The ground state structure, optical properties and charge carrier dynamics of silicon nanowire (SiNW) grown in <211> crystallographic direction is studied as a function of wavevector using density functional theory. This nanowire can be used as fundamental unit of nanoelectronic devices. The optical properties are computed under assumption of momentum conservation$\Delta \vec{k} = 0$. The on-the-fly non-adiabatic couplings for electronic degrees of freedom are obtained along the ab initio molecular dynamics nuclear trajectories, which are used as parameters for Redfield density matrix equation of motion. By investigating the photo-induced process on this nanowire, it is shown that high-energy photoexcitation relaxes to the band gap edge within 75 ps. The results of these calculations help to understand the mechanism of electron transfer process on the Si nanowire.

Physical and chemical properties of graphene-metal interfaces have been largely examined with the objective of producing nanostructured carbon-based electronic devices. Although electronic properties are key to such devices, appropriate structural, thermal and mechanical properties are important for device performance as well. One of the most studied is the graphene-titanium (G-Ti) interface. Titanium is a low density, high strength versatile metal that can form alloys with desirable properties for applications ranging from aerospace to medicine. Small clusters and thin films of titanium deposited on graphene have also been examined. However, while some experiments show that thin films of titanium on graphene can be removed without damaging graphene hexagonal structure, others reported the formation of titanium-carbide (TiC) at G-Ti interfaces. In a previous work [ACS Appl. Mater. Interfaces, 2017, 9 (38), pp 33288-33297], we have shown that pristine G-Ti interfaces are resilient to large thermal fluctuations even when G-Ti structures lie on curved or kinked substrates. Here, using classical molecular dynamics with the third-generation Charge Optimized Many Body (COMB3) potential, we show that di-interstitial defective G-Ti structures on a copper substrate with a relatively large curvature kink, present signs of TiC formation. This result might help explain the different experimental results mentioned above.

An effective way to reduce the impact of cement production on the environment is to use supplementary cementitious materials (SCM) as a partial substitution to cement. In addition to the reduction in cost and energy saving, the use of SCM in cement for the manufacture of mortar and concrete offers technical advantages. In this paper, cement was partially substituted by fines obtained from crushed recycled bricks recovered from a brick plant. The level of substitution was either 0%, 5%, 10% or 15% by weight of cement. The results show that cement substitution by brick fines resulted in a slight loss of workability with the increase of the substitution rate. Substitutions rates of 5% and 10% produced at long-term comparable strength as control mortars. The differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) results show cement hydration improved significantly with different rates of substitutions at 28 and 180 days of age.

In this work, we report on the electron spin resonance (ESR) studies performed on few-layered nanocrystalline (NCs) MoS2, WS2, and TiS2 prepared using hydrothermal and vapor transport methods. From the temperature dependent ESR spectra collected from MoS2 NCs, we have identified adsorbed oxygen species, sulphur vacancies, thio- and oxo-Mo5+ related paramagnetic defect centers. WS2 NCs have exhibited W+3 and oxo-W+5 paramagnetic defect spin species. TiS2 NCs showed defects such as Fe3+ (unwanted), oxygen and sulfur vacancies. This work demonstrates the usage of spin-sensitive spectroscopy such as ESR in unravelling the defects which contain unpaired electron spin centers in layered NCs two-dimensional materials.

200 μm thick solution annealed AISI 316L stainless steel foils were implanted with Ar ions to produce a 0.25 at. % concentration-depth plateau extending from the near surface to a depth of ≈ 250 nm, and then annealed at 550°C for 2 hours to form small Ar bubbles and Ar-vacancy clusters. Distinct sets of samples (including control ones without Ar) were irradiated at the temperature of 550 °C with Au ions accelerated at 5 MeV to produce an average damage content about ≈36 dpa at the region containing the Ar plateau. These samples were investigated by transmission electron microscopy using plan-view specimens prepared by ion milling. In contrast with the control samples where the irradiation causes the formation of a high concentration of extended defects and large cavities, carbonite precipitation of 1:1 metal-carbon (MC) content with a cubic structure occurs only in the samples containing the Ar bubbles. This precipitation phenomenon is not commonly observed in the literature. The results are interpreted considering that the precipitate growth process requires the emission of vacancies which are synergistically absorbed by the growth of the Ar bubbles.

Carbon fibers and activated carbon fibers are materials of high industrial interest. When presented as a felt, its use becomes easier and more practical. This work aims to study the conditions for obtaining and characterizing an activated carbon felt, using sheep wool as a precursor. The wool felt was oxidized, carbonized in nitrogen atmosphere and activated in water vapor. The working temperatures were selected through thermogravimetric analysis. The products and intermediates were characterized through thermogravimetric analysis, infrared spectroscopy, scanning electron microscopy, Raman spectroscopy and nitrogen adsorption-desorption. The products were assessed as potential sorbents for methane-carbon dioxide separation by adsorption kinetics measurements at different pressures. Results revealed a high influence of the carbonization temperature on the physicochemical and textural properties of the products. The adsorption kinetics and capacities of the gases showed that selectivities in separation were related to both felt carbonization temperature and gas pressure. This work revealed that activated carbon wool felts are a good alternative to synthetic fibers felt and they can be used for methane/carbon dioxide separation.

Graphene oxide (GO) and its phosphonated analogue (pGO) have been incorporated into sulfonated poly(styrene-isobutylene-styrene) (SO3H SIBS) to generate membranes with enhanced water retention. The polymer nanocomposite membranes (PNMs) were prepared per SIBS sulfonation level (i.e., 38, 61, and 90 mole %), filler type (i.e., GO and pGO) and filler loading (i.e., 0.1, 0.5 and 1.0 wt.%). FT-IR and TGA confirmed the functionalization and incorporation of the fillers into SO3H SIBS. No significant changes were observed in the thermal stability or FTIR spectra of the PNMs after addition of the fillers. Dissimilar behaviors were observed for the water absorption capabilities (i.e., swelling ratio and water uptake) after incorporation of the fillers. The nanofillers enhanced the water absorption of the sulfonated polymer, possibly due to interconnections between the ionic groups. Therefore, the PNMs could not only potentially function as proton exchange membranes (PEMs) for several applications such as direct methanol fuel cells (DMFCs).

Poloxamer 407 (P407) is a biocompatible thermo-setting polymer, while agarose is a biocompatible thermo-softening material. It is interesting to mix them to examine any possible synergy in thermomechanical properties. In this study, rotational rheometer was adopted to study rheological properties of the mixtures of agarose/P407 gels with different concentrations at various frequencies, strain rates and temperatures. It has revealed that the addition of P407 decreased the gel stiffness by an order of magnitude. For the given combinations in this study, the increase in agarose concentration would increase both the storage modulus and loss modulus of the gel mixtures. The variation in P407 concentration (2.5%-10%) minimally changes the composite moduli. These agarose/P407 gel mixtures also exhibited shear thinning behavior. However, the addition of P407 (2.5%-10%) to agarose gel only has very small effect on thermomechanical properties of agarose gels. The overall transition temperature for these gel mixtures is governed by P407 melting point where the phase change starts around 55°C and the gels completely collapse at the melting temperature of agarose.

Though not often discussed explicitly in literature, sample handling and preparation for advanced characterization techniques is a significant challenge for radiological materials. In this contribution, a detailed description is given of method development associated with characterization of highly radioactive and, in some cases, hygroscopic oxides of technetium. Details are given on developed protocols, fixtures, and tooling designed for x-ray and neutron diffraction, x-ray absorption, Raman spectroscopy, magic angle spinning nuclear magnetic resonance, and electron paramagnetic resonance. In some cases, multiple iterations of improved sample holder design are described. Lessons learned in handling Tc compounds for these and similar characterization methods are discussed.

Mechanical exfoliation is performed to fabricate ultrathin SnS layers, and chemical/thermal stability of SnS layers is discussed in comparison with GeS, toward piezoelectric nanogenerator application. Both SnS and GeS are difficult to be exfoliated under 10 nm using tape exfoliation due to strong interlayer ionic bonding by lone pair electrons in Sn or Ge atoms. Au-mediated exfoliation enables to fabricate larger-scale ultrathin SnS and GeS layers thinner than 10 nm owing to strong semi-covalent bonding between Au and S atoms, but GeS surface immediately degrades during Au etching in an oxidative KI/I2 solution. Although the surface of SnS after the Au-mediated exfoliation reveals several-nm oxide layer of SnOx, the surface morphology retains the flatness unlike the case of GeS. The SnS layers are more robust than GeS against the thermal annealing as well as the chemical treatment, suggesting that SnOx works as a passivation layer for SnS. Self-passivated SnS monolayer can be obtained by a controlled post-oxidation.

A novel preparation method of B-doped p-type BaSi2 (p-BaSi2) is proposed to realize heterojunction crystalline Si solar cells with p-BaSi2. The method consists of thermal evaporation of BaSi2 on B-doped amorphous Si (a-Si). In this study, the effect of a-Si interlayers and substrate temperature during BaSi2 evaporation on the electrical characteristics and crystalline quality of the evaporated films were investigated. While no cracks were found in the BaSi2 films formed using hydrogenated a-Si deposited by plasma enhanced chemical vapor deposition (PECVD), the films formed with sputtered a-Si have cracks. In addition, BaSi2 films formed with a 600 °C substrate temperature using PECVD a-Si showed p-type characteristics. After a post-deposition anneal at 800 °C for 5 minutes, the film hole density was measured at 1.3×1019 cm-3 and boron was found to be uniformly distributed throughout the film. These results show that the proposed method using PECVD is promising to obtain p-BaSi2 thin films with high hole density for p-BaSi2/n-type crystalline Si heterojunction solar cells.

The structural descriptions of even the most basic amorphous materials are under considerable debate. In this work, an intuitive computational technique has been developed to construct 3D statistical density maps to directly visualize and identify local atomic structures from simple monatomic amorphous germanium (a-Ge) to complex multi-atom systems such as copper zirconium metallic glass. We show motifs in copper zirconium that are unresolvable through traditional tools such as Voronoi indexing. This self-sorted local atomic motif (SLAM) method builds upon the Kabsch algorithm incorporating techniques in computer vision to produce least-squares optimized 3D density maps. Simultaneously, the SLAM method incorporates self-contained categorization to define local motifs based upon atomic structures. We present the methodology of the SLAM method and also present resulting motifs comparing models a-Ge and demonstrate its broad capability on metallic glass.