Graphene transistor as a probe for streaming potential

We explore the dependence of electrical transport in a graphene field effect transistor (GraFET) on the flow of water/sodium chloride electrolyte within the immediate vicinity of that transistor. We find large and reproducible shifts in the charge neutrality point of GraFETs that are dependent on the liquid velocity and the ion concentration. We show that these shifts are consistent with the variation of the local electrochemical potential of the liquid next to graphene that are caused by the fluid flow (streaming potential). Furthermore, we utilize the sensitivity of electrical transport in GraFETs to the parameters of the fluid flow to demonstrate graphene-based mass flow and ionic concentration sensing. We successfully detect a flow as small as ～70 nL/min and detect a change in the ionic concentration as small as ～40 nM.     

Interaction of a high-energy proton beam with a thick target: A model description

We present a simple model to calculate energy distributions and multiplicities of the neutrons emitted in the interaction of a high-energy proton with a thick target. It is based on a dE/dx formula proposed by Cugnon for the proton energy loss inside nuclear matter and on the assumption that the dissipated energy eventually becomes thermalized. Comparison with the results of existing codes and available data is made. An application to the determination of the sensitivity of multiplicities to various input parameters (e.g. the level density parameter) is described. The model is shown to provide further physical insight into the standard spallation codes.     

Comparison of sensitivity functions for ideal probe and ring-type heads

Analytical models of ideal infinitesimally thin probe-type heads have been presented and compared with a model of an ideal ring-type head. It is shown that with respect to readback resolution the characteristics of probe models are inferior to those of the ring model. It is also shown that resolution of the probe model is reduced further if media with a soft magnetic underlayer is used.     

Xenon as a probe for minority sites on solid surfaces

Atomic-level microscopies have proved useful to map solid-surface sites directly, but, because of their lack of chemical specificity, they are less adept at identifying unique chemical activity on those sites. Here we present a dual-titration approach developed to probe minority sites on solid surfaces with unique chemical properties of potential relevance to heterogeneous catalysis. Our methodology involves the initial dosing of a chemical probe such as carbon monoxide or ammonia to drive its selective adsorption onto specific sites with particular chemical activity, and the subsequent adsorption of xenon to help identify the nature of those sites. A combination of photoelectron and temperature-programmed desorption spectroscopies are used to characterize the Xe adsorption. The chemistry of oxygen-modified Ni(110) single crystals was probed to test this technique. It was observed that whereas CO does not discriminate among the various sites present on those surfaces, ammonia binds preferentially to the end of -Ni-O rows and modifies their local electrostatic potential. In addition, it was determined that adsorbed CO aids in a reversible surface reconstruction involving the coalescence of fragmented surface -Ni-O rows at high (>350 K) temperatures.     

Effect of frictional force and nose shape on axisymmetric deformations of a thick thermoviscoplastic target

Summary We study thermomechanical deformations of a thermally softening viscoplastic thick target impacted at normal incidence by a cylindrical rod made of a material considerably harder than the target material. Thus we regard the penetrator to be rigid and analyze the effect of the penetrator nose shape and the frictional force at the target/penetrator interface on target's deformations. In the postulated expression for the frictional force, the coefficient of friction, defined as the ratio of the tangential force at a point to the normal force there, is a function of the relative speed of sliding between the two bodies. The computed depth of penetration is found to match very well with that observed in experiments by Forrestal et al. For each nose shape studied, the consideration of frictional forces reduces significantly the computed penetration depth. For the same kinetic energy of the penetrator, the penetrator with a sharp nose gives higher values of the penetration depth as compared to that obtained with a blunt nose.     

Unmodified gold nanoparticles as a colorimetric probe for visual methamphetamine detection

In recent years, in addition to the classic drugs, addiction to a series of new drug classes known as club drugs has increased significantly. Fast and low-cost bioassay for the detection of amphetamine-based drugs can be an effective strategy towards reducing their abuse. In this study, we designed a sensitive bioassay strategy using gold nanoparticles (GNPs) and the aptamers that possess high affinity toward methamphetamine (MA). It is suggested that the aptamer adopts different tertiary structures in the presence and/or absence of its specific target and GNPs can effectively differentiate between these two states by their characteristic surface plasmon resonance-based colour change. Visual detection of MA and 3,4-methylenedioxy-N-methylamphetamine (MDMA) in the low micromolar range is possible within minutes with the use of this method.     

Thermoresponsive MALDI probe surfaces as a tool for protein on-probe purification

Thin film depositions of rf plasma polymerized N-isopropylacrylamide (ppNIPAM) show a phase transition temperature below which the polymer surface is hydrophilic, and protein nonadsorptive, and above which the polymer surface is hydrophobic, and protein-retentive. Results presented here demonstrate that this thermoresponsive plasma polymer can be coated on the surface of a MALDI probe and subsequently used for on-probe biomolecule cleanup. Specifically, a contaminated biomolecule can be applied to the ppNIPAM coated MALDI probe surface at a temperature above the phase transition temperature, washed using solvent also held above the phase transition temperature, and then analyzed by reducing the probe temperature to room temperature before adding the MALDI matrix. With the use of this approach, it is demonstrated that cytochrome c contaminated with 0.3% SDS, which yields only a very weak MALDI ion signal as directly deposited, can be purified on-probe using the thermoresponsive plasma polymer to improve significantly the ion signal. It is further shown that the decontamination of whole cell protein extracts from cyanobacteria is augmented through the use of the ppNIPAM coated MALDI probe.     

Photoluminescence spectroscopy as a probe of silver doped zeolites as photocatalysts

Nanoclusters of silver ions, dicyanoaurate ions, and dicyanoargentate ions doped in zeolite hosts have been prepared. Luminescence, Raman, and FT-EXAFS spectroscopies along with extended Hückel calculations indicate the formation of silver and [M(CN)₂⁻]_m (M=Au and Ag) oligomers in the zeolite host. The silver and gold nanoclusters in zeolites enhance the photodecomposition rates of NO_x, malathion, and carbaryl when compared to the pollutant's behavior in the absence of silver doped zeolites with the observed rate increase attributed to excimer and exciplex formation.     

A robust formulation of SAW Green's functions for arbitrarily thick multilayers at high frequencies

This paper presents a robust formulation of SAW Green's functions for arbitrarily thick multilayers at high frequencies. The formulation is an alternative to that based on the transfer matrix method, which suffers from numerical instabilities when the frequency and/or thickness parameters become large. This numerical difficulty can be attributed to the mixture of exponentially growing and decaying terms during the transfer matrix calculations. To be more instructive, the numerical instability is delineated in terms of upward-bounded and downward-bounded waves within each layer. In accordance with such boundedness association, a recursive scheme not involving any growing terms is developed based on the scattering matrices to eliminate the instability. The resulting reflection matrix method is extremely concise and preserves the simplicity and convenience of the transfer matrix method. Using the reflection matrices, the generalized Green's functions that relate the particle velocity and the rate of electric potential change to the surface stress and charge are formulated succinctly. These Green's functions are useful for having incorporated the electrical properties of the vacuum above the surface. Numerical computations are exemplified to demonstrate the instabilities of the transfer matrix method and to justify the robustness of the reflection matrix formula     

对靶非平衡磁控溅射系统平面探针诊断

对靶非平衡磁控溅射系统由两个相对磁控溅射靶和一个磁镜场约束系统构成，通过强调电磁线圈的激励电流可以控制磁镜场的空间分布状态，测量了合成磁场的空间分布状态。采用平面探针方法，在两靶中间位置测量了收集电流密度。结果表明，探针的收集电流密度随磁镜场的激励电流增加显著增大，在偏压150V、工作气体Ar、压力0.2Pa和磁控溅射靶工作电流3A时，收集的电流密度可以达到5.77mA/cm^2。     

Measurements of radar wave speeds in polar glaciers using a down-hole radar target technique

A new technique for measuring the speed of radar waves in polar ice sheets was developed to investigate a previously reported disagreement between the permittivities of laboratory and glacier ice. The technique involves lowering a cylindrical radar target to several carefully measured depths in a borehole and measuring the travel time of a radar wave transmitted from a surface radar unit to the target in the borehole. The experiment was performed at Dome C, East Antarctica, and Dye-3, Greenland, and useable data were collected for target depths between 200 and 800 m. After computing the range to the target along a straight ray path and after correcting the travel time for delays in the radar receiver, the velocities determined from these experiments were found to be in good agreement with the velocities predicted by Robin's empirical formula. The apparent discrepancy between the permittivity of glacier ice, as measured using the radar wide-angle reflection method, and laboratory ice now seems to be due in large part to signal delay in the radar receiver that was ignored in earlier experiments.     

Diffusional surface voltammetry as a probe of adsorption energetics

Direct determination of the adsorption free energy for extremely low surface coverages (Henry limit) requires the use of a technique that must be highly sensitive to both the amount and the energetics of adsorbed molecules. Herein, we demonstrate that diffusional surface voltammetry (DSV), which embodies film and stripping voltammetries as two limiting cases, can be used to achieve this goal for electroactive adsorbates. To this end, a general analytical expression for the surface voltammetric peak potential of DSV is derived, which covers the full range of scan rates, bulk concentrations, and adsorptivity of the freely diffusing form of the redox couple, so that the surface redox conversion can be either equilibrated with or transport-isolated from the solution bulk. Strategies to get a quantitative insight into the energetics of electrosorption are outlined, and diagnostic criteria for their application are developed. In particular, it is demonstrated that DSV can be used in its stripping mode to determine group contributions to the adsorption free energy, avoiding possible interferences from intermolecular interactions or formation of oligomeric species. Application of this protocol to the reductive desorption of distinct homologous series of alkylthiolates adsorbed at mercury electrodes has allowed us to determine the contributions of the CH(n) groups (n = 0-3) to the free energy of adsorption of these molecules. These estimates are shown to correlate linearly with the corresponding group contributions to the octanol-water partition coefficient, revealing that adsorption of individual hydrocarbon groups at the mercury/solution interface scales with their hydrophobicity. Overall, the present work enlarges the capability of surface voltammetry to probe adsorption energetics down to the micromolar level, and it represents a first step toward the development of a unified treatment of stripping and film voltammetries.     

The image of a line width test object in a scanning electron microscope with different energies of the probe electrons

Results of studies of the influence of the energy of the probe electrons in the range 0.3–20 keV on the image of a line width test object in the nanometric range in a scanning electron microscope are presented. It is shown that the range of energies of the primary electrons may be divided into three sub-ranges. At electron energies less than 2.5 keV (low-voltage operating mode) and greater than 10 keV (high-voltage operating mode) the image that is formed in the course of collecting secondary slow electrons can be used to take measurements of the line width of a test object by means of known methods. For the intermediate range of energies of the primary electrons, there are no methods that may be used to measure the line width.     

Magneto-optical-trap-based, high brightness ion source for use as a nanoscale probe

We report on the demonstration of a low emittance, high brightness ion source based on magneto-optically trapped neutral atoms. Our source has ion optical properties comparable to or better than those of the commonly used liquid metal ion source. In addition, it has several advantages that offer new possibilities, including high resolution ion microscopy with ion species tailored for specific applications, contamination-free ion milling, and nanoscale implantation of a variety of elements, either in large quantities, or one at a time, deterministically. Using laser-cooled Cr atoms, we create an ion beam with a normalized rms (root-mean-square) emittance of 6.0 x 10 (-7) mm mrad M e V and approximately 0.25 pA of current, yielding a brightness as high as 2.25 A cm (-2) sr (-1) eV (-1). These values of emittance and brightness show that, with suitable ion optics, an ion beam with a useful amount of current can be produced and focused to spot sizes of less than 1 nm.     

Pair breaking as a probe of d-wave high-temperature superconductivity

A unified picture is obtained of the Cooper pair-breaking data by Cu-site Zn and Ni in Nd_2–z Ce _z CuO₄, La_2–SrCuO₄, Bi₂Sr₂CaCu₂O₈, Bi_1.8Pb_0.2Sr₂Ca₂Cu₃O₁₀, YBa₂Cu₃O₇, and YBa₂Cu₄O₈. The data are generally inconsistent with spin-fluctuation d-wave pairing mechanisms of superconductivity and with all two-dimensional cuprate-plane models. The data are consistent with superconductivity in the charge reservoirs.     

Surface-modified CdS nanoparticles as a fluorescent probe for the selective detection of cysteine

We present a novel method for the selective detection of cysteine, a sulfur-containing amino acid, which plays a crucial role in many important biological functions such as protein folding. Surface-modified colloidal CdS nanoparticles have been used as a fluorescent probe to selectively detect cysteine in the presence of other amino acids in the micromolar concentration range. Cysteine quenches the emission of CdS in the 0.5-10?μM concentration range, whereas the other amino acids do not affect its emission. Among the other amino acids, histidine is most efficient in quenching the emission of the CdS nanoparticles. The sulfur atom of cysteine plays a crucial role in the quenching process in the 0.5-10?μM concentration range. Cysteine is believed to quench the emission of the CdS nanoparticles by binding to their surface via its negatively charged sulfur atom. This method can potentially be applied for its detection in biological samples.     

Filter Radiometers as a Tool for Quality Assurance of Temperature Measurements with Linear Pyrometers

Measurements made with a pyrometer are vulnerable to errors if the pyrometer is misaligned, inaccurately characterized, or malfunctioning. In this work, thermodynamic temperatures between 1,373 and 1,773 K were studied by measuring a variable-temperature blackbody with a linear pyrometer and four absolutely characterized filter radiometers. The filter radiometer measurements were done in the irradiance mode. In the first set of measurements, there was a 3–5 K difference between the pyrometer and the filter radiometer data. The cause was tracked to malfunctioning of the pyrometer, which was afterwards sent for repair on the basis of these results. In the second set of measurements, with the repaired pyrometer, the agreement of the temperature results was good, the mean difference being −0.41 K with a standard deviation of 0.52 K. The differences between the pyrometer and the filter radiometer temperature measurement results showed no temperature dependence. It was concluded that the filter radiometers used in the irradiance mode provided a straightforward method for the quality assurance of pyrometers.