Size Of Surface Features Research Articles

Light-trapping effects and dye adsorption of ZnO hemisphere-array surface containing growth-hindered nanorods

Textured ZnO hemisphere-array films which consist of growth-hindered ZnO nanorods with different length are fabricated on ITO glass substrates and used for solar cell applications. The fabrication process includes formation of ZnO seed, self-assembled polymeric hollow particles as nanosphere mask, growth of ZnO nanorods, and removal of nanosphere mask. Fixing the nanosphere mask on the substrate and controlling the interstices size between adjacent spheres are very important to the fabrication of ZnO nanorods at selective sites. The surface roughness, feature size and shape of the hemisphere pore can be tuned by changing the ZnO rod-growth time and the nanosphere size. Compared with smooth ZnO films made by the electrochemical deposition process, the light-trapping effect of ZnO hemisphere-array film is proven by the decrease in the transmittance and reflectance. The energy-dispersive X-ray (EDX) spectrometry and scanning electron microscopy (SEM) images reveal that the amount of adsorbed N719 dye increased after the O 2 plasma treatment. The hemisphere-array surface texture enhances the light-trapping effects and increases the interface area. The performance of dye-sensitized solar cells is improved by introducing the ZnO hemisphere-array surface and the O 2 plasma treatment.

Role of surface chemistry and topology of chemoselectively tailored embossed films on shear adhesion

Surface topology has been shown to play a crucial role in the adhesive ability of gecko-inspired, embossed films. Herein, we report the use of Pattern Replication In Non-wetting Templates (PRINT) to design micro- and nano-embossed films in order to explore the relationship between surface chemistry, feature size, feature geometry, and shear adhesion. Ketone-containing elastomers were synthesized from various amounts of poly(ethylene glycol) diacrylate, 2-hydroxyethyl methacrylate, and 2-(methacryloyloxy)ethyl acetoacetate. Due to the presence of the ketone, elastomer functionalization was demonstrated with various oxyamine-, hydrazine-, and hydrazide-terminated ligands. Films were also shown to be non-cytotoxic for future applications in biomedically related fields. This system may allow for the design of flexible adhesives that can be selectively tailored for a range of applications.

Model experiments to mimic fracture surface features in metallic glasses

The vein-like fracture surface features which occur in metallic glasses have been modeled via experiments in which a thin layer of grease is tested in tension. The effects of layer thickness, substrate shape, viscosity of the grease layer, and stress state on the fracture surface features are investigated. The trend discovered in the relationship between the viscosity of the viscous layer and the fracture surface feature size in the model experiments is consistent with what is found in metallic glasses.

Is Surface Roughness a “Scapegoat” or a Primary Factor When Defining Particle−Substrate Interactions?

Extended DLVO interaction potentials were determined for spherical particles approaching nanopatterned substrates using the numerical surface element integration (SEI) technique. In most cases, nanopatterned ("rough") surfaces produced smaller interaction potentials than chemically identical planar ("smooth") surfaces. For unfavorable scenarios, electrostatic double layer and acid-base potentials were reduced to a greater extent than van der Waals potentials, which made rough surfaces "more attractive" than smooth ones. Two influential surface morphological descriptors emerged: (1) the ratio of particle size to asperity size, a/r, and (2) the ratio of asperity separation to asperity size, p/r. As a/r increased, particle-substrate interaction energy decreased, while the opposite was true for p/r. The simple morphological descriptors gave rise to an analytical model based on the Derjaguin integration (DI) method that compared reasonably well with numerical SEI results, where the size and density of nanopatterned surface features dictated the magnitude of interaction potentials. In fact, changes in the size of nanopatterned surface features impacted the magnitudes of interaction potentials to the same extent as similar changes in the magnitudes of acid-base free energy and zeta potential, which begs the question, "is surface morphology a 'scapegoat' or a primary consideration when defining particle-substrate interactions?"

Tilted bulk heterojunction organic photovoltaic cells grown by oblique angle deposition

We demonstrate small molecule bulk heterojunction organic photovoltaic cells using oblique angle vacuum deposition. Obliquely deposited donor chloroaluminum phthalocyanine (ClAlPc) films on indium tin oxide have surface feature sizes of ∼30 nm, resulting in ClAlPc/C60 donor-acceptor heterojunctions (HJs) with approximately twice the interface area of HJs grown at normal incidence. This results in nearly twice the external quantum efficiency in the ClAlPc absorption band compared with analogous, planar HJs. The efficiency increase is attributed to the increased surface area presented by the donor-acceptor junction to the incident illumination by ClAlPc protrusions lying obliquely to the substrate plane formed during deposition. The power conversion efficiency improves from (2.0±0.1)% to (2.8±0.1)% under 1 sun, AM 1.5G simulated solar illumination. Similarly, the power efficiency of copper phthalocyanine/C60 organic photovoltaic cells is increased from (1.3±0.1)% to (1.7±0.1)%.

Reverse atom transfer radical graft polymerization of 4‐vinylpyridine onto inorganic oxide surfaces

AbstractThin poly(4‐vinylpyridine) films terminally anchored onto nonporous inorganic oxide substrates were synthesized by aqueous phase reverse atom transfer radical graft polymerization (ATRGP). Surface initiators were immobilized on the inorganic substrate surface by chemically attaching glycidoxytrimethoxy silane onto the substrates followed by conversion of the glycidoxy silane into azobis silane by a reaction with 4,4′‐azobis(4‐cyanovaleric acid). Reverse ATRGP of 4‐vinylpyridine onto the active surface azo sites was carried out in a 1‐methyl‐2‐pyrrolidone/water solvent mixture using CuCl2/2,2′‐bipyridine as the catalyst‐ligand complex with initial monomer concentration [M]0 = 2.32M at 90°C. Controlled radical polymerization was achieved at catalyst to initiator molar ratios of 2 : 1 and 3 : 1, with a catalyst to ligand molar ratio of 1 : 2. Controlled polymerization was indicated by a first‐order rate of polymerization kinetics, with respect to monomer conversion at the surface and in solution, the linear increase of the P4VP graft yield with time, and a low polydispersity index (PDI < 1.40). The highest graft yield of 8 mg/m2 was achieved at a 3 : 1 catalyst to initiator molar ratio which corresponded to a number‐average molecular weight of 11,500 g/mol, surface density of 0.69 μmol/m2, and a polydispersity index of 1.28. AFM surface analysis of the grafted polymer films, prepared by reverse ATRGP of 4VP, revealed a decrease in the RMS surface roughness (RRMS = 1.04 nm) and feature size (feature diameter = 20–45 nm), relative to uncontrolled free radical graft polymerization (RRMS = 1.42 nm; feature diameter = 60–145 nm), thereby providing an additional indication that a denser and controlled reaction was achieved via reverse ATRGP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Morphological control and in vitro bioactivity of nanoscale bioactive glasses

In this study, nanoscale bioactive glasses with different morphologies were prepared through sol–gel process using lactic acid as hydrolysis promoter. The effect of lactic acid concentration on the morphology of bioactive glass was characterized. The influence of the morphology on the in vitro bioactivity of samples was investigated in simulated body fluid and examined by various methods. The results showed that nanoscale surface morphologies with high roughness, created by addition of lactic acid, greatly enhanced the in vitro bioactivity of as-prepared samples. It was found that the morphology with nanoscale surface feature and pore size distribution, in addition to specific surface area and pore volume, plays an important role in accelerating the formation of carbonated hydroxyapatite. According to our results, bioactive glasses possessing surface morphology with significant numbers of nanoscale bioactive glass particles and a narrow unimodal or bimodal mesopore structure, exhibit the best in vitro bioactivity.

Polymer structure and properties in micro- and nanomolding process

Injection molding of thin-wall parts with micro/nano-scale patterns using various polymers was performed to clarify the processability and surface replication of molded parts. Effects of process conditions on processability, higher-order structure and surface properties of molded parts were evaluated. The optical anisotropy in the vicinity of the gate became higher than at any other positions. The height replication ratio of surface patterns increased with increasing injection speed, holding pressure, injection temperature and mold temperature. In the case of nanomolding, negative birefringence toward the flow direction appeared higher than at the skin–shear region from the observation of skin–shear and core structure inside molded parts. Thus, the molecular orientation axis was oriented along the thickness direction because of deformation during the demolding process. Thermal stability of nano-surface patterns was influenced by the size of surface features and internal higher-order structure.

Reduced responses of macrophages on nanometer surface features of altered alumina crystalline phases

Extensive prolonged interactions of inflammatory cells (such as macrophages) at the host–implant interface may lead to implant failure. While previous studies have shown increased in vitro and in vivo bone cell adhesion, proliferation and mineralization on nanophase compared to currently implanted ceramics, few studies have been conducted to elucidate inflammatory cell responses on such nanophase ceramics. Controlling surface feature size and corresponding surface roughness on implants may clearly alter immune cell responses, which would be an extremely important consideration for the use of nanostructured materials as improved biomaterials. In this study, reduced macrophage density was observed on alumina (Al 2O 3) compacts with greater nanometer surface roughness accompanied by changes in crystallinity for up to 24 h in culture. Since alumina is a commonly used ceramic in orthopedic applications, this in vitro study continues to support the use of nanophase ceramics as improved orthopedic implants by demonstrating reduced macrophage responses.

Large area diffraction-based inspection of submicron periodic structures

An experimental study of diagnostics possibilities of periodic structures using visible light diffraction principles is presented. The goal of the study is to develop a simple method suitable for use in the inspection of large scale area periodically structured surfaces. It is shown that diffraction-based methods can be applied for surface feature size determination in the submicron region as well as for assessment of the surface profile modulation depth. In order to observe the periodic structure defects on the whole surface of 6–8 inch wafers, an optical filtration set-up is proposed using a white light illumination source. Diffraction efficiency has been acquired by photoelectric sensing of laser beam diffraction. Determined values, – of both the surface feature size and the depth of modulation coincide well with that obtained by AFM and SEM.

Effects of shadowing and steering in oblique-incidence metal (100) epitaxial growth

The effects of attraction in oblique-incidence metal (100) epitaxial growth are studied by comparing the results of simulations which include the effects of short-range (SR) and long-range (LR) attraction with results obtained in the absence of attraction. In general, we find that the qualitative dependence of the surface morphology on deposition angle and film thickness, including the existence of a transition from mounds to asymmetric ripples oriented perpendicular to the beam at large deposition angles, as well as a second transition from ripples to rods with (111) facets oriented parallel to the beam at larger deposition angles and film thicknesses, is not altered by the presence of attraction. However, we find that attraction can have two important effects. The first effect, which is a result of steering due to LR attraction and leads to decreased shadowing, leads to decreased anisotropy in the submonolayer regime and can also lead to decreased surface roughness for high-deposition angles and intermediate film thicknesses. The second effect, due to flux focusing, leads to an increase in the surface roughness and feature size and also reduces the critical thickness for ripple and rod formations. This effect also tends to limit the anisotropy in the rod phase for high-deposition angles and film thicknesses. Surprisingly, we also find excellent scaling for the surface roughness as a function of deposition angle and film thickness in the presence of attraction. We also present extensive results for the dependence of the surface morphology on a variety of other parameters including azimuthal angle, growth temperature, deposition flux, and crystal geometry. A comparison between our simulation results and recent experimental results for grazing incidence Cu/Cu(100) growth is also presented.

A micro-fluidic study of whole blood behaviour on PMMA topographical nanostructures

BackgroundPolymers are attractive materials for both biomedical engineering and cardiovascular applications. Although nano-topography has been found to influence cell behaviour, no established method exists to understand and evaluate the effects of nano-topography on polymer-blood interaction.ResultsWe optimized a micro-fluidic set-up to study the interaction of whole blood with nano-structured polymer surfaces under flow conditions. Micro-fluidic chips were coated with polymethylmethacrylate films and structured by polymer demixing. Surface feature size varied from 40 nm to 400 nm and feature height from 5 nm to 50 nm. Whole blood flow rate through the micro-fluidic channels, platelet adhesion and von Willebrand factor and fibrinogen adsorption onto the structured polymer films were investigated. Whole blood flow rate through the micro-fluidic channels was found to decrease with increasing average surface feature size. Adhesion and spreading of platelets from whole blood and von Willebrand factor adsorption from platelet poor plasma were enhanced on the structured surfaces with larger feature, while fibrinogen adsorption followed the opposite trend.ConclusionWe investigated whole blood behaviour and plasma protein adsorption on nano-structured polymer materials under flow conditions using a micro-fluidic set-up. We speculate that surface nano-topography of polymer films influences primarily plasma protein adsorption, which results in the control of platelet adhesion and thrombus formation.

Progess in superhydrophobic surface development.

Research into extreme water-repellent surfaces began many decades ago, although it was only relatively recently that the term superhydrophobicity appeared in literature. Here we review the work on the preparation of superhydrophobic surfaces, with focus on the different techniques used and how they have developed over the years, with particular focus on the last two years. We discuss the origins of water-repellent surfaces, examining how size and shape of surface features are used to control surface characteristics, in particular how techniques have progressed to form multi-scaled roughness to mimic the lotus leaf effect. There are notable differences in the terminology used to describe the varying properties of water-repellent surfaces, so we suggest some key definitions.

Computing a family of skeletons of volumetric models for shape description

Skeletons are important shape descriptors in object representation and recognition. Typically, skeletons of volumetric models are computed using iterative thinning. However, traditional thinning methods often generate skeletons with complex structures that are unsuitable for shape description, and appropriate pruning methods are lacking. In this paper, we present a new method for computing skeletons of volumetric models by alternating thinning and a novel skeleton pruning routine. Our method creates a family of skeletons parameterized by two user-specified numbers that determine respectively the size of curve and surface features on the skeleton. As demonstrated on both real-world models and protein images in bio-medical research, our method generates skeletons with simple and meaningful structures that are particularly suitable for describing cylindrical and plate-like shapes.

In Situ AFM Study of the Effect of Additives on the Morphology of Electrodeposited Copper

The effect of thiourea and polyethylene glycol (PEG) on the early stages of the electrodeposition of copper on a polycrystalline gold substrate in acidic CuSO4 was examined by in situ atomic force microscopy (AFM). Addition of 1 ppm thiourea resulted in much smaller more nodular features. Feature size decreased as the thiourea concentration was increased. At any given concentration of thiourea, the RMS roughness initially increased as the film thickness increased but eventually reached a saturated value. Copper electrodeposited in the presence of 300 ppm PEG showed much smaller feature sizes than in the absence of additives but not as small as those obtained in the presence of 20 ppm thiourea. The lateral size of surface features was also estimated. After 800 s of deposition at -100 mV (Cu/Cu2+), lateral feature sizes were 730 nm, 460 nm and 280 nm in the case of no additives, 300 ppm PEG and 20 ppm thiourea respectively.

Focused ion beam structured Co/Pt multilayers for field-coupled magnetic computing

ABSTRACTWe fabricated and patterned magnetic dots from Co/Pt multilayers and optimized the structure for strong inter-dot magnetic coupling. SQUID measurements show strong perpendicular anisotropy with characteristic sheared hysteresis loops. The films are fabricated by RF-magnetron sputtering and then patterned with a 50 keV Ga+ focused ion beam (FIB) tool. This keeps surface roughness low and feature sizes in the hundred-nanometer-regime are achievable by a single processing step. Simulations with the well established SRIM (Stopping and Range of Ions in Matter) code give an estimation of the beam diameter and help to estimate the FIB patterning potential. In order to show antiferromagnetic ordering large 48×48 dot arrays of (200×200) nm2 single domain dots were fabricated. The samples were demagnetized and scanned by magnetic force microscopy (MFM) in the remanent state. The demagnetized checkerboard patterns show no frustration over hundreds of dots. The fabricated single domain magnets are prospective building blocks for field-coupled magnetic logic devices.

PLGA nanometer surface features manipulate fibronectin interactions for improved vascular cell adhesion

The largest cause of mortality in the Western world is atherosclerotic vascular disease. Many of these diseases require synthetic vascular grafts; however, their patency rate is only 30% in small (<6 mm) diameter vascular grafts after 5 years of implantation. In an effort to increase small diameter vascular graft success, researchers have been designing random nanostructured surface features which enhance vascular cell functions. However, for the present study, highly-controllable, nanostructured features on poly(lactic-co-glycolic acid) (PLGA) surfaces were formulated. To create ordered nanostructured roughness on PLGA surfaces, either 500, 200, or 100 nm polystyrene nanospheres were separately placed onto mica. These were then used as a template for creating an inverse poly(dimethylsiloxane) mold which was utilized to cast PLGA. Compared to all other PLGA films formulated, AFM results demonstrated greater initial fibronectin spreading on PLGA which possessed spherical 200 nm features. Compared to smooth PLGA, PLGA with 500 or 100 nm surface features, results further showed that PLGA with 200 nm spherical features promoted vascular cell (specifically, endothelial, and smooth muscle cell) adhesion. In this manner, the present study demonstrated a specific nanometer surface feature size that promoted fibronectin spreading and subsequent vascular cell adhesion; criteria critical to vascular graft success.

DEPOSITION AND CHARACTERIZATION OF PULSED-LASER-DEPOSITED AND CHEMICAL-SOLUTION-DERIVED SM-SUBSTITUTED BISMUTH TITANATE FILMS

ABSTRACT Polycrystalline fatigue-free Sm-substituted bismuth titanate thin films have been prepared on platinized silicon substrates by pulsed laser deposition (PLD) and chemical solution deposition (CSD), using similar annealing temperatures (∼700°C). X-ray diffraction and Raman spectroscopy results showed similar crystallographic orientations and structures for films fabricated using these different deposition methods. Atomic force microscopy showed that the surface roughness values were comparable, although PLD-grown films showed a more uniform and slightly larger surface feature size. Cross-sectional images obtained by scanning electron microscopy revealed dense, columnar grains for PLD-grown films compared to a more porous structure with isotropic grains for CSD-derived films. The piezoelectric response of both film types was studied using piezoresponse force microscopy, clearly showing domain switching and a strong correlation between grain structure and domain structure. The PLD-grown films showed higher remanent polarization, lower coercive field, lower leakage current density, and higher piezoelectric coefficient than CSD-derived films.

The effect of annealing temperature on the statistical properties of WO3 surface

We have studied the effect of annealing temperature on the statistical properties ofWO3 surface using atomic force microscopy (AFM) techniques. We haveapplied both level crossing and structure function methods. Levelcrossing analysis indicates an optimum annealing temperature of around400 °C at which theeffective area of the WO3 thin film is maximum, whereas the composition of the surface remainsstoichiometric. The complexity of the height fluctuation of surfaces wascharacterized by roughness, the roughness exponent and the lateral size ofsurface features. We have found that there is a phase transition at around400 °C from one set to two sets of roughness parameters. This happens due to microstructuralchanges from amorphous to crystalline structure in the samples, which have already beenfound experimentally.

Effect of probe tip size on atomic force microscopy roughness values for very smooth samples

Two-dimensional geometric models and experimental data are used to evaluate the effect of tip shape artifacts on atomic force microscopy images, roughness values, and power spectra. The effects of tip size are studied as a function of the surface feature height, spacing, and width. The models demonstrate that the need for sharp tips is dictated by the sample roughness and the size and spacing of surface features. In addition, the magnitude and direction of the error in the measured roughness parameters are related to artifact-induced changes in the skew in the distribution of the data points about the surface mean. Significantly, it is shown that either higher or lower roughness values can be measured using a smaller sized tip, depending on the surface character. These model results are supported by sample data obtained with 2 and 10 nm radii of curvature tipped probes on films used in semiconductor research and development. Sharp-tipped probes are clearly beneficial for imaging the surface microstructure of low-k materials. Tip size has a marked impact on the roughness values obtained on a somewhat smoother metal film sample. However, the high-k sample studied was smooth enough that no benefit was realized with the use of a sharper-tipped probe.