| With the quick development of high-quality large-area chemical vapour deposition?CVD?-grown graphene film,exploring a solution toward resist-free,substrate non-damaging and high-precision graphene patterning plays an important role in its applications in electronics and optoelectronics.Recently,we have for the first time proposed to pattern graphene film by magnetic-assisted UV/ozonation under 172 nm irradiation of a xenon excimer lamp.By virtue of the paramagnetic property of the ground state O?3P?atom,we can obtain graphene microstructure with a line width of 29?m and lateral under-oxidation less than 4?m.This method is applicable to fabricating graphene field-effect transistor?FET?arrays with the electron and hole mobilities up to1316 cm2·V-1·s-1and1682 cm2·V-1·s-1,respectively.In order to circumvent limitations stemming from the xenon excimer excitation,in this thesis,we further explore the feasibility of patterning graphene film under irradiation of a low-pressure mercury lamp and the underlying working mechanism.We first study graphene patterning varying with three different photochemical atmospheres of oxygen,oxygen/ozone mixture and nitrogen in the vertical magnetic-assisted UV/ozonation(BZ=0.31 T,???BZ=90 T·m-1).From the experimental results and analyses,we draw the following conclusions.?1?The best graphene patterning,though with the lateral under-oxidation up to 9?m,is obtained using an oxygen content of 2kPa after three cycles?3×10 min?of photochemical treatment.?2?A reduced content of 0.5 kPa oxygen/ozone mixture is sufficient to pattern graphene film after two-cycle?2×10 min?treatment in UV/ozonation,though its surface appears completely oxidized.?3?Addition of nitrogen molecules can weaken the directional photochemical etching of graphene.Then,influence of the lateral under-oxidation of graphene FET,induced in the patterning process,on shift of the Dirac point from positive to negative gate voltage under UV irradiation is studied.Raman analyses indicate that the 100 nm-thick metal contacts can increase gap between the mask and graphene,and as a result incur more severe lateral under-oxidation and p-type doping.Using a scanning 325 nm laser,we find the more the graphene FET is oxidized,the slower and lesser the Dirac point shifts toward the negative gate voltage.Finally,the photochemical working mechanism of graphene patterning by magnetic-assisted UV/ozonation is explored.The paramagnetic O2?X3?g-?molecules accelerate toward graphene film in the inhomogeneous vertical magnetic field.The dissociated ground state O?3P?atoms from the accelerated O2 molecules keep accelerating and results in an enhanced directional graphene etching.Instead,the O?3P?atoms dissociated and converted from ozone molecules have a lower oxidation capability based on energy and momentum conservation.Intermolecular or atomic-molecular collisions between the directional oxygen molecules/atoms and weak diamagnetic molecules can weaken the photochemical oxidation and increase lateral under-oxidation.Furthermore,the random dissipation and instability of the weak diamagnetic ozone molecules play an important role in the lateral oxidation of graphene.This study may shed light on our understanding and designing of graphene patterning by magnetic-assisted UV/ozonation,a potential solution to large-scale graphene electronics and optoelectronics in future. |
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