THESIS
2014
xxviii, 142 pages : illustrations (some color) ; 30 cm
Abstract
Based on graphene and the technique of quantum capacitance measurement, two
types of high-quality graphene capacitances with Y
2O
3 and BN dielectric layers are
fabricated respectively, and their electronic properties in the presence of resonant
impurities and artificial modulations are investigated systematically.
The properties of pristine single-layer graphene covered by Y
2O
3 layer as the
dielectric material are firstly evaluated using structural characterization, DC transport and
AC capacitance measurements, demonstrating the Y
2O
3 material to be a qualified
insulating dielectric. Then a special type of resonant impurities is introduced by the Ag
adatoms deposition, which creates midgap states in the vicinity of the charge neutrality
point (CNP). The quantum capacitance measu...[
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Based on graphene and the technique of quantum capacitance measurement, two
types of high-quality graphene capacitances with Y
2O
3 and BN dielectric layers are
fabricated respectively, and their electronic properties in the presence of resonant
impurities and artificial modulations are investigated systematically.
The properties of pristine single-layer graphene covered by Y
2O
3 layer as the
dielectric material are firstly evaluated using structural characterization, DC transport and
AC capacitance measurements, demonstrating the Y
2O
3 material to be a qualified
insulating dielectric. Then a special type of resonant impurities is introduced by the Ag
adatoms deposition, which creates midgap states in the vicinity of the charge neutrality
point (CNP). The quantum capacitance measurement presents pronounced resonant peaks around the Dirac point, with significant dependences on temperature, impurity
concentration and magnetic field. Moreover, under high concentration of Ag adatoms, an
unconventional phenomenon of negative quantum capacitance is observed. The Ag
adatoms with high concentration create a series of midgap states around the Dirac point,
quenching the kinetic energy and enhancing the Coulomb interaction energy
simultaneously, which results in the unconventional negative quantum capacitance.
Furthermore, a new type of high-quality BN-Graphene-BN capacitances is developed
by replacing the SiO
2 substrates and Y
2O
3 dielectric layers with the h-BN sheets, which
presents extremely high electronic performance. Under high magnetic field, the Landau
level (LL) oscillations are quite obvious, even with the LL splitting and slight negative
quantum capacitance observed at the 0
th LL position, mainly due to the magnetic-field-enhanced
electron-electron interactions. Afterwards the artificial modulations are
introduced by the Ga
+ ion-beam cutting and side-gate modulations. At high temperatures,
the graphene nano-ribbon capacitance presents outstanding electronic performance and
the side-gate modulations are consistent with the numerical simulations very well. While
at cryogenic temperatures, an unconventional phenomenon of capacitance vanishing is
observed, which is sensitive to the width of nano-ribbon and the type of edge-disorders.
It is demonstrated that the Ga
+ ions attached to the edges of graphene nano-ribbon will
not influence graphene’s electronic structure and DOS, but introduce strong localizations
and open the Coulomb quasigap, degrading the conductive abilities of graphene, leading
to the extraordinary capacitance vanishing.
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