Step-scan Method Research Articles

Direct in Situ Fabrication of Multicolor Afterglow Carbon Dot Patterns with Transparent and Traceless Features via Laser Direct Writing.

Multicolor afterglow patterns with transparent and traceless features are important for the exploration of new functionalities and applications. Herein, we report a direct in situ patterning technique for fabricating afterglow carbon dots (CDs) based on laser direct writing (LDW) for the first time. We explore a facile step-scanning method that reduces the heat-affected zone and avoids uneven heating, thus producing a fine-resolution afterglow CD pattern with a minimum line width of 80 μm. Unlike previous LDW-induced luminescence patterns, the patterned CD films are traceless and transparent, which is mainly attributed to a uniform heat distribution and gentle temperature rise process. Interestingly, by regulating the laser parameters and CD precursors, an increased carbonization and oxidation degree of CDs could be obtained, thus enabling time-dependent, tunable afterglow colors from blue to red. In addition, we demonstrate their potential applications in the in situ fabrication of flexible and stretchable optoelectronics.

Step-scan differential calorimetry of protein denaturation: Modeling and experiment

Calorimetric step-scan curves of the reversible protein denaturation were modeled numerically. The quasi-equilibrium denaturation regime can be realized if the duration of isothermal steps is long enough so that the system is able to settle to equilibrium. We show the changes in the real and imaginary parts of the complex heat capacity during the denaturation process depending on the kinetic regime of denaturation. The practical application of the step-scan method for denaturation of lysozyme in water has revealed the negative temperature coefficient of the excess heat capacity of lysozyme. In the case of denaturation of lysozyme in glycerol studied by fast scanning calorimetry, the step-scan technique can be used to improve the quality of the baseline and reveal a heat capacity step after during denaturation.

A Laser Scanner–Stage Synchronized System Supporting the Large-Area Precision Polishing of Additive-Manufactured Metallic Surfaces

This paper proposes a scanner–stage synchronized approach emphasizing a novel control structure for the laser polishing of Inconel 718 components manufactured by selective laser melting in order to address increasing demands for high surface quality in metal additive manufacturing. The proposed synchronized control system is composed of a motion decomposition module and an error synthesis module. The experimental results show that stitching errors can be avoided thanks to continuous motion during laser processing. Moreover, in comparison with the existing step-scan method, the processing efficiency of the proposed method is improved by 38.22% and the surface quality of the laser-polished area is significantly enhanced due to a more homogeneous distribution of the laser energy during the material phase change. The proposed synchronized system paves the way for high-speed, high-precision, and large-area laser material processing without stitching errors.

Fast diffraction-enhanced imaging using continuous sample rotation and analyzer crystal scanning.

Diffraction-enhanced imaging (DEI) has high sensitivity and a wide dynamic range of density and thus can be used for fine imaging of biological and organic samples that include large differences in density. A fast DEI method composed of continuous fast sample rotations and slow analyzer crystal scanning was developed to shorten the measurement period. Fine sectional images of a biological sample were successfully obtained within a half measurement period of the conventional step-scanning method while keeping the same exposure time. In addition, a fine three-dimensional image of a rat tail was obtained with a375 s measurement period.

Transient photoinduced phenomena in graphitic carbon nitride as measured at nanoseconds resolution by step-scan FTIR

Abstract Transient FTIR measurements were performed on graphitic carbon nitride using a step-scan method, facilitating temporal resolution of a few nanoseconds. Variations in the location and the intensity of specific peaks and emerging of new peaks were observed during the first 170 nanoseconds after excitation. A comparison was made between graphitic carbon nitride prepared at two temperatures: 510 °C and 650 °C. The material prepared at 650 °C revealed very strong non-specific absorption beginning 35 nanoseconds after excitation and lasting for 20 nanoseconds. This phenomenon, termed “IR-blackening” was observed neither in g-C3N4 prepared at 510 °C nor in g-C3N4 prepared at 650 °C that was exposed to hole scavengers (ethanol and benzyl alcohol). In contrast, exposure of material prepared at 650 °C to an electron scavenger (methyl viologen) hardly alter the “IR-blackening” phenomenon. The results were explained by a mechanism, predicting higher reductive activity for materials having imperfect heptazine polymerization, as indeed was found in the photocatalytic degradation of 4-nitrophenol.

Step-scan differential Fourier transform infrared photoacoustic spectroscopy (DFTIR-PAS): a spectral deconvolution method for weak absorber detection in the presence of strongly overlapping background absorptions.

The determination of small absorption coefficients of trace gases in the atmosphere constitutes a challenge for analytical air contaminant measurements, especially in the presence of strongly absorbing backgrounds. A step-scan differential Fourier transform infrared photoacoustic spectroscopy (DFTIR-PAS) method was developed to suppress the coherent external noise and spurious photoacoustic (PA) signals caused by strongly absorbing backgrounds. The infrared absorption spectra of acetylene (C2H2) and local air were used to verify the performance of the step-scan DFTIR-PAS method. A linear amplitude response to C2H2 concentrations from 100 to 5000ppmv was observed, leading to a theoretical detection limit of 5ppmv. The differential mode was capable of eliminating the coherent noise and dominant background gas signals, thereby revealing the presence of the otherwise hidden C2H2 weak absorption. Thus, the step-scan DFTIR-PAS modality was demonstrated to be an effective approach for monitoring weakly absorbing gases with absorption bands overlapped by strongly absorbing background species.

Heat capacity measurement with simultaneous comparison with a reference sample by step scanning method

Heat capacity measurement with simultaneous comparison with a reference sample by step scanning method

Continuous-scan capability at SSRL and applications to X-ray diffraction.

Typical X-ray diffraction measurements are made by moving a detector to discrete positions in space and then measuring the signal at each stationary position. This step-scanning method can be time-consuming, and may induce vibrations in the measurement system when the motors are accelerated and decelerated at each position. Furthermore, diffraction information between the data points may be missed unless a fine step-scanning is used, which further increases the total measurement time. To utilize beam time efficiently, the motor acceleration and deceleration time should be minimized, and the signal-to-noise ratio should be maximized. To accomplish this, an integrated continuous-scan system was developed at the Stanford Synchrotron Radiation Lightsource (SSRL). The continuous-scan system uses an in-house integrated motor controller system and counter/timer electronics. SPEC software is used to control both the hardware and data acquisition systems. The time efficiency and repeatability of the continuous-scan system were tested using X-ray diffraction from a ZnO powder and compared with the step-scan technique. Advantages and limitations of the continuous-scan system and a demonstration of variable-velocity continuous scan are discussed.

THz Vector Field Measurement Comparison Between On-the-Fly and Step Scan Method

A fast terahertz vector field measurement system based on the on-the-fly (OTF) scan method is investigated. Compared with the step scan method, which samples at certain step, the OTF scan obtains the data with the scanner moving continuously, thus improving the measurement efficiency to some extent. The phase stability of the system is fully studied. Demonstration at approximately 500 GHz is compared with the result by the step scan method, showing that the OTF method can improve the measurement speed by a factor of 7 while the data accuracy is almost the same. Measurements at different scanning speeds and with different probes are also compared to understand their effects.

Vectorization Algorithm of Optics Contact Angle Image Based on VB

The bitmap of contact angle image collected from optics contact angle system was processed on Vectorization with step-scan method. Then, the outline curve of image was got with sample`s curve-fitting. The precision of contact angle which was calculated from that curve compared with out of vectorization increased greatly. Moreover, it could edit to the image expediently.

INVESTIGATION OF SPACE CHARGE TRAP LEVELS IN Al2O3 NANO-POWDER DOPED POLYETHYLENE BY PHOTO-STIMULATED DISCHARGE METHOD

The trap levels of Al 2 O 3 nano-powder doped LDPE with different Al 2 O 3 contents are investigated by PSD technique. The variation of trap depth in the doped LDPE can be qualitatively estimated by PSD spectra in continuous scanning method, and the distribution of trap levels in the samples can be quantitatively described in step scanning method. It is indicated that the trap levels of LDPE can be evidently deepened by Al 2 O 3 nano-powder doping with the content more than 0.1 wt%. According to the relative reports on the effect of nano-powder doping to space charge injection, it is considered that the suppression of space charge is probably correlated to the deeper trap levels in Al 2 O 3 nano-powder doped LDPE.

Methodological investigation on photo-stimulated discharge to obtain accurate trap information in polymer dielectrics

Based on photo-stimulated discharge (PSD) theory about release of charges from the mono- and multi-levels of traps, two methods on the energy distribution of trapped charges (charge distribution)—step scanning method and combined calibration–scanning method are proposed. The typical polymeric dielectric, low-density polyethylene (LDPE), is selected to be investigated in this paper. The linear relation between PSD current and time at selected wavelengths in LDPE samples indicates that the effective interaction cross sections between the photons and trapped charges depend on the photon energy. It is indicated that both of the largest ratios in charge distributions based on the two methods are around the energy level of 4.97 eV for LDPE. Compared with the step scanning method, the experimental time is extremely shortened and thermal release of trapped charges is decreased in the combined calibration–scanning method, and charge distribution based on combined calibration–scanning method is more reliable.

Investigation on the Heat Capacity of Water in Poly(Acrylic Acid)/Water Mixtures Through Stepscan Method

The heat capacity of poly(acrylic acid)/water mixtures with low water contents were measured by the stepscan differential scanning colorimetry (DSC) method and the Cp of the bound water in the mixtures were obtained based on simple equations with an assumption that the effect of interaction between polymer and water molecules could be ignored. The results indicated that the water decreased the glass transition temperature of poly(acrylic acid) (PAA), evidently as a plasticizer, and PAA/water mixtures were thermodynamically homogeneous blends. It was found that the Cp of nonfreezable water in PAA/water mixtures was higher than those of glassy water and cubic ice. The Cp increased with the water content, showing that average interactions between polymer and water decreased with water content. The Cp of bound water in the mixtures in the liquid state was lower than that of bulk water and also increased with water concentration, since the water molecules’ regular structures were broken. It showed that the Cp of bound water in the mixtures was lower than that of free water. The Cp of glassy water was calculated based on experimental Cp values of the PAA/water mixtures, which provided an easy way to obtain the Cp values of glassy water through a simple experiment. The values, however, were higher than those obtained by other researchers.

Investigation of the heat capacity of poly (vinyl methyl ether)/water mixtures using the stepscan method

The heat capacity of poly(vinyl methyl ether) (PVME)/water mixtures was measured over a wide range of temperatures using the stepscan method. The results showed that water exists in different states in the mixtures. The Cp values of dry PVME and PVME/water mixtures with a low water content were obtained by the stepscan method, and the Cp of bound water in the mixtures was approximated. The results showed that the Cp of bound water in the mixtures with a low water content is higher than that of mixtures with glassy water and ice, and it shows no dependence on water content in the glassy state. Because of the larger conformational contribution to Cp, the heat capacity of water in the mixtures in the liquid state increases with water content. Because there is a weak interaction between PVME and water molecules, the structure of water in mixtures is different from that of glassy water. The Cp value of unfreezable bound water in the mixtures was calculated without considering the effect of polymer content, and the interaction between PVME and water was obtained; these calculations explained the phase separation observed at high temperature. The Cp calculation value (♦) of unfreezable bound water in PVME/water mixtures at low temperature. ◊: the experimental Cp of glassy water;21 □: the Cp of cubic ice.30

Synthesis and comparative study of biodegradable poly(alkylene sebacate)s

AbstractNovel biodegradable polyesters, such as poly(ethylene sebacate) (PESeb), poly(propylene sebacate) (PPSeb), and poly(butylene sebacate) (PBSeb), were synthesized and studied with respect to melting behavior, crystallization kinetics, and enzymatic hydrolysis. PESeb and PPSeb showed multiple melting behavior. Wide angle X‐ray diffractometry measurements at various temperatures, standard, step‐scan, and high‐rate differential scanning calorimetry methods were applied to elucidate the appearance of multiple endotherms in heating scans, which was interpreted in the context of partial melting‐recrystallization and final melting. PBSeb did not show any multiple melting behavior but only a weak tendency for recrystallization on heating. The melting temperatures of PESeb, PPSeb, and PBSeb were measured equal to 78, 57, and 71 °C, respectively. The equilibrium melting points were estimated to be Tm° = 90.2, 69.9, and 77.4 °C for PESeb, PPSeb, and PBSeb, while the corresponding enthalpy of fusion values were found to be ΔHf = 170 ± 10, 140 ± 10, and 155 ± 10 J/g, respectively. The polyesters showed fast crystallization rates under both isothermal and nonisothermal conditions. Crystallization kinetics was thoroughly investigated using macrokinetic models and isoconversional analysis. Enzymatic hydrolysis rate in the presence of lipases Rhizopus delemar and Pseudomonas cepacia was found to be fast for PPSeb, whereas PESeb and PBSeb showed slow rates and comparable with those of PCL. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 672–686, 2010

Time-Resolved Step-Scan Infrared Imaging System Utilizing a Linear Array Detector

A time-resolved infrared (IR) imaging system combined with a multichannel IR microscope, which utilizes a 16 channel linear array (LA) detector, and step-scan Fourier transform infrared (FT-IR) microscope was developed. The LA detector integrates a readout circuit on each detector element, so the detected signals can be read simultaneously. Thus, this system can perform high speed imaging using the step-scan method, similar to a single channel detector. To verify the capabilities of this system, a reflective sample was examined whose position was altered using a piezo actuator activated by an alternating voltage. In addition, the localization of relaxation dynamics for the liquid crystal (LC) molecules in an LC cell under oscillating electric field conditions was detected by this system.

NANOSTRUCTURED AND SURFACE POLYMERIZED IRON PARTICLES FOR MAGNETORHEOLOGICAL FLUIDS

A novel magnetorheological fluid, in which the surface of iron particles is coated with poly (butyl acrylate) by surface initiated atom transfer radical polymerization (ATRP), is investigated. The polymer coating procedure includes two steps, which are immobilization of initiator: 2-4(-chlorosulfonylphenyl)-ethytrichlorosilane (CTCS) on the iron particles surface and graft polymerization of butyl acrylate from the surface. The surface coating is characterized by FTIR and SEM. This magnetorheological fluid has controllable off-state viscosity and high shear yield stress. Coating polymer on the iron particles surface by ATRP can significantly reduce iron particles settling and improve stability of the MR fluid. Polymerization kinetics of bulk butyl acrylate are investigated using differential scanning calorimetry (DSC). Glass transition temperature is obtained using the step-scan DSC method. The molecular weight and conversion can be controlled by the molar ratio of monomer to initiator, reaction temperature and time. The reaction is first order determined by the plot of In ( M / M 0) against polymerization time. The overall activation energy is found to be 126kJ/mol by Kissinger's Method.

Heat capacity of glassy and crystalline Zr 0.55Al 0.10Ni 0.05Cu 0.30

The heat capacity ( C p) of Zr 0.55Al 0.10Ni 0.05Cu 0.30 (ZANC) alloy was measured for glassy rod, glassy ribbon, and the crystallized samples by a thermal relaxation technique between 1.8 and 310 K and by the step scanning method of differential scanning calorimetry (DSC) between 300 and 873 K. The low-temperature C p becomes larger as the sample turns from the crystal into the glassy rod and further into the glassy ribbon. The crystallized sample showed no anomaly in C p up to 873 K, while the glassy rod and glassy ribbon samples showed a glass transition around 680 K, and then crystallization at about 726 K. An exothermic phenomenon was observed in the glassy ribbon sample below the glass transition temperature, which was probably caused by another structural relaxation. These results suggest that the degree of vitrification becomes higher with increasing cooling rate in the vitrification process.

Dynamics of CO in Mesoporous Silica Monitored by Time-Resolved Step-Scan and Rapid-Scan FT-IR Spectroscopy

Carbon monoxide molecules generated in the channels of mesoporous MCM-41 silica sieve from a precursor (diphenyl cyclopropenone) by photodissociation with a nanosecond laser pulse were monitored by time-resolved Fourier transform infrared (FTIR) spectroscopy using the step-scan and rapid-scan methods. A very broad absorption of CO is observed in the region 2200-2080 cm(-1) at room temperature that decays in a biphasic mode. Two-thirds of the band intensity decays on the hundreds of microsecond scale (lifetime 344 +/- 70 micros). The process represents the escape of the molecules through the mesopores into the surrounding gas phase, and a diffusion constant of 1.5 x 10(-9) m(2)/s is derived (assuming control by intra-MCM-41 particle diffusion). The broad profile of the absorption is attributed to contact of the random hopping CO with siloxane and silanol groups of the pore surface. Measurements using MCM-41 with the silanols partially capped by trimethyl silyl groups gave further insight into the nature of the IR band profile. These are the first observations on the diffusion behavior of carbon monoxide in a mesoporous material at room temperature. The residual carbon monoxide remains much longer in the pores and features distinct peaks at 2167 and 2105 cm(-1) characteristic for CO adsorbed on SiOH groups C end on and O end on, respectively. The bands decrease with time constants of 113 +/- 3 ms (2167 cm(-1)) and 155 +/- 15 ms (2105 cm(-1)) suggesting that CO in these sites is additionally trapped by surrounding diphenyl acetylene coproduct and/or precursor molecules.

Atom transfer radical polymerized MR fluids

A novel magnetorheological fluid, in which the surface of iron particles is coated with poly(butyl acrylate) by surface-initiated atom transfer radical polymerization (ATRP), is investigated. The polymer coating procedure includes two steps, which are immobilization of initiator: 2-(4-chlorosulfonylphenyl)-ethyltrichlorosilane (CTCS) on the iron particles' surface and graft polymerization of butyl acrylate from the surface. The surface coating is characterized by FTIR and SEM. This magnetorheological fluid has controllable off-state viscosity and high shear yield stress. Coating polymer on the iron particles' surface by ATRP can significantly reduce iron particles' settling and improve stability of the MR fluid. Glass transition temperature is obtained using the step-scan DSC method. The molecular weight and conversion can be controlled by the molar ratio of monomer to initiator, reaction temperature and time. The reaction is first order determined by the plot of ln[M] 0/[M] against polymerization time.