Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DIAMONDS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Alignment of the diamond nitrogen vacancy center by strain engineering

The nitrogen vacancy (NV) center in diamond is a sensitive probe of magnetic field and a promising qubit candidate for quantum information processing. The performance of many NV-based devices improves by aligning the NV(s) parallel to a single crystallographic direction. Using ab initio theoretical techniques, we show that NV orientation can be controlled by high-temperature annealing in the presence of strain under currently accessible experimental conditions. We find that (89 ± 7)% of NVs align along the [111] crystallographic direction under 2% compressive biaxial strain (perpendicular to [111]) and an annealing temperature of 970 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Polarization dependent asymmetric magneto-resistance features in nanocrystalline diamond films

Polar angle-dependence of magneto-resistance (AMR) in heavily nitrogen-incorporated ultra-nanocrystalline diamond (UNCD) films is recorded by applying high magnetic fields, which shows strong anisotropic features at low temperatures. The temperature-dependence of MR and AMR can reveal transport in the weak-localization regime, which is explained by using a superlattice model for arbitrary values of disorder and angles. While a propagative Fermi surface model explains the negative MR features for low degree of disorder the azimuthal angle-dependent MR shows field dependent anisotropy due to the aligned conducting channels on the layers normal to film growth direction. The analysis of MR and AMR can extract the temperature dependence of dephasing time with respect to the elastic scattering time which not only establishes quasi-two dimensional features in this system but also suggests a potential application in monitoring the performance of UNCD based quantum devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Relationship between the structure and electrical characteristics of diamond-like carbon films

To elucidate the relationship between the structure and the electrical characteristics of diamond-like carbon (DLC) films, DLC films were synthesized in a well-controlled glow discharge with the aid of photoelectrons in an argon/methane atmosphere. The dielectric constant and breakdown strength of the films exhibited opposite behaviors, depending on the total pressure during the synthesis. The product of these two values decreased monotonically as the pressure increased. The Raman spectra were analyzed with a Voigt-type formula. Based on the results, the authors propose the “sp{sup 2} cluster model” for the DLC structure. This model consists of conductive clusters of sp{sup 2} carbons surrounded by a dielectric matrix sea of sp{sup 2} carbon, sp{sup 3} carbon, and hydrogen, and indicates that the dielectric constant of the whole DLC film is determined by the balance between the dielectric constant of the matrix and the total size of the clusters, while the breakdown strength is determined by the reciprocal of the cluster size. The model suggests that a high-κ DLC film can be synthesized at a middle pressure and consists of well-grown sp{sup 2} clusters and a dense matrix. A low-κ DLC film can be synthesized both at low and high pressures. The sp{sup 2} cluster model explains that a low-κ DLC film synthesized at low pressure consists of a dense matrix and a low density of sp{sup 2} clusters, and exhibits a high breakdown strength. On the other hand, a low-κ film synthesized at high pressure consists of a coarse matrix and a high density of clusters and exhibits a low breakdown strength.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Addressing a single spin in diamond with a macroscopic dielectric microwave cavity

We present a technique for addressing single nitrogen-vacancy (NV) center spins in diamond over macroscopic distances using a tunable dielectric microwave cavity. We demonstrate optically detected magnetic resonance (ODMR) for a single negatively charged NV center (NV{sup –}) in a nanodiamond (ND) located directly under the macroscopic microwave cavity. By moving the cavity relative to the ND, we record the ODMR signal as a function of position, mapping out the distribution of the cavity magnetic field along one axis. In addition, we argue that our system could be used to determine the orientation of the NV{sup –} major axis in a straightforward manner.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Local impedance imaging of boron-doped polycrystalline diamond thin films

Local impedance imaging (LII) was used to visualise surficial deviations of AC impedances in polycrystalline boron-doped diamond (BDD). The BDD thin film electrodes were deposited onto the highly doped silicon substrates via microwave plasma-enhanced CVD. The studied boron dopant concentrations, controlled by the [B]/[C] ratio in plasma, ranged from 1 × 10{sup 16} to 2 × 10{sup 21} atoms cm{sup −3}. The BDD films displayed microcrystalline structure, while the average size of crystallites decreased from 1 to 0.7 μm with increasing [B]/[C] ratios. The application of LII enabled a direct and high-resolution investigation of local distribution of impedance characteristics within the individual grains of BDD. Such an approach resulted in greater understanding of the microstructural control of properties at the grain level. We propose that the obtained surficial variation of impedance is correlated to the areas of high conductance which have been observed at the grain boundaries by using LII. We also postulate that the origin of high conductivity is due to either preferential boron accumulation, the presence of defects, or sp{sup 2} regions in the intragrain regions. The impedance modulus recorded by LII was in full agreement with the bulk impedance measurements. Both variables showed a decreasing trend with increasing [B]/[C] ratios, which is consistent with higher boron incorporation into BDD film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Critical boron-doping levels for generation of dislocations in synthetic diamond

Defects induced by boron doping in diamond layers were studied by transmission electron microscopy. The existence of a critical boron doping level above which defects are generated is reported. This level is found to be dependent on the CH{sub 4}/H{sub 2} molar ratios and on growth directions. The critical boron concentration lied in the 6.5–17.0 × 10{sup 20}at/cm{sup 3} range in the 〈111〉 direction and at 3.2 × 10{sup 21 }at/cm{sup 3} for the 〈001〉 one. Strain related effects induced by the doping are shown not to be responsible. From the location of dislocations and their Burger vectors, a model is proposed, together with their generation mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Study of narrowband single photon emitters in polycrystalline diamond films

Quantum information processing and integrated nanophotonics require robust generation of single photon emitters on demand. In this work, we demonstrate that diamond films grown on a silicon substrate by microwave plasma chemical vapor deposition can host bright, narrowband single photon emitters in the visible—near infra-red spectral range. The emitters possess fast lifetime (∼several ns), absolute photostability, and exhibit full polarization at excitation and emission. Pulsed and continuous laser excitations confirm their quantum behaviour at room temperature, while low temperature spectroscopy is performed to investigate inhomogeneous broadening. Our results advance the knowledge of solid state single photon sources and open pathways for their practical implementation in quantum communication and quantum information processing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The microstructural evolution of ultrananocrystalline diamond films due to P ion implantation process—the annealing effect

The microstructural evolution of UNCD films which are P-ion implanted and annealed at 600 °C (or 800 °C) is systematically investigated. The difference of interaction that the UNCD content undergoes along the trajectory of the incident P-ions is reflected in the alteration of the granular structure. In regions where the P-ions reside, the “interacting zone,” which is found at about 300 nm beneath the surface of the films, coalescence of diamond grains occurs inducing nano-graphitic clusters. The annealing at 600 °C (or 800 °C) heals the defects and, in some cases, forms interconnected graphitic filaments that result in the decrease in surface resistance. However, the annealing at 600 °C (800 °C) induces marked UNCD-to-Si layers interaction. This interaction due to the annealing processes hinders the electron transport across the interface and degrades the electron field emission properties of the UNCD films. These microstructural evolution processes very well account for the phenomenon elaborating that, in spite of enhanced conductivity of the UNCD films along the film's surface due to the P-ion implantation and annealing processes, the electron field emission properties for these UNCD films do not improve.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Fabrication of triangular nanobeam waveguide networks in bulk diamond using single-crystal silicon hard masks

A scalable approach for integrated photonic networks in single-crystal diamond using triangular etching of bulk samples is presented. We describe designs of high quality factor (Q = 2.51 × 10{sup 6}) photonic crystal cavities with low mode volume (V{sub m} = 1.062 × (λ/n){sup 3}), which are connected via waveguides supported by suspension structures with predicted transmission loss of only 0.05 dB. We demonstrate the fabrication of these structures using transferred single-crystal silicon hard masks and angular dry etching, yielding photonic crystal cavities in the visible spectrum with measured quality factors in excess of Q = 3 × 10{sup 3}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Recursive polarization of nuclear spins in diamond at arbitrary magnetic fields

We introduce an alternate route to dynamically polarize the nuclear spin host of nitrogen-vacancy (NV) centers in diamond. Our approach articulates optical, microwave, and radio-frequency pulses to recursively transfer spin polarization from the NV electronic spin. Using two complementary variants of the same underlying principle, we demonstrate nitrogen nuclear spin initialization approaching 80% at room temperature both in ensemble and single NV centers. Unlike existing schemes, our approach does not rely on level anti-crossings and is thus applicable at arbitrary magnetic fields. This versatility should prove useful in applications ranging from nanoscale metrology to sensitivity-enhanced NMR.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

X-ray imaging of subsurface dynamics in high-Z materials at the Diamond Light Source

In this paper, we describe a new approach enabling study of subsurface dynamics in high-Z materials using the unique combination of high-energy synchrotron X-rays, a hybrid bunch structure, and a new dynamic loading platform. We detail the design and operation of the purpose-built, portable small bore gas-gun, which was installed on the I12 high-energy beamline at the Diamond Light Source and used to drive compression waves into solid and porous metal targets. Using a hybrid bunch structure and broadband X-ray pulses of up to 300 keV, radiographic snapshots were captured during various dynamic deformation processes in cm-scale specimens, thereby contributing to a more complete understanding of the evolution of mesoscale damage. Importantly, we highlight strategies for overcoming the challenges associated with using high-energy X-rays, and suggest areas for improvement needed to advance dynamic imaging through large-scale samples of relevance to engineering scenarios. These preliminary measurements demonstrate the feasibility of probing highly transient phenomena using the presented methodology.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Kelvin probe characterization of buried graphitic microchannels in single-crystal diamond

In this work, we present an investigation by Kelvin Probe Microscopy (KPM) of buried graphitic microchannels fabricated in single-crystal diamond by direct MeV ion microbeam writing. Metal deposition of variable-thickness masks was adopted to implant channels with emerging endpoints and high temperature annealing was performed in order to induce the graphitization of the highly-damaged buried region. When an electrical current was flowing through the biased buried channel, the structure was clearly evidenced by KPM maps of the electrical potential of the surface region overlying the channel at increasing distances from the grounded electrode. The KPM profiling shows regions of opposite contrast located at different distances from the endpoints of the channel. This effect is attributed to the different electrical conduction properties of the surface and of the buried graphitic layer. The model adopted to interpret these KPM maps and profiles proved to be suitable for the electronic characterization of buried conductive channels, providing a non-invasive method to measure the local resistivity with a micrometer resolution. The results demonstrate the potential of the technique as a powerful diagnostic tool to monitor the functionality of all-carbon graphite/diamond devices to be fabricated by MeV ion beam lithography.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Stress reduction of Cu-doped diamond-like carbon films from ab initio calculations

Structure and properties of Cu-doped diamond-like carbon films (DLC) were investigated using ab initio calculations. The effect of Cu concentrations (1.56∼7.81 at.%) on atomic bond structure was mainly analyzed to clarify the residual stress reduction mechanism. Results showed that with introducing Cu into DLC films, the residual compressive stress decreased firstly and then increased for each case with the obvious deterioration of mechanical properties, which was in agreement with the experimental results. Structural analysis revealed that the weak Cu-C bond and the relaxation of both the distorted bond angles and bond lengths accounted for the significant reduction of residual compressive stress, while at the higher Cu concentration the increase of residual stress attributed to the existence of distorted Cu-C structures and the increased fraction of distorted C-C bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A Bayesian method to estimate the neutron response matrix of a single crystal CVD diamond detector

Detectors made from artificial chemical vapor deposition (CVD) single crystal diamond are very promising candidates for applications where high resolution neutron spectrometry in very high neutron fluxes is required, for example in fusion research. We propose a Bayesian method to estimate the neutron response function of the detector for a continuous range of neutron energies (in our case, 10 MeV ≤ E{sub n} ≤ 16 MeV) based on a few measurements with quasi-monoenergetic neutrons. This method is needed because a complete set of measurements is not available and the alternative approach of using responses based on Monte Carlo calculations is not feasible. Our approach uses Bayesian signal-background separation techniques and radial basis function interpolation methods. We present the analysis of data measured at the PTB accelerator facility PIAF. The method is quite general and it can be applied to other particle detectors with similar characteristics.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Doped GaN nanowires on diamond: Structural properties and charge carrier distribution

In this work, we present a detailed study on GaN nanowire doping, which is vital for device fabrication. The nanowires (NWs) are grown by means of molecular beam epitaxy on diamond (111) substrates. Dopant atoms are found to facilitate nucleation, thus an increasing NW density is observed for increasing dopant fluxes. While maintaining nanowire morphology, we demonstrate the incorporation of Si and Mg up to concentrations of 9× 10{sup 20}cm{sup −3} and 1 × 10{sup 20}cm{sup −3}, respectively. The dopant concentration in the nanowire cores is determined by the thermodynamic solubility limit, whereas excess dopants are found to segregate to the nanowire surface. The strain state of the NWs is investigated by X-ray diffraction, which confirms a negligible strain compared to planar thin films. Doping-related emissions are identified in low-temperature photoluminescence spectroscopy and the temperature quenching yields ionization energies of Si donors and Mg acceptors of 17 meV and 167 meV, respectively. At room temperature, luminescence and absorption spectra are found to coincide and the sub-band gap absorption is suppressed in n-type NWs. The charge carrier distribution in doped GaN nanowires is simulated under consideration of surface states at the non-polar side facets. For doping concentrations below 10{sup 17}cm{sup −3}, the nanowires are depleted of charge carriers, whereas they become highly conductive above 10{sup 19}cm{sup −3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Superlinear generation of exciton and related paramagnetism induced by forward current in a diamond p-i-n junction

The concentration of excitons generated in a high-quality diamond p-i-n junction is investigated considering the forward current characteristics of the junction. As the forward current in the junction increases, the exciton concentration increases superlinearly, contrary to the linear increases of the electron and hole concentration. This tendency suggests a superlinear increase in emission intensity due to exciton recombination. The increase rate is more radical than quadratic, in accordance with the observed increase of the integrated intensity of free exciton emission. To estimate the concentration of triplet excitons generated in the p-i-n junction, observation of the paramagnetism due to the exciton spin moment is proposed. The magnetic susceptibility superlinearly increases with the increase in the forward current, unlike any other magnetic property of the device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Inhomogeneous broadening of optically detected magnetic resonance of the ensembles of nitrogen-vacancy centers in diamond by interstitial carbon atoms

We study the impact of the negatively charged nitrogen-vacancy (NV{sup –}) center density on the lattice strain resulting in the splitting of the optically detected magnetic resonance of HPHT diamond. A simple model, taking into account the presence of the interstitial carbon atoms, acting like a wedge force on the crystal lattice, explains the broadening and splitting of the optically detected magnetic resonance of the ensemble of NV{sup –} centers at densities within the range of 10{sup 13} ÷ 10{sup 14 }cm{sup −3}. This model uses a complete generalized spin Hamiltonian, takes into account the strain-effect of each center in the ensemble and gives good agreement with experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Graphene diamond-like carbon films heterostructure

A limitation to the potential use of graphene as an electronic material is the lack of control over the 2D materials properties once it is deposited on a supporting substrate. Here, the use of Diamond-like Carbon (DLC) interlayers between the substrate and the graphene is shown to offer the prospect of overcoming this problem. The DLC films used here, more properly known as a-C:H with ∼25% hydrogen content, have been terminated with N or F moieties prior to graphene deposition. It is found that nitrogen terminations lead to an optical band gap shrinkage in the DLC, whilst fluorine groups reduce the DLC's surface energy. CVD monolayer graphene subsequently transferred to DLC, N terminated DLC, and F terminated DLC has then been studied with AFM, Raman and XPS analysis, and correlated with Hall effect measurements that give an insight into the heterostructures electrical properties. The results show that different terminations strongly affect the electronic properties of the graphene heterostructures. G-F-DLC samples were p-type and displayed considerably higher mobility than the other heterostructures, whilst G-N-DLC samples supported higher carrier densities, being almost metallic in character. Since it would be possible to locally pattern the distribution of these differing surface terminations, this work offers the prospect for 2D lateral control of the electronic properties of graphene layers for device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗