157,900 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
Shallow NV- colour centres in diamond
No full textNegatively charged Nitrogen-Vacancy (NV-) colour centre in diamond is a well-known and characterised point defect with notable properties such as photostable bright fluorescence and spin states that can be initialised and read out, making it of great appeal for quantum technology applications.
Specifically, the latter can benefit from forming NV- defects in the proximity of the diamond surface. As an example, for nuclear magnetic resonance (NMR) sensing, it is necessary to have the NV- spins close to the surface as the coupling strength between magnetic dipoles decreases with the cubic distance of the defects from the surface. Shallow NV- defects can also be easily coupled with nanophotonic cavities for photon extraction. Furthermore, shallow NV- can also be beneficial in the biomedical field since the proximity to the surface allows the coupling with biomaterials for sensing applications, such as nano thermometry. However, the fabrication of shallow NV colour centres is challenging since it faces with several issues such as charge stability and low formation efficiency due to the behaviour of the diamond surface as an electron and a vacancy sink. The surface effects (i.e. vacancy sink, band bending and electron tunnelling) tend to convert NV- in NV0 centres which do not possess the same spin properties and are not commonly used for quantum technologies
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
Low temperature growth of ultrananocrystalline diamond film and its field emission properties
No full textUltrananocrystalline diamond (UNCD) film is deposited at a substrate temperature lower than 500 °C. This film possesses diamond crystal of nanometer size embedded in a graphitic (or non-diamond carbon) phase. The presence of non-diamond carbon in the grain boundaries of diamond crystal plays a crucial role to the film properties and its corresponding application such as electron field emission. The present work reports the growth of UNCD films at different methane concentrations to alter the film properties that could make it suitable for higher electron field emission. The surface morphology of an as-grown film was examined with a field emission scanning electron microscope. Nucleation density in the range of 1011–1012/cm2 is obtained in the as-grown films. The grain size of diamond increases from 5 nm to 25 nm with an increase in CH4 concentration from 1% to 7.5% in the argon plasma. The presence of different carbon phases in the diamond films was investigated qualitatively by Raman studies. Near edge X-ray fine structure study ascertains that the as-grown films mainly possess diamond phase. A direct correlation of field emission properties with the CH4 concentration during UNCD growth is obtained.補正完畢US
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
A multilevel analysis of the effects of rurality and social deprivation on premature limiting long term illness
No full textSTUDY OBJECTIVE---To examine the geographical variation in self perceived morbidity in the south west of England, and assess the associations with rurality and social deprivation.DESIGN---A geographically based cross sectional study using 1991 census data on premature Limiting Long Term Illness (LLTI). The urban-rural and intra-rural variation in standardised premature LLTI ratios is described, and correlation and regression analyses explore how well this is explained by generic deprivation indices. Multilevel Poisson modelling investigates whether Customised Deprivation Profiles (CDPs) and area characteristics improve upon the generic indices.SETTING---Nine counties in the south west of EnglandPARTICIPANTS---The population of the south west enumerated in the 1991 census.MAIN RESULTS---Intra-rural variation is apparent, with higher rates of premature LLTI in remoter areas. Together with high rates in urban areas and lower rates in the semi-rural areas this indicates the existence of a U shaped relation with rurality. The generic deprivation indices have strong positive relations with premature LLTI in urban areas, but these are a lot weaker in semi-rural and rural locations. CDPs improve upon the generic indices, especially in the rural settings. A substantial reduction in unexplained variation in rural areas is seen after controlling for the level of local isolation, with higher isolation, at the wider geographical scale, being related to higher levels of LLTI.CONCLUSIONS---This study highlights the need to treat rural areas as heterogeneous, although this has not been the tendency in health research. Generic deprivation indices are unlikely to be a true reflection of levels of deprivation in rural environments. The importance of CDPs that are specific to the area type and health outcome is emphasised. The significance of physical isolation suggests that accessibility to public and health services may be an important issue, and requires further research
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
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 Surface Structuring via Carbon Transport at Diamond-Transition Metal Interfaces
No full textDiamond is a kind of promising material with many unique properties that can be used in many fields. However, the extreme high hardness makes diamond surface manufacturing difficult and limits its application. In this research, a novel diamond surface manufacturing technique that based on the thermomechanically induced mass transport at diamond and transition metal interface are introduced. First, thermally induced mass transport between diamond and FeCoB, Fe, Co, or Ni were investigated. The transition metal thin films were selectively deposited on diamond surface through masks fabricated by photolithography and nanosphere lithography. The structures of interaction interfaces were characterized by SEM, XRD, Raman Spectroscopy, and TEM. The surface topographies corresponding to each treatment step were characterized by optical profilometer and AFM. The mechanism to illustrate the diffusional interaction between diamond and different transition metals was firstly presented based on the characterization results. The role of the transition metal-diamond interface is key to controlling the material removal; the stability of the interface determines the ability to faithfully replicate the ultrafine features that were patterned by transition metals.
Second, purely mechanically induced mass transport between diamond and transition metals are investigated using transition metal thin film deposited AFM tip scratching and in-situ TEM scratching test. Due to the weak strength of the transition metal - diamond joints and transition metal thin films, AFM scratching rarely activated the mass transport interaction at the diamond – transition metal thin film interfaces. The in-situ TEM scratching tests were performed using a Nanofactory STM holder. The interaction at diamond and W interface was successfully activated by nanoscale in-situ scratching under room temperature. The lattice structure of diamond and W were characterized by HRTEM. The stress to activate the interaction was estimated by measuring the interplanar spacing change of W nanotips before scratching and at the frame that the interaction was activated
LATTICE DISTORTION NEAR VACANCIES IN DIAMOND AND SILICON .2.
No full textFor pt.i, see ibid., vol.4, 1971, 143. The previous method, based on a dynamic relaxation procedure, coupled with a valence force potential function to represent the interaction between the atoms of the perfect crystal, has been applied to the isolated neutral vacancy in diamond and silicon for two alternative choices of rebonding forces for the vacancy electrons. In one case the electronic forces have been estimated from a detailed molecular orbital calculation, while in an alternative approach a generalized morse-type potential relationship has been used. The formation energy of the neutral vacancy has also been calculated. The volume changes associated with the diamond-type system containing a vacancy are also calculated
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