Ambient Molecules Research Articles

Thermoreflectance imaging of percolation effects and dynamic resistance in indium tin oxide nanoparticle layers

Thin films of indium tin oxide nanoparticles are studied using charge-coupled device thoermoreflectance. High resolution sub-micron thermal images confirm that percolation in current conduction induces strongly inhomogeneous heat loads on the thin film. We experimentally show that the inhomogeneous current densities induce thousands of “micro-hotspots” that can be 20% hotter than the average Joule heating in the thin film layer and show comparable behavior in a resistor network. In addition to the percolation induced “micro-hotspots,” we report major hotspots, with non-Joule behavior, whose temperature response is greater than I2. We demonstrate that a temperature dependent resistor can account for an effective exponent larger than 2. Finally, it is shown that while ambient molecules modify the thin film conductivity by at least 20%, current conduction and percolation effects remain largely unchanged, but such chemical reactions can be nonetheless detected with thermoreflectance.

On Effective Mass of Charged Clusters in Liquid Media

General difficulties related to experimental determination of charged cluster masses Mi in liquid media are stressed (normally Mi strongly exceed typical masses m0 of ambient solvent molecules, Mi≫m0). This well-known feature deteriorates the product ωiτ vital in different resonance phenomena by shifting it to the domain ωiτ≤1 which is hardly suitable for the experiment. Here ωi is one of the typical frequencies used to measure the mass Mi in the liquid (e.g., the cyclotron resonance frequency) and τ is the relevant relaxation time. Discussed in the paper are the details of the scenario allowing to extract experimental data on Mi under the conditions ωiτ≤1 where most usual techniques are very difficult to apply.

Regulation of Ambient GABA Levels by Neuron-Glia Signaling for Reliable Perception of Multisensory Events

Activities of sensory-specific cortices are known to be suppressed when presented with a different sensory modality stimulus. This is referred to as cross-modal inhibition, for which the conventional synaptic mechanism is unlikely to work. Interestingly, the cross-modal inhibition could be eliminated when presented with multisensory stimuli arising from the same event. To elucidate the underlying neuronal mechanism of cross-modal inhibition and understand its significance for multisensory information processing, we simulated a neural network model. Principal cell to and GABAergic interneuron to glial cell projections were assumed between and within lower-order unimodal networks (X and Y), respectively. Cross-modality stimulation of Y network activated its principal cells, which then depolarized glial cells of X network. This let transporters on the glial cells export GABA molecules into the extracellular space and increased a level of ambient (extrasynaptic) GABA. The ambient GABA molecules were accepted by extrasynaptic GABA(a) receptors and tonically inhibited principal cells of the X network. Cross-modal inhibition took place in a nonsynaptic manner. Identical modality stimulation of X network activated its principal cells, which then activated interneurons and hyperpolarized glial cells of the X network. This let their transporters import (remove) GABA molecules from the extracellular space and reduced tonic inhibitory current in principal cells, thereby improving their gain function. Top-down signals from a higher-order multimodal network (M) contributed to elimination of the cross-modal inhibition when presented with multisensory stimuli that arose from the same event. Tuning into the multisensory event deteriorated if the cross-modal inhibitory mechanism did not work. We suggest that neuron-glia signaling may regulate local ambient GABA levels in order to coordinate cross-modal inhibition and improve neuronal gain function, thereby achieving reliable perception of multisensory events.

Dynamic Rearrangement of Stearic Acid Molecules Adsorbed on a Gold Surface Induced by Ambient Water Molecules Studied by Infrared Spectroscopy

Molecular adsorbates of stearic acid on a gold surface prepared as an imperfect Langmuir–Blodgett (LB) film is found to exhibit dynamic molecular rearrangement when the humid atmosphere about the sample is changed. The molecular adsorbates stored in a thoroughly dried sample room of FT-IR is found to have a unique adsorption structure; the hydrocarbon chains have a nearly parallel orientation to the substrate surface while the molecules are highly packed to have the orthorhombic subcell packing, which is confirmed by infrared reflection–absorption (RA) spectrometry. When the sample is pulled into an ambient air, the adsorption structure exhibits a drastic change in about only 15 min, which is pursued by polarization-modulation infrared reflection–absorption spectrometry (PM-IRRAS). The spectra clearly indicate that the molecular stance has largely been changed to have a standing-up orientation, whereas the molecular conformation is largely degraded. When the sample is got back to the dried sample room, the molecular conformation largely improves while the standing orientation is kept. These irreversible changes are induced by ambient water molecules adsorbed on the lying stearic acid molecules, which was monitored by analyzing absorption bands of the hydronium ion.

Influence of gas type on velocity splitting of ablated particles

The transport dynamics of the ablated particles is simulated via Monte Carlo simulation. The influences of ambient gases (He, Ne, and Ar dummy gas) on velocity splitting of the ablated particles under 100 Pa are investigated. The results show that the velocity splitting appears in four types of gases. The formation times of velocity splitting of the ablated particles decrease in sequence of He, Ne, dummy gas and Ar. The influences of the mass and radius of ambient gas molecule on the velocity splitting are also investigated. The formation time of the velocity splitting decreases with mass/radius of ambient gas molecule increasing. The intensity is the smallest when the two velocity peak intensities are equal. The formation time of velocity splitting is explained by the underdamping oscillation model and the inertia fluid model. These results give a good foundation for the further study of the Si nanoparticle growth.

Active role of hydrogen bond and ambient water in Meyer–Schuster rearrangements in high‐temperature water

AbstractMeyer–Schuster rearrangements of 2‐phenyl‐3‐butyn‐2‐ol with H3O+ and (H2O)6 model in high‐temperature water (HTW) have been investigated by the use of density functional theory calculations. In the substrate 2‐phenyl‐3‐butyn‐2‐ol catalyzed by H3O+ and (H2O)6, the Meyer–Schuster rearrangements were predicted by the frontier molecular orbital theory. The results show that the rearrangement does not involve the carbonium ion intermediates, but the first transition state is carboniumion like. Dehydration and hydration may occur via the intermolecular proton relay along the hydrogen‐bond chains and the second step of reaction path is a total acid–base catalytic process. Based on the results, a model considered both HTW ambient and water molecules are proposed to represent mechanisms of other reactions in HTW. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Naphthalene and perylene diimides for organic transistors

The development of ambient stable organic n-channel semiconductor molecules for thin-film transistors has experienced a tremendous impetus in the last decade to close the gap in performance in comparison to that of their p-channel counterparts. Especially naphthalene and perylene tetracarboxylic diimides (NDI and PDI) have shown to be the most valuable building blocks to achieve this challenging goal and to gain insight into the molecular structure-transistor performance relationship. Remaining challenges and new emerging research fields for these n-type semiconductors are the optimization of their deposition on flexible substrates, the control of their long term ambient stability and their implementation in complementary transistor circuits, display and sensor devices.

Trap of Biomolecular Ions in the Gas Phase Produced by IR-laser Ablation of Droplet Beam

Abstract We describe a novel method to trap biomolecular ions in the gas phase produced by an IR-laser ablation of a droplet beam. The IR-laser ablation is performed in an ion trap so that the product ions are readily trapped with high efficiency. The ions are thermalized in collisions with the ambient water molecules which are simultaneously produced with the ions by the IR-laser ablation.

Perfluorosulfonic Acid Membrane Catalysts for Optical Sensing of Anhydrides in the Gas Phase

Continuous, on-site monitoring of personal exposure levels to occupational chemical hazards in ambient air is a long-standing analytical challenge. Such monitoring is required to institute appropriate health measures but is often limited by the time delays associated with batch air sampling and the need for off-site instrumental analyses. In this work, we report on the first attempt to use the catalytic properties of perfluorosulfonic acid (PSA) membranes to obtain a rapid, selective, and highly sensitive optical response to trimellitic anhydride (TMA) in the gas phase for portable sensor device application. TMA is used as starting material for various organic products and is recognized to be an extremely toxic agent by the National Institute for Occupational Safety and Health (NIOSH). Resorcinol dye is shown to become immobilized in PSA membranes and diffusionally constrain an orange brown product that results from acid-catalyzed reaction with more rapidly diffusing TMA molecules. FTIR, UV/vis, reaction selectivity to TMA versus trimellitic acid (TMLA), and homogeneous synthesis are used to infer 5,7- dihydroxyanthraquinone-2-carboxylic acid as the acylation product of the reaction. The color response has a sensitivity to at least 3 parts per billion (ppb) TMA exposure and, in addition to TMLA, excludes maleic anhydride (MA) and phthalic anhydride (PA). Solvent extraction at long times is used to determine that the resorcinol extinction coefficient in 1100 EW PSA membrane has a value of 1210 m(2)/g at 271.01 nm versus a value of 2010 m(2)/g at 275.22 nm in 50 vol% ethanol/water solution. The hypsochromic wavelength shift and reduced extinction coefficient suggest that the polar perfluorosulfonic acid groups in the membrane provide the thermodynamic driving force for diffusion and immobilization. At a resorcinol concentration of 0.376 g/L in the membrane, a partition coefficient of nearly unity is obtained between the membrane and solution concentrations and a maximum conversion rate of one ambient TMA molecule for every two membrane-immobilized resorcinol molecules is observed in 15 min.

Optical emission spectroscopy of deposition process of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films by using a coaxial arc plasma gun

Deposition processes of ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films in a hydrogen atmosphere using a coaxial arc plasma gun were spectroscopically investigated with an intensified charge-coupled device (ICCD) camera equipped with narrow-bandpass filters. Strong emissions lasted for more than 100 μs. From the emission time and deposition rate, a supersaturated condition should be strongly realized. This might contribute to the formation of UNCD crystallites. A UNCD crystallite size was estimated to be 2.3 nm from an X-ray diffraction peak. The extremely small value implies that nuclei are repeatedly generated without the subsequent growth. A probable reason is as follows: since the number of carbon species caused using the arc plasma gun is so large as compared to that of hydrogen atoms, which generate from ambient hydrogen molecules by the collision with carbon species, the hydrogen atoms do not effectively contribute to the UNCD crystallite formation. This consideration does not contradict the fact that a coaxial arc plasma gun makes possible UNCD crystallite formation even in vacuum.

Electrical Detection of Negatively Charged Proteins Using n-Type Carbon Nanotube Field-Effect Transistor Biosensors

We fabricated n-type carbon nanotube field-effect transistor (CNTFET) biosensors. To prevent the single-wall carbon nanotube (SWNT)/metal contacts from adsorption of ambient molecules, SiNx passivation films were deposited on CNTFETs by catalytic chemical vapor deposition. CNTFETs with SiNx passivation films on SWNT/metal contacts, but SWNT channels are exposed to environment for sensing, exhibit n-type behavior both in air and solution. Negatively charged bovine serum albumin is successfully detected using the fabricated n-type CNTFET biosensors with SiNx passivation films. Electrical detections of both negatively and positively charged proteins are achieved using n- and p-type CNTFET biosensors, respectively.

Radiation of X-Rays in Low-Pressure Gas Using LiNbO<sub>3</sub> Single Crystal

The gas pressure and the types of ambient gas dependence of X-ray intensity were investigated for LiNbO3 single crystals polarized in the c-axis direction at pressures of approximately 1 to 30 Pa. The integrated X-ray intensity showed a local maximum value at the pressure Pmax. Pmax moved to the high-pressure side in the ambient with a large first ionization energy. Pmax was proportional to the Boltzmann factor using the first ionization energy of each ambient gas molecule. The X-ray intensity was approximated using the quadratic function, which was convex upward for the pressure. It was found that one of the causes of the decrease in X-ray intensity on the pressure side higher than Pmax was the adsorption of positive ions on the crystal electric surface.

Structure and Formation Mechanism of Surface Film of Ag-MoS2 Composite during Electrical Sliding Wear

Abstract Ag-MoS2 composite brushes were fabricated by means of powder metallurgy process. The composite was detected by the method of XRD after sintering, and the worn surface of the brush was analyzed by XPS after the wearing experiments with current. Results showed that the components of the composite didn't change during sintering, but the surface components of it changed upon wearing and some matters such as MoO3 and MoO2 were produced. At the same time, Cu2O, CuO and Cu2S were detected due to the adhesion transfer of elemental Cu from the slipping ring to the brush surface and the reaction between the elemental Cu and the ambient air molecules. During electrical sliding wearing, the surface film can reduce the friction coefficient and be beneficial to the frictional performance of the material.

Radiation of x-rays using polarized LiNbO3 single crystal in low-pressure ambient gas

The dependence of X-ray intensity on the pressure and type of ambient gas was investigated for LiNbO(3) single crystals polarized in the c-axis direction at pressures of approximately 1 to 30 Pa. Ionization of surrounding gas molecules by the electric field generated by the crystal led to the production of both positive ions and free electrons. The electrons were accelerated toward a Cu target, radiating both white X-rays and X-rays specific to the crystal or target material by bremsstrahlung. The integrated X-ray intensity per cycle in the energy range 1 to 20 keV showed a local maximum value at a pressure P(max). The logarithm of P(max) was proportional to the Boltzmann factor using the first ionization energy of each ambient gas molecule. The value of P(max) was found to be independent of the electrical surface area of the crystal. The integrated X-ray intensity was approximated qualitatively by a quadratic function with pressure, which was upwardly convex. It was found that one of the causes of the reduction in X-ray intensity at pressures P > P(max) is the adsorption of positive ions generated by the ionization of gas molecules on the negative electric surface. It was also discovered that the lifetime of the X-ray radiation device could be improved when the X-ray radiation case was covered with another hermetically sealed decompression case. The gas with the smallest first ionization energy, with a partial pressure of P(max), was enclosed inside the X-ray radiation case (inner case) and the gas with the largest first ionization energy was enclosed at a suitable pressure between the inner and outer cases.

Visible laser–induced photoreduction of silver 4‐nitrobenzenethiolate revealed by Raman scattering spectroscopy

AbstractWe have investigated the photochemical characteristics of silver 4‐nitrobenzenethiolate (Ag‐4NBT) by means of Raman spectroscopy. When Ag‐4NBT is irradiated with an argon ion laser at 514.5 nm, its Raman spectrum changes over time, resulting in the production of 4NBT‐capped silver nanoparticles. The surface‐enhanced Raman scattering (SERS) spectrum of 4NBT adsorbed on those Ag nanoparticles is subsequently converted to that of 4‐aminobenzenethiol (4ABT). These surface‐induced photoreduction characteristics were investigated by monitoring the growth of Raman peaks of 4ABT as a function of the laser exposure time. Water vapor or ambient conditions were more effective than vacuum conditions for the photoreduction of 4NBT to 4ABT. Nonetheless, the occurrence of photolysis even under vacuum conditions suggests that the benzene ring hydrogen atoms might be the H‐atom source of the nitro‐to‐amine group conversion although in ambient conditions water or solvent molecules trapped inside the Ag‐4NBT should be the primary H‐atom source and facilitate the transfer of electrons, as well as the diffusion of Ag atoms to form highly SERS‐active nanoaggregates. Copyright © 2009 John Wiley & Sons, Ltd.

N-channel thin-film transistors based on 1,4,5,8-naphthalene tetracarboxylic dianhydride with ultrathin polymer gate buffer layer

N-channel operation of thin-film transistors based on 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) with a 9-nm-thick poly(methyl methacrylate) (PMMA) gate buffer layer was examined. The uniform coverage of the ultrathin PMMA layer on an SiO 2 gate insulator, verified by X-ray reflectivity measurement, caused the increase of electron field-effect mobility because of the suppression of electron traps existing on the SiO 2 surface. In addition, air stability for n-channel operation of the NTCDA transistor was also improved by the PMMA layer which possibly prevented the adsorption of ambient water molecules onto the SiO 2 surface.

Doping of Conjugated Polythiophenes with Alkyl Silanes

AbstractA strong modification of the electronic properties of solution‐processable conjugated polythiophenes by self‐assembled silane molecules is reported. Upon bulk doping with hydrolized fluoroalkyl trichlorosilane, the electrical conductivity of ultrathin polythiophene films increases by up to six orders of magnitude, reaching record values for polythiophenes: (1.1 ± 0.1) × 103 S cm−1 for poly(2,5‐bis(3‐tetradecylthiophen ‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) and 50 ± 20 S cm−1 for poly(3‐hexyl)thiophene (P3HT). Interband optical absorption of the polymers in the doped state is drastically reduced, making these highly conductive films transparent in the visible range. The dopants within the porous polymer matrix are partially crosslinked via a silane self‐polymerization mechanism that makes the samples very stable in vacuum and nonpolar environments. The mechanism of SAM‐induced conductivity is believed to be based on protonic doping by the free silanol groups available within the partially crosslinked SAM network incorporated in the polythiophene structure. The SAM‐doped polythiophenes exhibit an intrinsic sensing effect: a drastic and reversible change in conductivity in response to ambient polar molecules, which is believed to be due to the interaction of the silanol groups with polar analytes. The reported electronic effects point to a new attractive route for doping conjugated polymers with potential applications in transparent conductors and molecular sensors.

Isotopically Selective Infrared Multiphoton Dissociation of 2,3-Dihydropyran

Oxygen isotopic selectivity on infrared multiphoton dissociation of 2,3-dihydropyran has been studied by the examination of the effects of excitation frequency, laser fluence, and gas pressure on the dissociation probability of 2,3-dihydropyran and isotopic composition of products. Oxygen-18 was enriched in a dissociation product: 2-propenal. The enrichment factor of 18O and the dissociation probability were measured at a laser frequency between 1033.5 and 1057.3 cm-1, the laser fluence of 2.2-2.3 J/cm2, and the 2,3-dihydropyran pressure of 0.27 kPa. The dissociation probability decreases as the laser frequency being detuned from the absorption peak of 2,3-dihydropyran around 1081 cm-1. On the other hand, the enrichment factor increases with detuning the frequency. The enrichment factor of 18O increases with increasing the 2,3-dihydropyran pressure at the laser fluence of 2.7 J/cm2 or less and the laser frequency of 1033.5 cm-1, whereas the yield of 2-propenal decreases with increasing the pressure. A very high enrichment factor of 751 was obtained by the irradiation of 0.53 kPa of 2,3-dihydropyran at 2.1 J/cm2. Collisional effect of vibrationally excited molecules with ambient molecules on isotopic selectivity is discussed on the basis of a rate equation model including a collisional vibrational de-excitation process.

Hybrid QM/MM calculations on the structure and electronic properties of hydrated RNA base pair

Structures of hydrated A–U base pair were investigated by using DFT and hybrid ONIOM methods in order to examine the efficacy of the ONIOM (QM:MM) approach in describing the structure of the hydrated RNA base pair. Comparison of these results reveals that the ONIOM (DFT:AMBER) approach, in which the nucleic acid base pair is treated quantum chemically by DFT and ambient water molecules treated by AMBER molecular mechanics, maintains the structures of the hydrated A–U base pair optimized by full DFT quantum chemical methods.

Distribution of 1G0 Plateau Length of Au Contacts at Room Temperature

We have measured the 1G0 (G0 is the conductance quantum unit) plateau length τ of Au breaking contacts at room temperature and examined the plateau-length distribution P(τ) for biases 0.1–2.0 V. We observed that P(τ) exhibits a long tail and obeys the power-law distribution P(τ)∝τ-γ with γ∼1, indicating a strong diversity in the atomic configuration of the Au single-atom contacts. The exponent γ little varies with the bias voltage and ranges between 0.8 and 1.1. We changed the contact breaking conditions, by slowing down the breaking speed and lowering the contact current, and again observed the same power-law distribution for P(τ) with γ∼1, whereas the average plateau length <τ> increases at slower breaks. We also found that the Au 1G0 contacts in air show longer <τ> than those in ultrahigh vacuum, suggesting contact stabilization by ambient air molecules.