We measure near-field radiative cooling of a thermally isolated nanostructure up to a few degrees and show that in principle this process can efficiently cool down localized hotspots by tens of degrees at submicrometer gaps. This process of cooling is achieved without any physical contact, in contrast to heat transfer through conduction, thus enabling novel cooling capabilities. We show that the measured trend of radiative cooling agrees well theoretical predictions and is limited mainly by the geometry of the probe used here as well as the minimum separation that could be achieved in our setup. These results also pave the way for realizing other new effects based on resonant heat transfer, like thermal rectification and negative thermal conductance.

Near-field heat transfer recently attracted growing interest but was demonstrated experimentally only in macroscopic systems. However, several projected applications would be relevant mostly in integrated nanostructures. Here we demonstrate a platform for near-field heat transfer on-chip and show that it can be the dominant thermal transport mechanism between integrated nanostructures, overcoming background substrate conduction and the far-field limit (by factors 8 and 7, respectively). Our approach could enable the development of active thermal control devices such as thermal rectifiers and transistors. KEYWORDS: Thermal transport, thermal radiation, near-field radiation, microelectromechanical systems (MEMS), surface phonon-polariton R ecently, there has been a growing interest in controlling radiative heat transfer in the near-field, 1−11 for applications in thermal microscopy, 12−14 thermophotovoltaic energy generation, 15−18 noncontact cooling, 19,20 and heat flow control.21−28 Near-field heat transfer occurs when objects supporting surface phonon-polaritons (e.g., SiO 2 and SiC) or infrared plasmon-polaritons (e.g., doped silicon) are brought to submicron separation, such that their surface modes can evanescently couple. This heat transfer occurs over a narrow frequency range (as opposed to the broadband nature of solid state conduction) and can exceed the blackbody limit by several orders of magnitude.It has been shown theoretically that near-field heat transfer can enable active functionalities such as thermal rectifiers, 21−23,25−27 thermal transistors, 28 and thermal switches; 24 however, these devices would only be relevant to actual systems if shown to occur in integrated geometries, where unfortunately other conduction channels might dominate, rather than in macroscopic object. To date, near-field heat transfer has only been shown using macroscopic objects, i.e., one or two semiinfinite surfaces, 7,8,[10][11][12][13][14][15]19 or a large probe tip approximated as a sphere.20 Scaling up these macroscopic geometries to an actual thermal circuit composed of several components would be extremely challenging since even a single thermal transistor requires at least two near-field heat transfer junctions. On-chip integration is therefore necessary for the development of several applications. Moreover, miniaturization could eventually yield fundamental performance advantages over macroscopic experiments. For example, nanopatterned objects can significantly relax the distance requirement for efficient near-field heat transfer between two objects, 9 while size-induced discretization of thermal modes could allow ultrahigh contrast rectification of heat transfer. 27Here we show strong near-field radiative heat transfer in a novel on-chip geometrical configuration of two parallel suspended nanobeams where the distance between the beams can be tuned electrostatically. Our geometrical configuration is shown in Figure 1a. We use silicon dioxide (SiO 2 ) for its surface phonon polariton resonances, at 495 ...

We describe a novel approach for CMOS-compatible passively temperature insensitive silicon based optical devices using titanium oxide cladding which has a negative thermo-optic (TO) effect. We engineer the mode confinement in Si and TiO2 such that positive TO of Si is exactly cancelled out by negative TO of TiO2. We demonstrate robust operation of the resulting device over 35 degrees.

A passive CMOS-compatible thermal stabilization scheme for resonant photonic devices will go a long way towards enabling the implementation of ultralow power optical interconnects. This is because resonant devices such as microring resonators are ideally suited for dense integration of optical networks due to their compact size, high extinction ratio per unit length, low insertion loss and low power consumption 5,6,7 . But they are also highly sensitive to temperature (~ 0.11 nm/K) because of their narrow bandwidth. Typical temperature fluctuations in a commercial microprocessor can be 10s of degrees within a local hotspot 8 , degrading considerably the performance of these resonant devices. There has been significant effort in stabilizing these devices by delocalizing the mode and overlaying a polymer coating with a negative TO coefficient 9, 10, 11, 12 , but polymers are currently not compatible with CMOS process.Temperature independent operation over a small range has been shown in multiple cavity coupled devices 13 . Another approach is to use local heating of silicon itself to dynamically compensate for any temperature fluctuations 14,15,16 . However, an active

We present a novel design approach for integrated Mach-Zehnder interferometers to minimize their temperature sensitivity and demonstrate, for the first time, near zero spectral shifts with temperature (approximately 0.005 nm/K) in these devices. This could lead to fully CMOS-compatible passively compensated athermal optical filters and modulators.