Single Deflection Research Articles

Single stage deflection amplification mechanism in a SOG capacitive accelerometer

This work discusses on a novel mechanical amplification concept for micro-electro-mechanical systems (MEMS). A single stage deflection amplifying mechanism, comprising microlevers, is implemented for a single axis in-plane capacitive accelerometer. Such a mechanism can provide a higher signal to noise ratio in a wide bandwidth with improved performance. Results from the analysis and evaluation of the fabricated prototype sensor are presented in this paper.

Combined electrohydraulic and holmium: YAG laser ureteroscopic nephrolithotripsy of large (>2 cm) renal calculi

Percutaneous nephrolithotripsy (PCL) is a standard treatment for renal calculi >2 cm. Modern flexible ureteroscopes and accessories employing the complementary effects of electrohydraulic lithotripsy (EHL) and Ho:YAG laser lithotrites can treat these renal calculi in a minimally invasive fashion with similar or superior results.Objective:To assess the safety and efficacy of ureteroscopic nephrolithotripsy monotherapy for the management of >2 cm renal calculi in the community setting.Materials and Methods:Fifty nine patients with 63 renal calculi ranging from 20 to 97 mm (mean 44 mm) in length and 175 to 3300 mm2 (mean 728 mm2) area underwent staged ureteroscopic nephrolithotripsy monotherapy. Obesity (BMI > 30) was present in 54% and 19% were morbidly obese (BMI > 40). An infectious etiology was present in 49% and hard stone components in 89%. All patients presented with hematuria, pain, and/or recurrent urinary tract infection (UTI). Lithotripsy was performed with a single deflection flexible ureteroscope and predominantly EHL. Laser drilling was employed (n = 6) to weaken very hard stones prior to EHL. Low intrarenal pressure was maintained by continuous bladder drainage and placement of a stiff safety wire. Visibility was maintained using manual pulsatile irrigation.Results:All patients were rendered pain and infection-free. No patient required a blood transfusion and there was no change in serum creatinine. Mobile stone-free status was achieved in 60/63 (95%) with a mean of 1.7 nephrolithotripsy stages and 0.38 secondary or ancillary procedures. Outpatient management was sufficient for 121/131 (92%) of the procedures. Operative time averaged 46 min/stage and 79 min/calculus. Complications included endotoxic shock (3), fever (5), ureteral fragments requiring treatment (11), delayed extubation (2), delayed pneumonia (1), and urinary retention (1).Conclusion:Staged ureteroscopic nephrolithotripsy of large renal calculi is feasible with low morbidity and stone clearance rates that compare favorably with PCL. It has largely replaced PCL at this institution.

Modeling a layer 4-to-layer 2/3 module of a single column in rat neocortex: Interweaving in vitro and in vivo experimental observations

We report a step in constructing an in silico model of a neocortical column, focusing on the synaptic connection between layer 4 (L4) spiny neurons and L2/3 pyramidal cells in rat barrel cortex. It is based first on a detailed morphological and functional characterization of synaptically connected pairs of L4-L2/3 neurons from in vitro recordings and second, on in vivo recordings of voltage responses of L2/3 pyramidal cells to current pulses and to whisker deflection. In vitro data and a detailed compartmental model of L2/3 pyramidal cells enabled us to extract their specific membrane resistivity ( approximately 16,000 ohms x cm(2)) and capacitance ( approximately 0.8 microF/cm(2)) and the spatial distribution of L4-L2/3 synaptic contacts. The average peak conductance per L4 synaptic contact is 0.26 nS for the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and 0.2 nS for NMDA receptors. The in vivo voltage response for current steps was then used to calibrate the model for in vivo conditions in the Down state. Consequently, the effect of a single whisker deflection was modeled by converging, on average, 350 +/- 20 L4 axons onto the modeled L2/3 pyramidal cell. Based on values of synaptic conductance, the spatial distribution of L4 synapses on L2/3 dendrites, and the average in vivo spiking probability of L4 spiny neurons, the model predicts that the feed-forward L4-L2/3 connection on its own does not fire the L2/3 neuron. With a broader distribution in the number of L4 neurons or with slight synchrony among them, the L2/3 model does spike with low probability.

Frequency Adaptation Modulates Spatial Integration of Sensory Responses in the Rat Whisker System

The generation of perceptual experiences requires the integration of complex spatiotemporal patterns of sensory input. The rodent whisker system is a useful model for understanding the cellular mechanisms of sensory integration, which often include the operation of local circuits distributed throughout the brain. An example is cross-whisker suppression, where the neuronal response to whisker deflection is strongly reduced by preceding deflection of a neighboring whisker. Suppressive interactions between whisker-evoked responses have largely been studied using pairs of single whisker deflections. However, rats typically sweep their whiskers across surfaces at frequencies ranging from 5 to 25 Hz. Repetitive afferent activation induces frequency-dependent adaptation of neuronal responses and alters the synaptic dynamics of circuits that play a role in suppression, suggesting that adaptation could modulate the spatial integration of whisker evoked responses. We tested this hypothesis by comparing the cross-whisker suppression of principal whisker (PW)-evoked cortical and thalamic responses when preceded by either a single deflection of an adjacent whisker (AW) or a train of AW deflections at frequencies covering the normal whisking range. We found that periodic deflection of the preceding AW significantly reduced the magnitude of cross-whisker suppression. Surprisingly, although higher frequencies resulted in greater adaptation of the AW-evoked response, the effect on suppression was independent of frequency. We suggest that these results follow from known local circuit operations at multiple levels within the afferent path. Our findings support the view that repetitive whisking subserves a transformation of the integrative and functional properties of the whisker system.

Facilitating Sensory Responses in Developing Mouse Somatosensory Barrel Cortex

The sensory responses in the barrel cortex of mice aged postnatal day (P)7-P12 evoked by a single whisker deflection are smaller in amplitude and spread over a smaller area than those measured in P13-P21 mice. However, repetitive 10-Hz stimulation or paired pulse whisker stimulation in P7-P12 mice evoked facilitating sensory responses, contrasting with the depressing sensory responses observed in P13-P21 mice. This facilitation occurred during an interval ranging 300-1,000 ms after the first stimulus and was measured using whole cell recordings, voltage-sensitive dye imaging, and calcium-sensitive dye imaging. The facilitated responses were not only larger in amplitude but also propagated over a larger cortical area. The facilitation could be blocked by local application of pharmacological agents reducing cortical excitability. Local cortical microstimulation could substitute for the first whisker stimulus to produce a facilitated sensory response. The enhanced sensory responses evoked by repetitive sensory stimuli in P7-P12 mice may contribute to the activity-dependent specification of the developing cortical circuits. In addition, the facilitating sensory responses allow long integration times for sensory processing compatible with the slow behavior of mice during early postnatal development.

Combined Electrohydraulic and Holmium:YAG Laser Ureteroscopic Nephrolithotripsy of Large (Greater Than 4 cm) Renal Calculi

Percutaneous nephrolithotripsy is standard treatment for renal calculi larger than 2 cm. Modern flexible ureteroscopes and accessories using the complimentary effects of electrohydraulic lithotripsy and holmium:YAG laser lithotrites can treat large (greater than 4 cm) branched renal calculi in a minimally invasive fashion with similar or superior results. This report is an assessment of the safety and efficacy of ureteroscopic nephrolithotripsy monotherapy for the management of large (greater than 4 cm) branched renal calculi in the community setting. A total of 16 patients with 17 branched renal calculi ranging from 41 to 97 mm (mean 65) in length and 560 to 2,425 mm2 (mean 1,169) in area underwent staged ureteroscopic nephrolithotripsy monotherapy. Obesity (body mass index greater than 30) was present in 81% and 38% were morbidly obese (body mass index greater than 40). An infectious etiology was present in 81% and hard stone components were present in 94%. All patients presented with hematuria, pain and/or recurrent urinary tract infection. Lithotripsy was performed with a single deflection flexible ureteroscope and predominantly electrohydraulic lithotripsy. Laser drilling was used (in 4) to weaken hard stones before electrohydraulic lithotripsy. Low intrarenal pressure was maintained by continuous bladder drainage and placement of a stiff safety wire. Visibility was maintained using manual pulsatile irrigation. All patients were rendered pain and infection-free. No patient required a blood transfusion and there was no change in serum creatinine. Mobile stone-free status was achieved in 15 of 17 renal units (88%) with a mean of 2.4 stages and 36 of 40 (90%) procedures performed on an outpatient basis. Operative time averaged 49 minutes per stage and 115 minutes per calculus. There were 3 patients admitted for fever and 1 patient (90 years old) admitted for pneumonia 3 days postoperatively. There were also 3 patients with calculi larger than 75 mm who required ureteroscopic management of steinstrasse. Staged ureteroscopic nephrolithotripsy of large renal calculi is feasible with low morbidity and stone clearance rates that compare favorably with percutaneous nephrolithotripsy.

Two psychophysical channels of whisker deflection in rats align with two neuronal classes of primary afferents.

The rat whisker system has evolved into in an excellent model system for sensory processing from the periphery to cortical stages. However, to elucidate how sensory processing finally relates to percepts, methods to assess psychophysical performance pertaining to precise stimulus kinematics are needed. Here, we present a head-fixed, behaving rat preparation that allowed us to measure detectability of a single whisker deflection as a function of amplitude and peak velocity. We found that velocity thresholds for detection of small-amplitude stimuli (<3 degrees) were considerably higher than for detection of large-amplitude stimuli (>3 degrees). This finding suggests the existence of two psychophysical channels mediating detection of whisker deflection: one channel exhibiting high amplitude and low velocity thresholds (W1), and the other channel exhibiting high velocity and low amplitude thresholds (W2). The correspondence of W1 to slowly adapting (SA) and W2 to rapidly adapting (RA) neuronal classes in the trigeminal ganglion was revealed in acute neurophysiological experiments. Neurometric plots of SA and RA cells were closely aligned to psychophysical performance in the corresponding W1 and W2 parameter ranges. Interestingly, neurometric data of SA cells fit the behavior best if it was based on a short time window integrating action potentials during the initial phasic response, in contrast to integrating across the tonic portion of the response. This suggests that detection performance in both channels is based on the assessment of very few spikes in their corresponding groups of primary afferents.

Balanced Excitation and Inhibition Determine Spike Timing during Frequency Adaptation

In layer 4 (L4) of the rat barrel cortex, a single whisker deflection evokes a stereotyped sequence of excitation followed by inhibition, hypothesized to result in a narrow temporal window for spike output. However, awake rats sweep their whiskers across objects, activating the cortex at frequencies known to induce short-term depression at both excitatory and inhibitory synapses within L4. Although periodic whisker deflection causes a frequency-dependent reduction of the cortical response magnitude, whether this adaptation involves changes in the relative balance of excitation and inhibition and how these changes might impact the proposed narrow window of spike timing in L4 is unknown. Here, we demonstrate for the first time that spike output in L4 is determined precisely by the dynamic interaction of excitatory and inhibitory conductances. Furthermore, we show that periodic whisker deflection results in balanced adaptation of the magnitude and timing of excitatory and inhibitory input to L4 neurons. This balanced adaptation mediates a reduction in spike output while preserving the narrow time window of spike generation, suggesting that L4 circuits are calibrated to maintain relative levels of excitation and inhibition across varying magnitudes of input.

Propagation of intense plasma and ion beams across B-field in vacuum and magnetized plasma

This paper summarizes experimental results on the injection and transport of intense, wide cross-section H+ plasma (PB), and ion beams (IB), in vacuum and ambient H+ plasma across an applied B-field. The injection of plasma and ion beams into magnetic confinement devices have the potential to heat and support current in these systems (e.g., field-reversed configurations). The translational energies of the PB and IB ranged between Epb = 60 to 120 eV and EIB = 60 to 120 keV, with temperatures and densities in the range of Tb ∼ 2 to 10 eV, nb ∼ 1012 to 1013 cm−3, and Tb ∼ 200 eV, nb 1010 to 1011 cm−3, respectively. Compared to earlier studies (Peter et al., 1979; Wessel et al., 1988, 1990), this research extends the experimental parameter space to higher beam current densities (up to 30 A/cm2) and higher B-field strengths up to 1.6 kG. The PB and IB were both about 10 cm in diameter at the injection port, and the ratio of beam specific energy to ambient B-field specific energy, β, was in the range of 0.1 to 10. Ratios of beam Larmor radius to beam size, ρ, ranged from 10−1 to 1 and 1 to 10 for the PB and IB, respectively. Cross B-field propagation of the PB in vacuum was undeflected as a whole with a sharp increase (one order or more) in the current density of the central beam core at B-field levels &gt; 1 kG accompanied by a significant loss of beam peripheral layers, beam “braking” and preferential beam expansion along the B-field lines. Cross B-field propagation of the PB in ambient plasma did not differ substantially from the case without B-field, that is, no deflection of the PB as a whole, which could be due to an insufficient neutralization of the induced E-field inside the PB. Cross B-field propagation of the IB in ambient plasma followed a single particle trajectory deflection with a simultaneous significant loss of IB intensity without any detectable bunching, indicating an adequate shorting of the polarization E-field inside the IB.

Fatigue crack paths in coarse‐grained magnesium

ABSTRACTThis paper examines fatigue crack paths in coarse‐grained magnesium alloys. Visualization of the microstructure by etching and continuous crack monitoring with a microscope provide evidence of the crack‐grain interaction at different fatigue crack growth regimes. Near‐threshold fatigue crack growth promotes the development of rough surfaces by the activation of single slip mechanisms and crack deflection. The R‐ratio effect on near‐threshold results is discussed in the light of the partial crack‐closure model. The role of grain boundaries and grain‐to‐grain crack deflections on fatigue crack growth rates is discussed.

Clinical utility of dual active deflection flexible ureteroscope during upper tract ureteropyeloscopy

Objectives To evaluate the clinical utility of a dual active deflection ACMI DUR-8 Elite ureteroscope in a referral endourology practice. Methods Retrospective chart review was performed on 54 consecutive patients who underwent flexible ureteroscopy by a single surgeon (S.Y.N.) from February to July 2003. Cases in which standard flexible ureteroscopes alone could complete the procedure, cases in which standard flexible ureteroscopy could not complete the procedure and the DUR-8 Elite ureteroscope did, and cases in which both ureteroscopes failed to complete the procedure were analyzed. Results A total of 54 procedures were performed on 37 patients. Three cases were not analyzed because they were distal ureter procedures. Of the remaining 51 procedures, 6 were removed from analysis because they were second-look procedures. When classified by diagnosis, 27 patients had stones (79.4%), 5 had cancer (14.7%), and 1 had hematuria (2.9%). The global success rate was 91.1%. The average use rate of the DUR-8 was 28.9%, and the success rate using the DUR-8 Elite was 69.2% in those cases in which it was necessary. Of the 13 cases in which the DUR-8 was used, 61.5% were for lower pole pathologic findings. The DUR Elite use and success rate in the lower pole was 57.1% and 75%, respectively. A statistically significant association was found between the diagnosis and procedure location ( P = 0.00128). Conclusions Our preliminary data indicate that the dual deflecting DUR-8 Elite ureteroscope may be helpful in cases in which the single deflection flexible instruments fail to access and treat upper urinary tract pathologic findings.

753 Comparison of a single active deflection ureteroscope with two new active primary and secondary deflecting flexible ureteroscopes in terms of movements: A 3D representation of spatial accessibility

753 Comparison of a single active deflection ureteroscope with two new active primary and secondary deflecting flexible ureteroscopes in terms of movements: A 3D representation of spatial accessibility

Nonlinear encoding of tactile patterns in the barrel cortex.

Cells in the rodent barrel cortex respond to vibrissa deflection with a brief excitatory component and a longer suppressive component. The response to a given deflection is thus scaled because of suppression induced by a preceding deflection, causing the neuronal response to be linked to the temporal properties of the peripheral stimulus. A paired-deflection stimulus was used to characterize the postexcitatory suppression and a 3-deflection stimulus was used to investigate the nonlinear response to patterns of whisker deflections in barbiturate-anesthetized Sprague-Dawley rats. The postexcitatory suppression was not dependent on a sensory-evoked action potential to the first deflection, implying that it is likely a subthreshold property of the network. The suppression induced by a deflection served to suppress both the excitatory and suppressive components of a subsequent neuronal response, thus effectively disinhibiting it. Two different response properties were observed in the recorded cells. Approximately 65% responded to a vibrissa deflection with an excitatory component followed by a suppressive component and 35% responded with excitation, suppression, and a subsequent rebound in excitation. Based on these observations of postexcitatory dynamics, a prediction method was used to estimate neuronal responses to more complex stimulus trains. Using the 2nd-order representation obtained from the paired-deflection stimulus, responses to general periodic deflection patterns were well predicted. A higher cutoff frequency was predicted for rebound cells compared with cells not exhibiting rebound excitation, consistent with experimental observations. The method also predicted the response of neurons to a random aperiodic deflection pattern. Therefore the temporal structure of cortical dynamics after a single deflection dictates the response to complex temporal patterns, which are more representative of stimuli encountered under natural conditions.

Morphometric analysis of the columnar innervation domain of neurons connecting layer 4 and layer 2/3 of juvenile rat barrel cortex.

We have investigated the dendritic and axonal morphology of connected pairs of L4 spiny neurons and L2/3 pyramidal cells in rat barrel cortex. The 'projection' field of the axons of L4 spiny neurons in layers 2/3, 4 and 5 has a width of 400-500 microm thereby defining an anatomical barrel-column. In layer 2/3, the averaged axonal 'projection' field of L4 spiny neurons together with the dendritic 'receptive' field of the connected L2/3 pyramidal cells form a mostly column-restricted anatomical L4-to-L2/3 'innervation domain' that extends 300-400 microm and includes mostly basal dendrites. In the L4-to-L2/3 innervation domain a single L4 spiny neuron contacts approximately 300-400 pyramidal cells while in the L4-to-L4 innervation domain it contacts approximately 200 other L4 spiny neurons. Similarly approximately 300-400 L4 spiny neurons converge onto a single pyramidal cell and approximately 200 L4 spiny neurons innervate another L4 spiny neuron. The L2/3 pyramidal cell axon has a vertical projection field spanning all cortical layers, and a long-range horizontal field in layers 2/3 (width 1,100-1,200 microm) and 5 (700-800 microm) projecting across column borders. The results suggest that the flow of excitation within a barrel-column is determined by the largely columnar confinement of the L4-to-L4 and L4-to-L2/3 innervation domains. A whisker deflection activates approximately 140 L4 spiny neurons that will generate EPSPs in most barrel-related L2/3 pyramidal cells of a principal whisker column. The translaminar synaptic transmission to layer 2/3 and the axonal projection fields of L2/3 pyramidal cells are the major determinants of the dynamic, multi-columnar map in which a single whisker deflection is represented in the cortex.

Use of flexibility tests in the manufacturing process of 60° björk-shiley convexo-concave valves and the risk of outlet strut fracture

ObjectivesOutlet strut fracture remains a concern for 30,000 patients living with a Björk-Shiley convexo-concave heart valve (Shiley, Inc, Irvine, Calif, a subsidiary of Pfizer, Inc). Previous studies (Netherlands and United Kingdom) investigating valve manufacturing aspects identified multiple performance of the hook deflection test as a risk factor for 60° valves. The present study validated this finding using new data with a greater number of valves implanted worldwide. Risks of outlet strut fracture associated with other manufacturing aspects were also investigated. MethodsA matched case-control study design was used including 416 outlet strut fracture cases and 803 controls. ResultsAnalyses similar to that of the Dutch and United Kingdom studies produced odds ratios of 3.4 (95% confidence interval [CI]: 1.1-10.3) and 2.8 (95% CI: 1.1-7.3), respectively, for multiple hook deflection tests. Load deflection test, which replaced the hook deflection test, showed a statistically significant association with outlet strut fracture: odds ratio of 5.0 (95% CI: 2.1-11.8) and 6.2 (95% CI: 2.2-18.0) for single and multiple load deflection tests, respectively. An analysis where hook deflection tests were separated from load deflection tests showed significantly elevated odds ratios with performance of any type of flexibility test, and the highest odds ratio was observed with a combined performance of load and hook deflection tests. ConclusionsMultiple hook deflection tests can now be considered for inclusion in the risk model used for guidelines on explant surgery to improve prediction of outlet strut fracture and provide patient reassurance. Load deflection tests and combined performance of hook and load deflection tests were found to be significant risk factors. No outlet strut fractures were reported for valves manufactured after March 1984 when the load deflection test was still in place. Examining manufacturing documents for these valves may identify new risk factors that could be responsible for the outlet strut fractures risk that remains unexplained to date.

Spatiotemporal Dynamics of Sensory Responses in Layer 2/3 of Rat Barrel Cortex MeasuredIn Vivoby Voltage-Sensitive Dye Imaging Combined with Whole-Cell Voltage Recordings and Neuron Reconstructions

The spatiotemporal dynamics of the sensory response in layer 2/3 of primary somatosensory cortex evoked by a single brief whisker deflection was investigated by simultaneous voltage-sensitive dye (VSD) imaging and whole-cell (WC) voltage recordings in the anesthetized rat combined with reconstructions of dendritic and axonal arbors of L2/3 pyramids. Single and dual WC recordings from pyramidal cells indicated a strong correlation between the local VSD population response and the simultaneously measured subthreshold postsynaptic potential changes in both amplitude and time course. The earliest VSD response was detected 10-12 msec after whisker deflection centered above the barrel isomorphic to the stimulated principal whisker. It was restricted horizontally to the size of a single barrel-column coextensive with the dendritic arbor of barrel-column-related pyramids in L2/3. The horizontal spread of excitation remained confined to a single barrel-column with weak whisker deflection. With intermediate deflections, excitation spread into adjacent barrel-columns, propagating twofold more rapidly along the rows of the barrel field than across the arcs, consistent with the preferred axonal arborizations in L2/3 of reconstructed pyramidal neurons. Finally, larger whisker deflections evoked excitation spreading over the entire barrel field within approximately 50 msec before subsiding over the next approximately 250 msec. Thus the subthreshold cortical map representing a whisker deflection is dynamic on the millisecond time scale and strongly depends on stimulus strength. The sequential spatiotemporal activation of the excitatory neuronal network in L2/3 by a simple sensory stimulus can thus be accounted for primarily by the columnar restriction of L4 to L2/3 excitatory connections and the axonal field of barrel-related pyramids.

Dynamic representation of whisker deflection by synaptic potentials in spiny stellate and pyramidal cells in the barrels and septa of layer 4 rat somatosensory cortex.

Whole-cell voltage recordings were made in vivo from excitatory neurons (n = 23) in layer 4 of the barrel cortex in urethane-anaesthetised rats. Their receptive fields (RFs) for a brief whisker deflection were mapped, the position of the cell soma relative to barrel borders was determined for 15 cells and dendritic and axonal arbors were reconstructed for all cells. Three classes of neurons were identified: spiny stellate cells and pyramidal cells located in barrels and pyramidal cells located in septa. Dendritic and, with some exceptions, axonal arborisations of barrel cells were mostly restricted to the borders of a column with a cross sectional area of a barrel, defining a cytoarchitectonic barrel-column. Dendrites and axons of septum cells, in contrast, mostly extended across barrel borders. The subthreshold RFs measured by evoked postsynaptic potentials (PSPs) comprised a principal whisker (PW) and several surround whiskers (SuWs) indicating that deflection of a single whisker is represented in multiple barrels and septa. Barrel cells responded with larger depolarisation to stimulation of the PW (13.7 +/- 4.6 mV (mean +/- S.D.), n = 10) than septum cells (5.7 +/- 2.4 mV, n = 5), the gradient between peak responses to PW and SuW deflection was steeper and the latency of depolarisation onset was shorter (8 +/- 1.4 ms vs. 11 +/- 2 ms). In barrel cells the response onset and the peak to SuW deflection was delayed depending on the distance to the PW thus indicating that the spatial representation of a single whisker deflection in the barrel map is dynamic and varies on the scale of milliseconds to tens of milliseconds. Septum cells responded later and with comparable latencies to PW and SuW stimulation. Spontaneous (0.053 +/- 0.12 action potentials (APs) s(-1)) and evoked APs (0.14 +/- 0.29 APs per principal whisker (PW) stimulus) were sparse. We conclude that PSPs in ensembles of barrel cells represent dynamically the deflection of a single whisker with high temporal and spatial acuity, initially by the excitation in a single PW-barrel followed by multi-barrel excitation. This presumably reflects the divergence of thalamocortical projections to different barrels. Septum cell PSPs preferably represent multiple whisker deflections, but less dynamically and with less spatial acuity.

TOF analysis of reflection of low-energy light ions from solid targets using coaxial impact collision ion scattering spectroscopy (CAICISS)

The energy spectra of He and D particles reflected from the Si(1 1 1)- 3 × 3 Sb surface at the angle of π in the sub-keV regime have been studied by means of a CAICISS system. The quantum efficiency of the microchannel plate for the particle detector in the CAICISS system has been determined as a function of the kinetic energy from the comparison of the experimental peak intensity from Sb atoms in the sub-monolayer regime with the theoretical one. The latter is calculated by use of the elastic scattering cross-section derived from the Thomas–Fermi model of the screened Coulomb potential. The energy spectra of He particles backscattered from the Si(1 1 1) substrate on incidence of 2 keV He + ions have been also obtained by use of the quantum efficiencies determined and compared with the theoretical ones calculated on the large angle single deflection model.

Angular distribution of surface excitations for electrons backscattered from Al and Si surfaces

Spectra of electrons reflected from non crystalline Aluminum and Silicon surfaces have been measured for energies between 300 and 3400 eV. Angular distributions of the elastic peak as well as multiple surface and bulk excitations were recorded for two geometrical arrangements, being each others mirror image with respect to the trajectory of each detected electron. These geometries allow to distinguish between incoming and outgoing electrons in the case such a difference depends on the direction of the electrons with respect to the surface normal. Theoretical calculations [Surf. Interf. Anal. 26 (1998) 682] suggest that such a difference exists in the ratio of the elastic peak and the intensity of the first surface plasmon. The present paper compares experimental results on this quantity that is closely related to the so-called surface excitation parameter for Aluminum and Silicon with theory. The angular distribution of the elastic peak was found to closely follow the single deflection model. Within the experimental accuracy of ∼5% no difference regarding the surface excitation parameter for incoming and outgoing electron trajectories was observed.

Elastic electron reflection for determination of the inelastic mean free path of medium energy electrons in 24 elemental solids for energies between 50 and 3400 eV

Abstract Elastic electron backscattering coefficients have been measured for 24 elemental solids (Ag, Al, Au, Be, Bi, C, Co, Cu, Fe, Ge, Mg, Mn, Mo, Ni, Ta, Te, Ti, Pb, Pd, Pt, Si, V, W and Zn) for energies between 50 and 3400 eV. Values for the electron inelastic mean free path (IMFP) were derived from the experimental intensities on the basis of a simple physical model that accounts for bulk elastic and inelastic scattering only. The internal consistency of the data set and the evaluation procedure is satisfactory for energies >150 eV. For energies ≥200 eV the IMFP values were found to be well described by the Bethe equation for inelastic scattering, as found earlier by analysis of optical scattering data with the aid of the linear response theory [Surf. Interface Anal. 21 (1994) 165]. We also compare the parameters β (being related to the total dipole matrix elements for inelastic scattering) and γ (determining the details of the energy dependence of the IMFP) that appear in the Bethe equation with corresponding results based on optical data. Both parameters were found to agree well with the earlier analysis by Tanuma et al. [Surf. Interface Anal. 21 (1994) 165] within the statistical accuracy of the present analysis. Experimental data on the recoil energy in elastic scattering were also analyzed and compared with detailed results of Monte Carlo simulations of this phenomenon. The recoil energies are correctly predicted to within 10% by the single deflection model based on the Rutherford cross section.