In this study, we demonstrate that colloidal PbSe quantum dots (QDs) can be a viable active material for room temperature semiconductor radiation detectors (RTSDs). QDs were synthesized with two different recipes and ligand exchanged with NH4SCN and 1-octanethiol when needed. When the QDs were fully dried, simple pellet architectures were manually pressed and I-V sweeps were performed to determine material resistivity. By varying QD diameters and ligand combinations the pressed pellet resistivity could be tuned between 104–1013Ω cm. When exposing devices to 133Ba radiation, full energy deposition peaks in pulse height spectra proved difficult to obtain. Sensitivity to the radiation could be ascertained once material resistivity reached ≥108 Ω cm. Several devices demonstrated that resolution (peak full width half max over peak centroid) at 81 keV could be achieved with values of 4.75% and 5.98%. We found that performance was highly dependent on the contact point of a given superstructure. A comparison to other studies using colloidal QDs as an RTSD materials indicate that our results show similar performance. Further, our results are an improvement in performance compared to recent single crystalline RTSD materials such as CdSe.

Aceticacid on Pd(111) is an excellent model system to study theeffect of water on thermal decomposition of fatty acids and otheroxygenates. Acetic acid is a simple molecule that has both methyland acid groups, where its decomposition involves many of the keybond-breaking steps involved in more complex chemical decompositions.Here, we use ambient-pressure X-ray photoelectron spectroscopy andmass spectrometry supported by density functional theory (DFT) calculationsof the core-level binding energies to study the effect of co-adsorbedwater on the decomposition of acetic acid. The addition of water toacetic acid results in an increased acetic acid/acetate coverage anda decreased CO coverage. Moreover, when water is co-dosed with aceticacid, the gas phase composition from the reaction shows an approximately30% increase in the CO2/CO ratio, suggesting a shift towardCO(2) production in the presence of water. These observationsare supported by previous DFT calculations, which show that the presenceof co-adsorbed water lowers the barriers for O-H bond breakingbut increases the barriers for C-O bond breakage, leading toincreased CO2 production.

Synthesizing functional materials from water contributes to a sustainable energy future. On the atomic level, water drives complex metal hydrolysis/condensation/speciation, acid-base, ion pairing, and solvation reactions that ultimately direct material assembly pathways. Here, we demonstrate the importance of Nb-polyoxometalate (Nb-POM) speciation in enabling deposition of Nb2O5, LiNbO3, and (Na, K)NbO3 (KNN) from high-concentration solutions, up to 2.5 M Nb for Nb2O5 and ∼1 M Nb for LiNbO3 and KNN. Deposition of KNN from 1 M Nb concentration represents a potentially important advancment in lead-free piezoelectrics, an application that requires thick films. Solution characterization via small-angle X-ray scattering and Raman spectroscopy described the speciation for all precursor solutions as the [HxNb24O72](x-24) POM, as did total pair distribution function analyses of X-ray scattering of amorphous gels prior to conversion to oxides. The tendency of the Nb24-POM to form extended networks without crystallization leads to conformal and well-adhered films. The films were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, ellipsometry, and X-ray photoelectron spectroscopy. As a strategy to convert aqueous deposition solutions from {Nb10}-POMs to {Nb24}-POMs, we devised a general procedure to produce doped Nb2O5 thin films including Ca, Ag, and Cu doping.

A strategy for enhancing the photocatalytic performance of MOF-based systems (MOF: metal-organic framework) is developed through the construction of MOF/MOF heterojunctions. The combination of MIL-167 with MIL-125-NH2 leads to the formation of MIL-167/MIL-125-NH2 heterojunctions with improved optoelectronic properties and efficient charge separation. MIL-167/MIL-125-NH2 outperforms its single components MIL-167 and MIL-125-NH2, in terms of photocatalytic H2 production (455 versus 0.8 and 51.2 μmol h-1 g-1, respectively), under visible-light irradiation, without the use of any cocatalysts. This is attributed to the appropriate band alignment of these MOFs, the enhanced visible-light absorption, and long charge separation within MIL-167/MIL-125-NH2. Our findings contribute to the discovery of novel MOF-based photocatalytic systems that can harvest solar energy and exhibit high catalytic activities in the absence of cocatalysts.

Current and future power systems require chromia-forming alloys compatible with high-temperature CO 2 . Important questions concerning the mechanisms of oxidation and carburization remain unanswered. Herein we shed light onto these processes by studying the very initial stages of oxidation of Fe22Cr and Fe22Ni22Cr model alloys. Ambient-pressure X-ray photoelectron spectroscopy enabled in situ analysis of the oxidizing surface under 1 mbar of flowing CO 2 at temperatures up to 530 °C, while postexposure analyses revealed the structure and composition of the oxidized surface at the near-atomic scale. We found that gas purity played a critical role in the kinetics of the reaction, where high purity CO 2 promoted the deposition of carbon and the selective oxidation of Cr. In contrast, no carbon deposition occurred in low purity CO 2 and Fe oxidation ensued, thus highlighting the critical role of impurities in defining the early oxidation pathway of the alloy. The Cr-rich oxide formed on Fe22Cr in high purity CO 2 was both thicker and more permeable to carbon compared to that formed on Fe22Ni22Cr, where carbon transport appeared to occur by atomic diffusion through the oxide. Alternatively, the Fe-rich oxide formed in low purity CO 2 suggested carbon transport by molecular CO 2 .

Controlling the grown oxide composition, the oxide/semiconductor interface properties, and the semiconductor surface composition is of interest for SiGe devices. We have used ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) to study the initial stages of dry thermal oxidation of an epitaxial Si0.60Ge0.40(001) film on Si(001). Si 2p and Ge 3d chemical-state resolved AP-XPS was performed at 300 °C and O2 pressures (PO2) of 10−4, 10−2, and 1 mbar during oxide growth. The National Institute of Standards simulated electron spectra for surface analysis (SESSA) was used to analyze both the oxide composition and the thickness versus time for each pressure. At all three PO2, the SESSA analysis indicated that oxidation proceeds via three oxide growth rate regimes: an initial rapid regime, an intermediate transitionary regime, and finally a quasisaturation slow regime. The Si and Ge oxidation rates were found to be pressure dependent during the rapid regime with both rates decreasing monotonically with decreasing pressure. Results indicated that Ge was much more sensitive to changes in PO2 compared to Si. As a result, a decrease in PO2 resulted in significant suppression of GeO2 formation compared to SiO2. Using SESSA, we were able to quantify the grown oxide composition and the thickness, both of which were strongly dependent on O2 pressure. The Ge composition, in Si1−xGexO2, was found to decrease monotonically with decreasing PO2.

The use of renewable electricity to prepare materials and fuels from abundant molecules offers a tantalizing opportunity to address concerns over energy and materials sustainability. The oxygen evolution reaction (OER) is integral to nearly all material and fuel electrosyntheses. However, very little is known about the structural evolution of the OER electrocatalyst, especially the amorphous layer that forms from the crystalline structure. Here, we investigate the interfacial transformation of the SrIrO3 OER electrocatalyst. The SrIrO3 amorphization is initiated by the lattice oxygen redox, a step that allows Sr2+ to diffuse and O2- to reorganize the SrIrO3 structure. This activation turns SrIrO3 into a highly disordered Ir octahedral network with Ir square-planar motif. The final Sr y IrO x exhibits a greater degree of disorder than IrO x made from other processing methods. Our results demonstrate that the structural reorganization facilitated by coupled ionic diffusions is essential to the disordered structure of the SrIrO3 electrocatalyst.

Tin dioxide (SnO2) has various applications due to its unique surface and electronic properties. These properties are strongly influenced by Sn oxidation states and associated defect chemistries. Recently, the oxidation of volatile organic compounds (VOCs) into less harmful molecules has been demonstrated using SnO2 catalysts. A common VOC, 2-propanol (isopropyl alcohol, IPA), has been used as a model compound to better understand SnO2 reaction kinetics. We have used ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) to characterize the surface chemistry of IPA and O2 mixtures on stoichiometric, unreconstructed SnO2(110)-(1 × 1) surfaces. AP-XPS experiments were performed for IPA pressures ≤3 mbar, various IPA/O2 ratios, and several reaction temperatures. These measurements allowed us to determine the chemical states of adsorbed species on SnO2(110)-(1 × 1) under numerous experimental conditions. We found that both the IPA/O2 ratio and sample temperature strongly influence reaction chemistries. AP-XPS valence-band spectra indicate that the surface was partially reduced from Sn4+ to Sn2+ during reactions with IPA. In situ mass spectrometry and gas-phase AP-XPS results indicate that the main reaction product was acetone under these conditions. For O2 and IPA mixtures, the reaction kinetics substantially increased and the surface remained solely Sn4+. We believe that O2 replenished surface oxygen vacancies and that SnO2 bridging and in-plane oxygen are likely the active oxygen species. Moreover, addition of O2 to the reaction results in a reduction in formation of acetone and an increase in formation of CO2 and H2O. Based on these studies, we have developed a reaction model that describes the catalytic oxidation of IPA on stoichiometric SnO2(110)-(1 × 1) surfaces.

The light-soaking effect is the observation that under constant illumination the measured power conversion efficiency of certain solar cells changes as a function of time. The theory of the light-soaking in metal halide perovskites is at present incomplete. In this report, we employ steady-state microwave conductivity, a contactless probe of electronic properties of semiconductors, to study the light-soaking effect in metal halide perovskites. By illuminating isolated thin films of two mixed-cation perovskites with AM1.5 solar illumination, we observe a continual increase in photoconductance over a period of many (>12) hours. We can fit the experimentally observed changes in photoconductance to a stretched exponential function, in an analogous manner to bias-stressed thin-film transistors. The information provided in this report should help the community better understand one of the most perplexing open problems in the field of perovskite solar cells and, ultimately, lead to more robust and predictable devices.

Solution-based organometallic nanoclusters are unique nanoscale precursors due to the ability to precisely control their size, shape, structure, and assembly. The interaction of extreme ultraviolet (EUV) or X-ray photons with these organometallic nanoclusters can result in processes that can lead to a change in solubility. This makes these materials prime candidates for next-generation photoresists for EUV nanolithography. In this study, we investigate the interaction of X-ray radiation with a charge neutral, sodium templated, butyl-tin Keggin (beta-NaSn13) nanocluster. This nanocluster is used as a model EUV photoresist to better understand the radiation induced solubility transition. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was used to characterize the beta-NaSn13 thin films, where Sn 3d, O ls, and C is core levels were measured under a range of ambient conditions, including ultrahigh vacuum and 1 mbar of oxygen, water, methanol, or nitrogen. A photon dose array was obtained for each ambient condition to determine their effect on the photon induced chemistries which result in the solubility transition. The resulting contrast curves indicate that an oxygen ambient significantly reduces the required photon dose for the solubility transition relative to UHV, while all other ambients increase the required photon dose for the solubility transition relative to UHV. We performed in situ XPS after postexposure annealing beta-NaSn13 thin films in multiple ambients to study the chemistry that occurs after a postexposure bake (PEB). The beta-NaSn13 thin films retained a significant amount of aliphatic carbon following the PEB in all the ambients we studied. On the basis of our studies, we propose that the solubility transition for beta-NaSn13 thin films occurs through radical hydrogen abstraction and radical-radical coupling reactions. These studies further improve the understanding of photon induced chemistries in a beta-NaSn13 model resist and provide mechanistic insights for EUV lithography processing with organometallic nanomaterials.

Three organotin carboxylate species stabilized by the same ligands, but varying in size and structure, were studied to elucidate the effects of the structure on reactivity in the context of direct-write electron beam patterning. The chemical reactions that occur between the organotin reagents and the electron beam, the patterned film products, and the ligand decomposition and desorption byproducts were compared across all species. We found that both the metal-oxo content and the ligand coordination mode of each organotin reagent affected the reaction efficiency during electron beam patterning. In each case, an insoluble metal-oxo product formed after irradiation, but the composition, structure, and surface morphology of the products were nearly indistinguishable from the initial films. Examining the byproducts of the irradiation chemistry using electron-stimulated desorption confirmed that many of the organic ligands remained in the film during the reaction, likely crosslinking the clusters together to form a metal oxo polymer product. Finally, we discuss the implications of the chemical transformations that occur during patterning for the use of these organotin reagents as both photoresists for lithography and direct-write functional nanomaterials.

Cobalt germanides have been widely studied as semiconductor contact materials, but recent theoretical studies suggest that they may also be excellent catalysts for methane steam reforming with stabilities and activities comparable to more expensive noble metal catalysts. We have sputter deposited CoGe alloy films and characterized their structure and morphology after post-deposition annealing in high vacuum up to 1000 degrees C. We used X-ray photoelectron spectroscopy to study the initial oxidation of amorphous and crystalline CoGe alloy surfaces under low pressures of O-2 and H2O. The oxidation rate in O-2 was found to be faster for an amorphous CoGe surface compared to a crystalline surface. We also found that there was little difference in the oxidation rate in H2O for either amorphous or crystalline surfaces. During O-2 oxidation, the crystalline surface preferentially forms GeO and the amorphous surface preferentially forms GeO2. We have also observed preferential oxidation of Ge in the CoGe thin films. During temperature programmed desorption studies, we found that GeO desorption begins near 350 degrees C and that GeO2 decomposes to GeO and desorbs near 700 degrees C. More studies of CoGe catalysts are warranted, however GeO desorption may be a concern under reaction conditions when the film is subjected to an oxidizing environment.

Recently, monoalkyl oxo-hydroxo tin clusters have emerged as a new class of metal-oxide resist to support the semiconductor industry's transition to extreme ultraviolet (EUV) lithography. Under EUV exposure, these tin-based clusters exhibit higher performance and wider process windows than conventional polymer materials. A promising new monoalkyl precursor, [(BuSn)(12)O-14(OH)(6)][OH](2) (BuSn), is still in its infancy in terms of film formation. However, understanding potential environmental effects could significantly affect future development as a commercial product. We synthesized and explored the toxicity of nano-BuSn in the alga Chlamydomonas reinhardtii and the crustacean Daphnia magna at exposure concentrations ranging from 0 to 250 mg/L. Nano-BuSn had no effect on C. reinhardtii growth rate irrespective of concentration, whereas high nanoparticle concentrations (>= 100 mg/L) increased D. magna immobilization and mortality significantly. To simulate an end-of-life disposal and leachate contamination, BuSn-coated film wafers were incubated in water at various pH values and temperatures for 14 and 90 d to investigate leaching rates and subsequent toxicity of the leachates. Although small quantities of tin (1.1-3.4% of deposited mass) leached from the wafers, it was insufficient to elicit a toxic response regardless of pH, incubation time, or temperature. The low toxicity of the tin-based thin films suggests that they can be an environmentally friendly addition to the material sets useful for semiconductor manufacturing. Environ Toxicol Chem 2019;00:1-8. (c) 2019 SETAC

The electronic structure of multimetal, amorphous oxides can be varied across a wide range of elemental compositions. Bulk properties such as conductivity, work function, and absorption can thus be tailored to suit a range of applications spanning from carrier-selective contacts to catalysis. Missing, however, is an understanding of how the surface reactivity is impacted in mixed metal-oxide amorphous films. Here we investigate the propensity of Al(1-x)M(x)Oy (M = Fe, Mn) amorphous oxide films to dissociate water into hydroxyl groups in a humid environment and find comparable hydroxylation at the low relative humidity (similar to 0.3% RH) probed by ambient pressure X-ray photoelectron spectroscopy. In contrast, films with both Al and Fe show an increased formation of methoxy groups upon methanol exposure compared to pure Al- and Fe-oxide end members, indicating that the coordination environment of the amorphous oxide network impacts the acidity and redox character of surface metal and oxygen sites. These results provide guidance for the rational design of amorphous oxide layers with tailored chemical reactivity or passivity for a given application.

Organotin photoresists have shown promise for next-generation lithography because of their high extreme ultraviolet (EUV) absorption cross sections, their radiation sensitive chemistries, and their ability to enable high resolution patterning. To better understand both temperature and radiation-induced reaction mechanisms, we have studied a model EUV photoresist, which consists of a charge-neutral butyl-tin cluster. Temperature-programmed desorption (TPD) showed very little outgassing of the butyl-tin resist in ultrahigh vacuum and excellent thermal stability of the butyl groups. TPD results indicated that decomposition of the butyl-tin resist was first order with a fairly constant decomposition energy between 2.4 and 3.0 eV, which was determined by butyl group desorption. Electron-stimulated desorption (ESD) showed that butyl groups were the primary decomposition product for electron kinetic energies expected during EUV exposures. X-ray photoelectron spectroscopy was performed before and after low-energy electron exposure to evaluate the compositional and chemical changes in the butyl tin resists after interaction with radiation. The effect of molecular oxygen during ESD experiments was evaluated, and it was found to enhance butyl group desorption during exposure and resulted in a significant increase in the ESD cross section by over 20%. These results provide mechanistic information that can be applied to organotin EUV photoresists, where a significant increase in photoresist sensitivity may be obtained by varying the ambient conditions during EUV exposures.

The precise control of both the size and shape of Ag nanoparticles strongly influences their optical properties. Although the synthesis of Ag nanocubes with sharp corners and edges has been demonstrated, the ability to scale these approaches with high selectivity remains elusive. In this study, a continuous flow microwave-assisted reactor was used to separate nucleation from growth events, which provides a method to synthesize very uniform single crystalline Ag nanocubes. Nucleation in the microwave zone was enhanced through seed-mediated processes by sulfide formation, and a chemical regulator was used in the growth zone to further improve the sharpness of the edges of the nanocubes. Transmission electron microscopy and optical properties were used to optimize the reaction conditions and Ag nanocubes with edge lengths of 28 and 45 nm were readily synthesized with narrow particle size distributions and high selectivities (>70%). Nanocubes with 28 nm edge lengths were used to prepare films to demonstrate the detection of Rhodamine 6G with concentrations down to 10 nM using surface enhanced Raman spectroscopy. These results indicate that continuous flow approaches have the potential to produce large quantities of uniform Ag nanocubes that can be used for sensing or other applications.