NANOSTRUTURES AND NANOTECHNOLOGIES AT SURFACES: AN AMAZING REVOLUTION IN SCIENCE

The general trend in condensed matter physics is toward smaller objects having a low dimensionality, 2D, 1D and 0D. This is of strong fundamental interest since these nano-objects have very different physical properties. Also, they are potentially very useful in technology like e.g. in microelectronics where the density of integration is doubling every 18 months (Moore law). However, such a “downsizing up-down” approach will, within less than a decade, reach physical limits. Therefore, a “bottom-up” approach has to be considered in nano-object fabrication. This includes atom-manipulation and/or the implementation of self-organized mechanisms to fabricate nanostructures having advanced properties. It requires the atomic scale control and understanding of surfaces and the use of state-of-the-art experimental techniques and theoretical approaches. Silicon carbide (SiC) is a wide band gap IV-IV compound semiconductor having a strong interest in advanced applications such as high temperature, high power, high frequency electronic devices/sensors and in nanotechnology. In addition, it is one of the best biocompatible material. SiC exists in more than 170 different polytypes including cubic ( ), hexagonal ( ) and rhombohedric phases. Cubic SiC surface properties and nanostructures are investigated by advanced experimental techniques including: i) atom-resolved scanning tunneling microscopy (STM) and spectroscopy (STS), ii) synchrotron radiation-based core level/valence band photoemission spectroscopies, iii) infrared absorption spectroscopy (IRAS) and iv) grazing incidence X-ray diffraction. Among some of the discoveries, the following ones will be presented and discussed: • Massively parallel self-organized Si atomic lines having unprecedented characteristics with very long lengths ≥ 1 µm and the highest thermal stability ever achieved for nanostructures (> 900°C) - Fig. 1, [1,2]. • sp3 C atomic lines formation and sp sp3 diamond-type surface transformation of the C-terminated -SiC(100) c(2x2) surface reconstruction (Fig. 2), [3]. • The first example of H-induced semiconductor surface metallization resulting from H atoms inducing an asymmetric attack on the Si-Si sub-surface dangling bonds of the -SiC(100) 3x2 surface reconstruction. The metallization process results from a H-creating a specific defect coming from competition between hydrogen termination of surface dangling bonds and hydrogen-generated steric hindrance below the surface (Fig. 3) [4]. In addition, H is found to also metallize pre-oxidized -SiC(100) 3x2 surfaces [5]. This very interesting feature resulting from H-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides means to develop electrical contacts on wide band-gap chemically passive materials, particularly exciting for interfacing e.g. with biological systems. Such systems could also exhibit interesting frictional behavior, with hydrogen acting as an atomic scale “lubricant”, important e.g. for passive elements of nano-motors. All these characteristics are unprecedented. They show a novel aspect of SiC in its ability to also be a very promising material in nanotechnologies.