Fused Quartz Surface Research Articles

Electromagnetic particle simulation of secondary electron multipactor characteristics in inner surface of 110 GHz microwave output window

The secondary electron multipactor on the inner surface of the output window is one of the main factors limiting the power capacity of high power microwave. Therefore, it is of great significance to carry out relevant research. In this work, the process of secondary electron multipactor and the resulting loss of power are numerically simulated by using the electromagnetic particle model with one-dimensional spatial distribution and three-dimensional velocity distribution at the microwave frequency of 110 GHz. The influences of microwave electric field at the surface and dielectric material type on the power loss are studied. The simulation results show that the electron number density is higher than the critical cut-off number density after the secondary electron multipactor has reached the steady state, but the microwave electric field does not show obvious change. This is because the electrons in a very high electrostatic field are mainly concentrated in the domain of several micrometers near the dielectric surface, which is far less than the corresponding skin depth. The electron number density in the multipactor steady state increases with the microwave electric field increasing, but the ratio of the power loss to the microwave power at the surface increases slowly. After the multipactor reaches the steady state, the number density of electrons near the sapphire surface is the highest, followed by the number density near the crystal quartz surface, and the number density near the fused quartz surface is the lowest, so the corresponding power loss decreases successively. In order to verify the accuracy of the model, the simulated value of the multipactor threshold is compared with the experimental data, and the difference between them is discussed.

Polylysine Adsorption on Fused Quartz Surface

The kinetics of adsorption of two polylysine samples with different molecular weights from aqueous solutions on the surface of fused quartz has been studied by the capillary electrokinetics method. It has been found that the adsorption of positively charged polylysine on the negatively charged quartz surface decreases the absolute value of the initial ζ potential; moreover, in the case of polylysine with the higher molecular weight, it leads to the reversal of the surface charge. The constant values of the ζ potential and the times for which these values are reached depend on the molecular weight and concentration of polylysine. The rate of variations in the ζ potential is highest during the first several minutes of the solution contact with the surface. A decrease in the electric conductivity during polylysine adsorption has, for the first time, been observed, thus leading to a hypothesis that large aggregates are formed on the quartz surface. The measurement of the deformability of the layers has shown that, under our experimental conditions, dense undeformable layers are formed. Polylysines are irreversibly adsorbed on the quartz surface.

Molecular-Dynamics-Derived Gas–Surface Models for Use in Direct-Simulation Monte Carlo

In the present work, molecular dynamics is used to study molecular nitrogen impinging on multilayered graphene and fused-quartz surfaces at different incidence speeds and angles to obtain energy accommodation coefficients for use in direct-simulation Monte Carlo. The trajectory molecular dynamics simulations were performed on these two surfaces to study the difference between atomistically smooth and rough cases. Based on the postcollision behavior of the nitrogen molecule, the molecular dynamics trajectories were classified into three categories, namely, single, and multiple with and without escape. The collision statistics for the three categories were found to depend on the incidence angle and the speed, and a strong correlation among incidence speed, angle, and surface topology in the probability distribution of the energy accommodation coefficients was observed. A direct-velocity-sampling gas–surface interaction model was implemented in direct-simulation Monte Carlo, which was found to predict flow and surface properties comparable to the Maxwell gas–surface interaction model when the molecular dynamics data used for velocity sampling were obtained from a rough (diffuse) surface.

Production of hyperpolarized H_{2} molecules from H[over →] atoms in gas-storage cells.

The preservation of the nuclear polarization of hydrogen atoms during the recombination to molecules was observed on different surface materials in the temperature range from 45 to 100K and for magnetic fields up to 1T. On a gold and a fused quartz surface, the expected molecular polarization of about 50% or lower of the atomic polarization was measured, while a surface layer of perfluoropolyether (Fomblin) shows a nearly complete preservation (at least 97%) of the atomic polarization during the recombination process. Further experiments have the possibility of storing polarized deuterium molecules and to use them in nuclear-fusion installations. Another application might be the production of polarized substances for enhanced NMR techniques.

Time Correlation Function Modeling of Third-Order Sum Frequency Vibrational Spectroscopy of a Charged Surface/Water Interface.

Sum frequency vibrational spectroscopy (SFVS), a second-order optical process, is interface-specific in the dipole approximation [Perry, A.; Neipert, C.; Moore, P.; Space, B. Chem. Rev. 2006, 106, 1234-1258; Richmond, G. L. Chem. Rev. 2002, 102, 2693-2724; Byrnes, S. J.; Geissler, P. L.; Shen, Y. R. Chem. Phys. Lett. 2011, 516, 115-124]. At charged interfaces, the experimentally detected signal is a combination of enhanced second-order and static-field-induced third-order contributions due to the existence of a static field. Evidence of the importance/relative magnitude of this third-order contribution is seen in the literature [Ong, S.; Zhao, X.; Eisenthal, K. B. Chem. Phys. Lett. 1992, 191, 327-335; Zhao, X.; Ong, S.; Eisenthal, K. B. Chem. Phys. Lett. 1993, 202, 513-520; Shen, Y. R. Appl. Phys. B: Laser Opt. 1999, 68, 295-300], but a molecularly detailed approach to separately calculating the second- and third-order contributions is difficult to construct. Recent work presented a novel molecular dynamics (MD)-based theory that provides a direct means to calculate the third-order contributions to SFVS spectra at charged interfaces [Neipert, C.; Space, B. J. Chem. Phys. 2006, 125, 224706], and a hyperpolarizability model for water was developed as a prerequisite to practical implementation [Neipert, C.; Space, B. Comput. Lett. 2007, 3, 431-440]. Here, these methods are applied to a highly abstracted/idealized silica/water interface, and the results are compared to experimental data for water at a fused quartz surface. The results suggest that such spectra have some quite general spectral features.

Structure of adsorbed molecular layer on fused quartz surface determined sequentially in sodium stearate solution, dry Ar, pure water, and dry Ar by sum frequency generation spectroscopy

Adsorption behavior of sodium stearate molecules at fused quartz/solution interface was studied by sum frequency generation (SFG) spectroscopy. SFG spectra were sequentially obtained at the interface of sodium stearate solution/fused quartz, Ar gas/fused quartz, water/fused quartz, Ar gas/fused quartz. No peak due to sodium stearate was observed in the sodium stearate solution but strong peaks due to CH stretching of CH3 group and a small peak due to CH stretching of CH2 group appeared after the stearate solution was replaced by Ar, showing the presence of the stearic acid monolayer with very high conformational order under Ar gas flow. No SFG signal was detected when pure water was made contact to the fused quartz surface and SFG signal reappeared again after water was replaced by Ar, showing that the stearic acid monolayer was present on the fused quartz surface but was totally disordered in water. Time dependent SFG measurements showed that the adsorption of stearic acid molecules on the fused quartz surface was very fast and completed within 5s. Furthermore, it was found that the amount and conformational order of stearic acid molecules on the fused quartz surface determined by SFG measurements under Ar flow depended on the concentration of stearate in solution. They increased as concentration increased and were almost constant when the concentration was higher than 100μM. A slightly decreased was detected at critical micelle concentration (CMC), 400μM. No peaks were observed above CMC due to a totally disordered structure.

Evanescent wave spectroscopy of methylene blue solutions at surfaces using a continuum generated by a nonlinear fiber

The way organic thin films properties are affected by molecular interactions at surfaces is an important research topic because thin molecular films constitute a model system for biological research and have applications ranging from light-emitting diodes and solar cells to chemical sensors. In this work, the formation of thin films of Methylene Blue in aqueous solution at a fused quartz surface was investigated with evanescent wave absorption spectroscopy, using a continuum spectrum generated in a non-linear fiber by short laser pulses.

Dipole effects on molecular and electronic structures in a novel conjugate of oligo(phenyleneethynylene) and helical peptide

A novel conjugate of a helical nonapeptide and an oligo(phenyleneethynylene) (OPE) having a nitro group at a molecular terminal was synthesized. Both components have a dipole. The peptide has a disulfide group at the N-terminal for immobilization on gold. In order to investigate the electric field effect of the helical peptide dipole on the OPE and molecular structure by the dipole-dipole interaction between the two components, the electronic structure of the OPE was spectroscopically studied in solution, the self-assembled monolayer on gold, and Langmuir-Blodgett (LB) layers on a fused quartz surface. The absorption maximum (lambda(max)) of the OPE component in chloroform is red-shifted by 4 nm from the reference OPE derivative without the helical peptide component. The red shifts of the OPE component are also observed in the LB monolayer and bilayer compared with that of the self-assembled monolayer. The observed dipole effect of the peptide on the OPE electronic structure was quantitatively discussed with ab initio calculations. Antiparallel orientation on the dipole directions of the peptide and the OPE components is considered to explain the red shifts via the dipole effect on the electronic structure of the OPE.

A29 Ion-bombardment-enhanced etching of quartz(M4 processes and micro-manufacturing for science)

Mask-free and rapid patterning of fused quartz surface is useful for various applications, such as rapid prototyping of optical elements and UV nanoimprint molds. We examined the fabrication of patterned quartz for such applications by ion-bombardment-enhanced etching using buffered hydrofluoric acid as the etching solution.

Second‐harmonic generation from Langmuir–Blodgett film of cyclic peptide carrying two disperse red 1 on fused quartz surface

Cyclic octapeptide carrying one or two nonlinear optical chromophores, disperse red 1 (DR-1), was synthesized and immobilized on a substrate to attain an active surface for second-harmonic generation (SHG). Each cyclic octapeptide was transferred on a fused quartz substrate by the Langmuir-Blodgett (LB) method to afford a uniform monolayer. Infrared reflection-absorption spectroscopy of the LB monolayer revealed that the cyclic skeleton lay roughly flat on the surface. The SHG intensity from the monolayer of the cyclic peptide with two DR-1 units was stronger than that from that with one DR-1 unit. The difference is discussed in terms of molecular orientation and surface density of the active chromophores. The cyclic peptide is shown here to be an effective scaffold to modify a substrate surface with functional groups of a monolayer with taking stability of the monolayer and orientation of the functional group into consideration.

Nanoscale slip measurements using a torsional ultrasonic oscillator

The first experimental measurements of surface slip using a torsional ultrasonic oscillator have been carried out. Slip was measured at the interface between water and a roughened fused quartz surface coated with a hydrophobic fluoropolymer surfactant. The magnitude of the slip length b was calculated to be 50nm for 40kHz oscillations at shear rates ranging from 500 to 3500s−1. This value is broadly in agreement with comparable data in the literature. Reliable quantitative measurements of this type are important for effective study of the surface slip mechanism for Newtonian fluids.

Basic Study of Nano-Grinding

The purpose of this study is to obtain a basic knowledge required to analyze the material removal mechanism in the nano-grinding. In this report, in order to make clear the nanoscale removal processes in constant-force grinding, fundamental experiments to generate a nanoscale grinding groove on an ultra-precise polished fused quartz surface are conducted under a constant normal force using the atomic force microscope combined with two-axis capacitive force/displacement transducer. When increasing the normal force, three different regions in the normal force in which the different mechanism of groove formation take places are found. They are an elastic deformation region without remaining deformation, a plastic deformation region in which the groove is dominantly formed by plastic flow and a removal process region in which the groove is dominantly formed by removal process. The minimum normal force fnR at which the removal process begins is about 33.7 μN and in this case the groove with a depth of about 4.3 nm is formed. The critical normal force fnR is identified from a characteristic change in a ratio of normal and tangential forces with increasing normal force.

Regularities of the Two-Layer Adsorption of Anionic Surfactant and Cationic Polyelectrolyte on the Fused Quartz Surface

The adsorption of sodium dodecyl sulfate (SDS) on the quartz capillary surface that was preliminarily covered with a layer of cationic polyelectrolyte (CPE) is studied. The charge sign change of the modified quartz surface and subsequent increase of negative surface charge observed upon the adsorption of SDS indicate the formation of the second adsorption layer composed of surfactant molecules. It is shown that the surfactant layer is stronger attached to the surface at a higher charge of the CPE adsorption layer. Upon the formation of the surfactant layer on a looser CPE adsorption layer, the desorption of SDS molecules decreases, which can be associated with the partial penetration of these molecules into the CPE layer.

Formation of two-dimensional periodic nanostructures on fused quartz, polyimide, and polycrystalline diamond by pulsed four-wave interference laser modification

Atomic force microscopy is used to examine the topography of submicron periodic structures formed on the surfaces of synthetic polycrystalline diamond and polyimide films. The films are deposited on fused quartz substrates by four-wave interference modification using a pulsed 308-nm UV XeCl excimer laser. It is demonstrated that a two-dimensional periodic relief with a submicron period can be formed on the diamond surface directly by laser evaporation in the absence of a photoresist. Depending on the exposure, two mechanisms of polyimide film modification are observed. At exposures less than 100 mJ/cm2, the relief is formed due to swelling at the positions of interference maxima. At exposures greater than 100 mJ/cm2, holes are formed in the films. A periodic relief on the fused quartz surface is formed by using a UV photoresist exposed to pulsed interference laser radiation and subsequent Ar ion etching.

Spectroscopy of cesium atoms adsorbing and desorbing at a dielectric surface

We use evanescent waves in a counterpropagating beams configuration to study the adsorption/desorption processes at a Cs vapor/dielectric interface in a sealed cell. Atoms close to the surface are velocity-selectively spin-polarized before adsorption by an amplitude-modulated pump beam. We subsequently observe the contribution of the desorbed atoms to the probe-beam absorption by way of phase-sensitive detection. We measure the number of desorbing polarized Cs atoms as a function of the surface temperature. The analysis of results is done through a simple thermodynamical model for the atomic desorption and we discuss its validity to infer the adsorption energy of the cesium atoms on a fused-quartz surface.

Growth of c-diamond, n-diamond and i-carbon nanophases in carbon-ion-implanted fused quartz

Abstract Combined high-resolution transmission electron microscopy, selected-area electron diffraction and parallel electron-energy-loss spectroscopy are used to characterize nanophases of carbon found embedded in fused quartz. These appear after implantation of 1 MeV carbon ions, followed by annealing in argon, oxygen and forming gas for lh at 1100°C. For argon, virtually all the carbon diffuses out of the substrate with no observable carbon clusters for all doses studied. After annealing in oxygen, a crystalline CO x phase is identified at the end of range, following a dose of 5 × 1017 carbon ions cm−2. Three nanocrystalline carbon phases, including diamond, appear after annealing in forming gas; these form a layer 170 nm beneath the fused quartz surface for all ion doses. The average size of these clusters and the corresponding phases depend on the ion dose; the smallest clusters of 5-7 nm diameter crystallize as fcc Fd3m diamond following a dose of 0.5 × 1017 carbon ions cm−2, whereas clusters of 8–13...

NANO-CRYSTALS OF c-DIAMOND, n-DIAMOND AND i-CARBON GROWN IN CARBON-ION IMPLANTED FUSED QUARTZ

Combined high-resolution transmission electron microscopy, selected area electron diffraction and parallel electron energy loss spectroscopy are used to characterise carbon nano-phases found embedded in fused quartz. These appear after implantation of 1 MeV carbon ions, followed by annealing in argon, oxygen and forming gas for 1 hour at 1100°C. For Ar, virtually all of the carbon diffuses out of the substrate with no observable carbon clusters for all doses studied. After annealing in oxygen, a crystalline CO x phase is identified at the end of range, following a dose of 5×1017 C/cm 2. Three nano-crystalline carbon phases, including diamond, appear after annealing in forming gas: these form a layer 170 nm beneath the fused quartz surface for all ion doses. The average size of these clusters and the corresponding phases depend on the ion dose; the smallest size of 5–7 nm diameter crystallise as fcc [Formula: see text] diamond following a dose of 0.5× 1017 C/cm 2, whereas clusters of 8–13 nm diameter, for a higher dose of 2× 1017 C/cm 2, have a [Formula: see text] modified phase of diamond known as n-diamond. The largest clusters, diameter 15–40 nm, for a dose of 5× 1017 C/cm 2, have the cubic P2 13 (or P4 232) structure known as i-carbon. These buried layered diamond and diamond-related materials may have applications for field emission and optical waveguide type devices.

Sum frequency generation study on the molecular structures at the interfaces between quartz modified with amino-terminated self-assembled monolayer and electrolyte solutions of various pH and ionic strengths

The structures of water at the interfaces between a fused quartz surface modified by a self-assembled monolayer (SAM) of an amino-terminated silane molecule and electrolyte solutions of various pH and ionic strengths were investigated using sum frequency generation (SFG) vibrational spectroscopy. The structure of the interfacial water strongly depended on the pH of the solution. The effect of the electric double layer generated by the protonation of the amino groups in the SAM and unreacted silanol groups on the quartz substrate at low and high pH, respectively, is considered to be responsible for the pH-dependent SFG behavior.

Sum frequency generation (SFG) study of the pH-dependent water structure on a fused quartz surface modified by an octadecyltrichlorosilane (OTS) monolayer

The interface-sensitive spectroscopic method, sum frequency generation (SFG), has been used to investigate the interfacial water structure on a fused quartz surface modified by an octadecyltrichlorosilane (OTS) self-assembled monolayer in phosphate buffered solutions at various pHs. The experimental results demonstrate that the water molecules at the quartz/OTS surface flip while the water molecules at the OTS surface maintain their orientation when the solution pH is changed from neutral to acidic. The results show that most of the silanol groups still exist on the fused quartz surface even after a silane coupling reaction of OTS under the reported experimental conditions.

PH-Dependent Water Structure at a Quartz Surface Modified with an Amino-Terminated Monolayer Studied by Sum Frequency Generation (SFG)

Abstract The structures of water at the interfaces between a fused quartz surface modified by a self-assembled monolayer (SAM) of an amino-terminated silane molecule and electrolyte solutions of various pHs were investigated using sum frequency generation (SFG) vibrational spectroscopy. The structure of the interfacial water significantly depended on the solution pH. The effect of the electric double layer generated by the protonation of the amino groups in the SAM and unreacted silanol groups on the quartz substrate is considered to be responsible for the pH-dependence.