P. Barthold, T. Luedtke, R. J. Haug
An atomic force microscope is used to structure a film of multilayer graphene. The resistance of the sample was measured in-situ during nanomachining narrow trenches. We found a reversible behavior in the electrical resistance which we attribute to the movement of dislocations. After several attempts also permanent changes are observed.
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We have developed a unique micromechanical method to extract extremely thin graphite samples. Graphite crystallites with thicknesses ranging from 10 - 100 nm and lateral size $\sim$ 2 $μ$m are extracted from bulk. Mesoscopic graphite devices are fabricated from these samples for electric field dependent conductance measurements. Strong conductance modulation as a function of gate voltage is observed in the thinner crystallite devices. The temperature dependent resistivity measurements show more boundary scattering contribution in the thinner graphite samples.
Electric field effect devices based on mesoscopic graphite are fabricated for galvanomagnetic measurements. Strong modulation of magneto-resistance and Hall resistance as a function of gate voltage is observed as sample thickness approaches the screening length. Electric field dependent Landau level formation is detected from Shubnikov de Haas oscillations in magneto-resistance. The effective mass of electron and hole carriers has been measured from the temperature dependant behavior of these oscillations.
We investigate the dependence of friction forces on normal load in incommensurate micrometer size contacts between atomically smooth single-crystal graphite surfaces under ambient conditions. Our experimental results show that these contacts exhibit superlubricity (super-low friction), which is robust against the application of normal load. The measured friction coefficients are essentially zero and independent of the external normal load up to a pressure of 1.67 MPa. The observation of load-independent superlubricity in micro-scale contacts is a promising result for numerous practical applica…
We investigate the magnetotransport properties of a thin graphite wire resting on a silicon oxide substrate. The electric field effect is demonstrated with back and side gate electrodes. We study the conductance fluctuations as a function of gate voltage, magnetic field and temperature. The phase coherence length extracted from weak localization is larger than the wire width even at the lowest carrier densities making the system effectively one-dimensional. We find that the phase coherence length increases linearly with the conductivity suggesting that at 1.7 K dephasing originates mainly from…
In this work we investigated correlations between the internal microstructure and sample size (lateral as well as thickness) of mesoscopic, tens of nanometer thick graphite (multigraphene) samples and the temperature $(T)$ and field $(B)$ dependence of their electrical resistivity $ρ(T,B)$. Low energy transmission electron microscopy reveals that the original highly oriented pyrolytic graphite material -- from which the multigraphene samples were obtained by exfoliation -- is composed of a stack of $\sim 50 $nm thick and micrometer long crystalline regions separated by interfaces running paral…
Ion-beam-milled graphite nanoribbons as mesoscopic carbon-based polarizers
研究通过离子束刻蚀抛光边缘的新型石墨纳米带，发现当入射光垂直于c轴时其拉曼模式具有强烈偏振依赖性，并证明该器件可作为碳基片上偏振器，制备方法优于机械抛光。
We present scanning tunneling microscopy (STM) images of single-layer graphene crystals examined under ultrahigh vacuum conditions. The samples, with lateral dimensions on the micron scale, were prepared on a silicon dioxide surface by direct exfoliation of single crystal graphite. The single-layer films were identified using Raman spectroscopy. Topographic images of single-layer samples display the honeycomb structure expected for the full hexagonal symmetry of an isolated graphene monolayer. The absence of observable defects in the STM images is indicative of the high quality of these films.…
Excess conductance fluctuations with peculiar temperature-dependence from 1.4 to 250 K were observed in curved nano-graphite sheets with an electrode gap length of 300 and 450 nm, whereas the conductance fluctuation is greatly suppressed above 4.2 K when the electrode gap length increases to 800 and 1000 nm. The former is discussed in the context of the presence of a small energy bandgap in the nano-graphite sheets, while the latter is attributed to the crossover from coherent transport to diffusive transport regime.
Isolating the natural edges of bilayer graphene in gate-defined mesoscopic devices
本研究提出石墨栅极架构隔离双层石墨烯天然边缘，实现静电定义霍尔棒，揭示边界散射特征，制备的场效应晶体管获创纪录量子迁移率。
Magnetic-field periodic quantum Sondheimer oscillations in thin-film graphite
本文发现薄膜石墨在准量子极限下表现出周期为1-3 T的量子Sondheimer振荡，并通过台阶样品验证其周期与厚度成反比，将其重新解释为Landau能级间共振，扩展了量子振荡家族。
We studied the influence of 30keV Ga$^+$-ions -- commonly used in focused ion beam (FIB) devices -- on the transport properties of thin crystalline graphite flake, La$_{0.7}$Ca$_{0.3}$MnO$_3$ and Co thin films. The changes of the electrical resistance were measured in-situ during irradiation and also the temperature and magnetic field dependence before and after irradiation. Our results show that the transport properties of these materials strongly change at Ga$^+$ fluences much below those used for patterning and ion beam induced deposition (IBID), limiting seriously the use of FIB when the i…
A novel method for fast fabrication of mesoscopic multilayered graphene electronic devices utilizing nanoprobes to exfoliate graphite flakes is developed. The magnetoresistance of these devices exhibit pronounced Shubnikov-de Haas oscillations at magnetic fields above 4 T and at temperatures below 30 K. From the analysis of the SdH oscillations we show that multilayer graphene devices have a carrier density and effective mass (m*= 0.042me - 0.083me) comparable to those of bilayer and trilayer graphene. The quantum lifetime in this multilayered graphene is in the range 22 to 90 fs corresponding…
Cryogenic shock exfoliation for ultrahigh mobility rhombohedral graphite nanoelectronics
介绍低温冲击剥离法制备大面积菱面体石墨烯薄片，结合保留堆叠顺序的低压范德华组装技术，制成高均匀性、高产率器件，展现优异性能，克服材料瓶颈，推动二维纳米电子学发展。
Transport in multilayer graphene: resistance from stacking faults
本文构建理论框架计算任意堆垛石墨烯的c轴电阻，发现堆垛无序的多层石墨烯电阻非自平均、中位电阻随尺寸指数增长，可作为堆垛层错特征并探测局域化物理。
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