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Transport Gap in Dual-Gated Graphene Bilayers Using Oxides as Dielectrics
Kayoung Lee,Fallahazad, B.,Hongki Min,Tutuc, E. IEEE 2013 IEEE transactions on electron devices Vol.60 No.1
<P>Graphene bilayers in Bernal stacking exhibit a transverse electric (E) field-dependent band gap, which can be used to increase the channel resistivity and enable higher on/off ratio devices. We provide a systematic investigation of transport characteristics in dual-gated graphene bilayer devices as a function of density and E field and at temperatures from room temperature down to 0.3 K. The sample conductivity shows finite threshold voltages along the electron and hole branches, which increase as the E field increases, similar to a gapped semiconductor. We extract the transport gap as a function of E field and discuss the impact of disorder. In addition, we show that beyond the threshold, the bilayer conductivity shows a highly linear dependence on density, which is largely insensitive to the applied E field and the temperature.</P>
뜬 마이크로 디바이스를 이용한 Ge-Si<SUB>x</SUB>Ge<SUB>1-x</SUB> Core-Shell Nanowires의 열전도율 측정
박현준(Hyun Joon Park),David Dillen,나정효(Jung Hyo Nah),Emanuel Tutuc,설재훈(Jae Hun Seol) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Several theoretical studies suggested that the thermal conductivity in core-shell nanowires would be decreased. To experimentally verify that phenomenon, the thermal conductivity of Ge–SixGe1-x core-shell nanowires was measured using suspended microdevices. The core-shell structure of the nanowires was synthesized using the chemical vapor deposition (CVD) and subsequent vapor-liquid-solid (VLS) methods. Based on material characterization with transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS), the crystallinity of the Ge cores and the SixGe1-x shells was clearly confirmed and the silicon composition (x) in the shells is 0.65. The measured thermal conductivity values are in the range of 9–13 W/mK at room temperature and are lower by at most ~30 percent than that of a germanium nanowire with a comparable diameter.
뜬 마이크로 디바이스를 이용한 Ge-Si<SUB>x</SUB>Ge<SUB>1-x</SUB> Core-Shell Nanowires 의 열전도율 측정
박현준(Hyun Joon Park),나정효(Jung hyo Nah),Emanuel Tutuc,설재훈(Jae Hun Seol) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.10
나노선에서 코어-셸 헤테로 구조를 도입함으로써 열 전도율을 낮출 수 있으며, 이로 인해 열전 효율(ZT)을 향상시킬 수 있다는 것이 이론 연구를 통해 제안되었다. 본 논문에서는 코어-셸 나노선의 열전도율 감소를 실험적인 방법을 통해 확인하였다. 화학증기 증착법을 통해 만든 게르마늄-규소 x 게르마늄 1-x(Ge?SixGe1-x) 코어-셸 나노선의 열전도율을 마이크로 크기의 뜬 디바이스를 이용하여 측정하였다. 셸에서 측정된 실리콘의 함유율(x)는 0.65 로 확인하였으며, 게르마늄은 코어와 셸 사이에서, 격자 불일치(lattice mismatch)에서 비롯된 결점(defect)와 같은 역할을 한다. 또한, 4-point I-V 측정실험에, 휘트스톤 브릿지 실험을 추가 진행함으로써 측정 민감도를 강화하였다. 측정된 열전도율은 상온에서 9~13 W/mK 으로써, 비슷한 지름을 가지는 게르마늄 나노선과 비교하였을 때, 열전도율이 약 30 % 낮아졌음을 확인하였다. Theoretical calculations suggest that the thermoelectric figure of merit (ZT) can be improved by introducing a core-shell heterostructure to a semiconductor nanowire because of the reduced thermal conductivity of the nanowire. To experimentally verify the decrease in thermal conductivity in core-shell nanowires, the thermal conductivity of Ge?SixGe1-x core-shell nanowires grown by chemical vapor deposition (CVD) was measured using suspended microdevices. The silicon composition (Xsi) in the shells was measured to be about 0.65, and the remainder of the germanium in the shells was shown to play a role in decreasing defects originating from the lattice mismatch between the cores and shells. In addition to the standard four-point current? voltage (I-V) measurement, the measurement configuration based on the Wheatstone bridge was attempted to enhance the measurement sensitivity. The measured thermal conductivity values are in the range of 9? 13 W/mK at room temperature and are lower by approximately 30 than that of a germanium nanowire with a comparable diameter.
Low-Frequency Acoustic Phonon Temperature Distribution in Electrically Biased Graphene
Jo, Insun,Hsu, I-Kai,Lee, Yong J.,Sadeghi, Mir Mohammad,Kim, Seyoung,Cronin, Stephen,Tutuc, Emanuel,Banerjee, Sanjay K.,Yao, Zhen,Shi, Li American Chemical Society 2011 Nano letters Vol.11 No.1
<P>On the basis of scanning thermal microscopy (SThM) measurements in contact and lift modes, the low-frequency acoustic phonon temperature in electrically biased, 6.7−9.7 μm long graphene channels is found to be in equilibrium with the anharmonic scattering temperature determined from the Raman 2D peak position. With ∼100 nm scale spatial resolution, the SThM reveals the shifting of local hot spots corresponding to low-carrier concentration regions with the bias and gate voltages in these much shorter samples than those exhibiting similar behaviors in the infrared emission maps.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-1/nl102858c/production/images/medium/nl-2010-02858c_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl102858c'>ACS Electronic Supporting Info</A></P>