In photo-thermal actuation, heat is added locally to a micro-cantilever by means of a laser. A fraction of the irradiation is absorbed, yielding thermal stresses and deformations in the structure. Harmonic modulation of the laser power causes the cantilever to oscillate. Moreover, a phase lag is introduced which is very sensitive to the spot location and the cantilever properties. This phase lag is theoretically predicted and experimentally verified. Combined with thermo-mechanical properties of the cantilever and its geometry, the location of the laser spot, the thermal diffusivity, and the layer thicknesses of the cantilever can be extracted. V C 2014 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4893461] Nano-cantilevers are used in applications from scanning probe microscopy 1 to chemical analysis 2,3 and bio-sensing. 4The principle is based on measuring changes in the motion of a micro-cantilever that are caused by the interaction with the subject. This is typically done using the optical beam deflection (OBD) method. 5 In this method, a laser is focused on the cantilever and the reflected beam is registered on a position sensitive detector. A fraction of the irradiation, however, is absorbed and causes a temperature gradient over the length of the cantilever that results in thermal stresses and deformations. Through modulation of the absorbed power, the cantilever can be actuated; a technique which is known as photo-thermal actuation.6-9 Because the heat is absorbed in only a small area, time is required to dissipate the heat through the structure and for the temperature gradient to change. The dissipation time results in a phase lag between the actuation signal and the thermo-mechanical response which can be predicted theoretically based on material properties and the geometry. The phase lag information can be used for extraction of both thermal and mechanical properties of the cantilever and the location of the laser spot along its length. In this Letter, the methodology and its applications are outlined.Photo-thermal actuation relies on temperature gradient induced stresses that cause deformation of a microcantilever. The temperature gradient along the length of a cantilever is described by the one-dimensional heat equation. Given in its general formit describes the temperature T as a function of time t, location along the cantilever x, the thermal diffusivity D (m 2 s À1 ), the characteristic time constant for convective heat transfer B (s À1 ), the ambient temperature T env , and forcing function f.

Optical near-field technologies such as solid immersion lenses and hyperlenses are candidate solutions for high resolution and high throughput wafer inspection and metrology for the next technology nodes. Besides subdiffraction limited optical performance, these concepts share the necessity of extreme proximity to the sample at distances that are measured in tens of nanometers. For the instrument this poses two major challenges: 1) how to measure the distance to the sample? and 2) how to position accurately and at high speed? For the first challenge near-field thermal radiation is proposed as a mechanism for an integrated distance sensor (patent pending). This sensor is realized by making a sensitive calorimeter (accuracy of 2.31 nW root sum squared). When used for distance measurement an equivalent uncertainty of 1 nm can be achieved for distances smaller than 100 nm. By scanning the distance sensor over the sample, thermal profilometry is realized, which can be used to inspect surfaces in a non-intrusive and non-contact way. This reduces wear of the probe and minimizes the likelihood of damaging the sample.

High resolution and high throughput imaging are typically mutually exclusive. The meta-instrument pairs high resolution optical concepts such as nano-antennas, superoscillatory lenses and hyperlenses with a miniaturized opto-mechatronic platform for precise and high speed positioning of the optical elements at lens-to-sample separations that are measured in tens of nanometers. Such platform is a necessary development for bringing near-field optical imaging techniques to their industrial application.Towards this purpose, we present two designs and proof-of-principle instruments that are aimed at realizing sub-nanometer positional precision with a 100 kHz bandwidth.

Multilayer cantilever beams are used in the measurement of near-field radiative heat transfer. The materials and dimensions of the cantilever probe are chosen in order to improve system performance in terms of sensitivity and noise. This is done using an analytical model that describes the thermo-mechanical and mechanical behavior of the cantilever and its influences at the system level. In the design, the optical reflectance and the sensitivity of cantilever rotation to the heat input are maximized under constraints for thermal noise, temperature drift, and a lower bound for the spring constant. The analytical model is verified using finite element analysis, which shows that the effects of radiative losses to the environment are insignificant for design purposes, while the effects of ignoring three-dimensional heat flow introduces larger errors. Moreover, the finite element analysis shows that the designed probes are up to 41 times more sensitive than the often used commercial-of-the-shelf benchmark and have a four times lower thermal noise. Experimental validation of the designed probes shows good agreement with the theoretical values for sensitivity. However, the most sensitive designs were found to be susceptible to damage due to overheating and carbon contamination.