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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Scanning Tunneling Microscopy Studies of Diamond Films and Optoelectronic Materials

We present a summary of the research, citations of publications resulting from the research and abstracts of such publications. We have made no inventions in the performance of the work in this project. The main goals of the project were to set up a Chemical Vapor Deposition (CVD) diamond growth system attached to an UltraHigh Vacuum (UHV) atomic resolution Scanning Tunneling Microscopy (STM) system and carry out experiments aimed at studying the properties and growth of diamond films using atomic resolution UHV STM. We successfully achieved these goals. We observed, for the first time, the atomic structure of the surface of CVD grown epitaxial diamond (100) films using UHV STM. We studied the effects of atomic hydrogen on the CVD diamond growth process. We studied the electronic properties of the diamond (100) (2x1) surface, and the effect of alkali metal adsorbates such as Cs on the work function of this surface using UHV STM spectroscopy techniques. We also studied, using STM, new electronic materials such as carbon nanotubes and gold nanostructures. This work resulted in four publications in refereed scientific journals and five publications in refereed conference proceedings.

Perez, Jose M.↗
DOE OSTI2026

Atomic-scale imaging and charge state manipulation of NV centers by scanning tunneling microscopy

Nitrogen-vacancy (NV) centers in diamond are among the most promising solid-state qubit candidates, owing to their exceptionally long spin coherence times, efficient spin-photon coupling, room-temperature operation, and steadily advancing fabrication and integration techniques. Despite significant progress in the field, atomic-scale characterization and control of individual NV centers have remained elusive. In this work, we utilize a conductive graphene capping layer to enable direct imaging and manipulation of NV - defects via scanning tunneling microscopy (STM). By investigating over 40 individual NV - centers, we identify their spectroscopic signatures and spatial configurations. Our dI/dV conductance spectra reveal the ground state resonance approximately 300 meV below the Fermi level and density-of-states maps uncover a two-lobed wavefunction aligned along the [111] crystallographic direction. Remarkably, we demonstrate the ability to manipulate the charge state of the NV centers from NV - to NV 0 through STM tip-induced gating. This work represents a significant advance in the atomic-scale imaging, spectroscopic characterization, and charge-state manipulation of NV centers, potentially paving the way for future quantum device development.

Raghavan, Arjun [Univ. of Illinois at Urbana-Champ↗
DOE OSTI2026

Atomic‐Scale Surface Imaging of Bulk Epitaxial CsPbBr 3 Perovskite Single Crystals on Mica Using Light Assisted Scanning Tunneling Microscopy at Low‐Temperature (80 K)

Epitaxial single-crystalline CsPbBr 3 perovskite films on mica, prepared ex situ, are explored using a low-temperature scanning tunneling microscope (STM) by probing the unoccupied electronic states of their surface in ultra-high vacuum (UHV) at 80 K. Light-assisted STM measurements under a broadband illumination with visible light were employed to enhance and stabilize surface conductivity. STM imaging across the surface of macroscopic bulk CsPbBr 3 films reveals large flat terraces characterized by a specific type of surface reconstruction, consisting of parallel rows of U-shaped atomic nanostructures. These structures are spaced by 12 Å and exhibit an internal feature size of 5.1 Å. Density functional theory (DFT) calculations reproduce the experimental observations and reveal a competition between different orthorhombic CsPbBr 3 (110) surface reconstructions: a Cs-rich structure, identified as the most energetically stable, and three alternative Pb–Br-rich reconstructions, which are slightly higher in energy yet remain consistent with the STM data. Additional analyses that explicitly account for the mica substrate exclude the cubic CsPbBr 3 phase and other orthorhombic surface orientations, while showing that variations in the mica surface termination do not alter the preferred CsPbBr 3 (110) reconstruction. In conclusion, this combined approach thereby confirms our assignment and resolves previous STM interpretations of CsPbBr 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2025

Phase transition in two-dimensional monolayer (1L)-molybdenum disulfide induced by atomic S-basal plane gliding via synchrotron X-ray monochromatic beam radiation for superior electronic performance

Here, in this work, we report a novel approach to reduce the channel resistance by inducing a phase transition behavior from 2H to 1T in a monolayer MoS 2 (1L-MoS 2 ) by a synchrotron X-ray monochromatic beam (mono-beam) radiation. The effects of the biphase structure by the mono-beam on the 1L-MoS2 film were investigated using Raman spectra, photoluminescence (PL) spectra, scanning tunneling microscopy, and scanning tunneling spectroscopy, respectively. Through material characterization, we identified that the lateral sliding of S-vacancies along the S-plane in the 1L-MoS 2 is the key reason for the origin of unidirectional phase transition. The precise phase engineering triggered by the mono-beam radiation process allows the realization of field-effect transistors (FET) with 2X improvement in mobility toward a high on/off ratio (~10 8 ) and a near-ideal subthreshold swing of ~88 mV per decade. The validity of the phase engineering could be further extended for its application as a memory device, exhibiting a gate tunable conduction modulation behavior and a high resistance ratio of ~10 2 at a gate bias of 5 V with endurance of ~100 cycles. Furthermore, an artificial neural network using the synaptic weight update with accuracy of ~93 % was achieved.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Nanoscale Structure and Interfacial Electrochemical Reactivity of Moiré-Engineered Atomic Layers

Here, the electronic properties of atomically thin van der Waals (vdW) materials can be precisely manipulated by vertically stacking them with a controlled offset (for example, a rotational offset─i.e., twist─between the layers, or a small difference in lattice constant) to generate moiré superlattices. In recent years, the application of this “twistronics” concept to interfacial electrochemistry has unveiled unique pathways for tailoring the electrochemical reactivity. Furthermore, this Account provides an overview of our work that leveraged a suite of structural characterization methods, such as interferometric four-dimensional scanning transmission electron microscopy, dark-field transmission electron microscopy, and scanning tunneling microscopy, along with nanoscale electrochemical measurement techniques, namely, scanning electrochemical cell microscopy (SECCM), to uncover and dissect the profound impact of electrode electronic structure, controlled by interlayer twist, on interfacial electron transfer kinetics.

Charge transfer↗
NASA NTRS1994

JOVE NASA-FIT program: Microgravity and aeronomy projects

This semi-annual status report is divided into two sections: Scanning Tunneling Microscopy Lab and Aeronomy Lab. The Scanning Tunneling Microscopy (STM) research involves studying solar cell materials using the STM built at Florida Tech using a portion of our initial Jove equipment funding. One result of the participation in the FSEC project will be to design and build an STM system which is portable. This could serve as a prototype STM system which might be used on the Space Shuttle during a Spacelab mission, or onboard the proposed Space Station. The scanning tunneling microscope is only able to image the surface structure of electrically conductive crystals; by building an atomic force microscope (AFM) the surface structure of any sample, regardless of its conductivity, will be able to be imaged. With regards to the Aeronomy Lab, a total of four different mesospheric oxygen emission codes were created to calculate the intensity along the line of sight of the shuttle observations for 2972A, Herzberg I, Herzberg II, and Chamberlain bands. The thermosphere-ionosphere coupling project was completed with two major accomplishments: collection of 500 data points on modulation of neutral wind with geophysical variables, and establishment of constraints on behavior of the height of the ionosphere as a result of interaction between geophysical and geometrical factors. The magnetotail plasma project has been centered around familiarization with the subject in the form of a literature search and preprocessing of IMP-8 data.

Patterson, James D.↗
DOE OSTI2025

Unraveling spin entanglement using quantum gates with scanning tunneling microscopy-driven electron spin resonance

Quantum entanglement is a fundamental resource for quantum information processing, and its controlled generation and detection remain key challenges in scalable quantum architectures. Here, we numerically demonstrate the deterministic generation of entangled spin states in a solid-state platform by implementing quantum gates via electron spin resonance combined with scanning tunneling microscopy (ESR-STM). Using two titanium atoms on a MgO/Ag(100) substrate as a model, we construct a two-qubit system whose dynamics are coherently manipulated through tailored microwave pulse sequences. We generate Bell states by implementing a Hadamard gate followed by a controlled-NOT gate, and evaluate its fidelity and concurrence using the quantum-master equation-based code TimeESR. Our results demonstrate that ESR-STM can create entangled states with significant fidelity. This study paves the way for the realization of atom-based quantum circuits and highlights ESR-STM as a powerful tool for probing and engineering entangled states on surfaces.

Switzer, Eric D. [Donostia International Physics C↗
DOE OSTI2024

Epitaxial 2D Magnet and Topological Insulator Heterostructures

I will discuss our latest advances on the epitaxial growth of 2D van der Waals (vdW) magnets and their integration with topological insulators (TI). This work is motivated by the realization of topological phases such as the quantum anomalous Hall effect and highly efficient spin-orbit torque produced by TIs. Our initial studies of MnSe2 growth on Bi2Se3 showed a tendency for the interdiffusion of Mn into the Bi2Se3. This ultimately led to the synthesis of MnBi2Se4 (MBS), a new magnetic TI. Interestingly, the vdW phase is not the thermodynamically stable phase and bulk crystals do not exist, so the epitaxial stabilization of MBS creates the opportunity to explore the magnetic and topological properties of this material. We find that MBS is a layered antiferromagnet, similar to MnBi2Te4, but a difference is that the magnetic moments lie in the plane of the film. Angle resolved photoemission experiments show the presence of a topological surface state with Dirac dispersion. For bilayers of 2D magnets and TIs, we have developed FGT films on Bi2Te3. We first optimized FGT by studying its growth on Ge(111) substrates, where we find that kinetic considerations play a major role. Using cross-sectional scanning transmission electron microscopy and scanning tunneling microscopy, we optimize the FGT films to have atomically smooth surfaces and abrupt interfaces with the Ge(111). Subsequently, we have developed the growth of FGT on Bi2Te3 for the integration of 2D magnets with Tis. Interestingly, we observe room temperature ferromagnetism in FGT/Bi2Te3 heterostructures by varying the growth conditions.

Kawakami, Roland↗
NASA NTRS2004

Information Content of the Near-Field I: Two-Dimensional Samples

Limits on the effective resolution of many optical near-field experiments are investigated. The results are applicable to variants of total-internal-reflection microscopy (TIRM), photon-scanning-tunneling microscopy (PSTM), and near-field-scanning-optical microscopy (NSOM) in which the sample is weakly scattering and the direction of illumination may be controlled. Analytical expressions for the variance of the estimate of the complex susceptibility of an unknown two-dimensional object as a function of spatial frequency are obtained for Gaussian and Poisson noise models, and a model-independent measure is examined. The results are used to explore the transition from near-zone to far-zone detection. It is demonstrated that the information content of the measurements made at a distance of even one wavelength away from the sample is already not much different from the information content of the far field. Copyright 2004 Optical Society of America

Frazin, Richard A.↗
DOE OSTI2024

Atomic-scale investigations of Ti 3 C 2 T x MXene surfaces

The family of two-dimensional (2D) carbides and/or nitrides, also known as MXenes, has generated great excitement within the scientific community and has been proposed for a wide variety of applications since its discovery. Despite this attention, there have been only limited studies of the atomically resolved local electronic and physical structure of MXene surfaces strongly affecting the physicochemical properties of these materials. Here, in this study, we report local structural, spectroscopic, and chemical investigations of the surfaces of Ti 3 C 2 T x flakes using scanning tunneling microscopy and spectroscopy, closely coupled to theoretical studies. Terminal groups are visualized and characterized, along with surface TiO 2 clusters formed upon exposure to air. Fundamental insight into the local electronic and chemical properties associated with different terminal groups on MXenes and their oxidation products is presented.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Possible coexistence of magnetism and paramagnetic singularity in lightly Fe-doped WTe 2

Topological semimetals possess nodal or nodal-line phases where conduction and valence bands touch at points or lines in momentum space, respectively. Such band touching is symmetry protected and gives rise to exotic and interesting electronic properties. Coupling topological order with magnetism provides a platform for exploring time-reversal (TR) symmetry breaking topological physics, such as axion electrodynamics, inverse spin-galvanic effect, and the quantized anomalous Hall effect. The Weyl semimetal (WSM) requires breaking either TR symmetry or lattice inversion symmetry (I). By doping inversion-symmetry-broken WSM with magnetic dopants, one can expect to create a WSM with both symmetries breaking simultaneously. Here, structural, electrical, and magnetic properties of Fe x ⁢W 1–x Te 2 (x = 0 and 0.011) are reported. It is revealed that, with a small Fe doping concentration (x = 0.011), a ferromagnetism is induced at low temperature (<10 K). Scanning tunneling microscopy and spectroscopy measurements in Fe 0.011 ⁢W 0.989 ⁢Te 2 further reveal only substitution and no intercalated dopants being observed. The probabilities of the Fe substitutions at the two nonequivalent W sites are quantified with equal probability. The dl/dV point spectra indicates that the Fe substitution in WTe 2 manifests itself as electron doping regardless of doping sites. The results clearly reveal the possible coexistence of magnetism and Weyl points in the lightly Fe doped WTe2 at low temperature. Furthermore, this provides an ideal system for further study on the interplay between the topological Weyl points and the TR symmetry breaking.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Scanning probe spectroscopy of sulfur vacancies and MoS 2 monolayers in side-contacted van der Waals heterostructures

We investigate the interplay between vertical tunneling and lateral transport phenomena in electrically contacted van der Waals heterostructures made from monolayer MoS 2 , hBN, and graphene. We compare data taken by low-temperature scanning tunneling spectroscopy to results from room-temperature conductive atomic force spectroscopy on monolayer MoS 2 with sulfur vacancies and with varying hBN layers. We show that for thick hBN barrier layers, where tunneling currents into the conductive substrate are suppressed, a side-contact still enables addressing the defect states in the scanning tunneling microscopy via the lateral current flow. Few-layer hBN realizes an intermediate regime in which the competition between vertical tunneling and lateral transport needs to be considered. The latter is relevant for device structures with both a thin tunneling barrier and a side-contact to the semiconducting layers.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Imaging Genetic Molecules At Atomic Resolution

Proposed method of imaging informational polymeric biological molecules at atomic resolution enables determination of sequences of component monomers about 10 to the 3rd power to 10 to the 4th power times as fast as conventional methods do. Accelerates research on genetic structures of animals and plants. Also contributes significantly to imaging processes like scanning electron microscopy (SEM), atomic-force microscopy (AFM), and scanning tunneling microscopy (STM) in cases in which necessary to locate or identify small specimens on relatively large backgrounds and subtract background images to obtain images of specimens in isolation. V-grooves on silicon wafer laid out in square pattern, intersections of which marked to identify coordinates. Specimen molecules held in grooves for reproducible positioning and scanning by AFM or STM.

Coles, L. Stephen↗
NASA NTRS1997

Characterizing Surfaces of the Wide Bandgap Semiconductor Ilmenite with Scanning Probe Microcopies

Ilmenite (FeTiO3) is a wide bandgap semiconductor with an energy gap of about 2.5eV. Initial radiation studies indicate that ilmenite has properties suited for radiation tolerant applications, as well as a variety of other electronic applications. Two scanning probe microscopy methods have been used to characterize the surface of samples taken from Czochralski grown single crystals. The two methods, atomic force microscopy (AFM) and scanning tunneling microscopy (STM), are based on different physical principles and therefore provide different information about the samples. AFM provides a direct, three-dimensional image of the surface of the samples, while STM give a convolution of topographic and electronic properties of the surface. We will discuss the differences between the methods and present preliminary data of each method for ilmenite samples.

Wilkins, R.↗
DOE OSTI2025

Spectra-Orthogonal Optical Anisotropy in Wafer-Scale Molecular Crystal Monolayers

Controlling the spectral and polarization response of two-dimensional (2D) crystals is vital for developing ultrathin platforms for compact optoelectronic devices. However, independently tuning optical anisotropy and spectral response remains challenging in conventional semiconductors due to the intertwined nature of their lattice and electronic structures. Here, we report spectra-orthogonal optical anisotropy─where polarization anisotropy is tuned independently of spectral response─in wafer-scale, one-atom-thick 2D molecular crystal (2DMC) monolayers synthesized on monolayer transition-metal dichalcogenide (TMD) crystals. Utilizing the concomitant spectral consistency and structural tunability of perylene derivatives, we demonstrate tunable optical polarization anisotropy in 2DMCs with similar spectral profiles, as confirmed by room-temperature scanning tunneling microscopy and cross-polarized reflectance microscopy. Additional angle-dependent analysis of the single-crystal and polycrystalline molecular domains reveals an epitaxial relationship between the 2DMC and TMD. In conclusion, our results establish a scalable, molecule-based 2D crystalline platform for unique and tunable functionalities unattainable in covalent 2D solids.

2D materials↗