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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology

» presentations   » 2012.05.15-18

Computing Raman and IR frequencies of nanostructures: prospects to sensor applications

F. Zörgiebel, D. Nozaki, J. Kunstmann, G. Cuniberti

Biosensors 2012

2012.05.15-18; Cancun, Mexico

Silicon nanowire (SiNW) field effect transistors (FETs) represent an efficient platform for a sensitive label-free detection of a large variety of bio-chemical species [1]. Electrically sensitive SiNW FETs can be built without the use of dopant using one dimensional Schottky barriers [2,3]. In order to use these Schottky barrier FETs for biosensing applications their surface must be chemically functionalized with biological receptors. Raman spectroscopy is known as a fundamental tool of microscopic material investigation used to characterize chemical surface modifications. Here we present a method to predict Raman and Infrared frequencies of nanostructures from atomistic simulations and we present its application to silicon nanowires [4]. Our method is based on molecular dynamics (MD) simulations and uses the symmetry of the atomic structure of the investigated structure. Explicit and computationally intensecalculations of the electric polarizability or the dipole moment are not required. Based on the density functional tight-binding method for the MD simulations, we apply our method to bulk silicon and to small-diameter hydrogen passivated silicon nanowires. For bulk silicon we study the frequency-shift of the Raman peak with temperature and obtain results that are in good agreement with experiments. By analyzing the bond lengths of different silicon nanowires, we found that surface stress manifests as a 0.37% shortening of bonds only in the outermost silicon layer. We further analyzed the diameter-dependent frequency shift of a Raman peak in silicon nanowires. We found that the frequency shift is mainly governed by the phonon confinement effect and surface stress leads to an additional shift of 9-22%. Considering the observed shift of the Raman peaks of the nanostructures as a response to surface stress, we propose to use our method to analyze the influence of chemical modifications of nanostructures on their Raman peak shifts.

[1] Patolsky et al., Nanowire-based nanoelectronic devices in the life sciences. MRS Bull 32 (2007) 142-149.
[2] Nozaki et al. Multiscale modeling of nanowire-based Schottky-barrier field-effect transistors for sensor applications. Nanotechnology 22 (2011) 325703.
[3] Weber et al. Silicon to nickel-silicide axial nanowire heterostructures for high performance electronics. Phys Stat Sol B 244 (2007) 4170-4175.
[4] Zörgiebel et al. Computing Raman and Infrared frequencies of Nanostructures: Application to silicon nanowires. submitted (2011).

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