Nanoscale Heaters Research Articles

Scanning SQUID-on-tip microscope in a top-loading cryogen-free dilution refrigerator.

The scanning superconducting quantum interference device (SQUID) fabricated on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile tool for the nanoscale imaging of magnetic, thermal, and transport properties of microscopic devices of quantum materials. We present the design and performance of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight cell mounted at the bottom of the probe and is suspended by springs to suppress vibrations caused by the pulse tube cryocooler. Two capillaries allow for the in situ control of helium exchange gas pressure in the cell that is required for thermal imaging. A nanoscale heater is used to create local temperature gradients in the sample, which enables quantitative characterization of relative vibrations between the tip and the sample. The spectrum of the vibrations shows distinct resonant peaks with a maximal power density of about 27 nm/Hz1/2 in the in-plane direction. The performance of the SQUID-on-tip microscope is demonstrated by magnetic imaging of the MnBi2Te4 magnetic topological insulator, magnetization and current distribution imaging in a SrRuO3 ferromagnetic oxide thin film, and thermal imaging of dissipation in graphene.

Dielectric functions evolution and electronic bandgap manipulation by silicon doping for Sb2Te3 phase change films: Temperature dependent spectroscopic ellipsometry study

The dielectric function evolution and electronic bandgap manipulation by silicon (Si) doping for Sb2Te3 phase change films have been investigated by temperature dependent spectroscopic ellipsometry measurements. During the phase change from amorphous to rhombohedral structures, the significant contrast of electronic band structure for pure Sb2Te3 and Si-doped Sb2Te3 (SST) films as functions of temperature (210–620 K) and Si concentration (0%–12%) has been systematically studied by analyzing the dielectric functions, Tauc gap energy, and partial spectral weight integral. The distinct differences can be mainly attributed to the increment of structure order degree, originated from the change of local bonding arrangement. Based upon the evolutions of Tauc gap energy and partial spectral weight integral with increasing temperature for all four samples, it can be concluded that Si doping can inhibit the crystallization of amorphous films and accelerate the phase change process by serving as nanoscale heaters, which is helpful in improving the thermal stability of amorphous films. The elevated crystallization temperature and phase change rate by Si doping contribute to the dependability and endurance for SST-based phase change memory. The present data provide an important direction on the physical mechanism investigation of Si doping Sb2Te3 by optical techniques.

Hydrodynamic thermal transport in silicon at temperatures ranging from 100 to 300 K

Energy dissipation in current microelectronic devices is an inefficient process due to its non-Fourier behavior. By using thermoreflectance imaging, the authors measure the temperature distribution around nanoscale heaters of different sizes and shapes on a silicon substrate to test state-of-the-art modeling. The results indicate that hydrodynamiclike thermal transport equations successfully predict the local system response at temperatures ranging from 100 to 300 K. This is contrasted with kinetic interpretations based on the suppression of long mean free path phonons, which are shown not to become manifest in the experiments.

An incandescent metasurface for quasimonochromatic polarized mid-wave infrared emission modulated beyond 10\u2009MHz

Incandescent sources such as hot membranes and globars are widely used for mid-infrared spectroscopic applications. The emission properties of these sources can be tailored by means of resonant metasurfaces: control of the spectrum, polarization, and directivity have been reported. For detection or communication applications, fast temperature modulation is desirable but is still a challenge due to thermal inertia. Reducing thermal inertia can be achieved using nanoscale structures at the expense of a low absorption and emission cross-section. Here, we introduce a metasurface that combines nanoscale heaters to ensure fast thermal response and nanophotonic resonances to provide large monochromatic and polarized emissivity. The metasurface is based on platinum and silicon nitride and can sustain high temperatures. We report a peak emissivity of 0.8 and an operation up to 20 MHz, six orders of magnitude faster than commercially available hot membranes.

Accurate quantification of photothermal heat originating from a plasmonic metasurface

Photothermal effect in plasmonic nanostructures (thermoplasmonic), as a nanoscale heater, has been widely used in biomedical technology and optoelectronic devices. However, the big challenge in this effect is the quantitative characterization of the delivered heat to the surrounding environment. In this work, a plasmonic metasurface (as a nanoheater), and a Fabry-Perot (FP) cavity including liquid crystal (as a thermometer element) are integrated. The metasurface is manufactured through a bottom-up deposition method and has a near perfect absorption that causes an efficient temperature rising in the photothermal experiment under a low intensity of irradiation ($0.25\; {\rm W}/{{\rm cm}^2}$0.25W/cm2). Generated heat from the metasurface dissipates to the liquid crystal (LC) layer and makes a spectral shift of FP modes. More than 50°C temperature elevation with accuracy of 1.3°C are measured based on the consistency of anisotropic thermo-tropic data of the LC and a spectral shift of FP modes. The calculated figure of merit (FoM) of the constructed device, which indicates the temperature sensitivity, is 22. The FoM is four times more than other reported thermometry devices with broad spectral width. The device can be also used as an all-optical device to control the plasmonic resonance spectrum.

Fast Spiking of a Mott VO2-Carbon Nanotube Composite Device.

The recent surge of interest in brain-inspired computing and power-efficient electronics has dramatically bolstered development of computation and communication using neuron-like spiking signals. Devices that can produce rapid and energy-efficient spiking could significantly advance these applications. Here we demonstrate direct current or voltage-driven periodic spiking with sub-20 ns pulse widths from a single device composed of a thin VO2 film with a metallic carbon nanotube as a nanoscale heater, without using an external capacitor. Compared with VO2-only devices, adding the nanotube heater dramatically decreases the transient duration and pulse energy, and increases the spiking frequency, by up to 3 orders of magnitude. This is caused by heating and cooling of the VO2 across its insulator-metal transition being localized to a nanoscale conduction channel in an otherwise bulk medium. This result provides an important component of energy-efficient neuromorphic computing systems and a lithography-free technique for energy-scaling of electronic devices that operate via bulk mechanisms.

Localized Triggering of the Insulator-Metal Transition in VO2 Using a Single Carbon Nanotube.

Vanadium dioxide (VO2) has been widely studied for its rich physics and potential applications, undergoing a prominent insulator-metal transition (IMT) near room temperature. The transition mechanism remains highly debated, and little is known about the IMT at nanoscale dimensions. To shed light on this problem, here we use ∼1 nm-wide carbon nanotube (CNT) heaters to trigger the IMT in VO2. Single metallic CNTs switch the adjacent VO2 at less than half the voltage and power required by control devices without a CNT, with switching power as low as ∼85 μW at 300 nm device lengths. We also obtain potential and temperature maps of devices during operation using Kelvin probe microscopy and scanning thermal microscopy. Comparing these with three-dimensional electrothermal simulations, we find that the local heating of the VO2 by the CNT plays a key role in the IMT. These results demonstrate the ability to trigger IMT in VO2 using nanoscale heaters and highlight the significance of thermal engineering to improve device behavior.

Polarization-dependent ultrafast plasmon relaxation dynamics in nanoporous gold thin films and nanowires

Metal materials structured at nanoscale are extensively used in a variety of applications, including molecular sensing, nanoscale heaters for photothermal therapy, etc. These applications depend on the strong absorption and electric field enhancements associated with localized surface plasmon resonance (LSPR). Despite multiple investigations of LSPR relaxation dynamics in plasmonic metallic nanoparticles (i.e. nanospheres, nanocubes, etc), no detailed studies of porous thin films or nanowires have been reported so far. In this paper, LSPR relaxation dynamics of nanoporous gold thin film, gold nanowires, and nanoporous gold nanowires (structures with the potential for a vast range of sensing and optical applications) were studied by means of transient absorption spectroscopy (TAS). Au and Au/Cu thin films produced by magnetron sputtering deposition over a nanograted silicon substrate enabled the creation of highly organized nanowire arrays of centimetres length. Nanoporous structures were created by the dealloying of Au/Cu alloy. We found that formation of such a subwavelength period grating structure in gold increases the efficiency of hot electron relaxation compared to continuous film, while the porosity of gold nanostructures has the opposite effect. The results also expressed a clear dependence of the TAS signal on the polarization (i.e. orientation of the electric field with respect to the nanoporous gold nanowires) of the pump and probe pulses, compared to non-porous gold nanowires.

Quasiballistic Thermal Transport from Nanoscale Heaters and the Role of the Spatial Frequency

Engineering heat transport at the nanoscale is important for thermal management in modern technology, but precisely how thermal resistance is affected by geometry and length scale has been a topic of debate. This study identifies a key parameter, the spatial frequency of a heating pattern, that governs thermal transport at the nanoscale. This result provides a means to quantitatively manipulate thermal dissipation at the nanoscale, simply by considering the spatial frequencies of the heating pattern.

Nanoclay-Based Self-Supporting Responsive Nanocomposite Hydrogels for Printing Applications.

Stimuli-responsive hydrogels and/or composite hydrogels have been of great interest for various printing applications including four-dimensional printing. Although various responsive hydrogels and/or composite hydrogels have been found to respond to given stimuli and change shapes as designed, the fabrication of three-dimensional (3D) structures from such responsive hydrogels is still a challenge due to their poor 3D printability, and most of the responsive material-based patterns are two-dimensional (2D) in nature. In this study, Laponite nanoclay is studied as an effective additive to improve the self-supporting printability of N-isopropylacrylamide (NIPAAm), a thermoresponsive hydrogel precursor while keeping the responsive functionality of NIPAAm. Graphene oxide (GO) is further added as a nanoscale heater, responding to near-infrared radiation. Due to the different shrinking ratios and mechanical properties of the poly( N-isopropylacrylamide) (pNIPAAm)-Laponite and pNIPAAm-Laponite-GO nanocomposite hydrogels, printed 2D patterns deform in a predictable way. In addition, 3D microfluidic valves are directly printed and cured in air, which can effectively control the flow directions in response to different stimuli as validated in a microfluidic system. Because Laponite nanoclay can be mixed with various responsive hydrogel precursors to improve their 3D printability, the proposed Laponite nanoclay-based nanocomposite hydrogels can be further expanded to prepare various 3D printable responsive nanocomposite hydrogels.

Dynamics of Surface Plasmon Polaritons in Metal Nanowires

Metal nanostructures have found extensive use in a variety of applications in chemistry, including as substrates for molecular sensing and surface enhanced spectroscopy and as nanoscale heaters for photothermal therapy. These applications depend on the strong absorption and field enhancements associated with localized surface plasmon resonance (LSPR). This has led to a number of studies of how the LSPR line width, which measures energy losses for the coherent electron motion, depends on the size and shape of different types of metal nanoparticles, and the environment around the particle. Extended metal nanostructures, such as nanowires and nanoplates, display propagating surface plasmon modes, termed surface plasmon polaritons (SPPs), in addition to LSPRs. These modes are important for applications where metal nanostructures are used as waveguides. However, less is known about the damping of the propagating SPPs compared to the LSPRs. The energy losses for the propagating SPP modes can be investigated by ...

Nanoscale steady-state temperature gradients within polymer nanocomposites undergoing continuous-wave photothermal heating from gold nanorods.

Anisotropically-shaped metal nanoparticles act as nanoscale heaters via excitation of a localized surface plasmon resonance, utilizing a photothermal effect which converts the optical energy into local heat. Steady-state temperatures within a polymer matrix embedded with gold nanorods undergoing photothermal heating using continuous-wave excitation are measured in the immediate spatial vicinity of the nanoparticle (referred to as the local temperature) from observing the rate of physical rotation of the asymmetric nanoparticles within the locally created polymer melt. Average temperatures across the entire (mostly solid) sample (referred to as the global temperature) are simultaneously observed using a fluorescence method from randomly dispersed molecular emitters. Comparing these two independent measurements in films having varying concentrations of nanorods reveals the interplay between the local and global temperatures, clearly demonstrating the capability of these material samples to sustain large steady-state spatial temperature gradients when experiencing continuous-wave excitation photothermal heating. These results are discussed quantitatively. Illustrative imaging studies of nanofibers under photothermal heating also support the presence of a large temperature gradient. Photothermal heating in this manner has potential utility in creating unique thermal processing conditions for outcomes such as driving chemical reactions, inducing crystallinity changes, or enhancing degradation processes in a manner unachievable by conventional heating methods.

Evaluating the Frequency Response of Nanoscale Thermocouples Using Temperature Oscillations in Nanoscale Heaters

Evaluating the Frequency Response of Nanoscale Thermocouples Using Temperature Oscillations in Nanoscale Heaters

Shape engineering of antenna-coupled single-metal nanothermocouples

We study the thermal response of antenna-coupled nanothermocouples (NTC) for long-wave infrared (IR) detection based on a single-metal nanostructure and shape engineering. The influence of the shape of the NTC junctions on the electrical and IR response of the sensor is studied. In particular, we compare detectors with abrupt and tapered junctions. We find that the thermoelectric behaviors of the two different NTC designs are identical when one of the junctions is selectively heated by a nanoscale heater to produce an open-circuit voltage. However, the IR responses are significantly different when the junctions are heated by the radiation-induced antenna current. Both simulations and experiments demonstrate that the tapered junction is more efficiently heated by the antenna, which results in nearly twice as large IR response compared with detectors having abrupt junctions.

Single-Metal Nanoscale Thermocouples

We study the generation of thermoelectricity by nanoscale thermocouples (TCs) formed from a single layer of metal with cross-sectional discontinuity. Typically, a TC is formed when a second conductor is inserted between two sections of a first conductor forming two junctions situated at different temperatures. Here, we investigate the behavior of TCs formed not of two conductors but rather nanowires of the same metal of two cross-sectional areas. Monometallic TCs were constructed from a lithographically defined nanowire having one abrupt variation in width along its length, and tested at room temperature; these structures exploit a change in Seebeck coefficient that is present at these size scales. To investigate the thermoelectric properties of such “shape-engineered” TCs, nanoscale heaters were employed to set the local temperatures. Temperature profiles at the hot and cold junctions of the TCs were determined both by simulations and experiments. Results demonstrate that the magnitude of the open-circuit voltage, and hence the relative Seebeck coefficient, is a function of the parameters of the variations in the segment widths. The fabrication complexity of such shape-engineered monometallic nanowire TCs is greatly reduced compared to that of conventional bimetallic TCs, and could be mass-produced using simpler manufacturing techniques.

Thermooptical Properties of Gold Nanoparticles Embedded in Ice: Characterization of Heat Generation and Melting

We investigate the system of optically excited gold NPs in an ice matrix aiming to understand heat generation and melting processes at the nanoscale level. Along with the traditional fluorescence method, we introduce thermooptical spectroscopy based on phase transformation of a matrix. With this, we can not only measure optical response but also thermal response, that is, heat generation. After several recrystallization cycles, the nanoparticles are embedded into the ice film where the optical and thermal properties of the nanoparticles are probed. Spatial fluorescence mapping shows the locations of Au nanoparticles, whereas the time-resolved Raman signal of ice reveals the melting process. From the time-dependent Raman signals, we determine the critical light intensities at which the laser beam is able to melt ice around the nanoparticles. The melting intensity depends strongly on temperature and position. The position-dependence is especially strong and reflects a mesoscopic character of heat generation. We think that it comes from the fact that nanoparticles form small complexes of different geometry and each complex has a unique thermal response. Theoretical calculations and experimental data are combined to make a quantitative measure of the amount of heat generated by optically excited Au nanoparticles and agglomerates. The information obtained in this study can be used to design nanoscale heaters and actuators.