Strain engineering in alloy nanoparticles

The mechanical and physical properties relationship from atomic level strain/stress causes dislocation density and electrical conductivity relationship, as well as crystallites deformation and hkl-parameter change in the severely deformed pure refractory rare metal Nb at ambient temperature and during short processing times. The above mentioned issues are discussed in this study. For ultrafine-grained and nanocrystalline microstructure forming in metal the equal-channel angular pressing and hard cyclic viscoplastic deformation were used. The flat deformation and heat treatment at different parameters were conducted as follows. The focused ion beam method was used for micrometric measures samples manufacturied under nanocrystalline microstructure study by transmission electron microscope. The microstructure features of metal were studied under different orientations by X-ray diffraction scattering method, and according to the atomic level strains, dislocation density, hkl-parameters and crystallite sizes were calculated by different computation methods. According to results the evolutions of atomic level strains/stresses, induced by processing features have great influence on the microstructure and advanced properties forming in pure Nb. Due to cumulative strain increase the tensile stress and hardness were increased significantly. In this case the dislocation density of Nb varies from 5.0E+10 cm –2 to 2.0E+11 cm –2 . The samples from Nb at maximal atomic level strain in the (110) and (211) directions have the maximal values of hkl-parameters, highest tensile strength and hardness but minimal electrical conductivity. The crystallite size was minimal and relative atomic level strain maximal in (211) orientation of crystal. Next, flat deformation and heat treatment increase the atomic level parameters of severely deformed metal. DOI: http://dx.doi.org/10.5755/j01.ms.18.4.3091

The effects of the process-control agents (PCAs) stearic acid and methanol on the mechanical alloying (MA) of a nanostructured aluminum alloy (Al93Fe3Ti2Cr2) have been investigated. The dependency of the powder-particle sizes, grain sizes, atomic-level strains, lattice parameters, formation of solid solutions, and microstructural evolution of the aluminum alloy on the types of PCAs and their concentrations have been studied using a variety of analytical instruments including X-ray diffraction scanning electron microscopy, and transmission electron microscopy. The results clearly indicate that prevention of excessive cold welding of Al particles can be achieved by the addition of a PCA at the expense of reductions in the grain size, formation rate of solid solutions, and rate of microstructural refinement, all of which are desired in MA of the Al alloy. Furthermore, a PCA that is more effective in preventing excessive cold welding will also impose more hindrance to the MA process. These phenomena have been discussed in the light of the adsorption of the PCA on the metal surface and the lubricating function of the PCA.

Unbeatable widespread antimicrobial resistance in nosocomial pathogens is a major public health concern in hospitals. In the present study, aqueous stem extract of C. tagal (CTSE) is used as a bioreducing agent for synthesis of various monometallic and alloy nanoparticles. Nanoparticle formation was dependent on time, temperature, and metal salts’ concentration. UV-Visible spectroscopy demonstrated peaks at 444 and 556 nm for silver and gold nanoparticles, respectively, while both alloy Ag–Au nanoparticles exhibited peaks at 535 nm. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy results revealed shape, size, and involvement of functional groups in formation of stable nanoparticles. Further, minimum inhibitory concentration (MIC) of two metal ions, four monometallic nanoparticles, and two alloy noble metal nanoparticles was evaluated against nosocomial pathogens. Silver nanoparticles synthesized from AgNO3 and Ag2SO4 exhibited cytotoxicity against all tested microorganisms. Alloy (Ag–Au) nanoparticles from salts of silver nitrate and gold were more effective than alloy nanoparticles prepared from salts of silver sulfate and gold. However, gold and copper nanoparticles were effective only against Staphylococcus aureus and Escherichia coli respectively. Ionic silver was more cytotoxic as compared to copper ions and monometallic and alloy nanoparticles. This is the first report on comparative antimicrobial activity of metal ions and various nanoparticles synthesized from CTSE against nosocomial pathogens from the intensive care unit (ICU) and burn wound intensive care unit (BWICU).

Perovskite materials have garnered significant attention over the past decades due to their applications, not only in electronic materials, such as dielectrics, piezoelectrics, ferroelectrics, and superconductors but also in optoelectronic devices like solar cells and light emitting diodes. This interest arises from their versatile combinations and physiochemical tunability. While strain engineering is a recognized powerful tool for tailoring material properties, its collaborative impact on both oxides and halides remains understudied. Herein, strain engineering in perovskites for energy conversion devices, providing mutual insight into both oxides and halides is discussed. The various experimental methods are presented for applying strain by using thermal mismatch, lattice mismatch, defects, doping, light illumination, and flexible substrates. In addition, the main factors that are influenced by strain, categorized as structure (e.g., symmetry breaking, octahedral distortion), bandgap, chemical reactivity, and defect formation energy are described. After that, recent progress in strain engineering for perovskite oxides and halides for energy conversion devices is introduced. Promising methods for enhancing the performance of energy conversion devices using perovskites through strain engineering are suggested.

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

In the past years lead free K x Na 1‐x NbO 3 ceramics with huge d 33 ‐values, comparable to that of PbZr 1‐x Ti x O 3 , have been demonstrated [1]. The high piezoelectric coefficients are generally attributed to the presence of a monoclinic phase at the morphotropic phase boundary and the associated symmetry reduction. A recent work by Schwarzkopf et al. [2] reports that monoclinic phases can also be stabilized in ferroelectric perovskite thin films by utilizing anisotropic epitaxial strain. Another advantage of using epitaxial strain is to engineer by an appropriate choice of the substrate and film composition the arrangement and size of domains, which in turn influences on the piezo‐ and ferroelectric material properties. Ferroelectric thin films and their domain structure are commonly characterized by combining X‐ray diffraction (XRD) and piezoresponse force microscopy (PFM). While XRD gives useful crystallographic information, its local resolution is limited and a detailed study of the domains is impossible. On the other hand PFM has sufficient spatial resolution but does not provide structural information. Plan‐view transmission electron microscopy (TEM) with its ability to study structural data with high accuracy at atomic resolution is in principle ideally suited to gain detailed information on the domain structure of the film. There is, however, one major challenge. In order to preserve the as‐grown strain state of the film and thus its domain structure plan‐view TEM samples with a thick substrate layer are necessary. Since TEM is a projective method it images typically the projected potential averaged along the beam direction including both film and substrate for a plan‐view observation geometry. In this paper we will show that this challenge can be overcome by appropriate imaging conditions using high resolution scanning TEM (STEM) annular dark field (ADF) imaging. Due to the channeling effect and the reduced depth of focus in STEM mode we are able to obtain information mainly from the monoclinic distorted film, while the substrate gives rise to a uniform background intensity. As an example we study a 26 nm thin film of K 0.95 Na 0.05 NbO 3 , which was epitaxially grown on top of a (110) NdScO 3 substrate and shows giant piezoelectricity. PFM reveals a complex periodic domain structure with the coexistence of two different monoclinic domains (yellow and purple stripes in Fig. 2 a). According to XRD these domains differ from each other by the orientation of the in‐plane monoclinic distortion. Based on the structural data provided by XRD and PFM we created a supercell consisting of a K 0.95 Na 0.05 NbO 3 film, which contains two domains with a difference of the in‐plane monoclinic distortion of 2β=8 mrad, on top of a 150 nm thick rigid NdScO 3 substrate without any lattice distortion (Fig. 1 a). The chosen thickness of the substrate is a minimum value necessary to preserve the as‐grown strain state of the film. Frozen phonon simulations reveal that if the incident electron probe is transmitted first through the film, then the final high resolution STEM ADF image pattern directly reflects the domain structure of the K 0.95 Na 0.05 NbO 3 film with the evaluated shear angle 2β as in the supercell (Fig. 1 b). However, if the electron beam direction is inverted, i.e. the beam is transmitted first through the substrate, then no lattice distortion corresponding to the domain structure of the film is found in the obtained high resolution STEM ADF image. An analysis of the evolution of the electron probe inside the supercell (Fig. 1 c) shows that this 3‐dimensional sensitivity is caused by the electron channeling effect. In the present case the high resolution pattern in the final image is produced basically in the first 20‐30 nm of transmitted material. After this thickness the wave function of the electron beam is widely dispersed, irrespectively of the initial position of the electron probe. Thus the subsequent part of the specimen mainly contributes to a uniform background intensity in the final image. Consequently, the frozen phonon simulations demonstrate the feasibility of our approach to study domains in epitaxially strained ferrolectic films by plan‐view high resolution STEM ADF imaging. An experimental example for the STEM analysis of the domain structure for the above mentioned K 0.95 Na 0.05 NbO 3 film is shown in Fig 2 c. A model of the complex domain pattern including the sub‐domain structure will be discussed in the paper.

Transmission electron microscopy (TEM) at sub-Angstrom resolution is important for nanotechnology. Identifying atom positions requires appropriate resolution, the ability to separate distinct objects in images. With Cs corrected, the information limit of the TEM controls resolution. The OAM has demonstrated that a resolution of 0.78A is possible. The TEAM (transmission electron achromatic microscope) will be a TEM using hardware correction of Cs with a monochromator to improve its information limit beyond that of the OAM by improvement of the electron-beam energy spread. It is shown that A 300keV HRTEM TEAM does not require a Cc corrector to reach 0.5A as long as beam energy spread and objective-lens current ripple are lowered sufficiently. A lower-voltage TEAM will require stricter limits on objective-lens current ripple to reach the targeted 0.5A resolution. No improvement in HT ripple or noise is required to improve the information limit per se since the monochromator determines the energy spread in the beam. However, improved HT ripple and noise will improve the beam current statistics (number of electrons passing through the monochromator) by placing more of the electrons closer to the center of the energy-spread distribution

The present investigation aims at understanding the effect of size on melting behaviour of free standing alloy nanoparticles. Alloy nanoparticles of Bi1-xSbx (x=0.12, 0.25, 0.50 and 0.75) have been synthesized by solvothermal route using sodium borohydride (NaBH4) as a reducing agent. The samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The melting behaviour of alloys was determined by differential scanning calorimetry (DSC). The formation of different solid solution phases of Bi-Sb alloy has been confirmed by detailed XRD studies. Uniform cuboctahedral as well as spherical morphology of alloy nanoparticles has been observed in TEM with average particle size of 40±9 nm in Bi0.75Sb0.25 specimen. DSC studies indicate the depression in the melting temperature of the nanoparticles as compared to the bulk alloy of same composition.

Revealing structure and electronic properties at organic interfaces using TEM

Understanding helium diffusion in iron: a multiscale modelling method based on the DFT and kinetic Monte Carlo, coupled to TEM and thermo-desorption spectroscopy experiments

In order to better understand the influence of certain substances on the nucleation, growth, and aggregation of crystals in urine, researchers have employed several different experimental approaches. Some have elected to carry out their investigations in a stationary test-tube arrangement (1), others have used flow systems (2), and still others have employed a method involving evaporation to produce crystallization (3). Besides these experimental approaches, investigators have demonstrated the usefulness of modelling the ionic equilibria in urine by computer simulation (4). The present study was undertaken to examine the qualitative and quantitative effect of certain ions on calcium oxalate (CaOx) crystallization in a synthetic urine using a combined experimental and theoretical approach.

Heterogeneous catalysis is an enabling technology that utilises transition metal nanoparticles (NPs) supported on oxides to promote chemical reactions. Structural mismatch at the NP–support interface generates lattice strain that could affect catalytic properties. However, detailed knowledge about strain in supported NPs remains elusive. We experimentally measure the strain at interfaces, surfaces and defects in Pt NPs supported on alumina and ceria with atomic resolution using high-precision scanning transmission electron microscopy. The largest strains are observed at the interfaces and are predominantly compressive. Atomic models of Pt NPs with experimentally measured strain distributions are used for first-principles kinetic Monte Carlo simulations of the CO oxidation reaction. The presence of only a fraction of strained surface atoms is found to affect the turnover frequency. These results provide a quantitative understanding of the relationship between strain and catalytic function and demonstrate that strain engineering can potentially be used for catalyst design.

Stabilization of the gamma phase in Fe–Pt alloy nanoparticles with low Pt contents prepared by chemical synthesis method

Investigation of structural and magnetic properties of thermal plasma-synthesized Fe1−xNix alloy nanoparticles

Amorphous Ni–P alloy nanoparticles were synthesized by chemical reduction of nickel acetate in water reacted with sodium hypophosphite under stirring. The nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Results of XRD and TEM showed that nanoparticles have an average diameter 100 nm. And XPS analysis indicated that part of the surface of Ni–P amorphous alloy nanoparticles was oxidized. The tribological properties of the prepared Ni–P nanoparticles as an additive in lithium grease were evaluated with a four-ball friction and wear tester. The worn surfaces of the lubricated GCr15 steel were analyzed by means of XPS and scanning electron microscopy (SEM). The lubricating mechanisms were discussed on the basis of XPS and SEM analyses of the worn steel surfaces. The results show that these nanoparticles as a grease additive can effectively enhance the friction-reduction and antiwear ability of lithium grease. Tribochemical reactions were involved for steel–steel frictional pair lubricated with the lithium grease containing amorphous Ni–P alloy nanoparticles, with the formation of a boundary lubricating and protecting film composed of additives of lithium grease and tribochemical reaction products (iron phosphate, iron oxides, nickel oxide, nickel, etc.) of the lubricants. This contributes to improve the tribological properties of the lithium grease.