Influence of gallium‐doped zinc‐oxide thickness on polymer light‐emitting diode luminescence efficiency

Conducting atomic force microscopy and scanning surface potential microscopy were used to study the local electrical properties of gallium‐doped zinc oxide (GZO) films prepared by pulsed laser deposition (PLD) on a polyimide (PI) substrate. For a PLD deposition process time of 8 min, the root‐mean‐square roughness, coverage percentage of the conducting regions, and mean work function on the GZO surface were 2.33 nm, 96.6%, and 4.82 eV, respectively. When the GZO/PI substrate was used for a polymer light‐emitting diode (PLED), the electroluminescence intensity increased by nearly 20% compared to a standard PLED, which was based on a commercial‐ITO/glass substrate. Microsc. Res. Tech. 76:783–787, 2013. © 2013 Wiley Periodicals, Inc.     

Formation of subwavelength grating on molybdenum mirrors using a femtosecond Ti:sapphire laser system operating at 10 Hz

We report formation of subwavelength surface grating over large surface area of molybdenum mirror by multiple irradiation of amplified femtosecond laser pulses from a homemade Ti:sapphire oscillator-amplifier laser system in a raster scan configuration. The laser system delivered 2 mJ, 80 fs duration laser pulses at a pulse repetition rate of 10 Hz. Various parameters such as pulse fluence, number of pulses, laser polarization, scan speed, and scan steps were optimized to obtain uniform subwavelength gratings. Energy dispersive x-ray spectroscopy measurements were conducted to analyze the elemental composition of mirror surfaces before and after laser treatment.     

A tracking‐based nanoimaging method for fast detection of surfaces' inhomogeneities using gold nanoparticles

The localization of surfaces inhomogeneities is central to many areas of technology, chemistry and biology, ranging from surface defects in industry to the identification and screening of early bio‐defects inside cells. The development of methods that enable direct, sensitive, and rapid detection of those inhomogeneities is both relevant and timely. To address this challenge, we developed a far‐field nanoimaging method to detect the presence of surface's nanodefects that modify the signal emitted by gold nanoparticles (AuNPs) under laser irradiation. Our technique is based on the formation of hot spots due to the confinement of light in the proximity of the AuNP, whose positions depend on the polarization direction of the incident beam. An inhomogeneity is detected as an increase in the intensity collected from the hot spots when a laser beam is orbiting the nanoparticle and the incident polarization direction of the laser beam is changed periodically.     

Investigation on infrared laser desorption of solid matrix using scanning electron microscope and fast photography

Infrared light from a pulsed optical parametric oscillator laser system was used to irradiate succinic acid (SA), a usual solid matrix used in matrix‐assisted laser desorption ionization, under vacuum. Ablated SA particles were trapped using a silica plate mounted 3.0 mm above and parallel to the sample surface. The morphology and particle size of ablated particles at different laser fluences were investigated using a scanning electron microscope (SEM). The dynamics of plume propagation for SA desorption process was studied with fast photography at atmospheric pressure. Plume expanding at 1.12 J/cm² laser fluence was recorded using a high‐speed CMOS camera and corresponding propagation distance was measured. The solid matrix desorption was driven by phase explosion according to plume model fitting, which was consistent with the results of SEM. Microsc. Res. Tech. 76:744–750, 2013. © 2013 Wiley Periodicals, Inc.     

Morphological alterations of radicular dentine pretreated with different irrigating solutions and irradiated with 980-nm diode laser

Background: The topographical features of intraradicular dentine pretreated with sodium hypochlorite (NaOCl) or ethylenediamine tetraacetic acid (EDTA) followed by diode laser irradiation have not yet been determined. Purpose: To evaluate the alterations of dentine irradiated with 980‐nm diode laser at different parameters after the surface treatment with NaOCl and EDTA. Study design: Roots of 60 canines were biomechanically prepared and irrigated with NaOCl or EDTA. Groups were divided according to the laser parameters: 1.5 W/CW; 1.5 W/100 Hz; 3.0 W/CW; 3.0 W/100 Hz and no irradiation (control). The roots were splited longitudinally and analyzed by scanning electron microscopy (SEM) in a quali‐quatitative way. The scores were submitted to two‐way Kruskal–Wallis and Dunn's tests. Results: The statistical analysis demonstrated that the specimens treated only with NaOCl or EDTA (control groups) were statistically different (P < 0.05) from the laser‐irradiated specimens, regardless of the parameter setting. The specimens treated with NaOCl showed a laser‐modified surface with smear layer, fissures, and no visible tubules. Those treated with EDTA and irradiated by laser presented absence of smear layer, tubules partially exposed and melting areas. Conclusions: The tested parameters of 980‐nm diode laser promoted similar alterations on dentine morphology, dependent to the type of surface pretreatment. Microsc. Res. Tech., 2009. © 2008 Wiley‐Liss, Inc.     

Quantifying Microwear on Experimental Mistassini Quartzite Scrapers: Preliminary Results of Exploratory Research Using LSCM and Scale‐Sensitive Fractal Analysis

Although previous use‐wear studies involving quartz and quartzite have been undertaken by archaeologists, these are comparatively few in number. Moreover, there has been relatively little effort to quantify use‐wear on stone tools made from quartzite. The purpose of this article is to determine the effectiveness of a measurement system, laser scanning confocal microscopy (LSCM), to document the surface roughness or texture of experimental Mistassini quartzite scrapers used on two different contact materials (fresh and dry deer hide). As in previous studies using LSCM on chert, flint, and obsidian, this exploratory study incorporates a mathematical algorithm that permits the discrimination of surface roughness based on comparisons at multiple scales. Specifically, we employ measures of relative area (RelA) coupled with the F‐test to discriminate used from unused stone tool surfaces, as well as surfaces of quartzite scrapers used on dry and fresh deer hide. Our results further demonstrate the effect of raw material variation on use‐wear formation and its documentation using LSCM and RelA. SCANNING 35:28‐39, 2013. © 2012 Wiley Periodicals, Inc.     

Spatially resolved recording of transient fluorescence‐lifetime effects by line‐scanning TCSPC

We present a technique that records transient changes in the fluorescence lifetime of a sample with spatial resolution along a one‐dimensional scan. The technique is based on scanning the sample with a high‐frequency pulsed laser beam, detecting single photons of the fluorescence light, and building up a photon distribution over the distance along the scan, the arrival times of the photons after the excitation pulses and the time after a stimulation of the sample. The maximum resolution at which lifetime changes can be recorded is given by the line scan period. Transient lifetime effects can thus be resolved at a resolution of about one millisecond. We demonstrate the technique for recording photochemical and nonphotochemical chlorophyll transients in plants and transient changes in free Ca²⁺ in cultured neurons. Microsc. Res. Tech. 77:216–224, 2014. © 2014 Wiley Periodicals, Inc.     

Effects of Er,Cr:YSGG laser parameters on dentin bond strength and interface morphology

Previous studies have shown the effects of Er,Cr:YSGG laser irradiation on the dentin bond strength; but there are few reports that show the significance of the irradiation with different laser parameters on dentin bond strength and interface morphology. This in‐vitro study attempted to evaluate the microtensile bond strength (μTBS) and interface morphology of resin‐dentin interfaces, either followed by treatment with Er,Cr:YSGG laser irradiation with different parameters or not. The flattened dentin samples of 35 bovine teeth were embedded into acrylic blocks and randomly divided into seven groups according to surface treatments using Er,Cr:YSGG lasers with different parameters: 3 W/20 Hz, 3 W/35 Hz, 3 W/50 Hz, 1.5 W/20 Hz, 1.5 W/35 Hz, 1.5 W/50 Hz, or no laser treatment (n = 5). Composite buildups were done over bonded surfaces and stored in water (24 hours at 37°C). Specimens were sectioned into sticks that were subjected to μTBS testing and observed under FE‐SEM. Control groups (27.70 ± 7.0) showed statistically higher values than laser‐irradiated groups. There were no significant differences among laser groups. Despite that, increasing the pulse frequency yielded slightly higher bond strength. Depending on laser settings, Er,Cr:YSGG laser irradiation caused interfacial gaps and resin tags with wings morphology. With the parameters used in this study, Er,Cr:YSGG laser irradiation promoted morphological changes within resin‐dentin interfaces and negatively influenced the bond strength of adhesive systems. Microsc. Res. Tech. 78:1104–1111, 2015. © 2015 Wiley Periodicals, Inc.     

Thermal,morphological, and spectral changes after Er,Cr:YSGG laser irradiation at low fluences on primary teeth for caries prevention

The aim of this study was to determine the temperature increase in the pulp chamber and possible thermal effects on molecular structure of primary teeth during the irradiation with Er,Cr:YSGG laser. Primary central incisors were divided into three groups (n = 20). Labial surfaces in each group were irradiated by Er,Cr:YSGG laser within different power and frequencies as following groups: I: 0.25 W, 20 Hz, II: 0.50 W, 20 Hz, III: 0.75 W, 20 Hz. A thermocouple was placed inside the pulp chamber so that the temperature increments were recorded during the enamel irradiation. Morphological changes of enamel surfaces were experimentally evaluated by SEM. Fourier‐transform infrared spectroscopy and RAMAN analyses were carried out to determine the differentiations in the molecular structure. The experimental results obtained were analyzed statistically by means of one‐way analysis of variance. Statistically significant differences were detected between groups (p < .05). Group III exhibited the highest values for the temperature parameters. Besides, the conical craters, cracks, and formation of ablation areas were observed for all the groups. Also, it was obtained that the hydroxyapatite lost the hydroxyl ions due to the thermal effect of the laser. Temperature rise throughout the Er,Cr:YSGG laser irradiation for prevention of primary enamel demineralization presented a positive correlation with the laser output power level. The formations of adverse morphological and spectral changes were detected on the surface of teeth after the laser application. On this basis, the Er,Cr:YSGG laser applications should be treated with much more caution considering enamel surface and pulpal tissues in primary teeth.     

Application of a high power Yb fiber‐based laser compatible with commercial optical parametric oscillator for coherent anti‐stokes raman scattering microscopy

Coherent anti‐Stokes Raman scattering (CARS) microscopy is a powerful tool for chemical analysis at a subcellular level, frequently used for imaging lipid dynamics in living cells. We report a high‐power picosecond fiber‐based laser and its application for optical parametric oscillator (OPO) pumping and CARS microscopy. This fiber‐based laser has been carefully characterized. It produces 5 ps pulses with 0.8 nm spectral width at a 1,030 nm wavelength with more than 10 W of average power at 80 MHz repetition rate; these spectral and temporal properties can be slightly modified. We then study the influence of these modifications on the spectral and temporal properties of the OPO. We find that the OPO system generates a weakly spectrally chirped signal beam constituted of 3 ps pulses with 0.4 nm spectral width tunable from 790 to 930 nm optimal for CARS imaging. The frequency doubling unconverted part is composed of 7–8 ps pulses with 0.75 nm spectral width compatible with CARS imaging. We also study the influence of the fiber laser properties on the CARS signal generated by distilled water. In agreement with theory, we find that shorter temporal pulses allow higher peak powers and thus higher CARS signal, if the spectral widths are less than 10 cm^?1. We demonstrate that this source is suitable for performing CARS imaging of living cells during several hours without photodamages. We finally demonstrate CARS imaging on more complex aquatic organisms called copepods (micro‐crustaceans), on which we distinguish morphological details and lipid reserves. Microsc. Res. Tech. 77:422–430, 2014. © 2014 Wiley Periodicals, Inc.     

<Emphasis Type="Bold">Cumulative Heat Effect in Excimer Laser Ablation of Polymer PC and ABS</Emphasis>

Analysis of the thermal effect and machining properties of PC (polycarbonate) and ABS (polyacrylonitrilebutadienestyrene) polymers when ablated using a KrF excimer laser is described. PC has less thermal effect on the geometric distortion than ABS in laser ablation. The cumulative heat during laser ablation results in geometric deformation in ABS micromachining. The number of laser pulses generates a greater geometric deformation in ABS than in PC according to experimental laser ablation observations. The PC ablation rate is proportional to the laser fluence, whereas ABS shows an exponential profile. The pulse repetition rate has no significant influence on PC during laser ablation, but affects the ablated patterns in ABS. During laser ablation, PC does not produce debris on the machining patterns, but debris is produced on the machining patterns with ABS.     

Two‐frequency CARS imaging by switching fiber laser excitation

To fully exploit the power of coherent Raman imaging, techniques are needed to image more than one vibrational frequency simultaneously. We describe a method for switching between two vibrational frequencies based on a single fiber‐laser source. Stokes pulses were generated by soliton self‐frequency shifting in a photonic crystal fiber. Pump and Stokes pulses were stretched to enhance vibrational resolution by spectral focusing. Stokes pulses were switched between two wavelengths on the millisecond time scale by a liquid‐crystal retarder. Proof‐of‐principle is demonstrated by coherent anti‐Stokes Raman imaging of polystyrene beads embedded in a poly(methyl methacrylate) (PMMA) matrix. The Stokes shift was switched between 3,050 cm^?1, where polystyrene has a Raman transition, and 2,950 cm^?1, where both polystyrene and PMMA have Raman resonances. The method can be extended to multiple vibrational modes.     

The low‐temperature method for study of coniferous tissues in the environmental scanning electron microscope

The use of non‐standard low‐temperature conditions in environmental scanning electron microscopy might be promising for the observation of coniferous tissues in their native state. This study is aimed to analyse and evaluate the method based on the principle of low‐temperature sample stabilization. We demonstrate that the upper mucous layer is sublimed and a microstructure of the sample surface can be observed with higher resolution at lower gas pressure conditions, thanks to a low‐temperature method. An influence of the low‐temperature method on sample stability was also studied. The results indicate that high‐moisture conditions are not suitable for this method and often cause the collapse of samples. The potential improvement of stability to beam damage has been demonstrated by long‐time observation at different operation parameters. We finally show high applicability of the low‐temperature method on different types of conifers and Oxalis acetosella. Microsc. Res. Tech., 78:13–21, 2015. © 2014 Wiley Periodicals, Inc.     

248 nm excimer laser drilling PI film for nozzle plate application

In this study, drilling of polyimide (PI) film by using a 248 nm excimer laser through photomask projection is presented. The parameter effects of laser fluence, shot number and repetition rate on the processing results are realized. A high-quality of microhole array with 50 μm thick PI film has been fabricated. When the projection process is carried out, differences in the diameters of the microhole in the front and back sides of the PI are observed, which cause a conical shape in the kerf. The formation of this conical shape in terms of laser process parameters is discussed. Besides, to improve the laser machining quality of PI microholes, the effects of the process parameters are investigated and characterized. In addition, before excimer laser drilling PI is conducted, the PI surface is pre-coated with, or left without, a thin film material to observe the formation of debris. The results shows that the formation of debris can be reduced significantly when a pre-coated thin film is applied on the PI surface.     

Study of SU-8 photoresist cross-linking process by atomic force acoustic microscopy

In this paper, a method is presented to detect the different phases of epoxy cross-linking process and the subsurface structures of SU-8 thin films by atomic force acoustic microscopy (AFAM). The AFAM imaging of SU-8 thin films was investigated under different exposure and bake conditions. Optimized conditions were obtained for the cross-linking of SU-8 thin film at the exposure does of eight laser pulses with the laser fluence 10 mJ cm^–2 per pulse and the post exposure bake (PEB) time at 90 s. The subsurface structures of undeveloped SU-8 thin films were visible in the AFAM images. This method provides an effective and low-cost way for the determination of different phases of epoxy cross-linking process in nanostructured compounds, for the non-destructive testing of subsurface defects, and for the evaluation of the quality of patterned structures.     

Long‐term chlorhexidine effect on bond strength to Er:YAG laser irradiated‐dentin

This study evaluates the bond strength of dentin prepared with Er:YAG laser or bur, after rewetting with chlorhexidine on long‐term artificial saliva storage and thermocycling. One hundred and twenty human third molars were sectioned in order to expose the dentin surface (n = 10). The specimens were randomly divided in 12 groups according to treatment and aging: Er:YAG laser rewetting with deionized water (LW) and 24 h storage in artificial saliva (WC); LW and 6 months of artificial saliva storage + 12.000 thermocycling (6M), LW and 12 months of artificial saliva storage + 24.000 thermocycling (12M), Er:YAG laser rewetting with 2% chlorhexidine (LC) and WC, LC and 6M, LC and 12M, bur on high‐speed turbine rewetting with deionized water (TW) and WC, TW6M, TW12M, bur on high‐speed turbine + 2% chlorhexidine (TC) and WC, TC and 6M, TC and12M. The specimens were etched with 35% phosphoric acid, washed, and dried with air. Single Bond 2 adhesive was applied and the samples were restored with a composite. Each tooth was sectioned in order to obtain 4 sticks, which were submitted to microtensile bond strength test (µTBS). The two‐way ANOVA, showed no significant differences for the interaction between the factors and for the aging factor. Tukey 5% showed that the LC group had the lowest µTBS. The rewetting with chlorhexidine negatively influenced the bond strength of the preparation with the Er:YAG laser. The artificial saliva aging and thermocycling did not interfere with dentin bond strength. Microsc. Res. Tech. 77:37–43, 2014. © 2013 Wiley Periodicals, Inc.     

Micro‐fabrication and monitoring of three‐dimensional microstructures based on laser‐induced thermoplastic formation

This article reports a novel laser‐induced micro‐fabrication method and its monitoring system for three‐dimensional (3D) microstructures. The mechanism of the method is that a small zone of thermoplastic material melted by laser heating grows in liquid surrounding environment, solidifying into a convex microstructure, such as micro‐dot or micro‐pillar. A laser diode (808 nm) with maximum power output of 130 mW is used as power source, and a kind of paraffin mixed with stearic acid and paint serves as the thermoplastic material for 3D microstructure formation experiments. A light microscope system consisting of a charge‐coupled device (CCD) and a computer is utilized to realize real‐time observation of the micro‐fabricating process. The distribution of local temperature rise on material surface created by laser irradiation is simulated. The effects of liquid environment on microstructure formation have been theoretically analyzed and experimentally studied. Experiments are further carried out to investigate the relationship between laser spot and fabricated microstructures. The results indicate that the widths of micro‐dots or micro‐pillars are mostly determined by the size of focal spot, and their heights increase with the enlargement of laser power density. With this method, a micro‐dot array of Chinese characters meaning “China” has been successfully fabricated through computer programming. This method has the advantages of implementing direct, mask‐less, real‐time and inexpensive 3D microstructure fabrication. Therefore, it would be widely applied in the fields of micro/nano‐technology for practical fabrication of different kinds of 3D microstructures. Microsc. Res. Tech., 2009. © 2009 Wiley‐Liss, Inc.     

Influence of the artificial saliva storage on 3‐D surface texture characteristics of contemporary dental nanocomposites

The aim of this study was to analyse the influence of the artificial saliva on a three‐dimensional (3‐D) surface texture of contemporary dental composites. The representatives of four composites types were tested: nanofilled (Filtek Ultimate Body, FUB), nanohybrid (Filtek Z550, FZ550), microfilled (Gradia Direct, GD) and microhybrid (Filtek Z250, FZ250). The specimens were polymerised and polished by the multistep protocol (SuperSnap, Shofu). Their surface was examined, before and after 3 weeks’ exposure to artificial saliva storage. The surface texture was analysed using the atomic force microscope (AFM). The obtained images were processed to calculate the areal autocorrelation function (AACF), anisotropy ratio S_tr (texture aspect ratio), and structure function (SF). The log–log plots of SF were used to calculate fractal properties, such as fractal dimension D, and pseudo‐topothesy K. The analysis showed changes in surface anisotropy ratio S_tr values, which became higher, whereas the S_q roughness (root‐mean‐square) reduced after the artificial saliva storage. All the samples exhibited bifractal structure before the saliva treatment, but only half of them remained bifractal afterwards (GD, FZ250), whereas the other half turned into a monofractal (FUB, FZ550). The cube‐count fractal dimension D_cc was found to be material‐ and treatment‐insensitive.     

Influence of surface texture shape,geometry and orientation on hydrodynamic lubrication performance of plane‐to‐plane slider surfaces

This paper investigates the effect of surface texturing on the tribological performance of hydrodynamic slider surfaces. The geometric parameters of the texture considered were the texture shape, bottom profile, orientation and depth. A theoretical model based on the steady‐state Reynolds equation was solved numerically by finite difference method to analyse the effect of surface texturing. The optimum geometry of each texture shape was determined, for which, the film thickness was maximised and the friction coefficient was minimised. Among all the shapes, the square with a single wedge bottom profile outperformed. The performance of the triangle, the chevron and the ellipse was highly influenced by their orientation with respect to the sliding direction. Texture density was found to be more dominant in impacting the tribological performance than the texture aspect ratio. The results obtained were further discussed with respect to the studies available in literature to emphasise the significance of the findings. Copyright © 2016 John Wiley & Sons, Ltd.