Nanoparticles of high-refractive-index materials like semiconductors can achieve confinement of light at the subwavelength scale because of the excitation of Mie resonances. The nanostructures out of high-refractive-index materials have extensively been studied theoretically and realized in experiments exploring a wide range of photonic applications. Recently, transition metal dichalcogenides (TMDCs) from the family of van der Waals layered materials have been shown to exhibit tailorable optical properties along with high refractive index and strong anisotropy. We envision that TMDCs are a promising material platform for designing metasurfaces and ultra-thin optical elements: these van der Waals materials show a strong spectral response on light excitations in visible and near-infrared ranges, and metasurface properties can be controlled by nanoantenna dimensions and their arrangement. In this work, we investigate a periodic array of disk-shaped nanoantennas made of a TMDC material, tungsten disulfide WS2, placed on top of a silicon layer and oxide substrate. We show that the nanostructure resonance in TMDC disk-shaped nanoantenna array can be controlled by the variation in silicon layer thickness and have a dependence on the presence of index-match superstrate cover. We also report on the spectral features in absorption and reflection profiles of the same structure with different surrounding index.

Propagating inhomogeneous electromagnetic waves called surface plasmon polaritons (SPPs) can be excited by free-space beams on corrugated conducting surfaces at resonance angles determined by corrugation period, permittivity, and optical frequency. SPPs are coupled to and co-propagate with surface charge displacements. Complete electrical isolation of individual conducting corrugations prevents the charge displacement necessary to sustain an SPP, such that excitation resonances of traveling SPPs are absent. However, SPPs can be excited via electric induction if a smooth conducting surface exists below and nearby the isolated conducting corrugations. The dependence of SPP excitation resonances on that separation is experimentally investigated here at long-wave infrared wavelengths. We find that excitation resonances for traveling SPPs broaden and disappear as the dielectric’s physical thickness is increased beyond ~1% of the free-space wavelength. The resonance line width increases with refractive index and optical thickness of the dielectric.

Bolometric arrays dominate in commercial terahertz and millimeter wave imagers. Bolometers tend to be slow and require an operating bias that increases the power budget. This paper presents first results on antenna-coupled thermo-electric junction detectors, a potentially attractive alternative to microbolometers. The nanoscale junctions have small thermal mass and can be much faster than bolometers. These junctions are heated by currents excited in spectrally-selective antennas and generate a voltage based on the Seebeck effect without any externally applied power. A pixel comprising a series array of antenna coupled junctions with peak response at 7.5 THz (40 μm wavelength) is designed and experimentally demonstrated. Responsivity of 5 MV/W, 500 Hz chopping frequency, and D* of 3.5 x 1010 Jones are demonstrated.

Hot carrier based methods constitute a valuable approach for efficient and silicon compatible sub-bandgap photodetection. Although, hot electron excitation and transfer have been studied extensively on traditional materials such as Au and Ti, reports on alternative materials such as titanium nitride (TiN) are rare. Here, we perform hot hole photodetection measurements on a p-Si/metal thin film junction using Ti, Au and TiN. This material is of interest as it constitutes a refractory alternative to Au which is an important property for plasmonic applications where high field intensities can occur. In contrast to Au, a TiN/Si junction does not suffer from metal diffusion into the Si, which eases the integration with current Si-fabrication techniques. This work shows that a backside illuminated p-Si/TiN system can be used for efficient hot hole extraction in the IR, allowing for a responsivity of 1 mA/W at an excitation wavelength of 1250 nm and at zero bias. Via a comparison between TiN and other commonly used materials such as Au, the origin of this comparably high photoresponse can be traced back to be directly linked to a thin TiO2-x interfacial layer allowing for a distinct hot-hole transfer mechanism. Moreover, the fabrication of TiN nanodisk arrays is demonstrated which bears great promise to further boost the device efficiency.

Deep UV photoluminescence (PL) spectroscopy was employed to study optical properties of a sapphire substrate sample. The sample was photo-excited by the third harmonic laser of a Ti:sapphire pulse laser at wavelength ~ 266 nm which is a below bandgap excitation. In the low temperature (12 K) PL measurement, we observed two sharp atomic-like emissions in the ultraviolet region with peaks at 3.361 eV and 3.315 eV with spectral line-width of 0.85 and 3.30 nm respectively, in the PL spectrum. We performed temperature and power-dependent PL measurements of the sample and observed that the emission peak positions did not change with changing excitation power and sample temperature. We also performed X-ray photoelectron spectroscopy for chemical composition analysis of the sample to explore the origin of the atomic-like emission that could be used for single photon sources for quantum information technology. We will discuss a possible electronic transition and its origin in sapphire.

Recent studies have shown spray-pyrolysis is a low-cost, simple and efficient technique for deposition of metal oxide semiconductors (such as zinc oxide) as the active layer of thin-film transistors (TFTs). However, to allow the translation from laboratory scale to industry the reproducibility of such method needs to be evaluated. We present herein a representative study concerning the reproducibility and uniformity of spray-coated ZnO TFTs using several devices, from different production batches, following the same fabrication protocol. We demonstrate that it is possible to obtain transistors with high performance and reproducibility by controlling the most relevant deposition factors, corroborated by a low deviation rate (below 10%) from the characteristic TFT parameters (mobility in saturation, threshold voltage and on/off ratio), which is compatible to commonly available commercial electronic devices.

In this study, optical absorption properties of copper oxide (II) (CuO) nanoleaf structures grown by hot water treatment (HWT) method were investigated by a numerical simulation method and were compared to experimental results. For this purpose, 3D CuO nanoleaves (NLs) were synthesized by HWT, which simply involved immersing a Cu plate or thin film sample in hot deionized (DI) water. For comparison, we prepared a conventional CuO thin film by thermal oxidation of copper film at about 300 °C. Optical transmission and reflection were measured by UV/Vis/NIR (ultraviolet-visible-near-infrared) spectrophotometer, which were used to calculate optical absorptance. Numerical simulation was performed with finite difference time domain (FDTD) simulation software. Reflectance, transmittance, and absorptance of CuO NLs of different roughness (i.e. CuO NLs layer thickness) were calculated through FDTD method and compared with the experimental results. FDTD simulations predict that nanoleaves morphology enhances light absorption by improving diffuse light scattering and light trapping properties which effectively increases the optical path length without using more material as compared to the thin film structure. This can be useful for developing thinner nanostructured optoelectronic devices with low cost and high efficiency.

Silicon telluride (Si2Te3) is a silicon-based 2D chalcogenide with potential applications in optoelectronics. It has a unique crystal structure where Si atoms form Si-Si dimers to occupy the “metal” sites. In this paper, we report an ab initio computational study of its optical dielectric properties using the GW approximation and the Bethe-Salpeter equation (BSE). Strong in-plane optical anisotropy is discovered. The imaginary part of the dielectric constant in the direction parallel to the Si-Si dimers is found to be much lower than that perpendicular to the dimers. The optical measurement of the absorption spectra of 2D Si2Te3 nanoplates shows modulation of the absorption coefficient under 90-degree rotation, confirming the computational results. We show the optical anisotropy originates from the particular compositions of the wavefunctions in the valence and conduction bands. Because it is associated with the Si dimer orientation, the in-plane optical anisotropy can potentially be dynamically controlled by electrical field and strain, which may be useful for new device design. In addition, BSE calculations reduce GW quasiparticle band gap by 0.3 eV in bulk and 0.6 eV in monolayer, indicating a large excitonic effect in Si2Te3. Furthermore, including electron-hole interaction in bulk calculations significantly reduces the imaginary part of the dielectric constant in the out-of-plane direction, suggesting strong interlayer exciton effect in Si2Te3 multilayers.

Bismuth telluride have regained significant attention as a prototype of topological insulator. Thin films of high quality have been investigated as a basic platform for novel spintronic devices. Low mobility of bismuth and high desorption coefficient of telluride compose a scenario where growth parameters have drastic effects on structural and electronic properties of the films. Recently [J. Phys. Chem. C 2019, 123, 24818−24825], a detailed investigation has been performed on the dynamics of defects in epitaxial films of this material, revealing the impact of film/substrate lattice misfit on the films’ lateral coherence. Very small lattice misfit (<0.05%) are expected to have no influence on quality of epitaxial system with atomic layers weakly bonded to each other by van der Waals forces, contrarily to what was observed. In this work, we investigate the correlation between lattice misfit and size and morphology of the film crystalline domains. Three-dimensional reciprocal-space maps of film Bragg reflections obtained with synchrotron X-rays are used to visualize the spatial conformation of the crystallographic domains through film thickness, while atomic force microscopy images provide direct information of the domains morphology at the film surface.

We are proposing a novel fabrication method for single crystal diamond scanning probes for atomic force microscopy (AFM), exploiting Faraday cage angled etching (FCAE). Common, oxygen-based, inductively coupled plasma (ICP) dry etching processes for diamond are limited with respect to the achievable geometries. The fabrication of freestanding micro- and nanostructures is therefore challenging. This is a major disadvantage for several application fields e.g., for realizing scanning magnetometry probes based on nitrogen vacancy (NV) centres and capable of measuring magnetic fields at the nanoscale. Combining a planar design with FCAE and state-of-the-art electron beam lithography (EBL) yields a reduction of process complexity and cost compared to the established fabrication technology of micro-opto-mechanical diamond devices. Here, we report on the direct comparison of both approaches and present first proof-of-concept planar-FCAE-prototypes for scanning probe applications.