Surface Structure Of Substrate Research Articles

The effects of substrate surface structure on yttria-stabilized zirconia thin films

Thin film properties can be controlled to a large degree by the substrate upon which the film is grown. The substrate surface can affect the film's crystal phase and microstructure and, thereby, many other properties. In this study, yttria-stabilized zirconia films on single crystal MgO and Al2O3 substrates with polished, ion cleaned, or milled surfaces were studied. The different substrate surfaces influenced the thin films’ microstructures and ionic conductivities. The increased roughness of the milled surfaces led to significant decreases in both the crystallinity and the ionic conductivity of the films. Ion cleaning of the substrate surface immediately before deposition did not affect the conductivity of films on MgO substrates but led to conductivity reductions by a factor of about 4 on sapphire substrates.

Influence of Thin Films Structure of Gd0.5Sr0.5CoO3 Cathode on Impedance Spectroscopy

Thin films of the perovskite Gd0.5Sr0.5CoO3 (GSCO), a cathode material, were fabricated by pulsed laser deposition methods. Two kinds of single-crystal (100) 8-mol% Y2O3 doped zirconia (YSZ) were used as substrate: with one surface polished and with both surfaces polished. GSCO thin films deposited on YSZ substrates with a polished surface had a columnar polycrystalline structure. The surface structure of the GSCO thin film was strongly affected by the substrate surface structure. The GSCO films on the unpolished YSZ were much rougher. From impedance measurements, because of the large surface contact area, the symmetrical cell with GSCO thin film deposited on YSZ with only polished one surface exhibited at a temperature of 400°C small resistances that were five times lower than the resistances of the cell which contained a GSCO thin film deposited on YSZ with both surfaces polished.

Self-organized pattern formation on silicon, stainless steel and zinc coated steel substrates

In this research, a self-organized pattern formation employing polystyrene/aluminum bilayer coatings on three different substrates was studied. Two new substrate materials, stainless steel and zinc coated steel for self-organization application were introduced. Influence of polystyrene molar mass on pattern formation was studied with five different polystyrene samples having molar masses between 27 and 247×103g/mol. Polystyrene/toluene solutions were applied onto the substrates using the spin coating technique and aluminum layer was created by chemical vapor deposition (CVD). Self-organized pattern formation was induced thermally, by heating the layered substrate/polystyrene/aluminum structures above the glass transition temperature of polystyrene. Sub-micron–micron sized wrinkles or island-like surface patterns were achieved on all substrates. The molar mass of polystyrene was found to have effect on the dimensions of the formed structures. It was also observed that the characteristic surface structure of substrates influences self-organization and thereby directs the structure formation.

Solid-state wetting on nanopatterned substrates

Abstract We review some recent results on the morphology of heteroepitaxial overlayers deposited on nanopatterned substrate surfaces. We mainly focus on modeling based on kinetic Monte Carlo (KMC) simulations. On arrays of parallel grooves or arrays of pillars, we find three main classes of states similar to those known for liquids: (i) Cassie–Baxter states, where solid islands sit on top of the substrate structure; (ii) Wenzel states, where solid islands are in contact with the bottom of the substrate; and (iii) solid imbibition (also denoted as capillary filling for parallel grooves), where the solid forms a film in the substrate surface structure. This multi-stability is controlled by the wettability parameter χ, and shape transitions exhibit hysteresis. We discuss the dynamics of the collapse of a Cassie–Baxter to Wenzel state, and the collapse of the Wenzel state to an imbibition film. We also discuss the possibility to grow crystals in the CB state on nanopatterned substrates. During growth, the crystals formed in CB state merge, leading to a continuous polycrystalline overlayer where the size of the grains is controlled by the distance between pillars.

Tetrathiafulvalene–tetracyanoquinodimethane thin films grown by physical vapor deposition: Influence of substrate structures and substrate materials

We present results on the formation of thin films of the charge transfer salts tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) prepared by physical vapor deposition on several substrates in a high vacuum. We mainly investigate the influence of the substrate materials and surface structures on the surface morphology of the thin films. The obtained results show that the surface structure of the substrate has a stronger influence on the film morphology than that of the material. In particular, we report the influence of surface nano-structure on the growth mode of TTF–TCNQ. The flat TTF–TCNQ thin films were continuously grown on both 2° off-SiO2/Si(111) and NaCl(100) substrates. The maximum conductivities of the films grown on 2° off-SiO2/Si(111) and NaCl(100) were 0.4 and 4Ω−1cm−1, respectively. With a CaF2 substrate, a large number of TTF–TCNQ nano-scale ribbon-like crystals grew on the as-deposited CaF2/CaF2(110) substrate. This indicates that we could realize a TTF–TCNQ adsorption site by depositing CaF2.

Light trapping scheme of ICP-RIE glass texturing by SF6/Ar plasma for high haze ratio

Inductive coupled plasma-reactive ion etching (ICP-RIE) offers an anisotropic texturing with superior surface structure of glass substrate. We report light trapping scheme of ICP-RIE glass texturing by SF6/Ar plasma. We observed that surface structure is an important factor to improve the diffused transmittance and haze ratio of textured glass. The presence of metal elements like Al, B, F and Na are responsible for low etching rate (22.66–27.33 nm/min) of textured glass. The total transmittance remains high whereas the diffused transmittance increased with the pattern size due to the variation of surface morphology of glass. Our textured glass substrates showed the high diffused transmittance and haze ratio in the visible-NIR wavelength region. The electrical properties of the ITO films are independent of glass surface structure that may be suitable for high performance of thin film solar cells.

The surface structure of a complex substrate revealed by enzyme kinetics and Freundlich constants for α-amylase interaction with the surface of starch

BackgroundStarch is a main source of carbohydrate in human diets, but differences are observed in postprandial glycaemia following ingestion of different foods containing identical starch contents. Such differences reflect variations in rates at which different starches are digested in the intestine. In seeking explanations for these differences, we have studied the interaction of α-amylase with starch granules. Understanding this key step in digestion should help with a molecular understanding for observed differences in starch digestion rates. MethodsFor enzymes acting upon solid substrates, a Freundlich equation relates reaction rate to enzyme adsorption at the surface. The Freundlich exponent (n) equals 2/3 for a liquid-smooth surface interface, 1/3 for adsorption to exposed edges of ordered structures and 1.0 for solution–solution interfaces. The topography of a number of different starch granules, revealed by Freundlich exponents, was compared with structural data obtained by differential scanning calorimetry and Fourier transform infrared spectroscopy with attenuated total internal reflectance (FTIR-ATR). ResultsEnzyme binding rate and FTIR-ATR peak ratio were directly proportional to n and ΔgelH was inversely related to n. Amylase binds fastest to solubilised starch and to granules possessing smooth surfaces at the solid–liquid interface and slowest to granules possessing ordered crystalline surfaces. ConclusionsFreundlich exponents provide information about surface blocklet structures of starch that supplements knowledge obtained from physical methods. General SignificanceNanoscale structures at the surface of starch granules influence hydrolysis by α-amylase. This can be important in understanding how dietary starch is digested with relevance to diabetes, cardiovascular health and cancer.

Growth direction manipulation of few-layer graphene in the vertical plane with parallel arrangement

Vertical few-layer graphene (FLG) sheets have potential applications as field emitters and super capacitors. However, it remains a challenge to controllably grow FLG with vertical and parallel orientations. We intentionally designed the substrate surface structure to manipulate the distribution of the plasma sheath and induce the direction of the built-in electric field to guide the growth direction of the FLG in two dimensions. The effects of the plasma sheath and the built-in field on the FLG growth are discussed. The electrical and field emission characteristics of single sheet FLG with parallel and random types were measured, and they demonstrate similar and good characteristics. This method provides a way to controllably grow parallel and vertical FLG arrays.

The Effects of Structure on the Formation of Schottky Barriers at Nanoparticle-Oxide Interfaces

ABSTRACTThe surface structure of oxide materials may be the limiting factor in controlling switching properties at interfaces. Here we investigate and correlate the surface structure and electronic properties of BaTiO3 substrates. By using low energy electron diffraction and scanning tunneling microscopy we are able to identify surface reconstructions based on annealing treatments. We then investigate the effect of contact size on the transport properties on oxide surfaces utilizing atomic force microscopy. Our results show the critical importance of controlling surface structure to optimize electronic properties at oxide interfaces.

Insight in cysteamine adsorption behaviors on the copper surface by electrochemistry and Raman spectroscopy

The inhibition effect of cysteamine (CA) on the corrosion behavior of copper in 3wt% NaCl solution was studied by electrochemical impedance spectroscopy (EIS), electrochemical polarization measurement and surface-enhanced Raman scattering (SERS) spectroscopy. The polarization experimental results indicate that CA acts as a mixed type inhibitor and exhibits the anticorrosive effect on copper surface with a high efficiency of 90.00%.SERS spectra of CA were measured and the relationship between SERS bands and the surface structure of SERS-active substrates was studied. The SERS investigation of CA film on the copper surface found that the conformation of the adsorbed molecules and the gauche-/trans-ratio depended on the immersion time and pH of CA solution. A majority of trans-conformers was obtained directly when the immersion time was 5h and pH of CA solution was 2.85. SERS spectra of CA combined with the electrochemical measurements explored that trans-conformer exhibited better inhibition ability.

Room-temperature heteroepitaxy of single-phase Al1 − xInxN films with full composition range on isostructural wurtzite templates

Al1−xInxN heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane AlN, GaN, and ZnO templates at room temperature (RT). Both Al1−xInxN single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AlN (~13% mismatch), heteroepitaxy is achieved. However, RT-grown Al1−xInxN films directly deposited on non-isostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al1−xInxN structural quality with increasing indium content is attributed to the formation of more point- and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al1−xInxN films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown AlN layers thanks to their low amount of defects. We found that Vegard’s rule is applicable to determine x in the RT-grown Al1−xInxN epilayers if the lattice constants of RT-sputtered AlN and InN films are used instead of those of the strain-free bulk materials.

Effect of Substrate Wettability and Surface Structure on Nucleation of Crystal

The heterogeneous nucleation behaviors of NH4Cl crystal on rough aluminum substrate surface immerged in NH4Cl-H2O solution were experimentally analyzed, and the influence mechanism of the micro/nano-scale surface structures on heterogeneous nucleation was investigated. It has been shown that wettability and nucleation are affected by substrate surface condition. The intrinsic wetting properties between nucleus and substrate surface, and the surface structure of certain geometrical scales, both impose effects on the heterogeneous nucleation properties. For a nucleus-wetting substrate surface, heterogeneous nucleation is promoted by a higher complexity of the surface morphology; but for a nucleus-nonwetting substrate surface, heterogeneous nucleation is inhibited by a higher complexity of the surface morphology.

Microdroplet evaporation on superheated surfaces

A comprehensive experimental investigation on water microdroplet evaporation is presented from the standpoint of phase-change cooling technologies. The study investigates microdroplet evaporation on a variety of different surface materials at surface temperatures ranging from 25°C to 250°C. The temporal evolution of the droplet profile and contact line dynamics are measured using high-speed photography and image analysis methods. The material systems tested consist of (1) thin-film surface coatings on glass substrates (e.g., Al, Ti, Cu, and SAMs) and (2) Cu substrates with different surface morphologies (e.g., mirror polished, 800-grit sanded, and micron-sized Cu pillar arrays). As expected, changes in surface energy influences the contact line dynamics. Changes in surface energy, however, showed no systematic influence on the evaporation efficiency. For all systems studied, the evaporation rate (m˙LG) scales linearly with the microdroplets contact radius (i.e., m˙LG∝R) and stick-slip contact line dynamics are observed. For example, the evaporation efficiency reduces after contact line depinning due to a reduction in the total length of the solid-liquid-vapor contact line, whereas, before depinning, m˙LG is a constant and directly proportional to the surface temperature, contact radius, and substrate thermal conductivity. For microdroplet evaporation on thin-film surfaces, maximum evaporation rates (m˙LGmax≅32±8μg/s) and evaporative heat fluxes (qmax≅600±100W/cm2) are observed at superheats of 70°C≲ΔT≲130°C. These maxima in the evaporative heat transfer performance signify a transition in the heat transfer process from a purely microdroplet evaporation regime to a droplet/film boiling regime (which is analogous to the critical heat flux observed in pool boiling). For microdroplet evaporation on Cu substrates, droplet/film boiling occurs at much lower superheats (e.g., 10°C≲ΔT≲25°C); yet, comparable maximum evaporation rates (m˙LGmax≅36±8μg/s) and evaporative heat fluxes (qmax≅750±150W/cm2) are observed. In short, this work suggests a reliable upper limit for the evaporation efficiency of m˙LGmax≅35±5μg/s during water microdroplet evaporation on superheated surfaces (which turns out to be independent of substrate thermal conductivity, surface structure, and surface hydrophobicity).

Comparing the growth of a molecular semiconductor on amorphous and semi-crystalline polycarbonate substrates

Polymeric substrates are of importance in plastic electronics. However, polymeric surfaces can exhibit different morphologies depending on whether they are amorphous or semi-crystalline. This work focuses on the impact of the surface structure of bisphenol A polycarbonate substrates on the nucleation and growth of a p-type semi-conductor, namely zinc phthalocyanine (ZnPc). ZnPc films were deposited under high vacuum at different substrate temperatures on oriented semi-crystalline as well as amorphous substrates of PC. The oriented substrates of PC were prepared by a method combining mechanical rubbing and solvent induced crystallization: the substrates show a periodic and regular alternation of oriented crystalline lamellae. Grazing incidence X-ray diffraction shows that the crystalline lamellae of PC have a preferential (a, c) contact plane. Moreover, the substrates show a bilayer structure made of a 60nm-thick semi-crystalline overlayer atop an amorphous underlayer. UV–vis spectroscopy shows that the polymorphism of the ZnPc films is not modified by the surface structure of the PC substrate (amorphous versus semi-crystalline). However, the statistical analysis of domain size and density versus substrate temperature Ts evidences different apparent activation energies of the growth mechanism. High Resolution Transmission Electron Microscopy suggests that twinning along a (2−10) plane accounts for the bifurcations of the in-plane b-axis direction of the ZnPc nanocrystals. On oriented substrates of PC, such bifurcations are partly suppressed by the nanocorrugation of the surface, resulting in larger apparent domain sizes and unidirectional in-plane orientation.

Pd-Modified Shape-Controlled Pt Nanoparticles Towards Formic Acid Electrooxidation

Formic acid electrooxidation on Pd-modified Pt nanoparticles with well-characterised surfaces was studied. Polyoriented and preferential (100), (100)–(111) and (111) Pt nanoparticles were used as substrate on which Pd was electrochemically deposited. The incorporation of Pd gave rise to a remarkable enhancement towards formic acid electrooxidation, which was strongly dependent of the surface structure and shape of the Pt nanoparticles substrate in a similar way to that previously shown in fundamental studies with Pt single crystal electrodes. Among the Pt nanoparticles studied, these containing a (100) preferential orientation were clearly the most active towards formic acid electrooxidation both in voltammetric and chronoamperometric experiments. These findings clearly demonstrate that the use of adatom-modified preferentially oriented Pt nanoparticles is an interesting new route in the design of new and better electrocatalytic materials.

Influence of the substrate's surface structure on the mechanism and kinetics of the electrochemical UPD formation of a copper monolayer on gold

The copper electrodeposition process was studied onto different gold substrates, single crystal (111) and polycrystalline, using electrochemical techniques. It was found, from the analysis of the experimental current density transients, that the potentiostatic formation of a full copper monolayer onto the gold electrode under UPD conditions follows the same mechanism, regardless of the crystallinity of the substrate. The mechanism involved the simultaneous presence of an adsorption process and of two 2D nucleation processes, progressive and instantaneous, respectively.

Effect of substrate structure on the performance of thin-film composite forward osmosis hollow fiber membranes

Forward osmosis (FO) membranes have gained increasingly attention due to their potential advantages for various FO-based wastewater treatment, seawater desalination and power generation. In the present study, an attempt was made to systematically investigate the effects of substrate structure on the formation of the selective layer in a two-step preparation – a phase inversion for a hollow fiber substrate followed by interfacial polymerization for the ultra-thin selective layer, and on the FO performance in non-ideal situations, i.e., the feed stream contains foulants. Experimental results revealed that the substrate surface structure is very important for fabricating a RO-like thin film. A substrate with <300 kDa MWCO is preferred to obtain a good semipermeable skin based on current study. It may not be appropriate to use DI water and a low concentration draw solution (i.e., an ideal situation) to evaluate the FO membrane, as the water permeation through the RO-like skin is the rate-determining step, and the effect of the substrate structure cannot be fully reflected in this ideal situation. In addition, the surface structure of the FO membrane facing the feed is critical as it is directly associated with the tendency of FO membrane fouling, and a relatively dense membrane substrate surface is desirable in the membrane orientation of active layer facing draw solution. An ideal FO membrane should also possess anti-fouling capability or less fouling propensity in addition to high water permeability, low salt permeability and minimized structural parameter.

Carrier lifetime, diffusion length and mobility in (100) CVD diamond samples pre-treated in an O2/H2-plasma

ABSTRACTIn this article, (100) Ib diamond substrates are pre-treated for different durations in an O2/H2-plasma, influencing the etching of defects like unepitaxial crystals, flat top hillocks, and pyramidal hillocks [1-3]. Such procedure is used to prevent those to incorporate into the ~ 100μm thick CVD diamond film, which is subsequently grown on top. While the surface morphology and structure of substrates and films are studied by SEM, the time-resolved Light-Induced Transient Grating (LITG) technique provides information on the excess carrier parameters close to the front surface of the grown layers. This technique is particularly useful as it does not requires a separation of the CVD film from its substrate. It will be shown that O2/H2-plasma treatments of more than 150 minutes but less than 240 minutes largely reduce the incorporation of defects in the bulk of the grown film. This, in turn, influences the carrier dynamics as measured by LITG, but also the surface roughness and growth rate as shown by SEM.

Fomitopsis palustris의 균체 외 효소에 의한 볏짚 당화에 관한 연구

갈색부후균인 Fomitopsis palustris에서 균체 외 cellulase 생산 특성과 이 효소를 이용하여 목재와 볏짚의 당화특성, mediator 첨가 효과, 목질기질의 미세 표면구조나 결정화도가 효소 당화에 미치는 영향 등에 대해 연구하였다. F. palustris의 균체 외 효소의 생산에 혼합목분을 탄소원으로 이용 시 endo-<TEX>${\beta}$</TEX>-1,4-gulcanase (EG)는 12.0 U/<TEX>$m{\ell}$</TEX>, <TEX>${\beta}$</TEX>-glucosidase (BGL)는 116.68 U/<TEX>$m{\ell}$</TEX>, cellobiohydrolase (CBH)는 18.82 U/<TEX>$m{\ell}$</TEX>, 그리고 <TEX>${\beta}$</TEX>- xylosidase (BXL)는 13.33 U/<TEX>$m{\ell}$</TEX>의 활성을 보였다. 이러한 활성은 BGL, CBH, 그리고 BXL이 볏짚을 이용한 경우보다 약 2~4배 정도 높았다. 볏짚을 탄소원으로 이용하여 생산한 cellulase-RS의 효소 최적반응 온도 및 pH는 <TEX>$45^{\circ}C$</TEX>와 pH 5.0이었으며, 혼합 목분을 탄소원으로 이용하여 생산한 cellulase-SW의 경우에는 <TEX>$50^{\circ}C$</TEX>와 pH 5.0이었다. Cellulase-SW는 볏짚을 기질로 사용할 때 <TEX>$40.6{\pm}0.6%$</TEX>로 가장 높은 당화율을 보였다. 또한 당화촉매제인 Tween 20의 첨가로 당화율이 44%로 상승하여 상용화 효소인 Celluclast 1.5L의 53.7%의 당화율 대비 약 82% 수준으로 상승되었다. 이는 본 실험에서 사용한 효소가 조효소 형태임을 고려하면 상용화 효소에 매우 근접한 당화율을 얻은 것으로 판단된다. 또한 볏짚의 낮은 조직 결정화도와 주사전자현미경을 이용한 볏짚 표면의 섬유화를 통한 표면적 증대 효과는 목재에 비해 높은 볏짚의 당화율에 대한 원인을 제시하였다. In the enzymatic hydrolysis of rice straw and wood meals using extra-cellular enzymes from Fomitopsis palustris, key factors which enhanced the sugar conversion yield were investigated in this work, such as enzyme production and enzyme reaction conditions, surfactant effects, and the surface structure of substrates. F. palustris cultured with softwood mixture produced 12.0 U/<TEX>$m{\ell}$</TEX> for endo-<TEX>${\beta}$</TEX>-1,4-gulcanase (EG), 116.68 U/<TEX>$m{\ell}$</TEX> for <TEX>${\beta}$</TEX>-glucosidase (BGL), 18.82 U/<TEX>$m{\ell}$</TEX> for cellobiohydrolase (CBH), and 13.33 U/<TEX>$m{\ell}$</TEX> for <TEX>${\beta}$</TEX>-xylosidase (BXL). These levels of BGL, CBH, and BXL activities were two to four folds more than enzyme activities of F. palustris cultured with rice straw. The optimum reaction conditions of cellulase-RS which produced by F. palustris with rice straw and cellulase-SW which produced by F. palustris with softwood mixture were pH 5.0 at <TEX>$45^{\circ}C$</TEX> and pH 5.0 at <TEX>$50^{\circ}C$</TEX>, respectively. The sugar conversion yield of cellulase-SW had the highest value of <TEX>$40.6{\pm}0.6%$</TEX> within 72 h when rice straw was used as substrate. By adding 0.1% Tween 20 (w/w-substrate), the sugar conversion yield of rice straw was increased to 44%, which was about four fifths sugar conversion yield of commercial enzyme, Celluclast 1.5L (Novozyme A/S). A low crystallinity and an intensive fibril surface observed by the scanning electron microscope may explain the high sugar conversion yield of rice straw.

Nanoscale metal-silicide films prepared by surfactant sputtering and analyzed by RBS

Surfactant sputtering has been applied to modify the surface structure of Si substrates and to produce ultrathin metal-silicide films with nickel and platinum surfactants, utilizing the steady state coverage of a Si-substrate surface with surfactant atoms simultaneously during sputter erosion by combined ion irradiation and surfactant atom deposition. Si (1 0 0) substrates were eroded using 5 keV Xe-ions and 10–30 keV Ar ions at incident angles of 65° and 70° with fluences of up to 2 × 10 18 /cm 2 under continuous sputter deposition of platinum and nickel from targets irradiated simultaneously by the same ion beam. These surfactant atoms form metal-silicides in the surface near region and strongly modify the substrate sputter yield and the surface nanostructure. Atomic force microscopy and scanning electron microscopy were carried out to observe a transition of surface topography from ripple to relief patterns, granular patterns or smooth surfaces. The Si and metal sputter yield as function of the steady state metal coverage were determined by combination of Rutherford-backscattering spectroscopy (RBS) and profilometry. The composition and the depth distributions of metal-silicide films were analyzed via high-resolution RBS and transmission electron microscopy. We show that RBS results in comparison with SRIM and TRIDYN sputter yield simulations allows us to identify the silicide surface structure on the nanometer scale.