| Si nanomembranes are two dimensional thin Si sheets, which are only a couple hundreds nanometer thick or even thinner. They can be generated from silicon-on-insulator wafers and transferred and bonded to other substrates. Because of their thinness, they possess different properties from their bulk counterparts, including mechanical, optical and electrical properties. As a result, novel application opportunities are enabled.;Due to their large surface-to-volume ratio, Si nanomembranes are extremely sensitive to surface effects, which renders them possible candidates for chemical sensing. Their sheet resistances vary several orders of magnitude after different surface treatments. From van der Pauw and Hall measurements on HF treated SiNMs, it is found that thinner membranes are more strongly influenced by surface effects. However, the membrane transport property is also affected by the underlying Si/SiO2 interface. Moreover, ambient factors, such as humidity, interact with the surface and modify the membrane charge carrier concentration.;Ultra-high vacuum conditions provide good control of measurement environments. Experiments thus could be performed continuously with minor changes in the surface condition. Furthermore, the SOI geometry makes it possible to use the Si substrate as an additional gate and sheet resistance to be measured at varying back gate voltage. While the surface potential at both front and back surface can be effectively tuned with the back gate, the front one is also dependent on membrane thickness. The thinner the membrane, the stronger the back gate control. With the aid of self-consistent simulations, the front surface electronic structure of a hydrogenated Si surface is successfully extracted from membrane transport measurements, in which both membrane thickness and back gate voltage were varied.;The surface also contributes to conduction through the surface bands. By changing the back gate voltage, the membrane conductance could be made smaller than the surface conductance, and the measured total conductance mainly represents the surface contribution. This provides a systematic way to measure the small surface conductance and leads to a new approach to examine surface effects in nauostructures. |
