Density of diamond

A diamond is a pure sample of the element carbon. The tabulated density of diamond is 3.51 g/cm. Jewelers use a unit called a carat to describe the mass of a diamond 1 carat = 0.200 g. What is the volume of the stone In a 2.00-carat diamond engagement ring ... 

Diamond and graphite are allotropes of carbon. The density of diamond is 3.5 g/cm3 and that of graphite is 2.2 g/cm3. Diamond is used to cut other hard materials such as glass because of its hardness. On the other hand, softer graphite is used in pencils. 

For the following calculations, assume a total pressure of 20 Torr, surface temperature of 1200 K, and density of Diamond(b) of 3.5 g/cm3. 

A.l 1 Calculate the average density of a single carbon atom by assuming that it is a uniform sphere of radius 77 pm and that the mass of a carbon atom is 2.0 X 10 23 g. The volume of a sphere is f-nr , where r is its radius. Express the density of carbon in grams per cubic centimeter. The density of diamond, a crystalline form of carbon, is 3.5 g-cm 3. What does your answer suggest about the way the atoms are packed together in diamond ... 

This equilibrium can only exist under very special conditions. Density of diamond = 3.5 density of graphite = 2.3 g/cm3. 

The nucleation density of diamond on a pristine Si wafer surface is in the order of only 10 /cm. Since the average distance between diamond nuclei is 10 pm, it is virtually impossible to make a continuous film on this substrate. To increase the nucleation density, the Si surface is mechanically polished with diamond powder or paste. Alternatively, the Si substrate is immersed in alcohol with diamond powder suspension, and ultrasonicated. As a result, the Si surface is subject to mechanical... 

In order to achieve a high nucleation density of diamonds on substrates, higher than 10 /cm, the following three methods are most frequently used ... 

The nucleation density of diamond on as received Si wafer is only in the order of 10 cm by a NIRIM-type MPCVD reactor under standard CVD conditions, e.g. c = 0.5%CH4/H2, P = 30 Torr, and = 800 °C. To make a continuous diamond film within one hour or so under these CVD conditions, a nucleation density of >10 cm is necessary. To achieve this, the Si surface is scratched with diamond powder or paste. The powder size is usually 0.1-30 pm. The nucleation density is increased to approximately 10 cm by this treatment. Alternatively, the Si wafer is ultrasonically treated in alcohol with diamond powder suspension for several minutes. The nucleation density can be increased to 10 -10 cm by this treatment. In both cases, the Si surface is roughened. 

The deposition of carbon particles under a positive bias voltage to the substrate was attributed to the electron flux to the substrate, giving the same effects as the electron-assisted HFCVD [219], in which a negative bias was applied to the filament and a high density of diamond nucleation occurred even without any pretreatment of Si substrates. Figure 10.11 shows the I-V characteristics of the plasma without substrate, indicating that the electron flux was approximately 10 times higher than the ion flux. 

Gerber et al. [221] investigated the nucleation density of diamond on Si, which was placed on a heated stage, by changing the BEN parameters the CH4 concentration c< 15%CH4/H2, V, the biasing time, and T. The nucleation density became maximum of approximately 10 °/cm for 7],. >740°C at F = -250V, and did not depend on the CH4 concentration. Indeed, c = 5 and 15%CH4/H2 resulted in the same saturated nucleation density. An estimated ion energy for optimum nucleation was 70-80 eV, and hence it was concluded that the BEN process proceeds by a subplantation of hydrocarbon ions. 

Electronic Stopping and Momentum Density of Diamond from First-Principles Treatment of the Microscopic Dielectric Function... 

O. C (5, diamond) C s, graphite) (This equilibrium can exist only under very special conditions.) Densities of diamond and graphite are 3.5 and 2.3g/cm , respectively. 

The density of diamond is comparatively high, 3.514gcm h Its hardness according to Mohs is 10, which is the highest value ever measured for a natural material. (Note that today there are several synthetic materials with a hardness higher than that of diamond these include some of the polymeric fuUerenes (Chapter 2) obtained under high pressure.) Still hardness is not equal for each crystal plane. 

Surface nucleation rates and densities of diamond on non-diamond substrates vary fi-om 10 to 10 cm h and from 10 to 10 cm, respectively, depending on substrate materials, surface pretreatment methods, and synthesis conditions. The possible maximum nucleation density of diamond would be 10 cm . ... 

Table 5. Typical Surface Nucleation Densities of Diamond After Various...

Kim et al.f studied the effect of gas pressure on the nucleation behavior of diamond on a Si(lOO) substrate in HFCVD. The pressure was varied from 2 to 50 torr, while a filament temperature of2200°C, a substrate temperature of 850°C, a total flow rate of 20 seem and a CH4 concentration of 0.8 vol.% were used. The characterization of diamond deposits using micro-Raman spectroscopy, SEM and OM revealed that the maximum nucleation density of diamond parades on the unscratched Si substrate occurred at a pressure of 5 torr. The pressure dependence of the nucleation density was explained by the competition effect between P-SiC formation, which increases the diamond nucleation density, and atomic-hydrogen etching, which decreases the nmnber of nucleation sites. On the basis of this finding, a new fabrication approach for high-quality diamond films without... 

Y. Hibino, and Y. Hayashi, Increase in nucleation density of diamond film growth by D plasma chemical vapor deposition, Stof. Coat Technol, 54-55(l-3) 365-367... 

Take the C-C bond energy to be 376kJ/mol. Calculate the surface energy of the (111) plane in diamond. Repeat for the (100) plane. Which plane do you think would cleave more easily Information you may find useful density of diamond is 3.51 g/cm and its lattice parameter is 0.356 nm. 

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