FTIR Ellipsometry Research Articles

Enhance hydrogen storage in lightweight solid-state systems based on Poly(vinylnaphthalene)

This article highlights the potential of poly(2-vinylnaphthalene) (PVN) as a novel light-weight solid-state hydrogen storage system for various applications. With an impressive theoretical gravimetric hydrogen capacity of 5.2 wt.-%, PVN stands out for its attractiveness as a hydrogen carrier. The material possesses advantageous characteristics, including moldability, low toxicity, and ease of storage, making it a promising candidate for both stationary and mobile hydrogen storage applications. Experimental findings demonstrate that PVN can be hydrogenated by up to 76 % utilizing an Ru/Al2O3 catalyst at 250 °C for 24 h. Confirmation of the hydrogenation reaction, which results in poly(2-vinyldecalin), was achieved through characterization techniques such as FTIR, 1H NMR, and spectroscopic ellipsometry. The study of the effects of hydrogen pressure and reaction time identified moderate conditions as favorable, though a further exploration of different catalysts is suggested for optimal conversion. A palladium-based catalyst was employed to release hydrogen from the hydrogenated polymer, demonstrating almost complete reversibility of the hydrogenation of poly(2-vinylnaphthalene) with a dehydrogenation yield of 90 %.

The Role of Optical Phonon Confinement in the Infrared Dielectric Response of III-V Superlattices.

Polar dielectrics are key materials of interest for infrared (IR) nanophotonic applications due to their ability to host phonon-polaritons that allow for low-loss, subdiffractional control of light. The properties of phonon-polaritons are limited by the characteristics of optical phonons, which are nominally fixed for most "bulk" materials. Superlattices composed of alternating atomically thin materials offer control over crystal anisotropy through changes in composition, optical phonon confinement, and the emergence of new modes. In particular, the modified optical phonons in superlattices offer the potential for so-called crystalline hybrids whose IR properties cannot be described as a simple mixture of the bulk constituents. To date, however, studies have primarily focused on identifying the presence of new or modified optical phonon modes rather than assessing their impact on the IR response. This study focuses on assessing the impact of confined optical phonon modes on the hybrid IR dielectric function in superlattices of GaSb and AlSb. Using a combination of first principles theory, Raman, FTIR, and spectroscopic ellipsometry, the hybrid dielectric function is found to track the confinement of optical phonons, leading to optical phonon spectral shifts of up to 20 cm-1 . These results provide an alternative pathway toward designer IR optical materials.

In Operando Spectroscopic Ellipsometry Investigation of MOF Thin Films for the Selective Capture of Acetic Acid.

The emission of polar volatile organic compounds (VOCs) is a major worldwide concern of air quality and equally impacts the preservation of cultural heritage (CH). The challenge is to design highly efficient adsorbents able to selectively capture traces of VOCs such as acetic acid (AA) in the presence of relative humidity (RH) normally found at storage in museums (40-80%). Although the selective capture of VOCs over water is still challenging, metal-organic frameworks (MOFs) possess highly tunable features (Lewis, Bronsted, or redox metal sites, functional groups, hydrophobicity, etc.) suitable to selectively capture a large variety of VOCs. In this context, we have explored the adsorption efficiency of a series of MOFs thin films (ZIF-8(Zn), MIL-101(Cr), and UiO-66(Zr)-2CF3) for the selective capture of AA based on a UV/vis and FT-IR spectroscopic ellipsometry in operando study (2-6% of relative pressure of AA under 40% of RH), namely conditions close to the realistic environmental storage conditions of cultural artifacts. For that purpose, optical quality thin films of MOFs were prepared by dip-coating, and their AA adsorption capacity and selectivity were evaluated under humid conditions by measuring the variation of the refractive index as a function of the vapor pressures while the chemical nature of the coadsorbed analytes (water and AA) was identified by FT-IR ellipsometry. While thin films of ZIF-8(Zn) strongly degraded upon exposure to AA/water vapors, films of MIL-101(Cr) and UiO-66(Zr)-2CF3 present a high chemical stability under those conditions. It was shown that MIL-101(Cr) presents a high AA adsorption capacity due to its high pore volume but exhibits a poor AA adsorption selectivity under humid conditions. In contrast, UiO-66(Zr)-2CF3 was shown to overpass MIL-101(Cr) in terms of AA/H2O adsorption selectivity and AA adsorption/desorption cycling stability because of its high hydrophobic character, suitable pore size for adequate confinement, and specific interactions.

Influence of magnetron sputtering conditions on the chemical bonding, structural, morphological and optical behavior of Ta1 − xOx coatings

In this work Ta1−xOx coatings were deposited by DC magnetron sputtering in an Ar+O2 atmosphere. The influence of the oxygen partial pressure on the morphology (SEM), structure (XRD), chemical bonding (XPS), thermal oxidation and optical response (FTIR and spectroscopic ellipsometry) of Ta-based films was study.Cross-section morphology revealed that the increase of oxygen content in the coatings change the columnar morphology to featureless. Likewise, structural results showed that the small increase of oxygen amount leads to a change from Ta stable phase (α-Ta: bcc) to a mixture of phases achieving oxide phases with large amounts of oxygen. Whereas at room temperature the oxide coatings mainly revealed an amorphous character, at 700°C the coating reached the crystallization Ta2O5 orthorhombic phase, which is promoted by the temperature. Further, although not observed in XRD, for the coatings deposited close to the reactive mode threshold IR showed absorption bands corresponding to amorphous phase containing some crystals embedded on it, while for the coatings deposited in the poisoned regime the IR suggests a marked amorphous nature. Refractive index varied between 2.09 and 2.27 at 0.65μm, within the range reported for Ta2O5 thin films. The changes in refractive index are correlated with the different crystallinity of the coatings, which is corroborated with the IR results.

Backbone-Degradable Polymers Prepared by Chemical Vapor Deposition.

Polymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine. Herein, we demonstrate, for the first time, a backbone-degradable polymer directly synthesized via CVD. The CVD co-polymerization of [2.2]para-cyclophanes with cyclic ketene acetals, specifically 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), results in well-defined, hydrolytically degradable polymers, as confirmed by FTIR spectroscopy and ellipsometry. The degradation kinetics are dependent on the ratio of ketene acetals to [2.2]para-cyclophanes as well as the hydrophobicity of the films. These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability.

Backbone‐Degradable Polymers Prepared by Chemical Vapor Deposition

AbstractPolymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine. Herein, we demonstrate, for the first time, a backbone‐degradable polymer directly synthesized via CVD. The CVD co‐polymerization of [2.2]para‐cyclophanes with cyclic ketene acetals, specifically 5,6‐benzo‐2‐methylene‐1,3‐dioxepane (BMDO), results in well‐defined, hydrolytically degradable polymers, as confirmed by FTIR spectroscopy and ellipsometry. The degradation kinetics are dependent on the ratio of ketene acetals to [2.2]para‐cyclophanes as well as the hydrophobicity of the films. These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability.

Self-Assembly and Post-Fabrication Functionalization of Microphase Separated Thin Films of a Reactive Azlactone-Containing Block Copolymer

We report on the thin film self-assembly and post-fabrication functionalization of cylinder-forming poly(styrene-block-2-vinyl-4,4-dimethylazlactone) (PS-b-PVDMA) block copolymers (BCPs). Thermal annealing of an asymmetric BCP composition, to drive microphase separation in thin films, results in high defect densities and poor long-range order. Using FTIR spectroscopy and ellipsometry, we demonstrate that thermal annealing results in reactions between the azlactone groups and the underlying substrate leading to BCP “pinning”. We demonstrate that solvent annealing circumvents these issues and drives high fidelity microphase separation of the BCP in thin films. The solvent annealing approach also enables control over domain orientation; we show that parallel and perpendicularly oriented cylinders with diameters of 11.7 ± 1.2 nm and a center-to-center distance of 25.2 ± 2.6 nm can be obtained using a BCP with Mn = 29.5 kDa and fS = 0.75. The PVDMA segments in these self-assembled thin films remain available f...

FTIR Ellipsometry Study on RF sputtered Permalloy-Oxide Thin Films

The optical properties of RF sputtered polycrystalline permalloy oxide (PyO) thin films were studied in the infrared by variable angle ellipsometry. The dispersion of PyO shows a Lorentzian dispersion peak at 381.5 cm-1. We attribute this peak to the transverse optical phonon of PyO. This peak is consistent with a rocksalt crystal structure for the Ni0.81Fe0.19O1-d thin films.

RF plasma enhanced MOCVD of yttria stabilized zirconia thin films using octanedionate precursors and their characterization

Yttria stabilized zirconia thin films have been deposited by RF plasma enhanced MOCVD technique on silicon substrates at substrate temperature of 400°C. Plasma of precursor vapors of (2,7,7-trimethyl-3,5-octanedionate) yttrium (known as Y(tod)3), (2,7,7-trimethyl-3,5-octanedionate) zirconium (known as Zr(tod)4), oxygen and argon gases is used for deposition. To the best of our knowledge, plasma assisted MOCVD of YSZ films using octanediaonate precursors have not been reported in the literature so far. The deposited films have been characterized by GIXRD, FTIR, XPS, FESEM, AFM, XANES, EXAFS, EDAX and spectroscopic ellipsometry. Thickness of the films has been measured by stylus profilometer while tribological property measurement has been done to study mechanical behavior of the coatings. Characterization by different techniques indicates that properties of the films are dependent on the yttria content as well as on the structure of the films.

Investigation of structural disorder using electron temperature in VHF-PECVD on hydrogenated amorphous silicon films for thin film solar cell applications.

Electrode distances and gas flow ratios are important parameters for fabricating intrinsic (i-type) layers of hydrogenated amorphous silicon (a-Si:H) films using a very high frequency plasma-enhanced chemical-vapor deposition (VHF-PECVD) system. In this work, we investigated the relationship between the electrode distances and gas flow ratios on the properties of i-type a-Si:H films. The electrical, chemical and structural properties are improved with decreasing electrode distances (20-40 mm) at a hydrogen ratio [R (H2/SiH4) = 4], due to the low electron temperature and heating effect. A low electron temperature generates silane-related-reactive species (SiH3) and decreases structural disorder resulting in high quality i-type a-Si:H films. The electrical, chemical and structural properties of the a-Si:H films are confirmed using Al coplanar electrodes, FTIR, Raman spectroscopy, and spectroscopy ellipsometry (SE). When a solar cell is fabricated using the a-Si:H film, J(sc) of 13.2-14.8 mA/cm2, photoconductivity of 1.5 x 10(-5)-8.6 x 10(-6) S/cm, Si--H2 content of 0-1.24 at.%, and hydrogen content of about 10 at.% are obtained. These results together with a model of the plasma chemistry indicate that H atoms and SiH3 radicals play an important role in the deposition process.

Epitaxy of polar semiconductor Co3O4 (110): Growth, structure, and characterization

The (110) plane of Co3O4 spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co3+ species at the surface. However, experimental studies of Co3O4 (110) surfaces and interfaces have been limited by the difficulties in growing high-quality films. We report thin (10–250 Å) Co3O4 films grown by molecular beam epitaxy in the polar (110) direction on MgAl2O4 substrates. Reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction, and transmission electron microscopy measurements attest to the high quality of the as-grown films. Furthermore, we investigate the electronic structure of this material by core level and valence band x-ray photoelectron spectroscopy, and first-principles density functional theory calculations. Ellipsometry reveals a direct band gap of 0.75 eV and other interband transitions at higher energies. A valence band offset of 3.2 eV is measured for the Co3O4/MgAl2O4 heterostructure. Magnetic measurements show the signature of antiferromagnetic ordering at 49 K. FTIR ellipsometry finds three infrared-active phonons between 300 and 700 cm−1.

Room-temperature preparation of metal-oxide nanostructures by DUV lithography from metal-oxo clusters

A versatile, fast and easy route towards preparation of metal-oxide nanostructures by a full-optical method at room temperature is presented here. The concept relies on the preparation of photosensitive metal-oxo clusters (MOCs) that can be crosslinked and mineralized in a single step process, by Deep-UV (DUV) irradiation (ArF laser emission band at 193 nm). The oxo-clusters are prepared by complexation between metal alkoxides and methacrylic acids followed by a partial hydrolysis. These molecular building blocks are designed to absorb DUV light and they can react from an excited state to give rise to crosslinking reactions. Photocrosslinking of Ti, Zr and Hf oxo-clusters was investigated by means of in situ FTIR and spectroscopic ellipsometry. In the case of Ti-oxo clusters, we demonstrate that the material can be fully mineralized into TiO2 by DUV irradiation. A photocatalytic process involving TiO2 nanoparticles is proposed to explain the DUV mineralization process. Finally, we used DUV interferometric lithography to illustrate nanopatterning based on these photoresists. These inorganic photoresists open new doors towards room temperature preparation of high-resolution inorganic nanostructures with strong interest for practical applications in electronics, optics, photonics or biology.

Preparation, characterization and mechanical properties of Bi12SiO20–PMMA composite films

Abstract This paper investigates processing and characterization of polymer composite material PMMA–Bi 12 SiO 20 (BSO). Thin films of pure PMMA and composites with 0.5 and 1.0 wt% of Bi 12 SiO 20 powder were made using solution casting method. Characterization of starting components and composites was performed with XRD, FTIR, Raman spectroscopy, SEM, DCS, tensile tests, nanoindentation and spectroscopic ellipsometry method in order to obtain information of their morphology, structure, thermal stability, mechanical and optical properties. Refractive index measurements using spectroscopic ellipsometry method have shown that refractive index of composites increases with the powder content. Nanoindentation and tensile tests have shown mechanical improvements with the addition of the crystal through Young’s and reduced Young’s modulus and hardness values. DSC analysis has shown an increase in T g for composite with BSO.

Development of pinhole-free amorphous aluminum oxide protective layers for biomedical device applications

This paper describes synthesis of ultrathin pinhole-free insulating aluminum oxide layers for electronic device protection in corrosive liquid environments, such as phosphate buffered saline (PBS) or clinical fluids, to enable emerging biomedical applications such as biomolecular sensors. A pinhole-free 25-nm thick amorphous aluminum oxide layer has been achieved using ultra-high vacuum DC magnetron reactive sputtering of aluminum in oxygen/argon plasma followed by oxygen plasma post-processing. Deposition parameters were optimized to achieve the best corrosion protection of lithographically defined device structures. Electrochemical deposition of copper through the aluminum oxide layers was used to detect the presence (or absence) of pinholes. FTIR, XPS, and spectroscopic ellipsometry were used to characterize the material properties of the protective layers. Electrical resistance of the copper device structures protected by the aluminum oxide layers and exposed to a PBS solution was used as a metric to evaluate the long-term stability of these device structures.

Covalently cross-linked poly(acrylamide) brushes on gold with tunable mechanical properties via surface-initiated atom transfer radical polymerization

Versatile surface coatings, which exhibit anti-fouling properties and allow one to tune surface functionality and the state of internal (macro)molecular organization, are of central importance as platforms for the study of cell–surface interactions. To enable studies of various cell characteristics, such including cell migration, proliferation and adhesion, we investigated how the mechanical properties of poly(acrylamide) (PAAm) brushes on gold can be controlled by the varying the cross-link density. Brushes and covalently cross-linked hydrogel brushes were synthesized using self-assembled monolayers (SAMs) of ω-mercaptoundecyl bromoisobutyrate (MUBiB) on gold to initiate the surface-initiated atom transfer radical polymerization (SI-ATRP) of AAm with different fractions of (N,N′-methylenebis(acrylamide)) bisAAm in the feed. The polymer layers prepared with varied polymerization times or cross-linking densities were characterized by water contact angle measurements, grazing incidence reflection FTIR spectroscopy, ellipsometry and atomic force microscopy (AFM). It was found that during PAAm brush synthesis the film thickness increased markedly in early stages of the reaction, whereas after 60min a plateau of approximately 50nm (dry) film thickness was reached. The introduction of bisAAm into the feed resulted in reduced film thicknesses. AFM force–displacement measurements revealed that the variation of cross-linking density of polymer brush films influenced both the surface morphology and the films’ nanomechanical properties. The stiffness of the polymer brush films increased with increasing fraction of bisAAm, while the swelling ratio decreased. Hence the elastic modulus of the cross-linked PAAm brushes, as determined by AFM nanoindentation, could be varied between 20 and 700kPa, which will find application in the study of cell–surface interactions.

Wavelength selective refractive index modulation in a ROMP derived polymer bearing phenyl- and ortho-nitrobenzyl ester groups

Patterning and tuning of the refractive index in polymers by means of UV-light is of great interest for optical applications such as polymeric waveguides or optical data storage devices. In this contribution, we report on the synthesis of a polynorbornene based copolymer bearing ortho-nitrobenzyl and phenyl ester groups capable of undergoing the photo-induced cleavage reaction and in a subsequent step optionally the photo-Fries rearrangement upon irradiation with UV-light. The photoreaction of these aromatic ester groups was investigated by means of FTIR, UV-VIS and spectroscopic ellipsometry. Due to the difference in UV absorption of the photoreactive units, the o-nitrobenzyl ester can be selectively excited by UV-light above 300 nm, while a subsequent illumination with 254 nm induces the photo-Fries rearrangement of the remaining phenyl ester groups. The structural changes in the chemical composition upon UV illumination lead to significant changes in the refractive index of the polymeric materials. Whilst the photo-Fries rearrangement of the phenyl ester groups causes a remarkable increase in the refractive index, it was found that the photo-induced cleavage reaction of ortho-nitrobenzyl ester moieties causes a decrease of the refractive index. This fact enables a selective tailoring of the refractive index by the choice of the applied wavelength. In addition, a two-step irradiation procedure using a sequence of different wavelengths provides the possibility of erasing and even inverting the index contrast.

TiO<SUB align="right">2 thin films studied by FTIR, AFM and spectroscopic ellipsometry

TiO2 thins films were prepared on Si (100) substrates by a sol-gel dip coating process. Effect of the annealing temperatures in different atmospheres (air and O2) on the properties of the films has been examined. FTIR results indicated a dominant feature centred around 438 cm–1, which is characteristic of the anatase TiO2. This peak is quite sharp at higher temperature, indicating the film is well-crystallised, especially for the film annealed at 500°C under oxygen. The bands at 3,400 and 1,620 cm–1 represented the stretching and bending vibrations of O-H hydroxyl groups, and those bands could be normally reduced by the calcination process. The morphology of the films annealed at 500°C under air and oxygen showed relatively uniform surface, densely packed nanoparticles and quite low mean average roughness values. The determination of the refractive index, packing density and the band gap by the ellipsometry is presented.

Microstructural and optical investigations of Ce-doped barium titanate thin films by FTIR and spectroscopic ellipsometry

(BaTiO3)1− x (CeO2) x (with x = 0, 1, 3, 5.7 and 16 at.%) thin films were prepared by electron beam evaporation method. According to X-ray diffraction, nanosized and amorphous Ce-doped barium titanate thin films were obtained. The crystallinity diminished as Ce content increased. The increase in the Ce slightly shifts the absorption peaks at 433–450 and 416–424 cm−1 to higher wavenumbers. A two-layer model was used to describe the experimental ellipsometric data. The Bruggeman effective medium approximation (BEMA) was used to describe the surface roughness layer and the Cauchy dispersion relation was used to describe the main Ce-doped barium titanate layer. The refractive index and the extinction coefficient were found to increase with increasing Ce content; however, the optical band gap decreased with increasing Ce content. The accurate determination of the optical constants of Ce-doped barium titanate thin films may favor them in the applications of optical thin film devices.

Block Copolymer Supramolecular Assembly beyond Hydrogen Bonding

Supramolecular assemblies of block copolymers (BSAs) with low molecular weight additives require preferential interactions between the additive and one of the blocks. So far, only hydrogen bonds (HB) were explored to obtain BSAs. We report on three novel BSAs of block copolymer PS-block-P4VP with commercially valuable additives of the EDOT family. Two of the additives ((3,4-ethylenedioxythiophene) (EDOT) and 3,4-(2,2-dimethylpropylenedioxy)thiophene (ProDOT)) form the BSAs based on interactions others than HB. The morphology and some properties of the BSAs were studied by means of AFM, FTIR, and spectroscopic ellipsometry. The BSAs reveal cylindrical morphology with periodicity of ∼30 nm. In thin films the orientation of the cylinders can be switched from perpendicular to parallel by annealing in vapors of a suitable solvent. Extraction with a selective solvent results in porous films with porosity of ∼15%. These non-HB BSAs were compared with the HB BSA of HMeDOT as well as HABA BSA reported recently. Th...

Synthesis of ZnO thin films by 40 ps @ 532 nm laser pulses

The synthesis by pulsed laser deposition of ZnO thin films with a Nd:YAG laser system delivering pulses of 40 ps @ 532 nm is reported. The laser beam irradiated the target placed inside a vacuum chamber evacuated down to 1.33×10−1 Pa. The incident laser fluence was of 28 J/cm2 in a spot of 0.1 mm2. The ablated material was collected onto double face polished (111) Si or quartz wafers placed parallel at a separation distance of 7 mm. The AFM, SEM, UV-Vis, FT-IR and absorption ellipsometry results indicated that we obtained pure ZnO films with a rather uniform surface, having an average roughness of 37 nm. We observed by SEM that particulates are present on ZnO film surface or embedded into bulk. Their density and dimension were intermediary between particulates observed on similar structures deposited with fs or ns laser pulses. We noticed that the density of the particulates is increasing while their average size is decreasing when passing from ns to ps and fs laser pulses. The average transmission in the UV-Vis spectral region was found to be higher than 85%.