in this focused Account, we exclusively review spintronic device results of this effect due to its immense potential for future spintronics. The first generation of CISS-based spintronic devices have primarily used chiral bioorganic molecules; however, many practical limitations of these materials have also been identified. Therefore, our discussion revolves around the family of chiral composite materials, which may emerge as an ideal platform for CISS due to their ability to assimilate various desirable material properties on a single platform. This class of materials has been extensively studied by the organic chemistry community in the past decades, and we discuss the various chirality transfer mechanisms that have been identified, which play a central role in CISS. Next, we discuss CISS device studies performed on some of these chiral composite materials. Emphasis is given to the family of chiral organic-carbon allotrope composites, which have been extensively studied by the authors of this Account over the past several years. Interestingly, due to the presence of multiple materials, CISS signals from hybrid chiral systems sometimes differ from those observed in purely chiral systems. Given the sheer diversity of chiral composite materials, CISS device studies so far have been limited to only a few varieties, and this Account is expected to draw increased attention to the family of chiral composites and motivate further studies of their CISS applications.

2D electron gas formation on InAs wurtzite nanosheet surfaces

The two-dimensional electron gas (2DEG) that forms on a semiconductor surface can be used to explore a variety of phenomena in quantum physics and plays an important role in nanoscale electronics, such as transistors. Controlling its formation is, thus, relevant. Using angle-resolved photoemission spectroscopy (ARPES) and accumulating the signal over many nanocrystals, we find that on clean InAs nanosheets with non-polar surfaces and wurtzite (WZ) crystal structures, a 2DEG can be observed at the Γ-point. We suggest that the step morphology on the WZ InAs specimens facilitates the appearance of the electron gas, since previous studies on InAs nanowire surfaces with the same crystal facet and a similar defect density did not exhibit a 2DEG. Subsequently, bismuth deposition leads to the disappearance of the 2DEG as well as a shift of the valence band. This is in contrast to previous observations on InAs surfaces, in which metal deposition would lead to the formation of a 2DEG. The control of the 2DEG with the addition of Bi atoms is relevant for applications of InAs nanosheets in quantum technologies. This study also illustrates that ARPES accumulated over several 2D materials oriented randomly around their normal axis can provide valuable information on their band structure with a fast turnover and low irradiation.

The Effect of Impact Load on the Atomistic Scale Fracture Behavior of Nanocrystalline bcc Iron.

Nanocrystalline metals have many applications in nanodevices, especially nanoscale electronics in aerospace. Their ability to resist fracture under impact produced by environmental stress is the main concern of nanodevice design. By carrying out molecular dynamics simulations under different fast loading rates, this work examines the effect of impact load on the fracture behavior of nanocrystalline bcc iron at an atomistic scale. The results show that a crack propagates with intergranular decohesion in nanocrystalline iron. With the increase in impact load, intergranular decohesion weakens, and plastic behaviors are generated by grain boundary activities. Also, the mechanism dominating plastic deformation changes from the atomic slip at the crack tip to obvious grain boundary activities. The grain boundary activities produced by the increase in impact load lead to an increase in the threshold energy for crack cleavage and enhance nanocrystalline bcc iron resistance to fracture. Nanocrystalline bcc iron can keep a high fracture ductility under a large impact load.

Inkjet Printing of Nanoscale Functional Patterns on 2D Crystalline Materials and Transfer to Soft Materials.

Nanometer-scale control over surface functionality is important in applications ranging from nanoscale electronics to regenerative medicine. However, approaches that provide precise control over surface chemistry at the nanometer scale are often challenging to use with higher throughput and in more heterogeneous environments (e.g., complex solutions, porous interfaces) common for many applications. Here, we demonstrate a scalable inkjet-based method to generate 1 nm-wide functional patterns on 2D materials such as graphite, which can then be transferred to soft materials such as hydrogels. We examine fluid dynamics associated with the inkjet printing process for low-viscosity amphiphile inks designed to maximize ordering with limited residue and show that microscale droplet fluid dynamics influence nanoscale molecular ordering. Additionally, we show that scalable patterns generated in this way can be transferred to hydrogel materials and used to create surface chemical patterns that induce adsorption of charged particles, with effects strong enough to overcome electrostatic repulsion between a charged hydrogel and a like-charged nanoparticle.

ADVANCEMENT IN NANOSCALE ELECTRONICS IN MOSFET

This research explores a novel approach for designing Cylindrical Surrounding Double-Gate (CSDG) MOSFETs with nanometer-scale precision through a layer- by-layer fabrication technique. Traditional top- down methods, such as photolithography and ion beam deposition, are widely used for semiconductor design but present challenges in creating complex heterostructures. In response, this study proposes an alternative method focusing on cylindrical structures to develop high- resolution morphological designs of CSDG MOSFETsThe research emphasizes the versatility of the proposed method, allowing the design of various cylindricalstructures with distinct properties, including periodic and non-periodic arrangements, symmetric andasymmetric configurations, and nanometer-scale gaps/dots. The focus is on the development of a symmetricCSDG MOSFET concerning the center core, providing valuable insights for fabricating structures over thecore of 2D Electron Gas (2DEG). Keywords— Cylindrical Surrounding Double-Gate MOSFET, Fabrication Steps Layer-by-Layer Approach Semiconductor Devices,Nanoscale Electronics ,Transistor Design ,Oxidation Process, Scalability, Simulation ,Oxidant Concentration.

Quantifying the Magnetic Interactions Governing Chiral Spin Textures Using Deep Neural Networks.

The interplay of magnetic interactions in chiral multilayer films gives rise to nanoscale topological spin textures that form attractive elements for next-generation computing. Quantifying these interactions requires several specialized, time-consuming, and resource-intensive experimental techniques. Imaging of ambient domain configurations presents a promising avenue for high-throughput extraction of parent magnetic interactions. Here, we present a machine learning (ML)-based approach to simultaneously determine the key magnetic interactions─symmetric exchange, chiral exchange, and anisotropy─governing the chiral domain phenomenology in multilayers, using a single binarized image of domain configurations. Our convolutional neural network model, trained and validated on over 10,000 domain images, achieved R2 > 0.85 in predicting the parameters and independently learned the physical interdependencies between magnetic parameters. When applied to microscopy data acquired across samples, our model-predicted parameter trends are consistent with those of independent experimental measurements. These results establish ML-driven techniques as valuable, high-throughput complements to conventional determination of magnetic interactions and serve to accelerate materials and device development for nanoscale electronics.

Phase-engineered heterostructures of Mo2C by plasma-assisted selenization and sulfurization processes toward excellent hydrogen evolution reaction

Due to the outstanding semiconducting and metallic properties, 2D materials such as Transition Metal dichalcogenides (TMDs) and Transition Metal Carbides (TMCs) appear to be promising candidate for Nano-scale electronics devices. Among them, 2D - Mo2C (Molybdenum carbide) has attracted attention as a new member of the MXene group, owing to its potential applications for superconductors, electronics devices, and catalysts for Hydrogen evolution Reactions (HER). Structural modification toward the creation of novel heterostructures with phase engineering opens new pathways for different applications. Herein, we prepared a large area Mo2C film by chemical vapor deposition method. The upper region of Mo2C layers can be oxidized to create Mo2C/MoOx heterostructures. Furthermore, those oxide layers were further transformed into MoSe2 and MoS2 by plasma-assisted selenization and sulfurization processes at different temperatures with a fixed plasma power of 150 W. The heterostructures demonstrated outstanding electrocatalytic activity for HER due to an existed metallic phase and active sites present after plasma-assisted selenization and sulfurization processes at the low temperature. The performance of the HER decreases at high temperatures owing to their semiconducting phase. The pristine Mo2C showed a Tafel slope of 72 mV dec−1 and an overpotential of 276 mV at 10 mA/cm2, while the Mo2C/MoSe2 heterostructure synthesized at 350 °C350 °exhibited an improved Tafel slope of 66 mV dec−1 and overpotential of 257 mV at 10 mA/ cm2. Additionally, the Mo2C/MoS2 heterostructure prepared at 350 °C also demonstrated a 263 mV improvement in overpotential at 10 mA/cm2. All the heterostructures showed excellent stability over a period of 10 h except Mo2C/MoOx. This work opens new strategies to fabricate high-quality MXene and TMDs heterostructures with metal-semiconductor interface.

Thermoelectric Power of a Single van der Waals Interface between Carbon Nanotubes.

Control of van der Waals interfaces is crucial for fabrication of nanomaterial-based high-performance thermoelectric devices because such interfaces significantly affect the overall thermoelectric performances of the device due to their relatively high thermal resistance. Such interfaces could induce different thermoelectric power from the bulk, i.e., interfacial thermoelectric power. However, from a macroscopic point of view, a correct evaluation of the interfacial thermoelectric power is difficult owing to various interface configurations. Therefore, the study of the thermoelectric properties at a single interface is crucial to address this problem. Herein, we used in situ transmission electron microscopy and nanomanipulation to investigate the thermoelectric properties of carbon nanotubes and their interfaces. The thermoelectric power of the bridged carbon nanotubes was individually measured. The existence of the interfacial thermoelectric power was determined by systematically changing the contact size between the two parallel nanotubes. The effect of interfacial thermoelectric power was qualitatively supported by Green's function calculations. When the contact length between two parallel nanotubes was less than approximately 100 nm, the experimental results and theoretical calculations indicated that the interface significantly contributed to the total thermoelectric power. However, when the contact length was longer than approximately 200 nm, the total thermoelectric power converged to the value of a single nanotube. The findings herein provide a basis for investigating thermoelectric devices with controlled van der Waals interfaces and contribute to thermal management in nanoscale devices and electronics.

Defeating depolarizing fields with artificial flux closure in ultrathin ferroelectrics

Material surfaces encompass structural and chemical discontinuities that often lead to the loss of the property of interest in so-called dead layers. It is particularly problematic in nanoscale oxide electronics, where the integration of strongly correlated materials into devices is obstructed by the thickness threshold required for the emergence of their functionality. Here we report the stabilization of ultrathin out-of-plane ferroelectricity in oxide heterostructures through the design of an artificial flux-closure architecture. Inserting an in-plane-polarized ferroelectric epitaxial buffer provides the continuity of polarization at the interface; despite its insulating nature, we observe the emergence of polarization in our out-of-plane-polarized model of ferroelectric BaTiO3 from the very first unit cell. In BiFeO3, the flux-closure approach stabilizes a 251° domain wall. Its unusual chirality is probably associated with the ferroelectric analogue to the Dzyaloshinskii–Moriya interaction. We, thus, see that in an adaptively engineered geometry, the depolarizing-field-screening properties of an insulator can even surpass those of a metal and be a source of functionality. This could be a useful insight on the road towards the next generation of oxide electronics.

Comparison of two methods for one-dimensional Ga2O3-ZnGa2O4 core–shell heterostructure synthesis

While gallium oxide Ga2O3 has recently shown promise as a new ultra-wide bandgap semiconductor in the form of thin films and nanowires (NWs), its widespread applicability is limited due to lack of native p-type conductivity, thus requiring fabrication of heterojunctions. A potential matching material is spinel zinc gallate ZnGa2O4. In this work we demonstrated and compared two novel approaches of one-dimensional Ga2O3-ZnGa2O4 core–shell NW heterostructure preparation: (a) a direct deposition of a ZnGa2O4 coating using a reactive magnetron co-sputtering; (b) annealing of a sacrificial few-nm-thick ZnO coating, deposited via atomic layer deposition, at high temperature to enable solid state reaction between ZnO and Ga2O3. The as-grown nanostructures were characterized via scanning and transmission electron microscopies, X-ray diffraction and X-ray photoelectron spectroscopy. Room temperature optical features were disclosed using photoluminescence and optical absorption. While both methods are viable for production of the heterostructures, smoother and more uniform ZnGa2O4 coating around Ga2O3 NWs was obtained via sacrificial layer conversion in comparison to the sputter-deposited one. These heterostructures could potentially be used for photocatalysis and nanoscale ultra-wide bandgap electronics.

Ionic transfer behavior of bipolar nanochannels resembling PNP nanotransistor

This article presents a study on the use of nanofluidic membranes containing straight nanopores as nanotransistors, with a specific focus on the PNP nanotransistor with its three regions representing the emitter, base, and collector. By applying a voltage to the base region, the current flowing between the emitter and collector regions is increased. The nanotransistor has two active intersections in its nanochannel where ions can either collect or deplete. Due to its nanoscale size, the PNP nanotransistor has unique properties that make it suitable for various applications, including ultra-sensitive biosensors, low-power electronics, and rapid computation. We investigated the effect of electrolyte concentrations on the performance of the PNP nanotransistor using a finite-element numerical computing method to determine the steady-state solutions of the Poisson-Nernst-Planck and Navier-Stokes equations. Our results show that the concentration profile in the system varies with voltage, and changing the concentration ratio of the tanks can improve the ionic current. For instance, our findings indicate that the passing ionic current at a Ca/Cg ratio of 3 and a Vapp=+1V is 84% higher than that at a Vapp=−1V. This study provides valuable insights into the performance of the PNP nanotransistor and its potential applications, particularly in the field of nanoelectronics. The results suggest that adjusting the electrolyte concentrations can improve the device's performance, leading to new opportunities for developing nanoscale electronics with enhanced functionality.

Writing-Speed Dependent Thresholds of Ferroelectric Domain Switching in Monolayer α-In2 Se3.

An electrical-biased or mechanical-loaded scanning probe written on the ferroelectric surface can generate programmable domain nanopatterns for ultra-scaled and reconfigurable nanoscale electronics. Fabricating ferroelectric domain patterns by direct-writing as quickly as possible is highly desirable for high response rate devices. Using monolayer α-In2 Se3 ferroelectric with ≈1.2nm thickness and intrinsic out-of-plane polarization as an example, a writing-speed dependent effect on ferroelectric domain switching is discovered. The results indicate that the threshold voltages and threshold forces for domain switching can be increased from -4.2 to -5V and from 365 to 1216 nN, respectively, as the writing-speed increases from 2.2 to 10.6µm s-1 . The writing-speed dependent threshold voltages can be attributed to the nucleations of reoriented ferroelectric domains, in which sufficient time is needed for subsequent domain growth. The writing-speed dependent threshold forces can be attributed to the flexoelectric effect. Furthermore, the electrical-mechanical coupling can be employed to decrease the threshold force, achieving as low as ≈189±41 nN, a value smaller than those of perovskite ferroelectric films. Such findings reveal a critical issue of ferroelectric domain pattern engineering that should be carefully addressed for programmable direct-writing electronics applications.

Chemical Dopant-Free Controlled MoTe2/MoSe2 Heterostructure toward a Self-Driven Photodetector and Complementary Logic Circuits.

Two-dimensional (2D) van der Waals heterostructures based on transition metal dichalcogenides are expected to be unique building blocks for next-generation nanoscale electronics and optoelectronics. The ability to control the properties of 2D heterostructures is the key for practical applications. Here, we report a simple way to fabricate a high-performance self-driven photodetector based on the MoTe2/MoSe2 p-n heterojunction, in which the hole-dominated transport polarity of MoTe2 is easily achieved via a straightforward thermal annealing treatment in air without any chemical dopants or special gases needed. A high photoresponsivity of 0.72 A W-1, an external quantum efficiency up to 41.3%, a detectivity of 7 × 1011 Jones, and a response speed of 120 μs are obtained at zero bias voltage. Additionally, this doping method is also utilized to realize a complementary inverter with a voltage gain of 24. By configuring 2D p-MoTe2 and n-MoSe2 on demand, logic functions of NAND and NOR gates are also accomplished successfully. These results present a significant potential toward future larger-scale heterogeneously integrated 2D electronics and optoelectronics.

Origin and Quantitative Description of the NESSIAS Effect at Si Nanostructures

AbstractThe electronic structure of SiO2‐ versus Si3N4‐coated low nanoscale intrinsic silicon (Si) shifts away from versus toward the vacuum level Evac, originating from the Nanoscale Electronic Structure Shift Induced by Anions at Surfaces (NESSIAS). Using the quantum chemical properties of the elements involved to explain NESSIAS, an analytic parameter Λ is derived to predict the highest occupied energy level of Si nanocrystals (NCs) as verified by various hybrid‐density functional calculations and NC sizes. First experimental data of Si nanowells (NWells) embedded in SiO2 versus Si3N4 were measured by X‐ray absorption spectroscopy in total fluorescence yield mode (XAS‐TFY), complemented by ultraviolet photoelectron spectroscopy (UPS), characterizing their conduction band and valence band edge energies EC and EV, respectively. Scanning the valence band sub‐structure over NWell thickness yields an accurate estimate of EV shifted purely by spatial confinement, and thus the actual EV shift due to NESSIAS. Offsets of ΔEC = 0.56 eV and ΔEV = 0.89 eV were obtained for 1.9 nm thick NWells in SiO2 versus Si3N4, demonstrating an intrinsic Si type II homojunction. This p/n junction generated by NESSIAS eliminates any deteriorating impact of impurity dopants, offering undoped ultrasmall Si electronic devices with much reduced physical gate lengths and CMOS‐compatible materials.