Surface characterization of plasma deposited nano-structured fluorocarbon coatings for promoting in vitro cell growth

Nano-structured “teflon-like” coatings characterized by highly-fluorinated, random, ribbon-shaped, micrometers-long structures were deposited on polyethylenetherephtalate (PET) substrates by plasma enhanced-chemical vapour deposition (PE-CVD) using modulated radiofrequency (RF, 13.56 MHz) glow discharges fed with C₂F₄ in modulated discharge (MD) and continuous wave (CW) regimes. Surfaces obtained in this way featured identical chemical composition and different roughness in the nanometric scale. Water contact angle (WCA) measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were utilized to characterize the surfaces. A positive relationship was shown to exist between the WCA value and the mean nano-structure height and the area root-mean-square (RMS) roughness of coatings. The possibility of obtaining coatings of varying nano-structure height, i.e., roughness, in a nanometric scale represents a promising result for further use of these surfaces as substrates for experiments on cell adhesion, proliferation and growth.     

Anchoring sulphur-headgroup organic molecules at Cu(1 0 0): Tailoring the interface electronic states

Sulphur-headgroup organic molecules have been chemisorbed on Cu(1 0 0) as self-assembled monolayers (SAMs) in highly-ordered two-fold symmetry structures, and the electronic states induced at the interface have been measured by photoemission: a close similarity of the main interface states for methane-thiolate and mercaptobenzoxazole on Cu(1 0 0) in the same p(2 × 2)-phase is observed. The bonding states for methane-thiolate/Cu(1 0 0) in the p(2 × 2) and c(2 × 2) structures have been compared to ab-initio calculation of the total density of states (DOS) for the S/Cu(1 0 0) system in the same phases. The major role of the S-Cu bonding to determine the density of state evolution at the interface is brought to light. The observed differences in the two phases depend mainly on the charge distribution associated to the different molecular packing, with a minor role of the radical group.     

First nucleation steps during deposition of SiO2 thin films by plasma enhanced chemical vapour deposition

The initial nucleation stages during deposition of SiO₂ by remote plasma enhanced chemical vapour deposition (PECVD) have been monitored by XPS inelastic peak shape analysis. Experiments have been carried out on two substrates, a flat ZrO₂ thin film and a silicon wafer with a native silicon oxide layer on its surface. For the two substrates it is found that PECVD SiO₂ grows in the form of islands. When the SiO₂ particles reach heights close to 10 nm they coalesce and cover completely the substrate surface. The particle formation mechanism has been confirmed by TEM observation of the particles grown on silicon substrates. The kinetic Monte Carlo simulation of the nucleation and growth of the SiO₂ particles has shown that formation of islands is favoured under PECVD conditions because the plasma species may reach the substrate surface according to off-perpendicular directions. The average energy of these species is the main parameter used to describe their angular distribution function, while the reactivity of the surface is another key parameter used in the simulations.     

First-principles study of the (0 0 1) surface of cubic SrZrO3

Density functional calculations have been used to investigate the (0 0 1) surface of cubic SrZrO₃ with both SrO and ZrO₂ termination. Surface structure and electronic structure have been obtained. The SrO surface is found to be similar to its counterpart in SrTiO₃, while there are marked differences between the ZrO₂ and TiO₂ terminations in SrZrO₃ and SrTiO₃, respectively, concerning surface relaxation and rumpling. For the ZrO₂-terminated surface of SrZrO₃, the covalency of the interaction between the outmost Zr and the O beneath is enhanced as a result of their bond contraction. The band gap reduction and the presence of the surface states are also discussed in relation with the behavior of the electrostatic potential.     

Effects of hydrogen flux on the properties of Al-doped ZnO films sputtered in Ar + H2 ambient at low temperature

Al-doped ZnO (AZO) transparent conductive thin films were grown by magnetron sputtering with AZO (98 wt.% ZnO, 2 wt.% Al₂O₃) ceramic target in Ar + H₂ ambient at a relatively low temperature of 100 °C. To investigate the dependence of crystalline and properties of as-grown AZO films on the H₂-flux, X-ray diffraction (XRD), X-ray photoemission spectrometer (XPS), Hall and transmittance spectra measurements were employed to analyze the AZO samples deposited with different H₂-flux. The results indicate that H₂-flux has a considerable influence on the transparent conductive properties of AZO films. The resistivity of 4.15 × 10⁻⁴ Ω cm and the average transmittance of more than 94% in the visible range were obtained with the optimal H₂-flux of 1.0 sccm. Such a low temperature growing method present here may be especially useful for some low-melting point photoelectric devices and substrates.     

Formation of the Si/Ti interface

The formation of the Si/Ti interface during the deposition of silicon on titanium polycrystalline substrates has been studied at room temperature (RT) using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS (ARXPS), ultraviolet photoelectron spectroscopy (UPS) and ion scattering spectroscopy (ISS). The experimental results are consistent with a two-stage mechanism for Si growth: a first stage characterized by the simultaneous formation of a uniform titanium silicide layer, that reaches a limiting thickness of ∼3 monolayer (ML), and pure silicon islands 1 ML thick that grow on top of this layer up to coalescence, followed by a second stage in which pure silicon islands, with an average thickness of 9 ML, grow on top of the uniform titanium silicide layer + pure silicon ML structure formed during the first stage. As a whole, pure silicon species grows according to a Stranski-Krastanov mechanism, where the first ML is formed during the first stage and the islands during the second stage. The comparison of Ti/Si and Si/Ti interfaces shows that the structure and composition of the interface do not depend substantially on the deposition sequence, suggesting that the bulk chemistry of the compound formed at the interface dominates over the surface kinetics and the bulk substrate chemistry in determining the composition and structure of the interface.     

The role of precursor gases on the surface restructuring of catalyst films during carbon nanotube growth

Catalyst films undergo considerable surface morphology restructuring prior to carbon nanotube nucleation, deeply influencing the nanostructures obtained. Here we study the influence of different gaseous atmospheres on the structure of thin Fe films. The morphology is influenced by process temperature and substrate interactions and varying the gas type and pressure can control the average catalyst island height.     

Synthesis of multi-walled carbon nanotubes for NH3 gas detection

It has been recently demonstrated that carbon nanotubes (CNTs) represent a new type of chemical sensor capable of detecting a small concentration of molecules such as CO, NO₂, NH₃.In this work, CNTs were synthesized by chemical vapor deposition (CVD) on the SiO₂/Si substrate by decomposition of acetylene (C₂H₂) on sputtered Ni catalyst nanoparticles. Their structural properties are studied by atomic force microscopy, high-resolution scanning electron microscopy (HRSEM) and Raman spectroscopy. The CNTs grown at 700 °C exhibit a low dispersion in size, are about 1 μm long and their average diameter varies in the range 25–60 nm as a function of the deposition time. We have shown that their diameter can be reduced either by annealing in oxygen environment or by growing at lower temperature (less than 600 °C).We developed a test device with interdigital Pt electrodes on an Al₂O₃ substrate in order to evaluate the CNTs-based gas sensor capabilities. We performed room temperature current–voltage measurements for various gas concentrations. The CNT films are found to exhibit a fast response and a high sensitivity to NH₃ gas.     

柔性ITO衬底电化学沉积制备Cu/Cu2O薄膜

研究了使用电化学沉积法于碱性条件下在柔性ITO衬底上制备Cu/Cu₂O薄膜的方法。循环伏安曲线表明Cu₂O与Cu的阴极峰分别位于-500 mV(vs Ag/AgCl)和-800 mV(vs Ag/AgCl)附近。利用循环伏安法考察了生长温度和电解液pH值等对Cu₂O与Cu阴极峰电位的影响,阴极峰随生长温度的升高以及pH值的降低而略向阳极移动,沉积电流也随之相应增大。与弱酸性条件相比,上述两个阴极峰随pH值升高而移动的程度明显减小,这可能与碱性条件下C₃H₆O电离程度增大以及C₃H₆O根作为配体的过量程度有关。通过X射线衍射光谱和扫描电子显微镜的表征证实,在所研究的生长温度区间和pH值内可利用电化学沉积法在柔性ITO衬底上制备Cu/Cu₂O纳米混晶薄膜。在相同的生长温度和pH条件下,电化学沉积电位对样品表面形貌和晶体性质具有较大影响。     

CdS films deposited by chemical bath under rotation

Cadmium sulfide (CdS) films were deposited on rotating substrates by the chemical bath technique. The effects of the rotation speed on the morphological, optical, and structural properties of the films were discussed. A rotating substrate-holder was fabricated such that substrates can be taken out from the bath during the deposition. CdS films were deposited at different deposition times (10, 20, 30, 40 and 50 min) onto Corning glass substrates at different rotation velocities (150, 300, 450, and 600 rpm) during chemical deposition. The chemical bath was composed by CdCl₂, KOH, NH₄NO₃ and CS(NH₂)₂ as chemical reagents and heated at 75 °C. The results show no critical effects on the band gap energy and the surface roughness of the CdS films when the rotation speed changes. However, a linear increase on the deposition rate with the rotation energy was observed, meanwhile the stoichiometry was strongly affected by the rotation speed, resulting a better 1:1 Cd/S ratio as speed increases. Rotation effects may be of interest in industrial production of CdTe/CdS solar cells.