Kim JunHo
Department of Physics, University of Incheon, Incheon, Korea.
Scanning. 2010 Sep-Oct;32(5):320-6. doi: 10.1002/sca.20201. Epub 2010 Sep 17.
We have made nanoindents on Ge(2)Sb(2)Te(5)(GST) films using electric field-assisted atomic force microscope (AFM) lithography. GST shows increase of material density and electric conductivity as it changes from amorphous to crystalline phases. By applying electric field between AFM probe-tip and GST surface, nanoscale crystallization could be induced on tip contact area. As the crystallized GST exhibits increase of material density, that is to say depression of volume, nanoindented surface with crystallization is created on host amorphous GST (a-GST) film. For the AFM lithography, a highly conductive tip, which showed voltage-switching characteristics in current-voltage spectroscopy of GST film, was found to be very suitable for recording and sensing crystallized nanoindents on the GST film. By varying sample bias voltages, we performed nanoscale crystallization, and measured the nanostructured film in AFM conductance-image (C-image) mode and topography-image (T-image) mode, simultaneously. Two types of crystallized wires were fabricated on (a-GST) film. Type-I was sensed in only C-image, whereas Type-II was sensed in both C-image and T-image. These nanowires are discussed in terms of crystallization of GST and sensitivity of current (or topography) sensing. By repeated lithography, larger size of nanoindented wires were also produced, which indicates line-dimension controllability of AFM lithography.
我们使用电场辅助原子力显微镜（AFM）光刻技术在Ge(2)Sb(2)Te(5)（GST）薄膜上进行了纳米压痕。当GST从非晶相转变为晶相时，其材料密度和电导率会增加。通过在AFM探针尖端和GST表面之间施加电场，可以在尖端接触区域诱导纳米级结晶。由于结晶的GST表现出材料密度的增加，也就是说体积减小，因此在主体非晶GST（a-GST）薄膜上形成了带有结晶的纳米压痕表面。对于AFM光刻，发现一种在GST薄膜的电流-电压光谱中表现出电压切换特性的高导电尖端非常适合记录和检测GST薄膜上的结晶纳米压痕。通过改变样品偏置电压，我们进行了纳米级结晶，并同时在AFM电导图像（C图像）模式和形貌图像（T图像）模式下测量了纳米结构薄膜。在（a-GST）薄膜上制备了两种类型的结晶线。I型仅在C图像中可检测到，而II型在C图像和T图像中均可检测到。我们从GST的结晶和电流（或形貌）检测的灵敏度方面对这些纳米线进行了讨论。通过重复光刻，还制备了更大尺寸的纳米压痕线，这表明AFM光刻具有线尺寸可控性。
