High-pressure response of vibrational properties of b-AsxP1-x:in situRaman studies.

The structural evolution of black arsenic-phosphorous (b-AsxP1-x) alloys with varying arsenic concentrations was investigated under hydrostatic pressure usingin situRaman spectroscopy. High-pressure experiments were conducted using a diamond anvil cell, which revealed pressure-induced shifts in vibrational modes associated with P-P bonds (A1g,A2g,B2g), As-As bonds (A1g,A2g,B2g), and As-P bonds in b-AsxP1-xalloys. Two distinct pressure regimes were observed. In the first regime (region I), all vibrational modes exhibited a monotonic upshift, indicating phonon hardening due to hydrostatic pressure. In the second regime (region II), As0.4P0.6and As0.6P0.4alloys displayed a linear blueshift (or negligible change in some modes) at a reduced rate, suggesting local structural reorganization with less compression on the bonds. Notably, the alloy with the highest As concentration, As0.8P0.2, exhibited anomalous behavior in the second pressure regime, with a downward shift observed in all As-As and As-P Raman modes (and some P-P modes). Interestingly, the emergence of new peaks corresponding to theEgmode andA1gmode of the gray-As phase was observed in this pressure range, indicating compressive strain-induced structural changes. The anomalous change in region II confirms the formation of a new local structure, characterized by elongation of the P-P, As-As, and As-P bonds along the zigzag direction within the b-AsxP1-xphase, possibly near the grain boundary. Additionally, a gray-As phase undergoes compressive structural changes. This study underscores the significance of pressure in inducing structural transformations and exploring novel phases in two-dimensional materials, including b-AsxP1-xalloys.

Ligand-Free Ultrasmall Recyclable Iridium(0) Nanoparticles for Regioselective Aromatic Hydrogenation of Phosphine Oxide Scaffolds: An Easy Access to New Phosphine Ligands.

Herein, we developed the recyclable ligand-free iridium (Ir)-hydride based Ir0 nanoparticles (NPs) for the first regioselective partial hydrogenation of PV -substituted naphthalenes. Both the isolated and in situ generated NPs are catalytically active. A control nuclear magnetic resonance (NMR) study revealed the presence of metal-surface-bound hydrides, most likely formed from Ir0 species. A control NMR study confirmed that hexafluoroisopropanol as a solvent was accountable for substrate activation via hydrogen bonding. High-resolution transmission electron microscopy of the catalyst supports the formation of ultrasmall NPs, and X-ray photoelectron spectroscopy confirmed the dominance of Ir0 in the NPs. The catalytic activity of NPs is broad as showcased by highly regioselective aromatic ring reduction in various phosphine oxides or phosphonates. The study also showcased a novel pathway toward preparing bis(diphenylphosphino)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl (H8 -BINAP) and its derivatives without losing enantioselectivity during catalytic events.

Effect of Metal Nanoparticle Aggregate Structure on the Thermodynamics of Oxidative Dissolution.

Here, we compare the electrochemical oxidation potential of 15 nm diameter citrate-stabilized Au NPs aggregated by acid (low pH) to those aggregated by tetrakis(hydroxymethyl) phosphonium chloride (THPC). For acid-induced aggregation, the solution changes to a blue-violet color, the localized surface plasmon resonance (LSPR) band of Au NPs at 520 nm decreases along with an increase in absorbance at higher wavelengths (600-800 nm), and the peak oxidation potential (Ep) in anodic stripping voltammetry (ASV) obtained in bromide has a positive shift by as large as 200 mV. For THPC-induced aggregation (Au/THPC mole ratio = 62.5), the solution changes to a blue color as the LSPR band at 520 nm decreases and a new distinct peak at 700 nm appears, but the Ep does not exhibit a positive shift. Scanning transmission electron microscopy (STEM) images reveal that acid-induced aggregates are three-dimensional with strongly fused Au NP-Au NP contacts, while THPC-induced aggregates are linear or two-dimensional with ∼1 nm separation between Au NPs. The surface area-to-volume ratio (SA/V) decreases for acid-aggregated Au NPs due to strong Au NP-Au NP contacts, which leads to lower surface free energy and a higher Ep. The SA/V does not change for THPC-aggregated Au NPs since space remains between them and their SA is fully accessible. These findings show that metal NP oxidative stability, as determined by ASV, is highly sensitive to the details of the aggregate structure.

A scalable approach to topographically mediated antimicrobial surfaces based on diamond.

Bio-inspired Topographically Mediated Surfaces (TMSs) based on high aspect ratio nanostructures have recently been attracting significant attention due to their pronounced antimicrobial properties by mechanically disrupting cellular processes. However, scalability of such surfaces is often greatly limited, as most of them rely on micro/nanoscale fabrication techniques. In this report, a cost-effective, scalable, and versatile approach of utilizing diamond nanotechnology for producing TMSs, and using them for limiting the spread of emerging infectious diseases, is introduced. Specifically, diamond-based nanostructured coatings are synthesized in a single-step fabrication process with a densely packed, needle- or spike-like morphology. The antimicrobial proprieties of the diamond nanospike surface are qualitatively and quantitatively analyzed and compared to other surfaces including copper, silicon, and even other diamond surfaces without the nanostructuring. This surface is found to have superior biocidal activity, which is confirmed via scanning electron microscopy images showing definite and widespread destruction of E. coli cells on the diamond nanospike surface. Consistent antimicrobial behavior is also observed on a sample prepared seven years prior to testing date.

Insight the process of hydrazine gas adsorption on layered WS2: a first principle study.

The process of hydrazine gas adsorption on layered WS2 has been systematically studied from first principle calculations. Our results demonstrate that this adsorption process is exothermic, and hydrazine molecules are physically adsorbed. The layer-dependent adsorption energy and interlayer separation induced by van der Waals interaction exerted by hydrazine molecules lead to the difficulty in desorbing hydrazine molecules from layered WS2 as the number of layers increases. The most interesting finding is the emergence of localized impurity states below the Fermi level upon the hydrazine adsorption, irrespective of the number of WS2 layers, resulting in a significant effect on the band structures and subsequently changing its electrical conductivity. Furthermore, a layer-dependent small charge transfer occurs between hydrazine and layered WS2, leading to a charge redistribution and considerable polarization in the adsorbed systems. The existence of defects and the humidity, on the other hand, influences the sensitivity of layered WS2 to the hydrazine adsorption. Obtained results show that a perfectly layered WS2 might be a promising candidate as an efficient nanosensor to detect such toxic gas in dry environment.

Strain-induced vibrational properties of few layer black phosphorus and MoTe2 via Raman spectroscopy.

We studied and compared the effect of tensile strain on the Raman spectra of black phosphorus (BP) and molybdenum ditelluride (MoTe2) crystals by using a simple custom strain device. In-situ Raman spectroscopy on BP revealed clear red shifting of all three phonon modes, A1 g, B2g and A2 g, under tensile stress. From our theoretical analyses, we found that such red shifting strongly depends on the direction of the strain exerted on the system even within the elastic deformation limit (i.e. strain ≤ 1 %). In particular, calculated results for the strain along the armchair direction are consistent with our experimental data, confirming that the strain applied to the sample acts effectively along the armchair direction. In a comparative study, we found that the effect of strain on the Raman shifting is larger for BP than that for MoTe2, presumably due to the smaller Young's modulus of BP. We also see a remarkable resemblance between donor-type intercalation induced vibrational properties and tensile stress-induced vibrational properties in BP. We anticipate that our method of in-situ Raman spectroscopy can be an effective tool that can allow observation of strain effect directly which is critical for future flexible electronic devices.

Gas adsorption and light interaction mechanism in phosphorene-based field-effect transistors.

Phosphorene-based field effect transistor (FET) structures were fabricated to study the gas- and photo-detection properties of phosphorene. The interplay between device performance and environmental conditions was probed and analyzed using in situ transport measurements. The device structures were exposed to different chemical and light environments to understand how they perform under different external stimuli. For the gas/molecule detection studies, inert (Ar), as well as, oxidizing (N2O), and reducing (H2 and also N2H4) agents were selected. The FET structure was exposed to these different gases, and the effect of each gas on the device resistance was measured. The study showed varying response towards different molecules. Specifically, no significant resistance change was observed upon exposure to Ar, while H2 and N2H4 were found to decrease the resistance and N2O had the opposite effect resulting in an increase in resistance. This work is the first demonstration for the detection of N2H2 and N2O using a phosphorene-based system. These phosphorene-based FET structures were also found to be sensitive to light exposure. When such structure was irradiated with light, the current modulation was lost. The observed resistance changes can be explained as a result of the modulation of the Schottky barrier at the phosphorene-electrical contact interface due to the adsorbed molecules and charge transfer, and/or photo-induced carrier generation. The results were consistent with the transfer characteristics of Vdsvs. Vg.

ZnO ALD-Coated Microsphere-Based Sensors for Temperature Measurements.

In this paper, the application of a microsphere-based fiber-optic sensor with a 200 nm zinc oxide (ZnO) coating, deposited by the Atomic Layer Deposition (ALD) method, for temperature measurements between 100 and 300 °C, is presented. The main advantage of integrating a fiber-optic microsphere with a sensing device is the possibility of monitoring the integrity of the sensor head in real-time, which allows for higher accuracy during measurements. The study has demonstrated that ZnO ALD-coated microsphere-based sensors can be successfully used for temperature measurements. The sensitivity of the tested device was found to be 103.5 nW/°C when the sensor was coupled with a light source of 1300 nm central wavelength. The measured coefficient R2 of the sensor head was over 0.99, indicating a good fit of the theoretical linear model to the measured experimental data.

Bilayer phosphorene under high pressure: in situ Raman spectroscopy.

In this study, bilayer phosphorene samples were subjected to high pressure using a Diamond Anvil Cell (DAC) and their vibrational properties were studied via in situ Raman spectroscopy. Systematic shifting in the Raman frequency of A1g, B2g, and A2g modes was observed and theoretical calculations were performed to understand the relationship between the strain and the vibrational properties. The changes in the vibration modes under high pressure are found to reflect the deformation in the structure and its stiffness. Firstly, the study shows a substantial pressure-induced enhancement of the interactions between atoms for the out-plane mode A1g, mainly due to the directional nature of the lone pair of electrons and charge transfer. However, these interactions and the observed blue shift of the A1g Raman peak are much weaker than those in bulk black phosphorous. Secondly, while a significant enhancement of the atomic interactions due to bond length change is also observed for the in-plane mode B2g along the zigzag direction, there is almost negligible effect on the in-plane mode A2g along the armchair direction. The results add to the knowledge on mechanical properties and strain engineering in phosphorene towards novel functionalities and applications of this intriguing two-dimensional (2D) material.

Low-Temperature and Fast Kinetics for CO2 Sorption Using Li6WO6 Nanowires.

In this paper, lithium hexaoxotungstate (Li6WO6) nanowires were synthesized via facile solid-state reaction and were tested for CO2 capture applications at both low (<100 °C) and high temperatures (>700 °C). Under dry conditions, the nanowire materials were able to capture CO2 with a weight increment of 12% in only 60 s at an operating temperature of 710 °C. By contrast, under humidified ambience, Li6WO6 nanowires capture CO2 with weight increment of 7.6% at temperatures as low as 30-40 °C within a time-scale of 1 min. It was observed that the CO2 chemisorption in Li6WO6 is favored in the oxygen ambience at higher temperatures and in the presence of water vapor at lower temperatures. Nanowire morphology favors the swift lithium supply to the surface of lithium-rich Li6WO6, thereby enhancing the reaction kinetics and lowering time scales for high capacity adsorption. Overall, high chemisorption capacities, superfast reaction kinetics, wide range of operating temperatures, and reasonably good recyclability make 1-D Li6WO6 materials highly suitable for various CO2 capture applications.

Recyclable cellulose-palladium nanoparticles for clean cross-coupling chemistry.

Cheap, recyclable, and robust cellulose-palladium nanoparticles were developed and fully characterized by FTIR, TEM, XPS, TGA, and NMR. The nanoparticles enabled cross-coupling chemistry in a truly general fashion i.e., Suzuki-Miyaura, Heck, Sonogashira, and C-H activation. Notably, all types of transformations were achieved with a single type of nanocatalyst. Complete recyclability of the catalyst and low traces of palladium in the product demonstrates the greenness of the protocol.

Nanovalved Adsorbents for CH4 Storage.

A novel concept of utilizing nanoporous coatings as effective nanovalves on microporous adsorbents was developed for high capacity natural gas storage at low storage pressure. The work reported here for the first time presents the concept of nanovalved adsorbents capable of sealing high pressure CH4 inside the adsorbents and storing it at low pressure. Traditional natural gas storage tanks are thick and heavy, which makes them expensive to manufacture and highly energy-consuming to carry around. Our design uses unique adsorbent pellets with nanoscale pores surrounded by a coating that functions as a valve to help manage the pressure of the gas and facilitate more efficient storage and transportation. We expect this new concept will result in a lighter, more affordable product with increased storage capacity. The nanovalved adsorbent concept demonstrated here can be potentially extended for the storage of other important gas molecules targeted for diverse relevant functional applications.

Kr/Xe Separation over a Chabazite Zeolite Membrane.

Herein we demonstrate that chabazite zeolite SAPO-34 membranes effectively separated Kr/Xe gas mixtures at industrially relevant compositions. Control over membrane thickness and average crystal size led to industrial range permeances and high separation selectivities. Specifically, SAPO-34 membranes can separate Kr/Xe mixtures with Kr permeances as high as 1.2 × 10 (-7) mol/m(2) s Pa and separation selectivities of 35 for molar compositions close to typical concentrations of these two gases in air. In addition, SAPO-34 membranes separated Kr/Xe mixtures with Kr permeances as high as 1.2 × 10 (-7) mol/m(2) s Pa and separation selectivities up to 45 for molar compositions as might be encountered in nuclear reprocessing technologies. Molecular sieving and differences in diffusivities were identified as the dominant separation mechanisms.

Efficiency enhancement of cubic perovskite BaSnO3 nanostructures based dye sensitized solar cells.

Cubic perovskite BaSnO3 (BSO) is an important photoelectron transporting material due to its electronic structure that competes with TiO2 in dye-sensitized solar cells (DSCs). Separately, BSO/TiCl4 treated and BSO/scattering layer photoelectrodes have been used in DSCs that effectively increase the photoexcited charge carriers collection resulting in superior photovoltaic performance. In the present work, the different TiCl4 treatment time (1, 3 and 5 min), different scattering layer (tetragonal anatase TiO2 and hexagonal wurtzite ZnO) and different combinations thereof are successfully used on BSO nanocuboids/nanoparticle morphological structure photoelectrodes, and then we systematically inspected their performance in DSCs. Under the optimized conditions, a power conversion efficiency (PCE) of 3.88% is obtained by a BSO/TiCl4 treated photoanode. Furthermore, the BSO photoanodes made using a scattering layer such as anatase TiO2 and hexagonal ZnO i.e., BSO/anatase TiO2 and BSO/hexagonal ZnO, exhibited PCEs of 1.14% and 1.25% respectively. In the end, one of the highest PCEs (5.68%) was achieved using BSO/TiCl4 treated/TiO2 scattering layer photoanode. Another photoelectrode such as BSO/TiCl4 treated/ZnO scattering layer exhibited a PCE of 4.28% that is also higher than the BSO/TiCl4 treated/BSO scattering layer photoanodes. Electron lifetime versus current density studies illustrate the stability of the BSO photoelectrode in DSCs. From the observed results, it is realized that BSO is one of the most important future technological materials.

Morphologic Evaluation of Post-implanted Monofilament Polypropylene Mesh Utilizing a Novel Technique with Scanning Electron Microscopy Quantification.

Polypropylene mesh has been shown to shrink up to 50%; however, little is known about other changes that may occur while it is implanted. It is unclear whether such changes have clinical impact; nonetheless, knowledge of such can ultimately affect the technique of implantation and may affect outcomes. The objective of this study was to evaluate surgically explanted mesh after two years implantation for evidence of change in morphology using scanning electron microscopy (SEM). Secondly, we describe a novel technique for quantifying such changes with intentions for future validation. SEM imaging was conducted and mesh changes were visualized. SEM images revealed deep surface cracks both transverse and longitudinal, flaking and peeling of fibers, as well as fibrosis. Microstructural quantification of cracks was also completed. The fraction of transverse cracked area to whole surface area was 24.2%. Average crack length range was 0.58 to 71.46 µm and average crack thickness range was 0.99 to 25.46 µm. Polypropylene mesh is subject to structural changes after surgical implantation. It is important to investigate how these processes impact clinical outcomes. Validated techniques of quantifying such changes can prove useful in future research and aid in development of the ideal graft.

Evaluation of surgical instrument handling on polypropylene mesh using scanning electron microscopy.

INTRODUCTION AND HYPOTHESIS: To evaluate the effect of surgical instruments handling on polypropylene mesh using scanning electron microscopy (SEM). METHODS: We applied different surgical instruments, including a few robotic ones, to pieces of polypropylene mesh. SEM was used to evaluate the morphological changes with this intervention. RESULTS: Straight hemostat, laparoscopic atraumatic grasper, laparoscopic needle driver, and robotic instruments (Bipolar forceps, Cadiere forceps, PK dissecting forceps and SutureCut) were applied to the mesh. SEM images of tool-affected mesh regions in specimens handled by different instruments along with the images of intact mesh were obtained. Average mesh fiber diameters, as well as the average parameters characterizing instrument-affected regions, were measured. There was substantial widening of the fibers in specimens handled by hemostat or a needle holder. An elliptical but much longer and narrower tool marking with more surface roughness was observed in mesh handled by a grasper. A ∼25-µm-wide and ∼200-µm-long strap was split on one side from the core of the fiber caused by Cadiere. CONCLUSIONS: There are morphological changes to polypropylene mesh caused by instrument handling. These changes are different depending on the instrument used. These alterations vary from changes in the surface creating roughness of the fiber, compression of the mesh with narrowing of the fiber in at least one direction or actual splitting or pitting of the fiber. Since there are no data regarding the effect of these morphological changes to the ultimate functioning of the mesh, surgeons should minimize mesh handling by instruments.

Iron sulfide (FeS) nanotubes using sulfurization of hematite nanowires.

We report the phase transformation of hematite (α-Fe2O3) single crystal nanowires to crystalline FeS nanotubes using sulfurization with H2S gas at relatively low temperatures. Characterization indicates that phase pure hexagonal FeS nanotubes were formed. Time-series sulfurization experiments suggest epitaxial growth of FeS as a shell layer on hematite. This is the first report of hollow, crystalline FeS nanotubes with NiAs structure and also on the Kirkendall effect in solid-gas reactions with nanowires involving sulfurization.

Ultrasmall CuI Nanoparticles Stabilized on Surface of HPMC: An Efficient Catalyst for Fast and Organic Solvent-Free Tandem Click Chemistry in Water.

A simple and environmentally benign technology for synthesizing ultrasmall CuI nanoparticles (NPs) on the surface of the food additive hydroxypropyl methylcellulose (HPMC) and their application in completely organic solvent-free tandem alkyne-azide cycloaddition reactions were reported. The NP catalyst was thoroughly characterized by high-angle annular dark-field scanning transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analysis for its morphology, particle size distribution, chemical composition, and oxidation state analyses. The NP catalyst was highly efficient, affording products in 10-45 min. All products were obtained in high purity by simple filtration, obviating organic solvents from the reaction set-up to product isolation. The methodology is general and scalable as validated by a broad substrate scope.

Harnessing the cation-π interactions of metalated gold monolayer-protected clusters to detect aromatic volatile organic compounds.

The strong, non-covalent interactions between π-systems and cations have been the focus of numerous studies on biomolecule structure and catalysis. These interactions, however, have yet to be explored as a sensing mechanism for detecting trace levels of volatile organic compounds (VOCs). In this article, we provide evidence that cation-π interactions can be used to elicit sensitive and selective chemiresistor responses to aromatic VOCs. The chemiresistors are fitted with carboxylate-linked alkali metals bound to the surface of gold monolayer-protected clusters formulated on microfabricated interdigitated electrodes. Sensor responses to aromatic and non-aromatic VOCs are consistent with a model for cation-π interactions arising from association of electron-rich aromatic π-systems to metal ions with the relative strength of attraction following the order K+ > Na+ > Li+. The results point toward cation-π interactions as a promising research avenue to explore for developing aromatic VOC-selective sensors.

Photoelectrochemical activity of as-grown, α-Fe2O3 nanowire array electrodes for water splitting.

Undoped hematite nanowire arrays grown using plasma oxidation of iron foils show significant photoactivity (~0.38 mA cm(-2) at 1.5 V versus reversible hydrogen electrode in 1 M KOH). In contrast, thermally oxidized nanowire arrays grown on iron exhibit no photoactivity due to the formation of a thick (>7 µm Fe(1-x)O) interfacial layer. An atmospheric plasma oxidation process required only a few minutes to synthesize hematite nanowire arrays with a 1­5 µm interfacial layer of magnetite between the nanowire arrays and the iron substrate. An amorphous oxide surface layer on hematite nanowires, if present, is shown to decrease the resulting photoactivity of as-synthesized, plasma grown nanowire arrays. The photocurrent onset potential is improved after removing the amorphous surface on the nanowires using an acid etch. A two-step method involving high temperature nucleation followed by growth at low temperature is shown to produce a highly dense and uniform coverage of nanowire arrays.