Effects of Size and Load on Transport Properties of Nanoscale Metal-Oxide Interfaces
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Effects of Size and Load on Transport Properties of Nanoscale Metal-Oxide Interfaces Ramsey Kraya1 1
School of Engineering and Applied Science, University of Pennsylvania
ABSTRACT With interface sizes rapidly reducing to the nanometer scale, it has become vital to understand how size and structure can affect transport behavior between materials in order to tune the energy barrier for various applications. Here, the fabrication of Schottky Barriers between Au nanoparticles and doped SrTiO3 materials is reported. The effect of nanoparticle size on the transport properties is clearly evident providing an excellent opportunity to compare new theory on transport characteristics at the nanoscale to classical theory to determine the method that is most effective in predicting nanoscale transport properties. INTRODUCTION Transport characteristics of nanoscale metal-semiconductors contacts have been actively researched in recent years.1-9 Many physical models that apply to macroscopic junctions fail to accurately predict transport at the nanoscale. Newer models have been developed with the most basic premise being that as sizes decrease to the nanometer range, transport across a metal semiconductor junction will be dominated by tunneling mechanisms over conventional thermionic mechanisms creating tunnel contacts instead of rectifying contacts.10-11 This occurs when the interface size is smaller than the thickness of the transport barrier. In this letter, the measurements of electrical transport through interfaces between metal nanoparticles and SrTiO3 surfaces are presented. The results show that 20-30 nm sized interfaces exhibit rectifying behavior, with IV curves of the small diodes fitting the standard diode equation. By applying both classical and modern models to nanoscale interfaces, it is shown that rectifying behavior is possible for metal contacts to SrTiO3 as small as 7 nanometers in diameter. EXPERIMENTAL DETAILS The samples consist of gold nanoparticles on single-side epitaxially polished Nb-doped (.02at% Nb) SrTiO3 (100) (Princeton Scientific). (Figure 1) Before deposition of the nanoparticles the substrates are annealed in flowing oxygen at 750oC for 1 hour to flatten the surface and remove contamination. The nanoparticles were drop cast onto the surface of the SrTiO3 substrate. Interparticle distance was controlled by diluting the solutions with water so that aggolermations were limited and so that measurements were between a single nanoparticle and the SrTiO3 and not affected by the depletion region of other nanoparticles.12
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FIGURE 1: An AFM image of a typical gold nanoparticle on an SrTiO3 substrate. The isolated nanoparticle is smaller than it appears due to tip convolution effects. The size of the nanoparticle is determined by its height.
All experiments were performed in an ambient environment atomic force microscope (Asylum MFP3D). Topography images were taken in AC mode where the tip makes intermittent contact with the surface – preserving the nanoparticle-substrate junction. Once a nanop
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