High-speed Scanning Research Articles

The Interaction Pathway in the Mechano-Ultrasonically Assisted and Carbon-Nanotubes Augmented Nickel–Aluminum System

The influence of mechano-ultrasonic activation (MUA) and nano-additives (carbon nanotubes-CNT) on the interaction pathway of nickel–aluminum powder mixture at high heating rates was investigated. The optimum conditions of the mechano-ultrasonic activation, along with the phase and structure formation peculiarities of nickel–aluminum and nickel–aluminum–carbon nanotubes mixtures by thermal analysis method, the so-called high-speed temperature scanner (HSTS), were found out. The optimum duration of mechanical and ultrasonic activation aiming to achieve homogeneous distribution in the agitated mixtures was determined. A shift in characteristic temperatures of MUA mixtures by the influence of both heating rate and ultrasound on the Ni + Al interaction pathway for the mechano-activated (1, 3, 5 min) and 1 wt% CNT containing mixtures was observed. The formation patterns of NiAl + Ni3Al mixture or pure NiAl phase was manifested according to the interaction mechanism (depending on solid–liquid or solid–solid state of intermediates). The effective activation energy values for the Ni + Al exothermic reactions of all studied systems were determined by the isoconversional method of Kissinger.

A multiscale wavelet algorithm for atom tracking in STM movies

High-speed scanning tunneling microscopy (STM) data have become available that provide movies of time-dependent surface processes. To track adsorbed atoms and molecules in such data automatic routines are required. We introduce a multiresolution wavelet particle detection algorithm for this purpose. To identify the particles, the images are decomposed by means of a discrete wavelet transform into wavelet planes of different resolutions. An ‘à trous’ low-pass filter is applied. The coefficients from the wavelet planes are filtered to remove noise. Wavelet planes with significant coefficients from the particles are multiplied, and the product is transformed into a binary particle mask. The precision of the method is tested with data sets of adsorbed CO molecules and O atoms on a Ru(0001) surface. The algorithm can safely detect and localize these particles with high precision, even in the presence of the enhanced noise characteristic for high-speed, constant-height STM data. By linking the particle positions, we obtain extended trajectories with a resolution of ∼0.5 Å or better allowing us to investigate the detailed motion of single atoms on a surface.

Processability of recycled quasicrystalline Al-Fe-Cr-Ti composites by selective laser melting - A statistical approach

In situ Al-matrix quasicrystalline Al-Fe-Cr-Ti composites produced using recycled material were processed by selective laser melting (SLM). Three Al-Fe-Cr-Ti compositions (Al95Fe2Cr2Ti1, Al93Fe3Cr2Ti2, Al91Fe4Cr3Ti2) were gas atomized and, the powders range <75 µm, was used to produce SLM samples, where laser power and scan speeds were variated. The samples produced were analyzed by Optical and Scanning Electron Microscopy and Vicker hardness. The influence of the laser power and scan speed on the porosity, molten pool dimensions, structural characteristics of the in situ composite produced, and microhardness, was statistically interpreted using Pareto charts and main effects graphs. The three atomized powders presented similar physical characteristics and different microstructures; the higher the Fe, Cr, and Ti content, the higher the amount of quasicrystalline/approximant phases. By processing these powders by SLM, the processing window showed to become narrower with increasing the Fe, Cr, and Ti content. The laser power performs a dominant influence on the porosity of the SLMed samples; the higher the laser power, the higher the samples’ porosity. The length of the molten pools is mainly affected by the scan speed, while the depth is more dependent on the laser power. The largest molten pools dimensions were obtained under high laser power (> 250 W) or low scan speed (< 300 mm/s). Furthermore, laser power is the main factor for varying the cooling rates as, a consequence, the SLMed composites’ microstructure is varied, which directly influences the microhardness. These findings provide an effective way to fabricate tailored Al-Fe-Cr-Ti composites’ parts by SLM.

Low-cost electrothermally actuated MEMS mirrors for high-speed linear raster scanning

Electrothermally actuated MEMS mirrors are significantly lower in cost than their electrostatically actuated counterparts, largely due to their ability to perform well without hermetic packaging. However, their typical slower speeds, higher power requirement, and non-linear drive limit their widespread use. In this work, we address these limitations and achieve an electrothermally actuated MEMS mirror capable of reliable linear raster scanning at speeds up to 300 Hz with a large angular range of motion ( ± 40 ∘ optical). A simple pulse design technique is used to achieve ∼ 99 % scan linearity and correct for artifacts like overshoot and ringing. Furthermore, segmented polysilicon microheaters along the actuators are used for impedance matching to low-voltage electronics, resulting in lower power consumption and improved scan speed and angular range. These mirrors serve as an attractive option for low-cost and compact integrated beam-steering optical devices, and we demonstrate one such use case in an optical coherence tomography (OCT) system.

Time-resolved 3D visualization of liquid jet breakup and impingement behavior in a shallow liquid pool

A new three-dimensional laser-induced fluorescent (3D-LIF) technology to obtain the hydrodynamic behavior of liquid jets in a shallow pool were developed. In this technology, firstly, a refractive index matching was applied to acquire a clear cross-sectional image. Secondly, a series of cross-sectional images was obtained by using a high-speed galvanometer scanner. Finally, to evaluate the unsteady 3D interface shape of liquid jet, a method was developed to reconstruct 3D shapes from the series of cross-sectional images obtained using the 3D-LIF method. The spatial and temporal resolutions of measurement were 0.21 × 0.21 × 1.0 mm/pixel and 2 ms, respectively. The shape of a 3D liquid jet in a liquid pool and its impingement, spreading and atomization behavior were reconstructed using the proposed method, successfully. The behaviors of atomized particles detached from the jet were obtained by applying data processing techniques. Diameters distribution and position of atomized droplets after detachment were estimated from the results.

Choroidal imaging using optical coherence tomography:techniques and interpretations.

The choroid is vascularized membranous tissue that supplies oxygen and nutrients to the photoreceptors and outer retina. Choroidal vessels underlying the retinal pigment epithelium are difficult to visualize by ophthalmoscopy and slit-lamp examinations. Optical coherence tomography (OCT) imaging made significant advancements in the last 2 decades; it allows visualization of the choroid and its vasculature. Enhanced-depth imaging techniques and swept-source OCT provide detailed choroidal images. A recent breakthrough, OCT angiography (OCTA), visualizes blood flow in the choriocapillaris. However, despite using OCTA, it is hard to visualize the choroidal vessel blood flow. In conventional structural OCT the choroidal vessel structure appears as a low-intensity objects. Image-processing techniques help obtain structural information about these vessels. Manual or automated segmentation of the choroid and binarization techniques enable evaluation of choroidal vessels. Viewing the three-dimensional choroidal vasculature is also possible using high-scan speed volumetric OCT. Unfortunately, although choroidal image analyses are possible using the images obtained by commercially available OCT, the built-in function that analyzes the choroidal vasculature may be insufficient to perform quantitative imaging analysis. Physicians must do that themselves. This review summarizes recent choroidal imaging processing techniques and explains the interpretation of the results for the benefit of imaging experts and ophthalmologists alike.

Dependency of Conductive Atomic Force Microscopy and Lateral Force Microscopy Signals on Scan Parameters for Zinc Oxide Nanorods

Conductive atomic force microscopy (C-AFM) is one of the most commonly used characterization techniques for piezoelectric one-dimensional nanomaterials. However, a comprehensive understanding of the effects of certain scan parameters on the C-AFM signals remains elusive. In the present work, the dependency of C-AFM signals on the normal force, scan speed, and Z scanner feedback gain was studied in conjunction with lateral force microscopy (LFM) signals. As the normal force increased, the C-AFM and the LFM signals increased for the following two possible reasons. When larger normal force was applied, ZnO nanorods were more effectively deflected, intensifying the piezoelectric effect. Additionally, the triboelectric effect was enhanced via the increased force of friction between the AFM tip and the ZnO nanorods. When the scan speed increased to 0.5 Hz, the LFM signals and the C-AFM signals increased owing to the enhanced degree of deflection in the ZnO nanorods. However, when exceeding 0.5 Hz, both the LFM signals and the C-AFM signals started to decrease because the AFM tip did not come into contact with the short ZnO nanorods at a high scan speed. Finally, with an increase in the feedback gain to 0.5, both the LFM signals and the C-AFM signals increased. However, when the feedback gain exceeded 1.0, the Z scanner feedback loop was too sensitive to deflect the ZnO nanorod, considerably reducing the total LFM signals. In contrast, the total C-AFM signal showed only a moderate decrease.

Microstructural evolution and characterization of AlSi10Mg alloy manufactured by selective laser melting

Extensive investigation of the influence of the selective laser melting (SLM) process parameters on the evolution of the molten pool is of great significance to understanding microstructure control and SLM-fabricated part quality. This study focuses on the influence of the scan speed inducing the laser energy changes on the microstructural evolution, texture and phase of AlSi10Mg alloy during SLM. The microstructural evolution and characterization of the SLM-manufactured AlSi10Mg alloy were investigated by scanning electron microscope/electron backscattered diffraction (SEM/EBSD), transmission electron microscope/scanning transmission electron microscope (TEM/STEM) and X-rays diffraction (XRD). The microstructural features of the sample have shown that the primary cellular dendritic structure sizes in the coarse grain zones were about three times larger than those in fine grain zones due to the different cooling rates. Besides, the microstructure boundary contains a eutectic mixture of Al and Si while the matrix is mainly composed of α-Al. The interplanar distance between the fringes are measured as 3.84 Å and 2.86 Å corresponding to the (110) plane of Si and (110) plane of Al. On the other hand, the hardness measurement data show that the sample due to the high scan speed is larger than that of the low scan speed. Meanwhile, the (001) Al texture strength of samples in the low scan speed is stronger than those in the high scan speed. Finally, the XRD analysis reveals that no significant differences are found in the intensity of (111) α-Al, while the intensity of the (200) α-Al presents a difference because of the grain orientation and size.

Correlation of real-time thermal history with tribological properties of laser coated NiCrBSi with Ag and WS2 addition

The laser coating of NiCrBSi in pure form as well as with the addition of lubricious Ag or WS 2 has been developed on Ti6Al4V substrate. With the help of an IR pyrometer , real-time thermal history was monitored and correlated with the tribological properties of the coating. A matrix predominantly comprised of NiTi and NiTi 2 and reinforced with hard phases like CrB, TiC, TiB 2 , Cr 3 C 2 was formed for all the types of coatings. From the XRD and EDS analysis, it was observed that for the coating containing Ag, Ag was found to be present in elemental form, but in the case of coating containing WS 2 , WS 2 got dissociated during laser processing and formed TiS 2 , an anti-friction phase. Effects of heat input on the tribological behavior of both types of coatings (in-situ generated lubricating phase TiS 2 and ex-situ developed lubricating phase Ag) were analyzed with the help of real-time thermal history. For Ag-type coating, maximum hardness, minimum COF and, minimum wear rate were obtained as 968 HV, 0.25, and 2.21E-5 mm 3 /N-m respectively for lower power and higher velocity process parameters. For WS 2 coating, maximum hardness, minimum COF and, minimum wear rate were obtained as 1303 HV, 0.26, and 1.5E-4 mm 3 /N-m respectively for lower laser power and higher scan speed. Comparing both the coating, it can be stated that, low heat input led to a high cooling rate, low molten pool life, and a low peak temperature of the molten pool, which increased the lubricious phase in the coating thereby reducing the friction coefficient. The present study can be useful to develop the process maps for desired lubrication property of the coating by using real-time monitoring of the thermal histories during the laser coating process . • Correlation of real-time thermal history with performance of the laser coatings • Laser coating of NiCrBSi with addition of Ag and WS 2 as solid lubricant • Shorter molten pool life time and low peak temperature reduced friction. • Process map based on the correlation of online monitoring and tribological property • Minimum COF and wear rate of the coating was 0.25 and 2.21E-5 mm 3 /N-m respectively.

Investigation of Autostereoscopic Displays Based on Various Display Technologies.

The autostereoscopic display is a promising way towards three-dimensional-display technology since it allows humans to perceive stereoscopic images with naked eyes. However, it faces great challenges from low resolution, narrow viewing angle, ghost images, eye strain, and fatigue. Nowadays, the prevalent liquid crystal display (LCD), the organic light-emitting diode (OLED), and the emerging micro light-emitting diode (Micro-LED) offer more powerful tools to tackle these challenges. First, we comprehensively review various implementations of autostereoscopic displays. Second, based on LCD, OLED, and Micro-LED, their pros and cons for the implementation of autostereoscopic displays are compared. Lastly, several novel implementations of autostereoscopic displays with Micro-LED are proposed: a Micro-LED light-stripe backlight with an LCD, a high-resolution Micro-LED display with a micro-lens array or a high-speed scanning barrier/deflector, and a transparent floating display. This work could be a guidance for Micro-LED applications on autostereoscopic displays.

A crystal-processing machine using a deep-ultraviolet laser: application to long-wavelength native SAD experiments.

While native SAD phasing is a promising method for next-generation macromolecular crystallography, it requires the collection of high-quality diffraction data using long-wavelength X-rays. The crystal itself and the noncrystalline medium around the crystal can cause background noise during long-wavelength X-ray data collection, hampering native SAD phasing. Optimizing the crystal size and shape or removing noncrystalline sample portions have thus been considered to be effective means of improving the data quality. A crystal-processing machine that uses a deep-UV laser has been developed. The machine utilizes the pulsed UV laser soft ablation (PULSA) technique, which generates less heat than methods using infrared or visible lasers. Since protein crystals are sensitive to heat damage, PULSA is an appropriate method to process them. Integration of a high-speed Galvano scanner and a high-precision goniometer enables protein crystals to be shaped precisely and efficiently. Application of this crystal-processing machine to a long-wavelength X-ray diffraction experiment significantly improved the diffraction data quality and thereby increased the success rate in experimental phasing using anomalous diffraction from atoms.

Analysis of microstructure, mechanical properties, wear characteristics and corrosion behavior of SLM-NiTi under different process parameters

In this paper, the NiTi alloy is prepared by selective laser melting (SLM), and the influence of different process parameters on the microstructure, mechanical properties, corrosion and friction is compared and analyzed. The results of XRD, DSC and EDS showed that the sample prepared with high power and high scanning speed (HP) tends to form the B2NiTi phase, while the sample prepared with low power and low scanning speed (LP) tends to form the B19′NiTi phase. The electrochemical test, friction and wear experiments and tribocorrosion tests showed the LP sample had better corrosion resistance whether in simulated body fluids (SBF) or 3.5 wt% NaCl solution, while the HP exhibited better wear resistance and tribocorrosion resistance. The influence mechanism of different process parameters on the corrosion resistance and wear resistance of the samples is discussed in detail in this paper.

In-situ high-speed atomic force microscopy observation of dynamic nanobubbles during water electrolysis

The nanobubbles (NB) formed on a solid surface has been reported, although the stability in a solution is still discussed. The atomic force microscopy (AFM) has shown the unique shape of the flatted NB, however the dynamic behavior has not investigated yet. Recently, the high scanning speed AFM (HS-AFM) has been developed and applied to the several interfaces. Here, we present in-situ HS-AFM observation during water electrolysis. The hydrogen and oxygen NB evolution on highly oriented pyrolytic graphite (HOPG) electrode are studied. Our video data is the first time to demonstrate the NB nucleation and the growth. The processes are different between both gases. The hydrogen NB grows with active coalescence, while the oxygen one is smaller and irregularly moves on HOPG surface. Using this technique, we will be able to study the NB stability influence by some factors, such as the surface potential and electric capillarity.

Solid-state FMCW LiDAR with in-fiber beam scanner.

The beam scanner is a predominant part in the light detection and ranging (LiDAR) system to achieve three-dimensional (3D) imaging. The solid-state beam-steering device has emerged as a promising candidate technology for a beam scanner with the advantages of robustness, stability, and high scanning speed. Here we propose a frequency modulated continuous wave (FMCW) LiDAR system with an in-fiber solid-state beam scanner. A 45° tilted fiber grating (TFG) is first employed to achieve in-fiber solid-state spectral scanning in the LiDAR system. A maximum output efficiency of 93.7% is achieved with proper polarization control. A single-mode fiber is then used to fabricate a 2-cm 45° TFG, which significantly reduces the size and the cost of the beam scanner in the LiDAR system. We experimentally realize 3D imaging of targets placed at a distance of 1.2 m based on our proposed LiDAR system. In addition, the system can achieve a detection distance of 6 m with a ranging precision of 24 mm.

Surfing Scanning Probe Nanolithography at Meters Per Second.

Scanning probe lithography (SPL) as a maskless approach with a low tool price can pattern a variety of materials at a nanometer or even atomic resolution. However, the throughput of conventional SPLs is extremely low due to their limited scanning speeds. Here, we report a high-speed, probe-based method to continuously pattern the substrate surface at a linear velocity of meters per second. We demonstrated direct writings of nanoscale patterns by using ultrafast electron-induced deposition inside a nanoscale flow at a patterning frequency of 20 MHz. The fast scan motion of the writing probe is precisely controlled by using self-adaptive hydro- and aerodynamics functions of a patterning head. The microscale electro-hydrodynamic ejection and microfluid channels are used to deliver the precursor at high scanning speeds. One patterning head can carry parallel probes to further enhance the patterning throughput. This low-cost, maskless patterning method opens new avenues to develop high-throughput nanomanufacturing techniques.

Resolving atomic diffusion in Ru(0001)−O(2×2) with spiral high-speed scanning tunneling microscopy

An intermediate state in atomic diffusion processes in the $\mathrm{O}(2\ifmmode\times\else\texttimes\fi{}2)$ layer on Ru(0001) is resolved with spiral high-speed scanning tunneling microscopy (STM). The diffusion of atomic oxygen in the adlayer has been studied by density functional theory and STM. Transition state theory proposes a migration pathway for the diffusion in the oxygen adlayer. With spiral scan geometries---a new approach to high-speed STM---the oxygen vacancy mobility on the highly covered Ru(0001) surface is determined to be in the range of 0.1 to 1 Hz. Experimental evidence for the intermediate state along the oxygen diffusion pathway is provided in real space and real time.

Ultrashort pulsed laser ablation of zirconia-alumina composites for implant applications

• Influence of alumina content on fs-laser machining of zirconia-alumina composites was studied. • Significant influence of material composition on material removal behavior was demonstrated. • Single phase materials have larger laser ablation thresholds and smaller material removal rate than their composites. • A lower scan speed is preferred for single phase materials while a higher scan speed is beneficial for the composites. Laser texturing of zirconia-alumina ceramics is a promising surface modification method for many applications, such as enhancing osseointegration of alumina toughened zirconia (ATZ) dental implants or improving friction behavior of zirconia toughened alumina (ZTA) hip replacement bearing components. The common problems in laser texturing of ATZ/ZTA ceramics are thermal cracking, low material removal rate (MRR), and laser-induced phase transformation (LIPT). Furthermore, the compositional variation of those ceramics will complicate these problems. In order to improve the manufacturing processability, ultrashort pulsed laser ablation behavior of ATZ/ZTA composites was investigated in this research. Single phase zirconia and alumina were found to have smaller MRRs than their composites, and this behavior was negatively correlated to the materials single-pulse laser ablation threshold. However, under multi-pulse laser irradiation, the ablation thresholds of all materials saturated to the same level, indicating that single phase materials were more sensitive to the incubation effect than their composites. This led to the MRRs of the single phase materials being reduced at larger scan speeds, while the MRRs of their composites remained independent of scan speed. It was also shown that single phase materials were less susceptible to thermal cracking than their composites under excessive heat accumulation. These results suggest that a lower scan speed is preferred for single phase materials in order to achieve a larger MRR, while a higher scan speed is beneficial for the composites for suppressing thermal cracking without compromising ablation efficiency. In addition, no LIPT was detected for zirconia dominated materials after laser ablation.

A Large-Range Steering Optical Phased Array Chip and High-Speed Controlling System

The optical phased array (OPA) chip is becoming the core component of all-solid-state lidars. In order to realize the wide-angle range beam scanning and rapid control of OPA-based solid-state lidars, we design and fabricate a 64-channel silicon-based OPA chip based on thermo-optical modulation. In accordance with the optical phase control characteristics of the multichannel thermo-optic OPA chip, we propose a parallel random access memory (RAM) array technique to realize high-speed phase control for the OPA chip and build the hardware system with a field-programmable logic gate array (FPGA). This system is used to test the main performance indicators of the OPA chip and realizes the high-speed scanning control of the wide-angle range of the OPA output beam. The test results show that the OPA chip we designed can achieve fast beam scanning within a large angle range between &#x2212;32.5&#x00B0; and &#x002B;32.5&#x00B0;, and the chip has high working reliability. Combined with the control system we build, it can meet the high-speed radar scanning requirements of all-solid-state lidars. This work lays a good foundation for the subsequential development of our thermo-optical and electrooptic OPA all-solid-state lidar prototypes.

Understanding the Parameter Effects on Densification and Single Track Formation of Laser Powder Bed Fusion Inconel 939

Inconel 939 is a nickel-based superalloy highly preferred in aerospace applications where excellent material properties are required under extreme service conditions. However, Inconel 939 is a relatively challenging material due to densification behavior during laser processing, leading to micro-cracking and low density. Therefore, the correlation between the parameters and material properties requires a comprehensive evaluation to achieve desired results. In this study, the formation of single tracks and densification properties of Inconel 939 processed by laser powder bed fusion are investigated based on the different parameter combinations. The melt pool characteristics with respect to high laser power and scanning speed are analyzed.

Influence of temporal pulse-shaping on laser surface texturing of metals using fast modulated cw-fiber laser radiation

Remote ablation cutting with continuous wave laser radiation is a process commonly used for the surface pretreatment of large area metallic parts before joining of metal-polymer hybrid structures, due to their cost-effectiveness and high average powers when compared to short-pulsed lasers. The process requires high power-densities and multiple irradiations at high scanning speeds to achieve the desired kerf depth. In this work a fast modulated cw fiber laser is used to investigate the possibilities of increasing the material removal rate by periodically dropping the laser power and therefore modifying the recoil pressure at the vapor-liquid interface in the interaction zone to assist in melt expulsion. It was found that power modulation with frequencies in excess of 10 kHz can lead to an increased material removal rate when compared to continuous wave processing at comparable average and peak power levels, enabling higher kerf aspect ratios in a single irradiation.