Tissue simulating phantoms are an important part of instrumentation validation, standardization/training and clinical translation. Properly used, phantoms form the backbone of sound quality control procedures. We describe the development and testing of a series of optically turbid phantoms used in a multi-center American College of Radiology Imaging Network (ACRIN) clinical trial of Diffuse Optical Spectroscopic Imaging (DOSI). The ACRIN trial is designed to measure the response of breast tumors to neoadjuvant chemotherapy. Phantom measurements are used to determine absolute instrument response functions during each measurement session and assess both long and short-term operator and instrument reliability.

Tandem Z-scheme solar water splitting devices composed of two light-absorbers that are connected electrochemically by a soluble redox shuttle constitute a promising technology for cost-effective solar hydrogen production.

Rational design of hierarchical nanocomposites is a promising approach for efficient energy harvesting and conversion. A noble-metal-free ternary hierarchical composite, Cd0.5Zn0.5S-g-C3N4-MoS2, has been developed. Materials were chosen based on their relative band-edge alignments and they were studied as a composite for photocatalytic properties. The photocatalytic activity was evaluated by measuring the rate of photodriven H2 evolution with concomitant degradation of organic pollutants, such as Rhodamine B. Optimization of the loading of g-C3N4 and MoS2 onto Cd0.5Zn0.5S results in an enhanced yield of hydrogen evolution by ∼120% (Cd0.5Zn0.5S-g-C3N4) and ∼197% (Cd0.5Zn0.5S-g-C3N4-MoS2) compared to bare Cd0.5Zn0.5S. The ternary hybrid, Cd0.5Zn0.5S-g-C3N4-MoS2 resulted in an apparent quantum yield (AQY) of 38% at 420 nm. The significant improvement in photocatalytic performance in the composite can be attributed to enhanced interfacial charge transfer of electrons from g-C3N4 to Cd0.5Zn0.5S and MoS2. We surmise that the close proximity of the energies of conduction band edge for each component in the ternary composite promotes better charge separation.

Colloidal quantum dots (QDs) have attracted considerable attention as promising materials for solutionprocessable electronic and optoelectronic devices. Copper indium selenium sulfide (CuInSe x S 2−x or CISeS) QDs are particularly attractive as an environmentally benign alternative to the much more extensively studied QDs containing toxic metals such as Cd and Pb. Carrier transport properties of CISeS-QD films, however, are still poorly understood. Here, we aim to elucidate the factors that control charge conductance in CISeS QD solids and, based on this knowledge, develop practical approaches for controlling the polarity of charge transport and carrier mobilities. To this end, we incorporate CISeS QDs into field-effect transistors (FETs) and perform detailed characterization of these devices as a function of the Se/(Se+S) ratio, surface treatment, thermal annealing, and the identity of source and drain electrodes. We observe that as-synthesized CuInSe x S 2−x QDs exhibit degenerate p-type transport, likely due to metal vacancies and Cu In '' anti-site defects (Cu 1+ on an In 3+ site) that act as acceptor states. Moderate-temperature annealing of the films in the presence of indium source and drain electrodes leads to switching of the transport polarity to nondegenerate n-type, which can be attributed to the formation of In-related defects such as In Cu •• (an In 3+ cation on a Cu 1+ site) or In i ••• (interstitial In 3+ ) acting as donors. We observe that the carrier mobilities increase dramatically (by 3 orders of magnitude) with increasing Se/(Se+S) ratio in both nand p-type devices. To explain this observation, we propose a two-state conductance model, which invokes a highmobility intrinsic band-edge state and a low-mobility defect-related intragap state. These states are thermally coupled, and their relative occupancies depend on both QD composition and temperature. Our observations suggest that the increase in the relative fraction of Se moves conduction-and valence band edges closer to low-mobility intragap levels. This results in increased relative occupancy of the intrinsic band-edge states and a corresponding growth of the measured mobility. Further improvement in charge-transport characteristics of the CISeS QD samples as well as their stability is obtained by infilling the QD films with amorphous Al 2 O 3 using atomic layer deposition. KEYWORDS: CuInSe x S 2−x quantum dots, field-effect transistor, charge-carrier transport, charge-carrier mobility, n-and p-type, atomic layer deposition

The long-standing debate over the influence of oxygen vacancies and various dopants has been the center point in perovskite-based compounds for their photocatalytic applications. Hydrothermally synthesized cerium-doped BaZrO 3 (BZO) hollow nanospheres have been systematically studied by experimental and theoretical calculations to understand the effect of cerium doping and oxygen vacancies on the photocatalytic properties. Compounds synthesized by a template-free route were composed of hollow nanospheres generated by Ostwald ripening of spherical nanospheres, which were formed by agglomeration of nanoparticles. The high alkaline condition and high temperature during the hydrothermal condition may lead to the formation of local disorders and oxygen vacancies in the compounds, confirmed by ultraviolet−visible diffuse reflectance spectroscopy (UV−vis DRS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) analysis, and density functional theoretical (DFT) calculations. Combination of oxygen vacancies and progressive doping of Ce in BaZr 1−x Ce x O 3 (x = 0.00−0.04), creates additional energy levels stipulated by vacancy defects and Ce mixed valence states within the band gap of BZO, thereby reducing its band gap. The photocatalytic efficacy of the compounds has been examined by photodriven H 2 generation concomitant with oxidation of a sacrificial donor. In this study, BaZr 0.97 Ce 0.03 O 3 shows the highest efficiency (823 μmol h −1 g −1 ) with an apparent quantum yield (AQY) of 6% in photocatalytic H 2 production among all five synthesized samples. The data obtained from the UV−vis DRS, XPS, ESR analysis, and DFT calculations, the synergistic effect of decreasing the band gap due to Ce doping and the presence of Ce(III)/Ce(IV) pairs along with oxygen vacancies and lattice distortions could be the reasons behind the enhanced photocatalytic efficacy of BaZr 1−x Ce x O 3 (x = 0.00−0.04) under UV−vis light.

The U.S. Department of Energy recently announced its first Energy Earthshot on Clean Hydrogen, with a cost target of $1/kg-H2 by 2031. Assuming future utility-scale grid electricity prices from photovoltaics ($0.02/kWh), 80% of the cost of H2 would come from performing low-temperature water electrolysis at its thermoneutral voltage, with zero additional overpotential. This fact motivates alternative, less-expensive means of using light to generate mobile charge carriers than photovoltaics, and reactor designs with exceedingly low capital costs, like those we recently invented. Systems using low capital cost reactors benefit from low-voltage operation, which represents a paradigm shift from current state-of-the-art electrolyzers that aim to operate at high current densities. Analytical models predict that solar photocatalytic water splitting inherently operates at low voltages through use of an ensemble of optically thin photoabsorbers each operating at a low rate. Collectively the ensemble exhibits larger overall solar-to-hydrogen conversion efficiencies in comparison to optically thick designs. In efforts to attain these predicted higher efficiencies, we are performing detailed studies on the properties of state-of-the-art doped SrTiO3 and BiVO4 photocatalyst particles. During my talk, I will share our recent efforts in atomic-layer deposited ultrathin oxide coatings to impart redox selectivity and materials stability, single-photocatalyst-particle current–potential behavior and mobile charge carrier properties, and atomic-level information on dopant distributions and materials interfaces obtained from electron microscopies and X-ray spectroscopies. Collectively, our discoveries provide new design guidelines and additional research pathways for the development of effective composite materials to serve as active components in techno-economically viable artificial photosynthetic devices.

Solar hydrogen production could be a techno-economically viable alternative to steam methane reforming through development of new reactor designs and reaction schemes. Motivated by this fact, my group recently proposed a dual-bed batch reactor for Z-scheme solar water splitting that consists of stacked photocatalyst beds, which aid performance due to serial light absorption and short distances for redox shuttle mass transport. An unexpected discovery based on this design is that an ensemble of optically thin materials is more beneficial to theoretical solar-to-hydrogen conversion efficiencies than a standard single-light-absorber geometry. Through parallel experimental work we have shown that state-of-the-art doped and codoped SrTiO3 H2-evolving photocatalyst particles exhibit variability in homogeneity of dopant distributions, which correlates to overall performance. We have also observed that nanoscale coatings enable selective H2 evolution and desired redox shuttle reactivity over undesired reactions, which theoretically enable increased solar-to-hydrogen conversion efficiencies. Collectively these results provide new design guidelines and additional research pathways for the development of effective composite materials to serve as active components in techno-economically viable solar fuels devices.