Increasing Imaging Speed and Accuracy in Contact Mode AFM

Atomic force microscopy (AFM) has been successfully applied to image many biological specimens such as proteins, DNA molecules, membrane fragments, synthetic lipid bilayers and monolayers and even whole cells, with a resolution ranging from hundreds of nm to sub-nm. In particular, AFM has a unique capability of operating in solutions; thus, proteins in situ can be directly imaged to study their functional relationships to the structure. Because in AFM, the contrast reflects direct force interactions between the probe and the specimen surface, the resolution of AFM images is highly dependent on the specimen being studied. We, and others, found that atomic resolution images on hard crystal surfaces are among the easiest to be obtained in AFM. For example, periodic surface atomic structures with hexagonal, rhombohedral, and cubic lattices were clearly resolved by AFM [9-12]. Using the NanoScope II AFM with various home-made accessories, such as motion stages and fluid cells, we have studied several different biological materials with a resolution from tens of nm to subnm.

Atomic Force Microscopy (AFM) has been successfully used to characterize a variety of samples with different chemical composition. Polycrystalline sample preparation techniques, cleaving and careful adjustment of the imaging setup made it also possible to investigate materials with non-ideal geometry (small size, rough sample surface) down to the atomic scale. Pressed CaCO3 powder samples of different origin have been imaged with atomic resolution. Multilayer systems of AlGaAs/GaAs and Si/GaAs on top of a GaAs substrate could be imaged readily. Single δ-layers of Si in GaAs could be resolved. The results demonstrate that simple sample preparation techniques and the implementation of chemical reactions can greatly enhance the analytical scope and applicability of AFM.

Laser beam scanning technology has potential applications in various fields, including LIDAR, laser processing, and optical communication. However, the capability of non-mechanical beam scanning is limited by the response time of an optical element, posing challenges in achieving both high-speed scanning and reconfigurable output beams. Here we propose a new concept, to the best of our knowledge, of the frequency-encoded optical phased array (OPA) to enable high-speed reconfigurable dynamic scanning. This is achieved by employing the customized frequency deviations on the array elements of the OPA. It is turned out that, in this way, the dynamic spatiotemporal beams with continuous scanning capability can be realized. We further find that the scanning speed is linearly proportional to the frequency deviation. Moreover, we are able to give access to multi-directional and customizable structured spatiotemporal beam scanning by encoding the on-demand frequency and phase deviations. The approach proposed here might be useful for high-speed reconfigurable beam scanning with high-power output.

Microstructure and mechanical properties of WC-12Co cemented carbide fabricated by laser powder bed fusion on a WC-20Co cemented carbide substrate

Tilted S–O bonds on a CaSO4(100) surface exhibit asymmetry under frictional force microscopic observation. The detection mechanism of the directional bonds was explained as being an interaction between the probe surface and an array of tilted mass-spring systems at the sample surface. When the scan speed of the probe was changed in the range of 5–91 µm/s under 40% relative humidity, the asymmetric component of friction increased linearly with the speed, while the total friction signal remained constant at speeds higher than 25 µm/s. A higher scan speed is more suitable for the detection of the tilted bonds. At lower scan speeds, the total friction signal decreased in intensity and the asymmetry signal became unstable. This is due to the condensation of water beneath the tip. A similar experiment under 60–65% relative humidity yielded much smaller signals for both the total friction and the asymmetry component.

In this study, Ti-22Al-25Nb intermetallic compound alloys are fabricated through selective laser melting (SLM) at four scanning speeds (600, 700, 800, and 900 mm/s). The microstructure and mechanical properties of the selective laser melting fabricated alloys are systematically evaluated. The results indicate that scanning speed significantly affects microstructure characteristics (e.g., relative density, grain size, texture density, and the precipitation of secondary phases). The variation laws of the relative density, grain size, and texture density are likewise affected by scanning speed. The relative density, grain size, and texture density increase and then decrease with the increase in scanning speed. The alloy fabricated with the lowest scanning speed (600 mm/s) exhibits the maximum relative density, grain size, and texture density. By contrast, the alloy with the highest scanning speed (900 mm/s) exhibits the minimum relative density, grain size, and texture density. Furthermore, the precipitations of the O phase and Ti3Al phase are primarily distributed in regions with a high strain concentration near the pool boundary. The alloy fabricated with a 600 mm/s scanning speed simultaneously achieves the highest strength and elongation, which is closely correlated with the uniform distribution of secondary phases.

Temperature and pressure variations in salt compressed air energy storage (CAES) caverns considering the air flow in the underground wellbore

PurposeThis study aims to investigate the relationship between melt pool dimensions and acoustic emission (AE) signal magnitudes obtained during laser powder bed fusion (L-PBF) process of austenitic stainless steel. Specifically, by varying laser power and scan speed, the widths, depths and aspect ratios of melt pools were compared with AE signal magnitudes across a frequency range of 100–200 kHz.Design/methodology/approachExperiments were conducted under different laser powers at a fixed scan speed and scan speeds at a fixed laser power. Melt pool dimensions were measured from cross-sectional optical images, and AE signals were obtained using a piezoelectric AE sensor installed beneath the build plate. Short-Time Fourier Transform (STFT) was applied to AE signals, and the magnitudes of frequency components were obtained.FindingsA strong correlation between melt pool dimensions and STFT magnitude was obtained. Pearson correlation coefficients between melt pool dimensions and STFT magnitudes were above 0.9 and the p-values were below 0.05. Increasing the laser energy enlarged the volume of melt pool and intensified the oscillation of melt pool. When scan speed exceeded 1,100 mm/s, STFT magnitude showed a slight increase owing to the increase in the vapor pressure.Originality/valuePrevious studies used AE signals to detect defects, but this study found a correlation between STFT magnitude and melt pool dimensions in L-PBF process. It was also found that STFT magnitude was more affected by vapor pressure at higher scan speeds. Monitoring STFT magnitude can help to understand melt pool dynamics, maintain process consistency and identify irregularities in real time.

Improvement of densification and microstructure of ASTM A131 EH36 steel samples additively manufactured via selective laser melting with varying laser scanning speed and hatch spacing

Frequently, at scientific meetings proteome researchers meet after the formal program has ended to discuss the state of the field and their own situation over some drinks. Typically these discussions center around instrumentation, primarily mass spectrometers, with a faster scan rate, higher mass accuracy or sensitivity, and the results generated by these powerful instruments. Statements like, “this is the future,” “this will revolutionize proteomics,” or “this has changed what we do in the lab” can be heard around the table. These sentiments are certainly justified. The progress in mass spectrometric instrumentation in the short history of proteomics has been nothing but astounding. Just a decade ago virtually all proteomic data were generated on ion trap instruments with low resolution, low mass accuracy, and limited scan speed and sensitivity, compared with the instruments presently in common use. Today, a significant fraction of the proteomic data is collected on high performance hybrid mass spectrometers with high scan speed, high mass accuracy and resolution, and high sensitivity of detection. The effects of these dramatic improvements are apparent in the manuscripts being published. However, its importance notwithstanding, data collection is only half of the whole proteomic story. The capacity to annotate, analyze, store, manage, and distribute the many gigabytes of data collected is the other half of the proteomic technology tandem. Long gone are the days when the expert analyst pretended to have manually verified all the data supporting the conclusions in a proteomic paper. Therefore, proteomics today, particularly mass spectrometry-based proteomics, depends as much on computers and the software tools they use as it does on high tech instruments to generate the data. Surprisingly, at the sessions in the bar, no one ever seems to boast about the data analysis part of the proteomic enterprise. Statements such as “ this program just recovered 20% more true positive peptide identification from my data set,” “ this allowed me to analyze my data ten times faster and at a credible FDR,” or “this statistical model allowed me to identify statistically significant quantitative changes in my dataset” are seldom if ever uttered. It is unlikely that things in the realm of electronics and software are inherently less appealing or attractive than high performance devices because the same individuals boasting about their mass spectrometers are likely to also share interesting new iPhone apps. It is certainly also not the case that advances on the software side of proteomics have had a lower impact than publications describing new hardware. In fact some of the most highly cited proteomics papers are about software. I therefore propose the likely controversial thesis that the software world of proteomics is less generally discussed because few can keep up and know about the field in some depth. This view is supported by several observations. First, in a recent study (1), in which a standardized protein sample was analyzed by a number of laboratories, it was clearly apparent that the analysis of the collected data was a major weakness. Second, the adoption of new software tools for proteomic data analysis takes much longer than the adoption of new instruments or wet-lab protocols. To raise the level of awareness in the crucial area of proteomic software tools, Molecular and Cellular Proteomics will publish a series of mini reviews that summarize the current state of specific aspects of this often bewildering field. These are not tutorials, i.e. the reader still will have to figure out how to use the tools and which tools to use. The intent of this series is to discuss the significance of a particular type of analysis, the question(s) addressed, the currently available solutions and their strengths and weaknesses, and the availability and utility of germane software tools or computational resources. We expect that these mini reviews will help proteome researchers to extract more and better information from the data generated by the wonderful instruments available today and to increase the excitement about the topic so that statistical models, search engines, and XML schema can also claim the stature in bar discussions that they deserve.

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

A 4kW Yb: YAG solid-state disc laser, with a four-way co-axial cladding head with powder feeding technique was employed to fabricate single-layer clads of Ni-based hardfacing alloy (Colmonoy-5) on medium carbon steel (ASME SA105) substrate by varying the laser processing parameters namely, beam power level (designated as low: 1200 W, medium: 1400 W, and high: 1600 W) and scanning speed (designated as low: 300 mm/min, medium: 400 mm/min, and high: 500mm/min). The laser clads were evaluated for their microstructural characteristics, microhardness, and slurry erosive wear performance with an aim to understand the effect of process parametric variations on their properties. Microstructural analyses of the clads were carried out using an optical microscope and a field-emission scanning electron microscope with attached energy-dispersive X-ray spectrometer supplemented by their Vickers microhardness testing and X-ray diffraction examination. The variation in laser processing parameters exerted a strong influence on the microstructural features of the clads in terms of γ-Ni dendrite size as well as morphology and distribution of various complex precipitates such as Cr-carbides and borides with relatively uniform distribution observed for the clads corresponding to low laser power and high scanning speed. The variation in laser power had relatively a greater influence on microhardness than the scanning speed variation. Micro-cutting, plastic deformation, crater formation besides ploughing away of the softer matrix were the typical fracture features associated with slurry eroded clads when examined under field-emission scanning electron microscope. Results of the slurry erosive wear tests showed that the clads pertaining to low laser power and high scanning speed exhibited superior wear resistance as compared to their counterparts.

Phase-field modeling and Experimental investigation for rapid solidification in wire and arc additive manufacturing

To study the formation mechanism of a conductive layer in a laser-processed AlN ceramic plate, nanosecond laser treatment on an AlN ceramic was performed to generate an Al layer, which created conductivity on the surface. Changes in the resistance for different energy densities, pulse durations, line spacings and scanning speeds were studied by means of XPS and scanning electron microscopy. The results show that the resistance is inversely proportional to the duration of the pulse in the case of low energy density or low scanning speed. At a higher energy density or a higher scanning speed, the resistance is proportional to the duration of the pulse. The variation in the resistance as a function of line spacing is related to the energy density. As the energy density increases, the resistance value decreases slowly at first and then maintains an upward trend. The resistance is proportional to the scanning speed.

Melt‐grown Al2O3–ZrO2 eutectic (AZ eutectic) ceramics have attracted extensive attention for harsh environment applications. In this work, AZ eutectic ceramic is additively manufactured via one‐step laser powder bed fusion (LPBF). The role of scanning speed on phase formation, crystallographic characteristics, microstructure evolution, and mechanical properties were systematically investigated. The as‐fabricated specimens are mainly composed of α‐Al2O3 and t‐ZrO2. Lower scanning speeds induced the formation of cellular structures consisting of randomly oriented ZrO2. In contrast, nanometer eutectic lamellar structure with well‐defined multiple crystallographic orientation relationships, for example, {100} Al2O3 || {100} ZrO2 and {0001} Al2O3 || {001} ZrO2, occurred at higher scanning speeds. Both the cell size and lamellar spacing decreased with increasing scanning speed. With the microstructure refinement, the crack propagation mode changes from intergranular to transgranular fracture, leading to progressively enhanced fracture toughness with a maximum value of 7.76 MPa·m1/2. The present work could shed light on tailoring the microstructure of LPBF AZ eutectic ceramic via varying processing parameters.