Role of humidity in local anodic oxidation: A study of water condensation and electric field distribution

Abstract

This paper deals with the analysis of the influence of humidity on the process of local anodic oxidation carried out by atomic force microscope ͑AFM͒ on GaAs ͑100͒ surfaces. Recent experiments have shown that the height and half width of oxide nanolines do not increase monotonously with relative humidity, but for lower relative humidities ͑Ͻ50%͒ the lines comparable in size to those prepared at 90% were obtained. However, their height and width along the lines revealed significant variations. To better understand these phenomena, the AFM force-distance spectroscopy measurements together with computer simulations of an electric-field distribution and water bridge formation between the tip and the substrate at different relative humidities were carried out. Our experiments on AFM force-distance spectroscopy have not proved an enhanced water condensation between the tip and the surface at lower humidities. However, the simulations of the electric field in the vicinity of the tip at the early stages of the oxidation process at low relative humidities showed an increase in the average intensity in the oxide layer promoting the diffusion of oxidizing species toward the substrate and, hence, the formation of oxide lines under these conditions. Finally, our simulations on water bridge variations along the tip track showed that at lower humidities there are higher relative standard deviations in the size of the water bridge while the tip is being moved along the surface. This indicates why the oxide lines showed a bigger variability in size.

Application of scanning probe oxidation lithography in fabrication of micro-nano devices

“…[26~29] 来控制阳极氧化产物的大小、限 定纳米图案的尺寸. 因此水桥尺寸的控制是局部阳极 氧化的一个重要因素 [30] . 当相对湿度为40%~50%时, 针尖和样品表面会吸附一层水分子层, 吸附在样品表 面上的水分子和气体中的水分子有助于水桥的形 成 [31] , 在10%的相对湿度下, 即使不施加偏压, 亲水性 针尖和疏水性表面之间也能自发形成水桥 [32] .…”

“…Bartošík等 [30] 研究了水桥对针尖和样品表面之间电场 分布的影响. 由于水(ε r =81)、GaAs氧化物(ε r =3.5)、 GaAs(ε r =13.9)的相对介电常数有显著差异, 针尖和 [37] .…”

“…Marchi等 [42] 及Huang等 [35] 也发现, 当超过阈值电压2.7 V时, 硅氧化物线的厚度 随施加电压的增加而线性增加(图4(b)). Ulrich等 [43] [30,37] (网络版彩图) gime). 其中, 偏转电压正比于针尖-样品接触力, 即偏 转电压越大, 针尖-样品接触力也越大.…”

“…通常, 凝结的水 量会随着湿度的增加而增加, 因此局部阳极氧化产生 的氧化物的尺寸会随湿度的增加而增加. Bartošík 等 [30] 通过模拟计算, 发现水桥的高度和宽度随湿度单 调增加. Dehzangi等 [45] 和Abdullah等 [48] 通过对硅表面 进行氧化刻蚀, 也发现氧化物厚度随相对湿度的增加 而增加(图7(c)).…”

Nanodot deposition and its application with atomic force microscope

“…A laser beam and a position sensitive detector (PSD) are used to detect the deflection of cantilever. In nanoscale space, objects are covered by thin water films (Bartosik et al 2009). In contact mode AFM, the tip dips in the water films The dot is almost 100 nm high and 300 nm wide.…”