Innovative technology for improving the yield of large-flake graphite based on enhanced gravity concentration

The zoonotic pathogen Brucella abortus is part of the Rhizobiales, which are alpha-proteobacteria displaying unipolar growth. Here, we show that this bacterium exhibits heterogeneity in its outer membrane composition, with clusters of rough lipopolysaccharide co-localizing with the essential outer membrane porin Omp2b, which is proposed to allow facilitated diffusion of solutes through the porin. We also show that the major outer membrane protein Omp25 and peptidoglycan are incorporated at the new pole and the division site, the expected growth sites. Interestingly, lipopolysaccharide is also inserted at the same growth sites. The absence of long-range diffusion of main components of the outer membrane could explain the apparent immobility of the Omp2b clusters, as well as unipolar and mid-cell localizations of newly incorporated outer membrane proteins and lipopolysaccharide. Unipolar growth and limited mobility of surface structures also suggest that new surface variants could arise in a few generations without the need of diluting pre-existing surface antigens.

Thin vanadium and vanadium nitride films were grown on SiO2 by non-reactive and reactive high power impulse magnetron sputtering (HiPIMS), respectively. The film properties were compared to films grown by conventional dc magnetron sputtering (dcMS) at similar conditions. We explored the influence of the stationary magnetic confinement field strength on the film properties and the process parameters. The deposition rate is much lower for non-reactive sputtering by HiPIMS than for dcMS. Furthermore, for both dcMS and HiPIMS the deposition rate is lower for strong magnetic confinement. Structural characterization was carried out using x-ray diffraction and reflection methods as well as atomic force microscopy and scanning electron microscope. Both dcMS and HiPIMS grown vanadium films are polycrystalline with similar grain size regardless of magnetic field strength. For dcMS grown vanadium films the surface roughness is higher when a strong magnetic field is used. For both non-reactive growth of vanadium and reactive growth of vanadium nitride the HiPIMS process produces denser films with lower surface roughness than dcMS does. Lowering the magnetic field strength increases the deposition rate significantly for reactive HiPIMS while it increases only slightly in the reactive dcMS case. The films grown by HiPIMS with strong magnetic confinement exhibit higher density and lower roughness. We find that the operating pressure, growth temperature, discharge voltage and film thickness has influence on the properties of HiPIMS grown vanadium nitride films. The films are denser when grown at high temperature, high discharge voltage and low pressure. The density of those films is lower for thicker films and thicker films consist of larger grain size. For all the films explored, higher density coincides with lower surface roughness. Thus, the deposition method, magnetic field strength, growth temperature, discharge voltage, film thickness and growth pressure have a significant influence on the film quality and structural properties, including the grain size for the various orientations.

The assembly of polyelectrolytes and gold nanoparticles yields stratified multilayers with very low roughness and high structural perfection. The films are prepared by spin-assisted layer-by-layer self-assembly (LbL) and are characterized by X-ray reflectivity (XRR), UV-vis spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Typical structures have four repeat units, each of which consists of eight double layers (DL) of poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride), one monolayer of gold nanoparticles (10 nm diameter), and another layer of poly(allylamine hydrochloride). XRR scans show small-angle Bragg peaks up to seventh order, evidencing the highly stratified structure. Pronounced Kiessig fringes indicate a low global roughness, which is confirmed by local AFM measurements. TEM images corroborate the layered structure in the growth direction and nicely show the distinct separation of the individual particle layers. An AFM study reveals the lateral gold particle distribution within one individual particle layer. Interestingly, the spin-assisted deposition of polyelectrolytes reduces the roughness induced by the particle layers, leading to self-healing of roughness defects and a rather perfect stratification.

Characterization of sputter-deposited chromium oxide thin films

The results of a study of the structure and physical and mechanical properties of diamond-like coatings (DLC) on sublayers of different hardness are presented. The coatings have high hardness, but at the same time they are prone to delamination and destruction due to high residual internal stresses. The fracture toughness was determined by the nanoindentation method and the energy calculation method using approach-retraction curves. Atomic force microscopy was used to study the surface structure and deformation region after nanoindentation. A change in the surface structure and roughness of DLC was established depending on the sublayer. Low roughness is characteristic of DLC on a copper sublayer. Applying а titanium sublayer leads to an increase in the elastic modulus of the DLC. The microhardness of both coatings is practically the same. AFM studies have shown two different types of DLC deformation after nanoindentation with a Berkovich pyramid. A crack on coatings with a copper sublayer propagates around the indentation print, and on an DLC with a titanium sublayer, it propagates along the edges of the indentation. It was found that the fracture toughness of DLC on a Ti sublayer is 33 % lower compared to DLC on a Cu sublayer due to a decrease in stress relaxation inside the coating. The considered coatings can be used in microelectronics for protection against mechanical damage on contacting and rubbing surfaces.

Cu–Ag thin films with various atomic ratios were prepared using a co-sputtering technique, followed by rapid thermal annealing at various temperatures. The films’ structural, mechanical, and electrical properties were then characterized using X-ray diffractometry (XRD), atomic force microscopy (AFM), FESEM, nano-indentation, and TEM as functions of compositions and annealing conditions. In the as-deposited condition, the structure of these films transformed from a one-phase to a dual-phase state, and the resistivity shows a twin-peak pattern, which can be explained in part by Nordheim’s Rule and the miscibility gap of Cu–Ag alloy. After being annealed, the films’ resistivity followed the mixture rule in general, mainly due to the formation of a dual-phase structure containing Ag-rich and Cu-rich phases. The surface morphology and structure also varied as compositions and annealing conditions changed. The recrystallization of these films varied depending on Ag–Cu compositions. The annealed films composed of 40 at % to 60 at % Cu had higher hardness and lower roughness than those with other compositions. Particularly, the Cu50Ag50 film had the highest hardness after being annealed. From the dissolution testing, it was found that the Cu-ion concentration was about 40 times higher than that of Ag. The galvanic effect and over-saturated state could be the cause of the accelerated Cu dissolution and the reduced dissolution of the Ag.

This article describes the results of a study of Cu/Ni multilayer coatings applied on a monocrystalline Si(100) silicon substrate by the deposition magnetron sputtering technique. Composed of 100 bilayers each, the multilayers were differentiated by the Ni sublayer thickness (1.2 to 3 nm), while maintaining the constant Cu sublayer thickness (2 nm). The multilayer coatings were characterized by assessing their surface topography using atomic force microscopy and their mechanical properties with nano-hardness measurements by the Berkovich method. The tests showed that the hardness of multilayers was substantially influenced by the thickness ratio of Cu and Ni sublayers and by surface roughness. The highest hardness and, at the same time, the lowest roughness was exhibited by a multilayer structure with a Cu-to-Ni sublayer thickness ratio of 2:1.5.

A systematic approach to achieve a LRHH (low roughness and high hardness) electroforming process is developed in this study. Because electroformed molds with low roughness and high hardness are required for microlens array fabrication using the LIGA-like process, the invented Ni–Co alloy-pressurized electroforming process is used to fabricate a metallic micro-mold for microlens array molding. The electrolyte parameters such as Co content, current density, brightener content, pH value and temperature will be examined with respect to roughness and hardness. An artificial neural network (ANN) is used to construct a system model that accurately predicts the responses for arbitrary parameter settings. A genetic algorithm (GA) is applied to minimize the surface roughness and improve the micro-mold hardness. The results show that the micro-mold surface roughness and hardness could be significantly improved using the ANN/GA approach. A LRHH electroforming process is carried out using parameter design to improve the surface morphology and increase the service life of the micro-mold during the forming process.

Classical friction laws traditionally assume that the friction between solid pairs remains constant with a given normal load. However, our study has unveiled a remarkable deviation from conventional wisdom. In this paper, we discovered that altering the loading mode of micro graphite flakes led to significant changes in the lateral friction under identical normal loads. By adding a cap onto a single graphite flake to disperse the normal load applied by an atomic force microscope (AFM) tip, we were able to distribute the concentrated force. Astonishingly, our results demonstrated a notable 4-7 times increase in friction as a consequence of load dispersion. Finite element analysis (FEA) further confirmed that the increase in compressive stress at the edges of the graphite flake, resulting from load dispersion, led to a significant increase in friction. This study underscores the critical role of the loading mode in microscale friction dynamics, challenging the prevailing notion that friction remains static with a given normal force. Importantly, our research sheds light on the potential for achieving macroscale structural superlubricity (SSL) by assembling microscale SSL graphite flakes by using a larger cap.

The essential part of the flake graphite flotation apparatus is a micro-bubble generator. Developing a micro-bubble generator with a reasonable structure and superior self-absorption performance is crucial to improving flake graphite sorting. In this study, to realize the integrated treatment of the grinding and mineralization of flake graphite, the development and manufacturing of a double-nozzle jet micro-bubble generator were based on the concepts of shear-type cavitation water jets and jet pumps, among other theories. A numerical simulation of the air–water–flake graphite triple-phase flow field of the generator was conducted using the CFD method. The goal was to investigate the grinding and mineralization process of flake graphite by analyzing the distribution of the air phase’s volume percentage and the speed distribution of the air–water–flake graphite triple-phase flow field. The findings indicate that the air-phase volume percentage produced by the generator ranges from 98.3% to 99.9%, and the air-phase volume percentage is evenly distributed within the steady flow tube, achieving the mineralization function. Additionally, the flake graphite particles are dissociated from the flake graphite under the combined effect of friction shear and cavitation of the internal nozzles, thereby achieving the grinding function.

Ag-doped barium strontium titanate (Ag/BST) thin films deposited on Si (1 0 0) substrates at various substrate temperatures and oxygen partial pressures via pulsed laser deposition were investigated. The effects of the substrate temperature and oxygen partial pressure on the crystalline structure, chemical state, and morphology were investigated via x-ray diffraction analysis, field-emission scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy. The as-deposited thin films were found to be amorphous in nature. However, as the substrate temperature increased, the crystallinity of the films increased. The crystallite size varied from approximately 13 to 33 nm with respect to the substrate temperature. A uniform film with low roughness was obtained at high substrate temperatures with lattice parameters of a = 3.8272 Å and c = 4.4545 Å. A film prepared at 600 °C exhibited a better crystalline structure and a low surface roughness of approximately 70 nm. XPS revealed the core-level spectra of Ba3d, Sr3d, Ti2p, O1s, and Ag3d. An orange emission band at 571 nm was observed in photoluminescence studies of the Ag/BST thin films.

Properties of a-C:H:Si thin films deposited by middle-frequency magnetron sputtering

In this work, the reduced graphene nanosheets were synthesized from pre-exfoliated graphite flakes. The pristine graphite flakes were firstly pre-exfoliated to graphite nanoplatelets in the presence of acetic acid. The obtained graphite nanoplatelets were treated by Hummer’s method to produce graphite oxide sheets and were finally exfoliated to graphene nanosheets by ultrasonication and reduction processes. The prepared graphene nanosheets were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). From the results, it was found that the preexfoliation process showed significant influence on preparation of graphite oxide sheets and graphene nanosheets. The prepared graphene nanosheets were applied to the preparation of conductive materials, which yielded a greatly improved electrical resistance of 200 Ω/sq.

A novel method for producing graphene via enhanced shear exfoliation in a high-pressure fluid has been developed. In the process of exfoliation, graphite flakes, dispersed in a solution of N-methyl-2-pyrrolidone (NMP), were pushed through the exfoliation tube by a high-pressure pump, which produces high shear stresses on the graphite flakes due to the turbulent flow, causing the peeling-off of graphene sheets from the graphite flake. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images show that produced graphene sheets have thicknesses ranging from monolayer to about 12 layers. The results of X-ray photoelectron spectroscopy (XPS) and Raman and infrared (IR) spectroscopy analyses reveal that neither basal-plane defects nor oxides were noticeably introduced to graphene sheets in the process. The graphite solution can be continuously treated in a circular loop. At a pressure of 100 MPa and after 2 h of treatment, exfoliated graphene was obtained with a yield of about 15 ± 0.3%. T...

Use of graphene nanosheets and barium titanate as fillers in PMMA for dielectric applications