Gedda Murali, Subbarao Nimmakayala V V, Goswami Dipak K
Department of Physics and §Center for Nanotechnology, Indian Institute of Technology Guwahati , Guwahati 781039, India.
Langmuir. 2014 Jul 29;30(29):8735-40. doi: 10.1021/la502108a. Epub 2014 Jul 15.
We have studied the kinetic roughening in the growth of cobalt phthalocyanine (CoPc) thin films grown on SiO2/Si(001) surfaces as a function of the deposition time and the growth temperature using atomic force microscopy (AFM). We have observed that the growth exhibits the formation of irregular islands, which grow laterally as well as vertically with coverage of CoPc molecules, resulting rough film formation. Our analysis further disclosed that such formation is due to an instability in the growth induced by local diffusion of the molecules following an anomalous scaling behavior. The instability relates the (ln(t))(1/2), with t as deposition time, dependence of the local surface slope as described in nonequilibrium film growth. The roughening has been characterized by calculating different scaling exponents α, β, and 1/z determined from the height fluctuations obtained from AFM images. We obtained an average roughness exponent α = 0.78 ± 0.04. The interface width (W) increases following a power law as W ∼ t(β), with growth exponent β = 0.37 ± 0.05 and lateral correlation length (ξ) grows as ξ ∼ t(1/z) with dynamic exponent 1/z = 0.23 ± 0.06. The exponents revealed that the growth belongs to a different class of universality.
我们利用原子力显微镜（AFM）研究了在SiO₂/Si(001)表面生长的钴酞菁（CoPc）薄膜生长过程中的动力学粗糙化现象，该现象是沉积时间和生长温度的函数。我们观察到生长过程中出现了不规则岛状物的形成，这些岛状物随着CoPc分子的覆盖在横向和纵向生长，从而导致粗糙薄膜的形成。我们的分析进一步表明，这种形成是由于分子的局部扩散引起的生长不稳定性，遵循反常标度行为。这种不稳定性与(ln(t))(1/2)相关，其中t为沉积时间，这是在非平衡薄膜生长中描述的局部表面斜率的依赖性。通过计算从AFM图像获得的高度涨落确定的不同标度指数α、β和1/z，对粗糙化进行了表征。我们得到平均粗糙度指数α = 0.78 ± 0.04。界面宽度（W）按照幂律增加，即W ∼ t(β)，生长指数β = 0.37 ± 0.05，横向关联长度（ξ）按照ξ ∼ t(1/z)增长，动力学指数1/z = 0.23 ± 0.06。这些指数表明生长属于不同的普适类。
