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10000 12000 14000 16000 18000
1180 1230 1280 1330 1380 1430 Raman shift (cm-1)
Intensity (arb. unit)
Sample (b)
Sample (a)
Fig. 7. Raman spectra of two different diamond films deposited on copper. Excitation laser wavelength 633 nm.
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0 10000 20000 30000
1050 1150 1250 1350 1450 1550 Raman shift (cm-1)
Intensity (arb. unit)
2500 4500 6500 8500 10500 12500
Sample (b) Sample (a)
Fig. 8. Raman spectra taken from the samples used in Fig. 7. Excitation laser wavelength 514 nm.
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0 1 2 3
35 65 95 125
2 Theta (deg)
Intensity (arb. unit)
Sample (a) Sample (b)
Reference
(111) (220) (311) (400)
D
Cu Cu
Cu
Cu
Cu Cu
D
D
D D
D D
D
Fig. 9. XRD patterns of two different diamond coatings on copper.
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Fig. 10. SEM images of diamond nucleation on copper substrate with different polishing treatments. (a) No pretreatment. (b) Polished with Al
2O
3powder. (c) Polished with diamond powder.
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Fig.11. Variation in the crystal shape by the growth ratio of (100) face to (111) face.
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450 650 850 1050 1250
1100 1200 1300 1400 1500 1600 1700 Wave number (1/cm)
Intensity (arb. unit) Surface side
Back side
(c)
Fig. 12. SEM images and Raman spectra of the free-standing diamond film prepared by the two-step growth method. (a) film surface side, (b) film back side, (c) Raman spectra taken from the two sides under identical conditions. Wavelength of the laser source:
633 nm.
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8000 11000 14000 17000 20000
1100 1300 1500 1700
Wavenumber (1/cm)
Intensity (arb. unit)
0 20 40 60 80
back side surface side
(c)
Fig. 13. Diamond film grown directly on steel at a microwave power of 2500 W for 5 hrs. SEM images show the film surface side (a) and backside (b). Raman spectra taken from the two sides are shown in (c).
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1337
7600 8100 8600 9100 9600
1250 1300 1350 1400 1450 Wavenumber (1/cm)
Intensity (arb. unit)
Fig. 14. Raman spectrum of the diamond film grown on Ti at 2100 W for 3 hrs.
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1100 1200 1300 1400 1500 Wave number (cm-1)
Intensity (arb. unit)
(a) (b) (c) (d) (e)
Fig. 15. Raman spectra taken from diamond films grown on 0.3 mm-thick Si substrates. The film thickness is (a) 1.7 μm, (b) 4.0 μm, (c) 11 μm, (d) 23 μm, and (e) 48 μm.
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Fig. 16. SEM image of the profile of a thick diamond film.
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Fig. 18. UV Raman spectra of UNCD thin films grown with successive amounts of hydrogen added to the plasma. Reproduced with permission from [156], Elsevier.
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11 Table Captions
Table 1. Outstanding properties of diamond.
Table 2. Properties and application areas of CVD diamond.
Table 3. Parameter range for diamond synthesis by filament-assisted thermal CVD method [30].
Table 4. Present status of low pressure diamond CVD methods.
Table 5. XRD patterns for powdered diamond (Cu Kα radiation, λ=1.5405 Å).
Table 6. Classification of metal substrates for CVD diamond.
Table 7. Diffusion depth p of carbon in iron, where the concentration C(p,T) of carbon is one thousandth of its value C(0,T). Diffusion temperature is 1100 K.
Table 8. Raman shift and corresponding residual stress in diamond films of different thickness deposited on Si substrates. The Raman shift is an average value of five different points in each sample.
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Table 1. Outstanding properties of diamond.
1. Extreme mechanical hardness (~100 GPa).
2. Strongest known material, highest bulk modulus (1.2x1012 N/m2).
3. Highest known value of thermal conductivity at room temperature (2x103 W/m⋅K).
4. Thermal expansion coefficient at room temperature (0.8x10-6 /K) comparable with that of invar.
5. Broad optical transparency from the deep UV to the far IR region of the electro-magnetic spectrum.
6. Good electrical insulator (room temperature resistivity ~1016Ω·cm).
7. Very resistant to chemical corrosion.
8. High radiation hardness.
9. High bandgap (5.47 eV).
10. High breakdown field (~2×107 V/cm).
11. High carrier mobility (2400 cm2/(V·s) for electrons, 2100 cm2/(V·s) for holes.
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Table 2. Properties and application areas of CVD diamond.
Property Comments and
competing materials
Possible applications
Vicker’s hardness (kg/mm2)
Friction coefficient
12000-15000
~0.1 (in air)
As hard as bulk diamond
Depends on the grain size
Drill bits, polishing materials, cutting tools, sintered or brazed diamond compacts, wear resistant coatings on windows and moulds and bearing under vacuum Young’s modulus
(N/m2)
Sound propagation velocity (km/s)
1.2×1012
18.2
Twice the value of alumina, high mechanical strength 1.6x the value of alumina
Stiff membrane for lithography masks, tweeter components, micromechanical oscillators SAW filters
Chemical inertness Inert At room temp.
resistant to all acids bases and solvents
Coating for reactor vessels, diamond containers, diamond electrodes
Range of high transmittance (µm) Refractive index
0.22-0.25 and
>6 2.41
In the IR orders of magnitude lower than other materials;
1.6x the value of silica
UV-VIS-IR windows and coatings, microwave windows, optical filters, optical wave guides
Band gap (eV) Electron/hole mobility (cm2/V⋅s) Dielectric constant
5.47 2400/2100 5.5
1.1 for Si; 1.43 for GaAs; 3 for B-SiC 1500/600 for Si 8500/400 for GaAs 11 for Si
12.5 for GaAs
High power electronics, high frequency devices, high temperature devices, solid-state detectors
Thermal conductivity
(W/cm⋅K) 20 ~4x the value of Cu or
Ag
Heat sinks for electronic devices, heat spreading films on RF devices, laser packages
Thermal expansion coef. (1/K)
0.8×10-6 At room temp. close to silica value of
0.57×10-6
Thermal stable substrates, e.g. for x- ray lithography masks
Work function Negative The vacuum level lies below the conduction band
Light emitters, displays
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Table 3. Parameter range for diamond synthesis by filament-assisted thermal CVD method [30].
Gas mixture Total pressure Temperature (°C)
(Torr) Substrate Filament
H2 + CH4 (0.5-2%) 10-100 700-1000 2000-2300
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Table 4. Present status of low pressure diamond CVD methods.
Method Results
Rate
(µm/h) Area
(cm2)
Quality (Raman)
Substrates Advantages Drawbacks
Combustion flame Hot filament
DC plasma jet
Microwave plasma
DC discharge (low P) DC discharge (medium pressure) RF plasma (thermal, 1 atm) Microwave plasma (ECR 2.45GHz)
30-100
0.5-8
930
3 (low P) 30 (high P)
<0.1
20-250
180
0.1
<2
>250
<2
100
70
<2
3
100
+ +
+ + +
+ + +
+ + +
+
+ + +
+ + +
- / +
Si, Mo, TiN Si, Mo, silica etc.
MO, Si
Si, Mo, silica, WC, Cu etc.
Si, Mo, silica etc.
Si. MO, alumina
Mo
Si
Simple
Simple, large area Rate, quality
Quality, stability
Simple, large area
Rate, quality
Rate, quality
Area, low P, low T
Area, stability
Contaminations, stability
Contamination, homogeneity, stability Rate, area
Quality, rate
Area
Area, stability, homogeneity
Quality, rate, contaminations
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Table 5. XRD patterns for powdered diamond (Cu Kα radiation, λ=1.5405 Å).
hkl 2θ relative intensity
111 43.9 100
220 75.3 25
311 91.5 16
400 119.5 8
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Table 6. Classification of metal substrates for CVD diamond.
1. Little or no solubility or reaction Cu, Sn, Pb, Ag, Au, etc 2. Strong carbon dissolving and
weak carbide formation Pt, Pd, Rh, Fe, Ni 3. Strong carbide formation Si, Nb, Ta, Cr, Mo, W, etc.
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Table 7. Diffusion depth p of carbon in iron, where the concentration C(p,T) of carbon is one thousandth of its value C(0,T). Diffusion temperature is 1100ºK.
Diffusion time (min) 5 10 30
Diffusion depth (µm) 804 1138 1971