Angle Spectroscopic Ellipsometry Research Articles

Correlation between microstructural and optoelectronic properties of porous Si/ SnO2 composites coated Al2O3

In this work, Al2O3 coating effect on morphology, structure and optoelectronic properties of Si/SnO2/Al2O3 porous matrix composites (PMCs) were investigated. A three-staked thin layers deposited on a 〈100〉 oriented silicon substrate made these composites. First, porous silicon layers were achieved by electrochemical etching method. Then Al2O3 and SnO2 layers were successively deposited by physical and chemical vapor deposition, respectively. Morphological and micro-structural properties of the as prepared composites were evaluated by Scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction. Results proved that Al2O3 concentration alters notably the porosity of the PMCs.Variable angle spectroscopic ellipsometry (SE) revealed a high correlation between the optical constants (n, k) and the PMC microstructure. Impedance spectroscopy revealed a semiconductor-metallic transition at high frequency in the temperature range between 340 and 410 °C.

Europium Doped Silicon Oxide Thin Films Using an Integrated PECVD and Sputtering System

Over the last decades, silicon-based materials have exhibited outstanding electronic properties and been used in photovoltaic and electrical devices such as transistors [1]. However, due to their indirect band gap nature and poor light emitting properties, they are not satisfying candidates when it comes to photonics. One way through which this poor performance is sorted out is doping of rare earth (RE) elements into the silicon nanostructure thin film to enhance the light emission. The reason for the use of RE elements in silicon-based materials is the fact that they showed well-defined emission peaks and 4f electron shielding making them independence of the host matrix [2].In this study, luminescence properties of Europium (Eu) doped oxygen rich silicon oxide (ORSO) materials using two fabrication techniques are discussed as well as controlling of the Eu concentration, argon partial pressure and sputtering power. In addition, the effect of different annealing atmospheres is observed as here pure nitrogen (N2) and forming gas (N2+5% H2) are tested at a variety of deposition temperatures ranging between 300 °C and 1350 °C. In particular, samples subjected to the higher annealing temperatures of 1200 °C and 1350 °C behave differently in comparison with lower annealing temperatures where their structural and photoluminescence (PL) properties are investigated in more details.The introducing of Eu into ORSO host matrix was performed by two different deposition methods with the first one being the conventional method of metal organic powders where RE elements are introduced using electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) system. The second method involves the use of a novel and custom-made integration of ECR-PECVD and magnetron sputtering [3]. The investigation of a variation of optical and structural properties of the samples made with similar deposition parameters using these two different techniques resulted in insignificant light emission of the ones fabricated with metal organic precursor and remarkable emission of the samples produced using the integrated ECR-PECVD and sputtering method.Variable angle spectroscopic ellipsometry (VASE) measurements are carried to comprehend the refractive index and thin films thicknesses, and their dependence on the deposition parameters such as the sputtering power. Rutherford backscattering spectrometry (RBS) measurements provide the film composition and verify a good control of the Eu concentration using the second deposition method (integrated ECR-PECVD and sputtering). X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) confirm the formation of nanostructures in the Eu-ORSO thin films following post-deposition annealing beyond 1200 °C. The PL studies are performed to study the light emission properties of Eu-ORSO thin films and the changes introduced by the hydrogen passivation. Figure 1 shows the influence of hydrogen passivation on one of the Eu-ORSO thin films containing 0.1 ± 0.01 at. % of Eu. The sample is annealed at 1200 °C and 1350 °C using N2 and N2+H2 atmospheres for 1 hour in the quartz tube furnace. The hydrogen passivation enhances the PL emission by one order of magnitude possibly due to the passivation of the defects and dangling bonds.

Changes of UV Optical Properties of Plasma Damaged Low-k Dielectrics for Sidewall Damage Scatterometry

ABSTRACTPorous low-k dielectrics were studied to determine the changes of optical properties after various plasma treatments for development of scatterometry technique for evaluation of the trench/via sidewall plasma damage. The SiCOH porogen based low-k films were prepared by PE-CVD. The deposited and UV-cured low-k films have been damaged by striping O2Cl2, O2, NH3 and H2N2 based plasmas and CF4/CH2F2/Ar etching plasma. Blanket wafers were studied in this work for the simplicity of thin film optical model. The optical properties of the damaged low-k dielectrics are evaluated the using various angle spectroscopic ellipsometry in range from 2 to 9 eV. Multilayer optical model is applied to fit the measured quantities and the validity is supported by other techniques. The atomic concentration profiles of Si, C, O and H were stated by TOF-SIMS and changes in overall chemical composition were derived from FTIR. Toluene and water based ellipsometric porosimetry is involved to examine the porosity, pore interconnectivity and internal hydrophilicity.

Optical properties of a quinoid molecule

We report on linear and third order nonlinear optical properties of the quinoid molecule 5,5 ′-bis(3,5-di- tert-butyl-4-oxo-2,5-cyclohexadiene-1-ylidene)-5,5 ′-dihydro-2, 2 ′-bithiophene.Variable angle spectroscopic ellipsometry has been used to determine the dispersion of the dielectric in a spectral range from the near infrared to the near ultraviolet. We have measured a high value of the index of refraction in the transparency region (i.e., n=1.886 at λ=1.5 μ m), indicating the high polarisability of the molecule under study. The nonlinear optical properties have been measured by third harmonic generation in the near infrared spectral range. At λ=1.5 μ m the nonlinear coefficient of the molecule has been estimated to be 4.2 × 10 −19 m 2/V 2 (3.0 × 10 −11 esu).

Biomolecular modification of p(AAm-co-EG/AA) IPNs supports osteoblast adhesion and phenotypic expression

Interpenetrating polymer networks (IPNs) were designed to resist materials fouling caused by non-specific protein adsorption, and indiscriminate cell or bacterial adhesion. These IPNs were thin adherent films ( ~ 20 nm) comprised of acrylamide (AAm), ethylene glycol (EG), and acrylic acid (AA) grafted to either silicon waters or quartz substrates via photoinitiated free radical polymerization. These networks were further modified to promote specific cell adhesion by tethering bioactive groups such as peptides that mimic cell-binding domains found on extracellular matrix molecules. As a specific example of biomolecular surface engineering, peptides from the cell-binding domain of bone sialoprotein were tethered to a p(AAm-co-EG/AA) IPN to control cell behavior at the surface. The networks were characterized by contact angle measurements, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy to convey information on IPN wettability, thickness, and chemistry. The surface characterization data supported the theory that the PEG/AA layer formed an IPN with the underlying p(AAm) network, and after graft modification of this IPN with diamino PEG (PEG(NH2)2), the PEG(NH2)2 chains were enriched at the surface. Rat calvarial osteoblasts attached to Arg-Gly-Asp (RGD) modified IPNs at levels significantly greater than on clean quartz, Arg-Gly-Glu (RGE) modified, or the PEG(NH2)2 modified IPN, with or without serum in the media. Cells maintained in media containing 15% fetal bovine serum (FBS) proliferated, exhibited nodule formation, and generated sheets of mineralized extracellular matrix (ECM) with the addition on β-glycerophosphate to the media. Cell adhesion and mineralized ECM formation were specifically dependent on the peptide sequence present at the surface.

Biomolecular Surface Engineering of Materials for Controlling Bone Cell Adhesion and Spreading

AbstractModel biomaterial surfaces were modified with a peptide that contained a -RGD- (Arg-GlyAsp) sequence, unique to bone sialoprotein, to determine its effect on strength of adhesion, spreading, and focal contact formation of primary bone-derived cells. Peptide surfaces were fabricated by using a heterobifunctional crosslinker to graft the peptide to surfaces (quartz and silicon). Contact angle measurements, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy were used to confirm the chemistry and thickness of the overlayers. Furthermore, spectroscopic ellipsometry was used to estimate the density of immobilized peptide on metal oxide surfaces. A radial flow apparatus was used to measure the strength of adhesion on peptide grafted surfaces. Following 20 min of cell incubation, the strength of cell adhesion was significantly (p<0.05) higher on the -RGD- compared to -RGE- (control) surfaces. The mean area of cells contacting the -RGD- surface was significantly (p<0.05) higher than -RGE- surfaces. Vinculin staining revealed formation of focal contact patches on the periphery of bone cells incubated for 4 hr on the -RGD- surfaces; however, cells seeded on the -RGE- grafted surfaces formed little or no focal contacts. The methods of peptide immobilization utilized in this study can be applied to medical devices, biosensors, and diagnostic assays that require specificity in cell adhesion.

Cl2 Plasma Etching of Si(100): Surface Chemistry and Damage

AbstractThe interaction of a Cl2 plasma with a Si(100) surface has been investigated by angle resolved x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. From XPS, it was found that the amount of chlorine incorporated at the Si surface increases with ion energy. Chlorine is present as SiClx (x = 1-3) with average relative coverages (integrated over depth) of [SiCl]:[SiCl2]:[SiCl3] ≅ 1:0.33:0.1. These relative coverages don’t depend strongly on ion energy between 40 and 280 eV. Real-time spectroscopic ellipsometry measurements showed that the layer present during etching is stable when the plasma is extinguished and the gas pumped away. In addition, the equivalent thickness of damaged silicon and silicon-chloride within the surface layer increases with ion energy.

Microstructural Evolution of Titania Sol-Gel Thin Films

ABSTRACTThin films of crystalline titania with different grain sizes and porosities were prepared by dip-coating on Si (100) substrates starting from a sol-gel process. Three synthesis procedures were developed and compared, using acetylacetone (acac, with HCI) and acetic acid (HOAc) as modifying agents or directly using hydrochloric acid as catalyst. The structural evolution of the films was characterized by Glazing Angle X-ray Diffraction (XRD), Spectroscopic Ellipsometry and Atomic Force Microscopy (AFM). Anatase phase was observed on all of the films calcined at 440° C. The grain sizes and crystallinity generally increased with calcination temperature. Thin films obtained from acac- and HOAc-modified titanium sols had fine grains (50–80 nm) and less porosity (<10%) after calcination at 1000° C. Thin films derived from the sol catalyzed directly with acid had the largest grains (90–130 nm), higher crystallinity and greater porosity (17%).