Unsupported Films Research Articles

Noninvasive Real-Time Evaluation of the Anisotropic Thermal Diffusivity in Thin Polymer Films for Electronics Packaging

AbstractWe describe an experimental method capable of evaluating the in- and out-of-plane components of the anisotropic thermal diffusivity in supported and unsupported thin polymer films. The technique is used to quantify the in-plane thermal diffusivity in films of PMDA/ODA (Dupont's P12545), BTDA/ODA/MPD (Dupont's P12555), BPDA/PPD (Dupont's P12611), BCB (Dow's Cyclotene 3022) and HFDA-APBP (Amoco's UD4212) with thicknesses in the 1–10 micron range.

Oleochemical Monographs (No. 70) — Part 2

The manufacture of esters for eleostearic acid has been outlined and a number of their properties examined, e.g. monomeric auto‐oxidation and atmospheric oxidation of B‐ acid esters and also permeability to water of thin unsupported films of xeleostearate esters has been investigated.

TEM studies of spots crystallized in amorphous films by electron beam

Electron beam (e-beam) annealing is powerful method for local modifying and crystallization in desired modes of semiconductors and microelectronics components and is also interesting for information storing. Nevertheless, discussed in many papers mechanism of explosive crystallization of amorphous (a-Ge, a-Si) films is still not clear enough and requires new structure studies. It is more relevant for recently discovered growing of micro-crystals with strong internal lattice bending (gradient crystals) in some amorphous films. This paper reports our findings in the structure of spots crystallized in these unusual modes by TEM beam in vacuum deposited (Ge, Se, Se-Te) or prepared by pyrolysis (Fe2O3) unsupported amorphous films. Bendcontour technique was used to analyze the fields of lattice orientation for gradient crystals, including in situ crystal growth studies or videorecord analysis.Explosively crystallized spots in a-Ge, a-Si films are known to consist of 3 zones, Fig. 1. We observed the same zones for films 400-800Å thick, deposited at rates 1- 100Å/s: polycrystal central zone (O), surrounded by a fan of radially elongated single crystals (zone R) which in turn is surrounded by zone (C), formed by concentric or spiral shells (each subdivided into single-crystal subshell and polycrystal subshell).

Monte Carlo simulation of backscattered electrons and energy from thick targets and surface films

Electron-matter interaction is described by a Monte Carlo procedure in which the mean free path is calculated by using a screened Rutherford formula, while energy loss is computed by using the Kanaya and Okayama semiempirical expression. Monte Carlo simulation results of the backscattering coefficient have been compared with the available experimental data. The examined energy range was 5--30 keV, the atomic number range was 4--92, and the tilt angle range was 0\ifmmode^\circ\else\textdegree\fi{}--80\ifmmode^\circ\else\textdegree\fi{}. The agreement between simulated and experimental data is found to be excellent in the energy range 10--30 keV; also for 5 keV the agreement is very good when the atomic number is lower than 50. Then the mean backscattered energy was computed for bulk targets, unsupported thin films, and surface films.

Monte‐Carlo simulations of the point‐to‐point resolution in scanning Auger microscopy and x‐ray microanalysis of thin overlayers

AbstractThe point‐to‐point resolution of Auger electron spectroscopy is compared to that of x‐ray microanalysis of thin unsupported films and of thin films on a bulk material. Monte‐Carlo calculations are used in this respect. The incident beam is a Gaussian‐distributed curve with standard deviation σo = 40 Å and an energy range 10–100 keV. A Point‐Spread‐Function describing the radial distribution of the analysed signal is, in each case, determined from the Monte‐Carlo results. From this function and by using the Rayleigh criterion, the point‐to‐point resolution is calculated.

Layered antiferromagnetic structure in vanadium slabs

Layered antiferromagnetic structure is obtained for unsupported vanadium films. The magnetism is described in the unrestricted Hartree-Fock approximation of the Hubbard Hamiltonian for d electrons. Within the recursion method we show that the onset of antiferromagnetism depends strongly on the crystallographic faces investigated.

Kinetics of swelling of polymers and their gels

AbstractThe swelling limit or equilibrium swelling of semicrystalline or cross‐linked polymers and of their gels upon immersion in liquids has been investigated extensively. Few studies, however, have dealt with the kinetics of swelling. Theoretical considerations, based on diffusion‐controlled swelling, show that first‐order kinetics do not apply, even though deviations during the initial and even middle stages of the swelling process may be relatively small. Extensive studies of swelling rate and equilibrium swelling of supported and unsupported gelatin films have been published. Diffusion was always fast. After it was completed, the rate of swelling was controlled by stress relaxation in the amorphous portion of the polymer network. The rate equations for this process, which also apply to regenerated cellulose, are shown to represent second‐order kinetics with respect to the remaining swelling capacity. The following interpretation for the applicability of second‐order kinetics to the swelling of semicrystalline polymers, such as gelatin and cellulose, is given. The rate of swelling is assumed to be directly proportional to the percent swelling capacity still available at a given time and to the total internal specific boundary area enclosing those sites capable of swelling that have not yet become hydrated and swollen at that time. The latter, in turn, is also directly proportional to the percent unrealized swelling capacity.

Swelling kinetics of polymers

Abstract The equilibrium swelling of semicrystalline or crosslinked polymers and of their gels upon immersion in liquids has been investigated extensively. On the other hand, few studies have dealt with the kinetics of swelling. Swelling kinetics are important for designing controlled-release devices for drugs and agricultural pesticides based on swellable polymer matrices, and for predicting the release rates of the active ingredients. Theoretical considerations, based on diffusion-controlled swelling, show that first-order kinetics does not apply, even though deviations during the initial and even middle stages of the swelling process may be relatively small. Extensive studies of swelling rate and equilibrium swelling of supported and unsupported gelatin films have been published. The rate is controlled by stress relaxation in the swelling polymer network. The rate equations of these studies, which have also been reported to apply to cellulose, are shown to represent second-order kinetics with respect to the remaining swelling capacity. An interpretation for the applicability of second-order kinetics to the swelling of semicrystalline polymers such as gelatin and cellulose is given.

Evidence for the supermodulus effect and enhanced hardness in metallic superlattices.

A study of the mechanical properties of Cu/Nb superlattices shows that for modulation wavelengths below \ensuremath{\sim}50 \AA{} the biaxial modulus increases by \ensuremath{\sim}15%, the shear modulus decreases by \ensuremath{\sim}30%, and the flexural modulus does not change. These observations show that anomalies with different signs for elastic moduli can coexist in the same material. Measurements performed on both supported and unsupported films show that the anomalous effects are not induced by the presence of a substrate. The superlattices are also found to have a hardness larger than either Cu or Nb.

On the elastic behavior of composition-modulated superlattices

Atomistic computer simulations are used to systematically investigate the role of interfacial disorder on the elastic behavior of composition-modulated superlattices of fcc metals, represented by simple Lennard–Jones potentials. The structures, energies, and average elastic properties of four types of superlattices with various degrees of interfacial disorder are computed as a function of the modulation wavelength along [001]. The four superlattice types studied include perfectly coherent, incoherent, and two types derived from these by introducing relative twists about [001] between alternating layers. A 20% lattice-parameter mismatch between the two modulating materials is assumed. Results are compared with our earlier work on unsupported thin films, grain-boundary superlattices, and incoherent superlattices with a 10% lattice-parameter mismatch. The degree of structural disorder at the interfaces is found to correlate well with the magnitude of the elastic anomalies, which cannot be accounted for by anisotropic lattice-parameter changes alone. The grain-boundary superlattices studied earlier are found to provide a good model limit for the elastic behavior of interfacially disordered dissimilar-material superlattices.

A new ultrasonic method for measuring elastic moduli in unsupported thin films: Application to Cu-Pd superlattices

We have developed a new ultrasonic method for measuring the phase velocity of longitudinal and shear waves in self-supporting thin films. The film is bonded at one end to an interdigital transducer (IDT) which emits a continuous wave signal. The film is supported at the other end and maintained flat under a weak tension. A receiving IDT detects the in-phase and quadrature components of the sound waves as they propagate. A liquid bond is used between the receiving IDT and the film to allow a continuous variation of the path length. From the longitudinal and shear wave velocities, we can deduce the flexural and shear moduli of the film. For films of uniaxial or higher symmetry, the Young’s and biaxial moduli can be expressed as combinations of the flexural and shear moduli. We applied this technique to Cu-Pd composition modulated thin films. Contrary to previous reports, we have not observed the supermodulus effect in either the flexural, shear, Young’s or biaxial moduli for modulation wavelengths between 13 and 36 Å.

Superconducting free-standing thin films of YBa2Cu3Ox

We report a new technique of preparing unsupported thin films of YBa2Cu3Ox. These films are about 6×6 mm2 and less than half a micron thick. They were prepared via laser ablation on thin carbon films typically of order 50 μg/cm2 (∼2500 Å). When the film was annealed, the carbon oxidized leaving behind a free-standing film. The film has a superconducting orthorhombic phase and an onset temperature of ≂85 K.

Molecular Dynamics Study of (001) and (111) Thin Fcc Films

AbstractWe report on the results of molecular dynamics simulations of thin unsupported fcc films ranging in thickness from 20 layers to a monolayer. The films were oriented with either (001) or (111) free surface normals. The atomic interactions were modelled using a standard Lennard-Jones potential and a short range analytic form of the embedded atom potential. The elastic moduli of the films were determined by measuring their response to very low levels of applied stress.We find that the embedded atom and Lennard-Jones results are in relative agreement for (001) films and qualitative disagreement for (111) oriented films. We relate these differences to the nature of the interatomic potential and the thermodynamic instability of the (001) surface.

Pore structure characterization of composite membranes

Composite membranes, which consist of a thin fine-pored film (for separations with low transport resistance) on a substrate with one or more layers with larger pores (for mechanical strength), offer a particularly cumbersome or difficult pore structure analysis problem. Since the thickness of the film is usually less than 1 % that of the substrate, the specific pore volume associated with the pore region of practical interest, the film, is difficult to analyze by conventional methods such as nitrogen condensation and mercury porosimetry. Often, unsupported films are used for pore analysis and the structure of the film on the porous substrate is inferred. NMR spin-lattice relaxation measurements at 20 MHz and 303 K on water in a saturated alumina composite membrane resulted in only the substrate's pore size distribution. However, by changing the water content such that the pores in the film were saturated and only adsorbed water was in the large pores of the substrate, accurate pore size information was obtained for a supported film even though the pore volume of the film was less than 0.5% of the volume in the substrate. The pore size distribution for the supported film was significantly different from that for an unsupported film made from the same alumina sol.

A technical note on the casting of unsupported polymeric films

AbstractIn conducting research on the physical propertIes and durabIlIty of coating materials used in the conservation of art objects, difficulty was encountered In efforts to make uniformly thick, coherent, free-standing films for testing purposes. An efficientrapid casting technique has been developed utilizing reusable molds. The technique is applicable to the preparation of films from a wide range of materials.

A Technical Note on the Casting of Unsupported Polymeric Films

A Technical Note on the Casting of Unsupported Polymeric Films

Brillouin scattering from unsupported Al films.

Brillouin scattering measurements on unsupported Al films have been performed on films with thicknesses down to \ensuremath{\sim}23 nm. Both the line positions and relative intensities of the Lamb modes observed in the experimental spectra are well accounted for by theory with no adjustable parameters. Fits to the experimental dispersion curves in unsupported films are found to give somewhat more reliable values for elastic constants than fits to results on supported films.

Interference of surface relaxations in unsupported thin films.

We present embedded-atom simulations of interlayer relaxations in very thin slabs of Al and NiAl with (110) and (210) surfaces. The interlayer spacing at a given depth from the surface depends strongly on the slab thickness. For example, the value of the first-layer contraction exhibits a decaying oscillation about that for a semi-infinite solid as the slab thickness is increased. These effects can be understood as an interference of the relaxations from each of the two free surfaces of the slab. This interference model provides quantitative predictions of the slab interlayer spacings.

A Method for Preparation of Unsupported Sol–Gel Thin Films

Unsupported gel films 1 to 3 μm thick may be prepared from colloidal sol–gel systems by spin‐coating onto a camphor substrate. Sublimation of the camphor surface allows the film to separate and be freely sintered, giving a rapid indication of sintering behavior and microstructural development.

Lamb waves in unsupported thin films: A Brillouin-scattering study.

Using Brillouin scattering we have succeeded in observing the normal modes of vibration of unsupported films in a region where the dispersion relationship is quadratic. Extremely low-lying excitations were observed in thin films with thicknesses as small as 200 A\r{}. Contrary to what has been found in work on supported films, we are able to extract information on a number of the elastic moduli because the measured velocities in very thin films do not depend on the properties of the substrate. This technique should be a valuable addition to the tools which can be used in the study of materials in thin-film form.