Fast Scanning Mode Research Articles

Occurrence of particle debris field during focused Ga ion beam milling of glassy carbon

To explore the machining characteristics of glassy carbon by focused ion beam (FIB), particles induced by FIB milling on glassy carbon have been studied in the current work. Nano-sized particles in the range of tens of nanometers up to 400 nm can often be found around the area subject to FIB milling. Two ion beam scanning modes – slow single scan and fast repetitive scan – have been tested. Fewer particles are found in single patterns milled in fast repetitive scan mode. For a group of test patterns milled in a sequence, it was found that a greater number of particles were deposited around sites machined early in the sequence. In situ EDX analysis of the particles showed that they were composed of C and Ga. The formation of particles is related to the debris generated at the surrounding areas, the low melting point of gallium used as FIB ion source and the high contact angle of gallium on glassy carbon induces de-wetting of Ga and the subsequent formation of Ga particles. Ultrasonic cleaning can remove over 98% of visible particles. The surface roughness ( R a) of FIB milled areas after cleaning is less than 2 nm.

Comparison of Retinal Nerve Fiber Layer Thickness Measured by Cirrus HD and Stratus Optical Coherence Tomography

To study the relationship between retinal nerve fiber layer (RNFL) thickness measured by time domain (Stratus) and spectral domain (Cirrus HD) optical coherence tomography (OCT). Cross-sectional study. Sixty healthy participants, 48 glaucoma suspects, and 55 subjects with glaucoma. Participants were imaged by a single trained operator using the Stratus OCT (fast RNFL scan mode) and Cirrus HD-OCT (optic disc cube mode) at the same visit. The RNFL thickness as measured by the Stratus OCT (fast RNFL scan mode) and Cirrus HD-OCT (optic disc cube mode) was compared (paired t test). The relationship between RNFL thickness measurements of the 2 OCTs were evaluated using a Pearson correlation analysis. The presence of abnormal classification, as determined by using an internal normative data base in each machine was compared (chi-square test). The sensitivity and specificity of normative classification of 2 OCT measurements were calculated. Average RNFL thickness as determined by the 2 OCT machines was correlated (r = 0.94; P<0.001), but was significantly different with the 2 machines (Stratus, 98.0 mum, standard deviation [SD] 18.0; Cirrus, 85.6 mum, SD 14.6; P<0.001). The Cirrus HD-OCT classified a significantly higher percentage of eyes as abnormal (Stratus, 12.9%; Cirrus, 23.3%; P<0.001) in average RNFL thickness. Cirrus OCT demonstrated higher sensitivity and specificity (63.6% and 100%) than Stratus OCT (40.0% and 96.7%) in normative classification of average RNFL thickness. There were significant differences in RNFL thickness and normative classification as determined by Stratus OCT and Cirrus HD-OCT despite an excellent correlation of RNFL thickness measurement. Overall sensitivity and specificity were higher with Cirrus OCT. These findings are particularly relevant when an individual undergoes longitudinal follow-up with different OCTs.

In situ Sr isotopic analysis of low Sr silicates using LA-ICP-MS

We have developed a LA-ICP-MS technique for the in situ determination of 87Sr/86Sr in silicates having low Sr concentrations (30–400 µg g−1). Because of its high sensitivity we used a single collector sector-field ICP-MS, which was combined with a 193 nm Nd:YAG laser ablation system. Experiments were performed using the fast electrical scan mode (0.1 s per pass) of the mass spectrometer and a spot size of 50 µm. Various corrections were made for the determination of 87Sr/86Sr, such as dead time of the ion counting system, blank, isobaric interferences of Kr and Rb, mass discrimination for Sr and Rb. An external precision (1 SD) of the Sr isotope measurements of about 0.0002–0.0004 were achieved for samples having Sr of 100–400 µg g−1 and Rb/Sr < 0.1. Lower Sr concentrations (30–100 µg g−1) yielded higher SD values of up to about 0.0015. The LA-ICP-MS data for MPI-DING, USGS and NIST reference glasses agree within uncertainty limits with high-precision TIMS values. We have applied this technique for in situ isotopic analysis of 100–300 µm glassy melt inclusions from Hawaii and of small glass fragments of oceanic basalts.

Improved reproducibility of retinal nerve fiber layer thickness measurements with the repeat-scan protocol using the Stratus OCT in normal and glaucomatous eyes

Optical coherence tomography has become within the last years an established imaging technique with many applications in ophthalmology, and an important tool which contributes to earlier and more accurate diagnosis of glaucoma. As a consequence, detection sensitivity is highly valued. The aim of this study was to assess the reproducibility of peripapillary retinal nerve fiber layer (RNFL) thickness measurements by the Stratus Optical Coherence Tomograph (OCT) using the Fast- and Repeat-scan protocols in normal and glaucomatous eyes. In the clinical setting, RNFL thickness measurements were obtained from a control group of 40 subjects, consisting of 20 normal volunteers and 20 glaucoma patients. One eye was randomly chosen from each subject, and underwent five RNFL thickness measurements with the Fast- and five with the Repeat-scan protocol, which was also based on the Fast-scan mode. Reproducibility was assessed by the intraclass correlation coefficient (ICC) and the coefficient of variation (CV) for the overall mean RNFL thickness and for each quadrant and clock hour of the peripapillary area. The Repeat-scan protocol yielded higher ICC and lower CV values in all quadrants and clock hours of the peripapillary area, both in normal and glaucomatous subjects. The difference in CV values between Fast- and Repeat-scan protocol measurements reached statistical significance in the temporal quadrant (P = 0.021) and in clock hour sectors 8, 9 and 12 (P = 0.022, 0.017 and 0.03 respectively). ICC (and CV) for the temporal-, superior-, nasal- and inferior-quadrant RNFL thickness was: for the Fast-scan protocol, 0.913 (7.4%), 0.925 (6.97%), 0.828 (10.31%), 0.964 (4.89%) respectively; and for the Repeat-scan protocol, 0.965 (5.08%), 0.958 (5.26%), 0.906 (8.12%) 0.968 (4.6%) respectively. Reproducibility of RNFL thickness measurements with the Fast- and Repeat-scan protocols by the Stratus OCT is proved to be very high both in normal and glaucomatous subjects. The Repeat-scan protocol shows higher ICC and lower CV values, statistically significant especially on the temporal side of the peripapillary area, which may indicate a higher reproducibility and greater agreement of measurements. These findings support the fact that the Repeat-scan protocol might be considered as a more precise method for evaluation of RNFL thickness.

Association of retinal nerve fibre layer thickness measured by confocal scanning laser ophthalmoscopy and optical coherence tomography with disc size and axial length

Aims:To investigate the influence of age, disc size and axial length on the retinal nerve fibre layer (RNFL) thickness measurements of Heidelberg Retina Tomograph (HRT) and optical coherence tomography (OCT).Methods:A...

Photolytic Control and Infrared Probing of Amide I Mode in the Dipeptide Backbone-Caged with the 4,5-Dimethoxy-2-nitrobenzyl Group

Alanine dipeptide analog 1 backbone-caged with a photolabile linker, 4,5-dimethoxy-2-nitrobenzyl (DmNb), was synthesized. UV-pulse-induced photochemical reaction of 1 was monitored by Fourier transform IR absorption spectroscopy under a steady-state condition or in a fast-scan mode. Upon photolysis of 1, the amide I band is changed from a doublet to a singlet with concomitant line shape changes of several IR bands. The change of the amide I band is directly associated with the photocleavage of the covalent N-C bond connecting the backbone amide of 2 to DmNb. Therefore, IR spectroscopy is useful for directly probing the photocleavage of backbone-caged peptide 1 and the concurrent release of native peptide 2. In contrast, UV-vis spectroscopy probing the irradiation-induced structural change of the 2-nitrobenzyl moiety itself may not provide a clue directly relevant to the photocleavage of such N-C bond. Time-resolved IR spectra recorded in a fast-scan mode after pulsed UV irradiation of 1 reveal that such photocleavage occurs at least faster than a few seconds of our instrumental time resolution.

Multiscan time-domain optical coherence tomography for retina imaging

A versatile time-domain optical coherence tomography system is presented that can generate cross-sectional images by using either transverse priority or depth priority scanning. This is made possible by using a transmissive scanning delay line compatible with balance detection operating at a speed similar to that of the transverse scanner used to scan the beam across the target. In vivo images from the retina are generated and shown using the same system switched to either transverse or depth priority scanning regime, by using the scanning delay line either in slow or fast scanning modes, respectively. A comparative analysis of different scanning regimes depending on image size to fit different areas to be imaged is presented. Safety thresholds due to the different continuous irradiation time per transverse pixel in different scanning regimes are also considered. We present the maximum exposure level for a variety of scanning procedures, employing either A scanning (depth priority) or T scanning (transverse priority) when generating cross-sectional images, en face images, or collecting 3D volumes.

Fast scanning of a pulsed terahertz signal using an oscillating optical delay line

We describe a fast measurement of a pulsed terahertz signal generated by a femtosecond laser and a photoconductive antenna using an oscillating optical delay line. The method to measure the amplitude of the retroreflector in the oscillating optical delay line is proposed and the displacement of the retroreflector is exactly calculated to acquire the optical delay time in the fast scan mode. With the different oscillation frequency and amplitude of the retroreflector, the pulsed terahertz signals are measured and analyzed. The comparison of the temporal waveform and frequency spectrum between the fast scan mode and the slow scan mode shows a good agreement with the decrease in the scanning time from 60 to 1 s at a signal to noise ratio of 430.

Comprehensive two‐dimensional gas chromatography/mass spectrometric analysis of pepper volatiles

The headspace compositions of 13 pepper and peppercorn samples of different species, colloquially also referred to as pepper, were analyzed, and more than 300 compounds were tentatively characterized by means of comprehensive two-dimensional gas chromatography in tandem with flame ionization detection, quadrupole mass spectrometric detection and time-of-flight mass spectrometric detection (GC x GC-FID, GC x GC/qMS and GC x GC/TOFMS, respectively). The analysis of volatile organic compounds (VOCs) was performed after solid-phase microextraction (SPME) using a 75-microm PDMS/DVB fibre. Fingerprint comparison between the three techniques permitted peaks to be assigned in the GC x GC-FID experiment based on the analogous MS analysis, taking into account retention shifts arising from method variations. When using GC x GC/TOFMS, about five times more peaks were identified than in GC x GC/qMS. Retention indices for all peaks were calculated in the bi-dimensional column set comprising of a 5% phenyl polysilphenylene-siloxane primary column and a polyethylene glycol second column. The spectra obtained by both mass detection techniques (qMS and TOFMS) give very similar results when spectral library searching was performed. The majority of the identified compounds eluted as pure components as a result of high-resolution GC x GC separations, which significantly reduces co-elution, and therefore increases the likelihood that pure spectra can be obtained. The differences between TOFMS and qMS (in fast scanning mode) spectra were generally small. Whilst spectral quality and relative ion ratios across a narrow peak (e.g. w(b) approximately 100-150 ms) do vary more for the fast peaks obtained in GC x GC/qMS operation, than with TOFMS, in general adequate spectral matching with the library can be achieved.

Optical Coherence Tomography of the Optic Nerve Head

Optical coherence tomography may be a new technique for quantitative 3-dimensional assessment of the optic nerve head for diagnosis of optic nerve anomalies and diseases such as the glaucomas. The purpose of the present study was to examine its reproducibility. The clinical noninterventional study included 10 randomly chosen eyes of 10 healthy individuals who underwent 24 optical coherence tomographic examinations with the high-resolution and fast scan program, interactively corrected or uncorrected. The pupils were not dilated. All examinations were performed by 3 examiners independently of one another. The coefficient of variation was calculated as the ratio of the mean of the standard deviations divided by the mean of the means. The coefficients of variation for redetermination of optic disc area, ranging between 0.047 and 0.119, were lowest for the manually corrected fast scan mode and highest for the uncorrected fast scan mode. For remeasurements of the neuroretinal rim area, the best mean coefficient of variation was 0.073+/-0.026 (corrected fast scan mode). In healthy eyes, the morphometric measurements of the optic nerve head by optical coherence tomography show a relatively high reproducibility with mean coefficients of variation lower than 10% for remeasurements of the optic disc and neuroretinal rim area. With undilated pupils, reproducibility is better with the fast scan mode with interactive correction of the outlining of the optic disc border than it is with the high-resolution mode.

Improvement of in situ Pb isotope analysis by LA-ICP-MS using a 193 nm Nd:YAG laser

We have tested the capabilities of a new 193 nm Nd:YAG laser ablation system for in situ208Pb/206Pb and 207Pb/206Pb measurements by LA-ICP-MS. Experiments were performed with MPI-DING (KL2-G, ML3B-G, ATHO-G, T1-G) and USGS (GSE-1G) reference glasses using the fast electrical scan mode (0.075 s per pass) of a single collector sector-field mass spectrometer. Mass discrimination was determined by sample-reference material (e.g., NIST SRM 612) bracketing with linear interpolation. We typically obtained an external precision for 208Pb/206Pb and 207Pb/206Pb of 0.05–0.2% RSD for 50–100 μm three-spot analyses of the low-Pb (1–10 μg g−1) MPI-DING glasses. The precision of Pb isotope ratio data of the high-Pb GSE-1G sample (366 μg g−1) was <0.2% for spot sizes ≥10 μm. Even 2 and 5 μm spot size measurements could be performed with GSE-1G. The LA-ICP-MS isotope ratio data of the MPI-DING reference glasses agree within uncertainties (about 0.05% and 0.1% for 208Pb/206Pb and 207Pb/206Pb, respectively, and 100 μm spot size analyses) with the reference values obtained from TIMS and solution MC-ICP-MS. A comparison of the 193 nm Nd:YAG laser results with those obtained from a 213 nm Nd:YAG laser system shows that there is almost a factor of two improvement in precision using the new 193 nm Nd:YAG laser. Because of lower sample consumption of the 193 nm Nd:YAG laser, the Pb detection efficiency (2.5 × 10−3) of the mass spectrometer is a factor of 2.5 higher than that using the 213 nm laser. Reasons for these improvements are the shorter wavelength (193 nm compared with 213 nm) and the shorter pulse width (2.8 ns compared to 5 ns) of the new laser ablation system. Thus, the mean particle size of the ablated material and the localized heating of the sample is reduced, leading to a more uniform mass discrimination.

The Spectral Irradiance Monitor: Scientific Requirements, Instrument Design, and Operation Modes

The Spectral Irradiance Monitor (SIM) is a dual Fery prism spectrometer that employs 5 detectors per spectrometer channel to cover the wavelength range from 200 to 2700 nm. This instrument is used to monitor solar spectral variability throughout this wavelength region. Two identical, mirror-image, channels are used for redundancy and in-flight measurement of prism degradation. The primary detector for this instrument is an electrical substitution radiometer (ESR) designed to measure power levels ∼1000 times smaller than other radiometers used to measure TSI. The four complementary focal plane photodiodes are used in a fast-scan mode to acquire the solar spectrum, and the ESR calibrates their radiant sensitivity. Wavelength control is achieved by using a closed loop servo system that employs a linear charge coupled device (CCD) in the focal plane. This achieves 0.67 arcsec control of the prism rotation angle; this is equivalent to a wavelength positioning error of δλ/λ = 150 parts per million (ppm). This paper will describe the scientific measurement requirements used for instrument design and implementation, instrument performance, and the in-flight instrument operation modes.

Lead isotope ratio measurements in geological glasses by laser ablation-sector field-ICP mass spectrometry (LA-SF-ICPMS)

We have tested the capabilities of LA-SF-ICPMS for in situ Pb isotopic work on geological glasses using a 213 nm Nd:YAG laser system and a double focusing magnetic sector field ICP mass spectrometer. Experiments were done with the MPI-DING and USGS reference glasses, USGS rock powders molten as glass beads and basaltic glasses from Hawaii. In particular, the precision and accuracy of 208Pb/ 206Pb and 207Pb/ 206Pb ratios were investigated for three-spot analyses of glasses with different Pb contents (0.4–40 μg/g) at spot sizes of 12–160 μm. Using the fast and precise electrical scan mode, we obtained for samples with Pb concentration >1 μg/g in-run precisions (1 R.S.E.) of better than 0.1% and 0.2% for spot diameters of 120 and 40 μm, respectively. The LA-SF-ICPMS isotope ratios agree with the high-precision TIMS and MC-ICPMS data within the external precision (R.S.D. = 0.1–0.2%). The LA-SF-ICPMS results for 208Pb/ 204Pb, 207Pb/ 204Pb and 206Pb/ 204Pb are less precise (about 0.5–1%) due to the low abundance of 204Pb and correction from the 204Hg interference. In this paper, we present the first LA-SF-ICPMS Pb isotope data for the MPI-DING (KL2-G, ATHO-G) and USGS reference glasses (BCR-2G, BHVO-2G) which may be useful for microanalytical in situ Pb isotope analysis. The findings of small (<2%), but significant differences in Pb isotope ratios of Hawaiian glasses of different ages, demonstrate that LA-SF-ICPMS is a suitable tool for geochemical research.

High‐resolution observations of the small‐scale flow pattern associated with a poleward moving auroral form in the cusp

In this paper we present high‐resolution observations by the EISCAT Svalbard Radar of the localized ionospheric flow response due to one single flux transfer event and the relative location of a poleward moving auroral form. In a fast scan mode the radar was tracking a 50–60 km wide channel of westward flow in the cusp region. This flow channel was surrounded by flow running in the opposite direction. At the poleward edge of the narrow flow channel a poleward moving auroral form was situated, consistent with the auroral form being the signature of an upward Birkeland current filament. Our observations can be interpreted in terms of the Southwood [1985, 1987] flux transfer model, and the FTE twin‐cell flow pattern appears to be a ripple onto the larger‐scale background convection.

Fat mass measured by DXA varies with scan velocity.

To study the influence of scan velocities of DXA on the measured size of fat mass, lean body mass, bone mineral content and density, and total body weight. The subjects were 71 healthy white adults, 38 women and 33 men. The mean age was 41.7 +/- 13.5 years and body mass index was 28.6 +/- 5.6 kg/m(2). The subjects were scanned consecutively in slow, medium, and fast scan mode by a Lunar DPX-IQ DXA scanner. Throughout the body mass index and sagittal height ranges, scanned lean body mass significantly decreased with higher scan velocity and lean body mass was 2.7% lower in fast than in medium mode (p < 0.0001). In contrast, fat mass, percentage of body fat, and bone mineral contents were higher with increasing scan velocity. Areas not analyzed by the scanner, so called blue spots, increased with scan velocity and sagittal height, and their presence significantly enhanced the error. Body weight estimated by DXA in slow mode was -0.8% lower than scale weight in the women (p < 0.001) and -0.2% in men (not significant), and the difference was greater with increasing scan velocity. Scan velocity significantly influences the measured fat mass size, lean body mass, bone mineral content, and body weight. To obtain the most accurate results, slow mode is preferable and fast scans should be avoided. Future studies should report and take scan velocity into consideration.

Direct Voltammetric Observation of Reversible and Irreversible Oxidations of Two-Dimensional J-Aggregates of Cyanine Dye

The redox properties of two-dimensional (2D) J-aggregates of a typical thiacarbocyanine dye have been studied directly by the standard electrochemical method in conjunction with the recently developed technique for controlled layering of 2D J-aggregates on a self-assembled cysteamine monolayer on an atomically flat Au(111). The cyclic voltammograms measured at widely ranging scan rates from 10 mV/s to 100 V/s illuminated unique mechanistic features of the J-aggregate oxidation, which proved to be a convolution of reversible and irreversible oxidations involving the charge transfer of up to 4 electrons/molecule. The oxidation-induced irreversible bleaching of the J-band was accompanied by negligibly small changes in its peak position and sharpness, suggesting that the irreversible reaction occurs preferentially along the domain edges or boundaries. The two different phases of oxidation could be more or less clearly separated under the fast scan mode (scan rate larger than ∼10 V/s), giving us the unpreceden...

Scanning tunneling microscopy: a unique tool in the study of chirality, dynamics, and reactivity in physisorbed organic monolayers.

Scanning tunneling microscopy (STM) is applied to study organic monolayers, physisorbed at the liquid-graphite interface. Due to the very local nature of the probing, the structure of these adlayers has been imaged with very high detail. The high resolution allowed us to investigate the effect of molecular chirality on the monolayer formation and provided a unique way to study chemical reactions at the liquid-graphite interface. Making use of a fast scanning mode, dynamic processes in these adlayers have been visualized.

Inframetrics infrared scanner upgraded to a 12-bit digital thermography system for heat load measurements at nuclear fusion experiments

A commercially available Inframetrics Scanner (Modell 760) has been upgraded to 12-bit resolution in order to derive heat fluxes on tokamak devices (TEXTOR-94). The temperature resolution is high enough to detect—at the same camera settings—the small sawtoothing heat flux modulation and the large disruptive heat fluxes. Eight new boards have been developed and installed at TEXTOR-94 to perform the measurement, transmit the data from the experiment to the control room, and store the data in a PC. To ensure reliable data transmission, the data stream (1.1 MSPS) is transferred via optical fibers from the camera to the PC in the control room. The PC receives timing information from the TEXTOR-94 timing system such that a synchronization of the camera clock and the experimental clock is guaranteed. The new system includes a time reference to correct a small frequency drift of the original Inframetrics scanner. This feature permits to compare the heat flux with signals from other TEXTOR-94 diagnostics during fast events like disruptions for which the camera can also be operated in the fast line scan mode.

An automated ultrasonic immersion technique for the determination of three-dimensional elastic constants of polymer composites

Abstract An automated, ultrasonic immersion system based upon an original National Physics Laboratory design has been built and evaluated. Ultrasonic transducers operating at a frequency of 2.25 MHz have been used to investigate both tensile and shear velocities in fibre reinforced composite samples. The automation of the system allows fast and efficient large area scanning to be performed. Hence both large-scale, spatial variations in the tensile velocities can be investigated and also, all of the three-dimensional elastic moduli of fibre-reinforced polymer composites can be deduced by monitoring the variation of ultrasonic velocity with angle of incidence on orthogonal planes. Preliminary results indicate that the system will yield most of the three-dimensional elastic moduli to absolute accuracies of better than ± 1 % and in the fast scanning mode, will detect spatial variations of the time-of-flight of ultrasound with a fractional timing error of ± 0.001%. Work is in progress to correlate the ultrasonic propagation to three-dimensional mesostructural features. An automated, two-dimensional image analyser has been developed in-house and a Noran, three-dimensional confocal laser scanning microscope system is being automated at Leeds to determine the three-dimensional fibre orientation states and voidage within composite samples. Therefore it will soon be possible to evaluate existing models linking three-dimensional mesostructure to ultrasonic propagation and the stiffness constants of anisotropic materials.

Laser firing of transparent conducting SnO 2 sol—gel coatings

Sb doped sol—gel SnO 2 films were prepared from 0.5 M alcoholic solution of SnCl 2(OAc) 2 doped with 5 mol% SbCl 3 and deposited via a dip coating process on fused silica substrates. The coatings have been fired by CO 2 laser irradiation by means of a 700 W cw CO 2 laser using a fast scan mode in which the laser beam is scanned by a high speed rotating polygon scanner ( ω max = 8800 rpm) in one direction and the sample is moved perpendicularly at a speed up to 250 mm/s. Areas can be densified at a typical rate of ≈ 12 cm 2/s. The properties of the coatings have been measured by several methods: their sheet resistance, R□, has been measured using a four-probe technique, the structure of the coatings has been determined by X-ray diffraction at grazing incidence, their thickness by a surface profiler and their morphology by transmission electron microscopy. The thickness of the coatings, the crystallite size and the sheet resistance are determined by thermal driven processes. The coatings are made of dense aggregates of spherical shaped crystallites. The smallest resistivity obtained for a 100 nm thick coating is ϱ = 6 × 10 −3 ω cm a value that is three times lower than that obtained with conventionally heat treated samples.