Integrated Intensity Profiles Research Articles

Temperature induced modulation of resonant Raman scattering in bilayer 2H-MoS2

The temperature evolution of the resonant Raman scattering from high-quality bilayer 2H-MoS_{2} encapsulated in hexagonal BN flakes is presented. The observed resonant Raman scattering spectrum as initiated by the laser energy of 1.96 eV, close to the A excitonic resonance, shows rich and distinct vibrational features that are otherwise not observed in non-resonant scattering. The appearance of 1st and 2nd order phonon modes is unambiguously observed in a broad range of temperatures from 5 to 320 K. The spectrum includes the Raman-active modes, i.e. E_{text {1g}}^{2}(Gamma) and A_{text {1g}}(Gamma) along with their Davydov-split counterparts, i.e. E_{text {1u}}(Gamma) and B_{text {1u}}(Gamma). The temperature evolution of the Raman scattering spectrum brings forward key observations, as the integrated intensity profiles of different phonon modes show diverse trends. The Raman-active A_{text {1g}}(Gamma) mode, which dominates the Raman scattering spectrum at T = 5 K quenches with increasing temperature. Surprisingly, at room temperature the B_{text {1u}}(Gamma) mode, which is infrared-active in the bilayer, is substantially stronger than its nominally Raman-active A_{text {1g}}(Gamma) counterpart.

On the role of the second-order derivative term in the calculation of convergent beam diffraction patterns

The simulation of (scanning) transmission electron microscopy images and diffraction patterns is most often performed using the forward-scattering approximation where the second-order derivative term in z is assumed to be small with respect to the first-order derivative term in the modified Schrödinger equation. This assumption is very good at high incident electron energies, but breaks down at low energies. In order to study the differences between first- and second-order methods, convergent beam electron diffraction patterns were simulated for silicon at the [111] zone-axis orientation at 20 keV and compared using electron intensity difference maps and integrated intensity profiles. The geometrical differences in the calculated diffraction patterns could be explained by an Ewald surface analysis. Furthermore, it was found that solutions based on the second-order derivative equation contained small amplitude oscillations that need to be resolved in order to ensure numerical integration stability. This required the use of very small integration steps resulting in significantly increased computation time compared to the first-order differential equation solution. Lastly, the efficiency of the numerical integration technique is discussed.

High Resolution HAADF Characterization of Ir/TiO2 Catalyst Reduced at 500 °C: Intensity Profile Analysis

A comparison is presented between experimental and simulated high resolution-high angle annular dark field images (HR-HAADF) of Ir/TiO2 catalyst reduced at 500 °C where classical strong metal–support interaction develops. The analysis is based on integrated intensity profiles of the atomic columns of iridium nanoparticles on the TiO2 support. The results were as expected, that when Ir/TiO2 catalyst is reduced at high temperature, partially reduced species from the support (TiOx) migrate to the surface of iridium nanoparticles. Two very important facts can be highlighted: one is that the Ti atoms sited on atomic columns in the [110] direction preserve the atomic ordering of the metallic particle (epitaxial growth), while those located in atomic columns at perpendicular directions to the observation axis are disordered, and as a consequence, they appear as an amorphous thin film. Finally, changes in the (111) interplanar spacing of TiO2-rutile structure could be due to an enrichment of Ti3+ species at the ...

EXPANDED VERY LARGE ARRAY OBSERVATIONS OF THE BARNARD 5 STAR-FORMING CORE: EMBEDDED FILAMENTS REVEALED

We present a ~6.5'x8' Expanded Very Large Array (EVLA) mosaic observations of the NH3 (1,1) emission in the Barnard 5 region in Perseus, with an angular resolution of 6". This map covers the coherent region, where the dense gas presents subsonic non-thermal motions (as seen from single dish observations with the Green Bank Telescope, GBT). The combined EVLA and GBT observations reveal, for the first time, a striking filamentary structure (20" wide or 5,000 AU at the distance of Perseus) in this low-mass star forming region. The integrated intensity profile of this structure is consistent with models of an isothermal filament in hydrostatic equilibrium. The observed separation between the B5-IRS1 young stellar object (YSO), in the central region of the core, and the northern starless condensation matches the Jeans length of the dense gas. This suggests that the dense gas in the coherent region is fragmenting. The region observed displays a narrow velocity dispersion, where most of the gas shows evidence for subsonic turbulence, and where little spatial variations are present. It is only close to the YSO where an increase in the velocity dispersion is found, but still displaying subsonic non-thermal motions

The use of orthogonal projection to visualize mosaic domains from topographic data collected on protein crystals

Owing to the relatively low intensity of diffraction and resulting low contrast topographic images, and also the richly detailed domain structure, it can be difficult to extract individual mosaic domains (size and shape) for protein crystals. Here, orthogonal projection was tested and found to be a superior approach over previous methods to extract mosaic domain information from a fine-sliced topographic sequence of images. The topographic sequence was collected at room temperature from a lysozyme crystal with a low mosaicity. Orthogonal projection can be applied to image sequences that are spatially invariant and composed of linearly additive image formation processes. The domains were determined by using a particle swarm optimizer to fit Gaussians to the integrated intensity profile of the reflection as a function of angle, although any basis function could have been used. This optimization method was more amenable to automation and converged to the global minimum more efficiently. The number of domains can normally be determined by visually inspecting the integrated intensity profile; this only needs to be done once for each crystal, because the number of domains remains constant during collection, and not for each reflection. The results can be used to provide a picture of the internal structure of the crystal and may be useful to aid in the improvement of crystal growth techniques.

Dense Cores in Dark Clouds. XIV. N2H+(1–0) Maps of Dense Cloud Cores

We present results of an extensive mapping survey of N2H+(1-0) in about 60 low mass cloud cores already mapped in the NH3(1,1) inversion transition line. The survey has been carried out at the FCRAO antenna with an angular resolution about 1.5 times finer than the previous ammonia observations. Cores with stars typically have map sizes about a factor of two smaller for N2H+ than for NH3, indicating the presence of denser and more centrally concentrated gas compared to starless cores. Significant correlations are found between NH3 and N2H+ column densities and excitation temperatures in starless cores, but not in cores with stars, suggesting a different chemical evolution of the two species. Velocity gradients range between 0.5 and 6 km/s/pc, similar to what has been found with NH3 data. ``Local'' velocity gradients show significant variation in both magnitude and direction, suggesting the presence of complexmotions not interpretable as simple solid body rotation. Integrated intensity profiles of starless cores present a ``central flattening'' and are consistent with a spherically symmetric density law n ~ r^{-1.2} for r < ~0.03 pc and n ~ r^{-2} at larger r. Cores with stars are better modelled with single density power laws with n ~ r^{-2}. Line widths change across the core but we did not find a general trend. The deviation in line width correlates with the mean line width, suggesting that the line of sight contains ~ 10 coherence lengths. The corresponding value of the coherence length, ~ 0.01 pc, is similar to the expected cutoff wavelength for MHD waves. This similarity may account for the increased ``coherence'' of line widths on small scales. Despite of the finer angular resolution, the majority of N2H+ and NH3 maps show a similar ``simple'' structure, with single peaks and no elongation.

Chemical and Structural Characterization of Ultrathin Dielectric Films Using AEM

ABSTRACTThe structure of ultrathin silicon oxynitride films, used as gate dielectrics in integrated circuits (ICs), is studied using analytical electron microscopy (AEM). Laterally homogeneous blanket films approximately 2 nm in thickness are characterized in cross section using a 300 keV field emission TEM/STEM. High resolution imaging (HRTEM) is used to investigate the accuracy and precision of film thickness measurements and their comparability to other techniques such as secondary ion mass spectrometry, spectroscopic ellipsometry, x-ray reflectivity, x-ray photoelectron spectroscopy, and medium energy ion scattering. A two dimensional magnification calibration scheme that fits a pair of basis vectors to experimental images is presented, and integrated intensity profiles are used to define film boundaries for measurement. These image processing tools simultaneously improve the repeatability of the measurements and remove subjective operator bias from the measurement process.

Individual Pulse Polarization of Pulsars at Low Frequencies

AbstractThis paper presents the results of the measurements of linear polarization characteristics of individual pulses at frequencies 40, 60 and 103 MHz for 10 strong pulsars. We have measured total intensity, linear polarization percentage and angle along the pulse window and obtained distribution displays for these data.Two orthogonal polarization modes are common features in the radiation of pulsars at low frequency. The energy ratio of these two modes can change significantly between different frequencies. The linear polarisation percentage has a general tendency to increase at low frequencies, but by very different factors for different components of the integrated intensity profile. The relationship between the polarization properties of PSR 0943+10 and its mode changing behaviour was studied. It is shown that the energy ratio and the frequency of occurence of two polarization modes change simultaneously with changes in the integrated intensity profile.

Studies of Mo/Si multilayers with coherent electron beams

The Mo/Si multilayer system has been used to evaluate different methods employing coherent electrons from field-emission sources, in particular nanodiffraction and high-spatial-resolution parallel electron-energy-loss spectroscopy. Nanodiffraction patterns from the individual multilayer interfaces exhibited strong streaking on the transmitted disk, directed towards the Mo layer. The streaking increased with specimen thickness and reached a saturation value of ∼7 mrad. This effect can be interpreted as due to refraction of high-energy electrons at the interface, yielding a measured mean inner potential difference between Mo and Si of 8 ± 2 V. PEELS t/λ studies show that specimen thickness profiles are variable for the same multilayer sample. Core-loss integrated intensity profiles show asymmetry in interface width of sputtered multilayers, but proble deconvolution is needed to quantify the width of the intermixed interface. The nanodiffraction and PEELS methods are compared with previous studies with off-axis electron holography, shadow imaging, and with more established incoherent imaging methods.

A simple method to monitor the intensity profile of a pulsed laser beam with micrometer resolution

A simple method is demonstrated for monitoring the time integrated intensity profile of a pulsed laser beam based on desorption from homogeneous films of Rhodamine 6G dye. The method offers micrometer resolution, and for the case of a Gaussian beam profile the fluence scale may be calibrated.

Automated Chromosome Classification System by Using Integrated Intensity Profile

Automated Chromosome Classification System by Using Integrated Intensity Profile

A study of PSR1237 + 25 at 430 MHz

PSR1237 + 25, one of the first pulsars to be discovered1,2, is characterized by a striking five-peaked integrated intensity profile. Like many other pulsars, PSR1237 + 25 also exhibits the puzzling phenomena of drifting subpulses, ‘nulling’ and ‘mode-switching’. The period of pulsation is 1.38 s, but the radio-emission occurs within an 80 ms interval. We have analysed single-pulse data from this pulsar at 430 MHz to throw light on the still obscure mechanism of pulsar emission. We conclude that the behaviour of PSR1237 + 25 can be explained on the polar-cap model if regular short (S) bursts spiralling in towards the magnetic pole are occasionally interrupted by long (L) bursts along the magnetic axis.

Characterization of ultrasonic exposure fields

Acoustic field parameters were measured and calculated for an automatic-scan ultrasonic exposure apparatus designed for biological effects studies that has been previously reported. Free far-field pressure profiles of disk transducers resonant at 1.0 MHz were obtained under conditions using a hydrophone calibrated by a pendulum consisting of a stainless steel sphere on a bifilar suspension. Typical total acoustic power measurements using a radiation force balance technique agreed within ±10% of the integrated intensity profiles. An efficient computer program was used to calculate the pressure distribution for a baffled piston by means of an existing Fourier transform approach. These theoretical intensity profiles agreed well with the actual data. Several scans directly behind holders used to expose both biological solutions and cell suspensions showed disruption of the normal free-field pattern. Scans also demonstrated differences in the acoustic coupling to mice for various preparation methods prior to ultrasound exposure.