Phonon Confinement Effects in Hybrid Virus-Inorganic Nanotubes for Nanoelectronic Applications Vladimir A. Fonoberov ² and Alexander A. Balandin* ,²,‡ Nano-DeVice Laboratory, Department of Electrical Engineering, UniVersity of California, RiVerside, California 92521 Received June 29, 2005; Revised Manuscript Received August 28, 2005 ABSTRACT Genetically modified viruses have been proposed recently as templates for the assembly of nanometer-scale components of electronic circuits. Here we show that, in addition to their role as nanotemplates, viruses can actually improve the electron transport properties in semiconductor nanotubes grown on them. In the considered hybrid virus-inorganic nanostructures, which consist of silica or silicon nanotubes deposited on tobacco mosaic viruses, the confined acoustic phonons are found to be redistributed between the nanotube shell and the acoustically soft virus enclosure. As a result, the low-temperature electron mobility in the hybrid virus-silicon nanotube can increase by a factor of 4 compared to that of an empty silicon nanotube. Our estimates also indicate an enhancement of the low-temperature thermal conductivity in the virus- silicon nanotube, which can lead to improvements in heat removal from the hybrid nanostructure-based nanocircuits. In a continuous effort to the ultimate miniaturization of computer electronic circuits, nanowires, and nanotubes, as thin as a few atoms in diameter, have been employed recently. 1 The performance of such nanocircuits can be enhanced greatly by increasing the electron mobility and thermal conductivity in constituent nanowires and nanotubes. The former can be achieved by suppressing the inelastic scattering of electrons on phonons, whereas the latter can be achieved by properly tuning the acoustic phonon modes, which carry the bulk of the heat. 2-5 Genetically modified viruses, as “smart” nanotemplates for the chemical assembly of nanowire-interconnects and circuit elements, present one of the recent developments in the field. 6-8 Understanding the lattice vibration, that is, phonon, properties of such hybrid bioinorganic nanostructures is of great interest from the fundamental science point of view. In this Letter we consider inorganic nanotubes grown on plant viruses, which are used as nanotemplates. 6,7 We show, for the first time, that the viruses, previously thought of only as nanotemplates, can actually improve the electronic and thermal properties of the inorganic nanotubes grown on them because of the phonon confinement and redistribution effects in the acoustically mismatched hybrid nanostructures. It is demonstrated that the electron-phonon scattering in such hybrid nanotubes can be suppressed at low temperature. Our results suggest that the genetically programmed viruses, 8 such as the tobacco mosaic virus (TMV), may serve not only as vehicles for the self-assembly 9,10 and ordering 11,12 of nano- structures for nanoelectronic circuits but may also enhance the performance of the resulting circuits via the proposed phonon engineering approach. During the past few years there have been a number of reports on theoretical and experimental investigations of phonon modes in inorganic and organic nanowires. 2,4,13 The spatial confinement and quantization of phonon modes in such nanostructures was shown to influence their thermal and electronic properties. 14,15 At the same time, the phonon modes in coated nanowires, consisting of layers of materials with strongly dissimilar elastic properties, let alone in the hybrid bioinorganic nanostructures, have not been considered so far. It is well known that electronic states undergo strong modifications in such nanowires and quantum dots. 16-18 To answer the question if there are any unusual and practically important changes in the vibrational properties of hybrid bioinorganic nanostructures, we consider a real 3-nm-thick silica (silicon) nanotube grown on the 18-nm-in-diameter TMV. 6 In the following, we study the changes in the phonon dispersion, density of states, phonon spatial distribution, and low-field electron mobility of the hybrid virus/silica (virus/ silicon) nanotubes in comparison to empty silica (silicon) nanotubes. 19,20 The TMV-based nanotubes were selected as example hybrid systems because of the promises of robust TMVs as nanotemplates for chemical nanostructure self- assembly. 6,7 The benefits of TMVs as nanotemplates include * To whom correspondence should be addressed. E-mail: balandin@ ee.ucr.edu. ² These authors contributed equally to this work. ‡ Web address: http://ndl.ee.ucr.edu. NANO LETTERS 2005 Vol. 5, No. 10 1920-1923 10.1021/nl051245i CCC: $30.25 © 2005 American Chemical Society Published on Web 09/22/2005