Venugopal Gunasekaran, Kim Sang-Jae
Nano Materials and System Lab, Department of Mechanical System Engineering, School of Engineering, Jeju National University, Jeju 690-756, Korea.
J Nanosci Nanotechnol. 2011 Jan;11(1):296-300. doi: 10.1166/jnn.2011.3283.
We report in this paper on the observation of temperature-dependent anisotropic transport behavior for planar-type nanostructures (in-plane and out-of-plane) fabricated on a thin graphite layer using a three-dimensional focused-ion-beam (FIB) etching technique. The transport characteristics were studied for several in-plane areas with sizes of 6 x 6 microm2, 6 x 4 microm2 and 6 x 2 microm2 planar-type structures/patterns and out-of-plane structures with the dimensions of 2 x 1 x 0.3 microm3. Both in-plane (rho(a)) and out-of-plane (rho(c)) resistivities are measured for these structures and the ratio of resistivity anisotropy is determined. The observed values of anisotropy ratio rho(c)/rho(a) were approximately 12.5 at 300 K and approximately 54 at 25 K. The room temperature value of rho(c)/rho(a) varies by a few orders from the values of previously reported anisotropy results of bulk pyrolytic graphite. However, the value of resistivity anisotropy increases with decreasing temperature, which is an identical behavior to bulk pyrolytic graphite. From current (I)-voltage (V) characteristics, we observed an ohmic behavior at 300 K for both low- and high-current biasing. This behavior turns into nonlinear characteristics when the temperature goes down. As these fabricated structures consist of multiple elementary junctions along the c-axis, nonlinear I-V characteristics result. The impurity assisted interlayer hopping conduction and thermal excitation of carriers play a key role in this effect.
在本文中，我们报告了利用三维聚焦离子束（FIB）蚀刻技术在薄石墨层上制备的平面型纳米结构（面内和面外）的温度依赖各向异性输运行为的观察结果。对几个尺寸为6×6微米²、6×4微米²和6×2微米²的面内区域的平面型结构/图案以及尺寸为2×1×0.3微米³的面外结构的输运特性进行了研究。对这些结构测量了面内（ρ(a)）和面外（ρ(c)）电阻率，并确定了电阻率各向异性比。在300 K时，观察到的各向异性比ρ(c)/ρ(a)约为12.5，在25 K时约为54。室温下的ρ(c)/ρ(a)值与先前报道的块状热解石墨的各向异性结果值相差几个数量级。然而，电阻率各向异性值随温度降低而增加，这与块状热解石墨的行为相同。从电流（I）-电压（V）特性来看，我们在300 K时对低电流和高电流偏置都观察到了欧姆行为。当温度降低时，这种行为转变为非线性特性。由于这些制备的结构沿c轴由多个基本结组成，因此产生了非线性I-V特性。杂质辅助层间跳跃传导和载流子的热激发在这种效应中起关键作用。
