Showing papers on "Diamond published in 2019"

Conductive diamond: synthesis, properties, and electrochemical applications

Abstract: Conductive diamond possesses unique features as compared to other solid electrodes, such as a wide electrochemical potential window, a low and stable background current, relatively rapid rates of electron-transfer for soluble redox systems without conventional pretreatment, long-term responses, stability, biocompatibility, and a rich surface chemistry. Conductive diamond microcrystalline and nanocrystalline films, structures and particles have been prepared using a variety of approaches. Given these highly desirable attributes, conductive diamond has found extensive use as an enabling electrode across a variety of fields encompassing chemical and biochemical sensing, environmental degradation, electrosynthesis, electrocatalysis, and energy storage and conversion. This review provides an overview of the fundamental properties and highlights recent progress and achievements in the growth of boron-doped (metal-like) and nitrogen and phosphorus-doped (semi-conducting) diamond and hydrogen-terminated undoped diamond electrodes. Applications in electroanalysis, environmental degradation, electrosynthesis electrocatalysis, and electrochemical energy storage are also discussed. Diamond electrochemical devices utilizing micro-scale, ultramicro-scale, and nano-scale electrodes as well as their counterpart arrays are viewed. The challenges and future research directions of conductive diamond are discussed and outlined. This review will be important and informative for chemists, biochemists, physicists, materials scientists, and engineers engaged in the use of these novel forms of carbon.

Quantum nanophotonics with group IV defects in diamond.

Abstract: Diamond photonics is an ever-growing field of research driven by the prospects of harnessing diamond and its colour centres as suitable hardware for solid-state quantum applications. The last two decades have seen the field shaped by the nitrogen-vacancy (NV) centre with both breakthrough fundamental physics demonstrations and practical realizations. Recently however, an entire suite of other diamond defects has emerged—group IV colour centres—namely the Si-, Ge-, Sn- and Pb-vacancies. In this perspective, we highlight the leading techniques for engineering and characterizing these diamond defects, discuss the current state-of-the-art group IV-based devices and provide an outlook of the future directions the field is taking towards the realisation of solid-state quantum photonics with diamond. Diamond colour centres have applications in quantum sensing, quantum communication and other important technologies. Bradac et al. survey the progress made in using group IV defect centres, which are anticipated to have practical advantages over the more commonly-used nitrogen vacancy centres.

Ultra-long coherence times amongst room-temperature solid-state spins.

Abstract: Solid-state single spins are promising resources for quantum sensing, quantum-information processing and quantum networks, because they are compatible with scalable quantum-device engineering. However, the extension of their coherence times proves challenging. Although enrichment of the spin-zero 12C and 28Si isotopes drastically reduces spin-bath decoherence in diamond and silicon, the solid-state environment provides deleterious interactions between the electron spin and the remaining spins of its surrounding. Here we demonstrate, contrary to widespread belief, that an impurity-doped (phosphorus) n-type single-crystal diamond realises remarkably long spin-coherence times. Single electron spins show the longest inhomogeneous spin-dephasing time ( $$T_2^ \ast \approx 1.5$$ ms) and Hahn-echo spin-coherence time (T2 ≈ 2.4 ms) ever observed in room-temperature solid-state systems, leading to the best sensitivities. The extension of coherence times in diamond semiconductor may allow for new applications in quantum technology. The coherence times of nitrogen-vacancy centres are key factors influencing their performance in quantum applications. Here the authors show that synthesising phosphorus-doped diamond yields nitrogen-vacancy centres with significantly improved $$T_2^ \ast$$ and T2.

Ab initio theory of the nitrogen-vacancy center in diamond

Abstract: Abstract The nitrogen-vacancy (NV) center in diamond is a solid-state defect qubit with favorable coherence time up to room temperature, which could be harnessed in several quantum-enhanced sensor and quantum communication applications, and has a potential in quantum simulation and computing. The quantum control largely depends on the intricate details about the electronic structure and states of the NV center, the radiative and nonradiative rates between these states, and the coupling of these states to external spins, electric, magnetic, and strain fields, and temperature. This review shows how first-principles calculations contributed to understanding the properties of the NV center and briefly discusses the issues to be solved toward the full ab initio description of solid-state defect qubits.

Origins of Diamond Surface Noise Probed by Correlating Single-Spin Measurements with Surface Spectroscopy

Abstract: The nitrogen-vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing. NV centers near the surface can have strong interactions with external materials and spins, enabling new forms of nanoscale spectroscopy. However, NV spin coherence degrades within 100 nm of the surface, suggesting that diamond surfaces are plagued with ubiquitous defects. Prior work on characterizing near-surface noise has primarily relied on using NV centers themselves as probes; while this has the advantage of exquisite sensitivity, it provides only indirect information about the origin of the noise. Here we demonstrate that surface spectroscopy methods and single-spin measurements can be used as complementary diagnostics to understand sources of noise. We find that surface morphology is crucial for realizing reproducible chemical termination, and use this insight to achieve a highly ordered, oxygen-terminated surface with suppressed noise. We observe NV centers within 10 nm of the surface with coherence times extended by an order of magnitude.

High thermal conductivity in cubic boron arsenide crystals

Abstract: The high density of heat generated in power electronics and optoelectronic devices is a critical bottleneck in their application. New materials with high thermal conductivity are needed to effectively dissipate heat and thereby enable enhanced performance of power controls, solid-state lighting, communication, and security systems. We report the experimental discovery of high thermal conductivity at room temperature in cubic boron arsenide (BAs) grown through a modified chemical vapor transport technique. The thermal conductivity of BAs, 1000 ± 90 watts per meter per kelvin meter-kelvin, is higher than that of silicon carbide by a factor of 3 and is surpassed only by diamond and the basal-plane value of graphite. This work shows that BAs represents a class of ultrahigh-thermal conductivity materials predicted by a recent theory, and that it may constitute a useful thermal management material for high-power density electronic devices.

Photoelectrical imaging and coherent spin-state readout of single nitrogen-vacancy centers in diamond.

Abstract: Nitrogen-vacancy (NV) centers in diamond have become an important instrument for quantum sensing and quantum information science. However, the readout of NV spin state requires bulky optical setups, limiting fabrication of miniaturized compact devices for practical use. Here we realized photoelectrical detection of magnetic resonance as well as Rabi oscillations on a single-defect level. Furthermore, photoelectrical imaging of individual NV centers at room temperature was demonstrated, surpassing conventional optical readout methods by providing high imaging contrast and signal-to-noise ratio. These results pave the way toward fully integrated quantum diamond devices.

Principles and techniques of the quantum diamond microscope

Abstract: We provide an overview of the experimental techniques, measurement modalities, and diverse applications of the Quantum Diamond Microscope (QDM). The QDM employs a dense layer of fluorescent nitrogen-vacancy (NV) color centers near the surface of a transparent diamond chip on which a sample of interest is placed. NV electronic spins are coherently probed with microwaves and optically initialized and read out to provide spatially resolved maps of local magnetic fields. NV fluorescence is measured simultaneously across the diamond surface, resulting in a wide-field, two-dimensional magnetic field image with adjustable spatial pixel size set by the parameters of the imaging system. NV measurement protocols are tailored for imaging of broadband and narrowband fields, from DC to GHz frequencies. Here we summarize the physical principles common to diverse implementations of the QDM and review example applications of the technology in geoscience, biology, and materials science.

Reinforcement size dependence of mechanical properties and strengthening mechanisms in diamond reinforced titanium metal matrix composites

Abstract: Diamond particulates reinforced titanium matrix composites (TiMMCs) were fabricated by spark plasma sintering technique at different reinforcement sizes of 5, 100, 200 nm and 3 μm. The dependence of reinforcement size on the mechanical and tribological properties in the TiMMCs was studied, paying particular attention to the nanoscale effects. The enhancement in strength of the composites was elucidated on the basis of strengthening mechanisms characterized by load transfer, thermal mismatch, grain size, and Orowan strengthening. The strengthening mechanisms were quantitatively analyzed and evaluated as a function of particle size. The results revealed that the presence of 5 nm diamond particles enhance strength by interacting with dislocations, while simultaneously retarding grain growth. Although the micro-composite has a little higher strength than the nanodiamonds reinforced composite, the latter has a combination of high strength and high ductility as wells excellent tribological properties.

Diamond detectors for direct detection of sub-GeV dark matter

Abstract: We propose using high-purity lab-grown diamond crystal for the detection of sub–giga electron volt dark matter. Diamond targets can be sensitive to both nuclear and electron recoils from dark matter scattering in the mega-electron-volt and above mass range as well as to absorption processes of dark matter with masses between sub–electron volts to tens of electron volts. Compared to other proposed semiconducting targets such as germanium and silicon, diamond detectors can probe lower dark matter masses via nuclear recoils due to the lightness of the carbon nucleus. The expected reach for electron recoils is comparable to that of germanium and silicon, with the advantage that dark counts are expected to be under better control. Via absorption processes, unconstrained QCD axion parameter space can be successfully probed in diamond for masses of order 10 eV, further demonstrating the power of our approach.

Review Article: Synthesis, properties, and applications of fluorescent diamond particles.

Abstract: Diamond particles containing color centers—fluorescent crystallographic defects embedded within the diamond lattice—outperform other classes of fluorophores by providing a combination of unmatched photostability, intriguing coupled magneto-optical properties, intrinsic biocompatibility, and outstanding mechanical and chemical robustness. This exceptional combination of properties positions fluorescent diamond particles as unique fluorophores with emerging applications in a variety of fields, including bioimaging, ultrasensitive metrology at the nanoscale, fluorescent tags in industrial applications, and even potentially as magnetic resonance imaging contrast agents. However, production of fluorescent nanodiamond (FND) is nontrivial, since it requires irradiation with high-energy particles to displace carbon atoms and create vacancies—a primary constituent in the majority color centers. In this review, centrally focused on material developments, major steps of FND production are discussed with emphasis on current challenges in the field and possible solutions. The authors demonstrate how the combination of fluorescent spectroscopy and electron paramagnetic resonance provides valuable insight into the types of radiation-induced defects formed and their evolution upon thermal annealing, thereby guiding FND performance optimization. A recent breakthrough process allowing for production of fluorescent diamond particles with vibrant blue, green, and red fluorescence is also discussed. Finally, the authors conclude with demonstrations of a few FND applications in the life science arena and in industry.

3D macroporous boron-doped diamond electrode with interconnected liquid flow channels: A high-efficiency electrochemical degradation of RB-19 dye wastewater under low current

Abstract: Boron-doped diamond (BDD) has proved to be an ideal anode material for the electrolysis of organic sewage. However, the existing two dimensional BDD electrodes with small active area and low mass transfer rates, limit their further improvement in degradation efficiency. In this paper, a novel three dimensional macroporous BDD (3D-BDD) foam electrode with a structure of evenly distributed pores and interconnected networks in which wastewater can flow freely was prepared using a simple and reproducible method. Compared to two dimensional BDD electrodes of the same geometry, the electro-active surface area of 3D-BDD electrode increased by ˜20 times, and the electrochemical oxidation reaction rate constant of RB-19 increased by ˜350 times. Under optimized conditions, the energy consumption reduced to a minimum of 0.03 kWh(gTOC) −1, and the MCE reach a maximum of 325.86%.

Direct Bandgap Emission from Hexagonal Ge and SiGe Alloys

Abstract: Silicon crystallized in the usual cubic (diamond) lattice structure has dominated the electronics industry for more than half a century. However, cubic silicon (Si), germanium (Ge) and SiGe-alloys are all indirect bandgap semiconductors that cannot emit light efficiently. Accordingly, achieving efficient light emission from group-IV materials has been a holy grail in silicon technology for decades and, despite tremendous efforts, it has remained elusive. Here, we demonstrate efficient light emission from direct bandgap hexagonal Ge and SiGe alloys. We measure a subnanosecond, temperature-insensitive radiative recombination lifetime and observe a similar emission yield to direct bandgap III-V semiconductors. Moreover, we demonstrate how by controlling the composition of the hexagonal SiGe alloy, the emission wavelength can be continuously tuned in a broad range, while preserving a direct bandgap. Our experimental findings are shown to be in excellent quantitative agreement with the ab initio theory. Hexagonal SiGe embodies an ideal material system to fully unite electronic and optoelectronic functionalities on a single chip, opening the way towards novel device concepts and information processing technologies.

Coulomb-driven single defect engineering for scalable qubits and spin sensors in diamond

Abstract: Qubits based on colour centres in diamond became a prominent system for solid-state quantum information processing and sensing. But the deterministic creation of qubits and the control of their environment are still critical issues, preventing the development of a room-temperature quantum computer. We report on the high creation yield of NV centres of 75% (a tenfold enhancement) by charge-assisted defect engineering, together with an improvement of their spin coherence. The method strongly favours the formation and negative charge state of the NV centres with respect to intrinsic diamond, while it hinders the formation of competing and perturbing defects such as di-vacancies or NVH complexes. We evidence spectrally the charge state tuning of the implantation-induced vacancies from V0 to V-, key element of this Coulomb-driven engineering. The generality of the method is demonstrated using several donors (phosphorous, oxygen and sulphur) and applying it to other centres (SnV and MgV) in diamond.

Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield

Abstract: Atomic defects in wide-bandgap materials, such as the nitrogen-vacancy (NV) color center in diamond, show considerable promise for the development of a new generation of quantum information technologies, but progress has been hampered by the inability to produce and engineer the defects in a controlled manner. Here, we demonstrate an all-optical method for the deterministic writing of individual NV centers at selected locations with high positioning accuracy. Ultrashort pulse laser processing is used to both create and diffuse defects inside the crystal through local annealing. During the laser-annealing process, online fluorescence feedback provides a trigger to stop processing once the NV formation is detected. This method provides a new tool for the optical fabrication of engineered materials and devices for quantum technologies.

Principles and Techniques of the Quantum Diamond Microscope

Abstract: We provide an overview of the experimental techniques, measurement modalities, and diverse applications of the Quantum Diamond Microscope (QDM). The QDM employs a dense layer of fluorescent nitrogen-vacancy (NV) color centers near the surface of a transparent diamond chip on which a sample of interest is placed. NV electronic spins are coherently probed with microwaves and optically initialized and read out to provide spatially resolved maps of local magnetic fields. NV fluorescence is measured simultaneously across the diamond surface, resulting in a wide-field, two-dimensional magnetic field image with adjustable spatial pixel size set by the parameters of the imaging system. NV measurement protocols are tailored for imaging of broadband and narrowband fields, from DC to GHz frequencies. Here we summarize the physical principles common to diverse implementations of the QDM and review example applications of the technology in geoscience, biology, and materials science.

Optically coherent nitrogen-vacancy centers in micrometer-thin etched diamond membranes

Abstract: Diamond membrane devices containing optically coherent nitrogen-vacancy (NV) centers are key to enable novel cryogenic experiments such as optical ground-state cooling of hybrid spin-mechanical systems and efficient entanglement distribution in quantum networks. Here, we report on the fabrication of a (3.4 ± 0.2) μm thin, smooth (surface roughness rq < 0.4 nm over an area of 20 μm by 30 μm) diamond membrane containing individually resolvable, narrow linewidth (< 100 MHz) NV centers. We fabricate this sample via a combination of high-energy electron irradiation, high-temperature annealing, and an optimized etching sequence found via a systematic study of the diamond surface evolution on the microscopic level in different etch chemistries. Although our particular device dimensions are optimized for cavity-enhanced entanglement generation between distant NV centers in open, tunable microcavities, our results have implications for a broad range of quantum experiments that require the combination of narrow optical transitions and micrometer-scale device geometry.

Thermal conductance across β-Ga2O3-diamond van der Waals heterogeneous interfaces

Abstract: Because of its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt, β-Ga2O3 has attracted great attention recently for potential applications of power electronics. However, its thermal conductivity is significantly lower than those of other wide bandgap semiconductors, such as AlN, SiC, GaN, and diamond. To ensure reliable operation with minimal self-heating at high power, proper thermal management is even more essential for Ga2O3 devices. Similar to the past approaches aiming to alleviate self-heating in GaN high electron mobility transistors, a possible solution has been to integrate thin Ga2O3 membranes with diamond to fabricate Ga2O3-on-diamond lateral metal-semiconductor field-effect transistor or metal-oxide-semiconductor field-effect transistor devices by taking advantage of the ultra-high thermal conductivity of diamond. Even though the thermal boundary conductance (TBC) between wide bandgap semiconductor devices and a diamond substrate is of primary importance for heat dissipation in these devices, fundamental understanding of the Ga2O3-diamond thermal interface is still missing. In this work, we study the thermal transport across the interfaces of Ga2O3 exfoliated onto a single crystal diamond. The van der Waals bonded Ga2O3-diamond TBC is measured to be 17 −1.7/+2.0 MW/m2 K, which is comparable to the TBC of several physical-vapor-deposited metals on diamond. A Landauer approach is used to help understand phonon transport across a perfect Ga2O3-diamond interface, which in turn sheds light on the possible TBC one could achieve with an optimized interface. A reduced thermal conductivity of the Ga2O3 nano-membrane is also observed due to additional phonon-membrane boundary scattering. The impact of the Ga2O3–substrate TBC and substrate thermal conductivity on the thermal performance of a power device is modeled and discussed. Without loss of generality, this study is not only important for Ga2O3 power electronics applications which would not be realistic without a thermal management solution but also for the fundamental thermal science of heat transport across van der Waals bonded interfaces.

Evidence for Primal sp2 Defects at the Diamond Surface: Candidates for Electron Trapping and Noise Sources

Abstract: Many advanced applications of diamond materials are now being limited by unknown surface defects, including in the fields of high power/frequency electronics and quantum computing and quantum sensing Of acute interest to diamond researchers worldwide is the loss of quantum coherence in near-surface nitrogen-vacancy (NV) centers and the generation of associated magnetic noise at the diamond surface Here for the first time is presented the observation of a family of primal diamond surface defects, which is suggested as the leading cause of band-bending and Fermi-pinning phenomena in diamond devices A combination of density functional theory and synchrotron-based X-ray absorption spectroscopy is used to show that these defects introduce low-lying electronic trap states The effect of these states is modeled on band-bending into the diamond bulk and it is shown that the properties of the important NV defect centers are affected by these defects Due to the paramount importance of near-surface NV center properties in a growing number of fields, the density of these defects is further quantified at the surface of a variety of differently-treated device surfaces, consistent with best-practice processing techniques in the literature The identification and characterization of these defects has wide-ranging implications for diamond devices across many fields

Nanotesla sensitivity magnetic field sensing using a compact diamond nitrogen-vacancy magnetometer

Abstract: Solid state sensors utilizing diamond nitrogen-vacancy (NV) centers are a promising sensing platform that can provide high sensitivity and spatial resolution at high precision. Such sensors have been realized in bulky laboratory-based forms; however, practical applications demand a miniaturized, portable sensor that can function in a wide range of environmental conditions. Here, we demonstrate such a diamond NV magnetic field sensor. The sensor head fits inside a 11 × 7 × 7 cm 3 3D-printed box and exhibits sub-10 nT/ Hz sensitivity over a 125 Hz bandwidth. We achieve efficient fluorescence collection using an optical filter and diode in contact with the diamond, which is cut at the Brewster angle to maximize the coupling of 532 nm pump light. We discuss the potential of this flexible approach to achieve sub-nT/ Hz shot noise limited sensitivity suitable for detection of a wide range of low-level magnetic fields, particularly those from electrical power systems and from biological sources.

sp2/sp3 Framework from Diamond Nanocrystals: A Key Bridge of Carbonaceous Structure to Carbocatalysis

Abstract: Diamond nanocrystals in robust sp3 hybridization are appealing carbonaceous materials in the material community, whose structure can be transformed into unique sp2/sp3 nanohybrids as bulky nanodiam...

Optical coherence of diamond nitrogen-vacancy centers formed by ion implantation and annealing

Abstract: The advancement of quantum optical science and technology with solid-state emitters such as nitrogen-vacancy (NV) centers in diamond critically relies on the coherence of the emitters' optical transitions. A widely employed strategy to create NV centers at precisely controlled locations is nitrogen ion implantation followed by a high-temperature annealing process. We report on experimental data directly correlating the NV center optical coherence to the origin of the nitrogen atom. These studies reveal low-strain, narrow-optical-linewidth (l500 MHz) NV centers formed from naturally occurring N14 atoms. In contrast, NV centers formed from implanted N15 atoms exhibit significantly broadened optical transitions (g1 GHz) and higher strain. The data show that the poor optical coherence of the NV centers formed from implanted nitrogen is not due to an intrinsic effect related to the diamond or isotope. These results have immediate implications for the positioning accuracy of current NV center creation protocols and point to the need to further investigate the influence of lattice damage on the coherence of NV centers from implanted ions.

Lead-related quantum emitters in diamond

Abstract: We report on quantum emission from Pb-related color centers in diamond following ion implantation and high-temperature vacuum annealing. First-principles calculations predict a negatively charged Pb-vacancy (PbV) center in a split-vacancy configuration, with a zero-phonon transition around 2.4 eV. Cryogenic photoluminescence measurements performed on emitters in nanofabricated pillars reveal several transitions, including a prominent doublet near 520 nm. The splitting of this doublet, 5.7 THz, exceeds that reported for other group-IV centers. These observations are consistent with the PbV center, which is expected to have a combination of narrow optical transitions and stable spin states, making it a promising system for quantum network nodes.

Two-dimensional nuclear magnetic resonance spectroscopy with a microfluidic diamond quantum sensor.

Abstract: Quantum sensors based on nitrogen-vacancy centers in diamond have emerged as a promising detection modality for nuclear magnetic resonance (NMR) spectroscopy owing to their micrometer-scale detection volume and noninductive-based detection. A remaining challenge is to realize sufficiently high spectral resolution and concentration sensitivity for multidimensional NMR analysis of picoliter sample volumes. Here, we address this challenge by spatially separating the polarization and detection phases of the experiment in a microfluidic platform. We realize a spectral resolution of 0.65 ± 0.05 Hz, an order-of-magnitude improvement over previous diamond NMR studies. We use the platform to perform two-dimensional correlation spectroscopy of liquid analytes within an effective ∼40-picoliter detection volume. The use of diamond quantum sensors as in-line microfluidic NMR detectors is a major step toward applications in mass-limited chemical analysis and single-cell biology.

Inverse-designed diamond photonics.

Abstract: Diamond hosts optically active color centers with great promise in quantum computation, networking, and sensing. Realization of such applications is contingent upon the integration of color centers into photonic circuits. However, current diamond quantum optics experiments are restricted to single devices and few quantum emitters because fabrication constraints limit device functionalities, thus precluding color center integrated photonic circuits. In this work, we utilize inverse design methods to overcome constraints of cutting-edge diamond nanofabrication methods and fabricate compact and robust diamond devices with unique specifications. Our design method leverages advanced optimization techniques to search the full parameter space for fabricable device designs. We experimentally demonstrate inverse-designed photonic free-space interfaces as well as their scalable integration with two vastly different devices: classical photonic crystal cavities and inverse-designed waveguide-splitters. The multi-device integration capability and performance of our inverse-designed diamond platform represents a critical advancement toward integrated diamond quantum optical circuits.

Approaching diamond's theoretical elasticity and strength limits.

Abstract: Diamond is the hardest natural material, but its practical strength is low and its elastic deformability extremely limited. While recent experiments have demonstrated that diamond nanoneedles can sustain exceptionally large elastic tensile strains with high tensile strengths, the size- and orientation-dependence of these properties remains unknown. Here we report maximum achievable tensile strain and strength of diamond nanoneedles with various diameters, oriented in , and -directions, using in situ transmission electron microscopy. We show that reversible elastic deformation depends both on nanoneedle diameter and orientation. -oriented nanoneedles with a diameter of 60 nm exhibit highest elastic tensile strain (13.4%) and tensile strength (125 GPa). These values are comparable with the theoretical elasticity and Griffith strength limits of diamond, respectively. Our experimental data, together with first principles simulations, indicate that maximum achievable elastic strain and strength are primarily determined by surface conditions of the nanoneedles. While diamond is the strongest natural material, it fails to reach its theoretical elasticity limits and is brittle. Here, the authors show that thin -orientated diamond nanoneedles can reach diamond’s theoretical strength and elasticity limits in tension.

Phonon hydrodynamics and ultrahigh-room-temperature thermal conductivity in thin graphite

Abstract: Allotropes of carbon, such as diamond and graphene, are among the best conductors of heat. We monitored the evolution of thermal conductivity in thin graphite as a function of temperature and thickness and found an intimate link between high conductivity, thickness, and phonon hydrodynamics. The room temperature in-plane thermal conductivity of 8.5-micrometer-thick graphite was 4300 watts per meter-kelvin-a value well above that for diamond and slightly larger than in isotopically purified graphene. Warming enhances thermal diffusivity across a wide temperature range, supporting partially hydrodynamic phonon flow. The enhancement of thermal conductivity that we observed with decreasing thickness points to a correlation between the out-of-plane momentum of phonons and the fraction of momentum relaxing collisions. We argue that this is due to the extreme phonon dispersion anisotropy in graphite.

Quantum diamond spectrometer for nanoscale NMR and ESR spectroscopy.

Abstract: Nitrogen-vacancy (NV) quantum defects in diamond are sensitive detectors of magnetic fields. Owing to their atomic size and optical readout capability, they have been used for magnetic resonance spectroscopy of nanoscale samples on diamond surfaces. Here, we present a protocol for fabricating NV diamond chips and for constructing and operating a simple, low-cost 'quantum diamond spectrometer' for performing NMR and electron spin resonance (ESR) spectroscopy in nanoscale volumes. The instrument is based on a commercially available diamond chip, into which an NV ensemble is ion-implanted at a depth of ~10 nm below the diamond surface. The spectrometer operates at low magnetic fields (~300 G) and requires standard optical and microwave (MW) components for NV spin preparation, manipulation, and readout. We demonstrate the utility of this device for nanoscale proton and fluorine NMR spectroscopy, as well as for the detection of transition metals via relaxometry. We estimate that the full protocol requires 2-3 months to implement, depending on the availability of equipment, diamond substrates, and user experience.