Large thermal biasing of individual gated nanostructures

Stefano Roddaro, Daniele Ercolani, Mian Akif Safeen, Francesco Rossella, Vincenzo Piazza, Francesco Giazotto, Lucia Sorba, Fabio Beltram
2014 Nano Reseach  
We demonstrate a novel nanoheating scheme that yields very large and uniform temperature gradients up to about 1 K every 100 nm, in an architecture which is compatible with the field-effect control of the nanostructure under test. The temperature gradients demonstrated largely exceed those typically obtainable with standard resistive heaters fabricated on top of the oxide layer. The nanoheating platform is demonstrated in the specific case of a short-nanowire device. PACS numbers: 72.20.Pa,
more » ... 7.Gf, 85.30.Tv In the past decade much effort was directed to the investigation of the thermoelectric (TE) properties of innovative materials. Such a revival of TE science was largely driven by the interest in solid-state energy converters 1-4 and by the development of novel advanced materials 5 and, in particular, nanomaterials 6-8 . Indeed, the achievement of an efficient and cost-effective TE technology depends on the optimization of a set of interdependent material parameters of the active element: the Seebeck coefficient S and the heat and charge conductivities κ and σ. Recent developments in nanoscience yielded new strategies for the design of novel and more efficient nanomaterials in which the strong interdependency between S, κ and σ can be made less stringent 9-12 . Despite the host of available theoretical predictions 12-16 , however, the optimization of the TE behavior of nanostructured materials still remains an open and actively investigated problem 17,18 , in particular for what concerns the influence of electron quantum states engineering on the power factor σS 2 . This led to the development of a number of experimental arrangements designed to impose a controllable thermal bias over micrometric or even submicrometric active elements and to measure how this affects charge transport in the device. Differently from macroscopic active elements, nanoscale TE materials also allow the investigation of thermal effects in devices where fieldeffect can be used to control carrier density 18,19 or even quantum states energetics 20,21 and coupling 22 . While this may not be a directly scalable strategy in view of applications, it is particularly useful for what concerns the fundamental investigation of the impact of dopinga key parameter -on TE performance. Various examples of microheating systems were reported in the literature. These include (i) suspended SiN x microheaters, which enable a precise estimate of the κ of individual nanostructures, but also pose non-trivial technical challenges 23,24 and do not allow the field-effect control of the nanostructure behavior; (ii) resistive heaters fabricated on top of standard Si/SiO 2 substrates, which are instead typically used to estimate S and allow also the field-effect control of carrier density 19,22,25-28 . Here we demonstrate an innovative buried-heater (BH) FIG. 1: The measurement of field-effect dependence of thermoelectric effects in single nanostructures (a nanowire device is visible in panel (a)) requires the application of a strong thermal gradient (panel (b)). A standard approach consists in the fabrication of a top heating element (panel (c)). An alternative "buried" architecture exploiting current flows into the bulk is visible in panel (d). scheme based on current diffusion in the conductive bulk of a SiO 2 /Si substrate. This scheme is different from the more standard one of "top" heaters (THs) relying on resistive elements microfabricated on top of the oxide layer. We shall show that our architecture yields very large and uniform thermal gradients easily exceeding 5 K/µm and up to about 10 K/µm, far beyond typical values reported in the literature for THs. In addition, similarly to the case of TH architectures, our scheme allows the control of the nanostructure behavior by field effect. A sketch of the two alternative TH and BH schemes is visible in Fig. 1 . The TH scheme relies on the diffusion of heat from a metallic resistive element through the oxide, into the sub-arXiv:1312.2845v3 [cond-mat.mes-hall]
doi:10.1007/s12274-014-0426-y fatcat:nu2zplwb45fhllapqv3p5i6uoy