25,214 research outputs found
3D characterisation of tool wear whilst diamond turning silicon
No full textNanometrically smooth infrared silicon optics can be manufactured by the diamond
turning process. Due to its relatively low density, silicon is an ideal optical
material for weight sensitive infrared (IR) applications. However, rapid diamond
tool edge degradation and the effect on the achieved surface have prevented
significant exploitation. With the aim of developing a process model to optimise
the diamond turning of silicon optics, a series of experimental trials were
devised using two ultra-precision diamond turning machines. Single crystal
silicon specimens (1 1 1) were repeatedly machined using diamond tools of the
same specification until the onset of surface brittle fracture. Two cutting
fluids were tested. The cutting forces were monitored and the wear morphology of
the tool edge was studied by scanning electron microscopy (SEM). The most
significant result showed the performance of one particular tool was
consistently superior when compared with other diamond tools of the same
specification. This remarkable tool performance resulted in doubling the cutting
distance exhibited by the other diamond tools. Another significant result was
associated with coolant type. In all cases, tool life was prolonged by as much
as 300% by using a specific fluid type. Further testing led to the development
of a novel method for assessing the progression of diamond tool wear. In this
technique, the diamond tools gradual recession profile is measured by performing
a series of plunging cuts. Tool shape changes used in conjunction with flank
wear SEM measurements enable the calculation of the volumetric tool wear rate.Wea
Metastable Nanosized Diamond Formation from Fluid Systems
No full textThe model of nanosized diamond particles formation at metastable P-T parameters from fluid is presented. It explains the specific of CVD diamond synthesis gases mixtures and hydrothermal growth of diamond at low P-T parameters as well as it explains the geneses of metamorphic and magmatic nano- and microdiamond in the shallow depth Earth rocks and the genesis of interstellar nanodiamond formations in the space
An t-Eilean (The Island)
No full textAn t-Eilean (The Island, Gaelic) is an open-air, multi-purpose space (16 metres square) that occupies a central position in Inverness Campus for the University of the Highlands and Islands of Scotland.The space unites sculpture, building, and garden to form a distinctive landscape. Visitors experience An t’Eilean as a floating courtyard open to the sky and the surrounding landscape and connected to the land by a timber boardwalk. The project challenges scale and collapses normative design practices to unite architecture and landscape in ways that are subtle and sensitive to the rhythms of the days and seasons. An t-Eilean is a built ‘concept’ and an interstice – a constructed translation of the designer’s knowledge of theory and her landscape architectural practice. Mackenzie worked with leading expert David Bennett on the concrete specification for An t-Eilean. The concrete mix uses a by-product from coal-fired power stations called Pulverised Fuel Ash (PFA), to promote material re-use in construction. The mix allows a range of surface finishes to manifest through the structure, capturing and animating different qualities of light and shadow through the space. The project was presented and received input and approval from a wide range of stakeholders involved in the Campus development. The design was exhibited at the Royal Scottish Academy in 2014 before its completion. Over 20,000 people viewed the designs of just ten architects, including MacKenzie, selected for the exhibition, which aimed to explore the relationship between architecture, art and landscape. The design was awarded the Landscape Institute Scotland, Public Vote Prize in 2015. Mackenzie has been invited to talk about this project internationally to professional and educational groups in Amsterdam (2013), Xiamen (2016) and Oslo (2019)
Properties of nanostructured diamond-silicon carbide composites sintered by high pressure infiltration technique
No full textA high-pressure silicon infiltration technique was applied to sinter diamond–SiC composites with different diamond crystal sizes. Composite samples were sintered at pressure 8 GPa and temperature 2170 K. The structure of composites was studied by evaluating x-ray diffraction peak profiles using Fourier coefficients of ab initio theoretical size and strain profiles. The composite samples have pronounced nanocrystalline structure: the volume-weighted mean crystallite size is 41–106 nm for the diamond phase and 17–37 nm for the SiC phase. The decrease of diamond crystal size leads to increased dislocation density in the diamond phase, lowers average crystallite sizes in both phases, decreases composite hardness, and improves fracture toughness
Diamond polishing
No full textS.17-26The empirical know-how of single crystalline diamond polishing has been developed over centuries in the diamond gem cutting industry. Since the 1950s new and varied uses and potential applications for synthetically produced diamond have been consistently proposed and developed. This innovation process continues with the availability of ever better, more specialized and less costly single crystalline and polycrystalline diamond materials. Yet, the potential exploitation of this hardest of materials is still in its infancy. Polishing is a critical and limiting step for advancing diamond applications in terms of cost effective processing and the achievable material surface finish. The current state-of-the-art of polishing single crystalline and polycrystalline diamond materials is reviewed based on the published literature. The material removal process during traditional mechanical polishing using diamond grit and polishing wheels is strongly anisotropic and depends upon crystal planes and polishing directions. Wear debris analyses and molecular dynamic simulations led to the understanding that this anisotropy is primarily caused by a mechanically induced transition from diamond to an amorphous carbon phase rather than by microchipping as previously thought. Mechanical polishing also leads to subsurface damage and limits the achievable surface finish for single crystalline diamond. Advanced techniques are discussed to improve the polished crystal's surface quality. Mechanical polishing of polycrystalline diamond films and freestanding plates is particularly slow due to the intrinsic structure variations in such materials. To overcome these limitations faster polishing techniques have been developed and are reviewed and compared. These techniques introduce additional chemical and physical means of material removal extending the capabilities of mechanical polishing. There is no single method that can address all requirements, but the available variety affords the careful selection of an optimal process for a given task. Finally, while diamond polishing is a subject of interest since centuries, it still remains a very important research area required to unfold the promise of diamond as a technical material.3
Cathodoluminescence spectroscopy of synthetic diamond films
No full textA set of diamond films was grown by microwave chemical vapor deposition (MWCVD) using a CH4-H-2 gas mixture. Structural and crystallographic defects were induced in the samples either by choosing a relatively high substrate temperature, T-s = 950 degrees C, or by intentional contamination. In addition, different preferential orientations were obtained by appropriate changes to the CH4 concentration in the gas mixture. The resulting films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Room temperature and liquid nitrogen temperature cathodoluminescence (CL) were investigated in the 200-800 nm wavelength range. A clear correlation with the growth conditions of the so-called band-A emission (435 nm) and of some sharp spectral features was observed. An explanation of this effect is given in terms of crystal defects which are induced by the growth process. (C) 1997 Elsevier Science S.A
Investigation of the shape transferability of nanoscale multi-tip diamond tools in the diamond turning of nanostructures
No full textIn this article, the shape transferability of using nanoscale multi-tip diamond tools in the diamond turning for scale-up manufacturing of nanostructures has been demonstrated. Atomistic multi-tip diamond tool models were built with different tool geometries in terms of the difference in the tip cross-sectional shape, tip angle, and the feature of tool tip configuration, to determine their effect on the applied forces and the machined nano-groove geometries. The quality of machined nanostructures was characterized by the thickness of the deformed layers and the dimensional accuracy achieved. Simulation results show that diamond turning using nanoscale multi-tip tools offers tremendous shape transferability in machining nanostructures. Both periodic and non-periodic nano-grooves with different cross-sectional shapes can be successfully fabricated using the multi-tip tools. A hypothesis of minimum designed ratio of tool tip distance to tip base width (L/Wf) of the nanoscale multi-tip diamond tool for the high precision machining of nanostructures was proposed based on the analytical study of the quality of the nanostructures fabricated using different types of the multi-tip tools. Nanometric cutting trials using nanoscale multi-tip diamond tools (different in L/Wf) fabricated by focused ion beam (FIB) were then conducted to verify the hypothesis. The investigations done in this work imply the potential of using the nanoscale multi-tip diamond tool for the deterministic fabrication of period and non-periodic nanostructures, which opens up the feasibility of using the process as a versatile manufacturing technique in nanotechnology
Low-loss broadband antenna for efficient photon collection from a coherent spin in diamond
No full textWe report the creation of a low-loss broadband optical antenna giving highly directed output from a coherent single spin in the solid state. The device, a crystalline solid-state realization of a dielectric antenna, is engineered for individual nitrogen-vacancy electronic spins in diamond. We demonstrate a directionality close to 10. The photonic structure preserves the high spin coherence of single-crystal diamond ( T 2 ≳ 100 μ s). The single-photon count rate approaches a megahertz facilitating efficient spin readout. We thus demonstrate a key enabling technology for quantum applications such as high-sensitivity magnetometry and long-distance spin entanglement
Micro milling performance assessment of diamond-like carbon coatings on a micro-end mill
No full textThis is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2013 Institution of Mechanical Engineers.In micro milling, unpredictable tool life and premature tool failures are the major constraints for its industrial applications, and prolongation of the tool life so as to enhance the tooling performance presents great challenges. Appropriate coating techniques potentially offer a feasible and promising solution. In this study, diamond-like carbon films are deposited on a Ø500 µm diameter tungsten carbide (WC) micro-end mill by the plasma-enhanced chemical vapour deposition process. Coating characterisation has been undertaken and the diamond-like carbon coatings are found in good coverage on the tool except for a slight delaminating on the edge corners. Besides, the surface of the amorphous coatings is much smoother than that of WC. In addition, comprehensive cutting performance of the diamond-like carbon coated tool in dry slot milling of Al 6061-T6 has been compared with those of uncoated tools in both dry and wet conditions. It is observed that the use of diamond-like carbon coatings can reduce the cutting forces, lessen the tool wear, improves the surface roughness and minimise the micro-burr formation as compared to the corresponding performance of an uncoated tool in dry cutting. However, the performance improvement is still unreachable to those resulting from the cutting fluid influence.UK Technology Strategy Board and Kistler UK Ltd
Diamond based nanostructures for electronic applications
No full textResearch in the area of CVD diamond thin films has increased significantly during the last decades to the point where single crystal diamond is now commercially available. The remarkable properties of diamond including its extreme hardness, low coefficient of friction, chemical inertness, high thermal conductivity, transparency and semiconducting properties make it attractive
for a number of applications, among which electronic devices is one of the key areas. A detailed knowledge of electrical properties of diamond films is
therefore critical.
This thesis describes (1) a Hall effect study of highly boron-doped (111)
diamond films (2) a Hall effect and impedance spectroscopic study of boron δ-doped diamond structures and (3) the synthesis of carbon nanotubes on single crystal diamond.
Systematic investigations have been carried out on single crystal, boron-doped (111) diamond films. The influence of ultra pure gases, doping concentration and temperature on carrier transport are discussed in detail.
A comprehensive study on boron δ-doped diamond films is also performed;
Hall effect and impedance spectroscopy are used to evaluate these films, providing valuable insight into the complex carrier transport mechanisms
occurring in these structures. The influence of temperature on carrier
mobility and the free carrier density are discussed. This is allied with
valuable information gained from impedance spectroscopy, where the
presence of multiple semicircular responses (conduction pathways),
modelled using a RC parallel circuit, yields data which leads to a greater
understanding on the influence of the interface between the boron δ-doped
layer and the surrounding intrinsic diamond layers. These semicircular
responses are thus attributed to different crystalline regions in these
structures, namely the boron δ -doped layer and the interfacial regions surrounding δ-layer. The influence of this interface region on the structures
overall conductivity is discussed.
Finally the synthesis of carbon nanotubes (CNTs) on single crystal diamond
is reported for the first time. Scanning electron microscopy combined with
Raman spectroscopy is used to understand the influence of temperature and
differing growth gas mixtures on the yield and crystallinity of these as-grown CNTs
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