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Abstract: Nonsteroidal anti-inflammatory drugs (NSAIDs), which block the activity of cyclooxygenase (COX) isoenzymes and inhibit the synthesis of prostaglandin, have been used for pain relief. For the enhancement of the potency or the decrease of side-effects, NSAIDs are normally prescribed as a mixture with other chemical components including caffeine and proton pump inhibitor. Here, we developed a method to separate a mixture of three NSAIDs, such as aspirin, paracetamol, and naproxen, using reverse-phase high-performance liquid chromatography (RP-HPLC). An isocratic mobile phase consisting of acidic water and acetonitrile was selected to run at a low flow rate, such as 0.8 mL/min. The mixture of three NSAIDs was injected at a low volume into a C18 column having 150 mm in length and characterized using a UV detector at 230 nm. We identified three peaks in the chromatogram indicating three compounds. The elution time of the peaks was less than 10 min. The method proposed here can be used for identification of the combination of NSAIDs. Graphic Abstract:

Heavy-alkali post-deposition treatments (PDTs) utilizing Cs or Rb has become an indispensable step in producing high-performance Cu(In,Ga)Se2(CIGS) solar cells. However, full understanding of the mechanism behind the improvements of device performance by heavy-alkali treatments, particularly in terms of potential modification of defect characteristics, has not been reached yet. Here, we present an extensive study on the effects of CsF-PDT on material properties of CIGS absorbers and the performance of the final solar devices. Incorporation of an optimized concentration of Cs into CIGS resulted in a significant improvement of the device efficiency from 15.9 to 18.4% mainly due to an increase in the open-circuit voltage by 50 mV. Strong segregation of Cs at the front and rear interfaces as well as along grain boundaries of CIGS was observed via high-resolution chemical analysis such as atomic probe tomography. The study of defect chemistry using photoluminescence and capacitance-based measurements revealed that both deep-level donor-like defects such as VSeand InCuand deep-level acceptor-like defects such as VInor CuInare passivated by CsF-PDT, which contribute to an increased hole concentration. Additionally, it was found that CsF-PDT induces a slight change in the energetics of VCu, the most dominant point defect that is responsible for the p-type conductivity of CIGS.

Abstract

Abstract

While BiVO4is a promising photoanode for solar-driven photoelectrochemical (PEC) water splitting, fine control of its chemical composition (Bi/V ratio) and modification of its electrical properties via extrinsic doping are necessary to improve its PEC performance. Here, we performed compositional engineering of BVO—varying Bi/V ratio and inclusion of different concentrations of Mo dopants. Through physical and chemical analyses, we found that the materials properties of BiVO4and its PEC performance were highly sensitive to the chemical composition. Our optimized BiVO4-based photoanode exhibited the highest photocurrent density among the state-of-the-art SnO2/BiVO4heterojunction photoanodes reported in the literature: 2.62 and 4.20mAcm−2measured at 1.23V vs. a reversible hydrogen electrode for the oxygen evolution reaction and sulfite oxidation reaction, respectively. A complete picture explaining various PEC performances with different chemical compositions via the band structure of BiVO4has emerged. This work points to the importance of specific control of the chemical composition in achieving highly efficient BiVO4-based photoanodes, which will guide future research directions in the fabrication of other high performance photoelectrodes.

We report on the photoelectrochemical (PEC) performance and stability of Cu(In,Ga)Se2(CIGS)-based photocathodes for photocatalytic hydrogen evolution from water. Various functional overlayers, such as CdS, TiO2, ZnxSnyOz, and a combination of the aforementioned, were applied on the CIGS to improve the performance and stability. We identified that the insertion of TiO2overlayer on p-CIGS/n-buffer layers significantly improves the PEC performance. A multilayered photocathode consisting of CIGS/CdS/TiO2/Pt exhibited the best current–potential characteristics among the tested photocathodes, which demonstrates a power-saved efficiency of 2.63%. However, repeated linear sweep voltammetry resulted in degradation of performance. In this regard, we focused on the PEC durability issues through in-depth chemical characterization that revealed the degradation was attributed to atomic redistribution of elements constituting the photocathode, namely, in-diffusion of Pt catalysts, out-diffusion of elements from the CIGS, and removal of the metal-oxide layers; the best-performing CIGS/CdS/TiO2/Pt photocathode retained its initial performance until the TiO2overlayer was removed. It was also found that the durability of CIGS photocathodes with a TiO2-coated metal-oxide buffer layer such as ZnxSnyOzwas better than those with a TiO2-coated CdS, and the degradation mechanism was different, suggesting that the stability of a CIGS-based photocathode can be improved by careful design of the structure.

Fluorescent nanoparticles used in biomedical applications should be stable in their colloidal form in aqueous media and possess a high quantum yield (QY). We report ultrasmall Ln2O3(Ln = Eu, Tb, or Dy) nanoparticle colloids with high QYs in aqueous media. The nanoparticles are grafted with hydrophilic and biocompatible poly(acrylic acid) (PAA) to ensure colloidal stability and biocompatibility and with organic photosensitizer 2,6-pyridinedicarboxylic acid (PDA) for achieving a high QY. The PAA/PDA–Ln2O3nanoparticle colloids were nearly monodispersed and ultrasmall (particle diameter: ∼2 nm). They exhibited excellent colloidal stability with no precipitation after synthesis (>1.5 years) in aqueous media, very low cellular toxicity, and very high absolute QYs of 87.6, 73.6, and 2.8% for Ln = Eu, Tb, and Dy, respectively. These QYs are the highest reported so far for lanthanides in aqueous media. Therefore, the results suggest their high potential as sensitive optical or imaging probes in biomedical applications.

Zinc tin nitride (ZTN) compounds exhibit excellent optical and defect-tolerance properties desirable for optoelectronic applications. However, the synthesis of high-phase-purity ZTN is limited by oxidation. We report the synthesis of amorphous ZTN films with excellent oxidation resistance for a wide range of compositions (from pure Zn3N2to ZTN with Sn/(Sn + Zn) up to 66.9%). We employ modified pulsed plasma-enhanced chemical vapor deposition with alternating pulses of zinc and tin precursors. We observe a correlation between oxidation resistance and pulse duration of the Zn precursor. Furthermore, extensive structural, chemical, electrical, and optical characterizations are discussed for amorphous ZTN with varying Sn/Zn. Electron microscopy reveals a mixture of nanoscale domains with Zn-rich and Sn-rich phases in the synthesized films. Interestingly, the trends of the electrical and optical properties vs the Sn content of amorphous ZTN are similar to reported crystalline ZTN. Notably, amorphous ZTN of Sn/(Zn + Sn) ∼ 0.3 exhibited a carrier concentration of 5.3 × 1013cm–3, the lowest among those reported for ZTN of any composition, making it very promising for photovoltaic applications. Our study presents a new class of compounds with materials properties that are unaccessible by the conventional crystalline nitrides, which will be useful for future optoelectronic applications.

Amorphous Ge2Sb2Te5clusters with a size of 20 nm, self-enclosed by a thin layer of TiOx, were obtained by cosputtering Ge2Sb2Te5and TiO2targets at room temperature with the aim of reducing the reset current for phase change random access memory applications. Eutectic decomposition during the deposition caused a phase separation of Ge2Sb2Te5and TiOx. The temperature-dependent resistance change results showed that the activation energy for crystallization increased from 2.44±0.76to 3.84±1.43eVin the Ge2Sb2Te5film. The set resistance can be tuned within an acceptable range, and the reliability of this microstructure during repetitive laser melt-quenching cycles was tested.

We report an electric-field-induced directional mass movement of Ge2Sb2Te5in bottleneck geometry. Under high-electric-stress circumstances (106Acm−2), a mass of Ge2Sb2Te5tends to move toward the cathode (−) by the remaining mass depletion at the anode (+). The high electric stress induces an asymmetric compositional separation such that Sb is distributed toward the cathode (−) whereas Te is distributed toward the anode (+). Ionicity in Ge2Sb2Te5at high temperature and high electric stress can be one of the origins of the asymmetric behavior. The electric-field-induced mass movement may provide insight on the device reliability of phase-change random access memory.

We report the successful electron-beam patterning of Ge2Sb2Te5nanostructures, in the form of both lines and dots, using hydrogen silsesquioxane (HSQ) resist. Although HSQ has proven to be a good resolution electron-beam resist, the adhesion between Ge2Sb2Te5and the HSQ resist is problematic when trying to form fine patterns. To promote their adhesion, we introduced an amorphous Si (a-Si) layer between the Ge2Sb2Te5and HSQ layers, and the layers were then sequentially removed using Cl2reactive ion etching and Ar etching with good selectivity of each layer. The selectivities for HSQ:a-Si etched by Cl2reactive gas and a-Si:Ge2Sb2Te5etched by Ar gas were 1:2.7 and 1:17, respectively. On the basis of this multilayer structure and a two-step dry etching process, various Ge2Sb2Te5nanostructures as small as 40nmwere successfully fabricated.