Process of diamond growth from C.sub.70

A method of growing single crystal diamonds in excess of 10 .mu.m in diameter from industrial diamond "seeds" having mean diameters of approximately 1.5 .mu.m is disclosed. The diamonds are grown by exposing the seed diamonds to C.sub.70 in the presence of elemental reducing agents such as phosphorus or selenium in evacuated cells at moderate temperatures and pressures. In another aspect the invention diamonds are grown by exposing diamond seed particles to vapour phase C.sub.70 in the presence of a gas phase metal carbonyl, such as F.sub.5 e(CO) in a temperature range of 400.degree. C. to 700.degree. C. to cause at least some of the diamond seed particles to grow.

FIELD OF THE INVENTION 
The present invention relates to a method of growing diamonds by reduction 
of C.sub.70 Buckminster fullerenes in the presence of diamond seed 
particles. 
BACKGROUND OF THE INVENTION 
Diamond, being the hardest substance known, is of great commercial and 
scientific value. It is inert to chemical corrosion and can withstand 
compressive forces and radiation. It is an electrical insulator having 
extremely high electrical resistance but is an excellent thermal 
conductor, conducting heat better than most other electrical insulators. 
Diamond is structurally similar to silicon but is a wide-band-gap 
semiconductor (5 eV) and so is transparent to UV-visible light and to much 
of the infrared spectrum. It has an unusually high breakdown voltage and 
low dielectric constant. These properties, coupled with recent advances, 
have led to speculation that diamond might find widespread application in 
high speed electronic devices and devices designed to be operated at high 
temperature. If it can be doped successfully diamond could become an 
important semiconductor material on which new or replacement device 
applications may be based. While silicon chips can withstand temperatures 
up to 300.degree. C., it is estimated that diamond devices may be able to 
withstand considerably higher temperatures. Diamond film already find 
applications as hard protective coatings. 
Because of these useful properties, synthetic diamond has great potential 
in research and commercial applications. Synthetic diamonds are now 
produced by two known methods: a high pressure process in which 
carbonaceous material is compressed into diamond using high pressure 
anvils; and the more recent technique of chemical vapour deposition (CVD) 
in which diamond films are deposited on an appropriate substrate by 
decomposing a carbon containing gaseous precursor. 
Of recent particular scientific interest are a class of carbon structures 
known as Buckminster fullerenes which are formed by an integral number of 
carbon atoms which combine to form a closed, roughly spherical structure. 
Two prominent fullerenes are C.sub.60 and C.sub.70, which are spherical 
structures comprising 60 and 70 carbon atoms, respectively. The successful 
transformation of C.sub.60 and C.sub.70 into diamond at high pressure has 
been disclosed by Manuel Nunez Regueiro, Pierre Monceau, Jean-Louis 
Hodeau, Nature, 355, 237-239 (1992) and Manuel Nunez Regueiro, L. Abello, 
G. Lucazeau, J. L. Hodeau, Phys. Rev. B, 46, 9903-9905 (1992). The 
transition of C.sub.60 to diamond has also been studied by Hisako Hirai, 
Ken-ichi Kondo and Takeshi Ohwada, Carbon, 31, 1095-1098 (1993). It is 
also known that C.sub.70 can accelerate the nucleation of diamond thin 
film formation on metal surfaces using CVD as disclosed by R. J. Meilunas, 
R. P. H. Chang, S. Liu, M. M. Kappes, Appl. Phys. Lett., 59, 3461-3463 
(1991), and R. J. Meilunas, R. P. H. Chang, S. Liu, M. M. Kappes, Nature, 
354, 271 (1991). 
A high growth rate of diamond film using fullerene precursors in an argon 
microwave plasma with or without hydrogen has been reported by D. M. 
Gruen, S. Liu, A. R. Krauss and X. Pan, J. Appl. Phys., 75,1758-1763 
(1994), and D. M. Gruen, S. Liu, A. R. Krauss, J. Luo and X. Pan, Appl. 
Phys. Lett., 64, 1502-1504 (1994). 
Recently, dispersed diamond particles with diameters in the range of 20-150 
.ANG. have been observed in fullerene-rich soot as disclosed by Vladimir 
Kuznetsov, A. L. Chuvilin, E. M. Moroz, V. N. Kolomiichuk, Sh. K. 
Shaikhutdinov, Yu. V. Butenko, Carbon, 32, 873-882 (1994), and Vladimir L. 
Kuznetsov, Andrey L. Chuvilin, Yuri V. Butenko, Igor Yu. Malkov, Vladimir 
M. Titov, Chem. Phys. Lett., 222, 343-348 (1994). 
U.S. Pat. Nos. 5,370,855, 5,462,776, 5,328,676 and 5,209,916 issued to 
Gruen disclose methods of conversion of fullerenes to diamond. The methods 
comprise subjecting the fullerenes to highly energetic environments such 
as radio frequency plasma discharges, electron beams, intense laser beams 
to break down potassium modified fullerenes. Growth of diamond onto 
diamond seed substrates heated to 1000.degree. to 1200.degree. C. is 
disclosed in U.S. Pat. No. 5,462,776. A drawback to all these methods of 
fullerene conversion is the fact that at such high temperatures the 
diamond structure is prone to conversion to graphite. Another drawback is 
the expense of the energy imparting devices such as lasers, RF generators 
and the like. 
It would be very advantageous and of potentially significant commercial 
value to be able to grow single crystal diamond particles with much larger 
particle sizes at relatively low temperatures in an environment not 
requiring capital intensive equipment. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an economical process 
for growing single crystal diamonds which does not require high 
temperatures or pressures. 
The present invention provides a process for the formation of diamond 
particles of mean diameters in excess of 4.0.times.10.sup.-4 m, grown from 
diamond powder nucleation seeds of approximately 1.5.times.10.sup.-6 m 
mean diameter. C.sub.70 is reduced in the presence of reducing agents such 
as selenium or phosphorous at moderate temperatures and pressure. 
In one aspect of the invention there is provided a process for growing 
diamonds comprising exposing diamond seed particles to vapour phase 
C.sub.70 in the presence of an element selected from the group consisting 
of selenium and phosphorous at a temperature of at least 550.degree. C. to 
cause at least some of the diamond seed particles to grow. 
In another aspect of the invention there is provided a process for growing 
diamonds. The process comprises providing a plurality of diamond seed 
particles; providing a quantity of C.sub.70 powder and an element selected 
from the group consisting of selenium and phosphorous, the C.sub.70 and 
powder and the element being in flow communication with the diamond seed 
particles; and heating the C.sub.70 powder to produce C.sub.70 powder in 
vapour phase, and heating the element and the diamond seed particles at a 
temperature of at least 500.degree. C. and for a period of time of from 18 
days to 60 days to cause at least some of the diamond seed particles to 
grow. 
In another aspect of the invention there is provided a process for growing 
diamonds. The process comprises providing a plurality of diamond seed 
particles having a mean diameter and providing a quantity of C.sub.70 
powder and a reducing agent. The C.sub.70 powder and the reducing agent 
are in flow communication with the diamond seed particles. The process 
includes the step of heating the C.sub.70 powder to produce C.sub.70 in 
the vapour phase, and heating the reducing agent and the diamond seed 
particles under vacuum at a temperature of from about 500.degree. C. to 
about 600.degree. C. and for a period of time of from about 18 days to 
about 60 days to cause a portion of the C.sub.70 in the vapour phase to be 
reduced by the reducing agent and deposit onto and increase the mean 
diameter of at least one of the diamond seed particles. 
The present invention also provides a process for growing diamonds 
comprising exposing diamond seed particles to vapour phase C.sub.70 in the 
presence of a gas phase metal carbonyl at an effective temperature to 
cause at least some of the diamond seed particles to grow. The gas phase 
metal carbonyl is preferably on of the iron carbonyls and most preferably 
iron penta-carbonyl. 
The invention also provides a process for growing diamonds comprising 
exposing diamond seed particles to vapour phase C.sub.70 in the presence 
of a gas phase catalyst comprising at least CO constituent at an effective 
temperature to cause at least some of the diamond seed particles to grow. 
The catalyst is preferably Fe(CO).sub.5. 
In another aspect the present invention provides a process for growing 
diamonds comprising exposing said diamond seed particles to vapour phase 
C.sub.70 in the presence of a gas phase iron carbonyl at a temperature in 
the range from about 570.degree. C. to about 600.degree. C. to cause at 
least some of the diamond seed particles to grow. The iron carbonyl is 
preferably Fe(CO).sub.5.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, approximately 18 to 20 mg of C.sub.70 (98%), 
approximately 11 mg of elemental selenium powder (99.5%, -325 Mesh 
particle size, Alfa) or red phosphorous powder (99%, -100 Mesh particle 
size, Alfa) and trace quantities of diamond seed powder (average diameter 
of 1.5.times.10.sup.-6 m) were placed generally at 10 in a 1 cm 
diameter.times.10 cm long pyrex tube 12. A trace quantity (&lt;1 mg) of 
diamond powder shown generally at 14 was loaded into a small pyrex 
capillary (1.0 mm.times.50 mm) 16, which was then set into the larger 
pyrex tube 12 as shown in FIG. 1. The entire tube assembly was evacuated 
and sealed under vacuum of approximately 2.66.times.10.sup.-2 Pascals 
(.about.2.times.10.sup.-5 torr). After heating the tube assembly at a 
temperature of about 550.degree. C. in a tube oven (not shown) with 
controllable temperature for 20 to 30 days, various portions of the 
product were examined using laser micro-Raman Spectroscopy and scanning 
electron microscopy (SEM). 
Crystallite sizes and shapes of the diamond seeds and the reaction produces 
were examined using scanning electron microscopy (HITACHI model S-570, 
Japan). The identification of the crystallites as diamond was accomplished 
using Laser micro-Raman spectroscopy. An important advantage of 
micro-Raman spectroscopy is that the sample crystallite can be located by 
a charge coupled device (CCD) camera at high magnification. This enabled 
both the size of the crystallite and its identity to be determined 
simultaneously. A Kr ion laser tuned to 530.87 nm was used as the 
excitation source. An approximately 2 mW beam was focused down to a 3 
micrometer diameter spot. Raman spectra were detected in a back scattering 
geometry using a triplemate spectrometer (SPEX Industries Inc. model 
1877D) equipped with a microscope (Micromate model 1482D) and a liquid 
nitrogen cooled CCD detector (Princeton Instruments Inc. Model LN/CCD). 
An SEM image of the C.sub.70 powder that was used in the above-described 
experiment is shown in FIG. 2. The plate-like crystallites are shown for 
the purpose of comparison with diamond crystallites. FIG. 3 shows an SEM 
image of a sample of the diamond powder that was used as seed diamond. 
Examination of several such samples showed that particle diameters rarely 
exceeded 2.times.10.sup.-6 m and no particle with a diameter in excess of 
3.times.10.sup.-6 m was seen. In contrast, FIG. 4 shows four crystallites 
with average diameters of approximately 400 .mu.m that were found among 
the reaction products of the fullerene seeded with small diamond particles 
and with selenium used as the reducing or reacting agent after 20 days of 
heating at 550.degree. C. Only approximately 1% of the diamond seeds were 
found to be enlarged to this extent. However, on a volume basis the 
overall enlargement of the individual seeds was substantial. 
The micro-Raman spectrum of one of these crystallites is shown in FIG. 6 
over the wavelength range 1000 to about 1700 cm.sup.-1. The characteristic 
single peak at approximately 1328 cm.sup.-1 is unequivocal proof that the 
particle is diamond. The micro-Raman spectrum shown in FIG. 7 is similar 
to the spectrum of FIG. 6 but was taken in the wavelength range 500 to 
about 1700 cm.sup.-1. For comparison, the Raman spectrum of C.sub.70 that 
was used in this work is shown in FIG. 5. There is no such peak at 1328 
cm.sup.-1. The 26 relatively strong vibrational mode frequencies obtained 
from the spectrum of FIG. 5 are in good agreement with values previously 
disclosed in R. A. Jishi, M. S. Dresselhaus, G. Dresselhaus, Kai-An Wang, 
Ping Zhou, A. M. Rao and P. C. Eklund, Chem. Phys. Lett., 206, 187 (1993). 
These vibrational mode frequencies are also in good agreement with group 
theoretical analysis, see M. S. Dresselhaus, G. Dresselhaus and R. Saito, 
Phys. Rev. B, 45, 6234 (1992). In all C.sub.70 has 53 Raman active modes. 
The x-ray diffraction pattern shown in FIG. 8 for one of the grown diamond 
particles in FIG. 4 clearly shows the single crystal cubic structure of 
diamond and this is confirmed from the crystal structure shown in FIG. 9 
calculated from the x-ray diffraction pattern of FIG. 8. 
Most of the larger diamond particles that were produced were found in the 
capillary 16 (FIG. 1) in which the seed diamonds were deposited. This 
strongly suggests that gas-phase C.sub.70 was responsible for the growth 
of the seed diamonds. C.sub.70 has a substantial vapour pressure at 
550.degree. C. The Raman spectrum of the material that remained at the 
bottom of the larger tube 10 after 20 days corresponded to that of 
unreacted C.sub.70. 
Analogous experiments were also conducted using C.sub.60 instead of 
C.sub.70. These experiments using C.sub.60 did not produce any measurable 
growth in the size of the diamond seed particles based on comparison of 
SEMs taken before and after prolonged exposure of the seeds to C.sub.60 
under essentially the same conditions of temperature, pressure and time as 
with the C.sub.70. 
In addition to selenium and phosphorous, other elemental reducing agents 
such as sodium, potassium and sulphur are contemplated by the inventors to 
be effective in reducing C.sub.70 and at temperatures higher than in the 
range 500.degree. to 600.degree. C. 
The following is a possible growth mechanism proposed by the inventors. The 
mechanism is speculative, so it will be understood that the following is 
meant to be a non-limiting explanation. The structure of C.sub.70 is shown 
generally at 40 in FIG. 10 and can be compared to the structure of 
C.sub.60 shown at 70 in FIG. 11. The carbon atoms 42 comprising C.sub.70 
are hybridized intermediately between sp.sup.2 (as in graphite) and 
sp.sup.3, the hybridization of carbon in diamond. When one of the bonds is 
broken in a fullerene, the two carbons comprising the broken bond have a 
choice between sp.sup.2 and sp.sup.3 hybridization according to the nature 
of the reaction partner that reacts at the broken bond. Referring to FIG. 
11, C.sub.60 has two types of C--C bonds; a so-called "single bond" 44 at 
the edges between pentagonal and hexagonal faces, and a "double bond" 46 
at the edges between hexagonal faces. However, all carbon atoms are 
vertices of both hexagonal and pentagonal faces. Referring to FIG. 10, 
C.sub.70 has, additionally, C--C bonds 50 that are edges separating two 
hexagonal faces and, also, vertices of hexagonal faces only. The inventors 
speculate that it is these additional carbon-carbon bonds 50 in C.sub.70 
that break to initiate diamond growth. 
It is speculated that the diamond seed acts as a template whose surface 
dangling bonds ensure that the carbon atoms of the newly ruptured C--C 
bond of the C.sub.70 molecule adopt the sp.sup.3 hybridization required to 
continue the diamond growth. Ultimately all of the carbon atoms of the 
C.sub.70 molecule could be incorporated into the diamond. 
Metal carbonyls also exhibit an efficacy as catalysts for producing single 
crystal diamonds from C.sub.70. In one study, 110 mg of C.sub.70 a was 
placed in a glass capillary tube together with a small quantity of 1-3 
.mu.m mean diameter diamond powder which had previously been cleaned with 
ether, acetone, methanol, acetonitrile, toluene, acetone, water, nitric 
acid, HCl and water. The tube was evacuated and distilled iron carbonyl 
(Fe(CO).sub.5) was introduced to the level of the room temperature vapor 
pressure. The tube was sealed and baked at 580.degree. C. for 150 days. 
Twelve diamond particles were recovered from the cell, each in excess of 
0.1 mm mean diameter. These particles were identified as diamond using 
Raman spectroscopy and x-ray crystallography. Other metal carbonyls than 
iron also exhibit catalytic properties for growth of diamond from C.sub.70 
in addition to iron carbonyls other than the penta-carbonyl. The inventors 
reasonably believe the metal carbonyl is acting as a source of CO which 
may also be acting to catalyse diamond growth. 
The present process is very advantageous since gem diamonds may be grown 
under low pressures and low temperatures for example in the range from 
about 400.degree. C. to about 700.degree. C. As discussed above, prior art 
methods for growing diamonds involve very high pressures and temperatures 
or expensive equipment for generating various kinds of energetic 
environments. The present method provides a very economical method of 
growing diamonds. 
Although the process in accordance with the present invention occurs at 
relatively low temperatures and pressures, it makes use of the free energy 
stored in the C.sub.70 molecule during its formation at the very high 
temperatures of the carbon arc used to generate it. This increase in free 
energy (over that of the graphite precursor in the form of the electrodes 
of the arc) manifests itself in the intermediate hybridization 
characteristic of the fullerenes. Recent theory predicts the involvement 
of a non-planar intermediate which has one sp.sup.3 and one sp hybridized 
carbon, see Robert L. Murray, Douglas L. Strout, Gregory K. Odom and 
Gustavo E. Scuseria, Nature, 366, 665-667 (1993). 
In order to channel this free energy into diamond formation some of the 
C--C bonds in C.sub.70, must be induce to rupture. This is achieved by the 
presence of materials such as selenium, phosphorous and the carbonyl 
catalysts containing CO that donate electrons to the C.sub.70 and, 
therefore, facilitate bond breaking. 
The present invention advantageously provides an economical method of 
growing diamonds from seed diamond particles with C.sub.70 which does not 
require high pressures or temperatures as in the known methods. The result 
that C.sub.70, but not C.sub.60, can be readily reduced in the presence of 
a reducing agent was completely unexpected.