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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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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Diamond magnetometer enhanced by ferrite flux concentrators

Magnetometers based on nitrogen-vacancy (NV) centers in diamond are promising room-temperature, solid-state sensors. However, their reported sensitivity to magnetic fields at low frequencies (≲1 kHz) is presently ≳10 pTs 1/2 , precluding potential applications in medical imaging, geoscience, and navigation. Here we show that high-permeability magnetic flux concentrators, which collect magnetic flux from a larger area and concentrate it into the diamond sensor, can be used to improve the sensitivity of diamond magnetometers. By inserting an NV-doped diamond membrane between two ferrite cones in a bowtie configuration, we realize a ~ 250-fold increase of the magnetic field amplitude within the diamond. We demonstrate a sensitivity of ~ 0.9pTs 1/2 to magnetic fields in the frequency range between 10 and 1000 Hz. This is accomplished using a dual-resonance modulation technique to suppress the effect of thermal shifts of the NV spin levels. The magnetometer uses 200 mW of laser power and 20 mW of microwave power. This work introduces a new degree of freedom for the design of diamond sensors by using structured magnetic materials to manipulate magnetic fields.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Electrical and Thermal Performance of Ga₂O₃–Al₂O₃–Diamond Super-Junction Schottky Barrier Diodes

The design space of Ga 2 O 3 -based devices is severely constrained due to its low thermal conductivity and absence of viable p-type dopants. In this work, we discuss the limits of operation of a novel Ga 2 O 3 –Al 2 O 3 –diamond-based super-junction device concept, which can alleviate the constraints associated with Ga 2 O 3 -based devices. The improvements achieved using the proposed device concept are demonstrated through electrical and thermal simulations of Ga 2 O 3 –Al 2 O 3 –diamond-based super-junction Schottky barrier diodes (SJ-SBDs) and non-punch-through or conventional Schottky barrier diodes (NP-SBDs). The SJ-SBD enables operation below the R ON -breakdown voltage limit of Ga 2 O 3 NP-SBD, enabling >4 kV blocking voltage at R ON of 1–3 mΩ cm 2 . Here, the maximum switching frequency of SJ-SBD may be only a few kHz, as it is limited by the activation energy of acceptors (0.39 eV) in the diamond. Crucially, compared with NP-SBD, the use of diamond also results in ~60% reduction in temperature rise during static power dissipation. Polycrystalline diamond (PCD) properties depend on detailed microstructure and benefits compared to ideal Ga 2 O 3</sub NP-SBD arise for diamond critical fields ≥6 MV/cm and thermal conductivities as low as 50–150 W/(m • K).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Photonic devices fabricated from (111)‐oriented single crystal diamond

Abstract Diamond is a material of choice in the pursuit of integrated quantum photonic technologies. So far, the majority of photonic devices fabricated from diamond are made from (100)‐oriented crystals. In this work, we demonstrate a methodology for the fabrication of optically active membranes from (111)‐oriented diamond. We use a liftoff technique to generate membranes, followed by chemical vapor deposition of diamond in the presence of silicon to generate homogenous silicon vacancy color centers with emission properties that are superior to those in (100)‐oriented diamond. We further use the diamond membranes to fabricate microring resonators with quality factors exceeding ~ 3000. Supported by finite‐difference time‐domain calculations, we discuss the advantages of (111)‐oriented structures as building blocks for quantum nanophotonic devices. image

Regan, Blake↗
DOE OSTI2020

A Revisited Mechanism of the Graphite-to-Diamond Transition at High Temperature

The graphite-diamond transition, under high-pressure and high-temperature conditions, has been a central subject in physical science. However, its atomistic mechanism remains under debate. Employing large-scale molecular dynamics (MD) simulations, we report a mechanism whereby the diamond nuclei in the graphite matrix propagate in two preferred directions, among which the graphite [120] is about 2.5 times faster than [001]. Consequently, cubic diamond (CD) is the kinetically favorable product, while only a few hexagonal diamonds (HDs) can exist as the twins of CDs. The coherent interface of t-(100)gr//(11-1)cd + [010]gr//[1-10]cd observed in MD simulation was confirmed by our high-resolution transmission electron microscopy experiment. This proposed mechanism not only clarifies the role of HD in graphite-diamond transition but also yields atomistic insight into strengthening synthetic diamond via microstructure engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Electronic Spin Relaxation and Clustering in High-Pressure High-Temperature Synthesized Microcrystalline Diamond Particles with Reduced Nitrogen Content

The negatively charged nitrogen-vacancy (NV – ) color center in diamonds is widely studied because of numerous applications of this unique quantum system in sensing and quantum information sciences. While substitutional nitrogen is required to form the NV – centers in diamond, it also yields other paramagnetic defects─primarily the neutrally charged substitutional nitrogen centers (P1)─that decrease NV – spin coherence, which in turn degrades performance in applications. Herein, we investigate high-pressure high-temperature synthesized diamond microparticles (ca. 140–185 μm) having lower─ranging from 3 to 38 ppm─than the typical nitrogen content of type 1b diamond ( ca. 100 ppm and higher) typically used for the production of fluorescent diamond particles with NV – centers. A suite of electron paramagnetic resonance, optically detected magnetic resonance, and nuclear magnetic resonance methods are used to characterize spin properties of P1 and NV – centers in the particles. Upon decreasing the nitrogen content from 29 to 3 ppm, the ensemble NV – T 2 relaxation time increased by about 3-fold as measured directly in the Hahn Echo experiment at magnetic field of 1.2 T. Analysis of electronic relaxation of P1 centers revealed the existence of at least two distinct populations of P1 centers, consisting of fast and slower relaxing spins and allowed for an estimation of local concentrations. Even with <10 ppm nitrogen contents, the analysis indicated a highly heterogeneous distribution of P1 centers, suggesting the possibility of P1 spin clustering even at low nitrogen concentrations. The combined data demonstrate that the particles prepared from HPHT diamond with a low nitrogen content offer improved spin properties that are beneficial for NV – sensing applications.

Carbon↗
DOE OSTI2024

Improving the creation of SiV centers in diamond via sub-μs pulsed annealing treatment

Silicon-vacancy (SiV) centers in diamond are emerging as promising quantum emitters in applications such as quantum communication and quantum information processing. Here, we demonstrate a sub-μs pulsed annealing treatment that dramatically increases the photoluminescence of SiV centers in diamond. Using a silane-functionalized adamantane precursor and a laser- heated diamond anvil cell, the temperature and energy conditions required to form SiV centers in diamond were mapped out via an optical thermometry system with an accuracy of ±50 K and a 1 μs temporal resolution. Annealing scheme studies reveal that pulsed annealing can obviously minimize the migration of SiV centers out of the diamond lattice, and a 2.5-fold increase in the number of emitting centers was achieved using a series of 200-ns pulses at a 50 kHz repetition rate via acousto-optic modulation. Our study provides a novel pulsed annealing treatment approach to improve the efficiency of the creation of SiV centers in diamond.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Metastability and Ostwald step rule in the crystallisation of diamond and graphite from molten carbon

Abstract Experimental challenges in determining the phase diagram of carbon at temperatures and pressures near the graphite-diamond-liquid triple point are often related to the persistence of metastable crystalline or glassy phases, superheated crystals, or supercooled liquids. A deeper understanding of the crystallisation kinetics of diamond and graphite is crucial for effectively interpreting the outcomes of these experiments. Here, we reveal the microscopic mechanisms of diamond and graphite nucleation from liquid carbon through molecular simulations with first-principles machine learning potentials. Our simulations accurately reproduce the experimental phase diagram of carbon near the triple point and show that liquid carbon crystallises spontaneously upon cooling. Metastable graphite crystallises in the domain of diamond thermodynamic stability at pressures above the triple point. Furthermore, whereas diamond crystallises through a classical nucleation pathway, graphite follows a two-step process in which low-density fluctuations forego ordering. Calculations of the nucleation rates of the two competing phases confirm this result and reveal a manifestation of Ostwald’s step rule, where the strong metastability of graphite hinders the transformation to the stable diamond phase. Our results provide a key to interpreting melting and recrystallisation experiments and shed light on nucleation kinetics in polymorphic materials with deep metastable states.

Science & Technology - Other Topics↗
DOE OSTI2023

Probing itinerant carrier dynamics at the diamond surface using single nitrogen vacancy centers

Color centers in diamond are widely explored for applications in quantum sensing, computing, and networking. Their optical, spin, and charge properties have extensively been studied, while their interactions with itinerant carriers are relatively unexplored. Here, we show that NV centers situated 10 ± 5 nm of the diamond surface can be converted to the neutral charge state via hole capture. By measuring the hole capture rate, we extract the capture cross section, which is suppressed by proximity to the diamond surface. The distance dependence is consistent with a carrier diffusion model, indicating that the itinerant carrier lifetime can be long, even at the diamond surface. Measuring dynamics of near-surface NV centers offers a tool for characterizing the diamond surface and investigating charge transport in diamond devices.

Physics↗
DOE OSTI2026

Plasma-assisted atomic layer etching of single-crystal diamond

Applications of near-surface nitrogen-vacancy (NV) centers in diamond are often limited by surface defects created during processing. Understanding and controlling plasma-induced surface damage is important for preserving the optical and spin properties of diamond NV centers. We report molecular dynamics simulations of a novel form of plasma-aided atomic layer etching of diamond. In this proposed scheme, the initial surface modification step consists of Ar + ion bombardment. This creates an amorphous layer at the surface, the thickness of which is controlled by the ion energy. Amorphization is known to help smooth the surface, at least locally, and would also serve to sputter clean an initially contaminated surface. A second step impacts the amorphous carbon layer with O + between about 1 and 5 eV. Simulations show that this energy range will remove the amorphous carbon but will not etch the underlying diamond. Though this energy range is not trivial to achieve in a conventional low-temperature plasma, potential methods for creating these low-energy O + ions are discussed. In addition to a-C etching, the O + impacts are predicted to remove any isolated (100) diamond terraces by selectively attacking the edges of the terraces. The proposed atomic layer etching (ALE) approach reverses the conventional ALE sequence in which the surface modification step is usually chemical modification (oxidation in this case), followed by a removal step using Ar + impacts. This plasma ALE procedure is predicted to create a diamond surface that is atomically flat and defect free.

Draney, J. S. [Princeton University, NJ (United St↗
DOE OSTI2023

Imaging of the electronic bonding of diamond at pressures up to 2 million atmospheres

Diamond shows unprecedented hardness. Because hardness is a measure of resistance of chemical bonds in a material to external indentation, the electronic bonding nature of diamond beyond several million atmospheres is key to understanding the origin of hardness. However, probing the electronic structures of diamond at such extreme pressure has not been experimentally possible. The measurements on the inelastic x-ray scattering spectra for diamond up to 2 million atmospheres provide data on the evolution of its electronic structures under compression. The mapping of the observed electronic density of states allows us to obtain a two-dimensional image of the bonding transitions of diamond undergoing deformation. The spectral change near edge onset is minor beyond a million atmospheres, while its electronic structure displays marked pressure-induced electron delocalization. Such electronic responses indicate that diamond’s external rigidity is supported by its ability to reconcile internal stress, providing insights into the origins of hardness in materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Emergence of quantum-field theory in causal diamonds

The experimental successes of quantum-field theory do not justify using it to describe even a finite fraction of the entanglement entropy of a causal diamond with its exterior, in the limit of large diamonds. Susskind and Uglum and Jacobson conjectured that this divergent entropy could be thought of as a renormalization of Newton’s constant in the Bekenstein–Hawking formula, if we applied that formula to arbitrary causal diamonds. Jacobson showed that this leads to a derivation of the null projection of Einstein’s equations as the hydrodynamic equations of the area law for arbitrary diamonds, a derivation which has the added virtue of demonstrating that the cosmological constant is not an energy density. Using a gauge choice adapted to causal diamond boundaries, we revisit arguments of Carlip and Solodukhin that the proper theory of near horizon states is a (cut-off) (1 + 1)-dimensional conformal field theory, with central charge proportional to the transverse area. This leads to a universal formula for fluctuations of the modular Hamiltonian of a diamond, which we argue is compatible with the explanation of the temperature of de Sitter space in terms of an identification between localized energy and the number of constrained q-bits of the holographic degrees of freedom.

Astronomy & Astrophysics↗
DOE OSTI2022

High-resolution magnetic field fingerprinting of integrated circuit activity with a quantum diamond microscope

Devices for determining a state of a magnetic field-generating article are provided. In various embodiments, a device comprises: a single crystal diamond having a plurality of NV centers, the single crystal diamond configured to be disposed adjacent to a magnetic field-generating article, and configured to generate a fluorescent signal in response to being illuminated by a light source; a coherent light source configured to generate a light beam directed at the single crystal diamond; a microwave (MW) radiation source configured to irradiate the single crystal diamond with a MW signal; a magnetic field source configured to apply a bias magnetic field to the single crystal diamond; a photosensor configured to collect the fluorescent signal generated by the single crystal diamond; and a computing node operatively coupled to each of the coherent light source, the MW radiation source, the magnetic field source, and the photosensor.

Turner, Matthew James↗
DOE OSTI2021

Direct current response of a thin scCVD diamond detector under increased applied field to 14.1 MeV neutrons

An avalanche effect yielding inherent gain can be exploited in thin, single-crystal chemical vapor deposition (scCVD) diamond. It occurs when a high enough bias is applied across the diamond thickness while avoiding breakdown. This charge multiplication effect was studied previously with alpha particles and heavy ions either by using the transient current technique or by measuring the energy spectrum. The measurements we obtained to evaluate the charge multiplication performance of a 10 μm thick scCVD diamond detector used a novel approach—we employed an electrometer to characterize the response of the detector by performing directly coupled current measurements (time-averaged charge, at 1 Hz sampling) when exposed to 14.1 MeV neutrons from deuterium-tritium fusion. We measured both the dark and irradiated currents from the detector over a range of applied displacement field values from 2 to 75 V/μm. A histogram method with central mean and standard deviation width was used to determine the current over each measurement duration typically from 100 to 300 seconds. The dark-subtracted irradiated current (i.e., contrast) was used to evaluate the gain of the detector at each applied displacement field. The contrast at an applied displacement field between 15 and 20 V/μm was higher than the expected linear increase in contrast proportional to the increased applied bias, indicating the possible presence of avalanche events in the diamond. The detector response also indicated possible polarization and charge depletion effects. These results provide an opportunity to further explore the use of thin scCVD diamond as a fast neutron current mode detector with inherent gain.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Methods for Color Center Preserving Hydrogen‐Termination of Diamond

Abstract Chemical functionalization of diamond surfaces by hydrogen is an important method for controlling the charge state of near‐surface fluorescent color centers, an essential process in fabricating devices such as diamond field‐effect transistors and chemical sensors, and a required first step for realizing families of more complex terminations through subsequent chemical processing. In all these cases, termination is typically achieved using hydrogen plasma sources that can etch or damage the diamond, as well as deposited materials or embedded color centers. This work explores alternative methods for lower‐damage hydrogenation of diamond surfaces, specifically the annealing of diamond samples in high‐purity, non‐explosive mixtures of nitrogen and hydrogen gas, and the exposure of samples to microwave hydrogen plasmas in the absence of intentional stage heating. The effectiveness of these methods are characterized by x‐ray photoelectron spectroscopy (XPS), and comparison of the results to density‐functional modelling of the surface hydrogenation energetics implicates surface oxygen ligands as the primary factor limiting the termination quality of annealed samples. Finally, photoluminescence (PL) spectroscopy is used to verify that both the annealing and reduced sample temperature plasma methods are non‐destructive to near‐surface ensembles of nitrogen‐vacancy (NV) centers, in stark contrast to plasma treatments that use heated sample stages.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Physical Modeling and Design of a Nonvolatile Optically Gated High‐Power Diamond Transistor

In this work, we present the theory and modeling framework of a diamond optically gated junction field‐effect transistor (DOGFET). The device utilizes nitrogen substitutional centers in type‐1b diamond to optically modulate a p‐ boron doped diamond channel. Using sub‐gap lasers with intensities as low as 100 W/cm 2 , electrons are optically excited from substitutional nitrogen sites to the conduction band of the diamond substrate, thus enabling the optical gate to exercise control on modulating the space‐charge region at the junction and therefore the channel conductivity. We show that the device can deliver a current of 7 μA/μm, or equivalently 1750 A/cm 2 , while switching at a frequency greater than 100 kHz, in a form factor of 5 μm 2 . The breakdown voltage is found to be greater than 1850 V, with a breakdown field strength of ~13 MV/cm. Moreover, the device supports nonvolatile operation with a “memory effect” enabling single transistor state retention. The presented simulation framework provides a physically grounded insight into the limits and opportunities of optoelectronic diamond systems.

Engineering - Electronic and electrical engineerin↗
DOE OSTI2020

Ultra-high aspect ratio pores milled in diamond via laser, ion and electron beam mediated processes

Microfabrication techniques are critical for the rapid prototyping and development of applications for cutting edge materials. Recently diamond has gained considerable interest for quantum photonic, biosensing, inertial confinement fusion and magnetometer applications. In this article, ultra-high aspect ratio milling of diamond micropores by photon, ion and electron based methods is reported. A multiphoton absorption laser ablation approach is revealed to rapidly produce sub-10 μm diameter micropores in diamond with an aspect ratio of 14:1 and a tapered profile at the surface interface. Chemically active, oxygen focused ion beam milling produces high-aspect ratio pores in diamond with an aspect ratio of 65:1 and minimal tapering over the length of the pore, overcoming the physical interaction volume limitations imposed in conventional gallium based focused ion beam milling and laser ablation methods. Oxygen-mediated electron beam induced etching is revealed to negate the limitations imposed by physical sputtering mechanisms utilized in focused ion beam milling via the direct initiation of chemical reactions at the receding surface, producing aspect ratios on the order of 200:1. Numerical simulations reveal the physical basis for the superior aspect-ratio pore milling of the oxygen focused ion beam milling and electron beam induced etching methods. Our results demonstrate direct-write methods for the fabrication of ultra-high aspect micropores in diamond and provide insight into the underlying mechanisms of these physical processes. The three methods demonstrated here can be interchanged for applications based on the desired characteristic aspect ratio and process throughput.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Scintillation properties of diamond powders and feasibility of using them in thermal neutron detectors

Diamond offers unique properties for radiation detection, including high radiation hardness, very low gamma sensitivity, and fast response. Conventional diamond detectors rely on charge collection, but this approach requires ultra-pure single crystals and suffers from radiation-induced degradation. Here, in this work, we demonstrate an alternative approach using diamonds as scintillators for detection of charged particles and thermal neutrons. Prototypes were fabricated from commercially available diamond powders bonded to glass substrates and coupled with 6 LiF converters and silicon photomultipliers (SiPMs) and conventional PMTs. We characterized their scintillation properties under alpha particle excitation, x-ray photoluminescence, and thermal neutrons. The tryout detectors exhibit strong scintillation light signals, nanosecond-scale response times, and neutron detection efficiencies up to approximately 14 %, evaluated by comparison to conventional 3 He detector with known efficiency. These results demonstrate the feasibility of cost-effective, lightweight and robust diamond scintillation detectors for applications in space and planetary science, nuclear security, safeguards and environmental monitoring requiring efficient, robust, gamma-blind neutron detectors.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Record-Low Thermal Boundary Resistance between Diamond and GaN-on-SiC for Enabling Radiofrequency Device Cooling

The implementation of 5G-and-beyond networks requires faster, high-performance, and power-efficient semiconductor devices, which are only possible with materials that can support higher frequencies. Gallium nitride (GaN) power amplifiers are essential for 5G-and-beyond technologies since they provide the desired combination of high frequency and high power. These applications along with terrestrial hub and backhaul communications at high power output can present severe heat removal challenges. The cooling of GaN devices with diamond as the heat spreader has gained significant momentum since device self-heating limits GaN’s performance. However, one of the significant challenges in integrating polycrystalline diamond on GaN devices is maintaining the device performance while achieving a low diamond/GaN channel thermal boundary resistance. In this study, we achieved a record-low thermal boundary resistance of around 3.1 ± 0.7 m 2 K/GW at the diamond/Si 3 N 4 /GaN interface, which is the closest to theoretical prediction to date. The diamond was integrated within ~1 nm of the GaN channel layer without degrading the channel’s electrical behavior. Furthermore, we successfully minimized the residual stress in the diamond layer, enabling more isotropic polycrystalline diamond growth on GaN with thicknesses >2 μm and a ~1.9 μm lateral grain size. More isotropic grains can spread the heat in both vertical and lateral directions efficiently. Using transient thermoreflectance, the thermal conductivity of the grains was measured to be 638 ± 48 W/m K, which when combined with the record-low thermal boundary resistance makes it a leading-edge achievement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗