Journal of Nanomedicine & Nanotechnology

Nanopatterning on H-terminated Si(111) explained as dynamical equilibrium of the chemical reaction with methanol

Nanotechnology Congress & Expo

August 11-13, 2015 Frankfurt, Germany

Peter Thissen1, Ehud Fuchs2, Katy Roodenko3, Tatiana Peixoto3, Ben Batchelor3, Dennis Smith3, Wolf Gero Schmidt4 and Yves Chabal3

Poster-Accepted Abstracts: J Nanomed Nanotechnol

Abstract:

Silicon is by far the most important semiconductor material in themicroelectronic industry, mostly due to the high quality of theSi/ SiO2 interface. Consequently, applications requiring chemical functionalization of Si substrates have focused on molecular grafting of SiO2 surfaces. Unfortunately, there are practical problems affecting homogeneity and stability of many organic layers grafted on SiO2, such as silanes and phosphonates, related to polymerization and hydrolysis of Si?O?Si and Si?O?P bonds. These issues have stimulated efforts in grafting functional molecules onoxide-free Si surfaces, mostly with wet chemical processes. Nevertheless, there is a lack of understanding the fundamental reaction mechanism behind the formation of a SAM. In this work we look inside the formation mechanism of methanol reacting with a H-terminated Si(111) surface and find a very surprising result ? a nanopattern. The formation of a nanopattern as a result of this wet chemical reaction is surprising if one considers initial random grafting on a surface. Even if next nearest neighbor (NNN) sites were kinetically favorable, adsorption would lead to a disordered arrangement. We confirm this by calculating the kinetic barriers of the reaction of methanol with the H-terminated Si(111) surface by density functional theory (DFT) and implementing these values in a kinetic Monte Carlo (kMC) algorithm. Experimentally, we confirm the decomposition of methanol (FTIR and GCMS) to be an important factor, as it would increasethe chemical potential of H2. The presence of H2 initiates desorption of the methoxy groups and thereby leads to a kinetic equilibrium of the reaction of methanol with the H-terminated Si(111) surface. Finally, an input of all relevant values into the kMC algorithm provided a qualitative correct image of the formation mechanism of the nano pattern. This work is of broad interest to the materials community because silicon functionalization is critical for a wide range of applications including nanoelectronics, nanosensors, biomedical applications, energyabsorbing and ?storing devices, and even catalysis. In particular, chemical control of atomically smooth Si(111) surfaces is becoming more important as these surfaces are used as templates for both organic and inorganic layered systems.