The US Department of Energy (DOE) hydrogen production research and development portfolio focuses on low-cost, highly efficient and environmentally friendly production technologies based on diverse, domestic resources. Within the DOE, work on hydrogen production technologies integrates basic and applied research, as well as technology development and demonstration. The integration of basic and applied research is of particular importance in “transformational” production technologies, such as photoelectrochemical (PEC) hydrogen production, where scientific advances are needed for achieving the long-term DOE performance and cost targets. In the case of renewable hydrogen production via PEC solar water splitting, high solar-to-hydrogen conversion efficiency has been demonstrated to date on the laboratory scale, but only with high-cost, low-durability material systems. In order to identify and develop the appropriate high-efficiency, low-cost, durable and scalable PEC material systems, research and development efforts in the DOE EERE (Energy Efficiency and Renewable Energy) Office have keyed in on specific focus areas, including: 1) the engineering of solar energy absorption properties in PEC semiconductor materials, such as the bandgap lowering in stable metal oxides as well as bandgap raising in nanostructured sulfide catalysts; 2) the engineering of PEC solid-liquid interfaces for optimal reaction rates and stability, such as surface nitrogenation in III-V semiconductor systems; 3) the standardization of PEC measurement and reporting methodologies, using national and international peer-review process, for facilitating research progress; and 4) the design and analysis of integrated PEC device and system configurations for scalable hydrogen production. As described in this presentation, all of these research and development areas rely heavily on collaborative efforts among academia, industry and national laboratory partners, utilizing state of the art resources in materials theory, synthesis, characterization and analysis. The collaboration extends nationally among research programs supported by the DOE EERE as well as Office of Science; and internationally via networking through the International Energy Agency’s Hydrogen Implementation Agreement Annex-26. Key and encouraging accomplishments resulting from the collaborative work are highlighted in this presentation.

Classical molecular dynamics (MD) simulations in conjunction with opticalabsorption and AFM/nano-Raman experiments are employed to relate themolecular-scale arrangement and conjugation of poly-3-hexylthiophene (P3HT)adsorbed onto single-walled carbon nanotubes (SWNTs) and multi-walled carbonnanotubes (MWNTs). Taken together our results demonstrate the templatingrole of carbon nanotubes in increasing the π-conjugation length of the P3HTat the P3HT/carbon nanotube interface. The MD simulations show that SWNTsand MWNTs, due to their inherent 1-dimensional (1D) cylindrical shape andπ-conjugation, planarize the P3HT molecules adsorbed at their surface andthus quench their torsional disorder, regardless of the P3HT conformationand nanotube chirality. This effect is more significant for higher SWNTweight fractions in the sample (since it is an interface effect). Weinvestigated this effect experimentally by acquiring nano-Raman spectra inregions of high-MWNT/low-P3HT content in addition to optical absorptionspectra of P3HT-SWNT composites with different SWNT concentrations . Theincrease in the P3HT conjugation is confirmed by a shift of a P3HT featurein the Raman spectrum when going from P3HT-rich to SWNT-rich areas in themixture. The significance of this work for charge transfer at the P3HT-SWNTinterface in bulk-heterojunction solar cells is discussed.

Photoluminescence (PL) spectra obtained with correlated set of experiments investigating grain boundary characteristics and diffusion processes in nanocrystalline silicon alloys (nc-Si:H), provide insight regarding formation and passivation of electronic defects in these regions. Based upon current results and previous works we believe thermally driven processes induce a PL band centered at 0.7 eV upon thermal annealing, and most likely involve diffusion of hydrogen and oxygen near interfaces. A nc-Si:H sample set with varied crystal volume fraction, Xc, was subject to thermal annealing treatments at different temperatures – each exceeding the deposition temperature. Fourier-transform photoluminescence (FTPL) and Fourier-transform infrared absorption spectroscopy (FTIR), were employed to correlate the relative 0.7 eV defect band emergence with compositional changes indicative of Si–Hx and Si–O species, for each sample, at each temperature, respectively. Hydrogen effusion data provide additional perspective.

We find the Xc to strongly affect susceptibility of nc-Si:H to oxygen related effects. The higher the Xc, the more readily oxygen penetrates the nc-Si:H network. We attribute this relationship to elevated diffusivity of oxygen in highly crystalline nc-Si:H materials, owing to their abundance of gain boundaries and interfaces, which serve as pathways for impurity migration. These findings corroborate the expectation that oxygen impurities and diffusion processes contribute to development of microstructural features giving rise to radiative recombination through deep defects in nc-Si:H.

This study focuses on the impact of chemical solutions (hydrogen fluoride and tetramethylammonium hydroxide) on the change in properties of advanced porous low-k films. It was shown that there is no preferential removal of methyl groups during the dissolution process. With regard to wetting agents, the presence of isopropyl alcohol or surfactant (polyoxyethylene ether and alkoxylated diol type) in HF solution slowed down low-k film etching. Complete removal of surfactant residual usually requires an additional rinsing step using a low-molecular weight alcohol such as isopropyl alcohol.

We report simple and effective methods to develop long-term, stable silicon nanowire-based pH sensors and systematic studies of the performance of the developed sensors. In this work, we fabricate silicon nanowire pH sensors based on top-down fabrication processes such as E-beam lithography and conventional photolithography. In order to improve the stability of the sensor performance, the sensors are coated with a passivation layer (silicon nitride) for effective electrical insulation and ion-blocking. The stability, the pH sensitivity, and the repeatability of the sensor response are critically analyzed with regard to the physics of sensing interface between sample liquid and the sensing surface. The studies verify that the sensor with a passivation layer over critical thickness show long-term, stable sensor response without long-term drift. The studies also show the detection of pH level with silicon nanowire sensors is repeatable only after proper rinsing of sensor surfaces and there exists trade-off between the stability and the pH sensitivity of sensor response.

The metal gate high k interaction is one of the dominant processes influencing the electrical performance (Vt, charge accumulation,..) of advanced gate stacks. These interactions are influenced by the entire thermal budget and the presence of reactive elements (on top/ within the material gate) such that relevant measurements can only be performed after a full processing cycle and on a complete gate stack.

In such cases the relevant metal gate high k interface is a buried interface located below the metal gate (+ Si cap) and is not accessible for standard characterization methods like x-ray photoemission spectroscopy (XPS) due the limited escape depth of the photoelectrons. Moreover the presence of a conductive metal gate prevents the application of techniques such as conductive atomic force microscopy (C-AFM), to probe the local distribution of the defects, trapping sites and local degradation upon stressing. XPS in combination with layer removal steps like ion beam sputtering will destroy the bonding information and is thus not applicable. Chemical etching of the metal gate stack prior to the XPS measurements requires an extremely precious control of the etching in order to stop 1-2 nm before the high k metal interface.

As an alternative we have developed a backside removal approach, that allows us to investigate using techniques such as XPS and C-AFM, the metal gate high k interface.

Cell therapy has attained new heights with the current developments in the field of stem cell therapy and is often done in combination with gene therapy. Much research has gone into developing safe vectors to deliver genes to the cells used for cell therapy and also in tracking the transplanted cells and determining their fate. Even though viral vectors are very efficient in gene delivery, there are major safety concerns related to it. Herein, we report the use of novel fluorescent upconversion nanoparticles (UCNs) for simultaneous gene delivery and tracking of cells for cell-based therapies. It is a safe alternative to viral vectors and offers imaging capabilities too, which will give an insight on the fate of transplanted cells.

Crevice-corrosion tests were performed in gamma-ray irradiated high-temperature water of 288 °C on Type 316L stainless steel. The gamma-ray dose rate was about 30 kGy h−1. Tested specimen surfaces were analyzed using SEM, laser Raman spectroscopy and TEM/EDX. Experimental data were presented in order to show the differences made by the irradiation and crevice-shape simulated structure. Both gamma-ray irradiation and crevice-shape simulated structure changed the corrosion phenomena. On the gamma-ray irradiated crevice-shape simulated surface, α-Fe2O3 particles more than 5 μm in diameter were observed. It suggested that corrosion environment on the crevice-shape simulated surface became severer by gamma-ray irradiation.

Graphene and its derivatives have attracted much attention for potential applications in biological sensing systems because of their unique 2D structural, surface and electronic properties. Reports on graphene - based electrochemical impedance biosensors are emerging rapidly. In this research, we have explored the RF (radio frequency) impedance –based sensing feasibility of graphene and graphene derivative materials on the coplanar waveguide (CPW) device. The transmission line based sensing experiments demonstrated clear and significant blueshifts of resonance frequencies and decrease of the resistance at and beyond resonance frequencies after graphene oxide is absorbed with DNA. The results may lead to an alternative approach in developing graphene based chemical and biosensors.

Semiconductor heterostructures as quantum dots or quantum rings (QR) demonstrate discrete atom-like energy level structure. In an atom the position of an electron can be changed by electromagnetic field influence with accompaniment of quantum number change. In present work we show that in the weak coupled Double Concentric Quantum Ring (DCQR), the electron jumping is possible due to tunneling accompanied with level anti-crossing which has a place in a magnetic field. We study DCQR composed of GaAs in an Al0.70Ga0.30As substrate under influence of a magnetic field. In our model the DCQR is considered within three dimensional single sub-band effective mass approach. When a magnetic field is applied in the z direction, perpendicular to the DCQR plane. The results of the numerical calculations for DCQR are presented for DCQRs of different geometry.

Using chemical vapor deposition technique, a novel 3D carbon nano-architecture called a pillared graphene nanostructure (PGN) is in situ synthesized. The fabricated novel carbon nanostructure consists of CNT pillars of variable length grown vertically from large-area graphene planes. The formation of CNTs and graphene occurs simultaneously in one CVD growth treatment. The detailed characterization of synthesized pillared graphene shows the cohesive structure and seamless contact between graphene and CNTs in the hybrid structure. The synthesized graphene-CNT hybrid has a tunable architecture and attractive material properties, as it is solely built from sp2 hybridized carbon atoms in form of graphene and CNT. Our methodology provides a pathway for fabricating novel 3D nanostructures which are envisioned for applications in hydrogen storage, nanoelectronics, and supercapacitors.

Using Scanning Spreading Resistance Microscopy and direct current-voltage measurements, a long-relaxation transport current in polycrystalline PZT films is shown to depend on the polarization direction and voltage rise rate, the latter is typical for a capacitive current. The clockwise current hysteresis is observed at any polarization of the film. We suppose that the long current relaxation is due to recharge of traps, which participate in screening of polarization charges on PZT grain boundaries. The polarization charges response to applied bias for a short time, whereas the traps response to variation of the polarization charges takes much longer time.

We measured the surface free energy of a substrate by transmission electron microscopy (TEM) using sub-millimetre-sized inkjet droplets. By employing two types of TEM grids with different surface free energies, we investigated the relationship between the surface energy and the patterns of an organic solution dried on the grids. We confirmed that the generation of the porphyrin hexamer [(H2PAC15)6TPh] patterns was affected by the surface free energy of the TEM grid.

We have developed material (Bi0.7Dy0.3FeO3)(BDFO) which exhibits the multiferroic behavior at room temperature with significant coupling in bulk as well as thin films. If these properties could be fashioned in nano rods, implementation in devices could be certainly more prominent and straight forward. We have therefore used vertically aligned arrays of silicon rods (~5 μm in length and ~ 500 nm in diameter) as base material to direct the growth of BDFO in rod form. BDFO is deposited on the surface of Si rods by using pulsed laser deposition technique. These BDFO/Si rods are then separated from the support, dispersed into propanol and transferred onto SiO2/Si substrates for testing. X-ray diffraction (XRD) results indicate presence of phase pure BDFO layer on Si rods. Saturation observed at room temperature in magnetic and ferroelectric hysteresis loops confirm the coexistence of ferromagnetic and ferroelectric properties. Change in ferroelectric polarization measured on single rod in the presence of applied magnetic field suggests the coupling behavior between two order parameters. Moreover, change in magnetic domain pattern of BDFO rods associated with applied electric field further supports the presence of coupling behavior in both ways. The vertical and lateral displacement occurring in BDFO/Si rods with applied electric field helps to confirm their piezoresponce behavior. BDFO/Si nanorods with multifunctional properties could find variety of novel device applications with flexibility and simplicity in operation. It might include single rod power generation by means of applied stress or magnetic field.

The layered oxide LiVO2 recently has received more attention due to its interesting structural and magnetic behaviors involving the two-dimensional magnetic frustration in these systems. We synthesized a series of F-doped LiVO2 samples, and reported the F-doping effect on the structure and transition temperature Tt . The samples LiVO2-x Fx (x=0, 0.1, 0.2 and 0.3) were characterized by X-ray diffraction, scanning electron microscope (SEM), differential scanning calorimetry (DSC), magnetic susceptibility and specific heat measurement. The structural analysis shows that with increasing x, the ratio of lattice parameter c/a increasing, i.e. in the a-b plane the lattice is compressed while in the c-axis direction the lattice expands. The DSC measurements show that a first-order phase transition happens at around 500 K, and the thermal hysteresis around phase transition temperature Tt increases with increasing x. Substitution of O with F ions results in a change of two dimensional characteristics and the distortion of the VO6 block in structure, which significantly influence the magnetic ordering transition temperature Tt .

Titanium aluminide based alloys are candidate materials for high temperature structural applications. They are typically alloyed with elements such as Nb, Ta, Mo, Cr and B for property enhancement. To understand the relationship between microstructure and alloy composition/processing condition, detailed models of phase equilibria in multicomponent Ti-Al based alloys are needed. In this work, we developed thermodynamic models for the phases in the Ti-Al-Cr system based on critically assessed binary models and ternary experimental data in literature, using the CALPHAD approach. Isothermal sections at 1200, 1150, 1000 and 800°C, and the liquidus projection, were calculated from the currently developed thermodynamic models; these are in satisfactory agreement with experimental data. Isopleths were calculated at specified Cr concentrations, and solidification paths were simulated under the Scheil conditions for a range of Ti-Al-Cr alloys. From the calculated phase diagrams and solidification paths, the effect of Cr on the microstructure of Ti-Al alloys can be understood.

Effects of shot peening on fatigue properties of Zr-based amorphous matrix composite containing ductile crystalline particles were investigated, and fatigue processes were analyzed and compared with those of an as-cast composite. The microstructural analysis results of the shot-peened composite surface indicated that the deformation and surface flexion were observed as the shot-peening time or pressure increased. The compressive residual stress formed on the shot-peened surface was about the half of the ultimate tensile strength, and was not varied much with shot-peening time or pressure. The fatigue limit and fatigue ratio of the shot-peened composite were considerably higher than those of the as-cast composite. This was because the compressive residual stress formed by the shot peening induced the initiation of fatigue cracks at the specimen interior, instead of the specimen surface, thereby leading to the enhanced fatigue limit and fatigue life.

Surface photovoltage of three-dimensional networks composed of fused indium phosphide (InP) nanowires is discussed. Particular emphasis is given to the dependence of surface photovoltage on the chopping frequency of light that excites the nanowire network as observed in regions which are laterally separated from the excitation. The nanowire network is modeled as a thin film to simplify numerical solutions to transport equations which aids in the interpretation of diffusion and drift of photo-generated carriers within the nanowire network.

The potential of MgO and ZrO2 as catalytically active substrates for graphene formation via thermal CVD is explored. Experimental observations show the growth of single and multi-layer graphene nano-flakes over MgO and ZrO2 at low temperatures. The graphene nano-flakes are found to anchor at step sites. Ab initio calculations indicate step sites are crucial to adsorb and crack acetylene.