Development of Self-Supporting Polycrystalline Diamond Bridge

2007 ◽  
Vol 537-538 ◽  
pp. 145-150
Author(s):  
Hajnalka Csorbai ◽  
Gergely Kovách ◽  
P. Fürjes ◽  
P. Csíkvári ◽  
A. Sólyom ◽  
...  
Keyword(s):  
Industrial Application ◽  
Polycrystalline Diamond ◽  
Diamond Structure ◽  
Mechanical Tension ◽  
Etching Technique ◽  
Sio2 Substrate ◽  
Microwave Assisted ◽  
Cvd Method ◽  
Heat Expansion ◽  
Expansion Coefficients

Polycrystalline diamond layers are mostly used in various fields of industrial application. Mechanical tension is generated due to the different heat expansion coefficients of the substrate and the layer, which leads to fracturing in some cases. In this work a homogeneous polycrystalline diamond structure has been deposited on Si/SiO2 substrate by microwave assisted CVD method (MW-PECVD). An selective etching technique has been used to remove the silicon below the 2.5 micron thick diamond layer. A self-supporting diamond structure has been created this way. Polycrystalline diamond based heaters and thermometers can be made from doped diamond materials, which can resist corrosive and radiative environment.

Microstructure and Properties of the Sintered Diamond Reinforced by Diamond-MWCNTs Composite Fibers

2011 ◽  
Vol 175 ◽  
pp. 1-7
Author(s):  
Fu Ming Deng ◽  
Xue Jun Lu ◽  
Rui Ping Liu ◽  
Guo Jun Xu ◽  
Qi Wu Chen ◽  
...  
Keyword(s):  
Bending Strength ◽  
Polycrystalline Diamond ◽  
High Hardness ◽  
Composite Fiber ◽  
Strengthening Effect ◽  
Diamond Structure ◽  
Composite Fibers ◽  
New Type ◽  
Sintered Diamond ◽  
Walled Carbon Nanotubes

A new type of sintered diamond reinforced by diamond-MWCNTs composite fibers which were randomly orientated and even distributed in the diamond matrix was synthesized by using 3(wt)% mullti-walled carbon nanotubes(MWCNTs) as starting additive under high pressure of 5.8GPa at temperature of 1500°C for 1 min. A special polycrystalline diamond structure of direct bonding of both diamond to diamond and diamond to diamond-MWCNTs composite fiber was observed. The testing results show that it possesses not only high hardness (49-52GPa) and Young’s modulus (878GPa) but also high bending strength (1320~1540GPa) and fracture toughness (9.0~9.2MPa•M1/2) as it was theoretically predicted. The high performances of the composite were contributed to the fiber strengthening effect and the special structure which can offer more extensive diamond to diamond bonding.

scholarly journals Cracking of Copper Brazed Steel Joints Due to Precipitation of MnS upon Cooling

2020 ◽  
Vol 29 (12) ◽  
pp. 8183-8193
Author(s):  
Dheeraj Varanasi ◽  
Daniel Koncz-Horvath ◽  
Anna Sycheva ◽  
Peter Baumli ◽  
George Kaptay
Keyword(s):  
High Vacuum ◽  
Holding Time ◽  
Critical Conditions ◽  
Pure Liquid ◽  
Steel Grades ◽  
Heat Expansion ◽  
Mn Content ◽  
Expansion Coefficients ◽  
Time Required ◽  
Steel Joints

AbstractThe process of brazing of different steel grades by pure liquid copper foil was studied to reveal the critical conditions when cracks do or do not appear in the braze upon cooling without any external load. Steel grades C45 (S 0.030 wt.%, no Mn and no Cr), S103 (Mn 0.25 wt.% and S 0.020 wt.% with no Cr), CK60 (0.75 wt.% Mn, 0.07 wt.% S and 0.15 wt.% Cr) and EN 1.4034 (Cr 12 wt.%, Mn 1.0 wt.% and S 0.035 wt.%) are studied under identical conditions using copper foils of 70-microns-thick. The samples were held above the melting point of copper at 1100 °C under high vacuum for different time durations (between 180 and 3600 s) and then cooled spontaneously. The joints were found cracked during cooling after a certain critical holding time. This critical holding time for cracking was found to decrease with increasing the Mn content and the S content of steel. It is observed that cracking is due to the precipitation of a critical amount of MnS phase upon cooling. The MnS/Cu interface is the weakest interface in the joint (with adhesion ensured only by van-der-Waals bonds), which is broken/separated upon cooling due to difference in heat expansion coefficients of the sulfide and copper phases. Higher is the Mn and S content, shorter is the probable time required for crack to appear in the joint. The braze integrity diagram is constructed as function of solubility product of MnS in steel and holding time showing a stable crack-free technological region and an unstable technological region with high probability of crack formation.

scholarly journals Electrical properties and Mott parameters of polycrystalline diamond films synthesized by HF CVD method from hydrogen/methanol gas mixture

2018 ◽  
Vol 35 (4) ◽  
pp. 830-837 ◽  
Author(s):  
Agnieszka Banaszak-Piechowska ◽  
Kazimierz Fabisiak ◽  
Elżbieta Staryga ◽  
Kazimierz Paprocki
Keyword(s):  
Charge Transport ◽  
Synthetic Diamond ◽  
Electronic Conductivity ◽  
Diamond Films ◽  
Chemical Vapor ◽  
Polycrystalline Diamond ◽  
Temperature Dependent ◽  
Cvd Method ◽  
Crystallite Sizes ◽  
Hot Filament

Abstract The influence of diamond crystallinity and preferred orientation on electronic conductivity of synthetic diamond films grown by hot filament chemical vapor deposition (HFCVD) was investigated. The CVD diamond films of different morphologies and crystallite sizes varying from 36 nm to 67 nm, measured in h2 2 0i direction were considered. The charge transport mechanism in the diamond samples was studied using temperature dependent DC conductivity measurements. The obtained results showed that in the temperature range of 90 K to 300 K charge transport is realized via Variable Range Hopping (VRH, m = 1/4) mechanism. Using VRH model, the Mott parameters were evaluated i.e. density of states at Fermi level N(EF) (0.22 × 1015 eV-1·cm-3 to 1.7 × 1015 eV-1·cm-3), hopping energy W (43.5 meV to 142.3 meV) and average hopping distance R (1.49 × 10-5cm to 2.56 × 10-5cm). It was shown that above mentioned parameters strongly depend on diamond film preferential orientation.

scholarly journals Synthesis, characterisation and thermal behaviour of Cu-based nano-multilayer

2020 ◽  
Author(s):  
M. Czagány ◽  
D. Varanasi ◽  
A. Sycheva ◽  
D. Janovszky ◽  
D. Koncz-Horváth ◽  
...  
Keyword(s):  
Solid State ◽  
Thermal Behaviour ◽  
High Specific Surface Area ◽  
Solid State Diffusion ◽  
State Flow ◽  
Heat Treated ◽  
State Diffusion ◽  
42Crmo4 Steel ◽  
Heat Expansion ◽  
Expansion Coefficients

AbstractCu/AlN–Al2O3 nano-multilayer (NML) was deposited by magnetron sputtering method on 42CrMo4 steel samples, starting with a 15 nm AlN–Al2O3 layer and followed by 200 alternating layers of 5 nm thick Cu and 5 nm thick AlN–Al2O3 layers. The microstructure and thermal behaviour of the as-deposited and heat-treated multilayer was studied. Starting from about 400 °C, extensive coarsening of Cu nanocrystallites and the migration of Cu within the multilayer were observed via solid-state diffusion. Part of the initial Cu even formed micron-sized reservoirs within the NML. Due to increased temperature and to the different heat expansion coefficients of Cu and the AlN–Al2O3, the latter cracked and Cu appeared on the top surface of the NML at around 250 °C. Below 900 °C, the transport of Cu to the top surface of the NML probably took place as a solid-state flow, leading to faceted copper micro-crystals. However, above 900 °C, the Cu micro-crystals found on the top of the NML have rounded shape, so they were probably formed by pre-melting of nano-layered Cu due to its high specific surface area in the NML. Even if the Cu crystals appear on the top surface of the NML via solid-state flow without pre-melting, the Cu crystals on the top surface of the NML can be potentially used in joining applications at and above 250 °C.

scholarly journals Characterizations of microwave plasma CVD grown polycrystalline diamond coatings for advanced technological applications

2014 ◽  
Vol 8 (2) ◽  
pp. 69-80 ◽  
Author(s):  
Awadesh Mallik ◽  
Nandadulal Dandapat ◽  
Shirshendu Chakraborty ◽  
Ashok Mandal ◽  
Jiten Ghosh ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Microwave Plasma ◽  
Plasma Reactor ◽  
Polycrystalline Diamond ◽  
Potential Candidate ◽  
Diamond Coatings ◽  
Etching Technique ◽  
X Ray ◽  
Microwave Plasma Cvd ◽  
Scanning Electronmicroscopy

Polycrystalline diamond (PCD) coatings ranging from few microns to several hundred microns thickness have been grown by 915MHz microwave plasma reactor with 9000W power. The coatings were deposited on 100mm diameter silicon (Si) substrate from few hours to several days of continuous runs. PCD coatings were made freestanding by wet chemical etching technique. The deposited PCDs were evaluated by X-ray diffraction (XRD), scanning electronmicroscopy (SEM), Raman spectroscopy,X-ray photoelectron spectroscopy (XPS) for physical characterization and compared with authors? earlier work. Refractive index of 2.41 was obtained at 633 nm wavelength and a maximum of 6.6 W?cm-1K-1 value for thermal conductivity could be achieved with the grown coatings. The values are well above the existing non-diamond heat spreading substrates, which makes the grown PCDs as candidates for heat spreaders in different technological applications. High refractive in- dex along with translucent nature of the white freestanding PCDs, make them potential candidate for optical windows.

Novel Time-modulated Chemical Vapor Deposition Process for Growing Diamond Films

2002 ◽  
Vol 17 (7) ◽  
pp. 1563-1566 ◽  
Author(s):  
Q. H. Fan ◽  
N. Ali ◽  
Y. Kousar ◽  
W. Ahmed ◽  
J. Gracio
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Film Growth ◽  
Diamond Films ◽  
Chemical Vapor ◽  
Polycrystalline Diamond ◽  
Deposition Process ◽  
Cvd Method ◽  
Control Film ◽  
Hydrocarbon Gas

Smooth polycrystalline diamond films were deposited onto silicon substrates using a newly developed time-modulated chemical vapor deposition (TMCVD) process. The distinctive feature of the TMCVD process involves pulsing the hydrocarbon gas, methane, at different flow rates for varying durations into the vacuum reactor during the chemical vapor deposition (CVD) process. Generally, CVD diamond films display nonuniformity in the crystal sizes and surface roughness along the film growth profile. The TMCVD method was specifically developed to (i) deposit smooth films, (ii) control film microstructure and morphology, and (iii) improve film reliability. We show that the TMCVD process produces diamond films with improved surface smoothness as compared to films of similar thickness produced by conventional CVD method under similar conditions. Surprisingly perhaps, the TMCVD method gave growth rates much higher than the conventional CVD method without reducing the film quality as revealed by the SEM micrographs and micro-Raman spectra.

Diamond Dielectrics for Advanced Wakefield Accelerators

2013 ◽  
Vol 1549 ◽  
Author(s):  
Stanley S. Zuo ◽  
James E. Butler ◽  
Bradford B. Pate ◽  
Sergey P. Antipov ◽  
Alexei Kanareykin ◽  
...  
Keyword(s):  
Electric Field ◽  
Microwave Plasma ◽  
Polycrystalline Diamond ◽  
Dielectric Materials ◽  
Photoluminescence Spectroscopy ◽  
Diamond Structure ◽  
Plasma Enhanced Cvd ◽  
Field Strengths ◽  
Wakefield Accelerators

ABSTRACTDiamond was investigated as one of the superior dielectric materials for advanced wakefield accelerators. Both planar and cylindrical wakefield accelerating structures were constructed. An AsTex microwave plasma-enhanced CVD system was modified for synthesis of cylindrical polycrystalline diamond tubes. Cylindrical diamond tubes were successfully synthesized from hydrogen and methane and are characterized with micro Raman, photoluminescence spectroscopy and optical tests. In addition, planar wakefield structures were constructed from commercially available diamond. Wakefield tests on a rectangular diamond structure confirm that diamond can sustain microwave electric field strengths of 0.3 GV/m at its surface without material breakdown.

The Formation, Structure, Distribution and Frequency of Nuclear Pores

1971 ◽  
Vol 29 ◽  
pp. 518-519
Author(s):  
G. G. Maul
Keyword(s):  
Nuclear Pore Complex ◽  
Nuclear Membrane ◽  
Dynamic Structure ◽  
Nuclear Pore ◽  
Nuclear Pores ◽  
Filter Function ◽  
Etching Technique ◽  
Selective Filter ◽  
Membranous Part

The chromatin of eukaryotic cells is separated from the cytoplasm by a double membrane. One obvious structural specialization of the nuclear membrane is the presence of pores which have been implicated to facilitate the selective nucleocytoplasmic exchange of a variety of large molecules. Thus, the function of nuclear pores has mainly been regarded to be a passive one. Non-membranous diaphragms, radiating fibers, central rings, and other pore-associated structures were thought to play a role in the selective filter function of the nuclear pore complex. Evidence will be presented that suggests that the nuclear pore is a dynamic structure which is non-randomly distributed and can be formed during interphase, and that a close relationship exists between chromatin and the membranous part of the nuclear pore complex.Octagonality of the nuclear pore complex has been confirmed by a variety of techniques. Using the freeze-etching technique, it was possible to show that the membranous part of the pore complex has an eight-sided outline in human melanoma cells in vitro. Fibers which traverse the pore proper at its corners are continuous and indistinguishable from chromatin at the nucleoplasmic side, as seen in conventionally fixed and sectioned material. Chromatin can be seen in octagonal outline if serial sections are analyzed which are parallel but do not include nuclear membranes (Fig. 1). It is concluded that the shape of the pore rim is due to fibrous material traversing the pore, and may not have any functional significance. In many pores one can recognize a central ring with eight fibers radiating to the corners of the pore rim. Such a structural arrangement is also found to connect eight ribosomes at the nuclear membrane.

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