Abstract:The Ni-induced layer-exchange growth of amorphous carbon is a unique method used to fabricate uniform multilayer graphene (MLG) directly on an insulator. To improve the crystal quality of MLG, we prepare AlOx or SiO2 interlayers between amorphous C and Ni layers, which control the extent of diffusion of C atoms into the Ni layer. The growth morphology and Raman spectra observed from MLG formed by layer exchange strongly depend on the material type and thickness of the interlayers; a 1-nm-thick AlOx interlayer … Show more
“…A layer exchange mechanism of this kind was also observed for amorphous carbon/Ni heterostructures. 23 − 25 Then the graphitic layers are formed at T > 500 °C ( Figure 7 c) according to results observed from XPS measurements. Finally, the graphitic phase concentration increases with the annealing temperature ( T > 700 °C), and its concentration became higher than the concentration of the disordered phase ( Figure 7 d).…”
Section: Resultssupporting
confidence: 64%
“…It was observed that carbon film exchanges with Ni film and graphitizes at elevated temperature. 23 − 25 Recent theoretical studies explained the graphitization mechanism for RTA: a-C to graphene transformation entails the metal-induced crystallization and layer exchange mechanism. Carbon dissolution in Ni was excluded.…”
Graphene
on diamond has been attracting considerable attention
due to the unique and highly beneficial features of this heterostructure
for a range of electronic applications. Here, ultrahigh-vacuum X-ray
photoelectron spectroscopy is used for in situ analysis
of the temperature dependence of the Ni-assisted thermally induced
graphitization process of intrinsic nanocrystalline diamond thin films
(65 nm thickness, 50–80 nm grain size) on silicon wafer substrates.
Three major stages of diamond film transformation are determined from
XPS during the thermal annealing in the temperature range from 300 °C
to 800 °C. Heating from 300 °C causes removal of oxygen;
formation of the disordered carbon phase is observed at 400 °C;
the disordered carbon progressively transforms to graphitic phase
whereas the diamond phase disappears from the surface from 500 °C.
In the well-controllable temperature regime between 600 °C and
700 °C, the nanocrystalline diamond thin film is mainly preserved,
while graphitic layers form on the surface as the predominant carbon
phase. Moreover, the graphitization is facilitated by a disordered
carbon interlayer that inherently forms between diamond and graphitic
layers by Ni catalyst. Thus, the process results in formation of a
multilayer heterostructure on silicon substrate.
“…A layer exchange mechanism of this kind was also observed for amorphous carbon/Ni heterostructures. 23 − 25 Then the graphitic layers are formed at T > 500 °C ( Figure 7 c) according to results observed from XPS measurements. Finally, the graphitic phase concentration increases with the annealing temperature ( T > 700 °C), and its concentration became higher than the concentration of the disordered phase ( Figure 7 d).…”
Section: Resultssupporting
confidence: 64%
“…It was observed that carbon film exchanges with Ni film and graphitizes at elevated temperature. 23 − 25 Recent theoretical studies explained the graphitization mechanism for RTA: a-C to graphene transformation entails the metal-induced crystallization and layer exchange mechanism. Carbon dissolution in Ni was excluded.…”
Graphene
on diamond has been attracting considerable attention
due to the unique and highly beneficial features of this heterostructure
for a range of electronic applications. Here, ultrahigh-vacuum X-ray
photoelectron spectroscopy is used for in situ analysis
of the temperature dependence of the Ni-assisted thermally induced
graphitization process of intrinsic nanocrystalline diamond thin films
(65 nm thickness, 50–80 nm grain size) on silicon wafer substrates.
Three major stages of diamond film transformation are determined from
XPS during the thermal annealing in the temperature range from 300 °C
to 800 °C. Heating from 300 °C causes removal of oxygen;
formation of the disordered carbon phase is observed at 400 °C;
the disordered carbon progressively transforms to graphitic phase
whereas the diamond phase disappears from the surface from 500 °C.
In the well-controllable temperature regime between 600 °C and
700 °C, the nanocrystalline diamond thin film is mainly preserved,
while graphitic layers form on the surface as the predominant carbon
phase. Moreover, the graphitization is facilitated by a disordered
carbon interlayer that inherently forms between diamond and graphitic
layers by Ni catalyst. Thus, the process results in formation of a
multilayer heterostructure on silicon substrate.
“…For the samples with the IL, the I G / I D ratio is as low as for the samples without the IL for t ≤ 20 nm, while it dramatically increases for t ≥ 50 nm and exceeds 20. The crystal quality of the MLG, estimated from the I G / I D ratio, likely reflects the contamination from the substrate and the grain size enlargement by inserting the IL 42 . Although the I G / I D ratio of 20 is still lower than that of MLG formed by the transfer technique or high-temperature CVD 4 , this value is the highest among MLG synthesized on insulators by metal-induced solid-phase crystallization 18,19,23,25 .Figure 2Raman study of MLG formed by layer exchange.…”
Section: Resultsmentioning
confidence: 99%
“…AA and AB stacking) 44,45 . Unfortunately, because the current MLG is small-grained polycrystalline where the grains are randomly oriented in the in-plane direction 42 , it is difficult to identify the stacking.Figure 3Characterization of the cross-section of the sample for t = 10 nm without the IL before Ni removal. ( a ) Bright-field TEM image.…”
The layer exchange technique enables high-quality multilayer graphene (MLG) on arbitrary substrates, which is a key to combining advanced electronic devices with carbon materials. We synthesize uniform MLG layers of various thicknesses, t, ranging from 5 nm to 200 nm using Ni-induced layer exchange at 800 °C. Raman and transmission electron microscopy studies show the crystal quality of MLG is relatively low for t ≤ 20 nm and dramatically improves for t ≥ 50 nm when we prepare a diffusion controlling Al2O3 interlayer between the C and Ni layers. Hall effect measurements reveal the carrier mobility for t = 50 nm is 550 cm2/Vs, which is the highest Hall mobility in MLG directly formed on an insulator. The electrical conductivity (2700 S/cm) also exceeds a highly oriented pyrolytic graphite synthesized at 3000 °C or higher. Synthesis technology of MLG with a wide range of thicknesses will enable exploration of extensive device applications of carbon materials.
“…The chemical vapor deposition (CVD) method using metal catalysis with high carbon solubility are commonly utilized for the synthesis of the multilayer graphene. In the liquid–solid growth process, the graphene layers are easily rotated in the liquid phase of metal catalysis.…”
Anomalous carrier transport properties in turbostratic multilayer graphene have been studied by Ryota Negishi et al. in article number http://doi.wiley.com/10.1002/pssb.201900437. The conductance and carrier mobility in the synthesized turbostratic multilayer graphene are higher than those of the monolayer graphene used as growth template. The enhancement is caused by a screening effect in multistacking and by a turbostratic stacking effect where the band structure of the multilayer graphene is similar to that of the monolayer graphene.
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