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10 Electrochemical Manufacturing Methods Based on Surface …
Although the bubbling-induced graphene delamination and transfer became
widely accepted shortly after its appearance, some doubt arose concerning the delamination mechanism, and the picture on the graphene transfer process had to be refined.
When Ru was the growth substrate for the CVD graphene growth, the initiation of
the electrochemical delamination did not require any hydrogen bubbling but the
process started in the H-UPD potential regime in KOH solution [100]. The complete
delamination was achieved at highly negative potential. It seems to be likely that the
negative charge of the substrate surface after the partial delamination of the supported
graphene sheet and the corresponding cation ingress into the solution layer under
the graphene sheet contributes to the driving force of the delamination. A similar
bubbling-free transfer process was elaborated for Cu substrate [101] where oxygen
reduction was found to be responsible for the delamination in a potential range where
metallic Cu was stable but no hydrogen evolution could occur. Since the graphene
detachment did not work in the absence of the dissolved oxygen, the oxygen reduction leading to hydroxide ions was found to be responsible for the delamination
process.
A recent work published on the systematic study of the graphene delamination
opportunity with various solutions claimed that the major driving force is the ion
intercalation between the substrate and the graphene sheet at the applied potential,
and gas evolution is at most of secondary importance [102]. The major argument
for the intercalation effect is that from various solutions, the delamination takes
place at potentials where essentially no steady-state current flow. Since the variety
of solutions and experimental conditions tested so far is quite limited, it seems to be
too early to stand up a mechanism valid for all cases, and further progress can be
anticipated in this field.
10.5.5 Electrochemical Exfoliation of Various Inorganic
Materials
Among the chemical elements other than carbon, phosphorous has an allotrope with
atomic layer structure, i.e., black phosphorous. In contrast to graphite, the “atomic
plane” of black phosphorous is not planar but plaited. Anodic exfoliation from neutral
aqueous solution is possible [61, 103], just as the delamination with cathodic treatment where the application of an inert solvent is preferred [103–105]. Regardless
of the media used for the cathodic exfoliation (e.g., propylene carbonate with tetrabutylammonium hexafluorophosphate [104] or dimethyl sulfoxide with tetrabutylammonium tetrafluoroborate [105]), the thickness range of the nanosheets obtained
varied between 2 and 10 nm, but the diameter of the sheets achieved 10 μm. Anodic
treatment led to thinner lamellae but still not single atomic layers with a mean thickness of 1.4 nm [61]. Black phosphorous nanosheets can be used from dispersion
in a non-reactive solvent and applied for photosensors in thin-layer microelectronic
devices.
10 Electrochemical Manufacturing Methods Based on Surface …
Although the bubbling-induced graphene delamination and transfer became
widely accepted shortly after its appearance, some doubt arose concerning the delamination mechanism, and the picture on the graphene transfer process had to be refined.
When Ru was the growth substrate for the CVD graphene growth, the initiation of
the electrochemical delamination did not require any hydrogen bubbling but the
process started in the H-UPD potential regime in KOH solution [100]. The complete
delamination was achieved at highly negative potential. It seems to be likely that the
negative charge of the substrate surface after the partial delamination of the supported
graphene sheet and the corresponding cation ingress into the solution layer under
the graphene sheet contributes to the driving force of the delamination. A similar
bubbling-free transfer process was elaborated for Cu substrate [101] where oxygen
reduction was found to be responsible for the delamination in a potential range where
metallic Cu was stable but no hydrogen evolution could occur. Since the graphene
detachment did not work in the absence of the dissolved oxygen, the oxygen reduction leading to hydroxide ions was found to be responsible for the delamination
process.
A recent work published on the systematic study of the graphene delamination
opportunity with various solutions claimed that the major driving force is the ion
intercalation between the substrate and the graphene sheet at the applied potential,
and gas evolution is at most of secondary importance [102]. The major argument
for the intercalation effect is that from various solutions, the delamination takes
place at potentials where essentially no steady-state current flow. Since the variety
of solutions and experimental conditions tested so far is quite limited, it seems to be
too early to stand up a mechanism valid for all cases, and further progress can be
anticipated in this field.
10.5.5 Electrochemical Exfoliation of Various Inorganic
Materials
Among the chemical elements other than carbon, phosphorous has an allotrope with
atomic layer structure, i.e., black phosphorous. In contrast to graphite, the “atomic
plane” of black phosphorous is not planar but plaited. Anodic exfoliation from neutral
aqueous solution is possible [61, 103], just as the delamination with cathodic treatment where the application of an inert solvent is preferred [103–105]. Regardless
of the media used for the cathodic exfoliation (e.g., propylene carbonate with tetrabutylammonium hexafluorophosphate [104] or dimethyl sulfoxide with tetrabutylammonium tetrafluoroborate [105]), the thickness range of the nanosheets obtained
varied between 2 and 10 nm, but the diameter of the sheets achieved 10 μm. Anodic
treatment led to thinner lamellae but still not single atomic layers with a mean thickness of 1.4 nm [61]. Black phosphorous nanosheets can be used from dispersion
in a non-reactive solvent and applied for photosensors in thin-layer microelectronic
devices.