Isotropic Films Research Articles

An ultra-high Q silicon compound cantilever resonator for Young's modulus measurements

We describe the design of ultra-high Q mechanical cantilever resonators, fabricated from single-crystal silicon wafers. The mechanical resonance mode at f ≈ 8.5 kHz achieves a background damping of Q(-1) </~ 2 × 10(-8) at temperatures below 30 K, which is equal to that of a successful silicon torsional resonator with which the cantilever resonator shares several design elements. The new resonator can be used for accurate measurements of the Young's modulus and internal friction of thin films. It is compatible with both the mounting apparatus and measurement electronics of the torsional resonator, and the two resonators together can be used to provide a complete description of the elastic properties of isotropic thin films.

Phase-based method in heterodyne-modulated ellipsometer

A new common-path heterodyne-modulated ellipsometer with two-phase detection to measure the ellipsometric parameters of amplitude ratio (Ψ) and phase difference (Δ) between p- and s-polarizations of the thin film isotropic materials is proposed. Uniquely, the new scheme distinct from the other previous studies is only by taking two phases from heterodyne signals. Thus, the proposed system is a phase-sensitive modulated ellipsometer that can have the ability to measure the full range of the ellipsometric parameters with high sensitivity and eliminate the intensity fluctuation in system. The ability and performance of modulated ellipsometer on measurement of thin film thickness and ellipsometric parameters are verified by experiments. The errors regarding the ellipsometric parameter measurements are also discussed. The experimental results show that the average standard variation of measured ellipsometric parameters (Ψ and Δ) and the thickness measurement of silica thin film deposited on silicon substrate are 0.13°, 0.94°, and 0.55 nm, respectively. Accordingly, this new idea can be applied to measure isotropic thin film with extremely high absorbance that results in the poor signal/noise ratio in contrast extraction from heterodyne signals.

Study of the morphology and optical properties of anodic oxide layers on InAs (111)III

The effect of the electrolyte composition on the surface morphology and the dispersion dependences of the refractive index and extinction coefficient of ∼20-nm-thick anodic layers on InAs (111)III substrates is studied by atomic force microscopy and spectral ellipsometry. It is shown that oxidation in electrolytes with different acidities does not modify the surface morphology of the initial InAs substrates. The films formed upon oxidation exhibit close dispersion dependences, despite the difference in the chemical composition between the films. This makes possible the high-precision monitoring of the thickness of anodic layers on InAs substrates by means of ellipsometry with the optical model of a single-layer isotropic film on an absorbing substrate.

Electrically conducting film of silver sub-micron particles as mechanical and electrical interfaces for transfer printed micro- and nano-pillar devices

In this paper we report a novel application of electrically conductive film (ECF) of Ag sub-micron particles that includes both isotropic and anisotropic film technologies in providing simultaneous electrical contact and mechanical anchor between fracture transfer-printed (1-D) single crystal semiconductor micro- and nano-pillars and a carrier substrate. We assembled silver sub-micron particles (AgSP) monolayers with varying particle diameters and investigated their optical and electrical characteristics prior to their incorporation into thermoplastic polymers. It was found that transfer-printing of the Si micropillar arrays, into electrically conductive thermoplastic receiver substrates, made of films of AgSP/PMMA blends atop metallic substrates could be effectively achieved to yield electrically interfaced 1-D Si micropillar arrays with retention of their orientation and integrity according to the SEM images. The carrier substrate can potentially be reused to generate additional Si micropillar arrays that can be similarly harvested.

High Frequency Soft Magnetic Performance on Magnetically Isotropic Co-Al-N Films in External Bias Field

We have investigated the high frequency soft magnetic properties ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\mu}$</tex> </formula> - <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${f}$</tex></formula> properties) of magnetically isotropic Co <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$_{76}$</tex></formula> Al <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{11}$</tex></formula> N <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{13}$</tex> </formula> films with an external bias field <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(H_{\rm ex})$</tex></formula> applied in various directions. The films are prepared by <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$rf$</tex></formula> sputtering and consist of fine Co grains 5 nm in diameter in an amorphous AlN matrix. The films have relatively large magnetic anisotropy perpendicular to the film plane and are magnetically soft. The initial magnetization curve in the film plane varies slightly with changes in the direction of the magnetizing field. A clear peak of permeability <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(\mu^{\prime\prime})$</tex></formula> was found at a resonance frequency <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$({f}_{r})$</tex></formula> around 2.5 GHz when the film had been magnetically saturated normal to the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$rf$</tex></formula> -field <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(H_{rf})$</tex> </formula> in the film plane before measurement. After being magnetically saturated parallel to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$H_{rf}$</tex></formula> , the film shows a broad peak in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\mu^{\prime\prime}$</tex></formula> around 9 GHz; however <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$f_{r}$</tex></formula> decreases to 2.5 GHz with increasing <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$H_{\rm ex}$</tex></formula> normal to the film plane. Control of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$f_{r}$</tex></formula> between 2.5–9.65 GHz was achieved by changing the direction of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$H_{\rm ex}$</tex></formula> , which is attributed to the direction changes in magnetic moments of a magnetically isotropic film.

Structure of Alkyne Monolayers on Hydrogen-Terminated Si(100) Surfaces Investigated by External Reflection Infrared Spectroscopy

Monolayers of terminal alkynes with long hydrocarbon chains C(n)H(2n+1)C≡CH (n = 10, 13, 16) were prepared on Si(100) substrates via thermally induced hydrosilylation and the surface orientation of the hydrocarbon chains was investigated by external reflection infrared spectroscopy. It was found that under rigorous exclusion of oxygen in the monolayer preparation process, all three compounds yield highly characteristic IR reflection spectra, consisting of upward-pointing ν(CH(2)) absorptions and downward-pointing ν(CH(3)) absorptions, indicative of a highly ordered anisotropic film structure. Via spectral simulations it was found that the methylene backbones (CH(2))(n) in these films adopt a uniform, all-trans conformation with a tilt angle of about 30° toward the surface normal, whereas the chain termini are disordered and give an isotropic film surface composed of randomly oriented CH(3) groups. Lower quality films, which are hardly distinguishable from highly ordered films by other methods, but have been shown to exhibit inferior electrical properties, are clearly identified in their infrared (IR) spectra as partly disordered structures. External reflection IR therefore proves to be an exceptionally sensitive tool to detect structural defects in these monolayers.

Extended broadband achromatic reflective-type waveplate

This work demonstrates the feasibility of applying a symmetrical film stack on a silver mirror, resulting in broadband phase retardation. While functioning as a reflective-type achromatic waveplate, the symmetrical film stack comprises at least one anisotropic thin film. Additionally, selecting the birefringence and thickness of the thin film allows for the design of uniform phase retardation in both the passband and stopband. A symmetrical film stack that is composed of an anisotropic Ta(2)O(5) thin film and isotropic Ta(2)O(5) thin film is investigated for its achromatic performance in phase retardation.

Transport in Supported Polyelectrolyte Brushes

Functional polymers have a wide variety of applications ranging from energy storage to drug delivery. For energy storage applications, desirable material properties include low cost, high charge storage and/or mobility, and low rates of degradation. Isotropic thin films have been used for many of these types of applications, but research suggests that different structures such as polymer brushes can improve charge transport by an order of magnitude. Supported polymer brush structures produced by "grafting-from" polymerization methods offer a framework for a controlled study of these materials on the molecular scale. Using these materials, researchers can study the basis of hindered diffusion because they contain a relatively homogeneous polyelectrolyte membrane. In addition, researchers can use fluorescent molecular probes with different charges to examine steric and Coulombic contributions to transport near and within polymer brushes. In this Account, we discuss recent progress in using fluorescence correlation spectroscopy, single-molecule polarization-resolved spectroscopy, and a novel three-dimensional orientational technique to understand the transport of charged dye probes interacting with the strong polyanionic brush, poly(styrene sulfonate). Our preliminary experiments demonstrate that a cationic dye, Rhodamine 6G, probes the brush as a counterion, and diffusion is therefore dominated by Coulombic forces, which results in a 10,000-fold decrease in the diffusion coefficient in comparison with free diffusion. We also support our experimental results with molecular dynamics simulations. Further experiments show that, up to 50% of the time, Rhodamine 6G translates within the brush without significant rotational diffusion, which indicates a strong deviation from Fickian transport mechanisms (in which translational and rotational diffusion are related directly through parameters such as chemical potential, size, solution viscosity, and thermal properties). To understand this oriented transport, we discuss the development of an experimental technique that allows us to quantify the three-dimensional orientation on the time scale of intrabrush transport. This method allowed us to identify a unique orientational transport direction for Rhodamine 6G within the poly(styrene sulfonate) brush and to report preliminary evidence for orientational dye "hopping".

Finite element simulation of the effect of electric boundary conditions on the spherical indentation of transversely isotropic piezoelectric films

Finite element simulation was used to analyze the effect of electric boundary conditions on the indentation deformation of a transversely isotropic piezoelectric film with the contact radius much larger than the film thickness. Six different combinations of electric boundary conditions were used. The simulation results showed that the indentation load is proportional to the square of the indentation depth and the indentation-induced electric potential at the contact center is a linear function of the ratio of the indentation depth to the film thickness for all six cases. The contact stiffness is proportional to the contact area and inversely proportional to the film thickness. The nominal piezoelectric charge coefficient d33 is inversely proportional to the derivative of the electric potential with respect to the indentation depth for the indentation of a piezoelectric film by a conducting indenter with a grounded, rigid substrate.

In situ small-angle X-ray and neutron scattering measurements on a blend of deuterated and hydrogenated polyethylenes during uniaxial drawing

In situ small-angle X-ray and neutron scattering (SAXS and SANS) measurements were conducted on an isotropic blend of deuterated polyethylene and hydrogenated polyethylene (HPE; 3 wt%) during uniaxial drawing at 125 °C to clarify the formation mechanism of the shish-kebab from the isotropic film. In the early stage of drawing, two-spot scattering patterns were observed along the drawing direction in both the SAXS and SANS patterns, and the patterns gradually shifted to lower angles, which indicated that the isotropic lamellar crystals rotate and orient to align and that the long period increases because of the elongation of the amorphous region. In the late stage of drawing, the long-period peak gradually shifted to higher angles and the peak width broadened and finally disappeared at the local drawing ratio RD∼6.0, suggesting fragmentation of lamellar crystals (kebabs) and pulling of the polymer chains out of the kebab. However, only the 2D SANS patterns exhibited streak-like scattering in the direction normal to drawing above RD∼2.4, suggesting the preferential orientation and stretching of the HPE chains to form the extended chain crystal (shish). By analyzing the SANS data using the multicore-shell cylinder model, the diameter of the shish that consisted of HPE decreased from 9.0 to 4.5 nm when the drawing was increased from RD=3.8 to 8.0. In situ small-angle X-ray and neutron scattering (SAXS and SANS) measurements were conducted on an isotropic blend of deuterated polyethylene (97 wt%) and hydrogenated polyethylene (3 wt%) during uniaxial drawing at 125 °C to clarify the formation mechanism of shish-kebab from isotropic film. Figure shows that 2D SANS and SAXS patterns in the various drawing ratio, RD, conditions. The drawing direction is longitudinal. In RD=8, the streak-like scattering in the normal direction of drawing became stronger only in the SANS, showing that more hydrogenated polyethylene chains were merged into the shish.

Physical properties and surface/interface analysis of nanocrystalline WO3 films grown under variable oxygen gas flow rates

Nanocrystalline WO3 films were grown by reactive magnetron sputter-deposition in a wide range of oxygen gas flow rates while keeping the deposition temperature fixed at 400°C. The physical characteristics of WO3 films were evaluated using grazing incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), and transmission electron microscopy (TEM) measurements. Physical characterization indicates that the thickness, grain size, and density of WO3 films are sensitive to the oxygen gas flow rate during deposition. XRD data indicate the formation of tetragonal WO3 films. The grain size increases from 21 to 25nm with increasing oxygen gas flow rate to 65%, at which point the grain size exhibits a decreasing trend to attain the lowest value of 15nm at 100% oxygen. TEM analysis provides a model consisting of isotropic WO3 film (nanocrystalline)–SiO2 interface (amorphous)–Si(100) substrate. XRR simulations, which are based on this model, provide excellent agreement to the experimental data indicating that the normalized thickness of WO3 films decreases with the increasing oxygen gas flow rate. The density of WO3 films increases with increasing oxygen gas flow rate.

An Approach for Measuring the Ellipsometric Parameters of Isotropic and Anisotropic Thin Films Using the Stokes Parameter Method

A method is proposed for extracting the ellipsometric parameters of isotropic and anisotropic thin films from the Stokes parameters obtained for five different input polarization lights, namely four linearly polarized lights and one right-hand circular polarized light. In the proposed approach, the genetic algorithm in curve fitting is used to extract the refractive index and thickness properties of the isotropic or anisotropic sample from the experimental results obtained for the variation of the ellipsometric parameters with the incident angle. Finally, the experimental values of the ellipsometric parameters and the simulated values are compared. It is shown that for a typical isotropic thin film, the average standard deviations of Ψ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</i> and Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</i> are 0.020° and 0.464°, respectively. Meanwhile, for a typical anisotropic thin film, the average standard deviations of Ψ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</i> , Ψ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ps</i> , Ψ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sp</i> , Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</i> , Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ps</i> , and Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sp</i> are found to be 0.014°, 0.047°, 0.041°, 0.312°, 0.402°, and 0.571°, respectively. Overall, the results presented in this study confirm that the proposed method provides a straightforward and reliable means of extracting the ellipsometric parameters of isotropic and anisotropic materials by Stokes parameters using five independent input polarization lights. Specially, the ellipsometric parameters of anisotropic thin film expressed by Stokes parameters or Mueller elements are explicitly presented.

Chiral organic thin films: How far pulsed laser deposition can conserve chirality

We have investigated the pulsed laser deposition (PLD) technique to grow isotropic thin films based on bridged binaphthyls. We have focused on the conservation of the chiroptical properties during the deposition process. Chiral high purity liquid chromatography reveals that all the molecules are damaged at the same laser power threshold, but that below this threshold, neither bridged binaphthyl nor binaphthol undergo racemization. In situ circular dichroism spectra, as well as optical rotation (OR) measurements, confirm these findings. Isotropic 2μm thick films with OR of 20°/mm at 546nm were deposited. Furthermore, an estimation of the thermal load reveals that, due to its instantaneous nature, PLD does not induce thermal degradation. Only photochemical processes are involved in both racemization and degradation.

Isotropic and anisotropic dipeptide films based on gas phase deposition

We demonstrated the fabrication and application of well-ordered and vertically aligned dipeptide nanostructures based on a simple gas phase deposition. Deposited nanostructures exhibited the superhydrophobic property with a very low sliding angle. Highly reproducible SERS data have also been obtained after combining deposited films with a thin layer of gold. In addition to these, directional peptide films were, for the first time, successfully fabricated based on the oblique angle deposition technique. We believe that such bio-inspired materials would have a great impact in several technological applications involving catalysis, tissue engineering and biosensors.

Enhancement in coercivity of Pulsed Laser Deposition-fabricated Fe-Pt thick film magnets by reducing droplets

A high-speed Pulsed Laser Deposition method with the deposition rate of several ten microns per hour followed by a post-annealing process enabled us to obtain isotropic Fe-Pt thick film magnets with the L10 order phase. In the study, we investigated the relationship between droplets and coercivity of the post-annealing films. It was found that the reduction in the numbers of droplets enabled us to increase the coercivity although the average deposition rate decreased from 40 to 15 μm per hour. In the samples with Ra less than 0.5 μm, the coercivity exceeded 450 kA/m at the annealing temperature of 673 K. A SEM-EDX analysis of droplets revealed that they tended to have iron-rich or platinum-rich compositions compared with the average one of Fe50Pt50.

Asymptotic analysis of an adhesive joint with mismatch strain

This paper proposes the study of the equilibrium problem, where two elastic bodies are bonded to a thin elastic film under mismatch strain conditions resulting in a state of residual stress. The asymptotic behavior of the film/adherent system is modeled as the film thickness tends to zero, using a method based on asymptotic expansions and energy minimization procedures. This method yields a family of non-local imperfect interface laws, which define a jump in the displacement and the traction vector fields. The amplitudes of the jumps turn out to be correlated with the state of residual stress and the elastic properties of the materials. As an example, the interface law is calculated at order zero in the case of a pure homogeneous mismatch strain and a thin isotropic film consisting of Blatz-Ko material.

Thickness measurement of thin polymer films by total internal reflection Raman and attenuated total reflection infrared spectroscopy

For the first time total internal reflection (TIR) Raman spectroscopy was utilized for thickness measurements of thin isotropic polystyrene films on polypropylene substrate. In the presented method, the band intensity ratios of polystyrene to polypropylene were defined from the spectra, and the film thicknesses in a range from 50nm to 350nm were calculated mathematically from these ratios. The quantitativeness of the method was validated by applying the same principle to attenuated total reflection infrared (ATR-IR) spectroscopy and comparing the results to values obtained by ellipsometry and a spin-coating model. The results showed that the novel and non-invasive TIR Raman method reveals the film thickness quantitatively, and the method is applicable for thin films on soft substrates with similar refractive indices.

Contact instabilities of anisotropic and inhomogeneous soft elastic films

Anisotropy plays important roles in various biological phenomena such as adhesion of geckos and grasshoppers enabled by the attachment pods having hierarchical structures like thin longitudinal setae connected with threads mimicked by anisotropic films. We study the contact instability of a transversely isotropic thin elastic film when it comes in contact proximity of another surface. In the present study we investigate the contact stability of a thin incompressible transversely isotropic film by performing linear stability analysis. Based on the linear stability analysis, we show that an approaching contactor renders the film unstable. The critical wavelength of the instability is a function of the total film thickness and the ratio of the Young's modulus in the longitudinal direction and the shear modulus in the plane containing the longitudinal axis. We also analyze the stability of a thin gradient film that is elastically inhomogeneous across its thickness. Compared to a homogeneous elastic film, it becomes unstable with a longer wavelength when the film becomes softer in going from the surface to the substrate.

Thick mesostructured films via light induced self-assembly

As an alternative to solvent evaporation, we show that UV light can serve as a stimulus to promote self-assembly during the formation of surfactant-templated silica films. Despite practical and conceptual advantages, the Light Induced Self-Assembly (LISA) route has been poorly described in comparison with its evaporation induced analogue. In this article, we give an exhaustive overview of the potentiality of this photoinduced process using a range of PEO-b-PPO-b-PEO amphiphilic triblock copolymers, and investigating systematically the structural (29Si MAS NMR, XRD) and textural properties (TEM, N2 sorption) of the resultant worm-like mesostructured films. Practically, UV irradiation is applied directly to isotropic micrometric films consisting of a nonhydrolyzed alkoxide-amphiphilic copolymer-photoacid generator mixture, obviating the addition of solvent and water. Photoliberation of Bronsted photoacid generates on demand hydrophilic silica species, driving the micellization of the copolymer. The process is single-step and fast, yielding transparent mesostructured films within a few seconds. A target addressed in this feature is to investigate the film structural evolution resulting from the UV irradiation by in situ Fourier transformed infrared analysis (FTIR). Without the interference of solvent, this powerful technique provides a new perspective on the course of the sol–gel process in mesostructured films. For the first time, hydrolysis is assessed kinetically as well as the silica network condensation and the water content of the film.

Predicting surface anchoring: molecular organization across a thin film of 5CB liquid crystal on silicon

Anchoring, i.e. the orientation and ordering of organic molecules at a surface and its persistence away from the interface, is a key phenomenon for liquid crystal (LC) physics and technology, as well as for organic transistors and photovoltaic cells where it strongly affects transport. Recent exciting experiments have started to explore anchoring at the nanoscale, but seemingly conflicting views are emerging, suggesting either a surface order very slowly decreasing with distance, or the expected exponential decay for adhesion energies. The current theoretical description of anchoring is, however, essentially empirical, and methods for predicting the molecular structuring and orientation are conspicuously lacking. Here we establish such predictive tools by using atomistic molecular dynamics simulations and obtain the order and molecular organization of 12 and 24 nm-thick nematic and isotropic films of the popular LC 4-n-pentyl-4-cyano biphenyl (5CB) at its interfaces with an atomically flat, H-terminated, (001) crystalline silicon surface and vacuum. We show that the film adopts a hybrid configuration, with a change of the 5CB preferred orientation from planar uniform at the silicon to perpendicular at the free surface. This variation is nearly discontinuous for the thin film, and continuous with twist and bend for the thicker one. Our findings provide for the first time a full description of the interfacial silicon-LC structure at the nanoscale level.