Predicting the microstructural evolution of radiation damage in materials requires handling the physics of infrequent-events, in which several time scales are involved. The reactions rates characterizing these events are the main ingredient for simulating the kinetics of materials under irradiation over large time scales and high irradiation doses. We propose here an efficient, finite temperature method to compute reaction rate constants of thermally activated processes. The method consists of two steps. Firstly, rare reactive trajectories in phase-space are sampled using a transition path sampling (TPS) algorithm supplemented with a local Lyapunov bias favoring diverging trajectories. This enables the system to visit transition regions separating stable configurations more often, and thus enhances the probability of observing transitions between stable states during relatively short simulations. Secondly, reaction constants are estimated from the unbiased fraction of reactive trajectories, yielded by an appropriate statistical data analysis tool, the multistate Bennett acceptance ratio (MBAR) package. We apply our method to the calculation of reaction rates for vacancy and di-vacancy migration in α-Iron crystal, using an Embedded Atom Model potential, for temperatures ranging from 300 K to 800 K.

The effects of poly (lactic-co-glycolic acid) (PLGA) surface properties on lung epithelial carcinoma cell functions were previously identified. Results demonstrated decreased lung epithelial carcinoma cell vascular endothelial growth factor (VEGF) synthesis on 23 nm surface featured PLGA compared to the PLGA nano-smooth substrates. To investigate the universality of nanopatterned PLGA on inhibiting cancer cell functions, here, breast epithelial adenocarcinoma cell, MCF-7, early functions were determined on different PLGA nanometer surface topographies. Moreover, the viability of healthy breast cells was determined by an MTT assay to investigate the effects of nanopatterning on healthy breast cell growth. Atomic force microscopy (AFM) verified the varied nanotopographies on the PLGA surfaces prepared in this study. Importantly, results demonstrated significantly decreased breast adenocarcinoma cell functions (including decreased proliferation rate and decreased VEGF synthesis) on 23 nm featured PLGA surfaces compared to the other PLGA surface topographies (specifically, nano-smooth, 300 nm and 400 nm surface featured PLGA surfaces). In contrast, healthy breast epithelial cell studies indicated a 24% higher cell proliferation on the 23 nm featured PLGA surfaces compared to all other PLGA samples. In summary, these results provided further insights into understanding the role surface nanotopographies can have on selectively inhibiting cancer cell functions for a wide range of anti-cancer applications.

Spatial intelligence plays an important role in the success of nanoscience students specific to their visual ability to perceive structures in three dimensions. The NSF-funded IDEAS project makes use of a unique interactive 3D visualization system, based on immersive environment technology, for research and learning in Materials Science and Engineering (MSE) at UC Merced. In order to determine the effectiveness of the immersive system on nanoscience learning, a pilot project was conducted with undergraduate students, which showed the success of immersive systems in the science learning process. Overall, the immersive environment provided complete control in the construction and analysis of carbon-based nanostructure models. Results also showed the 3D visualization system benefited students with low spatial abilities. To facilitate a better understanding of the structure and properties of nanostructures, the IDEAS project has recently been expanded to allow accelerated simulations for materials research. It is important to integrate these new applications into undergraduate level courses in order to strengthen materials science education, recruit and retain future students, and to adapt modern technologies for future materials science educators. The expansion of the IDEAS project relies on the flexibility of this system to serve as a research tool as well as an innovative resource for science education. To adapt the 3D visualization and computing system and help engage students early in engineering research, our research group gathered practical technical documentation geared towards education of science users, based on both Cognitive Science and MSE Education (MSE-Ed) research. The work presented here involves developing educational resources through the design of audio-visual manuals for effective nanoscience learning. The manuals are being created using commercial software to produce interactive electronic books (ebooks). During the planning of the audio-visual manuals, we discovered that it is imperative to provide adequate educational tools as well as efficient guiding principles for the large number of visual, inductive, and active learners in general engineering education. This interdisciplinary project combines fundamental concepts from materials science and cognitive science, particularly project-based learning and active processing, while considering the concepts of overloading, and the unreliability of natural language, among other topics. This investigation will serve society by enhancing materials science research and education, as well as influencing engineering, chemistry, computer science and cognitive science fields, among others.

Sustainable energy is currently limited by the ability of materials to store energy and deliver it on demand. Allotropes of carbon are attractive for their potential for use in energy storage due to low weight, high chemical stability and low production cost. Carbon nanotubes and graphene can be combined to provide an effective three-dimensional material with high conductivity and high surface area. We demonstrate the use of block copolymers to obtain patterned arrays of iron nanoparticles which give rise to ordered carbon nanotubes with good size distribution. A one-step chemical vapor deposition process for large-area fabrication of the graphene and carbon nanotube hybrid structure is described. Following chemical vapor deposition the hybrid material is demonstrated in a supercapacitor device. The fabricated supercapacitor exhibits high electrical conductivity, and has potential for extremely high energy storage capability.

We recently developed a scattering model based on the scalar scattering theory. In this contribution we present how we used the scattering model to investigate interface textures with optimized scattering properties. We used the simulated annealing algorithm to find optimized surface textures and applied the ASA device simulator to evaluate the influence of these optimized textures on the performance of thin film silicon solar cells. We found that the lateral feature size of the textures is crucial for efficient scattering of the incident light.

The excellent tribological performance of ultrananocrystalline diamond (UNCD) makes this material a potential candidate for the fabrication of long endurance micro/nano-electro-mechanical systems (MEMS/NEMS) that could involve contacting surfaces. In this work, UNCD and nitrogen incorporated UNCD (N-UNCD) microstructures have been produced and investigated, in order to analyze their intrinsic stress component. A solution for stress reduction is proposed: the application of a titanium stress-compensation coating seems to be an optimum route to obtain flat, free-standing N-UNCD films.

We investigated the fabrication and the memory characteristics of metal-oxide-semiconductor (MOS) capacitors with GaN quantum-dots (QDs) embedded in the gate insulator. The GaN-QDs, which act as discrete charge storage nodes, were deposited by radio-frequency molecular-beam-deposition (RF-MBD). The influence of the deposition dose on the QDs size and density was investigated by TEM studies. Subsequent electrical characterization measurements on memory capacitors revealed enhanced electron charge trapping leading to significant memory windows. Charge retention measurements at room temperature showed that the sample with the lowest concentration of QDs exhibits a significant programming window after ten-years.

The changes are brought in the elemental semiconductors Si and Ge by replacing them with II-VI and III-V binary analogs or their ternary analogs I-III-VI2 chalcopyrides and II-IV-V2 pnictides respectively. Such compounds exhibit transitions from their parent compound in terms of nature of band gaps (Eg) as indirect to direct in addition to the changes in the values of the Eg. These changes have direct consequence in their optical properties with degenerate states being lifted leading to crystal field splitting and so on. The Eg in ternary bulk semiconducting materials is engineered as a function of certain structural parameters such as anion position parameter (u), tetragonal compression parameter (η) through effective alloying. The contributions to Eg due to these effects are studied as band gap anomalies. The present paper discusses the results of the band gap engineering in some of the bulk ABC2(A= Cd; B=Si,Ge,Sn; C= P,As) semiconductors using theoretical methods. The influence of each of A, B and C atom is also discussed. The dependence of morphology of nano semiconducting particles and the band gap on the chemical environment, temperature is reported by us. The confinement energy of a compound which is the difference in energy between the bulk and nano forms is investigated.

Nuclear waste isolation programs both inside and outside the United States have provided evidence that there are many geologic options for a repository, but virtually all of them rely to some degree on an engineered barrier system (EBS) to isolate and/or retard the migration of radionuclides to the biosphere. At Yucca Mountain, the design of the EBS was unexpectedly challenging because of uncertainties in quantitatively determining the local environment of the EBS particularly during the thermal pulse. The EBS design for the Yucca Mountain site evolved from a thin-walled, limited-lifetime, corrosion-resistant canister through a corrosion-allowance canister, to the present design, which may have a lifetime of more than 106 years. The EBS proposed for the Yucca Mountain repository has many individual sub-barriers, beginning with the spent fuel and waste, the cladding of the spent fuel, the geometry of the package, etc. The anticipated modes of degradation of engineering materials, including corrosion of the fuel, of the canister, and of the drip shield proposed specifically for the Yucca Mountain project, and the consequences of the materials degradation on the performance of the repository are presented. The roles of conservative modeling and simplifying assumptions for radionuclide mobilization and transport in the EBS on characterization of the source term are addressed.

This investigation deals with the effect of cooling rate on the formation of carbide nodular iron alloyed with 2.2 % Cr and equivalent carbon near 4.3%. In the experimental stage three Y-blocks of 1.5, 3 and 5.5 cm in thickness are poured in green sand molds. Castings are sectioned in two positions (wall and center samples) in order to determine the characteristics of the precipitated carbides (fraction, distribution and relative size) from surface to center and from the bottom to the top of the castings applying quantitative analysis of images. The obtained results show the presence of carbides in all of the castings. Finer carbides are obtained in the thinnest casting but with a high variation between the samples located in the wall and center. All castings present massive carbides in the last freezing zone (LFZ). Therefore the cooling rate associated with casting thick has an important effect on the fraction and distribution of carbides.

In this paper we report the use of a device based on two multilayered a-SiC:H/a-Si:H stacked heterostructures to photodetect and demultiplex optical signals of the visible spectrum. Both heterostructures were optimized for the detection of short and long wavelengths within the visible range. The optoelectronic characterization of the device includes spectral response measurements under reverse bias and using different optical steady state light conditions to soak the device. Results show that the device photocurrent signal measured using appropriate steady state optical bias, allows the separate detection of the input transmitted signals which enables the demultiplexing task. A numerical simulation, gives insight into the transduction mechanism to explain the device wavelength selective behavior.

Zirconium is of interest in the development of high-density diffusion barriers in nuclear reactor applications because of its low thermal neutron absorption cross section and good thermal and mechanical properties. It is used in these applications to protect the low enriched fuel from interacting directly with the cladding material to prevent swelling and cracking of the fuel. In this work, we investigated the use of plasma spraying as a method to produce high quality, dense Zr barrier coatings over large surface areas. A thin sheet of 21Cr-6Ni-9Mn stainless steel (SS) was used as the substrate material. Both sides of the SS sheet were coated, one side at a time. A transfer arc (TA) current between a torch and the substrate was used to vary the substrate temperature to explore the effect of temperature and time on the film grain size, interface quality, and film porosity. The films were characterized using light optical microscopy (LOM), scanning probe microscopy (SPM) and Kelvin probe force microscopy (KPFM) and EDS-SEM Although the film quality did improved with temperature, at the elevated substrate temperatures used in this study, metal atoms from the substrate diffused into and, at the highest temperature and longest time, through the Zr coatings.

The thickness of non-freezing interfacial 1-decanol molecules has been estimated to be 1.44 ± 0.07 nm. This is smaller than what is estimated for cyclohexane, 2.25 ± 0.14nm. Furthermore, these interfacial molecules have higher density than corresponding bulk cyclohexane and 1-decanol, respectively. However, the change in density of the interfacial molecules is more significant in the case of cyclohexane than 1-decanol. This suggests that the cyclohexane molecules near the walls of the pore are more tightly packed than 1-decanol molecules. Presumably, this is due to the difference in size and shape of the molecules. Cyclohexane, a more spherical molecule, can easily be packed in smaller pores than the longer 1-decanol.

We present a set of density functional theory (DFT) calculations on the electronic structure of Ag and Sn in Ge2 Se3 in a periodic model. We show that electron self-trapping is a persistent feature in the presence of many defects. Ag and Sn autoionize upon entering Ge2 Se3 becoming Ag+ and Sn2+ , respectively, and the freed electrons self trap at the lowest energy site. Both Ag and Sn can substitute for Ge, and we present formation energies as a function of Fermi level that show that Sn can substantially alter the incorporation of Ag into the Ge2Se3 network.

We calculated the mobility of two-dimensional electron gas along an n-type interface in LaAlO3/SrTiO3 heterostructure using the linearized Boltzmann equation. By solving the Schrödinger equation with the Poisson equation self-consistently, it was found that the interface remained non-conducting up to four unit cells of LaAlO3 film. For five or higher unit cells, the interface became conducting due to the significant overlap between the SrTiO3 conduction band and the LaAlO3 valence band. The electron gas was localized within 7 nm from the interface and multi-subbands were occupied. The calculated mobility matches reasonably well with available experimental data. It was found that the mobility is limited by the remote ionic charged layers in LaAlO3 at low temperature. At high temperature, the polar optical phonon was found to be the dominant scattering center.

Using soft X-ray spectroscopy, we have studied the reactions between Cu2O and CuO with an aqueous solution of 1mM Na2S. Exposure to dissolved sulfide for several hours clearly reduces Cu(II) to Cu(I) compounds. However, there are still strong oxygen signals in the spectra, indicating a more complex surface composition than simple copper sulfides.

Corrosion and tribocorrosion tests have been conducted on titanium, Ti-6Al-4V and Ti-10Zr-10Nb-5Ta alloys. The experiments have been conducted in four different electrolytes: NaCl solution, Ringer’s solution, phosphate buffered saline solution (PBS) with and without an addition of bovine serum albumin (BSA).

The electrochemical study showed that, whatever the electrolyte, the passivating film formed on Ti-10Zr-10Nb-5Ta surface is more stable than those obtained on the surface of titanium or Ti-6Al-4V alloy. In addition, Ti-10Zr-10Nb-5Ta presents a better resistance to corrosion. In PBS solution, open circuit potential (OCP) moved to more positive value in comparison with results obtained in NaCl and Ringer’s solutions, whereas addition of BSA moved OCP value towards more negative potential indicating a detrimental effect.

Tribocorrosion tests have been conducted at OCP when sliding against an alumina ball. Friction coefficient, current and volume of material removal at the end of tests have been measured and the results discussed. The influence of the presence of proteins molecules has been particularly analyzed.

The organization of the fuel cycle is a legacy of World War II and the cold war. Fuel cycle facilities were developed and deployed without consideration of the waste management implications. This led to the fuel cycle model of an isolated single-purpose geological repository for disposal of wastes shipped from distant processing facilities. There is an alternative: collocation and integration of reprocessing and other backend facilities with the repository. Such an option alters waste form functional requirements by reducing storage and transport requirements. This, in turn, broadens the choice of waste forms by relaxing the incentives to minimize waste volumes. Waste forms can be chosen primarily on meeting two goals: repository performance and minimizing costs. Less restrictive waste volume constraints enable termination of safeguards on all wastes, enable use of solubility-limited waste forms, and reduce radiation damage as a waste form limitation. The implications of such changes in waste form requirements are discussed.

There is significant interest in optical sensors whose fabrication process is fully compatible with existing flat panel display thin film transistor (TFT) technology. Here, we report a field-effect phototransistor with a channel comprising a thin nanocrystalline silicon (nc-Si:H) transport layer and a thicker hydrogenated amorphous silicon (a-Si:H) absorption layer. The implementation of nc-Si:H layer improves device stability in comparison with a-Si:H phototransistors, resulting in reduced threshold voltage shift. Semiconductor and dielectric layers were deposited by radio-frequency plasma enhanced chemical vapor deposition at 280°C. The device characterization included the dark and light transfer characteristics, spectral-response and dynamic measurements. The external quantum efficiency was measured as a function of incident photon flux at different biasing conditions. The phototransistor with channel length of 24 microns and photosensitive area of 1.4 mm2shows an off-current of about 1 pA, and photo-conductive gain up to 200 at low incident intensities. Thus, the results demonstrate the feasibility of the phototransistor for low light level detection.