Polycarbonate Thin Films Research Articles

Effect of sub-micrometer polymer gratings generated by two-beam interference on surface plasmon resonance

Sub-micrometer periodic gratings were generated on thin poly-carbonate films spin-coated onto thin flat silver layer covered BK7 substrates by two-beam interference realized with the fourth harmonic of the Nd:Yag laser. The 416 nm period of the laser-induced grating was half of the applied master grating, the modulation depth was increased by the number of laser pulses at a given intensity. Attenuated total reflection measurements were performed in case of plasmon propagation directions parallel and perpendicular to the grooves, and on rotated gratings oriented at angles making the grating coupling effect detectable. Atomic force microscopy (AFM) was applied to determine the modulation depth of the gratings. It was shown that the periodically corrugated polymer surfaces resulted in the coupling of the surface plasmons already when the structure period was very close to the plasmon wavelength. The small shift of the resonance positions proved that the modulation depth cannot be explained by material removal, the material rearrangement plays an important role in the grating formation. These experimental results correlate with our temperature model calculations revealing that there is softening on the upper polymer surface and melting down to the silver layer at the lowest and highest applied laser fluences, respectively.

MICROBEAM ANALYSIS OF SINGLE AEROSOL PARTICLES AT TOHOKU UNIVERSITY

A microbeam system has been developed for the analysis of single aerosol particles. Combination of PIXE, RBS and off-axis STIM methods enabled simultaneous analysis for hydrogen to metal elements. Aerosol particles were collected on thin polycarbonate film (~0.3 μm) resulting in good signal-to-noise ratio. Quantitative elemental correlation was measured for single aerosol particles. A total of 270 particles were analyzed and clustered into 4 groups. The analysis system reveals the chemical composition of aerosol particles and is a powerful tool for source identification.

QUANTITATIVE ANALYSIS FOR Cr(III) AND Cr(VI) IONS IN ENVIRONMENTAL WATER SAMPLES BY USING PIXE

An enhanced sample preparation method for PIXE analysis is described allowing to separate and concentrate chromium ions of different valence in water samples. Cr 3+ ions are selectively adsorbed by ferric hydroxide colloids generated in the solution, and a PIXE target for analyzing the total concentration of chromium of hexavalent and trivalent states is prepared by depositing 0.15 ml of sample solution on a user-made thin polycarbonate film. PIXE analyses for the two kinds of targets reveal the fractions of chromium of different oxidation state. The standard method for collecting the colloids adsorbing Cr 3+ ions on Nuclepore filter of 0.2 μm pores is based on an investigation of the pH-dependence of the recovery of dissolved Cr 3+ ions and the calibration curve is measured. The prepared targets were examined for 5 to 10 minutes by 3 MeV proton beams (0.7-5 nA beam currents). The lower detection limit of chromium in a 25 ml aquatic sample is 1 ppb for the Cr 3+-precipitated targets and 3.4 ppb for the CrO 42--deposit targets based on the 3σ error of background counts integrated over the FWHM of chromium peak in the PIXE spectrum. The applicability of PIXE using these sample-preparation techniques for determining chromium oxidation states was confirmed using river water samples to which Cr 3+ and CrO 42- ions were added in 50 ppb concentrations.

Self-organization in thin polycarbonate films and its optical and electro-optical applications

Self-organization in thin polycarbonate films and its optical and electro-optical applications

Comparative Specular X-ray Reflectivity, Positron Annihilation Lifetime Spectroscopy, and Incoherent Neutron Scattering Measurements of the Dynamics in Thin Polycarbonate Films

There are many technological applications using thin polymer films that would be crucially influenced by confinement-induced changes in the transport properties of the film. In the present, we utilize specular X-ray reflectivity (SXR, to measure film thickness h), beam positron annihilation lifetime spectroscopy (PALS, to measure the nanometer-sized domains of unoccupied volume v), and incoherent neutron scattering (INS, to measure the mean-square atomic displacements 〈u2〉) to quantify the influence of film thickness in thin polycarbonate (PC) films. The thermal expansion coefficients of both h and v, as well as the amplitudes of 〈u2〉, indicate that thin film confinement affects reduced molecular mobility in PC. This reduced mobility is not necessarily reflected in the apparent glass transition temperature (Tg) derived from the same techniques. Specifically, SXR and PALS indicate a weak suppression of apparent Tg (the kink in the thermal expansion curve) when the film thickness becomes less than 200 A, wh...

Unusual Expansion and Contraction in Ultrathin Glassy Polycarbonate Films

The thermal expansion behavior of thin polycarbonate (PC) films supported on hydrophilic and hydrophobic silicon substrates is studied with specular X-ray reflectivity. These measurements suggest a suppression of the apparent glass transition temperature (Tg) with decreasing film thickness h on hydrophilic silicon oxide substrates, while no evidence for an h-dependent Tg shift is observed on hydrophobic passivated silicon substrates. More interestingly, we find that when h is comparable to the bulk radius of gyration, the expansion becomes nonmonotonic with temperature T in a reversible manner. Cooling one of these ultrathin PC films well below the apparent Tg gives rise to an apparently negative coefficient of thermal expansion (CTE). This unusual behavior stems from the fact that nominally Rg-thick glassy films exhibit an appreciable isothermal thickening over extended periods of time, with the propensity for this thickening increasing with the depth of cooling into the glassy state; normal thermal contraction upon cooling becomes convoluted with the sub-Tg thickening phenomenon. This is counterintuitive since deep in the glassy state the molecular mobility is anticipated to be small. The magnitude and rate of the isothermal thickening depend on the ratio of the macromolecular size to the film thickness, suggesting that chain distortion by the film boundaries is associated with this effect. The surface energy of the supporting substrate also influences these unusual behaviors.

PC薄膜を用いたガスケット面の接触状態の観察と漏れ量の予測(OS9-4 表面・接触問題)

PC薄膜を用いたガスケット面の接触状態の観察と漏れ量の予測(OS9-4 表面・接触問題)

Analysis of Trace Level Thorium and Uranium in Drainage from a Radioisotope Laboratory by Particle-Induced X-ray Emission

A procedure has been developed and tested for particle induced X-ray emission (PIXE) analysis for thorium and uranium in drainage from the radioisotope laboratory at Tohoku University. Two kinds of targets were prepared and analyzed by PIXE under the condition of 3-6 μC irradiation of 3 MeV protons. Concentrations higher than 40 ppb, regardless of the chemical forms of thorium and uranium ions in a sample solution, were determined for targets prepared by deposition of 0.15 ml solution containing Ga-internal standard on a thin polycarbonate film. Uranium was analyzed quantitatively down to 5 ppb with good precision by a pre-concentration method of dibenzyl-dithiocarbamate complexation combined with subsequent condensation into dibenzylidene-D-sorbitol gels. The PIXE analysis for these two kinds of targets can be applied to routine work for contamination control of drainage from a radioisotope laboratory using extremely long-lived actinides such as thorium and natural uranium in various experiments.

Pulsed Laser Deposition of Poly(tetrafluoroethylene), Poly(methylmethacrylate), and Polycarbonate Utilizing Anthracene-Photosensitized Ablation

A novel method of pulsed laser deposition (PLD) was applied to poly(tetrafluoroethylene) (PTFE), poly(methylmethacrylate) (PMMA), and polycarbonate (PC). The basis of the technique is that ablation is brought about by excitation not of polymers themselves but of anthracene doped in the polymer targets. Laser excitation of anthracene at 355/351 nm leads to efficient temperature elevation at the irradiated spot followed by ablation. Photosensitized PLD of these three polymers gave thin colorless films whose chemical structures and surface morphology were analyzed by infrared (IR) spectroscopy and optical/atomic force microscopy, respectively. For PTFE, IR spectra of the deposited films were almost identical to that of the PTFE target. For PMMA, a thin film was deposited, and it was assumed that crosslinking reactions occurred in the film. Furthermore, photosensitized PLD produced a thin film of PC whose chemical structure is somewhat complicated.

Study of chemical, optical and thermal modifications induced by 100 MeV silicon ions in a polycarbonate film

A thin film of polycarbonate was bombarded with 100 MeV Si 8+ ions. Fourier transform infrared and ultraviolet/visible spectroscopic techniques were employed for studying the changes in chemical and optical properties whereas differential scanning calorimetry was used for studying the changes in the thermal properties. It was observed that there was a slight shift in the optical absorption edge towards the red end of the spectrum when the ion fluence was increased. It was further observed that there was a substantial chemical and thermal modification in the sample such as breaking of CO single bond and formation of phenolic bond and gradual decrease in the glass transition temperature with the increase in ion fluence.

Incoherent neutron scattering and the dynamics of confined polycarbonate films.

Incoherent elastic neutron scattering measurements are performed on thin (75 to 1015 A) polycarbonate films supported on Si wafers. We find that the mean-square atomic displacement <u(2)> is diminished by thin film confinement. For film thicknesses comparable to the unperturbed dimensions of the macromolecule, we observe two characteristic crossover temperatures in <u(2)> as a function of temperature T, one above and the other below the bulk T(g). Furthermore, the harmonic force constant kappa, defined by the low temperature dependence of <u(2)> (i.e., kappa approximately k(B)T/<u(2)>), increases as the film thickness decreases. These observations suggest that the atoms are more strongly localized in the thin supported films.

Direct measurement of plowing friction and wear of a polymer thin film using the atomic force microscope

Nanometer-scale plowing friction and wear of a polycarbonate thin film were directly measured using an atomic force microscope (AFM) with nanoscratching capabilities. During the nanoscratch tests, lateral forces caused discrepancies between the maximum forces for the initial loading prior to the scratch and the unloading after the scratch. In the case of a nanoscratch test performed parallel to the cantilever probe axis, the plowing friction added another component to the moment acting at the cantilevered end compared to the case of nanoindentation, resulting in an increased deflection of the cantilever. Using free-body diagrams for the cases of nanoindentation and nanoscratch testing, the AFM force curves were analyzed to determine the plowing friction during nanoscratch testing. From the results of this analysis, the plowing friction was found to be proportional to the applied contact force, and the coefficient of plowing friction was measured to be 0.56 ± 0.02. Also, by the combination of nanoscratch and nanoindentation testing, the energetic wear rate of the polycarbonate thin film was measured to be 0.94 ± 0.05 mm3/(N m).

Study of Elastic Modulus and Yield Strength of Polymer Thin Films Using Atomic Force Microscopy

Nanometer-scale elastic moduli and yield strengths of polycarbonate (PC) and polystyrene (PS) thin films were measured with atomic force microscopy (AFM) indentation measurements. By analysis of the AFM indentation force curves with the method by Oliver and Pharr, Young's moduli of PC and PS thin films could be obtained as 2.2 ± 0.1 and 2.6 ± 0.1 GPa, respectively, which agree well with the literature values. By fitting Johnson's conical spherical cavity model to the measured plastic zone sizes, we obtained yield strengths of 141.2 MPa for PC thin films and 178.7 MPa for PS thin films, which are ∼2 times the values expected from the literature. We propose that it is due to the AFM indentation being asymmetric, which was not accounted for in Johnson's model. A correction factor, ε, of ∼0.72 was introduced to rescale the plastic zone size, whereupon good agreement between theory and experiment was achieved.

A Broad Perspective on the Dynamics of Highly Confined Polymer Films

ABSTRACTThe manner in which the dynamics of a polymer are affected by thin film confinement is of technological significance, impacting thin film applications such as lubricants, adhesives, and chemically amplified photoresists. In this manuscript we use specular X-ray reflectivity (SXR), beam positron annihilation lifetime spectroscopy (PALS), and incoherent neutron scattering (INS) to study the influence of thin film confinement on the apparent glass transition temperature Tg and the thermal expansion coefficients of thin polycarbonate (PC) films. Both the SXR and PALS indicate a significant suppression of Tg when the film thickness becomes less than 200 Å. However, the INS measurements suggest an increase in the apparent Tg below this same length scale. These disparate estimates of the thin film Tg seem to indicate that each technique is sensitive to slightly different aspects of the glass formation process. However, all three agree that thin film confinement results in reduced thermal motion, regardless of the precise temperature that is ‘designated' as the thin film Tg.

Effects of dipole orientation and birefringence on the optical emission from thin films

Polymers are frequently used as the emissive material in optical devices such as the light emitting diode. The long chain molecular structure of typical polymer materials together with the spin coating technique by which thin layers are fabricated results in significant optical birefringence. We outline a classical model for spontaneous emission from within such birefringent materials in planar multi-layer structures. We compare the results obtained using this model with experimental data on the radiation pattern produced by a thin film of the conjugated polymer poly[2-methoxy, 5-(2′-ethyl-hexyloxy) 1,4 phenylenevinylene] (MEH-PPV). As a control we also measured the radiation pattern from the dye Lumogen, dispersed as a guest in an optically isotropic thin film of polycarbonate. We find that birefringence and the orientation of the dipole moment of the polymer have to be taken into account to understand the departure from the expected Lambertian radiation pattern that we observe from MEH-PPV.

Extracellular matrix and culture substratum effects on trace metal content of epithelial cancer cells

The effect of extracellular adhesion factors, and of distinct culture substrata, on trace element content of epithelial cancer cells was investigated using nuclear microprobe analysis. Essential trace metal concentrations in human carcinoma cells cultured either onto tissue culture plastic dishes, onto microanalysis supports made of thin Formvar surfaces coated or not with gelatin gel, or onto polycarbonate films, were compared. Abnormally high copper concentrations were noticed specifically in cisplatin-resistant epithelial cancer cells cultured onto Formvar or polycarbonate surfaces with or without reconstituted extracellular matrix. Manganese, iron and zinc concentrations remained unchanged in these cells. These results indicate that (1) metal uptake of cells cultured onto substrata used for X-ray microanalysis can be different to that of cells cultured onto usual plastic dishes, (2) cisplatin-resistant epithelial cancer cells specifically accumulate copper when cultured onto thin Formvar or polycarbonate films, and could be used as in vitro models for copper overload studies.

Sensitized and Intrinsic Carrier Generation in Phenethylperylene/Tritolylamine Thin Film Structures

The photoconductivity mechanism was investigated for vacuum-evaporated phenethylperylene (PPEI) films deposited on a thin polycarbonate film doped with varying concentrations of tritolylamine (TTA) and subsequently exposed to methylene chloride vapors. Compared to structures without TTA in the polycarbonate layer, the presence of TTA leads to an increase of carrier generation efficiency and strong quenching of perylene fluorescence indicating a surface-sensitized carrier generation process. Fluorescence quenching measurements on samples with and without TTA show a linear correlation between fluorescence quenching and carrier generation at high fields. In the presence of TTA, significant photoconductivity is observed long before the appearance of fluorescence quenching. A marked change of curvature (inflection point) in carrier generation accompanies the appearance of fluorescence quenching at fields in excess of 100 MV/m. These results demonstrate that in samples containing TTA, two different carrier generation mechanisms are operating simultaneously. At low fields, carrier generation is dominated by the sensitized component. At high fields, although the sensitized component saturates, the intrinsic component causes a further increase in overall carrier generation. The experimental results are consistent with the notion that the intrinsic photoconductivity component originates from direct dissociation of the fluorescent first excited singlet state into free carriers.

Argon plasma-induced modifications at the surface of polycarbonate thin films

The chemical modification of the surfaces of polycarbonate films by microwave-induced argon plasma treatment has been followed by X-ray absorption spectroscopy (XAFS) and core level photoemission spectroscopy (XPS). Measurements have been made on thin films of both ex-situ spin-coated bis-phenol-A polycarbonate with phenol endgroups and the model compound bis-phenol-A polycarbonate ( n = 1) with tert-butyl phenyl endgroups evaporated in-situ in UHV on single crystal surfaces. A preferential orientation of a monolayer of the model compound on a Ag{111} surface was determined from the angular dependence of the XAFS spectra. Spectral features were assigned to contributing transitions within different moieties. Relatively mild microwave Ar plasma activation of the surfaces of both types of films led to a decrease in intensity of carbonyl features in both XAFS and XPS. Combined with the observation of new spectral features in XPS the data can be interpreted in terms of a formation of ester and ether groups in the near-surface region with possible cross-linking after desorption of CO or CO 2.

Sensitized and Intrinsic Carrier Generation in Phenethylperylene/Tritolylamine Thin Film Structures

The photoconductivity mechanism was investigated for vacuum evaporated phenethylperylene (PPEI) films deposited on a thin polycarbonate film doped with varying concentrations of tritolylamine (TTA) and subsequently exposed to methylene chloride vapors. Compared to structures without TTA in the polycarbonate layer, the presence of TTA leads to an increase of carrier generation efficiency and strong quenching of perylene fluorescence indicating a surface sensitized carrier generation process. Fluorescence quenching measurements on samples with and without TTA show a linear correlation between fluorescence quenching and carrier generation at high fields. In the presence of TTA, significant photoconductivity is observed much before the appearance of fluorescence quenching. A marked change of curvature (inflection point) in carrier generation accompanies the appearance of fluorescence quenching at fields in excess of 100 MV/m. These results demonstrate that in the samples containing TTA, two different carrier generation mechanisms are operating simultaneously. At low fields, carrier generation is dominated by the sensitized component. At high fields, although the sensitized component saturates, the intrinsic component causes a further increase in overall carrier generation. The change of slope in carrier generation at high fields is coincident with appearance of fluorescence quenching. The experimental results are consistent with the notion that the intrinsic photoconductivity component originates from direct dissociation of the fluorescent first excited singlet state into free carriers.

Photodegradation in Ballistic Laminates: Spectroscopy and Lifetime Extension*

Polycarbonate (PC), a critical component in ballistic laminates (BLs), is known to degrade upon exposure to ultraviolet (UV) light. For the purpose of reducing the photodegradation, a UV blocking chemical has been added to the adhesives used to join the layers of the BL. This report describes the development of a spectroscopic method for monitoring surface photodegradation of PC and the method's use in demonstrating the effectiveness of the UV blocker. Reports in the literature demonstrate that photodegradation in thin PC films may be detected by transmission infrared (IR) spectroscopy. The present work extends this approach to thick films, where small surface changes are detected by reflectance IR spectroscopy. We show that UV photodegradation of the PC surface produces a characteristic shift in the carbonyl absorption band at about 1775 cm−1. This shift is consistently observed in PC samples that have been subjected to direct artificial exposure and in PC samples that have been subjected through the outboard layers of the BL to both natural and artificial exposure. When a UV blocker is incorporated into the adhesive layers of the laminate, no peak shift is observed in the carbonyl band after the equivalent of 10 years of exposure.