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Formation of self-supporting hollow diamond helix and diamond sieve using “jet-flow” HFCVD
Solid State Communications, Vol. 93, No. 9, pp. 759-762, 1995 Elsevier Science Ltd Printed in Great Britain 0038-1098/95 $9.50+.00 0038-1098(94)00x47-7
Pergamon
FORMATION OF SELF-SUPPORTING HOLLOW DIAMOND HELIX AND DIAkKJNDSIEVE USING "JET-FLOW" HFCVD A.K. Dua, D.D. Pruthl, V.C. George and P.RaJ, Materials Science Section, Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay-400085,
INDIA
(Received 3 September 1YY4,accepted for publication 3 November 1YY4 by C.N.R.Rao) This describes the methodology for the paper preparation of selfsupporting hollow diamond helix and diamond sieve in addition to diamond microtubes. The key idea is to deposit thick, compact and sufficiently strong coating on a suitable mandrel and then dissolve the latter so as to form the required shape. For this purpose we have made use of ‘Jet-flow’ HFCVD which allows diamond deposition over larger area on three dimensional substrates both inside as well as outside. X-ray diffraction, laser macro-&man spectroscopy and scanning electron microscopy have been used to characterlse shape, morphology and the phase purity of the material
substrates to the materials which can .. 85O’C. withstand a temperature of For forming the hollow diamond helix, the mandrel consisted of a tungsten wire spiral (diameter = 3mm, length = 1.2cm, nine uniformly separated turns, the wire diameter = 0.3mm) and for microtube it was a tungsten wire 0.3mm On the other hand, for in diameter. the diamond sieve, tantalum strip (lcm x lcm X 125 wm) with O.Smm diameter through holes mechanically drilled in Hydrogen formed the mandrel. it SO’C) has been used for peroxide (at dissolution of tungsten and a mixture 7O’C 1 for the of HNo3 and HF (at
l.Introduction In a recent paper, May et al’ have reported some of the potential applications for solid and hollow diamond fibers as reinforcing agent in metal-matrix ’ smart’ composites. However, generating intricate diamond shapes is a challenging task. Conventional heated filament chemical vapour deposition (HFCVD) has been employed recently to form diamond tubes and f lbers”2 with several restrictions on their size and shape. Some of these restrictions may be overcome by the use of ’ Jet-f low’ HFCVD which al lows diamond appreciably deposition at larger distance from the filament (5 cm.) over larger area and on three dimensional substrates both inside as
dissolution of tantalum carbide compounds. 2.2
well as outslde3. Making use of these plus points and chemical etching, we have successfully engineered pure, self supporting hollow diamond helix and diamond sieve in addition to diamond mlcrotube. The key idea behind the process is to deposit a thick, compact and sufficiently strong coating on a suitable mandrel and then dissolve the latter so as to form the required shape. The present communlcatlon describes the details of the method employed and characterlsatlon of the material. 2. 2.1
Mandrel
HFCVD deposition
technique generally
Diamond deposition
described elsewhere’. Heating of the substrates is affected by heat radiated from the heated filament together with the passage of the required amount of electrical current through them. Deposition parameters optlmlsed for the filament to present studies are: substrate distance = 1.7 cm., Jet to filament distance = 3.4cm.; diameter of
solvents for restricts
interface
experimental set up is The essentially the same as normally used for heated filament chemical vapour deposition with the only difference that the inlet gases, at high flow rate pass through a flne nozzle thereby attaining high velocities which are then directed towards the heated filament. Details of the facility, the experimental procedure and the substrate preparation have already been
Experimental and the
and
diamond the 759
SELF-SUPPORTING
160
the jet hole = 1 mm; substrates tungsten (for helix and microtube) and substrate tantalum (for sieve I; temperature = 9oo"c. filament 5 mm diameter, 9 spiral, tungsten turns, 1.2 cm. long and made out of 0.5 mm diameter wire; filament temperature = 2050°C, chamber pressure = 12 torr; Flow rates: hydrogen - 1600 scc/min., methane - 6 scc/min. and oxygen - 2 scc/min., deposition time * 35 hours. 2.3 Diamond
characterisation:
has The morphology of the deposit been studied using a JEOL-JSM-A 300 X-ray scanning electron microscope. diffraction studies have been carried 1710 using a Philips PW out diffractometer employing copper K (L Laser Raman radiation. macro spectroscopy has been employed to study the quality of the diamond deposit in back-scattering geometry using 514.53 line of an Ar+ laser at a power of ;ZO mW. 3.
Results and Discussion
Studies have been carried out on effect of various deposition the parameters (including variation of flow rate, nozzle hole size, reactor pressure and role of oxygen) on the size, density, amount and quality of diamond crystallites deposited in our ‘jet flow' HFCVD facility and the results are being communicated". The main finding is that keeping the methane and oxygen flow rates fixed at
HOLLOW
DIAMOND
HELLX
Vol. 93, No. 9
6 and 2 scc/min respectively, intermediate hydrogen flow rates give crystallite size, larger higher crstallites density, greater deposition and better quality (i.e amount crystallites defined by sharp edges and faces and with minimum of non-diamond content) of the deposit as compared to (300scc/min. 1 low and high (2000scc/min.l flow rates. The flow rates used in the present work give best quality deposits and at appreciable rate of deposition. Optimum value of the reactor pressure, during operation, in our experiments was found to be in the range lo-20 torr. The size was found to have of the jet-hole appreciable effect coating on characteristics. Very large sized hole was akin to convert the ‘jet flow' system to conventional diffusion controlled type. It reduced the particularly so at deposition rate, distances larger than lcm from the filament. On the other hand , when the jet hole size was too small, larger acquired by velocity the gaseous mixture coming out of the hole reduced contact time with the heated their increasing the filament, thereby non-diamond content in the deposit. A jet hole of lmm diameter as used in the experiments gave present optimum performance. supporting hollow diamond Self helix is shown in fig. l(a) and l(b), while fig.2 shows the diamond sieve. These shapes were quite strong and be handled could Helix easily. stength was measured experimentally employing tensile pull method. The value of strength ( Young's modulus) was found to be approximately 200 GPa. This compares favourably with the extrapolated projected strength* value of 275 GPa for a hollow diamond tube having a void volume of 69 % as is the case for the tubular portion of the helix being measured here. Helix strength is expected to increase with decreasing void fraction and decreasing diameter of its tubular portion. Also a decrease in the overall diameter of the should helix enhance its strength. finer crystalline morphology Further,
Scanning electron micrographs Fig. 1 showing (a) Self supporting pure diamond helix (bl Hollowness of the helix and diamond crystallites forming it.
Fig. 2 SEM image of a self supporting pure diamond sieve.
Vol. 93, No. Y
SELF-SUPPORTING
HOLLOW DIAMOND
of the deposit, decrease in the number of bulk and surface irregularities (i.e gross defects1 and increase in the number of dislocation motion impeders in the all work in the deposit, direction of making the helix more strong. X- ray pattern of the material, obtained from the tubular shapes, after dissolution of the tungs$en mandrel in followed by heated hydrogen peroxide half an hour treatment in a 1:4 mixture of nitric acid and hydrofluoric acid (at 70°Cl, is shown in fig. 3(b). The spectrum is quite clean and Bragg diffraction lines due to diamond only On the other hand, after are present. the dissolution in heated hydrogen peroxide alone’ i.e. in the absence of with the mixture of the treatment nitric acid and hydrofluoric acid, the pattern [fig. 3(a)] shows xray tungsten due to lines additional
761
HELIX
hydrogen peroxide is able to dissolve tungsten but not tungsten carbides. Also within the sensitivity limit of the x-ray diffraction technique, the tubular shapes formed are of pure diamond. Further, similar result has obtained also been for the sieve material. Typical Raman spectrum of the material of the different shapes formed is shown in fig.4. Only 1332 cm-’ diamond Raman line is present and non-diamond content, if at all there, is insignificant. This again points to the shapes formed being pure diamond. The hollowness of the helix and the been microtube has confirmed by breaking these at random positions and finding that they are hollow. A wire could also be passed through the entire length of the microtube reconfirming its hollowness. Recently formation of the diamond tubes and fibers have also been reported by other workers”2. They used conventional HFCVD technique which the size and restrictions on puts that may be formed. In shapes contrast, the jet flow RFCVD used by us is more versatile. The mandrel for the helix in the present case was placed at a distance of 1.7 cm from the heated filament and in spite of its diameter being around 3mm, it could be more or less uniformly coated all around with pure diamond at a deposition rate of Further-,x-ray diffraction 0.65 gm/hr. pattern [fig. 3(a)] of the tube , prepared by dissolving tungsten (from the diamond coated tungsten wire) {n hot H202, as was done by May et al ,
These carbides get formed5’6 carbides. the tungstendiamond interface at under the HFCVD conditions normally Thus it follows that heated used.
clearly shows the presence of tungsten leads us to carbide lines. This suggest that the diamond tube formed by them may contain some tungsten cfrbides have and Noda impurity . Higuchi reported the formation of diamond mesh
1 03 6300.0
2700.0 50
60 28
70
80
w
(degrees)
Fig. 3 X - ray diffraction pattern of the tubular structure obtained after (a) Dissolution of the tungsten mandrel in hydrogen peroxide at 50 C. (b) Dissolution as in (al followed by half an hour treatment in a 1:4 mixture of nitric acid and hydrofluoric acid at 70°C.
IW 18W.O
-.“l-__-_1200.0
13w.o
1400.0
15CQ.0
IWO
Raman shift (cm-')
Fig. 4 Typical macro Raman spectrum of the material of the different shapes formed.
17W.I
762
SELF-SUPPORTING
Vol. 93, No. Y
HOLLOW DIAMOND HELIX
require an electrically insulating and thermally conducting link between the heater and the sample (e.g in VG mass spectrometer sample holder and heating assembly 1 and diamond helix may be gainfully employed for the purpose.
pattern on a substrate using selected area diamond deposition through a given photolithographically. formed mask However our diamond sieve Is self supporting and it has been formed by The holes entirely different method. in our diamond sieve (fig.21 are not so well defined, which is basically due to non-uniformity of the holes and due to burs present therein. Nevertheless the attempt has been to show that the method works. In our experiments on the diamond sieve AR/R (where &R is the coating thickness inside the hole and R is the dlameter of the hole) varied run and upto 15% upto 10% in a single from run to run. it may be concluding. Before mentioned that although the possible of diamond tube metal applications matrix composites have already been established well examined’, no hollow diamond helix applications of However are known to the authors. possibilities interesting several the The helix may replace exist. element in Bourdon expansion type gauges for measuring pressure of highly It may also find use reactive fluids. in devices where thermally conducting shock electrically insulating and in hostile required absorbers are chemical environment. Some applications
4.
Conclusions
We have successfully deposited pure self supporting hollow diamond helix and diamond sieve in addition to diamond microtubes. The Jet flow HFCVD method reported here may as well be used to prepare, within experimental limitations, any other desired shapes. These and other shapes, endowed with extreme and exceptional diamond properties are expected to be useful. Acknowledgements The authors are grateful to Dr. J.P.Mittal, Director of the Chemlstry Group and Dr. K.V.S. Rama Rao , Head of the Chemistry Division, for keen their interest and encouragement in this work. They are also thankful to Ms. M.A. Rekha of Solid State Physics Division for recording the laser Raman spectrum and Shri K.K. Kutty of Chemistry Division for help in scanning electron microscopy. References
P.W. May, C. A. Rego, R.M. Thomas, 1. M.N.R. Ashfold, K.N. Rosser ,P.G. Partridge and N.M. Everitt; J. Mater. 13 (19941 p. 247-49. Sci. Lett., J.W. Glesener, M. 2. A. A. Morrlsh, Fehrenbacher, P.E. Pehrsson, B.Maruyama and P.M. Natishan, Diamond and Related Materials, 3 (19941 173-176. 3. A.K. Dua. V.C. George, D.D. Pruthi and P.RaJ, Solid State Communications, 86 (19931 39-41. 4. A.K. Dua, D.D. Pruthi, V.C. George, P. RaJ, M.A. Rekha and A. P. Roy, To be Related communicated to Diamond and Materials, 1994.
5. C.P. Sung and H.C. Shih, J.Mater. Res., 7 (19921 105116. 6. A.K. Dua, D.D. Pruthi, V.C. George and P. BARC/1992/E/030, Bhabha RaJ, Atomic Research Centre, Bombay, India, 1992. 7. K. Higuchi and S. Noda, Diamond and Related Materials, l(19921 220-229.
Pergamon
FORMATION OF SELF-SUPPORTING HOLLOW DIAMOND HELIX AND DIAkKJNDSIEVE USING "JET-FLOW" HFCVD A.K. Dua, D.D. Pruthl, V.C. George and P.RaJ, Materials Science Section, Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay-400085,
INDIA
(Received 3 September 1YY4,accepted for publication 3 November 1YY4 by C.N.R.Rao) This describes the methodology for the paper preparation of selfsupporting hollow diamond helix and diamond sieve in addition to diamond microtubes. The key idea is to deposit thick, compact and sufficiently strong coating on a suitable mandrel and then dissolve the latter so as to form the required shape. For this purpose we have made use of ‘Jet-flow’ HFCVD which allows diamond deposition over larger area on three dimensional substrates both inside as well as outside. X-ray diffraction, laser macro-&man spectroscopy and scanning electron microscopy have been used to characterlse shape, morphology and the phase purity of the material
substrates to the materials which can .. 85O’C. withstand a temperature of For forming the hollow diamond helix, the mandrel consisted of a tungsten wire spiral (diameter = 3mm, length = 1.2cm, nine uniformly separated turns, the wire diameter = 0.3mm) and for microtube it was a tungsten wire 0.3mm On the other hand, for in diameter. the diamond sieve, tantalum strip (lcm x lcm X 125 wm) with O.Smm diameter through holes mechanically drilled in Hydrogen formed the mandrel. it SO’C) has been used for peroxide (at dissolution of tungsten and a mixture 7O’C 1 for the of HNo3 and HF (at
l.Introduction In a recent paper, May et al’ have reported some of the potential applications for solid and hollow diamond fibers as reinforcing agent in metal-matrix ’ smart’ composites. However, generating intricate diamond shapes is a challenging task. Conventional heated filament chemical vapour deposition (HFCVD) has been employed recently to form diamond tubes and f lbers”2 with several restrictions on their size and shape. Some of these restrictions may be overcome by the use of ’ Jet-f low’ HFCVD which al lows diamond appreciably deposition at larger distance from the filament (5 cm.) over larger area and on three dimensional substrates both inside as
dissolution of tantalum carbide compounds. 2.2
well as outslde3. Making use of these plus points and chemical etching, we have successfully engineered pure, self supporting hollow diamond helix and diamond sieve in addition to diamond mlcrotube. The key idea behind the process is to deposit a thick, compact and sufficiently strong coating on a suitable mandrel and then dissolve the latter so as to form the required shape. The present communlcatlon describes the details of the method employed and characterlsatlon of the material. 2. 2.1
Mandrel
HFCVD deposition
technique generally
Diamond deposition
described elsewhere’. Heating of the substrates is affected by heat radiated from the heated filament together with the passage of the required amount of electrical current through them. Deposition parameters optlmlsed for the filament to present studies are: substrate distance = 1.7 cm., Jet to filament distance = 3.4cm.; diameter of
solvents for restricts
interface
experimental set up is The essentially the same as normally used for heated filament chemical vapour deposition with the only difference that the inlet gases, at high flow rate pass through a flne nozzle thereby attaining high velocities which are then directed towards the heated filament. Details of the facility, the experimental procedure and the substrate preparation have already been
Experimental and the
and
diamond the 759
SELF-SUPPORTING
160
the jet hole = 1 mm; substrates tungsten (for helix and microtube) and substrate tantalum (for sieve I; temperature = 9oo"c. filament 5 mm diameter, 9 spiral, tungsten turns, 1.2 cm. long and made out of 0.5 mm diameter wire; filament temperature = 2050°C, chamber pressure = 12 torr; Flow rates: hydrogen - 1600 scc/min., methane - 6 scc/min. and oxygen - 2 scc/min., deposition time * 35 hours. 2.3 Diamond
characterisation:
has The morphology of the deposit been studied using a JEOL-JSM-A 300 X-ray scanning electron microscope. diffraction studies have been carried 1710 using a Philips PW out diffractometer employing copper K (L Laser Raman radiation. macro spectroscopy has been employed to study the quality of the diamond deposit in back-scattering geometry using 514.53 line of an Ar+ laser at a power of ;ZO mW. 3.
Results and Discussion
Studies have been carried out on effect of various deposition the parameters (including variation of flow rate, nozzle hole size, reactor pressure and role of oxygen) on the size, density, amount and quality of diamond crystallites deposited in our ‘jet flow' HFCVD facility and the results are being communicated". The main finding is that keeping the methane and oxygen flow rates fixed at
HOLLOW
DIAMOND
HELLX
Vol. 93, No. 9
6 and 2 scc/min respectively, intermediate hydrogen flow rates give crystallite size, larger higher crstallites density, greater deposition and better quality (i.e amount crystallites defined by sharp edges and faces and with minimum of non-diamond content) of the deposit as compared to (300scc/min. 1 low and high (2000scc/min.l flow rates. The flow rates used in the present work give best quality deposits and at appreciable rate of deposition. Optimum value of the reactor pressure, during operation, in our experiments was found to be in the range lo-20 torr. The size was found to have of the jet-hole appreciable effect coating on characteristics. Very large sized hole was akin to convert the ‘jet flow' system to conventional diffusion controlled type. It reduced the particularly so at deposition rate, distances larger than lcm from the filament. On the other hand , when the jet hole size was too small, larger acquired by velocity the gaseous mixture coming out of the hole reduced contact time with the heated their increasing the filament, thereby non-diamond content in the deposit. A jet hole of lmm diameter as used in the experiments gave present optimum performance. supporting hollow diamond Self helix is shown in fig. l(a) and l(b), while fig.2 shows the diamond sieve. These shapes were quite strong and be handled could Helix easily. stength was measured experimentally employing tensile pull method. The value of strength ( Young's modulus) was found to be approximately 200 GPa. This compares favourably with the extrapolated projected strength* value of 275 GPa for a hollow diamond tube having a void volume of 69 % as is the case for the tubular portion of the helix being measured here. Helix strength is expected to increase with decreasing void fraction and decreasing diameter of its tubular portion. Also a decrease in the overall diameter of the should helix enhance its strength. finer crystalline morphology Further,
Scanning electron micrographs Fig. 1 showing (a) Self supporting pure diamond helix (bl Hollowness of the helix and diamond crystallites forming it.
Fig. 2 SEM image of a self supporting pure diamond sieve.
Vol. 93, No. Y
SELF-SUPPORTING
HOLLOW DIAMOND
of the deposit, decrease in the number of bulk and surface irregularities (i.e gross defects1 and increase in the number of dislocation motion impeders in the all work in the deposit, direction of making the helix more strong. X- ray pattern of the material, obtained from the tubular shapes, after dissolution of the tungs$en mandrel in followed by heated hydrogen peroxide half an hour treatment in a 1:4 mixture of nitric acid and hydrofluoric acid (at 70°Cl, is shown in fig. 3(b). The spectrum is quite clean and Bragg diffraction lines due to diamond only On the other hand, after are present. the dissolution in heated hydrogen peroxide alone’ i.e. in the absence of with the mixture of the treatment nitric acid and hydrofluoric acid, the pattern [fig. 3(a)] shows xray tungsten due to lines additional
761
HELIX
hydrogen peroxide is able to dissolve tungsten but not tungsten carbides. Also within the sensitivity limit of the x-ray diffraction technique, the tubular shapes formed are of pure diamond. Further, similar result has obtained also been for the sieve material. Typical Raman spectrum of the material of the different shapes formed is shown in fig.4. Only 1332 cm-’ diamond Raman line is present and non-diamond content, if at all there, is insignificant. This again points to the shapes formed being pure diamond. The hollowness of the helix and the been microtube has confirmed by breaking these at random positions and finding that they are hollow. A wire could also be passed through the entire length of the microtube reconfirming its hollowness. Recently formation of the diamond tubes and fibers have also been reported by other workers”2. They used conventional HFCVD technique which the size and restrictions on puts that may be formed. In shapes contrast, the jet flow RFCVD used by us is more versatile. The mandrel for the helix in the present case was placed at a distance of 1.7 cm from the heated filament and in spite of its diameter being around 3mm, it could be more or less uniformly coated all around with pure diamond at a deposition rate of Further-,x-ray diffraction 0.65 gm/hr. pattern [fig. 3(a)] of the tube , prepared by dissolving tungsten (from the diamond coated tungsten wire) {n hot H202, as was done by May et al ,
These carbides get formed5’6 carbides. the tungstendiamond interface at under the HFCVD conditions normally Thus it follows that heated used.
clearly shows the presence of tungsten leads us to carbide lines. This suggest that the diamond tube formed by them may contain some tungsten cfrbides have and Noda impurity . Higuchi reported the formation of diamond mesh
1 03 6300.0
2700.0 50
60 28
70
80
w
(degrees)
Fig. 3 X - ray diffraction pattern of the tubular structure obtained after (a) Dissolution of the tungsten mandrel in hydrogen peroxide at 50 C. (b) Dissolution as in (al followed by half an hour treatment in a 1:4 mixture of nitric acid and hydrofluoric acid at 70°C.
IW 18W.O
-.“l-__-_1200.0
13w.o
1400.0
15CQ.0
IWO
Raman shift (cm-')
Fig. 4 Typical macro Raman spectrum of the material of the different shapes formed.
17W.I
762
SELF-SUPPORTING
Vol. 93, No. Y
HOLLOW DIAMOND HELIX
require an electrically insulating and thermally conducting link between the heater and the sample (e.g in VG mass spectrometer sample holder and heating assembly 1 and diamond helix may be gainfully employed for the purpose.
pattern on a substrate using selected area diamond deposition through a given photolithographically. formed mask However our diamond sieve Is self supporting and it has been formed by The holes entirely different method. in our diamond sieve (fig.21 are not so well defined, which is basically due to non-uniformity of the holes and due to burs present therein. Nevertheless the attempt has been to show that the method works. In our experiments on the diamond sieve AR/R (where &R is the coating thickness inside the hole and R is the dlameter of the hole) varied run and upto 15% upto 10% in a single from run to run. it may be concluding. Before mentioned that although the possible of diamond tube metal applications matrix composites have already been established well examined’, no hollow diamond helix applications of However are known to the authors. possibilities interesting several the The helix may replace exist. element in Bourdon expansion type gauges for measuring pressure of highly It may also find use reactive fluids. in devices where thermally conducting shock electrically insulating and in hostile required absorbers are chemical environment. Some applications
4.
Conclusions
We have successfully deposited pure self supporting hollow diamond helix and diamond sieve in addition to diamond microtubes. The Jet flow HFCVD method reported here may as well be used to prepare, within experimental limitations, any other desired shapes. These and other shapes, endowed with extreme and exceptional diamond properties are expected to be useful. Acknowledgements The authors are grateful to Dr. J.P.Mittal, Director of the Chemlstry Group and Dr. K.V.S. Rama Rao , Head of the Chemistry Division, for keen their interest and encouragement in this work. They are also thankful to Ms. M.A. Rekha of Solid State Physics Division for recording the laser Raman spectrum and Shri K.K. Kutty of Chemistry Division for help in scanning electron microscopy. References
P.W. May, C. A. Rego, R.M. Thomas, 1. M.N.R. Ashfold, K.N. Rosser ,P.G. Partridge and N.M. Everitt; J. Mater. 13 (19941 p. 247-49. Sci. Lett., J.W. Glesener, M. 2. A. A. Morrlsh, Fehrenbacher, P.E. Pehrsson, B.Maruyama and P.M. Natishan, Diamond and Related Materials, 3 (19941 173-176. 3. A.K. Dua. V.C. George, D.D. Pruthi and P.RaJ, Solid State Communications, 86 (19931 39-41. 4. A.K. Dua, D.D. Pruthi, V.C. George, P. RaJ, M.A. Rekha and A. P. Roy, To be Related communicated to Diamond and Materials, 1994.
5. C.P. Sung and H.C. Shih, J.Mater. Res., 7 (19921 105116. 6. A.K. Dua, D.D. Pruthi, V.C. George and P. BARC/1992/E/030, Bhabha RaJ, Atomic Research Centre, Bombay, India, 1992. 7. K. Higuchi and S. Noda, Diamond and Related Materials, l(19921 220-229.