Modification of Cd1−xMnxTe crystal surface layers by nanopulsed laser irradiation

The surface modification of Cd_1−xMn_xTe (x = 0-0.3) crystal wafers under pulsed laser irradiation has been studied. The samples were irradiated by a Q-switched ruby laser with pulse duration of 80 ns. Optical diagnostics of laser-induced thermal processes were carried out by means of time-resolved reflectivity measurements at wavelengths 0.53 and 1.06 μm. Laser irradiation energy density, E varied in the range of 0.1-0.6 J/cm². Morphology of irradiated surface was studied using scanning electron microscopy. The energy density whereby the sample surface starts to melt, depends on Mn content and is equal to 0.12-0.14 J/cm² for x ≤ 0.2, in the case of x = 0.3 this value is about 0.35 J/cm². The higher Mn content leads to higher melt duration. The morphology of laser irradiated surface changes from a weakly modified surface to a single crystal strained one, with an increase in E. Under irradiation with E in the range of 0.21-0.25 J/cm², the oriented filamentary crystallization is observed. The Te inclusions on the surface are revealed after the irradiation of samples with small content of Mn.     

Surface morphology of metal films deposited on mica at various temperatures observed by atomic force microscopy

Thin films of eight metals with a thickness of 150 nm were deposited on mica substrates by thermal evaporation at various temperatures in a high vacuum. The surface morphology of the metal films was observed by atomic force microscopy (AFM) and the images were characterized quantitatively by a roughness analysis and a bearing analysis (surface height analysis). The films of Au, Ag, Cu, and Al with the high melting points were prepared at homologous temperatures T/T_m = 0.22-0.32, 0.40, and 0.56. The films of In, Sn, Bi, and Pb with the low melting points were prepared at T/T_m = 0.55-0.70, where T and T_m are the absolute temperatures of the mica substrate and the melting point of the metal, respectively. The surface morphology of these metal films was studied based on a structure zone model. The film surfaces of Au, Ag, and Cu prepared at the low temperatures (T/T_m = 0.22-0.24) consist of small round grains with diameters of 30-60 nm and heights of 2-7 nm. The surface heights of these metal films distribute randomly around the surface height at 0 nm and the morphology is caused by self-shadowing during the deposition. The grain size becomes large due to surface diffusion of adatoms and the film surfaces have individual characteristic morphology and roughnesses as T increases. The surface of the Al film becomes very smooth as T increases and the atomically smooth surface is obtained at T/T_m = 0.56-0.67 (250-350 °C). On the other hand, the atomically smooth surface of the Au film is obtained at T/T_m = 0.56 (473 ± 3 °C). The films of In, Sn, Bi, and Pb prepared at T/T_m = 0.55-0.70 also show the individual characteristic surface morphology.     

Influence of surface topography and pore architecture of alkali-treated titanium on in vitro apatite deposition

Alkali-treated titanium surfaces have earlier shown to induce bone-like apatite deposition. In the present study, the effect of surface topography of two-dimensional and pore architecture of three-dimensional alkali-treated titanium substrates on the in vitro bioactivity was investigated. Titanium plates with a surface roughness of R_a = 0.13 μm, 0.56 μm, 0.83 μm, and 3.63 μm were prepared by Al₂O₃ grit-blasting. Simple tetragonal and face-centered Ti6Al4V scaffolds with spatial gaps of 450-1100 μm and 200-700 μm, respectively, were fabricated by a three-dimensional fiber deposition (3DFD) technique. After alkali treatment, the titanium plates with a surface roughness of R_a = 0.56 μm were completely covered with hydroxyapatite globules after 7 days in simulated body fluid (SBF), while the coverage of the samples with other surface roughness values remained incomplete. Similarly, face-centered Ti₆Al₄ scaffolds with spatial gaps of 200-700 μm exhibited a full surface coverage after 21 days in SBF, while simple tetragonal scaffolds with spatial gaps of 450-1100 μm were only covered for 45-65%. This indicates the importance of surface topography and pore architecture for in vitro bioactivity.     

Characterization of Ti6Al4V implant surface treated by Nd:YAG laser and emery paper for orthopaedic applications

A more noble and biocompatible Ti alloy was achieved at fluence of 140 J cm⁻² where the implant indicated a higher degree of hardness (825HV), higher corrosion resistance (−0.21 V) and highest hydrophilicity (i.e. θ_c = 37°) compared with 70° of the control sample. These values corresponded to 58 and 39 mN m⁻¹ of surface tension respectively. The laser treated samples at 140 J cm⁻² showed higher wettability characteristics than mechanically roughened surface. Cell growth and their spreading condition in a specific area were analyzed by SEM and Image J Program software. Clearly, more cells were attached (1.2 × 10⁵) to and spread (488 μm²) over the surface at 140 J cm⁻² than in any other condition. Pathologically, the treated samples indicated no sign of infection.     

Electronic state of ruthenium deposited onto oxide supports: An XPS study taking into account the final state effects

The electronic state of ruthenium in the supported Ru/EO_x (EO_x = MgO, Al₂O₃ or SiO₂) catalysts prepared by with the use of Ru(OH)Cl₃ or Ru(acac)₃ (acac = acetylacetonate) and reduced with H₂ at 723 K is characterized by X-ray photoelectron spectroscopy (XPS) in the Ru 3d, Cl 2p and O 1s regions. The influence of the final state effects (the differential charging and variation of the relaxation energy) on the binding energy (BE) of Ru 3d_5/2 core level measured for supported Ru nanoparticles is estimated by comparison of the Fermi levels and the modified Auger parameters determined for the Ru/EO_x samples with the corresponding characteristics of the bulk Ru metal. It is found that the negative shift of the Ru 3d_5/2 peak which is observed in the spectrum of ruthenium deposited onto MgO (BE = 279.5-279.7 eV) with respect to that of Ru black (BE = 280.2 eV) or ruthenium supported on γ-Al₂O₃ and SiO₂ (BE = 280.4 eV) is caused not by the transfer of electron density from basic sites of MgO, as considered earlier, but by the differential charging of the supported Ru particles compared with the support surface. Correction for the differential charging value reveals that the initial state energies of ruthenium in the Ru/EO_x systems are almost identical (BE = 280.5 ± 0.1 eV) irrespectively of acid-base properties of the support, the mean size of supported Ru crystallites (within the range of 2-10 nm) and the surface Cl content. The results obtained suggest that the difference in ammonia synthesis activity between the Ru catalysts supported on MgO and on the acidic supports is accounted for by not different electronic state of ruthenium on the surface of these oxides but by some other reasons.     

The water-silicas interfacial interaction energies

The water-silicas interfacial interaction energies were calculated for samples of quartz, silicas and silicas outgassed at high temperatures using own and published data of the spreading pressure of water, its surface tension, its contact angle and using formulas obtained by the combination of the Young equation with a general equation of pair interaction. The values obtained for 18 different samples were in the range 7.80-6.92 kJ mol⁻¹. Lower values of energies are for samples that contain relatively less amounts of water at P/P₀ = 0.25 and are characterized also by relatively low values of surface pressures.     

Surface excitation correction of the inelastic mean free path in selected conducting polymers

In earlier works, the inelastic mean free path (IMFP) of electrons was determined by elastic peak electron spectroscopy (EPES) using Ni and Ag reference standard samples, but fully neglecting surface excitation. Surface excitation that is characterized by the surface excitation parameter (SEP), and may affect considerably the elastic peak for the sample and the reference material. The SEP parameters of selected conducting polymers (polythiophenes, polyaniline and polyethylene) were determined by EPES using Si and Ge reference samples. Experiments were made with a hemispherical analyzer of energy resolution 100-200 meV in the E = 0.2-2.0 keV energy range. The composition of the sample surfaces was determined by in situ XPS, their surface roughness by AFM. The experimental SEP parameter data of eight polymer samples were determined by our new procedure, using the formulae of Chen and Werner et al. in the E = 0.2-2.0 keV energy range. The trial and error procedure is based on the best approach between the experimental and calculated IMFPs, corrected on surface excitation. The improvement in the SEP correction appears in the difference between the corrected and Monte Carlo calculated IMFPs, assuming Gries and Tanuma et al. IMFPs for polymers and standard, respectively. The term describing the improvement by SEP resulted in 50-72% (good correction for five polymers) 24% (poor correction for one polymer), 1-6% (no correction for two polymers). The 100% correction was not achieved, indicating that the difference between experimental and calculated IMFP cannot be entirely explained by surface excitation. Using the SEP data of Si and Ge reference samples based on Chen's and Werner's material parameter values resulted in similar SEP corrections for the polymer samples.     

Carbon monoxide oxidation over well-defined Pt/ZrO2 model catalysts: Bridging the material gap

Four different Pt/ZrO₂/(C/)SiO₂ model catalysts were prepared by electron beam evaporation. The morphology of these samples was examined before and after the catalytic reaction by Rutherford back-scattering (RBS), transmission electron microscopy (TEM) and grazing-incidence small-angle scattering (GISAXS). The catalytic behavior of such model catalysts was compared to a conventional Pt/ZrO₂ catalyst in the CO oxidation reaction using different oxygen excess (λ = 1 and 2). The so-called material gap was observed: model catalysts were active at higher temperature (620-770 K) and resulted in higher activation energy values (E_a = 77-93 kJ mol⁻¹ at λ = 1 and 129-141 kJ mol⁻¹ at λ = 2) compared to the powdered Pt/ZrO₂ catalyst (370-470 K, E_a = 74-76 kJ mol⁻¹). This material gap is discussed in terms of diffusion limitations, reaction mechanism and apparent compensation effect. Diffusion processes seem to limit the reaction on planar samples in the reactor system that was shown to be appropriate for the evaluation of the catalytic activity of powder samples. Kinetic parameters obeyed the so-called apparent compensation effect, which is discussed in detail. Langmuir-Hinshelwood-type of reaction, between CO_ads and O_ads, was proposed as the rate-determining step in all cases. Pt particles deposited on planar structures can be used for modeling conventional powdered catalysts, even though some limitations must be taken into account.     

Structural characterization and optical properties of ZnSe thin films

Zinc selenide (ZnSe) thin films (d = 0.11-0.93 μm) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. Their structural characteristics were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The experiments showed that the films are polycrystalline and have a zinc blende (cubic) structure. The film crystallites are preferentially oriented with the (1 1 1) planes parallel to the substrate surface. AFM images showed that the films have a grain like surface morphology. The average roughness, R_a = 3.3-6.4 nm, and the root mean square roughness, R_rms = 5.4-11.9 nm, were calculated and found to depend on the film thickness and post-deposition heat treatment.The spectral dependence of the absorption coefficient was determined from transmission spectra, in the range 300-1400 nm.The values of optical bandgap were calculated from the absorption spectra, E_g = 2.6-2.7 eV.The effect of the deposition conditions and post-deposition heat treatment on the structural and optical characteristics was investigated.     

Silver grain boundary diffusion in Pd

Two to ten nanometer thick polycrystalline Pd films were prepared on the (1 1 1) surface of Ag single crystal and investigations of the Ag diffusion along Pd grain boundaries were carried out using the Hwang-Balluffi method. The samples were monitored by Auger electron spectroscopy (AES) during isothermal heat treatments in the 438-563 K temperature range. Using plausible simplifying assumptions, the activation energy of the product of the grain boundary (GB) diffusion coefficient and k′ (k′ = c_s/c_gb; c_s and c_gb are the surface and GB concentration, respectively) was calculated (0.99 ± 0.08 eV) from the evaluated saturation coefficients of the surface accumulation. This energy, for weak temperature dependence of k′, is approximately equal to the activation energy of the GB diffusion.     

Processing of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80 (P(CPP:SA)20:80) by matrix-assisted pulsed laser evaporation for drug delivery systems

We have demonstrated successful thin film growth of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) by matrix-assisted pulsed laser evaporation using a KrF* excimer laser (λ = 248 nm, τ = 25 ns, ν = 10 Hz). The deposited thin films have been investigated by Fourier transform infrared spectroscopy, and atomic force microscopy. We have demonstrated that the main functional groups of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) are present in the deposited film. The effect of matrix on both thin film structure and surface morphology was also examined. The goal of this work is to explore laser processing of this material to create suitable constructs for drug delivery applications.     

Optical properties and electric conductivity of gold nanoparticle-containing, hydrogel-based thin layer composite films obtained by photopolymerization

Poly(acrylamide) [poly(AAm)] and poly(N-isopropyl-acrylamide) [poly(NIPAAm)] based gel films containing Au nanoparticles (d = 14 ± 2.5 nm) were synthesized. Monomers and cross-linker were added to a gold nanodispersion, and after the addition of the initiator, polymer films were prepared on the surface of an interdigital microelectrode by photopolymerization. In the course of the syntheses the gold concentration of the films was constant (10.8 μg/cm²) and the volume fraction of Au nanoparticles (?_Au) in the polymer gel films varied in the range of 0.58-85.3%. Poly(AAm)-based films swell when the temperature increases: due to a temperature shift of 15 °C the Au plasmon absorption maximum at λ = ∼532 nm was shifted towards shorter wavelengths by 16.6 nm (blue shift) through the swelling of the polymer gel film. In the case of poly(NIPAAm) the temperature-induced shrinking resulted in a red shift, namely the maximum was shifted by 18.07 nm by a temperature shift of 15 °C. In the case of both composites, the electric conductivity of the samples was shown to increase with increasing Au particle concentration. In the case of the poly(AAm)-based composite containing ?_Au = 0.85 gold the resistance of the film spread on the surface of the electrode was 0.16 MΩ at 25 °C and 0.66 MΩ at 50 °C, i.e. the conductivity of the sample decreased with increasing temperature. The opposite effect is observed in the case of the poly(NIPAAm)-based composite: as temperature is raised, the resistance of the composite abruptly drops at the point of collapse of the NIPAAm gel (it is 0.28 MΩ at 32 °C and only 0.021 MΩ at 35 °C). This thermosensitive effect was detectable only at sufficiently high Au contents (?_Au = 0.85) in both gels.     

Shallow hydroxyapatite coatings pulsed laser deposited onto Al2O3 substrates with controlled porosity: correlation of morphological characteristics with in vitro testing results

We studied the influence of porous Al₂O₃ substrates on Ce-stabilized ZrO₂-doped hydroxyapatite thin films morphology pulsed laser deposited on their top. The porosities of substrates were monitored by changing sintering temperatures and measured with a high pressure Hg porosimeter.The depositions were conducted in 50 Pa water vapors by multipulse ablation of the targets with an UV KrF* (λ = 248 nm, τ ∼ 25 ns) excimer laser. The surface morphology of synthesized nanostructures was investigated by scanning electron microscopy and atomic force microcopy. Ca/P ratio within the range 1.67-1.70 was found for hydroxyapatite coatings by energy dispersive spectroscopy.The films were further seeded with mesenchymal stem cells for in vitro tests. The cells showed good attachment and spreading uniformly covering the entire surface of samples. The complexity of film morphology which is increasing with substrate porosity was shown to have a positive influence on cultivated cells density.     

Fabrication of 550 nm gratings in fused silica by laser induced backside wet etching technique

A series of 550 nm spacing gratings were fabricated in fused silica by laser induced backside wet etching (LIBWE) method using the fourth harmonic of a Q-switched Nd:YAG laser (wavelength: λ = 266 nm; pulse duration: FWHM = 10 ns). During these experiments we used a traditional two-beam interference method: the spatially filtered laser beam was split into two parts, which were interfered at a certain incident angle (2θ = 28°) on the backside surface of the fused silica plate contacting with the liquid absorber (saturated solution of naphthalene-methyl-methacrylate c = 1.85 mol/dm³). We studied the dependence of the quality and the modulation depth of the prepared gratings on the applied laser fluence and the number of laser pulses. The surface of the etched gratings was characterized by atomic force microscope (AFM). The maximum modulation depth was found to be 180-200 nm. Our results proved that the LIBWE procedure is suitable for production of submicrometer sized structures in transparent materials.     

Combined laser/sol-gel synthesis of calcium silicate coating on Ti-6Al-4V substrates for improved cell integration

New studies have shown that tricalcium silicate powder is a bioactive material and can encourage bone-implant integration. This paper reports the synthesis of Ca₂SiO₄ coating on Ti-6Al-4V samples by laser irradiation under submerged conditions. The results of using a 160-1500 LDL 1.5 kW diode laser (rectangular spot = 2.5 mm × 3.5 mm, λ = 808 and 940 nm with equal intensities) is reported. A number of experiments were carried out varying laser parameters, such as scanning speed and laser power. Coatings are evaluated in terms of microstructure, elemental composition (XRD), SEM and wettability. The in vitro biocompatibility of the samples is investigated by monitoring 2T3 osteoblast cell growth on the samples.     

Effects of evolving surface morphology on yield during focused ion beam milling of carbon

We investigate evolving surface morphology during focused ion beam bombardment of C and determine its effects on sputter yield over a large range of ion dose (10¹⁷-10¹⁹ ions/cm²) and incidence angles (Θ = 0-80°). Carbon bombarded by 20 keV Ga⁺ either retains a smooth sputtered surface or develops one of two rough surface morphologies (sinusoidal ripples or steps/terraces) depending on the angle of ion incidence. For conditions that lead to smooth sputter-eroded surfaces there is no change in yield with ion dose after erosion of the solid commences. However, for all conditions that lead to surface roughening we observe coarsening of morphology with increased ion dose and a concomitant decrease in yield. A decrease in yield occurs as surface ripples increase wavelength and, for large Θ, as step/terrace morphologies evolve. The yield also decreases with dose as rippled surfaces transition to have steps and terraces at Θ = 75°. Similar trends of decreasing yield are found for H₂O-assisted focused ion beam milling. The effects of changing surface morphology on yield are explained by the varying incidence angles exposed to the high-energy beam.     

Zinc-ion implanted and deposited titanium surfaces reduce adhesion of Streptococccus mutans

While titanium (Ti) is a commonly used dental implant material with advantageous biocompatible and mechanical properties, native Ti surfaces do not have the ability to prevent bacterial colonization. The objective of this study was to evaluate the chemical composition and bacterial adhesive properties of zinc (Zn) ion implanted and deposited Ti surfaces (Zn-PIIID-Ti) as potential dental implant materials. Surfaces of pure Ti (cp-Ti) were modified with increasing concentrations of Zn using plasma immersion ion implantation and deposition (PIIID), and elemental surface compositions were characterized by X-ray photoelectron spectrometry (XPS). To evaluate bacterial responses, Streptococcus mutans were seeded onto the modifiedTi surfaces for 48 h and subsequently observed by scanning electron microscopy. Relative numbers of bacteria on each surface were assessed by collecting the adhered bacteria, reculturing and counting colony forming units after 48 h on bacterial grade plates. Ti, oxygen and carbon elements were detected on all surfaces by XPS. Increased Zn signals were detected on Zn-PIIID-Ti surfaces, correlating with an increase of Zn-deposition time. Substantial numbers of S. mutans adhered to cp-Ti samples, whereas bacterial adhesion on Zn-PIIID-Ti surfaces signficantly decreased as the Zn concentration increased (p < 0.01). In conclusion, PIIID can successfully introduce Zn onto a Ti surface, forming a modified surface layer bearing Zn ions that consequently deter adhesion of S. mutans, a common bacterium in the oral environment.     

Enhancement of low-field magnetoresistance in Fe3O4 particles induced by ball milling

A series of Fe₃O₄ particles with different size have been obtained by mechanical ball milling from t=0-450 h. Crystal structure and microstructure of the samples are analyzed by XRD and SEM. An emphasis has been placed on magnetic and transport properties. The experimental results indicate that the sample t=350 exhibits an enhancement of magnetoresistance (MR) comparing with initial powder compress sample (t=0). The low-field magnetoresistance reaches MR=−6.04% at Verwey temperature 120 K and MR=−2.54% at 290 K. Thermal behavior TGA analysis and investigation of magnetic properties have revealed that there is an oxide layer on surface of Fe₃O₄ particles. It is considered that the enhanced magnetoresistance can be taken into account in terms of spin-dependent tunneling effect between Fe₃O₄ particles.Temperature dependence of magnetization and resistivity are measured in order to study electrical and magnetic behavior near Verwey transition. In addition, we also discuss ball milling time dependence of coercivity H_c and specific magnetization M_s of these samples.     

CO2 adsorption on Cr(1 1 0) and Cr2O3(0 0 0 1)/Cr(1 1 0)

We attempt to correlate qualitatively the surface structure with the chemical activity for a metal surface, Cr(1 1 0), and one of its surface oxides, Cr₂O₃(0 0 0 1)/Cr(1 1 0). The kinetics and dynamics of CO₂ adsorption have been studied by low energy electron diffraction (LEED), Aug er electron spectroscopy (AES), and thermal desorption spectroscopy (TDS), as well as adsorption probability measurements conducted for impact energies of E_i = 0.1-1.1 eV and adsorption temperatures of T_s = 92-135 K. The Cr(1 1 0) surface is characterized by a square shaped LEED pattern, contamination free Cr AES, and a single dominant TDS peak (binding energy E_d = 33.3 kJ/mol, first order pre-exponential 1 × 10¹³ s⁻¹). The oxide exhibits a hexagonal shaped LEED pattern, Cr AES with an additional O-line, and two TDS peaks (E_d = 39.5 and 30.5 kJ/mol). The initial adsorption probability, S₀, is independent of T_s for both systems and decreases exponentially from 0.69 to 0.22 for Cr(1 1 0) with increasing E_i, with S₀ smaller by ∼0.15 for the surface oxide. The coverage dependence of the adsorption probability, S(Θ), at low E_i is approx. independent of coverage (Kisliuk-shape) and increases initially at large E_i with coverage (adsorbate-assisted adsorption). CO₂ physisorbs on both systems and the adsorption is non-activated and precursor mediated. Monte Carlo simulations (MCS) have been used to parameterize the beam scattering data. The coverage dependence of E_d has been obtained by means of a Redhead analysis of the TDS curves.     

Bioglass thin films for biomimetic implants

Pulsed laser deposition (PLD) method was used to obtain bioglass (BG) thin film coatings on titanium substrates. An UV excimer laser KrF* (λ = 248 nm, τ = 25 ns) was used for the multi-pulse irradiation of the BG targets with 57 or 61 wt.% SiO₂ content (and Na₂O-K₂O-CaO-MgO-P₂O₅ oxides). The depositions were performed in oxygen atmosphere at 13 Pa and for substrates temperature of 400 °C. The PLD films displayed typical BG of 2-5 μm particulates nucleated on the film surface or embedded in. The PLD films stoichiometry was found to be the same as the targets. XRD spectra have shown, the glass coatings obtained, had an amorphous structure. One set of samples, deposited in the same conditions, were dipped in simulated body fluids (SBFs) and subsequently extracted one by one after several time intervals 1, 3, 7, 14 and 21 days. After washing in deionized water and drying, the surface morphology of the samples and theirs composition were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), IR spectroscopy (FTIR) and energy dispersive X-ray analysis (EDX). After 3-7 days the Si content substantially decreases in the coatings and PO₄³⁻ maxima start to increase in FTIR spectra. The XRD spectra also confirm this evolution. After 14-21 days the XRD peaks show a crystallized fraction of the carbonated hydroxyapatite (HAP). The SEM micrographs show also significant changes of the films surface morphology. The coalescence of the BG droplets can be seen. The dissolution and growth processes could be assigned to the ionic exchange between BG and SBFs.