We evaluated the neutron bang time in fast-ignition inertial confinement fusion and the response function of deuterium-deuterium (DD) neutrons for burn history monitoring applications with a single-crystal CVD diamond detector. Signals were successfully obtained for the first time with a single-crystal diamond detector for DD neutrons of above 10(8) neutrons/shot.

Raman peaks with weak intensities at low wavelength were detected in dislocation areas of diamond substrates. Polarized Raman measurements were performed, and the origins of peaks were estimated. Based on the appearance of the Raman modes, the three peaks were estimated to be non-diamond owing to their structural asymmetries. Mapping measurements were carried out using one of the peaks and a small area of a high intensity region was estimated as the core of dislocation threading to the crystal surface. This method showed two dislocations on the surface, approximately 1.2 mu m apart. The imaging using the peaks will be a powerful tool for investigating the dislocations of diamond epitaxial layers.

The dislocation identification method using X-ray topography by reflection mode geometry was applied to characterize IIa, Ib and highly B doped high pressure high temperature (HPHT) grown crystals. In both IIa and Ib crystals, dislocations are found to propagate in the <111> grown direction, with dominant vectors of [110] and [1-10], neither of which has no c-axis segment. For Ib crystal, many dislocations are also generated in the <112> and <121> directions, which are slightly tilted to <111>. It was confirmed that the dislocations in the same direction have the same Burgers vectors, but the dislocations are spread in broad area. A total of up to 20 HPHT crystals were measured and found to exhibit different dislocation distributions. This indicates an immature growth technique in terms of dislocation. Measurements of four chemical vapor deposition (CVD) substrates showed numerous dislocation bundles, making individual dislocation directions analysis impossible. CVD substrates suffer from an increase in dislocations due to CVD growth, resulting in poor diamond quality in terms of dislocation. XRT analysis on dislocations of epitaxial growth will be very important prior to CVD substrates analysis.

Polarized Raman measurements were performed on P-doped diamond films to investigate the origin of the peaks in the lower wave numbers, which are unknown to date, and a comparative study of several P-doped substrates was conducted. The measurements with four configurations of the polarized geometries were carried out for five samples with different P and H concentration, [H]/[P] ratios, and film thickness. For four highly P-doped films, several Raman peaks were observed for all four configurations; retaining the Oh7 cubic structure of diamond, presumably relate to substitutional sites. For a sample of high [H]/[P] ratio (=1.17) and a very thick film, several other peaks were observed. The peak appearances for four configurations indicate that the origin is not in the Oh7 diamond structure but presumably interstitial sites. In the future, it may be possible to realize effective P doping by the improvement of film synthesis by utilizing the results of Raman polarization measurements, which are simple and nondestructive.

X-ray topography is an effective tool to investigate dislocations in semiconductor crystals. Due to low X-ray absorption coefficients of diamond, X-rays can penetrate deep into the crystal. Thus, deep three-dimensional (3D) dislocations are projected on two-dimension (2D) film, which makes dislocation analysis particularly challenging. Dislocation vectors from the films obtained using a set of the same diffraction vectors were identified using topographical and geometrical analyses. The depth and position of the dislocations in a crystal that was projected on a film were determined using geometrical relationship. The proposed analysis method was verified by analyzing several dislocations using four <404> diffraction films. The types of dislocation were identified through Burgers vector analysis.

Influence of dislocations on diamond Schottky barrier diode characteristics of vertical structure p- layer/p+ substrate is studied. Devices are intentionally fabricated at locations corresponding to specific dislocations, stacking faults and growth sector boundaries observed using X-ray topography (XRT) prior to device fabrication. Devices fabricated on [001] threading dislocation area, and threading dislocation with stacking fault (SF) areas showed very large leakage current compared with devices without dislocations. Dislocation vectors of four devices having threading dislocations with SFs, are analyzed using XRT images and compared with current to voltage (I–V) characteristics. The number of threading dislocations and their types vary significantly, and there is not much difference in the I–V characteristics. Thus, threading dislocations are fatal to the device characteristics regardless of their dislocation directions, types, and number counts.

The P dopant site control in diamond is critical to achieve high mobility n type channels and high concentration n+ layers for power device applications. In this study, the P doped diamond films grown by three institutes with varying hydrogen and dopant concentrations were analyzed by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). By XANES, the film with high H concentration (4.0 x 10(19) cm(-3)) was estimated to show a higher peak intensity of 2147.7 eV than that of a low H concentration film. H was likely to be incorporated in the diamond as P-H at the substitutional sites under H rich growth condition. Another film showed considerably low peak intensities at 2147.7 and 2148.6 eV because of the "substitutional with H" and "substitutional" sites, respectively. The EXAFS result revealed that the first nearest neighbor distance is slightly shifted from the "substitutional" to "interstitial" site. The low P concentration film showed different types of energy profiles, particularly in the high energy region, indicating that dopant sites change with dopant concentration. Overall, the P dopant site is likely to be influenced by the machine system, H and P concentrations.

High-frequency and wideband surface acoustic wave (SAW) devices have become an important topic in 5G communication systems and beyond. For this purpose, piezoelectric ScAlN thin films deposited on high SAW velocity diamond are studied in SAW resonators on the polycrystalline diamond (PCD) and hetero-epitaxial diamond (HED) substrates. A very strong c-axis orientation of ScAlN on HED was confirmed. Interdigital transducers of 0.8 mu m and 0.5 mu m were fabricated to realize 2.2 to 3.5 GHz high-frequency resonators. High Q values were obtained for the 2.3-2.5 GHz device on both PCD and HED. Additionally, a high electro-mechanical coupling coefficient (K-2) of 5.40-5.52% and high SAW velocities of 7400-7766 m/s were obtained in the 2.3-2.5 GHz devices. In comparison to the simulated coupling coefficient results of a previous report, ScAlN/diamond might have higher K-2 for the Sezawa wave.

A mosaic substrate is a promising candidate to create large size single crystal diamonds for various types of applications. In this study, the crystal orientations of the joint areas of four single crystal plates of a mosaic substrate were measured using the high resolution electron backscatter diffraction method. The lattice rotation of [110] to [–110] (X-Y direction) was less than 0.5° and the lattice rotation mappings of [001] to [110] (Z-X direction) and [1–10] (Z-Y direction) were less than 0.2°. Considering that plate alignment is not particularly considered during the fabrication process, further improvement can be expected to realize a well- aligned mosaic substrate.

The intrinsic exciton transitions of isotopically purified (C-13) and natural-abundance (C-N.A.) diamond are studied by photoluminescence and transmission spectroscopies at liquid helium temperatures. The comparative study shows that C-13 has the same fine structure splitting with C-N.A., indicating that the isotopic effect of diamond does not influence the internal excitonic structure. This approach also deduces the absolute energies of excitons and phonons in C-13 and C-N.A. at the Delta [k = (0.76, 0, 0) x (2 pi/a)] point. (C) 2019 The Japan Society of Applied Physics

There is a great need for high-quality diamond with low dislocation density for high-output power device applications. In this study, we attempted to identify dislocations originating from the homo-epitaxial film/substrate interface in relation to the off-angle of the initial substrate by comparing the dislocation images obtained using x-ray topography by synchrotron radiation facility. For homo-epitaxial film growth on (001) substrate tilted by ∼3°, 3 dislocations were found after growth in the 0.09 cm2 area, corresponding to a density of 30 cm−2. On the other hand, 23 dislocations generated from the film/substrate interface for homo-epitaxial growth on a (001) substrate with ∼1° tilt angle. This fact indicates that the lateral growth using a tilted substrate is an effective way to minimize the number of additional dislocations originating from the homo-epitaxial film/substrate interface.

Surface oxidation of nanodiamonds (NDs) is a primary step of their surface functionalization that is key to the success of their recent emerging applications in nanoscale quantum sensors in biological samples. Here, we investigate how the electron spin coherence of single nitrogen vacancy centers in NDs is extended by two major oxidizing techniques, that is, aerobic oxidation and anaerobic triacid oxidation with various processing parameters. Aerobic oxidation at 550 degrees C most effectively oxidizes the surface and extends T-2 by a factor of 1.44 +/- 0.33 to the original NDs. The ND size dependence of this T-2 extension shows that aerobic oxidation removes a constant decoherence contribution irrespective of the ND size, which clearly separates its origin from the surface-derived decoherence sources. The present results highlight the presence of the ND-specific decoherence sources other than surface termination spin noise and spin-active impurities, thereby improving the spin coherence of ND quantum sensors.

We report on the sensing stability of quantum nanosensors in aqueous buffer solutions for the two detection schemes of quantum decoherence spectroscopy and nanoscale thermometry. The electron spin properties of single nitrogen-vacancy (NV) centers in 25 nm-sized nanodiamonds have been characterized by observing individual nanodiamonds during a continuous pH change from 4 to 11. We have determined the stability of the NV quantum sensors during the pH change as the fluctuations of ±12% and ±0.2 MHz for the spin coherence time (T 2) and the resonance frequency (ω 0) of their mean values, which are comparable to the instrument error of the measurement system. We discuss the importance of characterizing the sensing stability during the pH change and how the present observation affects the measurement scheme of nanodiamond-based NV quantum sensing.

The orientation of growth sectors of highly B doped p+ high pressure and high temperature (HPHT) substrates were investigated by high angular resolution electron backscatter diffraction (HR-EBSD). The lattice rotation mapping images of the areas across the 〈111〉 growth sector boundaries were measured. The crystal orientation was found to be inclined approximately 0.03° for [001] to [-1-10], compared with the [-1-11] growth sector area at a given location. Other orientation inclinations were observed such as 0.02° for [001] to [110] and 0.025° for [001] to [1-10]. The same phenomena were confirmed for the other two crystals. Conventionally, it has been recognized that a HPHT-grown crystal is a perfect single crystal, however, our results indicate that “twin boundaries” are formed between the growth sectors for p+ HPHT substrates. To meet the requirements for the power device wafer specifications, the establishment of growth technology is desirable in the near future.

Photoluminescence (PL) spectroscopy is performed for natural-abundance (C-N.A.) and isotopically purified (C-13) synthetic diamond using a deep-ultraviolet continuous-wave laser. Because the excitation source creates low-density low-temperature excitons even under a moderate excitation power, the PL spectra show suppressed collisional and thermal broadening with a high signal-to-noise ratio. Our approach can accurately resolve the isotopic effects. The experimentally determined effects for phonons and excitons in diamond are Delta E-TA = -2.5 meV, Delta E-TO = -4.9 meV, Delta E-LO = -5.7 meV, and Delta E-ex = 14.5 meV. (C) 2018 The Japan Society of Applied Physics