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Charge recombination at the electrolyte–photoanode interface of a dye sensitized solar cell (DSSC) is a major efficiency-limiting factor of the cell. To mitigate this recombination effect it is necessary to ensure that the effective electron lifetime in the DSSC is longer than the electron’s transit time across the photoanode of mesoporous TiO2. While the efforts aimed at accomplishing this goal are often based on new materials/designs of photoanodes, a quantitative evaluation of these designs relies on the precision of the benchmarking measurements of electron lifetimes. The open circuit voltage decay (OCVD) technique offers an effective yet straightforward method for such measurements. The present work focuses on certain experimental criteria for ensuring the accuracy of these experiments, and probes the associated effects of temperature variations in the solar cell. The results demonstrate that, a high rate of data sampling is essential for adequately resolving the fast initial stages of charge recombination. The results also show the effects of nonlinear recombination where second order OCV variations are operative. The findings of the OCVD experiments are compared with a parallel set of tests carried out using impedance spectroscopy. The relative roles of the two sets of analytical measurements are examined.

The diode ideality factor ( m ) and the series resistance ( R s ) of a Si solar cell represent two critical performance-indicator parameters of the device. Since both m and R s are functions of voltage ( V ) and temperature ( T ), simultaneous electrical measurements of these parameters under variable conditions of V and T can often be difficult with traditional direct current (D.C.) techniques. Using the electro-analytical method of linear sweep voltammetry (LSV) and a commonly available Si solar cell, we explore these specific confines of such D.C. measurements. The results are compared with those obtained from a parallel set of alternating current (A.C.) measurements using impedance spectroscopy (IS). LSV provides the main D.C. parameters (open circuit voltage, short circuit current, fill factor, and efficiency) of the cell, but is limited in terms of independently measuring m and R s beyond strong forward biased conditions. The IS approach is free of the latter experimental constraints, and at the same time can provide several other important electrical parameters of the solar cell. Specifically, IS detects the presence of a low-high (p–p + ) junction at the back surface of the cell, and serves as an efficient probe of certain electrical characteristics of this junction.

Nonvolatile and nonflammable ionic liquids (ILs) have distinct thermal advantages over the traditional organic solvent electrolytes of lithium ion batteries. However, this beneficial feature of ILs is often counterbalanced by their high viscosity (a limiting factor for ionic conductivity) and, sometimes, by their unsuitable electrochemistry for generating protective layers on electrode surfaces. In an effort to alleviate these limiting aspects of ILs, we have synthesized a PEGylated imidazolium bis(trifluoromethylsulfonyl)amide (bistriflamide) IL that exhibited better thermal and electrochemical stability than a conventional electrolyte based on a blend of ethylene carbonate and diethyl carbonate. The electrochemical performance of this IL has been demonstrated using a cathode consisting of ball-milled LiMn2O4 particles. A direct comparison of the ionic liquid electrolyte with the nonionic low-viscosity conventional solvent blend is presented.

Chemical mechanical planarization (CMP) of Ru barrier lines is expected to become a critical processing step in the fabrication of the new interconnect-structures. However, due to its noble metal characteristics, Ru induces galvanic corrosion in its adjacent Cu lines in the wet CMP environment, and resists chemical surface modifications that are necessary to support CMP. The present work reports a slurry formulation to address these challenges of Ru-CMP, and explores the considerations for residual Cu removal using the same slurry. This alkaline (pH = 10) slurry with colloidal silica abrasives uses sodium percarbonate as an oxidizer/complexing agent in the CMP of both Ru and Cu. L-ascorbic acid is employed as a surface modifier to regulate the material removal rates of CMP, and benzotriazole is used to control galvanic corrosion of the Ru-Cu couple. With this slurry, wafer polish rates of ∼10 and ∼80 nm min −1 are measured for Ru and Cu, respectively, resulting in defect-free processed samples. Electrochemical measurements ofopencircuit potentials, potentiodynamicpolarization and impedancespectroscopy areperformedto investigatethedetailed surface reactions of Ru and Cu that facilitate material removal and control corrosion during the CMP of these metals.

We investigated the thermophysical and electrochemical properties of eight model protic ionic liquids (PILs) primarily because of our interest in their proton conductivity and low volatility. The chemical structures of the cations (ammonium vs imidazolium) and anions (mesylate vs triflate) were found to strongly govern properties such as density, viscosity, ionic conductivity, thermal and electrochemical stability, and phase transition behaviors. Structure–property relations were analyzed on the basis of charge delocalization, cation π-stacking, van der Waals interactions of alkyl tails, and hydrogen bonding interactions between cations and anions. The diffusion coefficients of the free proton, the cation, and the anion were determined by using NMR spectroscopy, and were used to differentiate between the vehicular and Grotthuss mechanisms of diffusion of protons. A correlation, based on the Sutherland–Einstein equation, was developed to predict ionic conductivity by using the room temperature molar volume...

In the fabrication of integrated circuits, certain steps of materials processing involve chemical mechanical planarization (CMP) of Al deposited on thin layers of diffusion barrier materials like Ta/TaN, Co, or Ti/TiN. A specific example of this situation is found in the processing of replacement metal gates used for high-k/metal-gate transistors. Since the commonly used barrier materials are nobler than Al, the Al interface in contact with the barrier can become prone to galvanic corrosion in the wet CMP environment. Using model systems of coupon electrodes and two specific barrier metals, Ta and Co, the present work investigates the electrochemical factors responsible for these corrosion effects in a moderately acidic (pH = 4.0) abrasive-free solution. The techniques of cyclic voltammetry and impedance spectroscopy are combined with strategic measurements of galvanic currents and open circuit potentials. l -ascorbic acid (AA) is employed as a surface modifying agent for controlling galvanic corrosions of Al in the Ta–Al and Co–Al bimetallic combinations. The results elaborate the chemical and electrochemical mechanisms responsible for activating and suppressing the corrosion processes in these systems.

Electrochemical and photo-electrochemical systems, often involving solid-liquid interfaces, have traditionally dominated the field of material/device characterization using electro-analytical tools such as linear sweep voltammetry (LSV) and impedance spectroscopy (IS). Recent developments in these measurement techniques have broadened their applications to various studies of non-electrochemical solid state systems. The present work provides further experimental illustration of these latter utilities of LSV and IS through a detailed study of the temperature and voltage sensitive features of the minority carrier lifetime, series resistance and back surface field (BSF) parameters of a mono-crystalline Si solar cell. Apart from displaying their characteristic temperature dependencies, the measured parameters respond to variations in the cell voltage, and exhibit certain mutually interacting features of the observed effects. The results also demonstrate how the characteristic features of charge recombination in the quasi-neutral and space charge regions of the solar cell can be resolved with D.C. voltage dependent A.C. impedance measurements.

Chemical mechanical planarization (CMP) of tantalum nitride is an essential step of material processing in the fabrication of integrated circuits. This CMP step often involves the chemical formation of a structurally weak oxide-complex film on the wafer surface, followed by selective removal of the film with mechanical abrasion under reduced loading. The present work investigates certain chemical aspects of this strategy of TaN-CMP by using guanidine carbonate (GC) as a surface complexing agent, and employing electrochemical experiments. The experiments are designed to study the chemical and electrochemical origins of the CMP-specific surface complex films formed on a TaN wafer in acidic solutions of GC and hydrogen peroxide. Open circuit potential, polarization resistance, and electrochemical impedance measurements are employed to probe the surface effects that facilitate material removal in chemically prevailing CMP of TaN. The results are discussed in view of designing slurry variables to support barrier layer planarization with reduced roles of mechanical abrasion.

The fabrication of interconnect structures for semiconductor devices requires low down-pressure chemical mechanical planarization (CMP) of Ta barrier layers. Guanidine carbonate (GC) serves as an effective surface-complexing agent for such CMP applications, where the rate of Ta removal can be chemically controlled through pH-tuned selectivity with respect to the removal of Cu lines. Electrochemical techniques are employed in this work to study the surface-modifying roles of GC that make this chemical an attractive complexing agent for Ta CMP. In addition, the effects of including H2O2 (an oxidizer) and dodecyl benzene sulfonic acid (DBSA, a dissolution inhibitor for Cu) in GC-based CMP solutions are investigated to examine the selective CMP mechanisms of Ta and Cu in these solutions. The results suggest that the removal of Ta is supported in part by structurally weak guanidinium–tantalic-acid surface complexes formed on Ta/Ta2O5. The bicarbonate/carbonate anions of GC also facilitate Ta removal through the generation of ion-incorporated tantalum pentoxide. DBSA strongly affects the CMP chemistry of Cu, but exhibits relatively weaker effects on the surface activity of Ta, and thus plays a vital role in dictating the selectivity of Ta:Cu polish rates.

A series of semi-inclusive deep-inelastic scattering measurements on deuterium, helium, neon, krypton, and xenon targets has been performed in order to study hadronization. The data were collected with the HERMES detector at the DESY laboratory using a 27.6 GeV positron or electron beam. Hadron multiplicities on nucleus A relative to those on the deuteron, R_A^h, are presented for various hadrons (\pi^+, \pi^-, \pi^0, K^+, K^-, p, and \bar{p}) as a function of the virtual-photon energy \nu, the fraction z of this energy transferred to the hadron, the photon virtuality Q^2, and the hadron transverse momentum squared p_t^2. The data reveal a systematic decrease of R_A^h with the mass number A for each hadron type h. Furthermore, R_A^h increases (decreases) with increasing values of \nu (z), increases slightly with increasing Q^2, and is almost independent of p_t^2, except at large values of p_t^2. For pions two-dimensional distributions also are presented. These indicate that the dependences of R_A^{\pi} on \nu and z can largely be described as a dependence on a single variable L_c, which is a combination of \nu and z. The dependence on L_c suggests in which kinematic conditions partonic and hadronic mechanisms may be dominant. The behaviour of R_A^{\pi} at large p_t^2 constitutes tentative evidence for a partonic energy-loss mechanism. The A-dependence of R_A^h is investigated as a function of \nu, z, and of L_c. It approximately follows an A^{\alpha} form with \alpha \approx 0.5 - 0.6., Comment: 33 pages, 12 figures

We have measured the neutron structure function g$_{2}^{n}$ and the virtual photon-nucleon asymmetry A$_{2}^{n}$ over the kinematic range $0.014\leq x \leq 0.7$ and $1.0 \leq Q^{2} \leq 17.0$ by scattering 48.3 GeV longitudinally polarized electrons from polarized $^{3}$He. Results for A$_{2}^{n}$ are significantly smaller than the $\sqrt{R}$ positivity limit over most of the measured range and data for g$_2^{n}$ are generally consistent with the twist-2 Wandzura-Wilczek prediction. Using our measured g$_{2}^{n}$ we obtain results for the twist-3 reduced matrix element $d_{2}^{n}$, and the integral $\int$g$_{2}^{n}(x)dx$ in the range $0.014\leq x \leq 1.0$. Data from this experiment are combined with existing data for g$_{2}^{n}$ to obtain an average for $d_{2}^{n}$ and the integral $\int$g$_{2}^{n}(x)dx$.

Azimuthal asymmetries in exclusive electroproduction of real photons are measured for the first time with respect to transverse target polarisation, providing new constraints on Generalized Parton Distributions. From the same data set on a hydrogen target, new results for the beam-charge asymmetry are also extracted with better precision than those previously reported. By comparing model calculations with measured asymmetries attributed to the interference between the deeply virtual Compton scattering and Bethe-Heitler processes, a model-dependent constraint is obtained on the total angular momenta carried by up and down quarks in the nucleon., 24 pages, 10 figures, 2 tables; 1 figure,3 references added, slight text change

A collection of student and intern research papers from Stanford Linear Accelerator center dealing with accelerator physics, crystal structure, BABAR, the GLAST mission, etc.

We have measured the spin structure functions g2p and g2d and the virtual photon asymmetries A2p and A2d over the kinematic range 0.02 < x < 0.8 and 1.0 < Q^2 < 30(GeV/c)^2 by scattering 38.8 GeV longitudinally polarized electrons from transversely polarized NH3 and 6LiD targets.The absolute value of A2 is significantly smaller than the sqrt{R} positivity limit over the measured range, while g2 is consistent with the twist-2 Wandzura-Wilczek calculation. We obtain results for the twist-3 reduced matrix elements d2p, d2d and d2n. The Burkhardt-Cottingham sum rule integral - int(g2(x)dx) is reported for the range 0.02 < x < 0.8., 12 pages, 4 figures, 1 table

In high-energy proton-proton collisions, the mean charged multiplicity M in the central region, associated with a high-PT hadron trigger at 90°, shows a linear dependence on both ln s and PT. M is measured to depend on the type (π±, K±, p or p) of the idenfied high-PT trigger particle.

We have measured the value of the correlation R (h 1 , h 2 ) between two identified charged hadrons ( h = π ± , K ± , p or p ) produced in pp collisions at the CERN ISR. One hardon was produced in the forward direction and the other at a large angle. Quantum number dependent effects have been observed.

A measurement of backward photoproduction of omega mesons on protons is reported. Data are presented which show a dip in the differential cross section at u = −0.15 (GeV/ c ) 2 and an s dependence which varies strongly with u . The s dependence suggests an incoherent sum of a Regge and a parton term and differential cross sections for the two components are presented.

A measurement of backward photoproduction of charged pion pairs on protons is reported. The pion pair mass spectrum shows strong ϱ ° and f production. Data are presented on the u and s dependence for ϱ O and f, together with the decay polarisation for the ϱ O .

The charged multiplicity density M , associated with identified charged hadrons up to 3.0 GeV/ c in p T , is presented at ISR energies from 23.4 to 63.4 GeV and at 3 laboratory angles, as a function of pseudorapidity and azimuth.

A search for narrow resonances produced in pp collisions at the CERN ISR has been carried out using two magnetic spectrometers to measure and identify two-final-state charged hadrons. The resultant two-particle invariant mass spectra show no strong structure suggesting any new narrow resonance. The statistical significance of various enhancements seen in the data is discussed, and upper limits on the cross section times branching ratio for new particle production are presented.