Tailoring the adhesion of optical films on polymethyl-methacrylate by plasma-induced surface stabilization

Adhesion of plasma-deposited optical and protective coatings, such as amorphous hydrogenated silicon nitride, SiN_1.3, on polymethyl-methacrylate (PMMA) substrates has been found to be limited by a cohesive failure inside the PMMA bulk. Using direct exposure to a low pressure plasma in helium or to vacuum ultraviolet (VUV) radiation generated from plasma, the adhesion of SiN_1.3 at high humidity and elevated temperature has been substantially increased. Using a multitechnique analytical approach, the enhanced adhesion was attributed to the initial etching of the weak boundary layer followed by formation of a crosslinked, graded, mechanically stabilized layer in the interfacial region (interphase), which possesses a physical thickness of 50 to 100 nm and a microhardness of about 2 GPa.     

Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate): Correlation between colloidal particles and thin films

We deal with correlation between sizes of colloidal particles and minimum thickness of spin-coated thin films of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) studied by a dynamic light scattering (DLS), a scanning transmission electron microscopy coupled with an energy dispersive X-ray spectroscopy (STEM-EDX), C₆₀-sputtering X-ray photoelectron spectroscopy (XPS), and an atomic force microscopy. Based on the various measurements, it was pointed out that, PEDOT/PSS colloidal dispersion contained majority of primary nanoparticles with mean diameter of 41 nm and 16 nm for BAYTRON P AG (denote P grade) or BAYTRON PH500 (denote PH grade) solutions, respectively, and small amount of clusters aggregated by the primary particles, based on the DLS measurement and STEM observation. On the other hand, PEDOT/PSS thin films with thickness of 44 nm and 16 nm were easily prepared by spin-coating on silicon wafers from the P and PH grade solutions, respectively. Results of STEM-EDX, DLS, and XPS measurements suggested that the PEDOT/PSS thin films consist of the randomly packed primary nanoparticle-“monolayer”.     

Damage mode tensile testing of thin gold films on polyimide substrates by X-ray diffraction and atomic force microscopy

In situ tensile testing has been performed on thin gold film, 320 nm thick, deposited on polyimide substrates. During the tensile testing, strain/stress measurements have been carried out by X-ray diffraction using the d-sin²ψ method. The X-ray stress analysis suggests crack formation in the films for stresses greater than 670 MPa. The surface of the deformed specimen observed by atomic force microscopy (AFM) exhibits both cracks and two types of straight-sided buckling patterns lying perpendicular to the tensile axis. These buckling patterns can have a symmetrical or asymmetrical shape. The evolution of these two kinds of buckling structures under tensile stress has been observed in situ by AFM and compared to X-ray stress data. The results indicate that symmetrical straight-sided buckling patterns are induced by the compressive stress during unloading, whereas the asymmetrical result from the delamination of the film during the tensile deformation.     

Nitrogen incorporation into titanium diboride films deposited by dc magnetron sputtering: Structural modifications

This work reports a study of titanium boron nitride (Ti-B-N) films deposited at room temperature by dc magnetron sputtering using a TiB₂ target in different Ar-N₂ gas mixture atmospheres. The influence of the nitrogen partial pressure on the structural, mechanical and tribological properties of these films has been studied. The films were analyzed by Rutherford backscattering spectrometry in order to determine their chemical composition and atomic density. X-ray diffraction (XRD) was used to probe the film microstructure and X-ray photoelectron spectroscopy (XPS) for the chemical characterization of the film surface. An atomic force microscope (AFM) was used to analyze the surface topography and, when operating in the lateral force mode, for the friction characterization of the films. The XPS results showed that the surface of the films deposited in pure argon atmosphere was composed essentially by Ti and B oxides, while TiB₂, TiB, TiN and BN phases were present in the sputtered Ti-B-N films. Characterization by XRD determined the nanocrystalline nature of the films structure. While internal stress and friction increase upon the nitrogen incorporation, AFM measurements reveal a strong reduction of the surface roughness.     

Atomic force microscopy and X-ray photoelectron spectroscopy evaluation of adhesion and nanostructure of thin Cr films

Chromium (Cr) thin films were deposited on float glass using electron beam (e-beam) physical vapor deposition and radio frequency (RF) magnetron sputtering techniques. Surface morphology of these Cr films was studied using atomic force microscopy (AFM). The e-beam deposited Cr films consisted of isolated surface mounds while in RF sputtered samples, these mounds combined to form larger islands. Lower surface adhesive properties were observed for e-beam deposited films, as determined from AFM force-distance curves, presumably due to the nanostructural differences. Similar amounts of adsorbed atmospheric carbonaceous contaminants and water vapor were detected on samples deposited using both methods with e-beam deposited samples having additional carbide species, as determined by X-ray photoelectron spectroscopy data. The dominant crystallographic plane in both e-beam deposited and RF sputtered Cr thin films was (110) of body-centered cubic Cr metal structure as determined from X-ray diffraction data. Weak (211) reflection was also observed in RF sputtered samples and was attributed to a different thin Cr film condensation and growth mechanism which resulted in nanostructural differences between films deposited using two different methods.     

Application of glow discharge butadiene coatings on plasticized cornstarch substrates

In the present work, cast thermoplastic starch films were successfully modified by plasma of 1,3-butadiene to reduce water sensitivity. To overcome the difficulties involved in plasma coating of substrates with high water content, high base pressure was used before the introduction of the working gas and mild deposition parameters were employed. The coatings produced at 6 Pa base pressure were smooth, oxygen free and presented low internal stress. After being coated under these mild conditions, cornstarch films were submitted to wettability measurements and atomic force microscopy (AFM) morphological evaluation. Results showed that the coating process improved significantly the cornstarch films' physical properties; water absorption was reduced up to 80%, while water contact angle increased more than 100%. AFM images indicated that the produced coatings cover homogeneously all the different regions of the cornstarch film.     

Characterization by optical emission spectroscopy of an oxygen plasma used for improving PET wettability

Polymers have excellent bulk physical and chemical properties but usually poor surface properties. For wettability improvement plasma technology is one of the most promising techniques. Several studies about surface modifications of polyethylene terephthalate (PET) exposed to an oxygen plasma have been already carried out. In this work an analysis of the plasma phase by optical emission spectroscopy (OES) has been employed in order to establish a correlation with the surface effects induced by plasma exposition on PET chemical composition and wettability, investigated by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements, respectively. The treatment has been carried out for a time of 60 s at a constant pressure (15 Pa) and at different process powers ranging from 20 to 200 W. As expected, the best performance has been obtained at a power of 200 W due to the larger presence of oxygen radicals (OI) with the assistance of ionic species (OII, O₂⁺) which create dangling bonds on the substrate surface.     

Preparation and tribological studies of self-assembled triple-layer films

A self-assembled triple-layer film was grafted onto a silicon surface with a simple three-step method. Firstly, 3-glycidoxypropyltrimethoxysilane molecules were self-assembled on silicon surfaces, then coupled to 3-aminopropyltriethoxysilane through a surface ring-opening reaction, and finally octadecyltrichlorosilane (OTS) molecules were attached to the resultant alkoxysilane-terminated surface via Si-O-Si bonds. The structure and morphology of this triple-layer film were characterized with various techniques, such as contact angle measurement, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). The influence of different surface chemical groups on surface adhesion properties was identified using the AFM force-volume technique. The micro- and macro-tribological properties of the triple-layer film were evaluated by friction force microscopy and a ball-on-plate tribometer. The triple-layer film shows good adhesive resistance and can greatly reduce the micro- and macro-friction force. Moreover, compared to self-assembled monolayer of OTS, this triple-layer film exhibited much better wear-resistance. This improvement was mainly ascribed to the network structure of a lateral cross-linked polysiloxane layer formed within the film which can enhance the stability of the film.     

Preparation and characterisation of silver particulate films on softened polystyrene substrates

The preparation of silver particulate films on softened polystyrene (PS) substrates and their characterisation using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and optical absorption spectroscopy is reported in this paper. Silver films of 150 nm thickness were vacuum deposited onto PS coated glass substrates held at temperatures in the range 415–475 K at different deposition rates of 4 to 12 Å/s. SEM studies indicate that films deposited at 415 K are close to a semicontinuous structure and the structure is discontinuous at higher temperatures. The film morphology is strongly dependent on the deposition rate at any given substrate temperature. The film agglomeration increases with increasing rate of deposition. In the XPS studies, considerable attenuation of the signal corresponding to silver is observed at lower electron take of angles (ETOAs). This indicates that Ag is formed beneath the PS surface. Optical absorption studies showed an interesting red shift of the plasmon resonance wavelength for lower deposition rates again indicating that a sub-surface particulate structure is formed at lower deposition rates. These results are consistent with reported observations.     

Controlled modification of octadecyltrichlorosilane self-assembled monolayer by CO2 plasma

CO₂-plasma is used to introduce functional groups on the uppermost surface of an alkoxysilane self-assembled monolayer (SAM). The structural and chemical modifications of the material surface were monitored by X-ray reflectometry, atomic force microscopy, X-ray photoelectrons spectroscopy and water contact angle measurements. Optimization of the plasma parameters is performed in order to achieve a maximum functionalization and to prevent degradation of the SAM. Finally, the ability of grafting organic compounds onto the plasma modified SAMS was demonstrated by the formation of an alkoxysilane bilayer.     

Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Functionalized interfaces by plasma treatments on silicon and silicon dioxide substrates

Plasma-enhanced chemical vapour deposition has been applied to the fabrication of high-quality SiO₂/Si interfaces and to the functionalization of the silicon dioxide surfaces for organic thin film transistor applications. The advantage of the method herein reported resides in the possibility of activating the substrate, depositing and functionalizing high-quality SiO₂ films in a single-run process, at low temperature. The structural properties of silicon dioxide samples have been studied by infrared spectroscopy, angle resolved and depth profiling X-ray photoelectron spectroscopy. The electronic properties have been retrieved from the leakage current values and the Fowler-Nordheim current plots.     

A study of titanium thin films in transmission laser micro-joining of titanium-coated glass to polyimide

Electron beam evaporation (EB-PVD) and cathodic arc physical vapor deposition (CA-PVD) techniques were used for the preparation of titanium (Ti) thin films onto Pyrex borosilicate 7740 glass wafers and the deposited films were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The microstructure and surface morphology of the films were studied as a function of the film deposition techniques. Film properties such as, adherence, microstructure and roughness were interconnected to the laser joint strength between Ti coated glass wafers and polyimide films. Ti thin films on glass had a natural oxide layer on the surface as found from XPS. AFM study showed the formation of a uniform Ti coating consisted of packed crystallites with average size of 35 nm by EB-PVD. The root-mean-square surface roughness of the films was 1-2 nm. Whereas, films prepared by CA-PVD had crystallites with an average size of 120 nm and defects in the form of macro-particles which is a common attribute of this deposition system. The surface roughness of the film was 125 nm. The laser joint strength was found to be influenced by the Ti film quality on the glass substrate.     

溅射靶功率对氮化碳薄膜结构的影响

利用双放电腔微波ECR等离子体增强非平衡磁控溅射技术,在Si(100)上制备氮化碳薄膜,并对薄膜进行了拉曼(Raman)、原子力显微镜(AFM)、X射线光电子谱(XPS)等结构的表征.发现溅射靶功率对制膜工艺、薄膜的结构和表面形貌产生很大影响.随着溅射靶功率的增大,薄膜的沉积速率减小,表面粗糙度增大,薄膜结构中的sp2含量增加.     

Effect of glycine and hydrogen peroxide on chemical-mechanical planarization of copper

Chemical-mechanical planarization (CMP) of copper is a vital process to produce sub-micron range and multilevel metallization to meet the demands of the current interconnect technology. The present investigation was focussed to understand the oxidation, dissolution and modification of Cu surface using hydrogen peroxide as oxidizer and glycine as inhibitor during Cu-CMP employing electrochemistry as well as dynamic and static removal rate measurements. Surface modification of copper was investigated in detail using X-ray photoelectron spectroscopy to understand the interaction of Cu-H₂O₂-glycine complex formation during CMP. Atomic force microscopy was employed to reveal any change in surface morphology during the CMP process. In the presence of 0.1 M glycine, copper removal rate was found to be high in the solution containing 2.5% H₂O₂ at pH 4 because of Cu²⁺-glycine complexation reaction. In the absence of glycine, the removal rate of copper decreased with increasing H₂O₂ concentration due to the formation of a less soluble copper oxide film. The present investigation helped understanding the mechanism of Cu surface alteration in presence of oxidizers and glycine for formulation of highly effective CMP-slurry.     

Formation and properties of surface-anchored amine-terminated poly(dimethylsiloxane) assemblies with tunable physico-chemical characteristics

Surface-anchored amine-terminated poly(dimethysiloxane) (PDMS) assemblies with tunable physico-chemical characteristics were fabricated with a simple two-step procedure. Firstly, 3-glycidoxypropylmethyldimethoxysilane (GPDMS) molecules were self-assembled on silicon surface, and then coupled to PDMS through a surface ring-opening reaction. The structure and morphology of the amine-terminated PDMS assemblies were characterized with various techniques such as ellipsometry, contact angle goniometer, grazing angle attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The GPDMS monolayers were truly monomolecular films with a virtually normal molecular orientation of densely packed molecules, which were firmly tethered to the hydroxylated silicon substrate. Self-assembly of PDMS molecules resulted in the formation of homogeneous films ~ 6.3 nm thick with the surface roughness ~ 0.898 nm. The calculation of grafting parameters from experimental measurements indicated that the presence of homogeneous and densely grafted PDMS films allowed us to predict a “brushlike” regime for the polymer chains in good solvents.     

Surface modification and characterization of photodefinable epoxy/copper systems

The effects of the wet-chemical and plasma treatments on the adhesion of electroless and sputter-deposited copper to the photodefinable epoxy have been investigated. The wet-chemical treatment increased the amounts of oxygen-containing functionalities on the epoxy surface mainly during the early stage of etching. With the longer etching the pronounced surface roughness was revealed in the form of microcavities. The plasma treatment increased significantly the polar component of surface free energy of the epoxy and produced low surface roughness. The physicochemical changes of the epoxy combined with the experimental adhesion results indicated that in the case of the electroless deposition the mechanical interlocking was the main adhesion mechanism. Sputter-deposited copper exhibited the highest pull strengths on the epoxy when the plasma pretreatment with oxygen was employed. The enhancement of the surface polarity of the epoxy and the enlarged surface contact area due to the increased roughness were the most important factors in the adhesion.     

Surface treatments of indium tin oxide films by using high density plasma

We investigated the effects of various surface treatments on the work function and chemical composition of an indium tin oxide (ITO) surface. Ultraviolet photoelectron spectroscopy (UPS) was used to measure the work function of ITO. X-ray photoelectron spectroscopy (XPS) was used to study the electron structures of ITO surface. We performed surface treatments on ITO using O₂ plasma and HCl solution. Our UPS/XPS analysis indicates increases in the work functions by O₂ plasma treatments. It is known that the Fermi energy level is controlled by the donor concentration, and thus the Fermi energy level is shifted toward the valence band minimum.     

Investigation of the growth of In2O3 on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy

Thin films of In₂O₃ have been grown on Y-stabilised ZrO₂(100) substrates by oxygen plasma assisted molecular beam epitaxy over a range of substrate temperatures between 650 °C and 900 °C. Growth at 650 °C leads to continuous but granular films and complete extinction of substrate core level structure in X-ray photoelectron spectroscopy. However with increasing substrate temperature the films break up into a series of discrete micrometer sized islands. Both the continuous and the island films have excellent epitaxial relationship with the substrate as gauged by X-ray diffraction and selected area electron diffraction and lattice imaging in high resolution transmission electron microscopy.     

Effect of particle size on iron nanoparticle oxidation state

Selecting catalyst particles is a very important part of carbon nanotube growth, although the properties of these nanoscale particles are unclear. In this article iron nanoparticles are analyzed through the use of atomic force microscopy and x-ray photoelectron spectroscopy in order to understand how the size affects the chemical composition of nanoparticles and thus their physical structure. Initially, atomic force microscopy was used to confirm the presence of iron particles, and to determine the average size of the particles. Next an analytical model was developed to estimate particle size as a function of deposition time using inputs from atomic force microscopy measurement. X-ray photoelectron spectroscopy analysis was then performed with a focus on the spectra relating to the 2p Fe electrons to study the chemical state of the particles as a function of time. It was shown that as the size of nanoparticles decreased, the oxidation state of the particles changed due to a high proportion of atoms on the surface.