Biomedical Engineering Reference
In-Depth Information
substrate holder, but may be a combination of these mechanisms. Our result was purely based on
negatively BEN related to the grounded filament. However, Polo et al. [66] reported that very low
electric biasing current values (μA) were detected for applied substrate biases voltages, either posi-
tive or negative. Furthermore, increasing negative biases of up to 200V resulted in value of nucle-
ation density, similar to that obtained with positively BEN. In contrast, an application of negative bias
applied to the substrate at 250V resulted in (10 10 cm 2 ) maximum values of nucleation density. The
enhancement in the nucleation density could be attributed to the electron current from the filament
by increasing the decomposition of H 2 and CH 4 [64,71] . The increase in the nucleation density is as
expected since negatively biasing the substrate increases the rate of ion bombardment into the surface
creating greater numbers and density of nucleation sites.
Therefore, the greater the density of nucleation sites the higher the expected nucleation density.
Kamiya et al. [68] reported that reproducibility of the experiment was poor and that no definite trend
in the nucleation density could be found with respect to different bias conditions.
(A)
(B)
HV
20.0 kV
HV
20.0 kV
Spot
5.0
Mag
7000x
Det
Etd
Sig
SE
WD
10.05 mm
Pre s sure
5 µ m
Spot
5.0
Mag
8000x
Det
Etd
Sig
SE
WD
9.98 mm
Pre ss ure
5 µ m
(C)
(D)
HV
30.0 kV
Spot
2.5
Mag
12000x
Det
Etd
Sig
SE
WD
11.54 mm
HV
30.0 kV
Spot
2.5
Mag
3000x
Det
Etd
Sig
SE
WD
11.54 mm
Pre s sure
20 µ m
Pre ss ure
5 µ m
FIGURE 15.14
SEMs showing (A) and (B) with 180 V negative substrate and (C) and (D) without bias of the bur
cutting edges.
 
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