Leonard Feldman

Rutgers, The State University of New Jersey | Rutgers · Department of Physics

A helium ion microscope (HIM) with a focused He+-ion beam of variable flux and energy can be used as a tool for local nanoscale surface modification. In this work, we demonstrate a simple but versatile use of the HIM focused He ion beam to fabricate conducting metallic nano- and microstructures on arbitrary substrates of varied types and shapes by...

Modern science is dependent on imaging on the nanoscale, often achieved through processes that detect secondary electrons created by a highly focused incident charged particle beam. Multiple types of measurement noise limit the ultimate trade-off between the image quality and the incident particle dose, which can preclude useful imaging of dose-sen...

Solution-processed light-emitting diodes based on non-toxic copper–iodide hybrids are a compelling solution for efficient and stable deep-blue lighting, attributed to their tunability, high photoluminescence efficiency, and environmental sustainability. Here we present a new hybrid copper iodide that exhibits near-unity photoluminescence quantum yi...

Characterization of the atomic level processes that determine optical transitions in emerging materials is critical to the development of new platforms for classical and quantum networking. Such understanding often emerges from studies of the temperature dependence of the transitions. We report measurements of the temperature dependent Er³⁺ photolu...

Doped semiconductor nanowires are emerging as next-generation electronic colloidal materials, and the efficient manipulation of such nanostructures is crucial for technological applications. In fluid suspension, pn nanowires (pn NWs), unlike homogeneous nanowires, have a permanent dipole, and thus, experience a torque under an external DC field tha...

Ultrathin superconducting MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films are desirable for device applications and for exploration of new quantum phenomena in reduced dimensions. We have reported recently that smooth ultrathin MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" x...

Hydrogen production by photoelectrochemical (PEC) water splitting has remained challenging for commercialization mainly due to the limited durability of integrated photoelectrodes owing to failure of the interfacial connection between the photoabsorber(s) and catalyst(s). Although multijunction III-V semiconductors have been popular choices as phot...

We report an N2 based annealing treatment to passivate interface traps (Dit) in n- and p-type 4H-SiC. The process has the potential to replace the commonly used hazardous and expensive gas nitric oxide (NO). N2 postoxidation annealing reduces Dit in both the upper and lower halves of the 4H-SiC bandgap, with a greater impact at the valence band edg...

Defect engineering is foundational to classical electronic device development and for emerging quantum devices. Here, we report on defect engineering of silicon with ion pulses from a laser accelerator in the laser intensity range of 10¹⁹ W cm⁻² and ion flux levels of up to 10²² ions cm⁻² s⁻¹, about five orders of magnitude higher than conventional...

The rapidly increasing solar conversion efficiency (PCE) of hybrid organic–inorganic perovskite (HOIP) thin‐film semiconductors has triggered interest in their use for direct solar‐driven water splitting to produce hydrogen. However, application of these low‐cost, electronic‐structure‐tunable HOIP tandem photoabsorbers has been hindered by the inst...

High-quality, ultrathin superconducting films are required for advanced devices such as hot-electron bolometers, superconducting nanowire single-photon detectors, and quantum applications. Using hybrid physical-chemical vapor deposition, we show that MgB2 films as thin as 4 nm can be fabricated on the carbon-terminated 6H-SiC (0001) surface with a...

High quality, ultrathin, superconducting films are required for advanced devices such as hot-electron bolometers, superconducting nanowire single photon detectors, and quantum applications. Using Hybrid Physical-Chemical Vapor Deposition (HPCVD), we show that MgB2 films as thin as 4 nm can be fabricated on the carbon terminated 6H-SiC (0001) surfac...

Silicon Carbide (4H-SiC) has emerged as a leading wide band gap semiconductor for high-power, high-temperature applications ¹ . 4H-SiC metal-oxide semiconductor-field-effect transistors (MOSFETs) have lower power dissipation compared to silicon, allowing for low-noise and high-efficiency all-electric vehicle drives, fast-charging stations, solar in...

We report the first experimental realization of the intrinsic (not dominated by defects) charge conduction regime in lead‐halide perovskite field‐effect transistors (FETs). The advance has been enabled by: i) a new vapor‐phase epitaxy technique that results in large‐area single crystalline cesium lead bromide (CsPbBr3) films with excellent structur...

The rapidly increasing solar conversion efficiency (PCE) of hybrid organic-inorganic perovskite (HOIP) thin-film semiconductors has triggered interest in their use for direct solar-driven water splitting to produce hydrogen. However, application of these low-cost, electronic-structure-tunable HOIP tandem photoabsorbers has been hindered by the inst...

Fabrication of nanostructured metasurfaces poses a significant technological and fundamental challenge. Despite developing novel material systems that support reversible elongation and distortion, their nanoscale patterning and control of optical properties remain an open problem. Herein we report the atomic force microscope lithography application...

Defect engineering is foundational to classical electronic device development and for emerging quantum devices. Here, we report on defect engineering of silicon single crystals with ion pulses from a laser accelerator with ion flux levels up to 10^22 ions/cm^2/s. Low energy ions from plasma expansion of the laser-foil target are implanted near the...

Fabrication of nanostructured metasurfaces poses a significant technological and fundamental challenge. Despite developing novel systems that support reversible elongation and distortion, their nanoscale patterning and control of optical properties remain an open problem. Herein we report the atomic force microscope lithography (AFML) application f...

Perovskite-based light-emitting diodes (PeLEDs) are promising candidates for next-generation solid-state lighting and display technologies. However, all current high-performance PeLEDs contain a toxic element (lead) and suffer from relatively low stability. Herein, we report a new type of lead-free LED using low-cost, eco-friendly, and robust coppe...

PdCoO2, belonging to a family of triangular oxides called delafossite, is one of the most conducting oxides. Its in-plane conductivity is comparable to those of the best metals and exhibits hydrodynamic electronic transport with an extremely long mean free path at cryogenic temperatures. Nonetheless, it is nonmagnetic despite the presence of the co...

PdCoO2 , belonging to a family of triangular oxides called delafossite, is one of the most conducting oxides. Its in-plane conductivity is comparable to those of the best metals, and exhibits hydrodynamic electronic transport with extremely long mean free path at cryogenic temperatures. Nonetheless, it is nonmagnetic despite the presence of the cob...

Silicon carbide (4H) based metal–oxide–semiconductor field-effect transistors provide capabilities in high power and high temperature inaccessible to silicon. However, the performance of thermally grown oxide-based devices remains limited by oxide/semiconductor interface defects. This research employs deposited dielectrics, Al2O3, rather than therm...

In the current paper, the structure and properties of AlGaN/GaN interfaces are studied, explaining the role of AlGaN layer thickness on the two-dimensional electron gas (2DEG) formation. It is found that the generation of a continuous electron gas requires AlGaN films with stable stoichiometry, which can be reached only above a certain critical thi...

Supplementary Information to the paper "Stimulus-responsive self-assembly of protein-based fractals by computational design". Contains the methods section, additional discussion and references section, Supplementary Figs. 1 to 37, Supplementary Tables 1 to 3 and descriptions of Supplementary Videos 1 to 3.

We report the confirmed occurrence of Fowler-Nordheim hole tunneling in p-4H-SiC metal-oxide-semiconductor capacitor structures. The effective mass for holes in the oxide is found to be in the range of 0.35m-0.52m, where m is the free electron mass. A fundamental process in the description of the current-voltage (I-V) characteristic of a metal-diel...

Single atom catalysts provide exceptional activity. However, measuring the intrinsic catalytic activity of a single atom in real electrochemical environments is challenging. Here, we report the activity of a single sulfur vacancy for electrocatalytically evolving hydrogen in two dimensional (2D) MoS2. Surprisingly, we find that the catalytic activi...

Probing Phonon and Infrared-Plasmons in Nanoscale Interfaces - Volume 25 Supplement - MJ Lagos, U Hohenester, A Trugler, V Amarasinghe, LC Feldman, PE Batson, GA Botton

Fractal topologies, which are statistically self-similar over multiple length scales, are pervasive in nature. The recurrence of patterns in fractal-shaped branched objects, such as trees, lungs and sponges, results in a high surface area to volume ratio, which provides key functional advantages including molecular trapping and exchange. Mimicking...

We have investigated the normal-state and superconducting properties of Co-doped BaFe2As2 (Ba122) and MgB2 thin films irradiated at room temperature using a 30 keV focused He+ ion beam with doses between 1012 and 1017 cm2. We show that superconductivity is suppressed and the normal-state resistivity is increased upon irradiation. The critical dose...

In the family of wide band gap materials (silicon carbide, the group III nitrides and diamond), SiC is the only semiconductor that has a native oxide, and metal-oxide-semiconductor field effect transistors (MOSFETs) have been fabricated using both 4H-and 6H-SiC. The 4H polytype has higher bulk carrier mobility [1], and is hence the polytype of choi...

Fractal topologies, which are statistically self-similar over multiple length scales, are pervasive in nature. The recurrence of patterns at increasing length scales in fractal-shaped branched objects, e.g. , trees, lungs, and sponges, results in high effective surface areas, and provides key functional advantages, e.g. , for molecular trapping and...

Efficient characterization of semiconductor nanowires having complex dopant profiles or heterostructures is critical to fully understand these materials and the devices built from them. Existing electrical characterization techniques are slow and laborious, particularly for multisegment nanowires, and impede the statistical understanding of highly...

We have fabricated series arrays of closely spaced planar Josephson junctions on MgB2 films using a 30 keV focused helium ion beam. Uniformity of junction parameters within the arrays is sufficient for achieving phase-lock into an applied microwave signal, and flat giant Shapiro steps are observed. The spread in critical current of a 60-Josephson j...

The unique capabilities of time domain Brillouin scattering (TDBS) for studying post-implantation effects on optical and opto-elastic properties of semiconductors are discussed. This method utilizes coherent acoustic phonons to measure depth-dependent optical and opto-elastic changes arising from structural damage caused by ion implantation. This n...

We have fabricated series arrays of closely spaced planar Josephson junctions on MgB2 films using a 30 keV focused helium ion beam. Uniformity of junction parameters within the arrays was sufficient for achieving phase-lock into an applied microwave signal and flat giant Shapiro steps were observed. The spread in critical current of a 60-Josephson...

The chemical nature of sub-monolayer phosphorous impurities at the SiC/SiO 2 interface is a critical surface science problem related to device performance and other applications. In this study, SiO 2 films containing phosphorus were deposited by sputtering on both the Si and C-faces of SiC substrates, and on silicon (Si(100)) substrates. After oxid...

AlGaN/GaN heterostructures are of high research and industrial interest for the production of high electron mobility transistors (HEMT) utilizing the two-dimensional electron gas (2DEG) induced at the interface due to polarization effects. In the current work, the effect of AlGaN thickness on 2DEG formation is under discussion. In particular, ultra...

The electron density and physical stress at the thermally oxidized SiC/SiO2 interface, and their change with nitrogen incorporation, were observed using x-ray reflectivity, Raman scattering, and in-situ stress measurement. There is no evidence for residual carbon species at the SiO2/SiC. Instead, a ∼1 nm thick low electron density layer is formed a...

Planar magnesium diboride Josephson junctions are fabricated using focused helium ion beam irradiation. A single track of ion irradiation with a 30 kV He⁺ beam with nominal beam diameter < 0.5 nm is used to create a normal-metal barrier on a MgB2 film deposited by hybrid physical-chemical vapor deposition. Josephson coupling is observed below the c...

Planar Josephson junctions and series arrays were fabricated in magnesium diboride (MgB2) thin films grown by hybrid physical-chemical vapor deposition. The junction barrier is created by locally damaging the crystal structure of the MgB2 with a 30 keV He+ ion beam focused to a diameter < 1 nm. Prior irradiation experiments over large areas showed...

Using spatially resolved Electron Energy-Loss Spectroscopy, we investigate the excitation of long-wavelength surface optical vibrational modes in elementary types of nanostructures: an amorphous SiO2 slab, an MgO cube, and in the composite cube/slab system. We find rich sets of optical vibrational modes strongly constrained by the nanoscale size an...

Little is known about how stony corals build their calcareous skeletons. There are two prevailing hypotheses: that it is a physicochemically dominated process and that it is a biologically mediated one. Using a combination of ultrahigh-resolution three-dimensional imaging and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy...

Physical stress in SiO2/SiC stacks formed by the thermal oxidation of SiC is studied experimentally through both room temperatureex-situ and variable temperature (25–1150 °C) in-situ investigations. Mechanisms giving rise to the stress are a thermal component, associated with differences in thermal expansion coefficients of the oxide and the substr...

We have investigated the normal and superconducting properties of Co-doped BaFe2As2 (Ba122) and MgB2 bridges irradiated at room temperature using a 30 kV He+ beam (ZEISS Orion Plus Helium ion microscope) and doses between 1013--1017/cm2. Our results show that the critical temperature of irradiated region reduces to \textless 2K for doses \textgreat...

Surface energy modification and surface wettability of 4H silicon carbide (0001) as a function of nitrogen adsorption is reported. The surface wettability is shown to go from primarily hydrophilic to hydrophobic and the surface energy was significantly reduced with increasing nitrogen incorporation. These changes are investigated by x-ray photoelec...

The innate immune system has been implicated in both AKI and CKD. Damaged mitochondria release danger molecules, such as reactive oxygen species, DNA, and cardiolipin, which can cause NLRP3 inflammasome activation and upregulation of IL-18 and IL-1β It is not known if mitochondrial damage persists long after ischemia to sustain chronic inflammasome...

Measuring and understanding electric fields in multilayered materials at the nanoscale remains a challenging problem impeding the development of novel devices. At this scale, it is far from obvious that materials can be accurately described by their intrinsic bulk properties, and considerations of the interfaces between layered materials become una...

Fluoroethylene carbonate (FEC) as an electrolyte additive can considerably improve the cycling performance of silicon (Si) electrodes in Li-ion batteries. However, the fundamental mechanism for how FEC contributes to solid electrolyte interphase (SEI) morphological changes and chemical composition is not well understood. Here, scanning transmission...

Silicon carbide (SiC) is a promising material for new generation electronics including high power/high temperature devices and advanced optical applications such as room temperature spintronics and quantum computing. Both types of applications require the control of defects particularly those created by ion bombardment. In this work, modification...

Existing nanowire electrical characterization tools not only are expensive and require sophisticated facilities, but are far too slow to enable statistical characterization of highly variable samples. They are also generally not compatible with further sorting and processing of nanowires. Here, we demonstrate a high-throughput, solution-based elect...

The correlation between phosphorus concentration in phospho-silicate glass (PSG) gate dielectrics and electrical properties of 4H-SiC MOS devices has been investigated. Varying P uptake in PSG is achieved by changing the POCl3 post-oxidation annealing temperature. The density of interface traps (Dit) at the PSG/4H-SiC interface decreases as the amo...

We report scanning tunneling microscopy and spectroscopy (STM and STS) studies of graphene formed from a nitrogen-seeded SiC( ) surface. STM indicates that much of the graphene consists of wide flat plateaus with hexagonal features bounded by pleats and regions with disordered character. Nitrogen impurities are not observed in the epitaxial graphen...

Using ultrafast time-resolved THz spectroscopy, we observe two-orders-of-magnitude increase in the relaxation rate in semiconducting epitaxial graphene relative to pristine epitaxial graphene, attributed to enhancement of the optical-phonon-mediated carrier cooling and recombination.

Phosphorous and nitrogen are electrically active species at the SiO2/SiC interface in SiCMOSFETs. We compare the concentration, chemical bonding, and etching behavior of P and N at the SiO2/SiC(0001) interface using photoemission, ion scattering, and secondary ion mass spectrometry. Both interfacial P and N are found to be resistant to buffered HF...

We utilize ultrafast time-resolved terahertz (THz) spectroscopy as a direct, sensitive, and non-contact all-optical probe to investigate the hot-carrier relaxation and cooling dynamics of buckled epitaxial graphene. This special form of graphene is grown epitaxially on nitrogen-seeded single-crystal silicon carbide (SiC( 000 1 ¯ )) substrates by...

Helium ion microscopy is used to provide new insight into the nano- and microscale morphology of cleaved surfaces of alkali-activated slag (AAS), revealing that AAS contains several types of gel with varying surface morphologies after being subjected to D-drying. It is seen that the bulk C-(N)-A-S-H gel is globular in nature in a silicate-activated...

div class="title">Characterization of the Oxide-Semiconductor Interface in 4H-SiC/SiO2 Structures using TEM and XPS - Volume 21 Issue S3 - Joshua Taillon, Karen Gaskell, Gang Liu, Leonard Feldman, Sarit Dahr, Tsvetanka Zheleva, Aivars Lelis, Lourdes Salamanca-Riba

Lateral MOSFET devices with a thin surface counter-doped layer using Sb and As with and without NO passivation have been fabricated and characterized. The results demonstrate that Sb and As counter-dope the interface without significant trap passivation while in combination with NO there is a superposition of both trap passivation and counter-dopin...

Nanowires of the same composition, and even fabricated within the same batch, often exhibit electrical conductivities that can vary by orders of magnitude. Unfortunately, existing electrical-characterization methods are time consuming, making the statistical survey of highly variable samples essentially impractical. Here, we demonstrate a contactle...