Surrounding Gas Molecules Research Articles

Analyze the characteristics of magnetic properties changes in NiFe2O4 induced by trapping polar gas

Our experiments aimed to show that highly polarized Ni-Fe-O materials are affected by polar gases, which change their magnetic properties. Gas molecules adsorbed onto the material changed its magnetic properties due to weak electronic interactions between metal atoms on the interface and surrounding gas molecules. The coercivity and blocking temperature of the material were found to change in opposite directions for ozone was -20 oe and 10 K decrease and carbon monoxide was +40 oe and 20 K increased, owing to their distinct electron affinities. Density Functional Theory calculations supported our findings, revealing that gas adsorption alters the electric field and the spin-charge distribution, leading to a shift in the Fermi level and the movement of the top two layers of atoms due to electrostatic force. These shifts cause changes in the magnetic anisotropy. These changes were reversible upon desorbing the gas from the material's surface, which was facilitated by the molecular attraction between the gas and the material. Overall, our experimental and theoretical results provide a deeper understanding of the impact of polar gas interactions with magnetic material surfaces.

Dynamics of C60 Molecule and Surrounding Gas Molecules

Dynamics of C60 Molecule and Surrounding Gas Molecules

Molecular dynamics simulation of energy transfer in reaction process near supported nanoparticle catalyst

Recent studies of catalysis have highlighted the importance of heat-driven reaction enhancement, suggesting the need for improved understanding of heat transfer in the vicinity of catalyst particles in the reaction process. Specifically, it is essential and necessary to understand the heat of reaction transferred to catalyst particles and surrounding gas molecules in the vicinity of the catalyst surface. In the present study, we developed a method to estimate the ratio of the heat of reaction transferred to the catalyst particle and the gas molecules in the framework of ReaxFF. A molecular dynamics (MD) simulation using the ReaxFF reactive force field is applied to the case of carbon monoxide oxidation on the surface of a platinum nanoparticle. To estimate the amount of thermal energy transferred to the catalyst particle and the gas molecules during the reaction, we propose a calculation method using the interfacial thermal conductance (ITC) between the gas molecules and the solid surface. The thermal energy transferred in the vicinity of the particle was calculated from the results of MD simulation, and the heat conduction from the gas molecules to the catalyst and the substrate was calculated using the ITC. This study found that the heat of reaction transferred to the catalyst particle was of the same order as that transferred to the gas molecules in the catalytic reaction process investigated.

Surrounding gas composition affects the calling song development in the two-spotted cricket (Gryllus bimaculatus).

Male crickets emit acoustic signals (i.e., songs) by chirping using their forewings. Although the mechanisms and adaptive functions of these songs are well studied, knowledge about how songs develop within a generation is relatively scarce. Our previous work demonstrated a stable peak frequency at 5.7 kHz in the calling songs recorded from mature adult male crickets (Gryllus bimaculatus). In the present study, we monitored changes in the frequency component over time from the sexual maturity stage (early adult stage). We recorded 300 calling songs from a pool of 122 adults. The peak frequency distribution was lower and unstable (i.e., greater coefficient of variance) in the early adult stage. The mean peak frequency was 4.9 kHz on day 3, but gradually converged to 5.8 kHz over the 2-week adult stage. Immature adult males (emitting immature songs) produced an appropriately tuned song with a peak frequency of 5.8 kHz in an environment of 80% helium and 20% oxygen. These results suggest that the frequency component of the calling song is acquired during the early to mid-adult stage, and may be related to sexual maturation in males. Findings from the helium substitution experiment revealed that physical resistance from surrounding gas molecules negatively affect the stability of male singing, and that muscle development and forewing hardening may contribute to the maturation of singing, suggesting that females may adaptively select sexually mature males based on song traits.

Detection of Airborne Nanoparticles through Enhanced Light Scattering Images.

A new method is proposed in this paper to detect airborne nanoparticles, detecting the light scattering caused by both the particle and the surrounding molecules, which can surpass the limitations of conventional laser optical methods while maintaining simplicity and cost-effectiveness. This method is derived from a mathematical analysis that describes the particle light scattering phenomenon more exactly by including the influence of light scattered from surrounding gas molecules. The analysis shows that it is often too much of a simplification to consider only light scattering from the detected nanoparticle, because light scattering from the surrounding gas molecules, whether visible or invisible to the sensor, is important for nanoparticle detection. An image detection approach utilizing the light scattering from surrounding air molecules is described for the detection of airborne nanoparticles. Tests using monodisperse nanoparticles confirm that airborne particles of around 50 nm in size can even be detected using a low-cost testing device. This shows further that even when using a simple image processing code, captured particle light scattering images can be converted digitally into instantaneous particle counts or concentrations. The factors limiting conventional pulse detection are further discussed. This new method utilizes a simple static light scattering (SLS) approach to enable the development of new devices with better detection capabilities, paving the way for the further development of nanoparticle detection technology.

Equivalent circuit model for the damping of micro-oscillators from molecular to viscous flow regime

This paper presents an equivalent circuit (EQC) model for describing the damping mechanism of micro-oscillators from the molecular flow regime up to the viscous flow regime. The EQC model consists of two parallel lines, representing the molecular and the viscous damping mechanism, respectively. The molecular line consists of an R–L circuit, which describes the intrinsic losses and the transfer of kinetic energy from the micro-oscillator to the surrounding gas molecules. The viscous line is formed by a resistor and a newly introduced inductive constant phase element. These elements represent the thermoviscous losses and the collision processes in the viscous flow regime. This EQC model was applied to the first fundamental bending mode of an oscillator vibrating in seven different types of gases (He, Ne, Ar, N2, CO2, N2O, SF6) as well as to the first five bending modes for another type of oscillator vibrating in nitrogen gas, only. In all cases, variations of an adjustable gap width to a fixed plate in the range of 150–3500 µm were also taken into account. The results from the presented EQC model are found to be in excellent agreement with the experimental data. Additionally, the electronic components of the EQC can be correlated to real physical properties of the setup, i.e. to the viscosity and density of the gas, as well as to the adjusted gap width and to the resonance frequency of the micro-oscillator. This allows the prediction of the quality factor curve of an oscillator over a large pressure range in a simple way for various configurations, concerning gas type, gap width, and bending mode/resonance frequency. Based on these results, an optimization model and design rules for enhancing the quality factor were derived.

An immersive resonant sensor with microcantilever for pressure measurement

A micro electromechanical systems (MEMS) resonant sensing chip with microcantilever has been developed to measure gas pressure by immersing it in gaseous environment. The microcantilever was designed to sense surrounding gas molecules loading, owing to the gas density sensitive to the pressure, then the resonant frequency shifts of sensing chip were induced under different pressures. Especially, the sensing chip featuring no diaphragm realized embedded package and installation for the immersive measurement. The resonance response of the sensing chip for target pressure was theoretically analyzed and simulated, and a packaged pressure sensor with the proposed sensing chip was tested under flexural and torsional modes of the microcantilever. The experimental results proved that the proposed sensor had preferable measuring performance under the torsional mode with the RSS (root sum square) accuracy of 0.21%FS in the working range of 10–560 kPa. The temperature compensation was presented to alleviate the temperature disturbance for the sensor, and the maximum deviation of the frequency was 59 ppm over the full pressure and the temperature range of 26–55 ℃. The proposed sensing chip is potentially a better choice for pressure sensors with measurement demand for immersive gas pressure.

Probing electron beam effects with chemoresistive nanosensors during in situ environmental transmission electron microscopy

We report in situ and ex situ fabrication approaches to construct p-type (CuO) and n-type (SnO2) metal oxide nanowire devices for operation inside an environmental transmission electron microscope (TEM). By taking advantage of their chemoresistive properties, the nanowire devices were employed as sensitive probes for detecting reactive species induced by the interactions of high-energy electrons with surrounding gas molecules, in particular, for the case of O2 gas pressures up to 20 mbar. In order to rationalize our experimental findings, a computational model based on the particle-in-cell method was implemented to calculate the spatial distributions of scattered electrons and ionized oxygen species in the environmental TEM. Our approach enables the a priori identification and qualitative measurement of undesirable beam effects, paving the way for future developments related to their mitigation.

The effect of a gas environment on the fluorescence intensity of quantum-dot composite systems

The fluorescence kinetics of a composite structure based on colloidal CdSe/ZnS core-shell quantum dots deposited on an array of GaAs nanowires in atmospheres of different gases is studied upon excitation by cw laser radiation. It is suggested that the fluorescence enhancement mechanism consists in the transfer of part of the vibrational energy of quantum dots to surrounding gas molecules due to inelastic collisions.

Suspended single-walled carbon-nanotube field-effect transistor for gas sensing application

We investigate the pressure dependence of transfer characteristics of suspended single-walled carbon-nanotube field-effect transistors. We find that the gate bias around the charge neutral point with low drain current is appropriate for gas sensing application, while the high gate bias condition with high drain current that induces Joule heating in the suspended region for the desorption of the adsorbed molecules is preferable for the vacuum gauge application based on the heat exchange surrounding gas molecules, where the temperature at the suspended channel is investigated based on the simple one-dimensional heat transport model. We also revealed that the pressure dependence of the channel conductance at the gate bias around the charge neutral point can be explained by the Langmuir isotherm.

Wear equation for adhesive wear established through elementary process of wear

The research covers the wear processes of adhesive wear from the origin of wear elements (the unitary debris of wear) with a size from a few nanometers to a few tens of nanometers to form transfer particles and lastly wear particles. These particles and wear phenomenon were observed by means of atomic force microscopy (AFM). Furthermore, the formation process of wear particles between the sliding surfaces was optically observed by means of an in situ observation system. From the results of observation of the wear process, we propose a basic wear model of the adhesive wear mechanism and present a wear equation for adhesive wear including physical properties of the sliding surfaces as well as the chemical effect of surrounding gas molecules to the surfaces.

Direct observation of heat dissipation in individual suspended carbon nanotubes using a two-laser technique

A two-laser technique is used to investigate heat spreading along individual single walled carbon nanotube (SWCNT) bundles in vacuum and air environments. A 532 nm laser focused on the center of a suspended SWCNT bundle is used as a local heat source, and a 633 nm laser is used to measure the spatial temperature profile along the SWCNT bundle by monitoring the G band downshifts in the Raman spectra. A constant temperature gradient is observed when the SWCNT bundle is irradiated in vacuum, giving direct evidence of diffusive transport of the phonons probed by the Raman laser. In air, however, we observe an exponentially decaying temperature profile with a decay length of about 7 μm, due to heat dissipation from the SWCNT bundle to the surrounding gas molecules. The thermal conductivity of the suspended carbon nanotube (CNT) is determined from its electrical heating temperature profile as measured in vacuum and the nanotube bundle diameter measured via transmission electron microscopy. Based on the exponential decay curves measured in three different CNTs in air, the heat transfer coefficient between the SWCNTs and the surrounding air molecules is found to range from 1.5 × 103 to 7.9 × 104 W/m2 K, which is smaller than the 1 × 105 W/m2 K thermal boundary conductance value calculated using the kinetic theory of gases. This measurement is insensitive to the thermal contact resistance, as no temperature drops occur at the ends of the nanotube. It is also insensitive to errors in the calibration of the G band temperature coefficient. The optical absorption is also obtained from these results and is on the order of 10−5.

Light-Powered Micromotor: Design, Fabrication, and Mathematical Modeling

This paper reports on the experimental and theoretical studies of a light-driven micromotor, which is a “light mill” that rotates by absorbing photon energy. This light mill has four curved blades to form an axially asymmetric geometry. Upon lateral irradiation, the shape of the light mill induces an asymmetric photon heating to the surrounding gas molecules, leading to a gas convection that forces the light mill to rotate. The light mill was applied to actuate a scanning mirror for a laser beam. Using a Direct Simulation Monte Carlo (DSMC) model, we investigated the working principle behind the operation of the light mill. The DSMC simulation yielded results consistent to our experimental data. The simulation results were used to explain the heat-induced light-mill rotation, in which the mean free path of the surrounding gas takes an important role.

The effect of gas environment on electrical heating in suspended carbon nanotubes

We report micro-Raman spectroscopy measurements of the temperature distribution of current-carrying, 5 μm long, suspended carbon nanotubes in different gas environments near atmospheric pressure. At the same heating power, the measured G band phonon temperature of the nanotube is found to be significantly lower in gaseous environments than in vacuum. Theoretical analysis of these results suggests that about 50%–60% of the heat dissipated in the suspended nanotube is removed by its surrounding gas molecules, and that the thermal boundary conductance is higher in carbon dioxide than in nitrogen, argon, and helium, despite the lower thermal conductivity of carbon dioxide.

Light-powered micromotor driven by geometry-assisted, asymmetric photon-heating and subsequent gas convection

We report on the design, fabrication, and analysis of a light-driven micromotor. The micromotor was created from a nanoporous polymer with close-packed gold nanoparticles which generate heat by absorbing light. The blades of the micromotor were curved, forming convex and concave sides. Upon lateral irradiation, by geometric effect the convex side transfers more photon-generated heat to the surrounding gas molecules, causing a convective motion of gas and leading to the rotation of the micromotor. The light-driven motions of gas molecules were analyzed using molecular dynamics modeling.

Batch-processed carbon nanotube wall as pressure and flow sensor

A pressure and flow sensor based on the electrothermal-thermistor effect of abatch-processed carbon nanotube wall (CNT wall) is presented. The negative temperaturecoefficient of resistance (TCR) of CNTs and the temperature dependent tunneling ratethrough the CNT/silicon junction enable vacuum pressure and flow velocity sensingbecause the heat transfer rate between CNTs and the surrounding gas molecules differsdepending on pressure and flow rate. The CNT walls are synthesized by thermal chemicalvapor deposition (CVD) on an array of microelectrodes fabricated on a silicon-on-insulator(SOI) wafer. The CNTs are self-assembled between the microelectrodes and substrateacross the thickness of a buried oxide layer during the synthesis process, and the simplebatch fabrication results in high throughput and yield. A wide pressure range, down to3 × 10 − 3 from105 Pa, and a nitrogen flow velocity range between 1 and 52.4 mm s − 1, are sensed. Further experimental characterizations of the bias voltage dependent responseof the sensor as a vacuum pressure gauge are presented.

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.

Photosynthesis of nanoparticles

This work is devoted to an overview of the physical processes that underlie a recently developed method for the photosynthesis of nanoparticles. The results of nanoparticle synthesis under the condensation of supersaturated atomic vapor produced by the photodissociation of carbon- and metal-bearing compounds are demonstrated. The different factors affecting the formation kinetics of carbon and metal nanoparticles are analyzed. The type and pressure of the diluent gas are shown to play a significant role in the particle growth processes. The influence of energy exchange processes between the excited clusters and surrounding gas molecules on the rate and mechanism of condensation is analyzed.

Photophoresis—Light induced motion of particles suspended in gas

When irradiated sideways, by visible light, a particle can perform different kinds of motion, (e.g. in direction of irradiation, opposite to irradiation, vertical movement, helicoidally, etc.). This phenomenon is called photophoresis. Photophoresis is based on momentum transfer between the aerosol particle and surrounding gas molecules. Photophoresis strongly depends on the pressure of the surrounding gas. Particles mostly influenced by photophoresis are those of μm size. Two main types of forces describe photophoretic motion: Δ T force: The thermal accommodation coefficient α is constant over the particle surface. As a result of the thermal accommodation, gas molecules on the warm side of a particle leave the surface faster than gas molecules on the cold side. This leads to Δ T force on the particle towards the colder side. Typical motion of the particle will be either away from light irradiation ( positive photophoresis), or in direction of light irradiation ( negative photophoresis). In the case of negative photophoresis, the back side of the particle, due the nature of light absorption, will be heated more than front side of the particle. Δ α force: If the particle is at a constant temperature, which is different from the temperature of the surrounding gas, and the thermal accommodation coefficient α varies over the particle surface, the net momentum between gas molecules and particle will be transferred. In this case, the result will be body fixed Δ α force. Depending on the particle surface properties, Δ α force can direct the particle in any possible photophoresis could also play important role in planet formation and astrophysics.

Molecular dynamics simulations of translational thermal accommodation coefficients for time-resolved LII

Time-resolved laser-induced incandescence demands precise knowledge of the thermal accommodation coefficient, but little is known about the gas-surface scattering physics that underlies this parameter. This paper presents a molecular dynamics simulation that shows how the thermal accommodation coefficient is influenced by the gas molecular mass and gas temperature. The molecular dynamics results also define scattering kernels that can be used as boundary conditions in Direct Simulation Monte Carlo simulations of heat and momentum transfer between soot aggregates and surrounding gas molecules.