graphene , a single layer of sp - bonded carbon , has fabulous electronic , mechanical , and optical properties .
owing to its industrial adaptability , epitaxial graphene ( eg ) formed by annealing of sic bulk crystal is attracting recent attentions [ 2 - 4 ] .
eg , however , face two challenges : the limited diameter of the substrate and the low cost - performance in the current price . to overcome these challenges ,
we have been investigating the use of sic thin films on si substrates , instead of sic bulk crystals , in the formation of graphene .
we have actually succeeded in fabricating a graphene on an epitaxial sic thin film on si substrate by sublimating silicon atoms from the surface of the epitaxial sic thin film .
this graphene - on - silicon ( gos ) method has a potential of forming graphene films on large - scale si wafers .
this undoubtedly requires detailed understanding of the graphitization mechanism in gos as a prerequisite . in the case of epitaxial graphene formation on si - face 4h- or 6h - sic(0001 ) substrates , several groups [ 2 - 4 ] have reported that graphene ( 1  1 ) is formed after the appearance of two sic reconstructions : ( 3  3)r30 and ( 63  63)r30 in this order .
gos process on si(111 ) substrates follows this process . to go further into the clarification of the mechanism of graphitization
conducted temperature - programmed desorption measurement on molecular hydrogen ( h2-tpd ) for each of the reconstructed surfaces of 6h - sic(0001 ) .
they concluded that the hydrogen adsorption site shifts from si to c after graphitization , but detailed identification of the h2-tpd peaks has not been given yet . in this study , we have conducted tpd using molecular deuterium ( d2-tpd ) to investigate the surface chemistry involved in the gos process on 3c - sic(111)/si(111 ) .
c1s core - level and raman spectroscopies have also been used as complementary means to support the understandings given by d2-tpd .
a p - type si(111 ) wafer ( 0.4000.600  cm ) was cut into pieces to form specimens sized with 7  40 mm . the specimen , after degreased by ultrasonication in acetone and ethanol ,
was introduced into the uhv chamber ( base pressure : ~10 torr ) and flash - annealed at 1,473 k ( sample a ) .
the epitaxial 3c - sic thin films , ~100 nm in thickness , were grown by exposing the dc - heated si substrate ( 1,323 k ) to a ch3sih3 ( mms ) gas .
the samples were then annealed either at 1,273 k for 10 s ( sample b ) , 1,423 k for 60 min ( sample c ) , or 1,523 k for 30 min ( sample d ) .
after annealing , each sample was exposed to a flux of atomic deuterium , made by cracking of d2 molecules ( ~10 pa ) by a hot tungsten filament ( 1,673 k ) .
d2-tpd spectrum was then obtained by gradually increasing the sample temperature at a rate of 5 k / s .
the x - ray source for the c1s core - level spectroscopy is non - monochromatized mg 
figure 1 compares the d2-tpd spectra for si ( sample a ) , ( 3  3)r30-reconstructed 3c - sic(111)/si(111 ) ( sample b ) , ( 63  63)r30-reconstructed 3c - sic(111)/si(111 ) ( sample c ) , and ( 1  1 ) graphene/3c - sic(111)/si(111 ) ( sample d ) surfaces .
the spectrum for si(111 ) ( sample a ) has two peaks at ~660 and ~780 k , which are ascribable to the deuterium desorption from d2-si and d - si , respectively .
the dominance of the latter peak indicates that the surface of the si(111 ) substrate is largely terminated with monodeuteride . in the spectrum of the ( 3  3)r30-reconstructed 3c - sic(111)/si(111 ) surface ( sample b )
, a new predominant peak appears at ~960 k. this peak is attributable to the deuterium desorption from d - si backbonded with carbon atoms ( d - si(c ) ) .
concomitant with the appearance of the predominant peak of d - si backbonded with carbon atoms , the peaks of d2-si ( 660 k ) and d - si ( 780 k ) backbonded with silicon atoms decrease .
the absence of peaks in the region ranging from 1,100 to 1,300 k indicates that no carbon atoms are present in the topmost layer .
the surface of the ( 3  3)r30-reconstructed 3c - sic(111)/si(111 ) is thus proven to be si - terminated .
d2-tpd spectra of sic thin film on si(a ) , after annealing at 1,273 k(b ) , 1,423 k(c ) , 1,523 k(d ) , respectively raman spectra of sic thin film on si , after annealing at ( i ) 1,273 k ( sample b ) , ( ii ) 1,423 k ( sample c ) , ( iii ) 1,523 k ( sample d ) , respectively on the ( 63  63)r30-reconstructed 3c - sic(111)/si(111 ) ( sample c ) , the tpd spectrum consists mainly of dx - si(c ) .
here , x = 1 stands for the peak at 960 k and x = 2 for the peak at 850 k .
it has been demonstrated in a previous report that the adsorption of hydrogen atoms onto the ( 63  63)r30-reconstructed sic surface breaks the bondings between the reconstructed layer and the sic interface , so that the surface carbon atoms in the layer are converted into graphene layer , and the sic interface is terminated with hydrogen .
the main peak at 960 k is thus attributable to the deuterium desorption from d - terminated sic interface that results from the breakage of the bonds between the ( 63  63)r30-reconstructed layer and the underneath sic surface .
small features appear in the temperature range of 1,1001,400 k. they are due to desorption of deuterium atoms bonded on sp - bonded carbon atoms by d - exposure .
the appearance of these peaks is in agreement with the presence of the ( 63  63)r30-reconstructed layer because the reconstructed layer mainly consists of sp - bonded atoms , and part of the carbon atoms are covalently bonded with the sic surface .
this d2-tpd result is in good agreement with the raman spectrum of the reconstructed layer .
the appearance of the broad g band ( ~1,600 cm ) indicates the formation of the cluster of sp - bonded carbon atoms , i.e. , nanographene .
the appearance of the d band ( ~1,350 cm ) and the absence of the g band ( ~2,700 cm ) , however , indicate a low degree of the crystallinity of the sp - bonded network of the carbon atoms . c1s
the surface components s1 ( ~285.2 ev ) and s2 ( ~284.0 ev ) appear as well as the component due to the bulk of the sic thin film ( ~283.0 ev ) . s1 and s2 are due to the carbon atoms connected with the sic surface and the sp - bonded carbon atoms , respectively , in the ( 63  63)r30-reconstructed layer .
the intensity ratio of s1 and s2 peak is 2 , as that of the spectrum of ( 63  63)r30-reconstructed layer on 6h - sic(0001 ) .
thus , the 3c - sic(111)/si(111 ) surface is proven to become c rich and ( 63  63)r30 reconstructed by annealing the si - terminated ( 3  3)r30-reconstructed surface .
this change in the surface chemistry of 3c - sic(111)/si(111 ) is quite similar to that of 6h - sic(0001 ) .
cls core - level spectra of sic thin film on si , after annealing at ( i ) 1,273 k ( sample b ) , ( ii ) 1,423 k ( sample c ) , ( iii ) 1,523 k ( sample d ) annealing , respectively the tpd spectrum of the graphene overlayer on 3c - sic(111)/si(111 ) ( sample d ) drastically changes , as demonstrated in fig .
two distinct peaks around 1,100 k and 1,300 k are due to desorption of deuterium bonded with sp - bonded carbon atoms in the graphene overlayer , while the peaks due to deuterium desorption from d - si of the sic thin film and si substrate ( < 1,000 k ) are not observed . the raman spectrum of the graphene overlayer ( fig .
2(iii ) ) displays the g band , in addition to the g and the d bands .
the presence of the g band indicates the well - ordered graphene overlayer because the appearance of g band is the consequence of the high degree of the crystallinity of the graphene layer .
further , the g band consists of multiple components , as can be seen from the line shape of the g band .
the peak due to sp - bonded carbon atoms ( ~284.3 ev ) is dominant , and the component due to the ( 63  63)r30-reconstructed layer ( ~285.2 ev ) is still observed .
it can be thus concluded that the graphene overlayer grows on the ( 63  63)r30-reconstructed layer as the epitaxy of graphene on 6h - sic(0001 ) .
this can explain the disappearance of the peaks ( dx - si(c ) ) that is related with the ( 63  63)r30-reconstructed layer in the tpd spectrum of sample d , because graphene overlayer blocks adsorption or desorption of deuterium onto the surface .
we have probed the epitaxial processes of graphene on 3c - sic(111)/si(111 ) in situ by d2-tpd spectroscopy , and complemental ex situ spectroscopies , such as raman spectroscopy and c1s core - level spectroscopy .
the results obtained in this study indicate that the epitaxy of graphene on 3c - sic(111)/si(111 ) proceeds in a similar manner to that on hexagonal sic(0001 ) bulk crystals .
the work was supported by crest , the japan science and technology agency ( jst ) , japan .
this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited .
this article is distributed under the terms of the creative commons attribution noncommercial license which permits any noncommercial use , distribution , and reproduction in any medium , provided the original author(s ) and source are credited .
 surface chemistry involved in the epitaxy of graphene by sublimating si atoms from the surface of epitaxial 3c - sic(111 ) thin films on si(111 ) has been studied . 
 the change in the surface composition during graphene epitaxy is monitored by in situ temperature - programmed desorption spectroscopy using deuterium as a probe ( d2-tpd ) and complementarily by ex situ raman and c1s core - level spectroscopies . 
 the surface of the 3c - sic(111)/si(111 ) is si - terminated before the graphitization , and it becomes c - terminated via the formation of c - rich ( 63  63)r30 reconstruction as the graphitization proceeds , in a similar manner as the epitaxy of graphene on si - terminated 6h - sic(0001 ) proceeds . 
Introduction
Experiment
Results and Discussion
Conclusion
Acknowledgments
Open Access