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Due to its outstanding mechanical characteristics, diamond is an ideal material for use in micro- and nano-electromechanical systems. In this paper, we report on the investigation of vibrational properties of singly clamped needlelike diamond microcrystallites with nanoscale tips. The single-crystal diamond needles were produced by selective oxidation of polycrystalline films grown using chemical vapor deposition. The study of resonant oscillations driven by the AC voltage indicated that the elastic modulus of such diamond needles is close to that of bulk single crystal diamond. A self-oscillation regime induced by the DC voltage during field emission from the apex of a diamond needle is also demonstrated. It is shown that this regime can be used for efficient DC–AC conversion in microdevices. The high structural quality of diamond needles, their remarkable mechanical properties, and the relative ease of their mass fabrication make them promising candidates for application in various electromechanical systems, field-emission devices, and scanning probe techniques. [ABSTRACT FROM AUTHOR]

Improving the thruster efficiency is a crucial challenge for the development of space electric propulsion systems, especially advanced air-breathing thrusters utilizing the surrounding rarefied atmosphere as fuel. A significant reduction in thruster power consumption can be achieved by using field emission (FE) cathodes that do not require heating and have the highest energy efficiency. In this work, we study FE from nano-graphite thin films, consisting of carbon nanostructures with a high aspect ratio, and demonstrate their suitability for use in the space electric propulsion systems. The films shown appropriate FE characteristics in a wide range of gas pressures at high current loads in constant and pulsed operation modes. Based on the obtained experimental results, nano-graphite cathodes were employed for the design of an electron gun with increased reliability and minimized energy losses associated with electron extraction. The possibility of using such a gun in a specific air-breathing satellite operating in low Earth orbits is demonstrated. [ABSTRACT FROM AUTHOR]

Mo-Zr-Si-B coatings were deposited by high-power impulse magnetron sputtering at a pulse frequency of 10, 50, and 200 Hz. The coating structure was studied by scanning electron microscopy, energy-dispersive spectroscopy, glow-discharge optical-emission spectroscopy, transmission electron microscopy, and X-ray diffraction. The mechanical characteristics, adhesive strength, coefficient of friction, wear resistance, resistance to cyclic-dynamic-impact loading, high-temperature oxidation resistance, and thermal stability of the coatings were determined. The coatings, obtained at 10 and 50 Hz, had an amorphous structure. Increasing the frequency to 200 Hz led to the formation of the h-MoSi2 phase. As the pulse frequency increased from 10 to 50 and 200 Hz, the deposition rate rose by 2.3 and 9.0 times, while hardness increased by 1.9 and 2.9 times, respectively. The Mo-Zr-Si-B coating deposited at 50 Hz was characterized by better wear resistance, resistance to cyclic-dynamic-impact loading, and oxidation resistance at 1500 °C. Thermal stability tests of the coating samples heated in the transmission electron microscope column showed that the coating deposited at 50 Hz remained amorphous in the temperature range of 20–1000 °C. Long-term annealing in a vacuum furnace at 1000 °C caused partial recrystallization and the formation of a nanocomposite structure, as well as an increased hardness from 15 to 37 GPa and an increased Young's modulus from 250 to 380 GPa, compared to those of the as-deposited coatings. [ABSTRACT FROM AUTHOR]

Surface graphitization as a result of Joule heating by a field-emission (FE) current is revealed for needlelike diamond nanotips. The apex temperature and electrical resistance of the diamond needles during FE were measured by electron spectroscopy. Transmission electron microscopy indicated that the diamond structure in the near-surface layer was transformed into well-ordered graphene layers after FE with currents of up to 30 μA. The resulting structure can be viewed as a multi-walled carbon nanotube (MWCNT) having a diamond core. Thus, the observed FE behavior exhibited by the graphitized diamond needles is qualitatively similar to that of MWCNTs. On the other hand, due to its outstanding thermal conductivity, the diamond core ensures an efficient Joule heat dissipation, which provides better emission stability and higher currents, up to at least 225 μA. It makes these graphitized diamond needles promising candidates for high-brightness point electron sources required for various applications, e.g., in electron microscopy or scanning electron lithography. [ABSTRACT FROM AUTHOR]

We report the observation of Coulomb blockade in electron field emission (FE) from single-wall carbon nanotubes (SWCNTs), which is manifested as pronounced steps in the FE current–voltage curves and oscillatory variations in the energy distribution of emitted electrons. The appearance of the Coulomb blockade is explained by the formation of nanoscale protrusions at the apexes of SWCNTs due to the electric field-assisted surface diffusion of adsorbates and carbon adatoms. The proposed adsorbate-assisted FE mechanism is substantially different from the well-known resonant tunneling associated with discrete electronic states of adsorbed atoms. The simulations based on the Coulomb blockade theory are in excellent agreement with the experimental results. The SWCNT field emitters controlled by the Coulomb blockade effect are expected to be used to develop on-demand coherent single-electron sources for advanced vacuum nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Modular nanotransporters (MNTs) are multifunctional chimeric polypeptides for the multistep transport of locally acting cytotoxic agents into the nuclei of cancer target cells. MNTs consist of several polypeptide domains (functional modules) for the recognition of a cell‐surface internalizable receptor, pH‐dependent endosomal escape and subsequent transport into the nucleus through the nuclear pores. MNTs are a promising means for cancer treatment. As has been shown previously, all of the modules of MNTs retain their functionalities. Despite their importance, there is no structural information available about these chimeric polypeptides, which hampers the creation of new MNT variants. Here, a low‐resolution 3D structure of an MNT is presented which was obtained by atomic force microscopy, transmission electron microscopy and small‐angle X‐ray scattering coupled to size‐exclusion chromatography. The data suggest that the MNT can adopt two main conformations, but in both conformations the protein N‐ and C‐termini are distanced and do not influence each other. The change in the MNT conformation during acidification of the medium was also studied. It was shown that the fraction of the elongated conformation increases upon acidification. The results of this work will be useful for the development of MNTs that are suitable for clinical trials and possible therapeutic applications. [ABSTRACT FROM AUTHOR]

To transform a monocrystalline diamond into monocrystalline graphite, the exposure of an ultrafast laser to a (111) diamond face was investigated for the first time. The single pulse of the third harmonic of a Ti:sapphire laser (100 fs, 266 nm) was used to produce graphitized inclusions embedded in a (111) diamond substrate. Three different regimes of (111) diamond graphitization are discussed in this paper. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to investigate the graphitized material, which was found to resemble highly oriented graphite at certain laser fluencies. The proposed approach to the problem of perfect local diamond graphitization is an important step toward creating all-carbon composite systems consisting of conductive and dielectric phases. [ABSTRACT FROM AUTHOR]

Under severe or prolonged stress, bacteria produce a nonspecific DNA‐binding protein (Dps), which effectively protects DNA against damaging agents both in vitro and in vivo by forming intracellular biocrystals. The phenomenon of protective crystallization of DNA in living cells has been intensively investigated during the last two decades; however, the results of studies are somewhat contradictory, and up to now, there has been no direct determination of a Dps–DNA crystal structure. Here, we report the in vitro analysis of the vital process of Dps–DNA co‐crystallization using two complementary structural methods: synchrotron small‐angle X‐ray scattering in solution and cryo‐electron tomography. Importantly, for the first time, the DNA in the co‐crystals was visualized, and the lattice parameters of the crystalline Dps–DNA complex were determined. [ABSTRACT FROM AUTHOR]

Field electron emission from thin films composed of solely metallic or semiconducting single‐walled carbon nanotubes is investigated using a scanning tip anode technique. Metallic and semiconducting nanotubes are separated by aqueous two‐phase extraction. Local field emission centers observed on nanotube films of both types showed non‐linear Fowler–Nordheim (FN) plots bent downwards. The curving of FN plots is much stronger for semiconducting nanotubes which is explained by their higher electrical resistance and stronger field penetration effect compared to metallic nanotubes. Particular nanotubes of both types revealed oscillations in current–voltage characteristics. The periodic oscillations indicated that the field emission current is modulated either by resonant tunnelling from confinement states in nano‐objects formed by adsorbates or by the Coulomb blockade effect that can occur for emission from short carbon nanotubes. [ABSTRACT FROM AUTHOR]

Luminescent properties of needle‐like single crystal diamonds are investigated in a wide range of wavelength. The luminescent spectra with zero phonon lines centered at 389, 442, 468, 534, 563, 575, and 738 nm are detected using excitation by photons and electrons. Obtained photo‐ and cathodo‐luminescent (PL and CL) spectra indicate presence in the single‐crystal diamond needles of nitrogen‐ and silicon‐vacancy centers as well as substitutional or/and interstitials related to these atomic impurities. The dependencies of PL intensities of the 575 and 738 nm lines (related, correspondingly, to nitrogen‐ and silicon‐vacancy centers) on excitation wavelength are determined. Time‐resolved measurements are performed for the 575 nm PL line. The luminescence decay behavior for this line demonstrates the presence of recombination processes with characteristic times of about 28 ns (on 200 ns time scale) and 2.8 ns (on 20 ns time scale). [ABSTRACT FROM AUTHOR]

Two-ply composite membranes with separation layers from chitosan and sulfoethylcellulose were developed on a microporous support based on poly(diphenylsulfone-N-phenylphthalimide) and investigated by use of X-ray diffraction and scanning electron microscopy methods. The pervaporation properties of the membranes were studied for the separation of aqueous alcohol (ethanol, propan-2-ol) mixtures of different compositions. When the mixtures to be separated consist of less than 15 wt % water in propan-2-ol, the membranes composed of polyelectrolytes with the same molar fraction of ionogenic groups (-NH3+ for chitosan and -SO3- for sulfoethylcellulose) show high permselectivity (the water content in the permeate was 100%). Factors affecting the structure of a non-porous layer of the polyelectrolyte complex formed on the substrate surface and the contribution of that complex to changes in the transport properties of membranes are discussed. The results indicate significant prospects for the use of chitosan and sulfoethylcellulose for the formation of highly selective pervaporation membranes. [ABSTRACT FROM AUTHOR]

Studies of the effects produced by the solubilization of hydrophobic substances by micellar aggregates in water medium are quite important for applications of viscoelastic surfactant solutions for enhanced oil recovery (EOR), especially in hydraulic fracturing technology. The present paper aims at the investigation of the structural transformations produced by the absorption of an aliphatic hydrocarbon (n-decane) by mixed wormlike micelles of cationic (n-octyltrimethylammonium bromide, C8TAB) and anionic (potassium oleate) surfactants enriched by C8TAB. As a result of contact with a small amount (0.5 wt%) of oil, a highly viscoelastic fluid is transformed to a water-like liquid. By small-angle neutron scattering (SANS) combined with cryo-TEM, it was shown that this is due to the transition of long wormlike micelles with elliptical cross-sections to ellipsoidal microemulsion droplets. The non-spherical shape was attributed to partial segregation of longer- and shorter-tail surfactant molecules inside the surfactant monolayer, providing an optimum curvature for both of them. As a result, the long-chain surfactant could preferably be located in the flatter part of the aggregates and the short-chain surfactant—at the ellipsoid edges with higher curvature. It is proven that the transition proceeds via a co-existence of microemulsion droplets and wormlike micelles, and upon the increase of hydrocarbon content, the size and volume fraction of ellipsoidal microemulsion droplets increase. The internal structure of the droplets was revealed by contrast variation SANS, and it was shown that, despite the excess of the cationic surfactant, the radius of surfactant shell is controlled by the anionic surfactant with longer tail. These findings open a way for optimizing the performance of viscoelastic surfactant fluids by regulating both the mechanical properties of the fluids and their clean-up from the fracture induced by contact with hydrocarbons. [ABSTRACT FROM AUTHOR]

This paper reports the analysis of the intensity of diamond line in the Raman spectra of laser modified layers with different thickness on a diamond surface. Since the diamond line passing from substrate through the absorbing layer of moderate thickness can be registered, the thickness of local area is estimated from its micro‐Raman spectra. The comparison between Raman scattering and direct observation of the graphitized layer by transmission electron microscopy shows that Raman spectroscopy can be used as an alternative non‐destructive method for measuring a moderate thickness of graphitized layers. [ABSTRACT FROM AUTHOR]

The synthesis of graphene on thin copper film deposited on quartz substrate is reported. The copper films are fabricated with different thickness of 300 and 1150 nm and then crystallized during thermal annealing that occurs at temperature of 950 and 1000 °C for 30 or 90 min. The size of copper grains increases with increasing of the temperature and the time of annealing that results in increasing of graphene film size. The deposited copper films are studied by electron backscatter diffraction and synthesized graphene films are analyzed by Raman spectroscopy and scanning probe microscopy. Proposed phase contrast mode of the scanning probe microscopy demonstrates high lateral resolution and sensitivity to the presence of graphene with different number of layers. It is found that graphene monolayer is preferably formed on the surface of copper grains with orientation {111} and proposed techniques can be used for the analysis of the evolution of graphene growth. [ABSTRACT FROM AUTHOR]

The field electron emission characteristics of individual tips of a silicon field emitter array are analyzed. The array of conical‐shaped tips is fabricated on a p‐type silicon wafer by using reactive ion etching and sharpening oxidation. The tips are decorated with single tungsten nanoparticles at their apexes. Furthermore, the focused ion beam is also used to increase surface conductivity of some of the tips. Comparative measurements of field emission are performed by using the scanning anode probe field emission microscopy technique. All types of tips demonstrated emission activation consisting of a sudden current increase at a certain value of the applied voltage. Compared to the pristine tips, a noticeable reduction of the saturation effect in the current–voltage characteristics and a smaller light sensitivity for the decorated tips is found. For ion‐treated tips, saturation effects and light sensitivity are completely suppressed. Scanning electron microscopy observations reveal the formation of single nanoscale protrusions extending from the metal particles and from the apexes of bare ion‐treated tips after exposure under strong electric fields during the field emission measurements. The influence of protrusions growth on characteristics of silicon field emitter arrays is discussed. [ABSTRACT FROM AUTHOR]

Field electron emission from the edges of large-area (∼1 cm × 1 cm) graphene films deposited onto quartz wafers was studied. The graphene was previously grown by chemical vapour deposition on copper. An extreme enhancement of electrostatic field at the edge of the films with macroscopically large lateral dimensions and with single atom thickness was achieved. This resulted in the creation of a blade type electron emitter, providing stable field emission at low-voltage with linear current density up to 0.5 mA/cm. A strong hysteresis in current–voltage characteristics and a step-like increase of the emission current during voltage ramp up were observed. These effects were explained by the local mechanical peeling of the graphene edge from the quartz substrate by the ponderomotive force during the field emission process. Specific field emission phenomena exhibited in the experimental study are explained by a unique combination of structural, electronic and mechanical properties of graphene. Various potential applications ranging from linear electron beam sources to microelectromechanical systems are discussed. [ABSTRACT FROM AUTHOR]

Abstract Exposure to toxic halogenated polyaromatic hydrocarbons, of which 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD) is the most potent, induces diverse skin pathologies in humans, including chloracne, hyperkeratosis, hamartomas, etc. While the toxic effects of TCDD have been extensively studied, effective approaches to their treatment are still lacking. Retinoids are commonly used in therapy of acneiform skin diseases. In vitro , retinoids elicit antagonistic effects on keratinocyte differentiation and proliferation, as compared to TCDD, suggesting their potential in treatment of TCDD-induced skin lesions. Nevertheless, the modulation of TCDD activity in skin by retinoids in vivo was never reported. We have used N-TERT keratinocyte cell line and hairless (hr) mice to determine if retinoic acid (RA) can lessen or reverse TCDD-induced effects in vitro and in vivo. RA co-treatment suppressed TCDD-induced changes in the expression of differentiation-associated genes and N-TERT keratinocyte viability in vitro. However, in hairless mice (in vivo), RA/TCDD co-treatment produced more severe effects, than treatment with either of the two compounds individually. RA/TCDD co-application to mouse skin strongly stimulated keratinocyte proliferation, resulting in dramatic epidermal hyperplasia. It has also led to massive immune cell infiltration into the dermis, and increased mRNA expression of inflammation markers, including IL1β , IL6 and S100A7. Thus, retinoids not only appeared ineffective in treatment of TCDD-induced skin lesions in hairless mice, but also resulted in their exaggeration. These in vivo results question previous cell culture-based claims that RA may reduce TCDD-induced skin effects and caution against the reliance on in vitro data in TCDD toxicology research. Highlights • Treatment with retinoic acid (RA) is ineffective for dioxin-induced skin lesions in mice. • Co-treatment with dioxin and RA results in psoriasis-like phenotype not seen under treatment with either compound alone. • Strong inflammation is the most prominent effect induced by combined treatment with dioxin and RA. [ABSTRACT FROM AUTHOR]

Pathogenesis of numerous diseases is associated with the formation of amyloid fibrils. Extrinsic fluorescent dyes, including Thioflavin T (ThT), are used to follow the fibrillation kinetics. It has recently been reported that the so-called deep-blue autofluorescence (dbAF) is changing during the aggregation process. However, the origin of dbAF and the reasons for its change remain debatable. Here, the kinetics of fibril formation in model proteins were comprehensively analyzed using fluorescence lifetime and intensity of ThT, intrinsic fluorescence of proteinaceous fluorophores, and dbAF. For all systems, intensity enhancement of the dbAF band with similar spectral parameters (∼350 nm excitation; ∼450 nm emission) was observed. Although the time course of ThT lifetime (indicative of protofibrils formation) coincided with that of tyrosine residues in insulin, and the kinetic changes in the ThT fluorescence intensity (reflecting formation of mature fibrils) coincided with changes in ThT absorption spectrum, the dbAF band started to increase from the beginning of the incubation process without a lag-phase. Our mass-spectrometry data and model experiments suggested that dbAF could be at least partially related to oxidation of amino acids. This study scrutinizes the dbAF features in the context of the existing hypotheses about the origin of this spectral band. [ABSTRACT FROM AUTHOR]

Squid β-chitin has been exfoliated in aqueous acrylic acid (AA), after which a composite film of chitin microfibrils in polyacrylic acid (PAA) has been prepared by in situ polymerization of the AA. The segregated chitin fibrils in the composite are 4–6 nm in diameter, with an aspect ratio >250. After drying cast films of the composites containing 1, 2 and 3% (w/w) chitin at 140 °C for four hours, there was a dramatic resistance to swelling in water, in that the dried films showed only small changes in shape and properties after four hours immersed in water.The most profound impact of the reinforcement on the mechanical properties is observed at high relative humidity (RH), when the PAA is in the rubbery state. At 97.5% RH and room temperature, the elastic moduli of the composites with 1, 2 and 3% (w/w) chitin were 150, 230 and 2100 MPa respectively, compared to 65 MPa for pure PAA. The main contribution to the filler-reinforcing effect is the high aspect ratio of fibrils and non-covalent interactions, but the stability in water suggests the presence of chemical bonding between the PAA and chitin. [ABSTRACT FROM AUTHOR]

In this study, variable-temperature grazing-incidence X-ray diffraction, transmission electron and scanning force microscopy were employed to address the semicrystalline structure and surface morphology of thin poly( p -xylylene) – silver nanocomposite films with Ag concentrations up to 12 vol.%. It was observed that the dominant crystalline modification of poly( p -xylylene) in the studied films is α -form, which is in contrast to thick poly( p -xylylene) films deposited at liquid nitrogen temperature where β -form prevails. The films exhibit planar texture that can be further enhanced on annealing. The optical properties of the films were studied by UV–vis and IR-spectroscopy. It was found that the samples display surface plasmon resonance, with the peak wavelength in the range of 435–445 nm. The peak positions undergo a redshift upon a long-term storage under ambient conditions. The IR-spectroscopy reveals the bands, which can be assigned to the vibrations of oxygen-containing groups, with intensity increasing with silver content. [ABSTRACT FROM AUTHOR]

The synthesis of magnetite (Fe 3 O 4 ) nanorods using reverse co-precipitation of Fe 3+ and Fe 2+ ions in the presence of a static magnetic field is reported in this work. The phase composition and crystal structure of the synthesized material were investigated using electron diffraction, Raman spectroscopy, and transmission electron microscopy. It was shown that the morphology of the reaction product strongly depends on the amount of OH - ions in the reaction mixture, varying from Fe 3 O 4 nanorods to spherical Fe 3 O 4 nanoparticles. Fe 3 O 4 nanorods were examined using high-resolution transmission electron microscopy proving that they are single-crystalline and do not have any preferred crystallographic orientation along the axis of the rods. According to the data obtained a growth mechanism was proposed for the rods that consists of the dipole-dipole interaction between their building blocks (small hexagonal faceted magnetite nanocrystals), which are formed during the first step of the reaction. The study suggests a facile, green and controllable method for synthesizing anisotropic magnetic nanoparticles in the absence of stabilizers, which is important for further modification of their surfaces and/or incorporation of the nanoparticles into different media., (Copyright © 2020, Shibaev et al.; licensee Beilstein-Institut.)