706,442 research outputs found
Extent of stacking disorder in diamond
Hexagonal diamond has been predicted computationally to display extraordinary
physical properties including a hardness that exceeds cubic diamond. However, a
recent electron microscopy study has shown that so-called hexagonal diamond
samples are in fact not discrete materials but faulted and twinned cubic
diamond. We now provide a quantitative analysis of cubic and hexagonal stacking
in diamond samples by analysing X-ray diffraction data with the DIFFaX software
package. The highest fractions of hexagonal stacking we find in materials which
were previously referred to as hexagonal diamond are below 60%. The remainder
of the stacking sequences are cubic. We show that the cubic and hexagonal
sequences are interlaced in a complex way and that naturally occurring
Lonsdaleite is not a simple phase mixture of cubic and hexagonal diamond.
Instead, it is structurally best described as stacking disordered diamond. The
future experimental challenge will be to prepare diamond samples beyond 60%
hexagonality and towards the so far elusive 'perfect' hexagonal diamond
Effect of surface pretreatments on the deposition of polycrystalline diamond on silicon nitride substrates using hot filament chemical vapor deposition method
The deposition of diamond films on a silicon nitride (Si3N4) substrate is an attractive technique for industrial applications because of the excellent properties of diamond. Diamond possesses remarkable physical and mechanical properties such as chemical resistant, extreme hardness and highly wears resistant. Pretreatment of substrate is very important prior to diamond deposition to promote nucleation and adhesion between coating and substrate. Polycrystalline diamonds films have been deposited on silicon nitride substrate by Hot Filament Chemical Vapor Deposition (HF-CVD) method. The Si3N4 substrates have been subjected to various pretreatment methods prior to diamond deposition namely chemical etching and mechanical abrasion. The structure and morphology of diamond coating have been studied using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) while diamond film quality has been characterized using Raman spectroscopy. The adhesion of diamond films has been determined qualitatively by using Vickers hardness tester. It was found that the diamond films formed on chemical pretreated substrates has cauliflower morphology and low adhesive strength but also have low surface roughness. Substrates that pretreated with sand blasting have yield diamond film with well-facetted morphology with high crystallinity and better adhesion. However, the surface roughness of the diamond film deposited on substrates pretreated with blasting are also higher
Single Color Centers Implanted in Diamond Nanostructures
The development of materials processing techniques for optical diamond
nanostructures containing a single color center is an important problem in
quantum science and technology. In this work, we present the combination of ion
implantation and top-down diamond nanofabrication in two scenarios: diamond
nanopillars and diamond nanowires. The first device consists of a 'shallow'
implant (~20nm) to generate Nitrogen-vacancy (NV) color centers near the top
surface of the diamond crystal. Individual NV centers are then isolated
mechanically by dry etching a regular array of nanopillars in the diamond
surface. Photon anti-bunching measurements indicate that a high yield (>10%) of
the devices contain a single NV center. The second device demonstrates 'deep'
(~1\mu m) implantation of individual NV centers into pre-fabricated diamond
nanowire. The high single photon flux of the nanowire geometry, combined with
the low background fluorescence of the ultrapure diamond, allows us to sustain
strong photon anti-bunching even at high pump powers.Comment: 20 pages, 7 figure
Surface texturing of CVD diamond assisted by ultrashort laser pulses
Diamond is a wide bandgap semiconductor with excellent physical properties which allow it to operate under extreme conditions. However, the technological use of diamond was mostly conceived for the fabrication of ultraviolet, ionizing radiation and nuclear detectors, of electron emitters, and of power electronic devices. The use of nanosecond pulse excimer lasers enabled the microstructuring of diamond surfaces, and refined techniques such as controlled ablation through graphitization and etching by two-photon surface excitation are being exploited for the nanostructuring of diamond. On the other hand, ultrashort pulse lasers paved the way for a more accurate diamond microstructuring, due to reduced thermal effects, as well as an effective surface nanostructuring, based on the formation of periodic structures at the nanoscale. It resulted in drastic modifications of the optical and electronic properties of diamond, of which “black diamond” films are an example for future high-temperature solar cells as well as for advanced optoelectronic platforms. Although experiments on diamond nanostructuring started almost 20 years ago, real applications are only today under implementation
Nucleation mechanism for the direct graphite-to-diamond phase transition
Graphite and diamond have comparable free energies, yet forming diamond from
graphite is far from easy. In the absence of a catalyst, pressures that are
significantly higher than the equilibrium coexistence pressures are required to
induce the graphite-to-diamond transition. Furthermore, the formation of the
metastable hexagonal polymorph of diamond instead of the more stable cubic
diamond is favored at lower temperatures. The concerted mechanism suggested in
previous theoretical studies cannot explain these phenomena. Using an ab initio
quality neural-network potential we performed a large-scale study of the
graphite-to-diamond transition assuming that it occurs via nucleation. The
nucleation mechanism accounts for the observed phenomenology and reveals its
microscopic origins. We demonstrated that the large lattice distortions that
accompany the formation of the diamond nuclei inhibit the phase transition at
low pressure and direct it towards the hexagonal diamond phase at higher
pressure. The nucleation mechanism proposed in this work is an important step
towards a better understanding of structural transformations in a wide range of
complex systems such as amorphous carbon and carbon nanomaterials
Partitioning 3-homogeneous latin bitrades
A latin bitrade is a pair of partial latin
squares which defines the difference between two arbitrary latin squares
and
of the same order. A 3-homogeneous bitrade has
three entries in each row, three entries in each column, and each symbol
appears three times in . Cavenagh (2006) showed that any
3-homogeneous bitrade may be partitioned into three transversals. In this paper
we provide an independent proof of Cavenagh's result using geometric methods.
In doing so we provide a framework for studying bitrades as tessellations of
spherical, euclidean or hyperbolic space.Comment: 13 pages, 11 figures, fixed the figures. Geometriae Dedicata,
Accepted: 13 February 2008, Published online: 5 March 200
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