Neurodynamic behavior of artificial neuron circuits made of Mott memristors provides versatile opportunities to utilize them for artificial sensing. Their compactness and energy-efficient spike generation enable integration into medical implants. This work demonstrates a low-power, biomimetic auditory sensing concept for fully implantable cochlear implants. The approach draws inspiration from the frequency selectivity and temporal encoding of the cochlea, and uses neuromorphic spike generation to replace conventional signal processing blocks. The auditory sensing unit is realized by a piezoelectric MEMS cantilever coupled to a single VO2 nanogap Mott memristor-based oscillator. This configuration enables FFT-free, frequency-selective sensing and direct spike generation, forming a biomimetic auditory front end. The sensing unit exhibits frequency-selective detection of mechanical vibrations in the nanometer to tens-of-nanometers displacement range and generates biomimetic spiking waveforms. Spike rate-encoding of the input amplitude is demonstrated, with output spiking frequencies tunable between approximately 100 Hz and 1 kHz depending on the excitation level. The waveform is finally converted to a biphasic shape suitable for cochlear implant stimulation. Through realizing temporal spike-encoding, a fundamental principle in the healthy auditory pathway, the proposed approach can provide significant benefits for cochlear implants. In addition, the circuit has the potential to reduce footprint, energy consumption, and latencies compared to current commercial solutions.

BaTiO3 (BTO) is a ferroelectric material that has a large Pockels coefficient. Recently, there has been increasing interest in epitaxial BTO films integrated on silicon as a promising material platform for building electro-optic (EO) modulators. For BTO integration on Si, a SrTiO3 (STO) buffer layer was first deposited on a Si (001) substrate by molecular beam epitaxy. BTO films were then grown on this STO-buffered Si template via pulsed laser deposition at various oxygen pressures (10–50 mTorr) and substrate temperatures (600–760 °C). We found that the measured electro-optic response of the BTO films is highly dependent on their domain orientations and film thickness. By adjusting the oxygen deposition pressure and substrate temperature, we were able to grow a-oriented BTO films which are a preferred domain structure for EO modulators due to the large Pockels effect in this configuration. An effective Pockels coefficient of up to 432 pm/V was demonstrated in 500 nm thick BTO films in transmission measurements using 1550 nm light, showing the potential of BTO films for use in integrated silicon photonic devices.

Applying coatings that suppress the radiance changes related to temperature-dependent blackbody emission enables temperature-independent optical and sensing systems. Phase-change materials can significantly modify their optical properties within their transition window, but compensating for the large mid-wave infrared (MWIR, 3–5 µm) variation is demanding: blackbody radiance at 3 µm increases nearly 10-fold as the temperature rises from 30 °C to 80 °C. Vanadium dioxide VO2, whose insulator–metal transition offers a sharp contrast and a low-loss insulating state, is attractive for applications in thermal management, but simple thin-film designs cannot provide full compensation. We demonstrate metasurface coatings that provide this compensation by constructing an array of metal–VO2–metal antennas tuned to maintain constant thermal emission at a target wavelength over a temperature range of 30 °C to 80 °C. Antennas of several lateral sizes are combined, so their individual resonances collectively track the Planck change. This design provides both optical contrast and the correct temperature derivative, which are unattainable with homogeneous layers. Our approach results in a negligible apparent temperature change of the metasurface across the 30–80 °C range, effectively masking thermal signatures from MWIR detectors stemming from the low losses of VO2.

Oscillating neural networks are promising candidates for a new computational paradigm, where complex optimization problems are solved by physics itself through the synchronization of coupled oscillating circuits. VO 2 Mott memristors are particularly promising building blocks for such oscillating neural networks. Until now, however, not only the maximum frequency of VO 2 oscillating neural networks, but also the maximum frequency of individual VO 2 oscillators is severely limited, which has restricted their efficient and energy‐saving use. In this study, it is showed how to increase the oscillating frequency by more than an order of magnitude into the 100 MHz range utilizing ultrasmall, ≈30 nm wide active volume VO 2 devices and optimizing the circuit layout for high frequency operation. In addition, the physical limiting factors of the oscillation frequencies are studied by investigating the complex switching dynamics of our nanoscale VO 2 devices. These dynamical studies, together with simulations, provide a clear conclusion on the maximum achievable operating frequencies and the optimal operating parameters under which these can be reached.

The ability to treat the surface of an object with coatings that counteract the change in radiance resulting from the object’s blackbody emission can be very useful for applications requiring temperature-independent radiance behavior. Such a response is difficult to achieve with most materials except when using phase-change materials, which can undergo a drastic change in their optical response, nullifying the changes in blackbody radiation across a narrow range of temperatures. We report on the theoretical design, giving the possibility of extending the temperature range for temperature-independent radiance coatings by utilizing multiple layers, each comprising a different phase-change material. These designed multilayer coatings are based on thin films of samarium nickelate, vanadium dioxide, and doped vanadium oxide and cover temperatures ranging from room temperature to up to 140 °C. The coatings are numerically engineered in terms of layer thickness and doping, with each successive layer comprising a phase-change material with progressively higher transition temperatures than those below. Our calculations demonstrate that the optimized thin film multilayers exhibit a negligible change in the apparent temperature of the engineered surface. These engineered multilayer films can be used to mask an object’s thermal radiation emission against thermal imaging systems.

Oscillating neural networks are promising candidates for a new computational paradigm, where complex optimization problems are solved by physics itself through the synchronization of coupled oscillating circuits. VO2 Mott memristors are particularly promising building blocks for such oscillating neural networks. Until now, however, not only the maximum frequency of VO2 oscillating neural networks, but also the maximum frequency of individual VO2 oscillators is severely limited, which has restricted their efficient and energy-saving use. In this study, it is showed how to increase the oscillating frequency by more than an order of magnitude into the 100 MHz range utilizing ultrasmall, approximate to 30 nm wide active volume VO2 devices and optimizing the circuit layout for high frequency operation. In addition, the physical limiting factors of the oscillation frequencies are studied by investigating the complex switching dynamics of our nanoscale VO2 devices. These dynamical studies, together with simulations, provide a clear conclusion on the maximum achievable operating frequencies and the optimal operating parameters under which these can be reached.

La-doped BaSnO3 (LBSO) epitaxial thin films were grown on (001) MgO substrates by pulsed laser deposition using a La0.04Ba0.96SnO3 target. The structural, electrical, and optical properties of the LBSO films were inves-tigated as a function of oxygen pressure during deposition. The carrier mobility can be tuned from 13 cm2V- 1s- 1 to 44 cm2V- 1s- 1 by varying oxygen partial pressure from 2 Pa to 12 Pa, respectively. This improved mobility is attributed to the reduced film strain via reducing oxygen defect concentration or reducing off-stoichiometry in the film. The optical permittivity of LBSO films can also be modified as a function of the oxygen pressure during deposition, allowing tuning of their epsilon-near-zero wavelength from 1.9 mu m to 5.6 mu m. These results demonstrate that LBSO thin films grown on MgO can be used for plasmonic devices at mid-wave infrared wavelengths.

VO2 is a thermochromic material well suited for smart radiation devices due to its dramatic change in infrared reflection near its phase transition temperature (-68 degrees C). In this work, we have demonstrated a layered thin-film radiator, which consists of a TiN bottom infrared mirror, an Al2O3 dielectric spacer and a VO2 top absorber layer, to achieve thermal emissivity control using a phase transition of the VO2 layer. An analytical modeling approach is used to optimize the optical response of the layered radiators with varying the thickness of Al2O3 spacers and VO2 layers for maximum emissivity change (delta epsilon) between 25 degrees C and 80 degrees C. These modeling results show that the radiators composed of the optimized thickness of VO2 (30 - 50 nm) and Al2O3 (600 - 800 nm) can provide the highest emissivity change (delta epsilon -0.48) between these two temperature states. Experimental results validate that the radiator with a 50 nm thick VO2 layer and a 600 nm of Al2O3 layer exhibits a maximum emissivity change (delta epsilon-0.46) under the same temperature range. Our experimental results agree very well with the modeling results obtained from the same radiator design. These results are of crucial importance for designing mechanically and thermally stable radiators for spacecraft thermal control due to the stability of both TiN and Al2O3 materials.

Architected materials present an opportunity to overcome the limited ability of brittle piezoelectric ceramics to strain under electromechanical load. In the absence of a commercially available resin containing piezoelectric nanoparticles, this work seeks to investigate the printability and thermal processability of a prepared piezoelectric particle loaded slurry using laser stereolithography. This was accomplished by comparing the cure depth, in-plane resolution, and the dimensional accuracy achieved with a piezoelectric slurry prepared with barium titanate, to a commercially available silica and alumina-based suspension. The study of thermal processability revealed the dimensional sensitivity of fabricated open architectures to sintering temperature and duration. The prepared piezoceramic slurry, containing barium titanate, was successfully polymerized using laser-stereolithography and its cure depth exhibited a similar response to exposure duration and fluence level as the commercial slurries. The in-plane resolution of the barium titanate-based slurry was unexpectedly high, and may be due to the opacity of the piezoelectric particles. Open architectures with millimeter sized features were successfully fabricated using laser stereolithography. Dimensional accuracy was highest for the alumina-based material system, and the inverse relationship between cured depth and in-plane resolution was reflected in the dimensions of the silica-based parts. Open architected structures further withstood thermal processing. During thermal processing, there was a greater reduction in height for all parts due to higher in-plane concentrations of ceramic particles, relative to the z-direction. Both an increase in sintering temperature and duration resulted in a uniform change of 1%, respectively, in part dimensions. Data collected in this work is to be used as a benchmark to inform formulation requirements, laser stereolithography parameter settings and thermal processing procedures for a custom ceramic slurry containing piezoelectric nanoparticles.

The application of lasers for energy storage materials is an emerging field that offers unique opportunities for advancement. This review will focus on various laser-material processing techniques, such as laser-induced-forward transfer (LIFT), pulsed laser deposition (PLD), and laser surface modification (LSM), for energy storage applications. This article will review PLD techniques for thin-film microbatteries, LIFT techniques for thick-film microbatteries and ultracapacitors, LSM processes for thin film electrodes, and discuss relevant challenging issues with future directions.

Recently, ternary perovskite oxides have attracted great attention as alternative transparent conducting oxides (TCOs) because their structures are compatible with many other perovskite oxides that allow devices to be fabricated comprised entirely of perovskite oxides. Among these perovskite oxides, BaSnO3 has attracted considerable attention as a promising TCO because of its high mobility at room temperature (~320 cm2V-1s-1 in bulk single crystals and ~100 cm2V-1s-1 in epitaxial thin films) and high temperature stability in oxygen atmospheres compared to other TCOs, such as In2O3, ZnO, and SnO2. The electrical and optical properties of the BaSnO3 can be improved by either inducing oxygen vacancies or cationic doping. We have grown epitaxial La-doped BaSnO3 (LBSO) thin films on MgO (001) substrates by pulsed laser deposition using a La0.04Ba0.96SnO3 target, and investigated their structural, electrical, and optical properties as a function of the oxygen pressure during deposition. The permittivity of the LBSO films can be modified as a function of the oxygen pressure during deposition allowing tuning of their epsilon-near-zero (ENZ) wavelength from 2.2 μm to 7 μm. We will present details of the deposition conditions on the properties of LBSO films and the ability to tune the permittivity in this infrared range.

Plasmonic materials have attracted great attention due to their ability to enhance light-matter interactions. Noble metals such as Au and Ag have been well studied as materials for plasmonic devices. However, these metals are not suitable for mid infrared (IR) plasmonic applications due to their relatively large optical losses, which are detrimental to device efficiency. Metal oxides, on the other hand, have been proposed for low loss metallic components in the mid IR because they can provide a tunable carrier density by varying the concentration of dopants or defects (oxygen vacancies). The epsilon-near zero wavelength of the real part of the dielectric permittivity of these metal oxides, for example, can easily be tuned from 1.5 μm to 4 μm by adjusting doping or defect levels. Optical losses in devices made from these metal oxide materials generally exhibit lower losses than those obtained with conventional metals. We have investigated laser processing techniques for synthesizing several types of metal oxides such as indium tin oxide and phase change materials such as VO2. First, pulsed laser deposition was used to grow these oxide thin films. Second, an ultrafast laser was used to spatially pattern the thin films via a direct laser interference patterning (DLIP) configuration while simultaneously producing laser induced periodic surface structures (LIPSS) resulting in a uniaxial surface morphology. We will present details of the laser processing conditions on surface morphology, electrical, and optical properties of these laser processed metal oxide films.

Self-assembled plasmonic metasurfaces are promising optical platforms to achieve accessible flat optics, due to their strong light-matter interaction, nanometer length scale precision, large area, light weight, and high-throughput fabrication. Here, using photothermal continuous wave laser lithography, we show the spectral and spatial tuning of metasurfaces comprised of a monolayer of ligand capped hexagonally packed gold nanospheres. To tune the spectral response of the metasurfaces, we show that by controlling the intensity of a laser focused onto the metasurface that the absorption peak can be reconfigured from the visible to near-infrared wavelength. The irreversible spectral tuning mechanism is attributed to photothermal modification of the surface morphology. Combining self-assembled metasurfaces with laser lithography, we demonstrate an optically thin (λ/42), spectrally selective plasmonic Fresnel zone plate. This work establishes a new pathway for creating flat, large area, frequency selective optical elements using self-assembled plasmonic metasurfaces and laser lithography.

By combining the enhanced photosensitive properties of zinc oxide nanoparticles and the excellent transport characteristics of graphene, UV-sensitive, solar-blind hybrid optoelectronic devices have been demonstrated. These hybrid devices offer high responsivity and gain, making them well suited for photodetector applications. Here, we report a hybrid ZnO nanoparticle/graphene phototransistor that exhibits a responsivity up to 4 × 104 AW−1 and gain of up to 1.3 × 105 with high UV wavelength selectivity. ZnO nanoparticles were synthesized by pulsed laser fragmentation in liquid to attain a simple, efficient, ligand-free method for nanoparticle fabrication. By combining simple fabrication processes with a promising device architecture, highly sensitive ZnO nanoparticle/graphene UV photodetectors were successfully demonstrated.

Many emerging applications in microscale engineering rely on the fabrication of 3D architectures in inorganic materials. Small-scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device-grade inorganic materials is still a key challenge toward the implementation of AM in microfabrication. Here, a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state-of-the-art AM methods that offer a spatial resolution ≤10 μm is presented. Standardized sets of samples are studied by cross-sectional electron microscopy, nanoindentation, and microcompression. It is shown that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin-film nanocrystalline materials. The large variation in materials' performance can be related to the individual microstructure, which in turn is coupled to the various physico-chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small-scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects-a significant step toward the potential establishment of AM techniques in microfabrication.

Laser-induced cell injury in closed micro physiological systems: a novel method to study regeneration processes in vitro

We report tunable permittivity of La-doped BaSnO3 (LBSO) epitaxial films in the near- and mid-infrared range. The structural, electrical transport, and optical properties of the LBSO thin films can be effectively modified by controlling oxygen concentration during film growth. The permittivity of the LBSO films can be modified as a function of the oxygen pressure and temperature during deposition, which allows the tuning of their epsilon-near-zero wavelength from 2 mu m to 5.6 mu m. The ability to tune the permittivity in this infrared range enables the use of LBSO films as active components in infrared plasmonic devices.

The formation of laser-induced oxide layers on titanium surfaces has been widely investigated for coloring and marking applications. Complex titanium-based oxides exhibiting multiple phases can be achieved through laser patterning. Laser processing offers several advantages in that discrete areas can be modified leading to patterns with differing optical and electronic properties. To date, most research has focused on the formation and thickness control of TiO2, a wide bandgap semiconductor (similar to 3.2 eV), as a means to control coloration. However, for many applications, including photodetectors and photocatalysts, a semiconductor oxide with a narrow bandgap (< 1 eV) is preferred to allow for strong absorption into the mid-IR. Other oxides and sub-oxides, such as Ti2O3, have been identified as a byproduct of laser surface processing. In addition to its narrow bandgap, bulk Ti2O3 offers the unique property of having a semiconductor-metal transition at around 150 - 200 degrees C where resistivity switches over an order of magnitude. Because of these properties, we investigate the optimization of laser processing conditions using picosecond and femtosecond laser irradiation to form Ti2O3. The effect of laser fluence, scan speed, pulse frequency, and sample chamber pressure will be discussed. Additionally, Ti2O3 thin films were grown via pulsed laser deposition to study structural phase purity, where the effect of growth temperature on optical and electrical properties is explored.