Contact Atomic Force Microscopy Research Articles

Innovative Surface Plasmon Resonance Aptasensor for Detecting Cocaine in Human Urine

This study describes the development of an optical-based surface plasmon resonance (SPR) aptasensor for the detection of cocaine. The aptasensor was prepared by first attaching gold nanoparticles to a clean SPR chip surface, followed by the addition of an aptamer to create a modified surface. This surface was characterized using contact angle and atomic force microscopy, revealing surface roughness values of 0.28 nm and 28.12 nm for the blank and modified surfaces, respectively. The detection of cocaine was carried out in the concentration range of 1 ng/mL to 1000 ng/mL, with a detection time of approximately 8 min and a cocaine limit of detection (LOD) of 0.43 ng/mL. Repeatability studies were conducted, and the stability of the signal response was examined at a concentration of 200 ng/mL. Adsorption isotherm models, including Scatchard, Langmuir, and Freundlich models, were calculated to assess the surface homogeneity of the SPR aptasensor chip, with the results indicating compatibility with the Langmuir isotherm model.

Molecular identification via molecular fingerprint extraction from atomic force microscopy images

Non–Contact Atomic Force Microscopy with CO–functionalized metal tips (referred to as HR-AFM) provides access to the internal structure of individual molecules adsorbed on a surface with totally unprecedented resolution. Previous works have shown that deep learning (DL) models can retrieve the chemical and structural information encoded in a 3D stack of constant-height HR–AFM images, leading to molecular identification. In this work, we overcome their limitations by using a well-established description of the molecular structure in terms of topological fingerprints, the 1024–bit Extended Connectivity Chemical Fingerprints of radius 2 (ECFP4), that were developed for substructure and similarity searching. ECFPs provide local structural information of the molecule, each bit correlating with a particular substructure within the molecule. Our DL model is able to extract this optimized structural descriptor from the 3D HR–AFM stacks and use it, through virtual screening, to identify molecules from their predicted ECFP4 with a retrieval accuracy on theoretical images of 95.4%. Furthermore, this approach, unlike previous DL models, assigns a confidence score, the Tanimoto similarity, to each of the candidate molecules, thus providing information on the reliability of the identification. By construction, the number of times a certain substructure is present in the molecule is lost during the hashing process, necessary to make them useful for machine learning applications. We show that it is possible to complement the fingerprint-based virtual screening with global information provided by another DL model that predicts from the same HR–AFM stacks the chemical formula, boosting the identification accuracy up to a 97.6%. Finally, we perform a limited test with experimental images, obtaining promising results towards the application of this pipeline under real conditions.Scientific contributionPrevious works on molecular identification from AFM images used chemical descriptors that were intuitive for humans but sub–optimal for neural networks. We propose a novel method to extract the ECFP4 from AFM images and identify the molecule via a virtual screening, beating previous state-of-the-art models.

The application of KMnO4 in reverse flotation separation of chalcopyrite and talc and its selective depression mechanism

Talc exhibits excellent floatability and, as a major silicate gangue mineral associated with chalcopyrite, significantly obstructs the purification and smelting of chalcopyrite. This study investigates the reverse flotation separation of chalcopyrite and talc using KMnO4 as a depressant and DDA (dodecylamine) as a collector within a reverse flotation system. Single mineral flotation experiments show that after adding KMnO4, the recovery of chalcopyrite in 38–74 μm is only 6.86 %, whereas the recovery of talc in 45–106 μm and 25–45 μm are 93.47 % and 89.25 %, respectively. Further experiments with artificially mixed ores demonstrate that KMnO4 effectively achieves the separation of chalcopyrite and talc. The depression mechanism of KMnO4 on chalcopyrite and talc was analyzed using Zeta potential, contact angle measurement, AFM (atomic force microscopy), FTIR (Fourier transform infrared spectroscopy), XPS (X-ray photoelectron spectroscopy), and DFT (density functional theory) calculations. Mechanistic analysis indicates that in an alkaline environment, chalcopyrite can undergo a redox reaction with KMnO4, forming hydrophilic hydroxide species (Cu(OH)2, Fe(OH)3) on the chalcopyrite surface, which depresses chalcopyrite flotation. In contrast, the surface properties of talc are relatively stable and difficult to react with KMnO4, which cannot depress the flotation of talc. Therefore, KMnO4 can be used as an efficient and selective depressant for the reverse flotation separation of chalcopyrite and talc.

Mitigation effect of a biodegradable surfactant N,N,N-trimethyl-2-(((hexadecyloxy)carbonyl)oxy)ethan-1-aminiumiodide for mild steel corrosion in 5% HCl: Experimental and theoretical insights

A cleavable cationic surfactant having carbonate linkage, N,N,N-trimethyl-2-(((hexadecyloxy)carbonyl)oxy)ethan-1-aminiumiodide referred to as THC was synthesised and characterized employing elemental analysis, FT-IR (Fourier Transform Infrared Spectroscopy), 1H NMR (Nuclear Magnetic Resonance) and 13C NMR. The extent of corrosion inhibition of THC was for the first time studied experimentally and theoretically on mild steel (MS) substrate in 5 % HCl solution at temperatures 303, 313, 323, 333, 343, 353 K. Experimental investigations include gravimetric analysis, potentiodynamic polarization (PDP) and electrochemical impedance analysis (EIS). THC provided maximum inhibition efficiency of 93.2 % at concentration of 1×10−4 M at 303 K which was further raised to 98.1 % at 353 K. PDP studies reveal that given surfactant is mixed type inhibitor. Surface studies such as contact angle measurement, AFM (Atomic Force Microscopy), SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray Analysis), and XPS (X-ray Photoelectron Spectroscopy) were employed to justify the adsorption of inhibitor molecules on MS surface. Furthermore, biodegradability test on THC was done to support the environment friendly nature of the surfactant.

Atomic force microscopy reveals morphological and mechanical properties of schistosoma mansoni tegument

Schistosoma mansoni, an intravascular parasitic worm and the causative agent of schistosomiasis, relies on its tegument (outer layer) for survival and host interaction. This study explored the morphology and mechanical properties of S. mansoni tegument using Atomic Force Microscopy (AFM). Notably, we employed the PeakForce Quantitative Nanomechanical Mapping (PF-QNM) mode in air, enabling simultaneous acquisition of 3D topography and mechanical property contrasts (adhesion, elastic modulus). Additionally, nanoindentation (AFM contact mode) was performed on female worm tegument for elastic modulus measurement. Both techniques revealed an elastic modulus range of fractions or units of GPa for the tegument. Interestingly, mechanical property maps, particularly adhesion contrast, displayed a recurring pattern of light and dark bands. We also measured the depth of annular furrows on the female tegument, finding an average of 128 ± 10 nm. These findings establish AFM, particularly PF-QNM, as a valuable tool to characterize S. mansoni tegument properties, offering insights for future investigations into parasite biology and its response to immunological or pharmacological challenges.

Design and Characterization of a Dual-Protein Strategy for an Early-Stage Assay of Ovarian Cancer Biomarker Lysophosphatidic Acid.

The overall 5-year survival rate of ovarian cancer (OC) is generally low as the disease is often diagnosed at an advanced stage of progression. To save lives, OC must be identified in its early stages when treatment is most effective. Early-stage OC causes the upregulation of lysophosphatidic acid (LPA), making the molecule a promising biomarker for early-stage detection. An LPA assay can additionally stage the disease since LPA levels increase with OC progression. This work presents two methods that demonstrate the prospective application for detecting LPA: the electromagnetic piezoelectric acoustic sensor (EMPAS) and a chemiluminescence-based iron oxide nanoparticle (IONP) approach. Both methods incorporate the protein complex gelsolin-actin, which enables testing for detection of the biomarker as the binding of LPA to the complex results in the separation of gelsolin from actin. The EMPAS was characterized with contact angle goniometry and atomic force microscopy, while gelsolin-actin-functionalized IONPs were characterized with transmission electron microscopy and Fourier transform infrared spectroscopy. In addition to characterization, LPA detection was demonstrated as a proof-of-concept in Milli-Q water, buffer, or human serum, highlighting various LPA assays that can be developed for the early-stage detection of OC.

Impact of Molecular Weight on Anti-Bioadhesion Efficiency of PDMS-Based Coatings

Silicone elastomer coatings have shown successful fouling release ability in recent years. To further enhance the design of silicone coatings, it is necessary to fully understand the mechanisms that contribute to their performance. The objective of this study was to examine the relationship between the molecular weight of polydimethylsiloxane (PDMS) and antibioadhesion efficiency. PDMS-based coatings were prepared via a condensation reaction, with a controlled molecular weight ranging from 0.8 to 10 kg·mol−1. To evaluate changes in surface wettability and morphology, contact angle experiments and atomic force microscopy (AFM) were performed. Finally, the antibioadhesion and self-cleaning performance of PDMS coatings was carried out during in situ immersion in Lorient harbor for 12 months. Despite small variations in surface properties depending on the molecular weight, strong differences in the antibioadhesion performance were observed. According to the results, the best antibioadhesion efficiency was obtained for coatings with an Mn between 2 and 4 kg·mol−1 after 12 months. This paper provides for the first time the impact of the molecular weight of PDMS on antibioadhesion efficiency in a real marine environment.

Anisotropic adsorption of xanthate species on molybdenite faces and edges and its implication on the flotation of molybdenite fines

Utilizing xanthate in bulk flotation of Cu-Mo sulfide ores is inevitable, but the implication of xanthate on the flotation of molybdenite fines is barely understood. In this study, the influence of sodium butyl xanthate (SIBX) on the flotation of molybdenite fines and the interaction mechanism was comprehensively investigated by micro-flotation tests, contact angle, adsorption capacity, electrochemical tests, atomic force microscopy (AFM), Fourier Transform Infrared Spectrometer (FTIR), X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) calculations. Micro-flotation tests indicated that SIBX significantly enhanced the flotation of molybdenite fines across a wide pH range. Contact angle, adsorption capacity, Tafel curves, AFM, FTIR and XPS results suggested both xanthate and dixanthogen species adsorbed on molybdenite surfaces, thus improving the hydrophobicity of both edges and faces. Rest potential measurements clarified dixanthogen species dominated on faces while xanthate ions prevailed on edges. DFT calculations elucidated dixanthogen physically adsorbed (−66.06 kJ/mol) on faces while xanthate chemisorbed (−235.62 kJ/mol) on edges via the hybridization of two S atoms within SIBX with two Mo atoms to form highly covalent bonds. This work first clearly unveiled the anisotropic adsorption mechanism of SIBX species on faces and edges, significantly improving the flotation efficiency of molybdenite fines.

Preparation, design, and characterization of an electrospun polyurethane/calcium chloride nanocomposite scaffold with improved properties for skin tissue regeneration

The present research paper explores the potential of electrospun nanofibers in the promising field of skin tissue engineering. Specifically, we propose an advanced preparation and characterization of an electrospun Polyurethane/Calcium Chloride (PU/CaCl2) nanocomposite scaffold, devised to boost the scaffold’s physicochemical and biological properties for skin tissue regeneration. By incorporating CaCl2 into the PU matrix using an electrospinning process, we were able to fabricate a novel nanocomposite scaffold. The morphological examination through Field Emission Scanning Electron Microscope (FESEM) revealed that the fiber diameter of the PU/CaCl2 (563 ± 147 nm) scaffold was notably smaller compared to the control (784 ± 149 nm). The presence of CaCl2 in the PU matrix was corroborated by Fourier-Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). Furthermore, the PU/CaCl2 scaffold exhibited superior tensile strength (10.81 MPa) over pristine PU (Tensile −6.16 MPa, Contact angle - 109° ± 1° and Roughness - 854 ± 32 nm) and revealed enhanced wettability (72° ± 2°) and reduced surface roughness (274 ± 104 nm), as verified by Contact angle and Atomic Force Microscopy. The developed scaffold demonstrated improved anticoagulant properties, indicating its potential for successful integration within a biological environment. The improved properties of the PU/CaCl2 nanocomposite scaffold present a significant advancement in electrospun polymer nanofibers, offering a potential breakthrough in skin tissue engineering. However, additional studies are required to thoroughly evaluate the scaffold’s effectiveness in promoting cell adhesion, proliferation, and differentiation. We aim to catalyze significant advancements in the field by revealing the creation of a potent skin scaffold leveraging electrospun nanofibers. Encouraging deeper exploration into this innovative electrospun composite scaffold for skin tissue engineering, the PU/CaCl2 scaffold stands as a promising foundation for pioneering more innovative, efficient, and sustainable solutions in biomedical applications.

Exploration of rigid double schiff base with a symmetrical plane as highly effective corrosion inhibitor for mild steel in hydrochloric acid environment: Experimental and theoretical approaches

A rigid double Schiff base with a symmetrical plane, (1E,1′E)-N,N’-(1,4-phenylene)bis(pyrazin-2-yl)ethanimine) (PBPE), has been synthesized and characterized by 1H NMR and FTIR spectroscopies. The corrosion inhibition performance of PBPE for mild steel in 1.0 mol L−1 HCl solution was systematically measured by weight loss method, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization technique, field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometer (EDS), atomic force microscope (AFM), and water contact angle measurement. The inhibition efficiency depends upon the PBPE concentration and the maximum inhibition efficiency by weight loss analysis is 93.10 % at 800 mg L−1 PBPE. The potentiodynamic polarization measurement revealed that PBPE behaves as a mixed-type inhibitor with a predominant anodic reaction. The thermodynamics adsorption analysis showed the adsorption of the PBPE molecules on the surface of mild steel obeys Langmuir adsorption isotherm, with both physisorption and chemisorption. In the corrosion reaction, the activation energy, activation enthalpy, and activation entropy all increased with increasing PBPE concentration. The surface morphology analysis such as SEM-EDS, AFM, and water contact angle further confirmed adsorption on the mild steel surface and resulted in the formation of protective film on the mild steel surface in PBPE solution. The quantum chemical parameters obtained such as global softness, electron transfer fraction, and energy gap together with Fukui indices can explain the good inhibition efficiency. Molecular dynamics simulations discovered that the PBPE molecules in a flat manner are adsorbed on the surface of mild steel, thus giving rise to a more effective adsorption and corrosion inhibition.

Study on Selective Adsorption Behavior and Mechanism of Quartz and Magnesite with a New Biodegradable Collector

Research on the efficient flotation desilication of low-grade magnesite is of great significance for the sustainable development of magnesium resources. Traditional collectors usually have some disadvantages, such as poor selectivity, severe environmental pollution, and weak water solubility. To strengthen the desilication flotation process of magnesite ore, the biodegradable surfactant, cocamidopropyl amine oxide (CPAO), was first utilized as the collector for the separation of the magnesite and quartz. The selective adsorption behavior and mechanism of the quartz and magnesite with the CPAO as the collector were studied through the micro-flotation experiments of the single mineral and the artificially mixed mineral, contact angle and atomic force microscopy (AFM) measurements, fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The flotation results indicated that the CPAO showed good selectivity and could effectively separate magnesite and quartz. When the concentration of the CPAO was 10.0 mg/L in the natural pulp pH (about 7.2), the concentrates with 97.67% MgO recovery and 45.62% MgO grade were obtained. The contact angle and AFM measurements indicated that the CPAO could selectively adsorb on the quartz surface rather than the magnesite surface to improve the interface difference between them, especially its surface hydrophobicity. The results of the FTIR and XPS analyses indicated that the CPAO is selectively adsorbed on the surface of the quartz, mainly through electrostatic interaction and hydrogen bonding. In conclusion, the CPAO had good selectivity and great potential as an effective collector in the reverse flotation desilication progress of magnesite.

A novel approach to enhance mechanical properties of Ti substrates for biomedical applications

The present study proposes a novel approach to flat rolling in order to improve the mechanical properties of pure Ti substrates, making it a promising alternative to the Ti-6Al-4V alloy commonly used in biomedicine. Commercially pure titanium grade 4 (TiG4) was subjected to a process of multi-rotational flat rolling (MRFR) that resulted in a refinement of the microstructure and an improvement in microhardness up to values comparable to those of the titanium alloy Ti-6Al-4V. The biggest advantage of the MRFR processing performed was that it maintained the square cross-section of the titanium product, which gives the possibility of fabricating relatively large products with improved mechanical properties for biomedical applications. The objective of this research was to compare TiG4 after MRFR processing with TiG5 (Ti-6Al-4V) to assess the influence of the processing on the properties of pure titanium. The products obtained were characterized in microstructure and chemical composition, wettability, surface energy, roughness, and stiffness; by using light microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy, contact angle measurements, optical profilometry, and atomic force microscopy. Bacterial and cell tests were conducted to consider the potential of the proposed methodology in biomedical applications. To this end, corrosion tests in Hank’s solution were performed to simulate the conditions in the peri-implant environment.

Understanding the anisotropic wettability of spodumene from direct force measurement using AFM and density functional theory calculations

Wettability directly reflects the interaction between minerals, reagents, and water, and is a key factor determining the flotation separation of minerals. Wettability differences of the spodumene anisotropic crystal surfaces are investigated in this study using contact angle relaxation, atomic force microscopy (AFM), and density functional theory (DFT) calculations. The contact angle relaxation and AFM tests confirm the anisotropic wettability of spodumene surfaces from macro and micro perspectives, respectively, and the order of hydrophilicity is (010) > (100) > (110). The DFT calculations based on surface fracture key points and broken bond density explain the differences in the wettability of spodumene crystal surfaces, that is, the types of broken bonds and the number of broken bonds per unit area are the main influencing factors. The wettability of water molecules on different crystal surfaces is simulated based on the DFT calculations of the broken surface bonds and surface energy, which further verifies the experimental results.

Characteristics and Functionality of Cantilevers and Scanners in Atomic Force Microscopy.

In this paper, we provide a systematic review of atomic force microscopy (AFM), a fast-developing technique that embraces scanners, controllers, and cantilevers. The main objectives of this review are to analyze the available technical solutions of AFM, including the limitations and problems. The main questions the review addresses are the problems of working in contact, noncontact, and tapping AFM modes. We do not include applications of AFM but rather the design of different parts and operation modes. Since the main part of AFM is the cantilever, we focused on its operation and design. Information from scientific articles published over the last 5 years is provided. Many articles in this period disclose minor amendments in the mechanical system but suggest innovative AFM control and imaging algorithms. Some of them are based on artificial intelligence. During operation, control of cantilever dynamic characteristics can be achieved by magnetic field, electrostatic, or aerodynamic forces.

Native Silicon Oxide Properties Determined by Doping.

The physico-chemical properties of native oxide layers, spontaneously forming on crystalline Si wafers in air, can be strictly correlated to the dopant type and doping level. In particular, our investigations focused on oxide layers formed upon air exposure in a clean room after Si wafer production, with dopant concentration levels from ≈1013 to ≈1019 cm-3. In order to determine these correlations, we studied the surface, the oxide bulk, and its interface with Si. The surface was investigated using the contact angle, thermal desorption, and atomic force microscopy measurements which provided information on surface energy, cleanliness, and morphology, respectively. Thickness was measured with ellipsometry and chemical composition with X-ray photoemission spectroscopy. Electrostatic charges within the oxide layer and at the Si interface were studied with Kelvin probe microscopy. Some properties such as thickness, showed an abrupt change, while others, including silanol concentration and Si intermediate-oxidation states, presented maxima at a critical doping concentration of ≈2.1 × 1015 cm-3. Additionally, two electrostatic contributions were found to originate from silanols present on the surface and the net charge distributed within the oxide layer. Lastly, surface roughness was also found to depend upon dopant concentration, showing a minimum at the same critical dopant concentration. These findings were reproduced for oxide layers regrown in a clean room after chemical etching of the native ones.

Complexing agents for potassium oleate removal after cobalt chemical-mechanical polishing: Prediction, verification and mechanism

A systematic approach for predicting the capability of malic acid (MA), tartaric acid (TA), and citric acid (CA), as carboxylic complexing agents, to remove potassium oleate (PO) in the cleaning of cobalt (Co) film after chemical mechanical polishing was investigated. Several quantum-molecular descriptors (frontier orbital energies, energy gap, and dipole moment) were calculated to establish the relationship between descriptors and the effectiveness of complexing agents. Further, the diffusion simulation was carried out in the aqueous phase model, and the detailed adsorption analysis of the three carboxylic complexing agents on Co(111) surface was performed to reveal the behavior of complexing agents on the passive film and the variation of the adsorption state of PO. The prediction was verified by characterization techniques, including contact angle, potentiodynamic polarization and atomic force microscopy measurements. Results show that the calculated chemical descriptors and molecular dynamics simulations successfully predict the removal efficiency of the cleaning experiment, i.e., MA has the strongest removal ability of PO adsorbed on cobalt surface. As well, the appropriate concentrations of the three complexing agents were optimized: MA was 0.1 wt%, TA was 0.1 wt% and CA was 0.075 wt%. The cleaning mechanism of MA was elucidated by X-ray photo-electron spectroscopy, density functional theory, and charge density difference: MA could break bonds between PO and Co surface via the ligand-exchange mechanism or etch the cobalt surface to promote the desorption of PO. This work makes a major contribution to estimating the effectiveness of complexing agents and exploring the removal mechanism of organic residue.

Flexible Ultrathin Chip-Film Patch for Electronic Component Integration and Encapsulation using Atomic Layer-Deposited Al2O3-TiO2 Nanolaminates.

Plasma-enhanced atomic layer deposition (PEALD) is utilized to improve the barrier properties of an organic chip-film patch (CFP) when it is used as an implant to prevent moisture and ions from migrating into the embedded electronic circuits. For this purpose, surface condition and material properties of eight modifications of Al2O3-TiO2 nanolaminates sequentially deposited on polyimide PI-2611 films are evaluated in detail. The effect of stress-induced warpage of the deposited Al2O3-TiO2 on the wafer level is calculated with the Stoney equation and reveals higher tensile stress values while increasing the thickness of Al2O3-TiO2 nanolaminates from 20 up to 80 nm. Contact angle measurement and atomic force microscopy are used to investigate the surface energy and wettability, as well as the surface morphology of polyimide-Al2O3-TiO2 interfaces. We show that plasma treatment of pristine polyimide leads to an enhanced adhesion force of the PEAL-deposited layer by a factor of 1.3. The water vapor transmission rate (WVTR) is determined by exposing the coated polyimide films to 85% humidity and 23 °C and yields down to 1.58 × 10-3 g(H2O)/(m2 d). The data obtained are compared with alternative coating processes using the polymers parylene-C and benzocyclobutene (BCB). The latter shows higher WVTR values of 1.2 × 10-1 and 1.7 × 10-1 g(H2O)/(m2 d) compared to the PEALD-PI-2611 systems, indicating lower barrier properties. Two Al2O3-TiO2 modifications with low WVTR values have been chosen for encapsulating the CFP substrates and exposing them in a long-time experiment to chemical and mechanical loads in a chamber filled with phosphate-buffered saline at 37 °C, pH 7.3, and a cyclically applied pressure of 160 mbar (∼120 mm Hg). The electrical leakage behavior of the CFP systems is measured and reveals reliable electrical long-term stability far beyond 11 months, highlighting the great potential of PEALD-encapsulated CFPs.

Comparing the nanoscale topography and interface properties of chitosan films containing free and nano-encapsulated copaiba essential oil: An atomic force microscopy (AFM) and Fractal Geometry study

This article compared chitosan films containing copaiba essential oil (CO) and nano-encapsulated CO using nanoscaled topographic characteristics and interface properties. The CO-loaded nanocapsules (CO-NC) were prepared by the polymer nanoprecipitation method, whereas the composite films were produced by the casting method. The films’ surface was evaluated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Wettability and adhesion were also investigated by measuring the contact angle and AFM. The results suggested that the film’s surface containing CO-NC presented characteristics that favor interface interactions at the nanoscale. Furthermore, these films showed greater interaction with water and superior adhesion force than the control and CO-loaded chitosan films. Thus, considering the surface characteristics and the evaluated properties, CO-NC seems to be a promising alternative for incorporating CO in chitosan films.

Contact Angle and AFM Analysis of Glassy Carbon Coatings after an Extended Stay on the International Space Station (ISS)

The proposed work presents the results for contact angle and atomic force microscopy (AFM), which are applied to characterize the surface of two types of samples, “reference” sample and “space” sample, both made of the same material – graphite covered with glassy carbon coating, but stored for 28 months in different environments (conditions). One “space” sample was mounted outside the International Space Station, and the other “reference” sample was stored on Earth.
 The technique applied to measure the contact angle of wetting of the surface of the samples (hydrophilicity-hydrophobicity) is using water droplets. Values of the energy surface area of the sample surfaces were determined by measuring the contact angle with the substances formamide and diiodomethane. Atomic force microscopy (AFM) was applied to characterize the glass surface morphology of carbon coatings.

M2 coating prepared by ultra-high speed laser cladding: Microstructure and interfacial residual stress

The coating of M2 high speed steel was prepared on 42CrMo steel substrate using ultra-high speed laser cladding technique (EHLA in German). Our results show that the M2 cladded coating formed a dentate metallurgical bonding with 42CrMo steel substrate. The morphology of the M2 coating involved from the “corn” shape structure at the interface, to “column” shape in the middle zone, and final a “basket” shape near the surface. The near-surface zone of the M2 coating is composed of residual austenite + lamellar twinning martensite + network carbides, and the latter being composed of unstable V4C3 and unstable Cr3(W10C3)2, in accordance with the parallel phase relationship of [5̅15̅3]V4C3[110]Cr3W10C32and (015)V4C3(1̅15)Cr3W10C32. The residual stress was measured using nanoindentation with the assistance of atomic force microscope (AFM) for direction measurement of residual indents to account for pile-up. An analysis method was proposed by combining the AFM measurement and contact mechanics calculation. Our results show high tensile residual stress existing across the whole M2 coating and even extended over 100 µm deep into the heat affected zone in the substrate; the peak value of about 311 MPa was found near the interface area and then dropped sharply. Good agreement was found in results obtained using our method and Oliver & Giannakopoulos (G&S) method, hence validating the G&S method for future application in this material system without the need to use AFM for evaluation of pile-up.