Ag Crystals Research Articles

Structural modulation and frictional, antibacterial and biocompatible properties of Ag-incorporated DLC films: Dependence on Ag precipitation behavior

Ag-incorporated DLC (Ag-DLC) film attracted widespread attention in the bio-alloy implants field due to its excellent mechanical, biocompatible, and antibacterial properties. However, how to balance the short-term efficient antibacterial and biocompatibility of films, and the correlation between Ag precipitation and structural properties are still unclear. Hence, Ag-DLC films with different Ag contents were deposited by modulating Ag target current, focusing on the influence of Ag precipitation behavior. Results show that Ag dopants exist in the form of Ag crystals rather than bond with carbon matrix, which can easily precipitate and aggregate to film surface. The precipitated Ag amount with Ag target current enhances from 2.75% to 35.04% while promotes the formation of sp2 carbon structure catalyzed by Ag, corresponding to decreased mechanical property. Interestingly, a small number of Ag dopants could effectively improve the friction behavior due to the lubrication effect of soft metal Ag and the friction interface transformation. Importantly, the best antibacterial property of film is obtained at high Ag precipitation content, while the surfaces with low Ag precipitation content are more favorable for cell adhesion and cytotoxicity reduction. Therefore, the Ag target current for better comprehensive performance is suggested within the range of 0.4 to 0.6 A.

The Optimization of the Synthesis of Antibacterial Coatings on Ti6Al4V Coupons Obtained by Electron Beam Melting

Prosthetic joint infection represents a problem that worsens the patient’s quality of life and produces an economic impact on health systems. We report the anodization of Ti6Al4V coupons obtained by electron beam melting to produce a nanostructured surface. Anodization at 10 V produced TiO2 nanopores with a diameter in the range of 15–20 nm. Thereafter, Ag nanoparticles (AgNPs) were deposited in three different ways to provide antibacterial functionality to the coatings: electrochemically, thermally, and chemically. The electrochemical method did not provide good coverage of AgNPs. At 0.1 V of synthesis potential, cubic, octahedral, and truncated octahedral Ag crystals were obtained. The thermal method provided a good distribution of AgNPs but it damaged the TiO2 nanostructure. The chemical method showed the best distribution of AgNPs over the anodized surface and preserved the anodized nanostructure. For this reason, the chemical method was selected to perform further studies. Ag+ release was monitored in simulated body fluid at 37 °C, reaching 1.86 mg Ag+/L after 42 days. The antibacterial coating showed excellent antibacterial activity and inhibited biofilm formation for Staphylococcus epidermidis RP62A and Staphylococcus aureus V329 strains (lethality > 99.9% for both bacteria and assays).

Growth and characterization of 6LiI:Ag crystal scintillators for thermal and epithermal neutron detection on the lunar surface

This paper discusses crystal growth and characterization of 1.0-inch 6LiI:Ag scintillators for thermal and epithermal neutron detection on the lunar surface as part of the Lunar Vehicle Radiation Dosimeter project. Zone purification method was employed to purify the raw material of 6LiI, and the crystals were grown using the Bridgman method. X-ray luminescence spectrum was measured to confirm the presence of Ag+ in the crystal lattice of 6LiI. The feasibility of neutron detection under 252Cf fast neutron irradiation was investigated. A hydrogen-rich paraffin wax moderator was used to slow down fast neutrons to obtain thermal and epithermal neutrons. The charge comparison method was used to perform pulse shape discrimination. The maximum value of the Figure of Merit was obtained to be 1.3, which demonstrates the capability of using 6LiI:Ag crystal scintillators in high neutron and gamma mixed fields. The energy resolution of the thermal neutron peak varied with the thickness of scintillators, achieving 12.0 % for the 0.5 cm thick samples. The potential for further improvement of the scintillation performance of 6LiI:Ag crystal relies on reducing impurities and color centers.

Highly selective photoelectrochemical CO2 reduction by crystal phase-modulated nanocrystals without parasitic absorption

Photoelectrochemical (PEC) carbon dioxide (CO2) reduction (CO2R) holds the potential to reduce the costs of solar fuel production by integrating CO2 utilization and light harvesting within one integrated device. However, the CO2R selectivity on the photocathode is limited by the lack of catalytic active sites and competition with the hydrogen evolution reaction. On the other hand, serious parasitic light absorption occurs on the front-side-illuminated photocathode due to the poor light transmittance of CO2R cocatalyst films, resulting in extremely low photocurrent density at the CO2R equilibrium potential. This paper describes the design and fabrication of a photocathode consisting of crystal phase-modulated Ag nanocrystal cocatalysts integrated on illumination-reaction decoupled heterojunction silicon (Si) substrate for the selective and efficient conversion of CO2. Ag nanocrystals containing unconventional hexagonal close-packed phases accelerate the charge transfer process in CO2R reaction, exhibiting excellent catalytic performance. Heterojunction Si substrate decouples light absorption from the CO2R catalyst layer, preventing the parasitic light absorption. The obtained photocathode exhibits a carbon monoxide (CO) Faradaic efficiency (FE) higher than 90% in a wide potential range, with the maximum FE reaching up to 97.4% at -0.2 V vs. reversible hydrogen electrode. At the CO2/CO equilibrium potential, a CO partial photocurrent density of -2.7 mA cm-2 with a CO FE of 96.5% is achieved in 0.1 M KHCO3 electrolyte on this photocathode, surpassing the expensive benchmark Au-based PEC CO2R system.

Ag-Fe2O3 nanocomposites for synergistically enhanced antibacterial activity

Doping of metal or metal ions in the host lattice with good dopant distribution or forming a local contact boosts materials properties for specific applications. This work used the solution combustion approach (SCA) to synthesize Ag-Fe2O3 nanocomposites (SICs) following the single-source precursor doping strategy with good final material stoichiometry. The elemental distribution and composition, crystallinity, and morphology of SCA-based synthesized materials were analyzed using common techniques such as TEM, FESEM-EDS, and XRD. Even though the Lewis hard and soft acids and bases (HSAB) idea was precise for inclusion of Ag dopant in the Fe2O3 lattice, the formation of Schottky junctions between Ag and Fe2O3 is dominance as a result of dopant-host radii size differences. The independent peak for both Ag and Fe2O3 crystals on the XRD pattern analysis without peak shift confirms the dominance of Schottky junction formation. The presence of local contact between Ag and Fe2O3 was also confirmed by the HRTEM analysis, with d-spacing values of 0.22 and 0.36 nm, respectively. Compared to the bare Fe2O3, the antibacterial potential of the SIC is much greater, with a 23-mm zone of inhibition on Pseudomonas aeruginosa gram-negative bacteria, which confirms the presence of a synergistic effect.

Antibacterial and Cytotoxicity Effect of Flavokawain B Loaded Silver Nanoparticles

: Silver nanoparticles (Ag NPs) are used in sterilizing nanomaterials, medical products, textiles, food storage bags, and personal care products. Ag NPs exhibited significant antibacterial activity due to the sustained release of free Ag. Flavokawain B (FKB) is a natural chalcone extracted from the roots of the kava-kava plant Piper methysticum. In this study, Ag NPs were synthesized by the chemical method using hydrazine hydrate and poly (vinyl alcohol) as reducing and stabilizing agents, respectively. FKB-loaded Ag NPs showed a red shift and were positioned at 421 nm, indicating Ag NPs presence. The FTIR spectrum confirmed the presence of the aromatic compoundand#39;s functional groups (at different absorption bands). The XRD pattern indicated the crystalline nature of the loaded Ag NPs with face-centered cubic (fcc) Ag crystals. SEM image revealed the crystalline nature of FKB-loaded Ag NPs. FESEM image revealed the loading of Ag NPs on the clear and flat surface of FKB, and a spherical shape of Ag NPs with an average size of 60 nm was obtained. The minimum inhibitory concentration (MIC) of AgFKB against Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa was found to be 100 μg/mL. However, 100 μg/mL of FKB discs did not show any inhibition zone in the activity. These findings indicated the improved antibacterial activity of FKB-loaded Ag NPs (Ag-FKB).

Influence of cation Si4+↔Ge4+ and P5+↔Ge4+ sub-stitution on the mechanical parameters of single crystals Ag7(Si1–xGex)S5I and Ag6+x(P1–xGex)S5I

Herein we present the results of microhardness investigations aimed at monocrystalline samples of Ag 7 (Si 1–x Ge x )S 5 I (0, 0.2, 0.4, 0.6, 0.8, 1) and Ag 6+x (P 1–x Ge x )S 5 I (0, 0.25, 0.5, 0.75, 1) solid solutions. The dependence of microhardness H on the load P and composition were investigated. It has been observed that the microhardness dependence on the applied load is characterized by a tendency to decrease with increasing the load. It indicates a presence of “normal” size effect in both Ag 7 (Si 1–x Ge x )S 5 I and Ag 6+x (P 1–x Ge x )S 5 I (0, 0.25, 0.5, 0.75, 1) solid solutions. The revealed size effects of hardness in single crystals of Ag 7 (Si 1–x Ge x )S 5 I and Ag 6+x (P 1-x Ge x )S 5 I solid solutions have been analyzed within the framework of the gradient theory of plasticity. The corresponding parameters of the model of geometrically necessary dislocations have been determined.

Mechanical Properties Analysis on the Reduced Graphene Oxide/Silver Nano Particle / Poly Lactic Acid Composites

We present the characteristics and mechanical strength of rGO-AgNPs nanocomposites in PLA-based 3D printing. The nanocomposites are characterized using X-ray diffraction and UV-Vis spectroscopy. The XRD spectrum reveals diffraction peaks at 38.14°, 44.30°, 64.50°, and 77.42°, corresponding to the (111), (200), (220), and (3111) planes of the Ag crystals, respectively. Surface observations under the microscope for pure PLA and PLA rGO-AgNPs showed that the surfaces of the samples were uniformly distributed. The results of 3D printing indicated that the 0.10 g rGO-AgNPs nanocomposite particles were evenly distributed, although digital microscopy confirmed the presence of a few small particles that were not uniformly distributed. Tensile tests demonstrated that rGO-AgNPs exhibited higher tensile strength compared to pure PLA. Tensile strength increased as the quantity of rGO-AgNPs decreased. Young's modulus results, ranging from pure PLA to rGO-AgNPs, consistently showed an increase, with the highest Young's modulus measuring 7624.45 kPa. Therefore, specimens containing rGO-AgNPs displayed a greater modulus than others, indicating that rGO-AgNPs enhanced the mechanical properties of PLA-based 3D printing.

Acoustic Studies of the Melting and Crystallization of Eutectic Gallium–Silver Alloys in Porous Glasses

The paper presents the results of acoustic studies of the melting and crystallization of Ag–Ga alloys with a silver content of 1.5 and 3 at % embedded into porous glasses with an average pore size of 13 nm. The temperature dependences of the velocity of longitudinal ultrasonic waves are measured by a modified pulse-phase method at a frequency of 7 MHz in the 200–325 K range for complete and partial cooling–heating cycles. The temperature dependences of the ultrasonic velocity showed regions corresponding to phase transitions. Significant changes in the phase diagram of the bulk alloy due to nanostructuring have been revealed. It is shown that segregates with different crystal structures are formed in the pores for alloy of different compositions.

DFT study of the formation of the Sb-Ag(1 1 1) (√3×√3) – R30° surface alloy

According to performed DFT calculations, the (√3×√3) – R30° structure, in which Sb atoms occupy hcp sites on Ag(111), is more energetically favorable than the related substitutional SbAg2 surface alloy. The difference in energies is significant, 0.66 eV per unit cell, and can be attributed to a larger size of Sb atoms compared to Ag. The obtained results of modeling the substitutional process explain the formation of adsorbed Sb layer on the Ag(111) surface by means of Sb deposition instead of the formation of the substitutional surface alloy. In turn, Ag deposition onto the alloy surface will cause a floating up (segregation to the surface) of Sb atoms thus restoring the alloy surface, which may serve as a surfactant in the process of the growth of Ag crystal.

Dynamic Metal-Ligand Coordination Boosts CO2 Electroreduction.

The interfacial structure of heterogeneous catalysts determines the reaction rate by adjusting the adsorption behavior of reaction intermediates. Unfortunately, the catalytic performance of conventionally static active sites has always been limited by the adsorbate linear scaling relationship. Herein, we develop a triazole-modified Ag crystal (Ag crystal-triazole) with dynamic and reversible interfacial structures to break such a relationship for boosting the catalytic activity of CO2 electroreduction into CO. On the basis of surface science measurements and theoretical calculations, we demonstrated the dynamic transformation between adsorbed triazole and adsorbed triazolyl on the Ag(111) facet induced by metal-ligand conjugation. During CO2 electroreduction, Ag crystal-triazole with the dynamically reversible transformation of ligands exhibited a faradic efficiency for CO of 98% with a partial current density for CO as high as -802.5 mA cm-2. The dynamic metal-ligand coordination not only reduced the activation barriers of CO2 protonation but also switched the rate-determining step from CO2 protonation to the breakage of C-OH in the adsorbed COOH intermediate. This work provided an atomic-level insight into the interfacial engineering of the heterogeneous catalysts toward highly efficient CO2 electroreduction.

The role of shear waves in electron-phonon relaxation and electrical resistivity of noble metals

• Shear waves make a main contribution to the resistivity of noble metals • At low temperatures, it is 95, 91, and 95% for crystals Au, Ag, and Cu, respectively • Results is aligns well with experiment in the temperature range from 10 to 1000 K The influence of elastic energy anisotropy on electron-phonon relaxation and electrical resistivity of noble metals has been studied within the Bloch-Grüneisen theory. Accounting for the influence of elastic anisotropy on spectrum, phonon polarization vectors, and electron relaxation by quasi-transverse modes makes it possible to quantitatively put in agreement the outcomes of calculating the temperature dependence of the electrical resistivity of noble metals with experimental data in the temperature range from 10 to 1000 K. A constant characterizing the interaction of electrons with shear waves in noble metals has been determined. The role of shear waves in electrical resistivity has been analyzed. It has been shown that the relaxation of electrons by shear waves, which was not previously taken into account, makes a dominant contribution to the electrical resistivity of noble metals in the entire temperature range from 10 to 1000 K. At temperatures well below the Debye temperature, this contribution is 95%, 91%, and 95% of the electrical resistivity for crystals Au, Ag, and Cu, respectively, and at T = 1000 K it decreases to 73%, 44%, and 68%.

The effect of the surface patterning by ion beam irradiation on the Ag directional outflow in Ag/AlN nano-multilayers

Surface templating of nano-multilayers is a promising step for the advanced industrial application of these nanomaterials. In the present work, the effect of focused ion beam modification of Ag/AlN nano-multilayer near-surface region on the Ag surface outflow is revealed. Surface patterning by ion beam irradiation leads to the formation of a higher amount of Ag crystals in relation to the intact surface region. Heat treatment initiates grooving of Ag grain boundaries, resulting in the formation of channels in the nano-multilayer volume. These channels act as pathways for mass transport of Ag to the film surface. Ion bombardment creates regions of high concentration of non-equilibrium defects, which locally increase the driving force for grooving and channeling, thereby promoting creation of more pathways for Ag surface migration. The obtained experimental results indicate that surface modification by focused ion beam can be used for production of nano-multilayers with designed templates of surface outflow.

Investigation of dye-sensitized solar cell performance based on vertically aligned TiO2 nanowire photoanode

In this work, we present our results related to the development of Dye-Sensitized Solar Cells (DSSCs) based on vertically aligned TiO2-nanowire (NW) and Ag nanoparticle (NP) assisted vertically aligned TiO2-NW (TAT) photoanode fabricated by the glancing angle deposition (GLAD) technique on fluorine doped thin oxide (FTO) substrates. The scanning electron microscopy (SEM) analysis reveals that the Ag-NP assisted vertically aligned TiO2-NW photoanode was successfully deposited on FTO substrates. The average length and diameter of the NW have been measured to be ~ 350 nm and ~ 90 - 100 nm, respectively. Moreover, transmission electron microscopy (TEM) and X-ray diffraction (XRD) manifest the presence of small crystals of TiO2 and Ag. Further, the absorption spectrum analysis reveals that the incorporation of Ag-NP in TiO2-NW increases absorption in the visible region, but decreases the efficiency of the cell after the incorporation of the nanoparticle. The calculated bandgap of the annealed Ag-NP (30 nm) assisted TiO2-NW (TAT@30nm) sample from the photoluminescence (PL) graph is ~ 3.12 eV. Finally, it is observed that the TiO2-NW based DSSC device shows better performance in terms of photo conversion efficiency (PCE) compared to the TAT@30nm photoanode based device, with an efficiency of ~0.61 % from the former and ~ 0.24 % from the latter. This reduction in the efficiency of TAT@30nm based devices is due to the larger size of Ag-NP, in which the nanoaprticle acts as an electron sink and acts as a blocking layer.

Study on gas sensibility of ethanol gas sensor based on flower-ball shaped Ag/Bi2WO6

• Flower-ball shaped Ag/Bi 2 WO 6 material was synthesized by hydrothermal method. • The gas sensing performance of Ag/Bi 2 WO 6 for ethanol was investigated for the first time. • Ag/Bi 2 WO 6 -based gas sensor has a fast response speed of up to 7s for ethanol. • The sensor based on Ag/Bi 2 WO 6 showed low operating temperature of 240℃ to ethanol. Although Bi 2 WO 6 has been applied in various field, there are few reports on the application of gas sensing. In this work, Ag loaded flower-ball shaped Bi 2 WO 6 composite nanomaterials were synthesised by hydrothermal method. The Ag content was optimized for the first time. It was found that when 2 % Ag was added, Ag/Bi 2 WO 6 material possessed high sensitivity and low optimal working temperature (240℃). Compared with pure Bi 2 WO 6 (11 s and 32 s), Ag/Bi 2 WO 6 possessed ultrashort response and recovery time of 7 s and 25 s. It exhibited better ethanol gas selectivity and stability. Unique crystal structure and Ag catalysis may lead to the improvement of gas sensing performance.

Augmented anticancer effect and antibacterial activity of silver nanoparticles synthesized by using Taxus wallichiana leaf extract.

Taxus wallichiana is an evergreen tree species found in the Himalayan region of Pakistan. The tree possesses important secondary metabolites such as Taxol that has been implicated in treating breast, ovarian and colon cancer. Therefore keeping in view the importance of this plant species, silver nanoparticles were synthesized using Taxus wallichiana aqueous leaf extract and evaluated for their anti-bacterial and anti-cancer properties. Silver (Ag) nanoparticles (NPs) were characterized for their optical, morphological and structural features using techniques such as UV-visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) and were evaluated for their antibacterial activity and anti-cancer activity using U251 cell line. The study showed that the UV-absorbance peak of Ag2O NPs at 450 nm shifted to 410 nm, affirming the formation of leaf extract Ag NPs. Similarly structural studies revealed the crystalline nature of the cubic structure of the Ag crystal with an average crystallite size of 29 nm. FTIR analysis exhibited the existence of different functional elements including O-H and N-H and phenolic groups. Non-spherical glomerular shaped Taxus wallichiana Ag NPs were observed from SEM studies and EDX profile showed Ag as the main element along with constituent of biological origin. The synthesized Ag NPs showed significant antibacterial activity against Salmonella typhi, and Staphylococcus aureus. The cytotoxic activity of Ag NPs on U251 brain cancer cells showed a synergistic effect with 10 ug/mL concentration after 48 and 72 h incubation based on cell viability assay indicating promising glioblastoma drug potential.

Effect of applied potential on metal surfaces: Surface energy, Wulff shape and charge distribution

We use grand canonical density functional theory to predict the surface energies, Wulff shapes, charge distributions and catalytically active sites of different metal surfaces under electrochemical conditions. We propose a method for computing surface energies from grand canonical density functional theory (GC-DFT) calculations of periodic slab models and use it to compute the surface energies of the facets of Pt, Cu, and Ag crystals to predict their Wulff shapes under electrochemical conditions. GC-DFT predicts that, for the pure metals studied, solvation only slightly affects the Wulff shape while applied potentials considerably affect the surface energies and corresponding Wulff shapes. We used Bader charge analysis of GC-DFT computed electron densities to investigate the effect of applied potential on the distribution of electron density over the atoms of the surfaces of Pt, Cu, Ag, and the 75–25 Ag-Pt and Au-Ni alloys. This analysis shows that, under an applied potential, the electron density is unevenly distributed over the surface atoms and that the charges of atoms more exposed to solvent are more sensitive to bias. Our results show that the most sensitive atom to bias can be used to identify the most favorable adsorption site and thus, the active sites of electrochemical reactions, which is computationally less demanding than calculating the adsorption energies on all possible adsorption sites.

Microstructure evolution and SERS performance of self-formed Ag nanoparticles/Ag-27.9 at% Co-8.9 at% Zr alloy films

Ag-27.9 at% Co-8.9 at% Zr alloy films were deposited on flexible polyimide (PI) by magnetron sputtering and annealed in argon atmosphere. Results show that many fine nanoparticles are formed on the surface of as-deposited Ag–Co–Zr alloy films. Furthermore, the average size of self-formed Ag nanoparticles gradually increases while the number of Ag nanoparticles decreases as alloy film thickness increases. In addition, it is worth noting that flake-like and polyhedral nanoparticles are formed spontaneously on the surface of annealed alloy films and are proved to be single crystal Ag nanoparticles. Moreover, the morphology of flake-like Ag nanoparticles is dependent on annealing temperature. In order to improve “hotspots” activity of the alloy films, a 12 nm pure Ag layer was deposited on the annealed alloy film surface to obtain Ag layer/Ag nanoparticles/Ag–Co–Zr alloy films SERS substrates which can detect 5 × 10−14 M R6G. This paper provides a potential candidate for preparation of SERS substrates with ultra-high sensitivity and stability.

Development of novel crystal scintillators for lunar surface science

The development of novel crystal scintillators for a lunar landed mission near future is reported. On that mission, we aim to assess the radiation dose, biological effect, water, and other resources on the lunar surface. To accomplish this, a Lunar Vehicle Radiation Dosimeter (LVRAD) made up of several radiation detectors has been proposed. New scintillation crystals are being developed for neutron and gamma measurements. Stilbene and undoped LaCl3 crystal were selected for fast neutron/gamma spectrometers. The mutual combination of organic and inorganic detectors benefits from direct fast neutron detection via 35Cl(n, p)35S reaction as well as the good gamma resolution of LaCl3 and the high detection efficiency of stilbene. LaCl3 crystals with the diameter of 38.1 mm were grown by a homemade modified Bridgman furnace. For epithermal neutron spectrometer, 6LiI:Ag crystal was selected due to its pulse shape discrimination capability and highest detection efficiency in terms of size for both thermal and epithermal neutron among scintillation materials. Enrich 6LiI was purified using the zone-refining technique. The crystal was then grown by the same Bridgman furnace.

Enhanced CO oxidation by reversible structural variation of supported Ag nanoparticle catalyst from single to twin by CO treatment

Twinned structure of metal nanoparticles can strongly affect catalysis because of its unique atomic alignment and bond strain in metal nanoparticles. Here, the twin and single crystal structures of supported Ag nanoparticles are controlled reversibly by gas treatment. The single crystal Ag nanoparticles were formed in Ag/Al2O3 by H2 treatment, and subsequent CO gas treatment changed the Ag particle structure to twin. The change in the Ag particle structure from single to twin caused enhancement of CO oxidation activity. In addition, the catalytic activity was reversibly changed from low to high by applying H2 and CO gas treatment to Ag/Al2O3. The kinetic analysis for CO oxidation revealed that the twin Ag nanoparticles have stronger CO adsorption energy than the single crystal ones, which is responsible for the enhanced CO oxidation activity of twin Ag nanoparticles.