This PDF file contains the front matter associated with SPIE Proceedings Volume 11801, including the Title Page, Copyright information, and Table of Contents.

UVC LEDs have progressed at a moderate pace since the early 2000’s and show development trends akin to those of visible wavelength LEDs. Researchers continue to improve UVC LED efficiencies, however manufacturer increases in wall plug efficiency have been outpaced by single chip radiometric powers increases, driven by commercial demand. This commercial demand can be segmented into regulated versus non-regulated applications and, increasingly since early 2020, applications where the germicidal efficacy may be questionable. This paper will discuss the landscape of UVC LED applications and the impact of regulations and perception. These applications touch a surprising breadth of industries with both critical and non-critical function.

We report a novel, environmentally-friendly, scalable subtractive process which allows for complex 3D optical, microfluidic and biomedical components and microstructures to be fabricated precisely in a wide variety of polymers. The reported technique is capable of producing submicron structures with <20 nm depth precision in common polymers (PMMA, ABS, etc.) as well as microchannels and 3D surfaces of >20 µm depth in biodegradable polymers. The process is based on a VUV (λ=172 nm) photoablative lithographic technique utilizing flat microplasma lamps and does not require a clean room environment or any chemical processing. The fabricated 3D surface may also be used as a mold for PDMS curing.

In this paper, a direct and cost-effective sol-gel method enables to produce stable titanium dioxide and titanium oxynitride photoresists is described. This approach is compatible with many photolithographic techniques. We show that laser interference lithography and nanosphere lithography can be used, respectively, to obtain homogeneous TiO₂ diffraction gratings and periodic nanopillars over large areas. Further developments permit to transform TiO₂ microstructured based sol-gel to TiN metallic microstructured layer, with good optical properties, by using an innovative rapid thermal nitridation process, which opens the way towards plasmonics and NIR filters based on periodic metallic microstructured layers.

UV radiation is highly effective in killing against viruses, bacteria, algae, molds, and yeasts. They are compact, have rapid turn-off and turn-on times, and provide UV radiation at different wavelengths allowing to target specific contaminants. The deep UV LEDs (UVC LEDs) do not contain hazardous substances, such as mercury. Since their operating voltage is low they could be powered by photovoltaic cells. Recent studies have shown that UV radiation at 222 nm is effective in killing viruses but safer for humans compared to 265 nm to 280 nm radiation. Another advantage of UVC LEDs is an ability of rapidly adjust the output power of UVC LED lamps that allows to use the feedback and Artificial Intelligence models to optimize the effects of the UV radiation, save power, and ensure safety. One example, where this is important, is the application of deep UVC LED systems with feedback in vaccine production. A more traditional application of UV LEDs is in water purification being enabled by the recent improvements in deep UV LED power, reliability, packaging, and lifetime. These improvements allow for scaling up the emerging deep UV LED applications and make it feasible to use deep UV LEDs for improving plant yield, extending produce storage time, disinfecting grain and chicken feed, and fighting Hospital Acquired Infections.

This study aims at exploring the potential of ATR-far-ultraviolet (FUV) spectroscopy in investigating electronic structure and transitions of various kinds of biological molecules. For this purpose, ATR-FUV spectra were measured for several kinds of proteins with the different secondary structures, several kinds of carbohydrates, nucleic acids, and lipids. Band assignments have been made for all kinds of biological molecules investigated based on our previous ATR-FUV studies on n-alkanes, alcohols, esters, and amides. For example, the proteins show a characteristic band near 200 nm due to π-π* transition of amide groups. The position of this band varies a little with the secondary structure of proteins but its intensity changes significantly depending on the secondary structure and solutions. All the carbohydrates studied yielded a band near 170 nm due to n-Rydberg transition of ether. In addition, acetylcarbohydrates give an additional band near 190 nm originating from π-π* transition of amide at 2’ carbon. The present study has demonstrated that ATR-FUV spectroscopy is a new powerful technique in exploring electronic structure and transitions of biological molecules, in general. It is also possible to use ATR-FUV spectroscopy for quantitative and qualitative analysis of biological molecules. Moreover, it is of note that information regarding electronic transitions collected by ATR-FUV spectroscopy is useful for UV resonance Raman (UVRR) spectroscopy studies of biological molecules. A combined ATR-FUV spectroscopy and UVRR spectroscopy method may provide a novel analytical tool for molecular and electronic structure of biological molecules.

Rapid and reliable detection of small amounts of hazardous substances remains highly desirable within defense and protective contexts. Raman scattering is one of the non-contact optical spectroscopic techniques that already has proven useful for different detection purposes and a large number of instruments exists on the market today. However, added performance may be gained by shifting the laser wavelength from the visible or near-infrared, generally used in currently available Raman instruments, to the UV band. This report covers different methods of acquiring UV Raman hyperspectral cubes using a tunable laser source and an imaging spectrometer as main components. Results obtained by setups resulting in coarse spectral resolution via fixed interference filters to relatively high spectral resolution UV Raman images when using random, binary transmission masks as coded apertures in a Compressed Sensing approach are shown and discussed.

FUV spectroscopy in the 145-200 nm region has recently been a matter of intense interest because many kinds of materials in the condensed phase. Rapid progress of the studies has been introduced by the development of attenuated total reflection spectroscopy in the FUV region (ATR-FUV), which has enabled us to measure the spectra in the complete FUV region for liquid and solid samples without facing problems such as peak saturation. Moreover, significant progresses of quantum chemical calculations for electronic excitation states of molecules improve our interpretations of the FUV spectra. We will present an investigation about the FUV spectroscopy for aqueous solutions of highly concentrated alkali-metal salts, named hydrate-melt which can be used as high-performance electrolytes.

Recently, there has been a surge in interest for the ultra wide bandgap (Eg ~ 4.9 eV) semiconductor gallium oxide (Ga2O3). A key driver for this boom is that single crystal wide area bulk β-Ga2O3 substrates have become commercially available and a variety of methods have been shown to give high quality epitaxial growth. Although Ga2O3 has a number of polymorph forms (α-, β-, γ-, δ- and ε) the more stable monoclinic phase (β-Ga2O3) has attracted the most attention. Amongst a whole range of potential applications power/switching electronics, solar-blind photodetectors and solar transparent electrodes offer exciting perspectives. In this talk we give an overview of these applications illustrated with examples from the β-Ga2O3 development work carried out at the French oxide semiconductor epiwafer company, Nanovation, www.nanovation.com.

The GaN photonic platform is of large interest for broadband integrated photonics applications, from near-UV to visible and near-IR. Here we present the latest developments in near-UV microlasers and their coupling to gratings and waveguides, based on GaN active layers. We demonstrate two iconic NUV microlasers: (i) a microdisk laser based on GaN/AlGaN quantum wells, coupled to a waveguide and an outcoupling grating; (ii) a ridge waveguide polariton laser operating with ultra-short Fabry-Perot ridge cavities (5-60µm), that is not governed by Bernard-Durrafourg condition (population inversion) as in standard ridge interband lasers. Both lasers operate around 380nm.

ZnO is a multifunctional nanomaterial having various applications. The real challenge is to produce large scale, well-aligned, reproducible ZnO nanowires (NWs) using low-cost techniques. The aim of this work is to show a simple approach for the uniform growth of NWs, on entire silicon wafers, using a low-temperature chemical method. A study of the substrate size dependent growth of NWs was conducted to understand the limitations in the growth. A time dependent growth study was performed on ZnO NWs grown on 3-inch wafers to track their morphological evolution. Simultaneous growth of ZnO NWs on two 4-inch wafers will be demonstrated.

Hexagonal boron nitride (hBN) is an ultrawide bandgap semiconductor with a large range of basic applications relying on its low dielectric constant, high thermal conductivity, and chemical inertness. The growth of high-quality crystals in 2004 has revealed that hBN is also a promising material for light-emitting devices in the deep ultraviolet domain, as illustrated by the demonstration of lasing at 215 nm by accelerated electron excitation [1], and also the operation of field emitter display-type devices in the deep ultraviolet [2]. With a honeycomb structure similar to graphene, bulk hBN has gained tremendous attention as an exceptional substrate for graphene with an atomically smooth surface, and more generally, as a fundamental building block of Van der Waals heterostructures [3]. I will discuss here our recent measurements by reflectivity spectroscopy shining a new light on the efficient light-matter interaction in hBN. I will first present experiments in monolayer hBN epitaxially grown on graphite. Compared to the reflectivity spectrum of the bare graphite substrate, a huge contrast is observed in the reflectivity of atomically-thin hBN deposited on graphite, demonstrating a radiative efficiency close to unity in monolayer hBN. I will then address the optoelectronic properties of bulk hBN where high-resolution measurements in high-quality samples allow to resolve the respective contributions of indirect and direct optical transitions and quantify the strength of the light-matter interaction in bulk hBN. References [1] K. Watanabe, T. Taniguchi, and H. Kanda, Nature Mater. 3, 404 (2004). [2] K. Watanabe, T. Taniguchi, T. Niiyama, K. Miya, and M. Taniguchi, Nature Photon. 3, 591 (2009). [3] A. K. Geim and I. V. Grigorieva, Nature 499, 419 (2013).

UV resonance Raman spectroscopy is uniquely suitable for standoff measurements due to its high sensitivity and selectivity. When excitation wavelength falls within an electronic transition of a molecule, Raman band intensities associated with the chromophore vibrations are significantly enhanced. This resonance Raman Effect, as well as negligible fluorescence interference in the deep UV, enable the detection and investigation of enhanced species at trace concentrations at a distance. We developed a state-of-the-art, high-efficiency standoff deep UV Raman spectrometer. This spectrometer is based on a custom deep UV F/8 Cassegrain telescope with a 200 mm primary mirror. This telescope is equipped with an electric secondary focus operating from infinity to 3 m distance. The UV Raman spectrograph utilizes high-efficiency deep UV transmission grating and custom Rayleigh rejection filter. As an excitation source for Raman measurements, we utilized a recently developed 228 nm compact solid state deep UV laser. The 228 nm resonance excitation enhances the Raman intensities of vibrations of NOx groups, peptide bonds, aromatic amino acid side chains, and DNA/RNA nucleotides. We used this novel spectrometer for detection of NOx-based explosive materials at trace concentrations at a stand-off distance.

Recently, we developed a novel attenuated total reflectance (ATR) spectroscopic system in far- and deep-ultraviolet (FUV and DUV) regions that operates under electrochemical conditions in order to investigate the electronic states of materials near the electrode surface. We succeeded to record the FUV-DUV spectra of various ionic liquids systematically using the ATR-FUV-DUV spectroscopy and theoretically assign the obtained spectra based on quantum chemical calculations. Subsequently, upon application of voltage to an ionic liquid consisting of imidazolium cations and iodide anions, electronic transition spectra in the 150−450 nm range varied. In particular, absorbance due to charge transfer from the anion to the cation drastically increased at positive potentials. According to the molecular dynamics simulations, the density of iodide anion near the electrode surface drastically changed depending on the electrode potential, which contributed to the spectral changes. Now, this technique is applied for organic semiconductor materials.