FTIR Ellipsometry Research Articles

FTIR and spectroscopic ellipsometry investigations of the electron beam evaporated silicon oxynitride thin films

FTIR and variable angle spectroscopic ellipsometer in conjunction with computer simulation were employed to investigate the electron beam evaporated SiO x N y thin films. FTIR showed a large absorption band located between 600 and 1250 cm −1, which indicates that Si–O and Si–N bands are overlap in SiO x N y films. A three layers model was used to fit the calculated data to the experimental ellipsometric spectra. The main layer was described by Cauchy model while the interface layer and the surface layer were described using Tauc–Lorenz oscillator and Bruggeman effective medium approximation, respectively. The thickness, the refractive index and the extinction coefficient were accurately determined. The refractive index at 630 nm was found to increase from 1.74 to 1.85 with increasing the film thickness from 191.6 to 502.2 nm. The absorption coefficient was calculated from the obtained extinction coefficient values and it has been used to calculate the Tauc and Urbach energies.

Photocatalytic Performance of Hybrid SiO2−TiO2 Films

In this paper, we have investigated the properties of a composite SiO2−TiO2/TiO2 nanoparticle system. Hybrid films have been prepared using a sol−gel process, starting from tetraisopropoxy titanate and 3-glycidoxipropyltrimethoxysilane as precursors and performing the synthesis at room temperature. The spin-coated films have been thoroughly characterized with UV−vis and FT-IR spectroscopies, TEM analysis, profilometry, and ellipsometry to evaluate their physical and structural properties. Particular attention has been devoted to the study of their photocatalytic action.

Optical and mechanical properties of diamond like carbon films deposited by microwave ECR plasma CVD

Diamond like carbon (DLC) films were deposited on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapour deposition (CVD) process using plasma of argon and methane gases. During deposition, a d.c. self-bias was applied to the substrates by application of 13·56 MHz rf power. DLC films deposited at three different bias voltages (−60 V, −100 V and −150 V) were characterized by FTIR, Raman spectroscopy and spectroscopic ellipsometry to study the variation in the bonding and optical properties of the deposited coatings with process parameters. The mechanical properties such as hardness and elastic modulus were measured by load depth sensing indentation technique. The DLC film deposited at −100 V bias exhibit high hardness (∼ 19 GPa), high elastic modulus (∼ 160 GPa) and high refractive index (∼ 2·16–2·26) as compared to films deposited at −60 V and −150 V substrate bias. This study clearly shows the significance of substrate bias in controlling the optical and mechanical properties of DLC films.

Preparation of Poly(acrylic acid) Nano‐films by In‐situ Polymerization of Acrylic Acid Macroclusters on Silicon Oxide Surfaces

AbstractA new method for preparing poly(acrylic acid) (PAA) films on silicon oxide surfaces with smooth morphology has been developed. Acrylic acid (AA) was preferably adsorbed on silicon oxide surfaces in AA/ chloroform binary liquids and formed a hydrogen‐bonded organized structure, which was called molecular macrocluster. AA macroclusters on silicon oxide surfaces were in‐situ polymerized to obtain molecularly flat polymer films with thickness up to 10 nm. In‐situ polymerizations were conducted by photo‐irradiation in the presence of a photo initiator, 2,2‐dimethoxy‐2‐phenylacetophenone (DPA). As a reference, the adsorption of PAA polymerized in the bulk solution was examined on silicon oxide surfaces. A series of techniques such as attenuated total reflection–FTIR (ATR‐FTIR) spectroscopy, ellipsometry and atomic force microscopy (AFM) was utilized for characterizing two types of films. It was found that flat PAA films with linear hydrogen‐bonded COOH could only be obtained by in‐situ polymerization, which demonstrated this method was an effective way for preparing molecularly uniform polymer films. The surface morphology and thickness of obtained PAA films were found to be dependent on the monomer concentration, initiator amount and photoirradiation time. Molecularly uniform and flat PAA films were obtained after 5 min irradiation at 0.8 mol% AA in the presence of 5 wt% DPA.

Properties of SiOxNy Thin Films Deposited with a Single Molecular Precursor by Using RF PECVD

We have deposited SiOxNy thin films on both Si(100) and glass substrates by using a tetraethyl orthosilicate (TEOS) single precursor at nitrogen flow rates of 0 ∼ 100 sccm by using a radiofrequency Plasma Enhanced Chemical Vapor Deposition (PECVD) method. The film growth orientation and microstructural characteristics were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Deposition at higher nitrogen flow rates results in finer clusters with smaller grain sizes. Moreover, we used UV/Vis and FT-IR spectroscopy and ellipsometry to investigate the optical properties for various nitrogen flow ratios. As-deposited SiO2 films showed an amorphous structure, but samples annealed in an O2 ambient at 900 ◦C showed increased crystallinity. Also, the leakage current densities of the SiO2 and the SiOxNy films annealed at 900 ◦C in an O2 ambient were about 4.0 × 10−8 and 1.5 × 10−7 A/cm.

FTIR Ellipsometry Analysis of the Internal Stress in SiC/Si MEMS

The resonant frequencies and quality factors of MEMS and NEMS depend critically on the layer quality and the residual stress in the SiC/Si heterostructure. It is demonstrated, that FTIRellipsometry is a suitable technique for monitoring the inhomogeneous residual stress inside SiC/Si heterostructures containing thin layers and their variation with during processing.

Interaction of Mono- and Diisocyanoazulenes with Gold Surfaces: First Examples of Self-Assembled Monolayer Films Involving Azulenic Scaffolds

The formation and properties of a new class of self-assembled monolayers (SAM) of aryl isocyanides and diisocyanides based on the nonbenzenoid azulenic framework have been investigated using FTIR spectroscopy and ellipsometry. Syntheses of several new members of the isocyanoazulene family, a recently established type of aryl isocyanides, are reported as well. The FTIR spectra for the isocyanoazulene derivatives absorbed on the gold surface indicate the terminal upright coordination of every isocyanoazulene molecule studied. In addition, the ellipsometric thicknesses have been measured and are consistent with those calculated for single monolayers of the isocyanides oriented along the surface normal. Unlike SAMs of some benzenoid aryl isocyanides, the nonbenzenoid isocyanoazule-based SAMs proved resistant to oxidation, oligomerization, and isomerization into the corresponding nitriles under ambient conditions, which is an important prerequisite to their future applications.

High-Capacity Binding of Proteins by Poly(Acrylic Acid) Brushes and Their Derivatives

Polymeric coatings with high protein-binding capacities are important for increasing the output of affinity-based protein purification and decreasing the detection limits of antibody microarrays. This report describes the use of thick poly(acrylic acid) (PAA) brushes to immobilize as much as 80 monolayers of protein. The brushes were prepared using a recently developed procedure that allows polymerization of 100-nm-thick poly(tert-butyl acrylate) films from a surface in just 5 min along with hydrolysis of these films to PAA in 15 min. Covalent binding of bovine serum albumin (BSA) to PAA brushes that were activated using standard coupling agents, however, resulted in immobilization of less than two monolayers of BSA because of competitive hydrolysis of the esters in the activated film. In contrast, derivatization of PAA with nitrilotriacetate (NTA)-Cu2+ complexes yielded films capable of binding many monolayers of protein via metal-ion affinity interactions. For example, derivatization of 55-nm-thick PAA films with NTA-Cu2+ allowed immobilization of about 15 monolayers (5.8 microg/cm2 or 58 nm) of BSA. The binding capacity was even higher for myoglobin (7.7 microg/cm2) and anti-IgG (9.6 microg/cm2). Remarkably, electrostatic adsorption of lysozyme in 55-nm-thick, underivatized PAA resulted in as much as 80 monolayers (16.2 microg/cm2 or 162 nm) of adsorbed protein. Polymer synthesis, derivatization, and swelling, as well as BSA immobilization kinetics and thermodynamics were characterized using reflectance FT-IR spectroscopy, ellipsometry, and protein assays.

Kinetic and Equilibrium Binding Analysis of Protein−Ligand Interactions at Poly(amidoamine) Dendrimer Monolayers

The interaction of streptavidin (SA) with a biotinylated surface has been of great interest in the development of an interfacial layer for protein immobilization based on self-assembled monolayers (SAMs) and polymeric layers. Here, we demonstrate the unique characteristics of protein-ligand interactions on dendrimer monolayers based on kinetic and equilibrium binding analyses. With amine-ended poly(amidoamine) dendrimers from the first (G1) to fourth (G4) generation, the formation of even, compact dendrimer monolayers on gold was confirmed using FT-IR spectroscopy and ellipsometry. For the SA-biotin interaction, quantitative analysis of bound SA using surface plasmon resonance showed that the saturation binding level of SA was fairly higher in all dendrimer layers when compared to other tested systems of 11-mercaptoundecylamine SAMs and a poly(L-lysine) layer. Kinetic studies revealed that the initial binding rate of SA up to the saturation level was 2-fold higher in all dendrimer layers than in the SAMs regardless of the surface density of functionalized biotin. Concurrently, the dendrimer layers led to much higher values of sticking probability, which is defined as the probability that the SA molecule adsorbs upon collision with a biotinylated surface, at a fixed SA coverage, and prolonged the significant levels around the maximum probability with increasing SA coverage. Plots of the saturation coverage of SA versus the SA concentration in solution showed that SA binding onto the biotinylated G1 and G3 layers fit to a Langmuir isotherm model. Taken together, faster binding of SA and highly ordered packing of the molecules seems to be achieved through typical properties of the dendrimer monolayers such as surface distribution of functionalized biotin, surface corrugation, and flexibility of highly branched larger dendrimers, which provides a guideline for the construction and analysis of an interfacial layer in biosensing applications.

Spectroscopic and electrochemical characterization of interfacial biomimetic assemblies on electrochemically generated gold oxide surfaces

We report on the formation of a gold oxide layer and the reaction of this oxide with an acid chloride to form a stable, relatively complete monolayer bound through an ester-like bond to the gold oxide surface. We have used cyclic voltammetry, FTIR and optical ellipsometry to characterize this novel monolayer structure. The exposed functional groups of this monolayer can participate in subsequent surface reactions, opening the door to the use of oxide-based surface attachment chemistry on metallic substrates. This chemistry will allow for the formation of films tailored to contain both hydrophobic and hydrophilic regions, stacked at predetermined distances from the substrate that may serve as biomembrane mimetic assemblies.

Application of FTIR ellipsometry to detect and classify microorganisms

Here is presented a new method to detect and to classify microorganisms from their ellipsometric response in the mid-infrared range (2–12 μm) measured by FTIR ellipsometry. Apart from the ellipsometric measurements, the performance of the method also stands on the simplicity of sample preparation and data analysis. In the mid-infrared range each molecule exhibits a characteristic absorption fingerprint, thus making ellipsometry chemically selective. FTIR ellipsometry is used here for the first time to analyze bacteria grown in culture media. Sample preparation is extremely simple and consists of the evaporation of a droplet of an aqueous suspension of microorganisms on a planar surface. Ellipsometric measurements are performed on the solid residue left on the surface after the evaporation of the droplet. Data analysis can be divided in two steps. First, simplification of the measured spectra by principal component analysis (PCA), which is a common multivariate statistical technique used to eliminate redundant information. Second, classification of the simplified spectra using a standard clustering method. As a result, we show how this method can be employed to discriminate and identify bacteria at the species level. The results of this experiment are very promising for the application of ellipsometry for analytical purposes in biochemistry and in medicine.

Mechanism of Surfactant Removal from Ordered Nanocomposite Silica Thin Films by Deep-UV Light Exposure

ABSTRACTIn recent years, methods have been developed for the generation of complex ordered nanocomposite materials through organic templating of inorganic structures. One approach involves preparation of composite materials by an evaporation induced self-assembly process involving organization of organic surfactants and formation of inorganic silica from soluble precursors. Recently, we have shown that deep-UV light (185–254nm) is efficient at removing the surfactant microphase for a routine production of well-ordered mesoporous silica thin films. Here we probe the evolution of surfactant removal from nanocomposite thin film silica mesophases as a function of deep-UV exposure using a combined application of FTIR and single wavelength ellipsometry. Taken together, these data indicate that surfactant removal occurs in a step-wise fashion with the formation of oxidized intermediates prior to complete removal of the surfactant from the thin film.

Patterned monolayer/polymer films for analysis of dilute or salt-contaminated protein samples by MALDI-MS.

This paper describes a surface science/mass spectrometry effort to develop and characterize a patterned gold surface that serves as a MALDI sample platform capable of concentrating and purifying proteins. Using microcontact printing, small (200-microm diameter) hydrophilic spots of bare gold or chemically anchored poly(acrylic acid) (PAA) are patterned at 5-mm intervals in a hydrophobic field consisting of a self-assembled monolayer of hexadecanethiol. Building on recent innovations by others, the small hydrophilic spots concentrate the sample to achieve good reproducibility and high sensitivity in the MALDI signal. One of the key features in this work is the combination of the high density of carboxylate groups in PAA with a small spot size to afford both concentration and purification of proteins via ionic interactions. This translates into detection limits for salt-contaminated proteins that are 20-100 times lower (low femtomole) than those reported for previous polymer- or monolayer-modified MALDI probes (using proteins in the 3-15-kDa range). Reflectance FT-IR spectroscopy and ellipsometry were used to determine the amount of protein adsorbed to a PAA-modified sample plate as a function of pH and salt concentration. Amide absorbances in IR spectra correlate well with MALDI-MS signals measured after addition of 2,5-dihydroxybenzoic acid as a matrix.

Gas phase deposition of hybrid coatings

AbstractA new approach for depositing polymer/inorganic hybrid films using gas phase deposition technology has been developed and is the focus of this work. These films combine the high hardness and scratch resistance of inorganic SiO2 films with properties such as flexibility and toughness usually associated with softer polymeric films. The gas phase deposition process eliminates several of the key problems associated with the traditional wet chemical preparation of hybrid materials namely, a reduction in process steps and the elimination of harmful solvents from the process. In addition, gas phase deposition processes generate inherently denser materials then wet chemical processes eliminating post deposition annealing procedures that may damage the substrate. In this study, films are deposited on polycarbonate (PC) and silicon substrates using a novel plasma reactor. In this system, two gas streams, activated by separate plasmas, are combined to form a hybrid thin film.Films are grown from the precursor Tetraethoxysilane (TEOS), 1,2 Bis(trimethylsiloxy)ethane (TMSE) and Tripropylsilane (TPS) evaluated with respect to mechanical, chemical and optical properties, using scratch resistance (Taber abrasion), Methyl Ethyl Ketone (MEK), adhesion and visible transmission measurements. Structural and chemical properties of the deposited films are determined using IR spectroscopic measurements coupled with spectroscopic ellipsometry. The process chemistry and mechanisms are studied using in situ mass spectroscopy, in situ FTIR and spectroscopic ellipsometry.

FTIR Ellipsometry as a Tool for Studying Organic Layers: From Langmuir-Blodgett Films to Can Coatings

The capabilities of infrared ellipsometry to examine structurally various thin organic layers deposited on different substrates are demonstrated in this contribution. The presented examples involve: Langmuir-Blodgett film on gold substrate, anisotropic film of polystyrene on a silicon wafer, implanted fluorinated surface layer into a bulk polyethylene fuel tank and can coating deposited on electrolytically-plated steel (tinplate). Different calculational procedures were used to determine the film optical constants and thickness.

Planar optical waveguide thin films grown by microwave ECR PECVD

Optical thin films of silicon dioxide were deposited from an electron cyclotron resonance SiH 4/O 2/Ar plasma onto a radio frequency biased substrate at a pressure of a few 10 −1 Pa, 100 W microwave power ( f=2.45 GHz) and low wafer temperature (<120°C). The optical and structural properties of films were characterized using FTIR, XPS, AFM, STM and multicolor ellipsometry. The relationship between the growth rates and deposition parameters was investigated and the characterizations of the films with a rf substrate bias were compared to those without bias. Furthermore, 1.17% of Ge-doped silica films were successfully deposited by feeding into GeCl 4. The concentration of Ge could be precisely controlled to satisfy the requirements of different planar optical waveguides and devices.

Silicon dioxide deposition in a microwave plasma reactor

SiOxCyHz films were deposited using hexamethyldisiloxane (HMDSO) in a 2.45 GHz microwave plasma reactor. The plasma was characterised by optical emission spectroscopy as a function of the HMDSO-to-oxygen ratio. The emission of species resulting from the dissociation and recombination of the monomer was identified. The film structure was investigated by means of FTIR spectroscopy and ellipsometry was used to determine the thickness and refractive index of the layer. The infrared spectrum and the deposition rate are strongly dependent on the HMDSO-to-O2 ratio, whereas the refractive index is quite constant and lower than expected.

Infrared Spectroscopy of LiF on Ag and Si

We present the results of infrared optical studies of thin lithium fluoride films evaporated on silver and silicon substrates. Polarized oblique-incidence reflectance and multiple-angle-of incidence FTIR ellipsometry has been used to study the spectral range of longitudinal optic (LO) lattice vibrations. We discuss in detail the lineshapes, and use the pronounced difference of the optical response of metallic and insulating substrates to elucidate their origin. In particular, we model the field distribution in the stratified structures, and specify the spatial distribution of the absorbed energy.

Dielectric Function of Polycrystalline SiC from 190 nm to 15 ?m

We have studied polycrystalline SiC using spectroscopic ellipsometry (from the mid-IR to the quartz-UV), X-ray diffraction, and Raman scattering. In the UV, the pseudodielectric function is affected by surface roughness, and the E1 peak is broadened due to the finite grain size. X-ray rocking curves indicate a preferred orientation with the hexagonal axis along the surface normal and a mosaic spread of 3.5°. FTIR ellipsometry shows a reststrahlen band due to phonon absorption and a strong anistropy peak near the zero crossing of the extraordinary dielectric function at its LO energy. The Raman phonon energies agree with the FTIR results. The Raman data also show the effects of finite grain size and stacking disorder. We conclude that the poly-SiC wafer is anisotropic, but does not have a well-defined polytype (such as 6H or 4H).

Visible photoluminescence of ion irradiated polysiloxane films

We have studied the photoluminescence (PL) of inorganic polymers submitted to irradiations with increasing fluences of energetic He, C or Au ions and correlated the changes in luminescence spectra to structural transformations, evidenced by means of ion beam analyses, Raman, FTIR and spectroscopic ellipsometry. The films exhibit a strong yellow emission when the energy transferred by the ions to electron shells of target atoms is within a given range of 20 to 60 eV/atom. For this optimal amount of ionizations, the precipitation of quantum dots made of free carbon becomes noticeable. The vanishing of the luminescence for larger energy transfers is attributed to the percolation or growth of these dots, combined with a subcritical depletion in the H content of the surrounding SiO 1.5 C x : H y matrix.