Peak Full-width At Half-maximum Research Articles

Spectral change of simulated X-ray photoelectron spectroscopy from graphene to fullerene

C1s X-ray photoelectron spectroscopy (XPS) spectra of graphene with two to eight pentagons and fullerene pentagons were simulated using density functional theory calculation. Peak shifts and full width at half maximum (FWHM) of calculated C1s spectra were compared with those of actual C1s spectra. Introduction of up to four isolated pentagons had no influence on shifts of the calculated peak maxima of graphene (284.0 eV), whereas the introduction of six or more pentagons shifted the calculated peak maximum toward low binding energies because the number of connected pentagons increased. The presence of pentagons also influenced FWHMs. Introduction of six pentagons increased the calculated FWHMs from 1.25 to 1.45 eV, whereas introduction of eight or more pentagons decreased the FWHMs. The FWHM reached at 1.15 eV by introducing twelve pentagons (fullerene). These calculated shifts and FWHMs were close to the actual shifts of graphite (284.0 eV) and fullerene (282.9 eV) and FWHMs of graphite (1.25 eV) and fullerene (1.15 eV). Based on the calculated and the actual results, we proposed peak shifts and FWHMs of graphene with the different number of pentagons, which can be utilized for analyzing actual XPS spectra. Proposed FWHMs can be adjusted by measuring actual FWHMs using each device.

Effect of thermal annealing on the thermoluminescent properties of nano-calcium fluoride and its dose-response characteristics.

Nano-CaF2, prepared by the co-precipitation method, was annealed under different annealing conditions to improve its thermoluminescence (TL) characteristics. Different annealing parameters, such as temperature (400-700°C), duration (1-4 h) and environment (vacuum and air), were explored. The effect on TL sensitivity, peak position (Tm) and full-width at half-maximum (FWHM) with respect to the different annealing conditions are discussed as they are the measure of crystallinity of the material. Annealing temperature of 500°C with annealing duration of two and a half hours in vacuum provided the highest luminescence response (i.e. maximum sensitivity, minimum peak temperature and FWHM). Wide detectable dose range (5 mGy to 2 kGy), absence of thermal quenching and sufficient activation energy (1.04 eV) of this phosphor make it suitable for dosimetric applications.

Temperature Dependence of Emission Properties of Self-Assembled InGaN Quantum Dots

Emission properties of self-assembled green-emitting InGaN quantum dots (QDs) grown on sapphire substrates by using metal organic chemical vapor deposition are studied by temperature-dependent photoluminescence (PL) measurements. As temperature increases (15–300 K), the PL peak energy shows an anomalous V-shaped (redshift—blueshift) variation instead of an S-shaped (redshift—blueshift—redshift) variation, as observed typically in green-emitting InGaN/GaN multi-quantum wells (MQWs). The PL full width at half maximum (FWHM) also shows a V-shaped (decrease—increase) variation. The temperature dependence of the PL peak energy and FWHM of QDs are well explained by a model similar to MQWs, in which carriers transferring in localized states play an important role, while the confinement energy of localized states in the QDs is significantly larger than that in MQWs. By analyzing the integrated PL intensity, the larger confinement energy of localized states in the QDs is estimated to be 105.9 meV, which is well explained by taking into account the band-gap shrinkage and carrier thermalization with temperature. It is also found that the nonradiative combination centers in QD samples are much less than those in QW samples with the same In content.

Influence of the transfer and chemical treatment of monolayer graphene grown for flexible transparent electrodes

It has become critically important to develop reliable method to transfer chemical vapor deposited (CVD) graphene from its growth substrate to the target substrate without leaving undesired polymer residues on the graphene surface. Here, we have found that for the two different transfer method – wet transfer using poly(methyl methacrylate) (PMMA) and dry transfer using polydimethylsiloxane (PDMS) as support layer, the amount of polymer residues and other impurities left on the graphene surface varies depending on the solvent used to remove those polymers. The exposure of the graphenes to different organic solvents such as acetone and chloroform resulted in different amount of polymer residues and impurities present on the graphene surface, which impact the electronic structure of the transferred graphene. It was found that the graphene obtained using the dry transfer method and acetone as solvent with a 2D to G (I2D/IG) intensity ratio of 4.58 and a 2D peak full width-half maximum (FWHM) of 24.66, which was higher than that using the wet transfer method and chloroform as solvent. These results showed that graphene was less affected by the polymer residues and impurities or the dry transfer method rather than the wet transfer method. In addition, using acetone rather than chloroform as solvent in the dry transfer method led to less contaminated graphene.

Relationship between Peak Wavelength and Dominant Wavelength of Light Sources Based on Vector-Based Dominant Wavelength Calculation Method

ABSTRACTCurve fitting and lookup table methods based on vector relationships are proposed to compute dominant wavelength (DW), which is used to characterize hue. A curve-fitting method using a DW–angle relationship is simple but not very accurate, with an error of about 1 to 2 nm. A lookup table method is proposed for higher precision. The methods have been applied to study the relationships between peak wavelength and DW for Gaussian models of light sources’ spectra. For Gaussian models, DW varies as full-width at half maximum (FWHM) increases from 5 to 500 nm, and the trends differ at different peak wavelengths. For purity, as peak wavelength changes from 430 to 530 nm, the purity’s decreasing rate monotonically increases with FWHM, whereas as peak wavelength changes from 530 to 680 nm, the purity’s decreasing rate monotonically decreases with FWHM. Peak wavelength contours and FWHM contours are drawn for determination of DW and purity. The results should be useful for estimating DW (hue) of the Gaussian models of light sources’ spectra, which can guide the spectral design of light sources.

A Dual Side Electroluminescence Measurement System for LED Wafer Manufacturing

A measurement system is presented for evaluating the characteristics of both sides of an LED wafer using electroluminescence (EL). Integrating spheres (IS), photodiodes, pico-ammeters, spectrometers were installed in the front and rear sides to measure optical characteristics with minimum EL loss. A probe was connected to a source meter with a thin wire and attached using a transparent fixture in the front IS. The EL characteristics in a measuring point were peak wavelength, FWHM (full width at half maximum), forward current, forward voltage and reverse current. EL images were created by combining the motion of a stage and the EL characteristics. The correlation between the EL and the chip-level tests and the repeatability test showed that the dual measurement is useful for LED manufacturing. Our patents were applied to install the probe and create the EL image. Keywords: Electroluminescence, EL imaging, epi-wafer, Optical spectrum, LED manufacturing.

Effects of electrical conductivity of substrate materials on microstructure of diamond-like carbon films prepared by bipolar-type plasma based ion implantation

Diamond-like carbon (DLC) films are prepared by a bipolar-type plasma based ion implantation, and the structural differences between DLC films deposited on different electrical conductive substrates, i.e., conductive Si wafers and insulating glass plates are examined by Raman spectroscopy and x-ray photo emission spectroscopy (XPS). In the Raman measurements, graphite (G) and disorder (D) peaks are observed for both samples. However, the additional photo luminescence is overlapped on the spectra in the case of on-glass sample. To elucidate the structural difference, the intensity ratio of D to G peak (I(D)/I(G)), G peak position and full width at half maximum (FWHM) are obtained by curve fitting using Gaussian function and linear baseline. It is found that the I(D)/I(G) is lower, G peak position is higher and FWHM of G peak is narrower for on-glass sample than for on-Si sample. According to Robertson [1], lower I(D)/I(G) seems more sp3 C-C bonding in amount for on-glass sample. In contrast, higher G peak position and narrower FWHM of G peak suggest less sp3 C-C bonding in amount for on-glass sample. The results of XPS analysis with C1s spectra reveal that sp3 ratio, i.e., the intensity ratio of sp3/(sp3+sp2) is smaller for on-glass sample than for on-Si sample. The inconsistency of the trend between I(D)/I(G) and other parameters (G peak position and FWHM of G peak) might be caused by the overlap of photo luminescence signal on Raman spectrum as to on-glass sample. From these results, it is considered that sp3 C-C bonding is reduced in amount when using insulating substrate in comparison with conductive substrate.

Correlation between full width at half maximum (FWHM) of XRD peak with residual stress on ground surfaces

The full width at half maximum (FWHM) of XRD profiles is used to characterize different material properties and surface integrity features. However, there is no literature available that discusses the nature of the correlation between the FWHM of XRD peaks with induced surface residual stress upon grinding with simultaneous occurrence of plastic deformation, formation of white layer, grain elongation, change in microhardness, etc. AISI 1060 steel samples were ground under different grinding domains, i.e. conventional abusive grinding, conventional grinding, cBN grinding and high speed grinding with moderately deep cut. Induction of tensile and compressive residual stress, microstructural changes, white layer formation, grain refinement, plastic deformation, grain elongation and change in microhardness were observed upon grinding AISI 1060 steel. A correlation was established between the FWHM of XRD peaks and surface residual stress when simultaneous changes in microhardness and microstructure, grain elongation, plastic deformation and formation of white layer take place due to grinding. The correlation between FWHM of XRD peak and residual stress appears to be nonlinear due to simultaneous change in other aspects of surface integrity.

Micrometer-scale synchrotron diffraction mapping analysis of carbide precipitation in deep cryogenically treated low carbon steel

Abstract

Time dependent thermal treatment of oxidized MWCNTs studied by the electron and mass spectroscopy methods

Purified and functionalized in boiling concentrated (68%) HNO3 acid the oxidized multiwall carbon nanotubes (ox-MWCNTs) under thermal treatment from RT to 630°C and at 350°C time dependent (1–4h) were investigated using the surface sensitive electron and mass spectroscopy methods.Mass spectroscopy indicates significant desorption of H2 and H2O to about 300°C. Higher H2 desorption rate from RT up to about 100°C is most likely caused by decomposition of organic acid impurities included within a bundle and in channels of the ox-MWCNTs after their functionalization by HNO3. In the range of 100–300°C part of the detected H2, accompanied by desorption of CO2, may origin from desorbed water. Above 300°C, the small amount of desorbing H2O may result from transformation of carboxylic groups into carboxylic acid anhydride. Significant desorption of CO2 starting from 150°C may result from decomposition of carboxylic groups, whereas desorption of CO starting at about 300°C from decomposition of acid anhydride groups created from carboxylic groups during thermal dehydration. Desorption of CO and CO2 at about 470°C may be due to decomposition of hydroxyl OH and carbonyl CO groups. Above 600°C mainly decomposition of CO groups takes place and results in small desorption of CO. Time dependent (1–4h) thermal treatment of ox-MWCNTs at 350°C shows in XPS spectra decreasing amount of CO in carboxyl groups and increasing amount of CO in carbonyl and acid anhydride groups arising from carboxyl groups decomposition. Between 350°C and 470°C the higher desorption rate of CO2 than CO indicates significant decomposition of carboxyl and carboxyl anhydride groups. At 350°C the dynamic changes are indicated by the energy, intensity and full width at half maximum (FWHM) of the π→π* interband transition and π loss peak, and quasi-elastic peak FWHM. During 4h at 350°C no C sp2 reconstruction is observed. For the applied procedure of MWCNTs oxidation, large amount of water and some organic acid impurities, resulting from the MWCNTs oxidation, remain in the CNTs channels, interstitial channels between tubes and at nanotubes surface.

Dependence of spectroscopic properties on doping content and temperature of bismuth-doped lanthanum aluminosilicate glass

The effects of bismuth doping content and temperature on the absorption property and near-infrared (NIR) luminescence of Bi-doped La2O3-Al2O3-SiO2 (LAS) glasses are presented. The emission intensity reaches the maximum when the Bi2O3 content in 3.0Bi-LAS is 1.83%. The emission spectra reach their peaks at 1 190 and 1 117 nm, with full-width at half-maximum (FWHM) values of 330 and 228 nm under 500 and 700-nm excitations, respectively. As the Bi2O3 content increases, the peak wavelengths and FWHMs of emission bands increase, but their lifetimes decrease. The lifetime of 2.0Bi-LAS is 460 ?s at 9 K, and is almost temperature independent until 350 K. The NIR emission of Bi in the system has strong resistance to thermal quenching from 9 to 350 K.

Experimental assessment of the phonon confinement in TiO2 anatase nanocrystallites by Raman spectroscopy

TiO2 aerogels prepared by sol‐gel method and followed by supercritical drying have been annealed at temperatures ranging between 400 and 550 °C. The obtained TiO2 anatase crystallites with the mean size between 6.4 and 13.9 nm, as obtained from transmission electron microscopy measurements, have been further investigated by Raman spectroscopy. It was found that the peak position and full width at half maximum (FWHM) of the TiO2 anatase Raman bands located around 144, 398, and 638 cm−1 are influenced by crystallite dimension. These spectral changes can be assigned to the combined action of several nanosize effects such as phonon confinement, phonon coupling, strain, and stoichiometry defects. Surprisingly, the best discrimination of the FWHM change with the nanocrystallite mean size was achieved for the 638 cm−1 band, whereas the best discrimination for the peak position was found for the 398 cm−1 band. The critical size values obtained from the peak position and FWHM evaluation were between 12.7 and 13.1 nm. Taking into consideration that only the phonon confinement and inhomogeneous strain can induce an asymmetric broadening of the Raman signal, the bands asymmetry was evaluated, and the critical size values of the nanocrystallites were determined to be between 10 and 11 nm. For a symmetric size distribution of TiO2 anatase crystallites with dimensions between 6.4 and 13.9 nm, the obtained result indicates that the phonon confinement contribution to the overall size effects is more than 75%. No evidence about the influence of the phonon coupling and vacancies on the Raman features was observed. The comparison of the data derived from the experimental analysis with those obtained by applying the theoretical phonon confinement model indicates the necessity of developing an improved phonon confinement model. The asymmetry approach can be applied for a great variety of nanostructures, as a measure of the confinement effect. Copyright © 2011 John Wiley & Sons, Ltd.

Characterization of damage behavior induced by low-temperature BGe molecular ion implantation in silicon

The present study utilized Raman scattering spectroscopy (RSS) to characterize damage behavior induced by implanting 77 keV BGe molecular ions into Si<100> wafers at low substrate temperatures under various ion fluences. The low substrate temperatures under investigation included liquid nitrogen temperature (LT) and room temperature (RT). Rapid thermal annealing (RTA) at 1050 °C for 25 s in nitrogen ambient was adopted in order to perform the post-annealing treatments. The as-implanted results revealed that the longitudinal optical (LO) phonon Raman peak (indicating the crystalline silicon phase) exhibited a decrease in peak intensity, peak position, and peak area but an increase in full-width at half-maximum (FWHM) of the peak as ion fluence increased or substrate temperature decreased. However, the transverse optical (TO) phonon Raman peak (indicating the amorphous silicon phase) decreased in peak position and FWHM of the peak but increased in peak intensity and peak area when ion fluence increased or substrate temperature decreased. The amount of implantation-induced damage in the LT specimens is greater than it is in the RT ones. However, the as-annealed results revealed that the amount of residual damage in the LT specimens is slightly smaller than it is in the RT ones and the difference widens as ion fluence increases.

Continuous analysis of dye-loaded, single cells on a microfluidic chip.

Continuous analysis of two dyes loaded into single mammalian cells using laser-based lysis combined with electrophoretic separation was developed and characterized on microfluidic chips. The devices employed hydrodynamic flow to transport cells to a junction where they were mechanically lysed by a laser-generated cavitation bubble. An electric field then attracted the analyte into a separation channel while the membranous remnants passed through the intersection towards a waste reservoir. Phosphatidylcholine (PC)-supported bilayer membrane coatings (SBMs) provided a weakly negatively charged surface and prevented cell fouling from interfering with device performance. Cell lysis using a picosecond-pulsed laser on-chip did not interfere with concurrent electrophoretic separations. The effect of device parameters on performance was evaluated. A ratio of 2 : 1 was found to be optimal for the focusing-channel : flow-channel width and 3 : 1 for the flow-channel : separation-channel width. Migration times decreased with increased electric field strengths up to 333 V cm(-1), at which point the field strength was sufficient to move unlysed cells and cellular debris into the electrophoretic channel. The migration time and full width half-maximum (FWHM) of the peaks were independent of cell velocity for velocities between 0.03 and 0.3 mm s(-1). Separation performance was independent of the exact lysis location when lysis was performed near the outlet of the focusing channel. The migration time for cell-derived fluorescein and fluorescein carboxylate was reproducible with <10% RSD. Automated cell detection and lysis were required to reduce peak FWHM variability to 30% RSD. A maximum throughput of 30 cells min(-1) was achieved. Device stability was demonstrated by analyzing 600 single cells over a 2 h time span.

Effect of indium incorporation on optical and structural properties of m-plane InGaN/GaN MQW on LiAlO 2 substrates

We report about the optical and structural characterization of m-plane InGaN/GaN multiple quantum well (MQW) structures. All samples were grown on 2-inch LiAlO 2 substrates in AIXTRON MOVPE reactors. By lowering the MQW growth temperature, an increase of an indium fraction from 5% to 30% is achieved. High-resolution X-ray diffraction (HRXRD) reciprocal space mapping reveals fully strained growth of the quantum wells. The photoluminescence (PL) peak full width half maximum (FWHM) values increase from ∼130 to ∼240 meV at room temperature when the indium fraction rises from 10% to 30% . Also, PL peaks show good wavelength stability for indium contents up to 10% when the excitation intensity is varied by two orders of magnitude. However, at 20% indium and above, a clear excitation intensity-induced peak shift of around 50 meV is detected which is likely caused by indium segregation. Cross-section transmission electron microscopy (TEM) hints at indium fluctuation near extended defects. We conclude that an improved growth process for nonpolar InGaN/GaN MQW is necessary to achieve high-performance long-wavelength light-emitting devices.

Improved multimodality imaging using alginate molding in xenograft tumor models

To allow for reproducible rodent positioning using molding in multimodal tomographic imaging (positron emission tomography [PET], magnetic resonance imaging/spectroscopy [MRI/MRS]), minimization of magnetic field inhomogeneity during MRI investigations of peripheral structures, and reproducible positioning for subsequent histological sectioning of the separated tumor. Chemical shift imaging (CSI) studies were carried out using phantoms and NMRI nu/nu mice bearing subcutaneous tumors. For embedding, three different materials were used: 1) alginate, 2) gelatin, and 3) a mixture of wheat flour and salt. The animals were placed in an animal chamber including position markers visible by MRI and PET. The frozen embedded explanted tumors were sliced and examined autoradiographically as well as histologically. Alginate showed a substantial improvement of magnetic field homogeneity and histological sectioning was superior to the other methods. This embedding led to a significant reduction of the full width at half maximum (FWHM) of the water peak in the peripheral rim of the tumor in comparison to the same peak FWHM without embedding (41 +/- 10 Hz vs. 80 +/- 20 Hz). Our research shows that animal positioning in an imaging chamber together with alginate embedding allows high-quality multimodality investigations including coregistration of MRI/MRS, PET, and histological images.

Improved Resolution and Reduced Clutter in Ultra‐Wideband Microwave Imaging Using Cross‐Correlated Back Projection: Experimental and Numerical Results

Microwave breast cancer detection is based on the dielectric contrast between healthy and malignant tissue. This radar-based imaging method involves illumination of the breast with an ultra-wideband pulse. Detection of tumors within the breast is achieved by some selected focusing technique. Image formation algorithms are tailored to enhance tumor responses and reduce early-time and late-time clutter associated with skin reflections and heterogeneity of breast tissue. In this contribution, we evaluate the performance of the so-called cross-correlated back projection imaging scheme by using a scanning system in phantom experiments. Supplementary numerical modeling based on commercial software is also presented. The phantom is synthetically scanned with a broadband elliptical antenna in a mono-static configuration. The respective signals are pre-processed by a data-adaptive RLS algorithm in order to remove artifacts caused by antenna reverberations and signal clutter. Successful detection of a 7 mm diameter cylindrical tumor immersed in a low permittivity medium was achieved in all cases. Selecting the widely used delay-and-sum (DAS) beamforming algorithm as a benchmark, we show that correlation based imaging methods improve the signal-to-clutter ratio by at least 10 dB and improves spatial resolution through a reduction of the imaged peak full-width half maximum (FWHM) of about 40–50%.

The electrical, optical, and structural properties of GaN epitaxial layers grown on Si(111) substrate with [formula omitted] interlayers

The effect of the in situ substrate nitridation time on the electrical, structural and optical properties of GaN films grown on Si(111) substrates by metal organic chemical vapor deposition (MOCVD) was investigated. A thin buffer layer of silicon nitride (SiN x ) with various thicknesses was achieved through the nitridation of the substrate at different nitridation times ranging from 0 to 660 s. The surface roughness of the GaN film, which was grown on the Si substrate 10 s, exhibited a root mean square (RMS) value of 1.12 nm for the surface roughness. However, further increments in the nitridation times in turn cause increments in the surface roughness in the GaN layers. The number of threading dislocation (TD) was counted from plan-view TEM (Transmission Electron Microscopy) images. The determined density of these threading dislocations was of the order of 9×10 9 cm −2. The sheet resistances of the GaN layers were measured. The average sheet resistance significantly increases from 2867 Ω sq −1 for sample A (without nitridation) to 8124 Ω sq −1 for sample F (with 660 s nitridation). The photoluminescence (PL) measurements of the samples nitridated at various nitridation times were done at a temperature range of 10–300 K. A strong band edge PL emission line, which was centered at approx. 3.453 eV along with its phonon replicas which was separated by approx. 92 meV in successive orders, was observed at 10 K. The full width at half maximum (FWHM) of this peak is approx. 14 meV, which indicates the reasonable optical quality of the GaN epilayers grown on Si substrate. At room temperature, the peak position and FWHM of this emission became 3.396 eV and 58 meV, respectively.

High-Resolution Ultraviolet Laser Spectroscopy in Atomic Erbium

High-Resolution Ultraviolet Laser Spectroscopy in Atomic Erbium

Reproducibility of the aortic input function (AIF) derived from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) of the kidneys in a volunteer study

Purpose The aim of this study was to investigate the maximum height, area under the curve (AUC) and full width at half maximum (FWHM) of the aortic input function (AIF) in renal dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) studies. We evaluated the significance of choice of size for regions of interest (ROI) in the aorta, reproducibility and inter-observer agreement of AIF measurements in healthy volunteers for renal DCE-MRI studies. Methods Fifteen healthy volunteers (nine males, six females), mean age 28.8 years (range 23–36 years), underwent two DCE-MRI kidney studies under similar conditions. Oblique-coronal DCE-MRI data volumes were acquired on a 1.5 T Siemens Avanto scanner with a 3D-FLASH pulse-sequence (TE/TR = 0.53/1.63 ms, flip angle = 17°, acquisition matrix = 128 × 104 voxels, strong fat saturation, PAT factor = 2 (GRAPPA) and 400 mm × 325 mm FOV). Each dynamic dataset consisted of 18 slices of 7.5 mm thickness (no gap) and an in-plane resolution of 3.1 mm × 3.1 mm, acquired every 2.5 s for >5 min. During the MR scan a dose of 0.05 mmol (0.1 mL) kg −1 body weight of dimeglumine gadopentetate (Magnevist) was injected intravenously (2 mL s −1 injection rate), followed by a 15 mL saline flush at the same rate, using a MR-compatible automated injector (Spectris). For each DCE-MRI study two observers each drew two ROIs in the abdominal aorta. Both ROIs were 3 voxels in width and had the same inferior limit (just above the emergence of the renal arteries from the aorta) but had different heights (4 voxels for one ROI and 10 voxels for the other). The dimensions, position and time of drawing the ROIs in the dynamic study were standardised between observers prior to data analysis. Mean signal intensities measured in the ROIs were plotted over time, representing the AIF. For each study, AIF 1 was derived from ROI 1 and AIF 2 was derived from ROI 2. Results and conclusion Paired t-tests for inter-observer comparison on the pooled 30 DCE-MRI studies, showed good correlations (correlation coefficients >0.85) with no significant differences ( p-values >0.82) when comparing the peak value, AUC and FWHM of the AIFs. Thus the results were operator independent. The size of the aortic ROIs significantly affected all measured parameters of the AIF ( p-values <0.039). However, correlation coefficients when comparing AIF 1 and AIF 2 were high for all evaluated AIF parameters (correlation coefficients >0.88), indicating a similar shape and temporal dynamic of the passage of the contrast agent through the aorta. When comparing the intra-individual DCE-MRI studies for each volunteer all AIF parameters had p-values >0.22 and correlation coefficients <0.82, with the exception of the FWHM, which had a correlation coefficient of 0.96 showing a significant variation in AIF parameters in the same volunteer on different days.