Raster Speed Research Articles

Direct visualization of highly resistive areas in GaN by means of low-voltage scanning electron microscopy

The damage-induced voltage alteration (DIVA) contrast mechanism in scanning electron microscope (SEM) at low electron energy has been presented as a fast and convenient method of direct visualization of increased resistivity induced by energetic ions irradiation in gallium nitride (GaN). Epitaxially grown GaN layers on sapphire covered with a metallic masks with etched windows were subjected to He2+ irradiations at 600 keV energy. The resulting two-dimensional damage profiles at the samples cross-sections were imaged at SEM at different e-beam currents and scan speeds. The gradual development of image contrast was observed with the increase of cumulative charge deposited by electron beam irradiation, to finally reach the saturation level of the contrast related to the local resistivity of the ion-irradiated part of GaN.The presented method allows one to directly visualize the ion-irradiated zone even for the lowest resistivity changes resulting from ion damage, i.e. all levels of insulation build-up in GaN upon irradiation with ions. Taking into account that it is not possible to apply the etch-stop technique by wet chemistry to GaN, it makes the presented technique the only available method of visualization of highly resistant and insulating regions in GaN-based electronic devices.Main aim of the presented work is to get a deeper insight into a DIVA contrast in GaN with the special emphasize to discuss the role of rastering speed and electron beam current, i.e. details of charge build-up ion the sample surface.

Adhesive Bonding of Copper Prepared by Laser-Interference near the Interference Structuring Limits.

Adhesive bonding requires adequate surface preparation for ensuring an appropriate joint quality. The interest in adhesive joining has recently expanded to thermal systems having a large number of joints employed for manufacturing and assembly. This study presents surface topology of copper 110 produced by a laser-interference setup that would theoretically yield a periodicity of 1.7 μm, which is near the 1.6–2 μm structuring limit that was estimated based on thermal diffusion length scale for an 8 ns laser pulse. The results show that although the expected periodic interference structuring was not attained, the melt-induced texturing was affected by the laser-interference profile. Single-lap shear tests were performed with specimen surfaces prepared by traditional abrasion and laser-interference structuring methods. Several laser processing parameters, such as the laser spot size, density, number of pulses, and raster speed, were studied. Scanning electron microscope and profilometry measurements were used to characterize the processed surface microstructures. Web-like structures, which indicate widespread melting, were shown to be formed at different processing conditions. Based on the surface topologies investigated, two laser raster speeds were selected to make single-lap-joint specimens. Baseline joints were prepared by abrading joining specimens. The shear-lap strength and displacement at maximum load were shown to be higher by 16.8% and 43.8% for the laser-structured specimens than those of the baseline specimens, respectively. Moreover, the load-displacement curves indicated that the laser-structured joints were more ductile than those without laser-structuring. The increased ductility for the laser-structured joints was found to yield an increase in the energy absorbed during shear-lap testing of approximately of 80–90% over those measured for baseline joints. It is another indicator that laser-interference structuring enhanced the bonding performance of single-lap shear joints.

Sequential Self-Folding of Shape Memory Polymer Sheets by Laser Rastering Toward Origami-Based Manufacturing

Abstract Origami-based fabrication strategies open the door for developing new manufacturing processes capable of producing complex three-dimensional (3D) geometries from two-dimensional (2D) sheets. Nevertheless, for these methods to translate into scalable manufacturing processes, rapid techniques for creating controlled folds are needed. In this work, we propose a new approach for controlled self-folding of shape memory polymer sheets based on direct laser rastering. We demonstrate that rapidly moving a CO2 laser over pre-strained polystyrene sheets results in creating controlled folds along the laser path. Laser interaction with the polymer induces localized heating above the glass transition temperature with a temperature gradient across the thickness of the thin sheets. This gradient of temperature results in a gradient of shrinkage owing to the viscoelastic relaxation of the polymer, favoring folding toward the hotter side (toward the laser source). We study the influence of laser power, rastering speed, fluence, and the number of passes on the fold angle. Moreover, we investigate process parameters that produce the highest quality folds with minimal undesired deformations. Our results show that we can create clean folds up to and exceeding 90 deg, which highlights the potential of our approach for creating lightweight 3D geometries with smooth surface finishes that are challenging to create using 3D printing methods. Hence, laser-induced self-folding of polymers is an inherently mass-customizable approach to manufacturing, especially when combined with cutting for integration of origami and kirigami.

Corrosion Behavior of Laser-Interference Structured AA2024 Coated with a Chromate-Containing Epoxy Primer

In this study, the corrosion behavior of laser-interference treated AA2024-T3 specimens, which are coated with a primer, is presented. The surface of as-received AA2024-T3 specimens were laser-interference structured by splitting the primary beam of a Q-switched Nd:YAG pulsed nanosecond laser into two beams and focusing them to the same spot on the specimen surface. After being stored in plastic cases for up to 70 d, without any additional cleaning, the specimens were spray painted with a chromate-containing epoxy primer, CA7233, compliant to MIL-PRF-23377 Type I Class C2 specification. The corrosion behavior of laser-interference specimens was assessed against that of specimens prepared by chromated conversion coating and sulfuric acid anodizing treatments. After the ASTM B117 corrosion exposure, it was found that the laser processed specimens exhibited only few blisters. On one hand, most specimens prepared at a laser fluence of 1.78 J/cm2, without any additional chemical cleaning, were found to develop one very small blister after only 96 h of exposure. However, the growth of these blisters was not significant even after 1,000 h of salt spray exposure. On the other hand, only a fraction of the specimens prepared at a laser fluence of 1.24 J/cm2 and acetone wiped right after the laser structuring were found to develop several tiny blisters after 790 h and longer exposure. Overall, it was found that the corrosion damage was minimized at a laser rastering speed of 4 mm/s, a condition for which only 33% of specimens developed very minor corrosion damage. The ASTM D1654 creepage ratings, which was used to evaluate the corrosion damage along the scribe lines, were found to be at least nine for all coated panels. These results indicate that the laser-interference technique with the additional acetone wiping has the potential to be further developed as a nonchemical surface preparation technique for chromate-containing epoxy primers coating systems.

Parameter Development via In Situ Residual Stress Measurement and Post-deposition Analysis of Cold Spray CuNi Coatings

Developing dense, well-adhered coatings with minimal heterogeneity via cold spray deposition has been a challenge because in-flight and layer-by-layer diagnostics has not yet been adequately adapted to complement existing post-deposition analyses and parameter process mapping. This study presents an empirical and analytical approach for development and optimization of requisite spray parameters via the cold spray solid-state consolidation process using the in situ beam curvature technique to assess particle dynamics during deposition, in conjunction with post-deposition analyses. Here, CuNi (62/38) powder was deposited onto CuNi (70/30) substrates and monitored with an in situ beam curvature sensor to provide real-time feedback of the coating’s evolving stress states during the deposition process and subsequent residual stress determination immediately after deposition. The resulting beam curvature compressive and tensile stress amplitudes detected layer-by-layer coating variations during deposition resulting from adjusted carrier gas flow rates, substrate surface preparations, nozzle deposition angle, robot raster speeds, powder feed rate, substrate preheat, as well as identifying nozzle clogging. The acquired stress-state data enhanced post-deposition analyses that directed and accelerated the downselection process to define and optimize cold spray parameters, as it pertained to coating adhesion, cohesion, and the corresponding microstructure.

Indium tin oxide nanowires manufactured via printing and laser irradiation

Metallic and semiconductor nanowires can provide dramatically increased electrical and optical properties in a wide range of fields, ranging from photovoltaics to sensors and catalysts. In this research, a rapid manufacturing process has been developed for printing indium tin oxide microparticles and converting them into nanowires. Microparticle indium tin oxide (ITO) inks were formulated and printed. These were then converted into hierarchical nanowire films via laser irradiation (980 nm, NIR) with raster speeds of 40 mm s−1 in air, much faster compared to traditional manufacturing processes. For a 4 cm2 film, only 40 s of processing were required. A full materials characterization was performed on the materials pre and post laser processing with the most probable conversion mechanism found to be a laser induced carbothermal reduction process. Microstructural, chemical, and crystallographic evidence of the laser induced carbothermal reduction process were derived from SEM, XRD, XPS and TEM analysis. Compared to conventionally heat-treated printed samples, laser processing was found to increase the conductivity of the printed ITO from 0.88% to 40.47% bulk conductivity. This research demonstrates the ability of printing and laser processing to form nanowires in a high-speed manufacturing context, thereby enabling the development of printed non-transparent ITO nanowire electronics and devices.

Tailoring Surface Hydrophobicity of Commercial Polyimide by Laser-Induced Nanocarbon Texturing

Abstract The growth of laser-induced nanocarbons, referred to here as laser-induced nanocarbon (LINC) for short, directly on polymeric surfaces is a promising route toward surface engineering of commercial polymers. This paper aims to demonstrate how this new approach can enable achieving varied surface properties based on tuning the nanostructured morphology of the formed graphitic material on commercial polyimide (Kapton) films. We elucidate the effects of tuning laser processing parameters on the achieved nanoscale morphology and the resulting surface hydrophobicity or hydrophilicity. Our results show that by varying lasing power, rastering speed, laser spot size, and line-to-line gap sizes, a wide range of water contact angles are possible, i.e., from below 20 deg to above 110 deg. Combining water contact angle measurements from an optical tensiometer with LINC surface characterization using optical microscopy, electron microscopy, and Raman spectroscopy enables building the process–structur–property relationship. Our findings reveal that both the value of contact angle and the anisotropic wetting behavior of LINC on polyimide are dependent on their hierarchical surface nanostructure which ranges from isotropic nanoporous morphology to fibrous morphology. Results also show that increasing gap sizes lead to an increase in contact angles and thus an increase in the hydrophobicity of the surface. Hence, our work highlight the potential of this approach for manufacturing flexible devices with tailored surfaces.

Effect of Deposition Rate and Deposition Temperature on Residual Stress of HVOF-Sprayed Coatings

In this paper, we examine the correlation between thermal spray process parameters that affect the deposition rate and the residual stress buildup in HVOF metallic and cermet coatings. Parameters of interest including feed-rate, raster speed, and substrate temperature (controlled via external cooling means) were evaluated in the context of their effect on the stress evolution in gas fuel HVOF-sprayed coatings. The process variables investigated are intended to change the deposition rate and subsequently the local deposition temperature (TLD) at the location of impact. The residual stress during the deposition tends to be more tensile with increased TLD, and this tendency is more significant when the change in TLD is produced by the feed rate. Compressive stresses result for lower TLD due to dominance of the peening effect. A systematic study of these effects was conducted for gas fuel HVOF-sprayed Ni- and WC-12%wt.Co-coatings. The Ni-coatings represent the family of ductile metallic materials, whereas the WC-12%wt.Co-coatings represent the behavior of hard cermets. Both materials develop compressive stress at low TLD and change into tensile stress at high TLD by manipulation of deposition rate parameters. Extensions to other materials and HVOF processes are also presented to support the analysis.

Ultrafast time-of-flight 3D LiDAR

Time-of-flight 3D imaging is an invaluable remote sensing tool, but raster speeds are currently limited by pulsed-laser scanning rates. By adapting techniques from ultrafast time-stretch imaging, a new LiDAR platform scans orders of magnitude faster than today’s commercial line-scanning pulsed-LiDAR systems.

Additive manufacturing by material extrusion with medical grade silicone elastomers and IR laser curing

PurposeTechniques of extrude and cure additive manufacturing for thermally cured, high viscosity and medical-grade silicone are investigated by using a small ram extruder and a near-infrared (IR) laser. The purpose of this study is to evaluate the process parameter effects on the stiffness of the final products.Design/methodology/approachProcess parameter effects on axial stiffness values and durometer are explored. Parameters such as extrusion layer height, laser speed, laser current, laser raster spacing and multiple laser passes were investigated and compared to traditional cast and cure methods. Dimensional changes were also recorded and compared.FindingsTensile and durometer tests show that certain curing parameters give tensile stress and durometers within 10 per cent of bulk material specifications at 200 per cent strain. Parameters that had the highest impact on tensile stress at 200 per cent strain were layer height (0.73 per cent) followed by laser power (0.69 per cent), and then laser raster spacing (0.45 per cent). Parameters that had the highest impact on durometer were laser power (1.00 per cent), followed by layer height, (0.34 per cent) and then laser raster speed (0.32 per cent). Three-dimensional printed samples had about 11.2 per cent more shrinkage than the bulk cast samples in the longest dimension.Originality/valueThis paper is one of the first that demonstrates near IR laser curing parameter effects on three-dimensional printed, commercial off-the-shelf, medical-grade and viscous silicone. The ability to cure very viscous thermosets locally enables interesting technologies such as wire encapsulation, high voltage actuators and drug delivery devices.

Ultrathin Ceramic Piezoelectric Films via Room-Temperature Electrospray Deposition of ZnO Nanoparticles for Printed GHz Devices.

High-frequency devices are key enablers of state-of-the-art electronics used in a wide and diverse range of exciting applications such as inertial navigation, communications, power conversion, medicine, and parallel computing. However, high-frequency additively manufactured piezoelectric devices are yet to be demonstrated due to shortcomings in the properties of the printed transducing material and the attainable film thickness. In this study, we report the first room-temperature-printed, piezoelectric, ultrathin (<100 nm) ceramic films compatible with high-frequency (>1 GHz) operation. The films are made of zinc oxide (ZnO) nanoparticles via near-field electrohydrodynamic jetting, achieving film piezoelectricity, without high-temperature processing, through a novel mechanism that is controlled during the deposition. Optimization of the printing process and feedstock formulation results in homogeneous traces as narrow as 213 μm and as thin as 53 nm as well as uniform field films as thin as 91 nm; the printing technique can be used with flexible and rigid, conductive and insulating substrates. The crystallographic orientation of the imprints toward the (100) plane increases if the rastering speed during printing is augmented, resulting in a larger piezoelectric response. The resonant frequency of film bulk acoustic resonators increases monotonically with the rastering speed, achieving transmission values as high as 4.99 GHz, which corresponds to an acoustic velocity of 2094 m/s, similar to the expected transverse value in high-temperature-grown ZnO films. Piezoresponse force microscopy maps of printed field films show local variation in the piezoelectric behavior across the film, with an average piezoelectric response as high as 21.5 pm/V, significantly higher than the d33 piezoelectric coefficient of single-crystal, high-temperature-grown ZnO, and comparable with reported values from ZnO nanostructures.

Nozzle-integrated pre-deposition and post-deposition heating of previously deposited layers in polymer extrusion based additive manufacturing

The adhesion and merging of adjacent filaments in polymer extrusion based additive manufacturing (AM) plays a key role in determining the thermal and mechanical properties of the built part. It is well known that maintaining the deposited filaments at a high temperature aids in the process of adhesion and merging. While external mechanisms such as laser and infrared heating have been used in the past to heat up deposited filaments, this paper presents a simpler, less invasive and in situ mechanism for heating of previously deposited layers using a hot metal block integrated with and rastering together with the filament-dispensing nozzle. Infrared thermography based quantitative measurement of temperature field along the raster line is carried out for two configurations – a preheater and a postheater traveling ahead of or behind the nozzle respectively. In each case, significant temperature rise in the deposited filaments is shown. A configuration comprising both preheater and postheater is shown to result in additional thermal benefits. The measured temperature rise is shown to be a function of process parameters such as raster speed and heater-to-base gap. Experimental measurements are shown to agree well with theoretical and simulation models. Cross-section imaging of samples printed without and with the in situ heating clearly show significant improvement in neck growth and filament-to-filament merging compared to the baseline case. Improvement in thermal and structural performance of printed samples is also demonstrated. Compared to other techniques proposed in the past, the heating approach presented in this work is passive and requires minimal additional costs or complexity. The improved temperature field and consequently enhanced filament adhesion reported here may help design and build parts with superior thermal and mechanical properties using polymer AM.

The Influence of MS Imaging Parameters on UV-MALDI Desorption and Ion Yield.

Ultraviolet matrix-assisted laser desorption/ionization mass spectrometry imaging (UV-MALDI MSI) is a widely used technique for imaging molecular distributions within biological systems. While much work exists concerning desorption in UV-MALDI MS, the effects of commonly varied parameters for imaging applications (repetition rate, use of continuous raster mode and raster speed), which determine spatial resolution and limits of detection for the technique, remain largely unknown. We use multiple surface characterization modalities to obtain quantitative measurements of material desorption and analyte ion yield in thin film model systems of two matrix compounds, arising from different UV-MALDI MSI sampling conditions. Observed changes in resulting ablation feature point to matrix-dependent spatial resolution and laser-induced matrix modification effects. Analyte ion yields of 10-9 to 10-6 are observed. Complex changes in ion yield, between spot and raster sampling and arising from varied laser repetition rate and raster speed, are observed. Graphical Abstract.

Design and Characterization of Electrically Conductive Structures Additively Manufactured by Material Extrusion

Multi-material additive manufacturing offers new design freedom for functional integration and opens new possibilities in innovative part design, for instance, a local integration of electrically conductive structures or heat radiant surfaces. Detailed experimental investigations on materials with three different fillers (carbon black (CB), carbon nanotubes (CNT) and nano copper wires) were conducted to identify process-specific influencing factors on electrical conductivity and resistive heating. In this regard, raster angle orientation, extrusion temperature, speed and flow rate were investigated. A variation of the raster angle (0°, ±45°, and 90°) shows the highest influence on resistivity. An angle of 0° had the lowest electrical resistance and the highest temperature increase due to resistive heating. The material filled with nano copper wires showed the highest electrical conductivity followed by the CNT filled material and materials filled with CB. Both current–voltage characteristics and voltage-dependent heat distribution of the surface temperature were determined by using a thermographic camera. The highest temperature increase was achieved by the CNT filled material. The materials filled with CB and nano copper wires showed increased electrical resistance depending on temperature. Based on the experiments, solution principles and design rules for additively manufactured electrically conductive structures are derived.

Feasibility of Metal Additive Manufacturing for Fabricating Custom Surgical Instrumentation for Hip and Knee Implants

The prevailing approaches for fabrication of orthopedic surgery instruments involve specialized machining processes on cast or stock parts. For high-volume fabrication of those instruments, machining is the most cost-effective approach. However, many trial components and various patient-specific (and/or physician-specific) tools and instruments have complex geometries and are needed only in very small batches sizes. Towards addressing this strong need for efficient manufacturing of customized surgical instruments for hip and knee implant surgeries, in this work, we performed a feasibility study by using a selective laser melting (SLM) process for this purpose. Additively manufactured (AM) 316L stainless steel parts (in both as-built and stress relieved conditions) were compared with the traditionally manufactured components from nominally the same material for both mechanical properties and microstructure. To improve the surface roughness of the AM parts, three different surface finishing post-processes were evaluated to achieve the required roughnesses better than 1.5 microns Ra. Experiments are then conducted to evaluate the effect of AM process parameters, including the laser power, hatch spacing and raster speed, on the resulting as-built surface quality. Lastly, two sample surgical instruments were fabricated and post-processed to demonstrate the methodology. Overall, the use of metal AM for fabrication of custom surgical instrumentation is deemed feasible and promising.

Investigations on laser-assisted interference-based rapid texturing of flexible polyimide substrate for photovoltaics applications

In this article, we demonstrate an elementary method for developing the long length periodic morphology using direct interaction of laser line beam (LLB) on polymeric substrate. The LLB is obtained by projecting the interference generated by employing hollow cylindrical lens. The interference is produced because of a failure of total internal reflection. Therefore, the projection of interferences on plane (normal to the center of lens) substantiates three distinct zones into the linearly formed trench by LLB on the substrate. The profile of impacted LLB is found on the flat top of dimension; length 50,000 μm and width 0.2 μm. The resulting pattern in the effective zone projected upon the substrate increases light absorption by 100% in the ultraviolet and visible range; compared to a pristine substrate. Moreover, the experimental system development takes three different aspects into account to integrate the LLB processing interaction with material, such as surface response of substrate, temperature dependent substrate properties, and its phase phase transformation. Therefore, the stable characteristics of processed material relate the productivity of the texturing, time consumption and laser rastering speed. Thus, LLB texturing has a competent potential for a wide variety of applications, especially in textured flexible solar photovoltaics.

Investigation of process-structure-property relationships in polymer extrusion based additive manufacturing through in situ high speed imaging and thermal conductivity measurements

Additive manufacturing has gained significant research attention due to multiple advantages over traditional manufacturing technologies. A fundamental understanding of the relationships between process parameters, microstructure and functional properties of built parts is critical for optimizing the additive manufacturing process and building parts with desired properties. This is also critical for a multi-functional part where the process needs to be optimized with respect to disparate performance requirements such as mechanical strength and thermal conductivity. This paper presents in situ high speed imaging and build-direction thermal conductivity measurements of polymer extrusion based additively manufactured parts in order to understand the effect of process parameters such as raster speed, infill percentage and layer height on build-direction thermal conductivity. Measurements of thermal conductivity using a one-dimensional heat flux method are correlated with in situ process images obtained from a high speed camera as well as cross section images of the built part. Results indicate strong dependence of build-direction thermal conductivity on raster speed, layer thickness and infill percentage, which is corroborated by high speed imaging of the printing process at different values of these process parameters. Key trade-offs between process throughput and thermal properties are also identified. In addition to enhancing our fundamental understanding of polymer extrusion based additive manufacturing and its influence on thermal properties of built parts, results presented here may facilitate process optimization towards parts with desired thermal and multi-functional properties.

Pulse smearing and profile generation in CO2 laser micromachining on PMMA via raster scanning

CO2 laser micromachining is an efficient and cost effective way for fabricating many polymeric microfluidic devices. Apart from direct laser writing also called vector cutting, raster scanning of CO2 laser beam is an indispensable part of fabrication process. Raster scanning is commonly used to create different types of microstructures on the surface. Polymethyl methacrylate (PMMA) is an important polymeric substrate for various microfluidic devices. In this research work, CO2 laser based raster scanning process has been explored for generation of microstructures of different widths and depths. The influence of high raster speeds on individual laser pulse shape has been discussed. Pulse smearing phenomenon was found to be detrimental to intensity of the laser beam. Reduction in energy intensity due to pulse smearing has been determined experimentally. Effects of process parameters on micromachined structure's output parameters have been detailed. An unique theoretical model has been developed for prediction of micromachined depth and profile on the basis of conservation of energy principal and superposition of Gaussian beams. The model takes into account the vertical pulse overlapping as well as pulse smearing effect. Evolution of surface in raster scanning has been discussed theoretically and experimentally. Developed model was found to be predicting the depth and evolved micro-structure profile close to actual depths and profile. The maximum prediction error for different power and scanning speed settings were less than 7.23%.

Optimization of Sample Preparation and Instrumental Parameters for the Rapid Analysis of Drugs of Abuse in Hair samples by MALDI-MS/MS Imaging

Matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) has been employed to rapidly screen longitudinally sectioned drug user hair samples for cocaine and its metabolites using continuous raster imaging. Optimization of the spatial resolution and raster speed were performed on intact cocaine contaminated hair samples. The optimized settings (100 × 150 μm at 0.24 mm/s) were subsequently used to examine longitudinally sectioned drug user hair samples. The MALDI-MS/MS images showed the distribution of the most abundant cocaine product ion at m/z 182. Using the optimized settings, multiple hair samples obtained from two users were analyzed in approximately 3 h: six times faster than the standard spot-to-spot acquisition method. Quantitation was achieved using longitudinally sectioned control hair samples sprayed with a cocaine dilution series. A multiple reaction monitoring (MRM) experiment was also performed using the ‘dynamic pixel’ imaging method to screen for cocaine and a range of its metabolites, in order to differentiate between contaminated hairs and drug users. Cocaine, benzoylecgonine, and cocaethylene were detectable, in agreement with analyses carried out using the standard LC-MS/MS method.Graphical ᅟ

Statistically Guided Development of Laser-Assisted Cold Spray for Microstructural Control of Ti-6Al-4V

Laser-assisted cold spray (LACS) was used to deposit Ti-6Al-4V powders onto Ti-6Al-4V substrates using nitrogen as a carrier gas. An L25 orthogonal array was created with three parameters independent of particle velocity considered thus to be the independent thermal parameters (ITPs) of LACS: powder feed rate, raster speed, and laser power. A signal-to-noise analysis of the influence of the ITPs on porosity, microhardness, and expected thickness was performed revealing that optimum parameter selection is highly dependent on the targeted property, with the ITPs having the largest influence on porosity. Additional bulk trials (>2.5 mm thick) were deposited using parameters of interest from the orthogonal study. These scaled trials demonstrate that it is possible to produce deposits of Ti-6Al-4V via LACS using nitrogen as a carrier gas with porosity less than 1 pct, which is comparable with values described in literature for more expensive helium-based cold spray of Ti-6Al-4V. Additionally, variation of the ITPs indicates that secondary phases and morphologies can be produced and controlled through the thermomechanical treatment caused in situ to LACS.