Here we report the use of luminescence thermometry to measure the temperature decay from single gold structure into the substrate of AlGaN:Er3+ film. We looked at Er3+ ion photoluminescence upon illumination by modulated 532 nm laser and recorded time-resolved luminescence of 2H11/2 → 4I15/2 and the 4S3/2 → 4I15/2 energy transitions. We calculated the heat generated from gold microdisk and observed the rate of heat dissipation to the environment. We directly calculated the absolute thermal conductivity of 1.7 W/mK for AlGaN: Er3+ film which was in agreement with the literature.

A new thermal imaging technique is characterized that uses an optically trapped erbium oxide nanoparticle cluster of approximately 150 nm. This technique can measure absolute temperature and has an imaging spatial resolution of the trapped particle. Scanning optical probe thermometry has been used to thermally image a cluster of gold nanowires that were excited with the trapping laser. Following a deconvolution of the measured thermal profile, a point spread function of the imaging technique has been determined to be a Gaussian with a FWHM of 165 nm. This width is a function of the clustering of Er2O3 nanoparticles used to image the nanowire. Optical probe thermometry has further been used to measure the temperature of nucleation events where a dichotomy of temperature for nucleated water occurs from degassed water and native water. Degassed water has been measured to nucleate at 555K confirming water adjacent to the gold nanoparticle superheats to the spinodal decomposition temperature before nucleating into a water vapor bubble. Following this event, the temperature inside the vapor bubble rises to the melting point of the gold nanoparticle, 1300 K which is followed by temperature stabilization. The rapid and significant temperature increase is attributed to the loss of a thermal dissipation pathway, to the surrounding water, previously available to the gold nanoparticle due to the insulator nature of the growing vapor envelope around the gold nanoparticle.

Lithographically fabricated gold nanowires are optically excited with 532nm CW laser and the local temperature change is measured in air, pure water and various concentration aqueous solutions of ionic solutes NaCl, Na2SO4 and MgSO4 using the thermal sensor film of Al0.94Ga0.06N embedded with Er3+ ions. The interface thermal resistance for heat transfer from the excited nanowires into the surrounding liquid is determined from the slopes of the temperature change versus laser intensity plots obtained for the nanowire excitation under various solutions. Addition of ionic solute molecules into the solution decreases the interface thermal resistance and hence leads to increased heat dissipation into the surrounding liquid. Interface thermal resistance decreases exponentially with the ionic strength of solution and saturates around zero for solution ionic strength of 0.3M and higher.

The thermal conductance of a gold/water interface has been found to change as a function of the surrounding’s adhesion energy. We measure the thermal conductance of a lithographically prepared gold nanowire with a thin film nanoscale thermal sensor composed of AlGaN:Er3+. The temperature of the nanowire is measured as a function of incident laser intensity. The slope of this plot is inversely proportional to the thermal conductance of the nanoparticle/surrounding’s interface. We show that the conductance of the nanoparticle/water interface increases with the molality of the solution. This was tested with multiple solutes including NaCl, and D-Glucose. The interfacial conductance of pure water is reported to be 44 MW/m2K and the conductance saturates to 100 MW/m2K at a molality of 0.21 m.

Lithographically prepared gold nanodots and nanowires were placed onto a thermal sensor film to measure heat absorption. These identical wires are also subjected to dark field scattering measurements allowing for a comparison between absorption and scattering at the excitation wavelength. An increasing liner trend is found to exist between nanowires of increasing aspect ratio. The nanostructures also exhibit a decreasing temperature change with increasing wire length with a constant laser flux of 1.3 x 1010 W/m2.

We characterize a temperature sensor made from Erbium ions embedded in an amorphous AlGaN matrix that is accessed remotely by measuring the relative intensities from photoluminescence peaks of Er3+. We use this sensor to measure the nanoscale temperature around an optically excited single gold nanoparticle that has been immobilized on the AlGaN substrate. The maximum temperature increase measured experimentally is 8.3 K. The temperature measurement is diffraction limited by our microscope to 490 nm. This temperature corresponds theoretically to a maximum local temperature increase of 22 K. A straight-forward analysis using energy balance gives the thermal conductivity of the amorphous AlGaN substrate as 4.5 W/m-K.

The thermo-optical properties of gold nanoparticles suspended in liquid water droplets have been explored. A water droplet containing suspended gold nanoparticles was irradiated with a laser beam and the efficiency of light-to-heat conversion (η) was determined. Heat generated by the optically stimulated nanoparticles was found to dissipate through several mechanisms. Convection currents were observed visually inside the droplet by the addition of silica beads (˜3-10 micrometers). This was determined to be the dominant mechanism of stirring within the droplet.

We have investigated the thermo-optical properties of gold NPs embedded in an ice matrix [1]. Resonant laser light of relatively weak intensity is able to melt ice with embedded Au NPs, whereas even a very intense laser beam does not melt ice alone. This comes from strong absorption in Au NPs in the regime of plasmon resonance. By recording time-resolved Raman signals, we observe the melting process and determine the threshold melting power , where is the background temperature. We also observe relatively large scattering in the threshold laser intensity that leads to melting of the ice because of the mesoscopic nature of the sample. We can understand this observation using the TEM images of NPs, showing that geometry of NP complexes varies greatly. In our recent theoretical paper we showed that the local temperature inside and around a NP complex depends strongly on its geometry, and this leads to large scattering for the measured as a function of the reduced temperature, for different complexes [2].

We recently discovered that NPs immobilized on glass surfaces can be characterized by single particle spectroscopy. Single and small NP clusters can be discriminated using the integrated intensity of the plasmon emission band. A cluster of four gold NPs has ∼ 4 times the intensity of a single gold NP. When the NPs are aggregated into a cluster then broadening of the intensity profile plot is not observed Gold NPs that are not clustered together but are found within the excitation volume will lead to a broadening of a cross sectional slice. We will use these principles to determine the amount of heat generation from single and clustered gold NPs.

[1] H. H. Richardson, Z. N. Hickman, A. O. Govorov, A. C. Thomas, W. Zhang, M. E. Kordesch, Nano Lett. (2006); DOI: 10.1021/nl060105l.

[2] A. O. Govorov, H. H. Richardson, W. Zhang, and T. Skeini, Nanoscale Res. Lett. 1, 100101 (2005).

Wide bandgap semiconductors have been sputter deposited onto non-crystalline substrates, low melting point materials, including polymer fibers, textiles and glasses. The semiconductors are amorphous and can be deposited over large (square meter) areas economically. The electro-optical properties of these materials are not defect limited, and do not require thermal processing. Alternating current electroluminescent device structures/coatings composed of rare-earth ion doped nitrides have been deposited onto point-bonded fabrics, polymer membranes, and polymer sheets. Light emission is detected from the coated fabrics over the entire visible range, UV and IR. A notable feature of fabric-based structures is the inclusion of ambient air in the fabric voids. Increased light emission intensity is obtained by extracting electrons from the plasma discharge during device operation. These fabrics do not require weaving, which could be difficult with semi-crystalline or brittle semiconductor materials. Multilayer assembly and bonding with continuous sheets, cladding, filling and or contact bonding are all available at any point in the fabric assembly. Non-woven, pin-bonded, materials may still function after some damage, e.g. rips or punctures, due to redundant connections at each pad. Further advantages are the simple incorporation of optically active ions, such as rare earths, high thermal conductivity, high breakdown voltage, and complete miscibility of the group III-A and -B nitrides, allowing bandgap engineering. The deposition process is scalable and may be applied to the fibers or yarns before or after fabric formation.

We have investigated the effects of oxygen incorporation on cathodoluminescence (CL) and photoluminescence (PL) from sputtered amorphous films of AlN:Eu3+. Ordinarily, these materials must be activated at elevated temperatures (~1000K) before appreciable luminescence can be observed. We have shown that oxygen doping is an effective alternative to thermal activation. Studies of CL intensity versus oxygen contamination indicate that luminescence turns on if the oxygen content of the sputtering plasma exceeds a few percent. Significantly, oxygen appears to have a greater impact (>600-fold) on luminescence than does thermal activation (100-fold). The oxygen dependence of PL intensity varies slightly from that of CL intensity. A possible explanation for this observation is proposed. The results suggest that low temperature alternatives to the customary thermal activation process may be available. Such alternatives would eliminate materials constraints and would permit the facile integration of plastic components or substrates with rare-earth-doped III-N luminescent devices.

Amorphous thin films of AlN doped with Cu (blue luminescence), Tb (green luminescence) and Cr (red luminescence) were deposited on p-doped Si (111) substrates using RF magnetron sputtering in a nitrogen atmosphere and made luminescent active by heat treatment at 1000°C. Single layered amorphous AlN films deposited with Tb and Cu showed cathodoluminescence from only the Tb3+ ions. Presumably, energy is transferred from Cu luminescence centers to Tb centers in close proximity. In contrast to this, double layered amorphous AlN films doped with Cu (∼200 nm) on top of Tb (∼50 nm) emits from both ions. This behavior is observed in a double layered amorphous AlN film doped with Cu (∼200 nm) on top of a Cr (∼200 nm) doped film. Secondary-ion mass spectrometry depth profiling revealed that the incorporated metals moved from one layer into the other during the heat treatment step necessary for luminescence activation.