Laser beam micromachining was applied to super-hard nano-polycrystalline diamond (NPD) synthesized by the direct conversion of graphite at high pressure and high temperature. Three types of pulsed ...lasers were tested: nanosecond near-infrared, nanosecond near-ultraviolet, and femtosecond near-infrared lasers. The latter two were also applied for synthetic single crystal of diamond to compare the results with those of the NPD. It was demonstrated that the nanosecond near-infrared laser was the most efficient device for rough shaping of the NPD, while the ultraviolet and femtosecond lasers give satisfactory results for precise surface finishing of it. The properties of the laser-processed surfaces were analyzed by scanning and transmission electron microscopy, laser scanning microscopy, and micro Raman spectroscopy. These analyses demonstrated that the three types of lasers play different and complementary roles, and that their combination is the best suitable solution for micromachining of the hardest diamond into any desired shapes.
Reverse Monte Carlo (RMC) calculation was performed to visualize the atomic arrangement in a disordered Fe
55
Ni
45
alloy, which is classified as an intermediate structure between the non-crystalline ...glass and crystalline structures. The optimized structure of the ferromagnetic phase at low pressures revealed that Fe and Ni atoms were displaced from a perfect fcc lattice to elongate the nearest neighboring Fe-Fe atomic pairs, therefore, Fe-Fe atomic pairs have longer bond length than Fe-Ni and Ni-Ni atomic pairs. Because the elongation becomes negligible during the pressure-induced destabilization of the ferromagnetic state, the elongation of Fe-Fe pairs is the atomic scale origin of the volume expansion due to a large magnetovolume effect. Compared with the atomic arrangement in the Fe
65
Ni
35
Invar alloy, a relationship between Fe-Fe atomic pairs, the Invar effect and elastic anomalies in the compression curve is elucidated.
Micrometer- to nanometer-scale structures of the cut surfaces of single- and polycrystalline diamonds by a pulsed ultraviolet laser have been thoroughly investigated by scanning and transmission ...electron microscopy. Within the laser-cut grooves, the processed diamond surfaces are extensively covered with laser-modified debris which consists of complex layered units of graphite with various crystallinities. The units consist of 1) highly oriented graphite, 2) corrugated graphite, and 3) nanocrystalline graphite, which are sequentially located from the surface of the underlying diamond substrate to the center of the grooves. Detailed textural examinations revealed that the highly oriented graphite unit is a product of the initial graphitization of diamond by a solid-state diffusion process, whereas the latter two units are deposition products from the liquid and/or vapor phases of carbon in the later stage. The present study demonstrates that the laser-cutting of diamonds proceeds in a two-step process: 1) extensive graphitization of laser-scanning path and 2) subsequent sublimation of the pre-formed graphite. These processes are basically identical among the three different types of diamonds (single crystal type Ib, single crystal type IIa and nano-polycrystalline aggregate) tested in this study.
The negatively charged silicon-vacancy (SiV super(-)) center in diamond is a promising single-photon source for quantum communications and information processing. However, the center's implementation ...in such quantum technologies is hindered by contention surrounding its fundamental properties. Here we present optical polarization measurements of single centers in bulk diamond that resolve this state of contention and establish that the center has a left angle bracket111right angle bracket aligned split-vacancy structure with D sub(3d) symmetry. Furthermore, we identify an additional electronic level and evidence for the presence of dynamic Jahn-Teller effects in the center's 738-nm optical resonance.
Nano-polycrystalline diamond (NPD) is a super-hard pure polycrystalline aggregate of nano-diamonds and has a characteristic microtexture composed of a mixture of granular and lamellar crystals. We ...investigated the origin of the unique microtexture and the influence of the crystallinity of initial graphite sources on the resulting microtexture of NPDs. Polycrystalline graphite rods used for NPD synthesis were found to consist of coke-derived relatively large crystals and pitch-derived nanocrystalline particles. Upon conversion to NPD, the former are converted to cubic and hexagonal diamond mixtures by the martensitic transformation and left a lamellar texture behind, while the latter transform to granular nano-diamonds by diffusion-controlled nucleation and subsequent crystal growth, which initiate preferentially at lattice defects and crystal surfaces. A clear correlation between the crystallite size of the initial graphite and the grain size of the granular nano-diamonds in the NPDs was also found. Our results suggest that the average grain size and the relative abundance of lamellar domains in NPD can potentially be controlled by carefully choosing initial graphite sources based on their crystallinity.
Polycrystalline diamond aggregates have been synthesized by direct conversion of graphite at pressures of 12–25
GPa and temperatures 1800–2500
°C using a multianvil apparatus. The synthesized diamond ...was optically transparent and colorless, and was of cubic symmetry as determined by micro-focus X-ray diffraction. TEM analyses revealed that the sample consists of minute crystals of typically 10–20
nm, and only a very weak and broad band at ∼1332
cm
−1 was observed by Raman spectroscopy. An indentation test demonstrated that the present polycrystalline diamond possesses a Knoop hardness of up to 140
GPa, which is equivalent to or even higher than those of natural and synthetic single-crystal diamonds (∼60–130
GPa) and nearly twice as high as those of synthetic polycrystalline diamonds containing binders (∼50–70
GPa). The present results imply that natural polycrystalline diamonds may have been formed by a rapid transformation from metastable graphite present in cold subducted crust, when encountering in warmer regions, such as rising plumes in the mantle transition region.
A linear machining technique using a nanosecond pulsed laser, adaptable for forming a single-point cutting tool made of nano-polycrystalline diamond, was developed. A basic study to find the ...principal rules of linear machining was conducted by forming an inclined face against the beam axis that is coincided with the Z axis. The face was formed by conducting repeatedly a set of machining processes, comprising linear machining to remove chips and zero-cut machining to remove the residual stock. It was verified through a machining test that the removal depth in the Z direction was independent of the inclined angle of the face. In addition, the stock removal in the Z direction coincided with the sum of the applied depths of cut in the Z direction when the residual stock removal in each machining step was eliminated by the zero-cut machining. These basic rules made it possible to accurately fabricate a convex dimple with a diameter of 0.2 mm, during which the inclined angle of the machined face against the beam axis varied at every position, by repeatedly conducting the set of machining processes. Also, it was verified through the forming test of a single-point cutting tool with a nose radius of 0.4 mm that the linear machining technique enabled the fabrication of the tool with a shape accuracy better than 1 μm and a cutting edge radius of less than 250 nm.
Superradiance is a fundamental collective effect where radiation is amplified by the coherence of multiple emitters1. Superradiance plays a prominent role in optics (where it enables the design of ...lasers with substantially reduced linewidths2,3) and quantum mechanics4, and is even used to explain cosmological observations such as Hawking radiation from black holes5. Resonators coupled to spin ensembles6–8 are promising future building blocks of integrated quantum devices that will involve superradiance. As such, it is important to study its fundamental properties within such devices. Although experiments in the strong-coupling regime have shown oscillatory behaviour in these systems9,10, a clear signature of Dicke superradiance has so far been missing. Here we explore superradiance in a system composed of a three-dimensional lumped element resonator in the fast cavity limit inductively coupled to an inhomogeneously broadened ensemble of nitrogen–vacancy centres. We observe a superradiant pulse being emitted a trillion times faster than the decay for an individual nitrogen–vacancy centre. This is further confirmed by the nonlinear scaling of the emitted radiation intensity with respect to the ensemble size. Our work provides the foundation for future quantum technologies including solid-state superradiant masers2.
Nuclear magnetic resonance (NMR) spectroscopy is a key analytical technique in chemistry, biology, and medicine. However, conventional NMR spectroscopy requires an at least nanoliter-sized sample ...volume to achieve sufficient signal. We combined the use of a quantum memory and high magnetic fields with a dedicated quantum sensor based on nitrogen vacancy centers in diamond to achieve chemical shift resolution in 1H and 19F NMR spectroscopy of 20-zeptoliter sample volumes. We demonstrate the application of NMR pulse sequences to achieve homonuclear decoupling and spin diffusion measurements. The best measured NMR linewidth of a liquid sample was ~1 part per million, mainly limited by molecular diffusion. To mitigate the influence of diffusion, we performed high-resolution solid-state NMR by applying homonuclear decoupling and achieved a 20-fold narrowing of the NMR linewidth.
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