Effect Of Surface Impurities Research Articles

Effect of surface impurities on downconversion luminescence of Pr3+, Yb3+ activated SrF2 nanoparticles

Pr3+,Yb3+ activated SrF2 nanoparticles synthesized by low-temperature hydrothermal method were studied. The composition and size of nanoparticles were intentionally changed by controlling synthesis conditions. After structural and morphological characterization, the spectroscopic properties of the nanoparticles were analyzed in the visible and near infrared spectra ranges. The results show correlation between the gradual change of the amount of carboxylate and hydroxyl moieties on the nanoparticle surface, varied by the size nanoparticles and the quenching of the luminescence. The size-related amount of surface quenchers is strongly connected to the decrease of the downconversion efficiency.

Kinetic model and effect of surface impurities on the crack healing of BK7 glass

When BK7 glass material is heated under appropriate conditions, surface cracks heal spontaneously under the action of viscous flow and capillary forces. In this paper, based on the theories of viscous fluid and capillary flow, a kinetic model for crack healing is established. A series of thermal healing experiments with different parameters are conducted on Vickers indentation radial cracks on BK7 glass, and the effects of surface impurities, heating temperature, crack size, and ambient humidity are studied. The results show that the surface impurities and humidity can promote crack healing. Upon combining the experimental results and relevant theories, the initial kinetic model is modified to accurately predict the healing process of the BK7 glass and describe the relationships among the crack healing length and these factors. In addition, the proposed model can be used for the healing of other materials with the mechanism of viscous capillary flow.

Impurity effect on surface states of Bi (111) ultrathin films**Project supported by the National Basic Research Program of China (Grants Nos. 2015CB921400 and 2011CB921802) and the National Natural Science Foundation of China (Grants Nos. 11374057, 11434003, and 11421404).

The surface impurity effect on the surface-state conductivity and weak antilocalization (WAL) effect has been investigated in epitaxial Bi (111) films by magnetotransport measurements at low temperatures. The surface-state conductivity is significantly reduced by the surface impurities of Cu, Fe, and Co. The magnetotransport data demonstrate that the observed WAL is robust against deposition of nonmagnetic impurities, but it is quenched by the deposition of magnetic impurities which break the time reversal symmetry. Our results help to shed light on the effect of surface impurities on the electron and spin transport properties of a 2D surface electron systems.

Effects of surface impurities on epitaxial graphene growth

The focus of this report is to explore the large scale growth of graphene on Ru(0001) and verify the possible effects of crystallographic defects and impurities in the quality of the synthesized material. After a Low Pressure Chemical Vapor Deposition (LP-CVD) process we obtained a graphene film accompanied by other types of graphitic structures. Impurities on the ruthenium surface behaved as nucleation sites in the formation of carbon islands several micrometers wide. The morphological structure of these islands is constituted by carbon discs with diameters in the range of few to several hundred nanometers and thicknesses always below 1nm.

The effect of surface impurities on photovoltaic panels

This paper deals with the surface impurities that occur onto operating solar cells, a widespread problem. The depositions on the photovoltaic cells, represented by dust and dirt which appear inevitably, lead to deterioration over time or to the decrease of efficiency of the panels that contain the affected cells, and as a result there are losses that appear in the system. Some local depositions create shady areas, causing significant overheating which is experimentally highlighted..

Effect of Surface Impurities on Oscillation in NO+CO/Pt(100) Reaction System

A lattice gas model was proposed to explore the effect of inert surface impurities on the oscillation in the NO+CO reaction system on Pt(100). It was found that when the fraction of the impurities is small, the (11) phase resulting from the surface restructuring can form a connected phase and the system exhibits a global sustained oscillation. With the fraction of the impurities increasing, the (11) phase only can form many isolated patches and the spatial coherence between the local oscillators with a random phase relationship lost, and as a result, the sustained oscillation changes into a damped one. When the diffusion rate of adsorbed CO and NO increases, the synchronization between local oscillators is enhanced and the global sustained oscillation can appear again.

Effect of Surface Impurities on the Microstructure Development during Sintering of Alumina

Microstructural evolution during sintering of alumina powder compacts prepared by cold isostatic pressing (CIP) was monitored. For CIP, rubber molds lubricated with silicone oil were used so that a very small amount of impurity was introduced to the surface of the powder compacts. During sintering at 1600°C, grain growth in the surface region was inhibited up to sintering for 1 h, but subsequently abnormal grain growth occurred. In the inner region, however, the grains grew uniformly without abnormal grain growth. Impurities that initially drag the boundary migration but form liquid at the end are suggested to cause abnormal grain growth.

Effects of Surface Impurities on the Reactivity of Metallic Lithium toward Propylene Carbonate

Changes in the reactivity of Li toward gas-phase propylene carbonate (PC) induced by the presence of a small amount of Li oxide or Li carbonate as a Li surface impurity have been examined in ultrahigh vacuum by infrared (IR) reflection absorption spectroscopy. Whereas the presence of Li 2 O simply attenuates the intensity of IR features characteristic of the corresponding alkoxide found upon exposure of clean Li to PC, small quantities of Li 2 CO 3 on Li led to the formation of detectable amounts of the Li alkyl carbonate derivative. Implications of these results to the interpretation of data obtained in situ for Li electrodes in electrochemical environments are discussed.

Effect of surface impurities on the Cu/Ta interface

Auger electron spectroscopy and temperature programmed desorption studies under ultra-high vacuum conditions demonstrate that even sub-monolayer coverages of oxygen or carbide on polycrystalline Ta significantly degrade the strength of Cu/Ta chemical interactions, and affect the kinetics of Cu diffusion into bulk Ta. On clean Ta, monolayer coverages of Cu will de-wet only above 600 K. A partial monolayer of adsorbed oxygen (3 L O 2 at 300 K) results in a lowering of the de-wetting temperature to 500 K, while saturation oxygen coverage (10 L O 2, 300 K) results in de-wetting at 300 K. Carbide formation also lowers the de-wetting temperature to 300 K. Diffusion of Cu into the Ta substrate at 1100 K occurs only after a 5-min induction period at this temperature. This induction period increases to 10 min for partially oxidized Ta, 15 min for carbidic Ta and 20 min for fully oxidized Ta.

Super strong effect of surface impurities on the resistance and Hall effect of quench condensed Cs films

Thin films of Cs, quench condensed onto a He cold quartz plate, possess electronic mean free paths which considerably exceed the film thicknesses. When theses films are covered in situ with sub monolayers of Au, Ag, In, Rh and Pb in the range between 0.01 and 1 monolayers the film resistance and the Hall constant increase dramatically. This corresponds to a scattering cross section of the surface impurities which is larger than 1 in units of Various models are explored to explain these unusual behavior. None yields a satisfactory explanation for this extremely strong effect of surface impurities on the resistance and the Hall effect.

Effects of surface impurities on surface diffusion of CO on Ni(110)

A small amount of coadsorbed impurity species could significantly alter the surface diffusion of CO on Ni(110). Three impurity species, sulfur, oxygen, and potassium are studied here. The former two are known as ``poisons'' and the latter as a ``promoter'' for CO hydrogenation on Ni. All three are found to impede CO diffusion drastically. The apparent diffusion activation energy ${E}_{D}$ increases from the clean-surface value of 2--3 kcal/mol, to a saturation value of 7--8 kcal/mol at sufficiently high impurity coverages. The impeding effect decreases from S to O to K. Mechanisms responsible for the effect are discussed in detail. With S and O, the impurity-covered step-controlled diffusion appears to be the dominant mechanism. With K, the nearest-neighbor attractive interaction between CO and K seems to be most important.

Surface melting of small particles, and the effects of surface impurities

This paper considers three situations in which surface melting may occur on small particles. The first is of small particles embedded in an inert matrix, where the surface melting is driven by a reduced surface energy of the liquid phase. We discuss the nature of the melting transition as the solid particle is warmed to the bulk melting point, and we show that the region over which the particle exists in a mixed solid-liquid phase becomes smaller as the particle is reduced in size. Secondly, we consider the effects of this surface layer on the stability of a particle if the particle was in the presence of its vapour, and show that this is essentially unaffected by the layer, though the amount of supersaturation needed to nucleate from the vapour phase is substantially smaller when surface melting is present. Thirdly, we show that even when the surface energy is unfavourable, surface melting may be driven by impurities in the liquid phase, and as in the first case we consider the nature of the phase transitions, and how it scales with the particle size.

Effect of surface impurities on the permeation of hydrogen through iron

The permeation of hydrogen through metal membranes can be strongly affected by surface impurities for conditions where surface processes dominate over bulk diffusion. Hydrogen permeation was measured in both the surface-limited and diffusion-limited regimes between 300 and 700 K using a membrane technique. Molecular hydrogen (1×10−3–3×104 Pa) was used to determine the membrane permeability and the overall surface-limited permeation rate constant. Atomic hydrogen (3×1015–2×1019 H0/m2 s) incident on either side of the membrane was used to determine the contribution of each surface to the overall surface-limited permeation rate. Impurity concentration on one of the membrane surfaces was monitored in situ with an Auger electron spectrometer. This same surface could also be sputter-cleaned by argon ions. Removal of surface carbon, oxygen, and sulphur had no measurable effect on the diffusion-limited permeation, but increased the surface-limited permeation rate constant by orders of magnitude.

Effect of surface impurities on the hydrogen recombination coefficient of first-wall materials

The “hydrogen recombination coefficient” k R was evaluated for such metals as stainless steel, vanadium and nickel from experimental data of the permeation rate of ion- and gas-driven hydrogen isotopes. The measured values of k R were found to decrease with increasing the surface concentration of certain impurity elements; oxygen for stainless steel, sulfur for vanadium and nickel as was determined by Auger electron spectroscopy. They were also compared to theoretical models and the role of surface impurities on the hydrogen recombination process was discussed with respect to these models.

ChemInform Abstract: Effects of Surface Impurities in Chemisorption and Catalysis

ChemInform Abstract: Effects of Surface Impurities in Chemisorption and Catalysis

A description of the high-pressure ammonia synthesis reaction based on surface science

A kinetic description is given of the high-pressure ammonia synthesis reaction over a Fe based catalyst. The description is based on a statistical mechanical treatment of the competitive adsorption of the reactants, intermediates, and product on identical surface sites. The kinetic expression with parameters taken from ultrahigh vacuum for the reactants on single-crystal surfaces is able to describe the observed ammonia kinetics for an industrial catalyst over a very broad range of conditions (1–300 atm, 375–500 °C). This provides a direct verification that the ‘‘pressure gap’’ between surface science and heterogeneous catalysis can be bridged. Further, the present description gives a detailed picture of the working catalyst. Variations in surface coverages down through the reactor bed and the origin of the activation enthalpy of the overall reaction are discussed. We also show that the microscopic picture of poisoning and promotion whereby the effect of surface impurities is to stabilize or destabilize the adsorbing molecules can account quantitatively for the observed promotion and poisoning of the high-pressure ammonia synthesis by potassium and water, respectively.

Effect of surface impurities and argon sputtering on deuterium permeation of nickel

To clarify the effect of surface impurities upon hydrogen isotope permeation through nickel, the deuterium permeation rate of variously treated nickel was measured in the pressure range of 3 × 10 −4 to 2 × 10 −1 Pa at 673 K. Surface segregation of sulfur proceeded during a thermal anneal at ∼ 673 K as was identified with in-situ AES analysis. Even in this low pressure range, the permeation rate of nickel obeyed Richardson's equation: the rate-limiting step is bulk diffusion. Neither carbon nor sulfur on the surface significantly affected the steady state permeation rate, which is different from the case for vanadium. On the other hand, argon ion sputtering decreased the deuterium permeation rate of nickel. This decrease in permeation rate can be recovered to some extent by an anneal at ∼ 673 K. Such behavior is probably attributable to some sort of irradiation damage produced during argon ion sputtering.

Effect of surface impurities on low-energy implanted-ion depth distributions

The depth distributions of 80-eV ${\mathrm{D}}^{+}$ implants in W (110) have recently been measured by field-desorption microscopy. Prominent structure, consisting of seven major and several minor peaks, is observed in the measured distributions. This contrasts with conventional implantation theory which predicts two peaks, one for the channeled ${\mathrm{D}}^{+}$ and one for the nonchanneled ${\mathrm{D}}^{+}$. The observed structure is explained in the present work by a model which ascribes the various peaks to ${\mathrm{D}}^{+}$ groups which have been scattered into planar channels by the surface impurities. The model allows a determination of ${\mathrm{D}}^{+}$ stopping powers in the various planar channels and the stopping power of C and O impurities which recoil down the $〈110〉$ axis. These are the first stopping-power values obtained in this energy region. The model suggests that surface location of the impurities as well as their elastic scattering cross section for ${\mathrm{D}}^{+}$ projectiles could be extracted from more elaborate calculations and experiments.

Effect of surface impurities on radiation-induced changes in MOS structures

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Effect of Surface Impurities on Tracer Diffusion in Insulators

In self-diffusion experiments performed on insulators in which a radioactive tracer is deposited as a thin source, heterovalent impurities, initially present on the sample surface or in the tracer solution, may diffuse into the sample along with the tracer. This effect may be important, even for very small amounts of impurity, since each heterovalent ion entering the lattice automatically introduces one or more extrinsic vacancies to maintain charge neutrality. If the extrinsic-vacancy concentration is comparable to the thermal-equilibrium concentration, this effect can cause a marked deviation from the expected Gaussian behavior. A model is developed for iteratively solving the nonlinear diffusion equation for the case of an unknown divalent impurity co-diffusing with a monovalent tracer in an alkali-halide lattice. The solutions show a strong curvature in the tracer profiles, the amount of curvature depending on the amount and relative diffusivity of the impurity, and on the diffusion time. The model permits fairly precise determination of the "true" tracer diffusion coefficient and approximate values for the concentration and diffusivity of the impurity. Experimental results are presented which show good agreement between the predicted time dependence of the model and experiment for "carrier-free" ${\mathrm{Na}}^{22}$ diffusing in NaCl.