Materials that exhibit very high absorption and low reflectance at optical frequencies are important in a variety of light harvesting applications. We explore nano-scale topography of bulk metallic glasses to realize metallic surfaces with controllable reflectance. Diffuse reflectance as low as 1.6% in the visible range is achieved with nano-patterned Pt-based model bulk metallic glass without further optimization. Effect of pattern dimensions (size, spacing, and aspect-ratio) on the reflectance of bulk metallic glasses is investigated using a combination of simulation and experiments.

Bio-polymer-based composites are appealing cost-effective and environmentally friendly materials for electronic applications. This project relates to bio-composites made of chitosan and cellulose and reinforced with strontium titanate nanoparticles. Upon their fabrication, relevant parameters studied were the acetic acid concentration, the cellulose content, and the amount of strontium titanate nanoparticles. The specimens were characterized using thermogravimetric and degradation analyses, as well as via creep and tensile tests. The results revealed how higher cellulose levels lowered the ultimate tensile strength and the degradation temperature of the bio-composites. Moreover, when nanoparticles are present, higher cellulose levels contributed to their tensile strength. Additionally, more acidic solutions became detrimental to the mechanical properties and the thermal degradation temperature of the composites. Furthermore, the creep studies allowed determining elastic coefficients and viscous coefficients using the Burgers’ model. Those creep results suggest that higher amounts of SrTiO₃ (STO) nanoparticles raised the composites creep strain rate. As a whole, the study provides a baseline characterization of these novel bio-composites when subject to aggressive environments.

Bio-ferroelectric composites represent an inexpensive and environmentally friendly electronic alternative for electrical applications such as capacitors, transistors, and actuators. The present research relates to the development of a biocomposite made of a chitosan–cellulose polymeric layer and bearing ferroelectric nanoparticles. The variables considered included the volume percentage of cellulose (15 v% and 25 v%) in the matrix and the amount of ferroelectric nanoparticles (0 wt.%, 10 wt.%, and 20 wt.%). Upon electrical characterization, the results indicated that the addition of the nanoparticles raised the capacitance and resistivity of the composite while the addition of cellulose lessened both electrical properties. The measured capacitance of the composites diminished as the applied voltage increased when contrasted with commercial capacitors where under similar testing conditions, as expected, the said capacity remained constant. Additionally, higher current flows were obtained for those capacitors than for a capacitor made with the nanocomposite. In general, it is proposed that capacitors made of this biopolymer reinforced with ferroelectric particles be suitable for radio frequency and microwave applications in which high electrical tunability and low dielectric loss are required.

Space-borne wireless communications systems have become ubiquitous with the advent of commercial space flight. To support robust wireless data transmission in Earth-orbiting and deep-space applications, a framework has been developed for radio-frequency (RF) designers and radiation-effects engineers to identify, model, visualize, and test single-event effects (SEEs) in wireless receivers. Digital RF communications receivers are introduced, including the constellation diagram, an important visualization tool. Then, the generation of single-event transients (SETs) is presented in multiple layers, starting from transistors, building to SETs at the outputs of each circuit block, and culminating in the response of the full receiver system. Circuit blocks addressed in this work include a low-noise amplifier (LNA), down-conversion mixer, and voltage-controlled oscillator (VCO). Analytical theory and numerical simulation are synthesized, accompanied with pulsed-laser SEE testing, to give an understanding of how deposited charge in constituent transistors convert to SETs and SEUs. As an example case, a SiGe-BiCMOS direct-conversion receiver carrying 100-Mbaud quadrature phase-shift keying (QPSK) at the X-band (8–12 GHz) is characterized using pulsed-laser SEE testing. This manuscript provides a useful review and analytical template that enable future designers and radiation-effects engineers to (a) model SET propagation in a wireless receiver a priori, without testing full systems, (b) identify the SEE mechanisms present in a wireless receiver with knowledge of the circuit components present, and (c) determine sensitive transistors and circuits to develop informed test plans for worst-case predictions.

In recent years, scientists advanced the study of bio-ferroelectric composites to develop new environmentally friendly and inexpensive electronic elements such as capacitors, actuators, and transistors. Accordingly, the present research relates to composites made of chitosan-cellulose polymeric matrix and strontium titanate (STO) nanoparticles. The variables considered include different percentages of cellulose (15 and 25 v%) and strontium titanate nanoparticles (10 and 20 wt%). The electrical characterization of the composites included measuring their dielectric constant, current density, and conductivity. The results suggest that the addition of STO nanoparticles raised the dielectric constant while lowering the current density and the conductivity of the nanocomposites. Moreover, although the cellulose addition increased the current density and the conductivity of the composites, it lowered their dielectric constant. Also, the resulting biocomposite capacitors could withstand up to 60 V without any detectable dielectric breakdown. The other two properties measured were the ultimate tensile strength (UTS) and the degradation temperature (Tdeg). Higher percentages of cellulose decreased the UTS and the Tdeg of the chitosan-cellulose composites while the addition of cellulose slightly raised these properties of the composites made of chitosan-cellulose and STO nanoparticles. The results proved that these types of biocomposites are apt as capacitors with adequate strength to withstand aggressive environments. This work was fully conducted in the facilities of the Nanotechnology Center hosted by the University of Puerto Rico – Mayagüez, from December 2014 to January 2017.

The present work investigates the impact of transistor layout on both the RF and thermal performance of 90-nm SiGe heterojunction bipolar transistors (HBTs). The resulting performance shows only slight degradation in small-signal RF figures-of-merit, while large-signal RF figures-of-merit relevant to power amplifiers (PAs) are improved. Thermal resistance and capacitance were extracted for five different SiGe HBT layouts with the same total emitter area. Additionally, a favorable trade-off exists between RF performance figures-of-merit and thermal parameters; namely, the thermal time constant can be reduced by up to 37% with optimal layout, with only slight degradation (up to 8%) in RF performance. These optimal device layout variations can help circuit designers mitigate thermal memory effects at the device level, thereby improving the overall large-signal linearity of PAs.