Biomedical Engineering Reference
In-Depth Information
energy of the process
Q
α
≈ 230 kJ/mol) and a TD peak
β
centered at
T
β
≈ 385 kJ/mol).
By the analysis of results [3, 4] and taking into account the
above consideration, one can attribute peak
≈ 1523 K
(
∆
T
β
≈ 250 K;
S
β
/
S
≈ 0.55;
Q
β
Σ
of TD to the process
III of dissociative chemisorption of hydrogen between graphene
layers (Table 2.1, model F* in Fig. 2.8). The rate-controlling stage of
the process related to peak
α
can be attributed to hydrogen atoms
diffusion, between two surface graphene layers (Fig. 2.23b), from
the nearest graphene blister to a “punctured” one. This diffusion is
accompanied by a diffuse reversible trapping, such as a C-H bonding
at chemisorption centers in the graphene layers (model F* in
Fig. 2.8). The characteristics of diffusion are as
α
D
,
D
and
Q
≈
III
0III
III
1/2
Q
α
is of 1-10 nm
order, i.e., as the separation between neighboring blisters walls
(Figs. 2.21d and 2.23b). It can be related to the results obtained
for the vibration contribution at 295 meV due to a single H atom
bonding to graphite (C-H) [9].
In the same way, one can attribute peak β of the TD to the
process IV of dissociative chemisorption of hydrogen between
graphene layers with some defects as, for instance, dislocation loops
(Table 2.1 and models C and/or D in Fig. 2.8). The rate-controlling
stage of the process (peak
(Table 2.1). The diffusion length (
D
×
∆
T
/
υ
)
III
α
) can be attributed to hydrogen atoms
diffusion between two surface graphene layers (Fig. 2.23b), from
available graphene blisters to a “punctured” one. This diffusion is
accompanied by a diffuse reversible trapping, such as C-H bonding
at chemisorption centers in the defective regions of the graphene
layers (models C and/or D in Fig. 2.8). The diffusion characteristics
are as
β
D
, D
and
Q
≈
Q
β
(Table 2.1). The diffusion length (
D
IV
0IV
IV
IV
1/2
× ∆
is of 10-100 nm order, i.e., as the separation between
neighboring etch-pits (Fig. 2.22b). Defects of the dislocation loop
type can be created due to the “shrinking” and/or disappearing of a
number of blisters.
The mechanism of etching proposed in Ref. [5], i.e., formation
of etch-pits on the surface (Fig. 2.23b) due to the emission of
carbon atoms, together with hydrogen, from holes edges in
punctured graphene blisters, can be attributed only to process II
of dissociative-associative chemisorption of hydrogen molecules
(Table 2.1 (I), model H in Fig. 2.8 (I)). As shown in Ref. [3, 4], only
process II is characterized by the production of a fairly small amount
of hydrocarbons (CH
T
β
/
υ
)
and others), as seen in the TD spectra.
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