Micromachining of Polyurethane (Pu) Polymer Using a Krf Excimer Laser (248nm)

Excimer laser micromachining has generated considerable research interest leading to numerous commercial applications in the last decade. Polyurethane (PU) polymer, due to its biocompatibility, weather resistance, and favorable physical properties, such as good flex-life, temperature resistance, electrical insulation and tear resistance finds a number of applications in medical implants, protective coatings, and as a prototype material for structural components in MEMS devices. An Excimer laser (wavelength = 248 nm, FWHM = 25 ns) is employed in this research work for micromachining of polyurethane (PU) polymer and pattern design for some potential MEMS applications. The main objective of this research is to establish a fundamental understanding of ablation mechanism in polyurethane (PU) polymer. The effect of various operating parameters, such as fluence per unit area, energy per pulse, number of pulses, repetition rates, and environment on the resulting geometries and ablation behavior are investigated. Micromachining is conducted in air and under water environments with variation in mask sizes and pattern geometries. Microgears (up to 360 μm diameter) are etched on the surface of polyurethane with several similar geometries used in MEMS devices, such as microfluidic channels, and microcircuits. It was observed that, for air environment, the ablation rate is 0.18 μm/pulse, and for underwater environment, the ablation rate is 0.07 μm/pulse (underwater ablation threshold: 0.10 J/cm2). The relationship was developed between wall taper angles behavior of the ablated regions with process parameters, which concluded low taper angles (~32°) for in air as compared to high taper angles (~65°) with underwater micromachining. The relationship between mask size and resulting seam quality, seam width and ablation depth for pattern generation was developed and analyzed. The experimental results for air and under water micromachining demonstrate that the ablation mechanism differs in polymers depending upon fluence (J/cm2), repetition rate (Hz), and working environment (in air or underwater). A combination of photo-thermal and photo-chemical ablation mechanism was attributed in the material removal process for polyurethane (PU) polymer. However, to be able to successfully and effectively produce MEMS devices, further research into the micromachining of polymers is required.Mechanical & Aerospace Engineerin

Photodegradation and Thermal Effects in Violet Phosphorus

Violet phosphorus (VP) has garnered attention for its appealing physical properties and potential applications in optoelectronics. We present a comprehensive investigation of the photo degradation and thermal effects of exfoliated VP on SiO2 substrate. The degradation rate of VP was found to be strongly influenced by the excitation wavelength and light exposure duration. Light exposure to above bandgap light (> 532 nm) leads to significantly faster degradation, attributed to interactions with reactive oxygen species (ROS) generated by the laser. In contrast, lower energy excitation resulted in slower degradation due to reduced ROS generation. Analysis of photoluminescence (PL) spectra showed a gradual decline in the exciton population, signifying reduced lifetime and alterations in formation and stability, ultimately affecting VP's quantum efficiency. Power-dependent PL measurements at low temperature (4 K) showed that the intensities of neutral excitons and trions linearly increased with excitation power, while the energy difference between their peak energies decreased, indicating changes in the exciton energy gap due to degradation at higher laser power. At ambient temperature VP exhibited visible neutral exciton (X0) and trion (T) peaks with higher X0 spectral weight, indicating reduced thermal stability of T in VP crystals. Temperature dependent Raman showed the presence of VP up to 673K and back down to room temperature; however, peak intensities decreased and two new unknown peaks were observed indicating some level of thermal degradation. Our results provide deeper understanding of VP's degradation behavior and implications for optoelectronic applications.Comment: 22 pages, 6 figure

Infrared Nanoimaging of Hydrogenated Perovskite Nickelate Synaptic Devices

Solid-state devices made from correlated oxides such as perovskite nickelates are promising for neuromorphic computing by mimicking biological synaptic function. However, comprehending dopant action at the nanoscale poses a formidable challenge to understanding the elementary mechanisms involved. Here, we perform operando infrared nanoimaging of hydrogen-doped correlated perovskite, neodymium nickel oxide (H-NdNiO3) devices and reveal how an applied field perturbs dopant distribution at the nanoscale. This perturbation leads to stripe phases of varying conductivity perpendicular to the applied field, which define the macroscale electrical characteristics of the devices. Hyperspectral nano-FTIR imaging in conjunction with density functional theory calculations unveil a real-space map of multiple vibrational states of H-NNO associated with OH stretching modes and their dependence on the dopant concentration. Moreover, the localization of excess charges induces an out-of-plane lattice expansion in NNO which was confirmed by in-situ - x-ray diffraction and creates a strain that acts as a barrier against further diffusion. Our results and the techniques presented here hold great potential to the rapidly growing field of memristors and neuromorphic devices wherein nanoscale ion motion is fundamentally responsible for function.Comment: 30 pages, 5 figures in the main text and 5 figures in the Supplementary Materia

Photodegradation and Thermal Effects in Violet Phosphorus

Abstract Violet phosphorus (VP) is garnering attention for its appealing physical properties and potential applications in optoelectronics. A comprehensive investigation of the photodegradation and thermal effects of exfoliated VP on SiO2/Si substrates is presented. The degradation rate of VP is strongly influenced by the wavelength and exposure duration of light. Light illumination of VP above the bandgap leads to faster degradation, attributed to interactions with reactive oxygen species. Power‐dependent photoluminescence (PL) measurements at low temperature (T = 4 K) show neutral exciton (X0) and trion (T) intensities linearly increase with excitation power, while the energy difference between peak energies decreases. The T/X0 spectral weight ratio increases from 0.28 at 300 K to 0.69 at 4 K, suggesting enhanced T formation due to reduced phonon scattering. Temperature‐dependent Raman is used to investigate the phonon properties of VP. Tracking peak positions of 9 Raman modes with temperature, the linear first‐order temperature coefficient is obtained and found to be linear for all modes. The results provide a deeper understanding of VP's degradation behavior and implications for optoelectronic applications

Utility of quantitative real time PCR in detection and monitoring of viral infections in post renal transplant recipients

Background: Viral infections cause significant morbidity and mortality in post-transplant period. A highly sensitive and specific detection tool if used may help in early diagnosis and better management in these patients. The study aimed to assess the utility of quantitative real-time polymerase chain reaction (qRT-PCR) as a diagnostic and monitoring tool for viral infections in post renal transplant patients. Methods: A quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect EBV and CMV infection in 50 patients on 1st, 2nd, 3rd, and after 6 months of renal transplantation. Results: CMV infection was found in 34%, EBV in 28% of recipients, and 17% showed dual infection. Viruses were detectable after the first month of transplantation followed by symptomatic infections within first three months of follow-up, with diarrhea being the commonest symptom. These patients were also at high risk for developing other infections. Anti-thymocyte globulin (ATG) induction was a definitive risk factor for CMV/EBV infection in post operative period. Conclusion: Renal transplant patients frequently develop one or more viral infections at a time. Regular monitoring with qRT-PCR and prompt antiviral therapy with reduction in immunosuppression may be an ideal approach for management of these patients

Infrared Nanoimaging of Hydrogenated Perovskite Nickelate Memristive Devices

Solid-state devices made from correlated oxides, such as perovskite nickelates, are promising for neuromorphic computing by mimicking biological synaptic function. However, comprehending dopant action at the nanoscale poses a formidable challenge to understanding the elementary mechanisms involved. Here, we perform operando infrared nanoimaging of hydrogen-doped correlated perovskite, neodymium nickel oxide (H-NdNiO3, H-NNO), devices and reveal how an applied field perturbs dopant distribution at the nanoscale. This perturbation leads to stripe phases of varying conductivity perpendicular to the applied field, which define the macroscale electrical characteristics of the devices. Hyperspectral nano-FTIR imaging in conjunction with density functional theory calculations unveils a real-space map of multiple vibrational states of H-NNO associated with OH stretching modes and their dependence on the dopant concentration. Moreover, the localization of excess charges induces an out-of-plane lattice expansion in NNO which was confirmed by in situ X-ray diffraction and creates a strain that acts as a barrier against further diffusion. Our results and the techniques presented here hold great potential for the rapidly growing field of memristors and neuromorphic devices wherein nanoscale ion motion is fundamentally responsible for function