205,955 research outputs found
Gradient layers of boron doped diamond on titanium substrates
No full textFor the deposition of well-adhesive, low-doped diamond layers on titanium substrates a gradient layer is designed. At first a highly boron-doped diamond layer is deposited, which shows good adhesion to the titanium substrate, followed by a low-boron doped diamond layer on the surface.
The boron-doped diamond layers were deposited on titanium stretch metal substrates by the hot-filament CVD method. It is shown that with increasing boron content during diamond deposition above 6000 ppm B/C the intermediate Ti(C,B) layers becomes very thin and so at high boron concentrations no problem with layer adhesion occurs. These Ti(C,B)-layers formed during diamond deposition were investigated by standard metallographic preparations. To form a diamond gradient layer on the highly boron doped diamond the boron content was reduced and a low doped diamond layer was deposited.
Electrochemical cyclic voltammetric measurements show that the lower boron contents at the diamond surface provide better electrochemical properties. These layers show extraordinary electrochemical properties in respect of the gained hydrogen and oxygen overvoltage
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
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
Tribological characterization of smooth diamond films grown in Ar-C-60 and Ar-CH4 plasmas
No full textIn this paper, we describe the fundamental tribological mechanisms of smooth, nanocrystalline diamond films grown in Ar-C-60 and Ar-CH4 plasmas. These films can provide very low friction coefficients (approximate to 0.04 to 0.15) to sliding SiC and Si3N4 surfaces in air or dry N-2. To understand the mechanisms of friction and wear behavior in relation to the chemical and physical states of the diamond films, we used a variety of analytical techniques (electron diffraction, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, atomic resolution transmission electron microscopy, near-edge X-ray absorption fine structure, and atomic force microscopy) both before and after sliding tests. The results of these studies verified that the films were made of sp(3)-bonded diamond nanocrystals (100-300 Angstrom) and that their surfaces were exceptionally smooth (i.e., 20-40 nm, root mean square). Additionally, pin-on-disk experiments verified that these films provided very low friction coefficients (0.04, in dry N-2) and wear rates, essentially comparable to those of natural diamond. Undoubtedly, such diamond films with smooth surface finish can have significant impact in a wide range of tribological applications
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
An atomistic investigation of FIB process damage on diamond
No full textocused Ion Beam (FIB) is one of the important machining techniques to fabricate diamond sensors/detectors used for drug analysis, chemical analysis and bio-sensing applications. In-depth understanding of the high energy collision process and the residual damage induced along the trace of gallium ion could undoubtedly facilitate the development and improvement of performance of such devices through the optimization of machining processes. Based on the merit offered by large-scale molecular dynamics (MD) simulation method and the new progress made in high performance computing technique (HPC), a new atomistic modelling system was proposed in this paper to investigate the high energy collision process involved two gallium ions. The simulation results indicated that the energetic ion collision process comprises a bombardment event with a pulse temperature and a lateral relative long period annealing recrystallization process. The peak temperature for the second ion collision was 129.2 K higher than the first one, which indicates the alternation of the thermal conductivity of diamond due to the formation of amorphous (sp2 graphite-like) structure during the first ion collision and annealing process. Besides giving the damage configuration and distribution in diamond after fully recrystallization, the simulation also used coordination number (CN) and radius distribution function (RDF) to revel the change of diamond lattice structure after the collision process, which provided an insight of damage induced by FIB process
Comparative study of nucleation processes for the growth of nanocrystalline diamond
No full textMethods for seeding silicon substrates with pretreatments and the in situ generation of diamond nuclei by the bias enhanced nucleation (BEN) have been studied to examine their effects on the nucleation density as well as the morphology of grown and seeded sides, the growth rate, and the quality of nanocrystalline diamond films. Pretreatments including mechanical abrasion by diamond paste, exposure of the silicon substrate to a hydrocarbon plasma, and ultrasonication of silicon in solvents with suspended nano- or micro-diamond powders were studied. With an optimized diamond seeding or nucleation process, ultra-thin, smooth and homogenous nanocrystalline diamond films can be fabricated.補正完
Boron-doped diamond with improved oxidation resistance
No full textS.47-52The oxidation behavior of pure and 0.2 wt.% B-containing diamond powders was investigated by thermal analysis, SEM analysis, and Raman spectroscopy of partially oxidized diamonds. Boron-doped diamond exhibited a much higher oxidation stability than that of pure diamond. The maximum oxidation rate shifted from 773 °C for the pure diamond to 1118 °C for the Bdoped diamond. SEM analysis of the surface of the partially oxidized diamonds revealed that the low boron content (0.2%) was sufficient for the formation of a protective B2O3 surface layer in the regions in which active oxidation took place. This layer was most probably the reason for the improved oxidation resistance.9
High thermal conductance across c-BN/diamond interface
No full textHigh thermal conductivity electronic components with low interfacial thermal resistance are of technological importance and fundamental interest of research. Diamond, a superhard material with ultrahigh thermal conductivity at room temperature, is desirable for microelectronics thermal management. Cubic polymorph of boron nitride (c-BN) is a promising material due to wide bandgap and diamond like structure and properties. To understand the nature in thermal transport of diamond, c-BN and the most commonly used silicon (Si) semiconductor, ab initio phonon Boltzmann transport equations are employed to investigate lattice vibrational properties of these three materials. At 300 K, the predicted thermal conductivity of Si, diamond and c-BN reached 142, 2112, and 736 W/(m·K), respectively. What's more, heat transport phenomena across the interfaces of Si/diamond, c-BN/diamond and Si/c-BN are unfolded. In comparison, the interfacial thermal conductance of c-BN/diamond is ten-fold of Si/diamond; besides, the thermal conductance across Si/c-BN interface is 20.2% larger than that of Si/diamond at 300 K and 18.9% larger at 340 K. These findings provide us new vision and potential solution to heat dissipation of high-local-power density devices, shedding light on future thermal management of c-BN and diamond related electronics.Peer reviewe
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
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