UV Transparent Substrates Research Articles

Deep-UV wavelength-selective photodetectors based on lateral transport in AlGaN/AlN quantum well and dot-in-well structures

We report on the development of deep-ultraviolet (DUV) wavelength-selective top-illuminated photodetectors based on AlGaN/AlN quantum-dots-in-wells. Structures consisting of 100 AlGaN wells and AlN barriers were grown by plasma-assisted molecular beam epitaxy on sapphire substrates. Interdigitated metal–semiconductor–metal photodetector devices were formed lithographically using indium as the contact metal. The effect of variation of the group III to group V flux ratio and the use of indium as a surfactant on the UV photoresponse were determined. Growth under near-stoichiometric conditions lead to a photocurrent peak in the 210–215 nm range with a peak width of ∼20 nm, with no other additional signatures in the entire UV–visible range. Under excess group III conditions, a second red-shifted peak was observed at ∼225 nm with significantly (up to 10×) higher responsivity. This enhancement was linked to the formation of quantum dots with truncated pyramidal structures with near-uniform size distribution and density of 6 × 1010 cm−2 within the quantum wells. Their formation was attributed to the process of droplet epitaxy. Such photodetectors do not require p-type doping or growth onto UV-transparent substrates and are appropriate for monitoring DUV skin-safe germicidal radiation in the presence of ambient visible light.

Porcine Ear Skin as a Biological Substrate for in vitro Testing of Sunscreen Performance

Purpose: The purpose of the study was to examine the use of skin from porcine ears as a biological substrate for in vitro testing of sunscreens in order to overcome the shortcomings of the presently used polymethylmethacrylate (PMMA) plates that generally fail to yield a satisfactory correlation between sun protection factors (SPF) in vitro and in vivo. Procedures: Trypsin-separated stratum corneum and heat-separated epidermis provided UV-transparent substrates that were laid on quartz or on PMMA plates. These were used to determine surface roughness by chromatic confocal imaging and to measure SPF in vitro of 2 sunscreens by diffuse transmission spectroscopy. Results: The recovered skin layers showed a lower roughness than full-thickness skin but yielded SPF in vitro values that more accurately reflected the SPF determined in vivo by a validated procedure than PMMA plates, although the latter had in part roughness values identical to those of intact skin. Combination of skin tissue with a high roughness PMMA plate also provided accurate SPF in vitro. Conclusions: Besides roughness, the improved affinity of the sunscreen to the skin substrate compared to PMMA plates may explain the better in vitro prediction of SPF achieved with the use of a biological substrate. i 2014 S. Karger AG, Basel

ZnTe nanocrystal formation and growth control on UV-transparent substrate

ZnTe nanocrystals (NCs) were successfully grown in a UV transparent, vitreous substrate synthesized by fusion and then annealed. The formation of dot structures, emitting in the UV-range, was investigated by optical absorption (OA), atomic force microscopy (AFM) and Raman spectroscopy. Dot growth was evidenced by an OA band red-shift with increasing annealing time. Average sizes of the ZnTe dots were determined using the effective mass fit model with OA spectra and comparing the results with estimates from AFM images. A UV-transparent PZABP vitreous matrix was used because it allowed ZnTe NC growth and displayed typical Raman active phonon modes.

Preparation of polymer-based composite with magnetic anisotropy by oriented carbon nanotube dispersion

A polymer-based nanocomposite film with partially oriented multi wall carbon nanotubes (MWCNTs) was synthesized by a facile technique. A small amount of MWCNTs (average diameter 50 nm, length 500 μm) containing ferromagnetic iron particles, mainly localized in the tips, were dispersed ultrasonically for over 30 h in a diacrylate resin (bisphenol-A-diglycydylether diacrylate, BHEDA). The liquid resin was cast between two UV transparent substrates and subjected to a unidirectional magnetic field before the mixture had been cationic photopolymerized. Magnetization and magnetoresistance measurements were performed at room temperature on the solid films produced both with zero and with an external magnetic field perpendicular with respect to the plane of the film. A complex anisotropic response has been observed and a simple model was developed to explain the results consistent with some ordering effect occurred by the application of the external magnetic field.

In vitro approaches to evaluation of Sun Protection Factor

The efficacy of sunscreen products has been recognized as an important public health issue. Adequate methods for assessment of the level of protection should be developed and standardised. While the SPF COLIPA testing method in vivo has been used for years, preference should be given to in vitro testing methods as in vivo methods raise ethical concern. The present study aims to assess possible in vitro approaches based on diffuse transmission spectroscopy, published previously by Diffey, and two methods based on measurements of UVB transmission through a defined layer of a sunscreen product applied on various UV-transparent substrates. The attenuated UVB intensity, using different UV light sources, is detected radiometrically and transformed to real SPF value by means of a calibration curve, which is based on an extensive number of measurements performed using both in vivo and in vitro method The outcome of the three in vitro methods employed in the study showed great differences in the obtained SPF values in comparison with reference SPF determined by means of the COLIPA method in vivo. The high variability of in vitro results suggests that main attention should be focused on substrate selection simulating the human skin surface and homogenous product application. The in vitro screening methods may represent a fast and reasonable tool reducing the number of in vivo experiments and risks related to UV exposure of human subjects, when the technical test parameters are adjusted and optimized.

Multidirectional UV Lithography for Complex 3-D MEMS Structures

Various three-dimensionally (3-D) complex MEMS structures are fabricated using multidirectional ultraviolet (UV) lithography, which includes reverse-side exposure through a UV-transparent substrate, inclined exposure with or without simultaneous substrate rotation, and the combination of these processes. A reverse-side exposure scheme through UV-transparent substrates (e.g., glass, sapphire, or quartz) has been exploited for implementing high-aspect-ratio structures (greater than 20:1), repeatable self-alignment photoresist patterning with subsequent metallization on a BST/sapphire substrate, and unconventional patterning using substrate optics such as proximity patterning or integrated lens techniques. Inclined exposure has been applied to a SU-8 substrate with differing inclination angles and incidence directions. The refractive index of SU-8 is experimentally determined to be 1.68 by means of test structures fabricated using this approach. Implemented structures using the inclined exposure include vertical screen structures, inclined tubes, and conical shape structures. Dynamic mode operation, in which the substrate is continuously rotated and tilted during exposure is also discussed. Examples of achievable 3-D structures using dynamic mode operation are presented.1581

High aspect ratio tapered hollow metallic microneedle arrays with microfluidic interconnector

We present a novel microfabrication method for a tapered hollow metallic microneedle array and its complete microfluidic packaging for drug delivery and body fluid sampling applications. Backside exposure of SU-8 through a UV transparent substrate was investigated as a means of fabricating a dense array of tall (up to 400 μm) uniformly tapered SU-8 pillar structures with angles in the range of 3.1–5° on top of the SU-8 mesa. Conformal electroplating of metals on top of the array of the tapered SU-8 pillars, lapping of the tip of the metallic microneedles with planarizing polymer, and removal of the SU-8 sacrificial layers resulted in an array of tapered hollow metallic microneedles with a fluidic reservoir on the backside. A microfluidic interconnector assembly was designed and fabricated using SU-8 and conventionally machined PMMA in a way that it has a male interconnector, which directly fits into the fluidic reservoir of the microneedle array at one end and the other male interconnector, which provides fluidic interconnection to external devices at the other end. The fluid flow rate was measured and it showed 0.69 μL/s. per microneedle when the pressure of 6.89 KPa (1 psi) was applied.

Laser patterning of SiO x-layers for the fabrication of UV diffractive phase elements

Diffractive phase elements (DPE), consisting of a patterned UV-transparent layer on a UV-transparent substrate, were fabricated by three steps. A UV-absorbing SiO x -coating ( x < 2) with a thickness matching to the required phase delay was deposited on a fused silica substrate. The coating was removed on a pixel array corresponding to a calculated two-dimensional quantized phase function (DPE-design). By a thermal annealing process the SiO x -coating was oxidised to UV-transparent SiO 2, resulting in a UV-grade surface relief element.

Sacrificial layer process with laser-driven release for batch assembly operations

A dry sacrificial layer process is presented in which microstructures fabricated on UV-transparent substrates are released by excimer laser ablation of a polymer sacrificial material using laser light incident from the reverse side of the substrate. We investigate the application of this technique to the batch assembly of hybrid microelectromechanical systems (MEMS) built from parts fabricated on different substrates. Preliminary measurements of initial velocity are presented for nickel test structures released from polyimide sacrificial layers using a KrF excimer laser. At fluences in the range 50-250 mJ/cm/sup 2/ (i.e., close to the ablation threshold), structures with heights of 100 /spl mu/m are shown to exhibit initial velocities in the range 15 ms/sup -1/, allowing controlled transfer of parts between substrates. Application of the new assembly method to a MEMS device is demonstrated by assembling arrays of electrostatic wobble motors from component parts fabricated on separate substrates by UV-LIGA processing.

Photodeposition of Amorphous Polydiacetylene Films from Monomer Solutions onto Transparent Substrates

Polydiacetylenes are a very promising class of polymers for both photonic and electronic applications because of their highly conjugated structures. For these applications, high-quality thin polydiacetylene films are required. We have discovered a novel technique for obtaining such films of a polydiacetylene derivative of 2-methyl-4-nitroaniline using photodeposition from monomer solutions onto UV transparent substrates. This heretofore unreported process yields amorphous polydiacetylene films with thicknesses on the order of I micron that have optical quality superior to that of films grown by standard crystal growth techniques. Furthermore, these films exhibit good third-order nonlinear optical susceptibilities; degenerate four-wave mixing experiments give x(3) values on the order of 10(exp -8) - 10(exp -7) esu. We have conducted masking experiments which demonstrate that photodeposition occurs only where the substrate is directly irradiated, clearly indicating that the reaction occurs at the surface. Additionally, we have also been able to carry out photodeposition using lasers to form thin polymer circuits. In this work, we discuss the photodeposition of polydiacetylene thin films from solution, perform chemical characterization of these films, investigate the role of the substrate, speculate on the mechanism of the reaction, and make a preliminary determination of the third-order optical nonlinearity of the films. This simple, straightforward technique may ultimately make feasible the production of polydiacetylene thin films for technological applications.

In situ studies of thin polymer film dissolution by laser interferometry plus fluorescence quenching

The dissolution characteristics of thin polymethyl methacrylate films, studied by simultaneous laser interferometry and fluorescence quenching (LIFQ) experiments, are reported. These require UVtransparent substrates. The influence of the substrate material on the LIFQ results was investigated. The results obtained with sapphire substrates allowed us to calculate the thickness of the solvent-swollen gel layer at the beginning and at the end of the dissolution process.