Properties Of Thin Solid Films Research Articles

Stability of trimethylsilyl acetate-based plasma polymers towards atmospheric and water environments

In the present work, SiOxCyHz coatings were prepared in capacitively coupled RF glow discharge from gaseous mixture of trimethylsilyl acetate (TMSAc) monomer and oxygen. Properties of thin solid films prepared using continuous wave (CW) plasma and pulsed wave (PW) plasma were examined, including long–term stability in contact with air and water environments. The presented study proves that it is possible to prepare organosilicon coatings showing properties in a wide range from soft organic polymeric structures to materials similar to SiO2 with Martens hardness of 4 GPa. The content of carbon species in organosilicon structure and water contact angle (WCA) decreased with increasing oxygen ratio from 7.7 % to 75.0 %. The water contact angle of TMSAc-based coatings prepared in CW mode decreased from 95° to 76°. The application of pulsed mode using an oxygen ratio of 50 % and pulse repetition frequencies in the range of 0.33 Hz to 300 Hz led to materials with hydrophobic character (WCA in range of 86°–94°) with increased content of CHx and Si-CH3 structures in comparison to CW mode. This study proves that the aging mechanism significantly depends on deposition parameters. The increase of oxygen ratio, as well as the increase of pulse repetition frequency, led to the higher resistance towards the atmospheric environment. On the other side, organosilicon coatings prepared in CW mode using high oxygen ratios (50–75 %) showed significant delamination after immersion in water. However, the use of PW plasma for the preparation of SiOxCyHz thin films significantly improved the stability of resulting materials under water environment.

Thermal conductivity of thin film-substrate systems from two-side scanning photothermal deflection measurements: Theoretical model and validation.

Photothermal deflection (PTD) has been frequently utilized to measure the thermal properties of thin solid films on a substrate. In the models commonly used to interpret PTD data, the substrate is assumed to be an ideal thermal insulator. This assumption poses important restrictions on the reliability of these thermal measurements and limits the possibility to use PTD for also measuring the specific heat of the samples. Simultaneous knowledge of specific heat and thermal diffusivity is necessary to determine the thermal conductivity of thin solid films. In this work, we calculated the phase and amplitude of the PTD signal at the two opposites sides (film-side and substrate-side) of a thin-film substrate system. We find that, on both sides, the phases of the PTD signal primarily depend on the thermal diffusivity of the thin film, while the amplitudes primarily depend on the specific heat. By using the phases and amplitudes at the two sides, we show that the accuracy of thermal conductivity measurements by PTD can be dramatically improved. We validate our theoretical model by measuring, in a scanning PTD apparatus, the thermal properties of gold thin films, which are in excellent agreement with, and improve on, existing data from the literature.

Cationic and anionic modification of CdS thin films by surface chemical treatment

Structural and physical properties of thin solid films can be modified by surface treatment. In this work, chemical bath deposited CdS thin films were treated both by a mercury chloride solution and by a saturated H2S gas. The effect of these treatments on electrical properties is clearly observed. Hg2+ doped CdS films show the highest dark and photo-conductivities, whereas the sulfurized CdS films become photo-insensitive. In Hg2+ doped CdS samples, new crystalline Hg3S2Cl2 and Hg2(ClO4)24H2O phases are found, and particle size reduction is observed at the surface. Both optical and electrochemical Mott-Schottky (M–S) analysis suggest an intraband level in the electronic structure of Hg2+ modified CdS. Sulfurized CdS films, on the other hand, keep unchanged their crystalline and morphological structure, as well as optical properties. Energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and M–S analysis indicate an increase of sulfur concentration at the surface of sulfurized CdS thin films, leading to a more stoichiometric CdS compound, which used to have lower conductivity. It demonstrates that ion exchange process or cationic substitution is effective for structural and physical property modification, whereas a gaseous saturation method or anionic modification results in a notable surface energy alteration in thin solid CdS films.

A Series of Lithium Pyridyl Phenolate Complexes with a Pendant Pyridyl Group for Electron-Injection Layers in Organic Light-Emitting Devices.

We report a new series of lithium pyridyl phenolate complexes with a pendant pyridyl group, Li2BPP, Li3BPP, and Li4BPP, in which the pendant pyridines are substituted at the 2-, 3-, and 4-positions, respectively. The most important difference between these complexes is their molecular planarity; Li3BPP and Li4BPP adopt twisted bipyridine structures, whereas Li2BPP adopts a planar structure owing to the steric hindrance and chelating effect of bipyridine on the Li core. The planar structure leads to crystallization through π-π stacking interactions, and the small differences in the molecular structures of the pendant pyridine rings cause drastic differences in the physical properties of thin solid films of these complexes. We applied these complexes as electron-injection layers (EILs) in Ir(ppy)3-based organic light-emitting devices. When thin EILs were used, Li3BPP and Li4BPP afforded lower driving voltages than Li2BPP; the order of the driving voltages followed the order of their electron affinity values. Moreover, the dependence of driving voltage on the EIL thickness was investigated for each complex. Among the three LiBPP derivatives, Li2BPP-based devices showed almost negligible EIL thickness dependence, which may be attributable to the high crystallinity of Li2BPP. All LiBPP-based devices also showed higher stability than conventional 8-quinolinolato lithium-based devices.

Cationic lipid binding control in DNA based biopolymer and its impacts on optical and thermo-optic properties of thin solid films

Biomaterials based on deoxyribonucleic acid (DNA) have shown notable potential in optoelectronic and photonic devices. In order to further investigate the optical properties of a DNA-based lipid complex such as DNA-cetyltrimethylammonium (CTMA), which is widely used in current DNA thin film research, a new refinement process was developed to minimize the relative bound water content and control binding of CTMA onto the DNA backbone. The water contents and CTMA binding in the DNA-CTMA precipitates were identified by spectrometric measurements to quantify effects of our refinement process. Dissolving these refined DNA-CTMAs in organic solvents, thin solid films were deposited on Si and quartz substrate using the spin coating process. Their refractive indices and absorbance were measured to quantitatively assess the impact of our refinement process on the optical properties of the DNA-CTMA films. In addition, thermo-optic coefficients, dn/dT, were also measured in a temperature range from 30 to 100°C to observe differences among refined DNA-CTMAs. Detailed quantitative spectroscopic analyses and optical measurements are reported.

In-Situ Gracing Incidence X-Ray Diffraction Cell for Electrochemically Formed Thin Films

Grazing incidence X-ray diffraction allows surface sensitive measurements of structural and phase properties of thin solid films. For the characterization of layers formed during electrochemical processes ex-situ techniques are usually employed which has the requirement of a stable structure and composition of the formed films even at atmospheric conditions. For cases where this requirement is not met, in-situ techniques have been developed. Existing designs of in-situ electrochemical cells normally have the disadvantage of high absorption of the beam in the setup and/or brittle window materials. The problem of high absorption of the X-ray in the setup is normally compensated by either using very thin electrolyte films or high intensity radiation as is provided by a synchrotron. This work presents a novel solution for a grazing incidence X-ray diffraction setup. Backside-illumination of a thin film working electrode applied on a Mylar® foil by magnetron sputtering as support is used to eliminate the problem of high absorption of the X-ray in the setup. It can be used in a three electrode setup and tackles the common problems of gas evolution, voltage drop and non-constant electrolyte bulk solution in in-situ X-ray setups. The setup is tested on the anodic and cathodic formation of Cu2O on copper as an example for X-ray irradiation from a Lab-scale (not synchrotron) source.Acknowledgement: This work was jointly funded by the Austrian Research Promotion Agency (FFG, Project No. 854247) and the Carinthian Economic Promotion Fund (KWF, contract KWF-1521/28101/40388).

Characterizing and improving performance properties of thin solid films produced by weatherable water-borne colloidal suspensions on bronze substrates

While the development and application for transparent protective coatings for metals continues and broadens, the use of these coatings on high-value outdoor bronze objects, such as statues and architectural elements, requires extensive testing before use. Recent efforts in coatings technology have produced high-performance water-borne latex dispersions containing polyacrylics and poly(vinylidene fluoride) (PVDF) targeting extended coating lifetimes and improved UV resistance. Our studies show that a two-layer polymer film with a solvent based primer (Paraloid™ B-44) and a high performance water-borne topcoat (Kynar Aquatec™ RC-10206) exhibits high impedance as measured by electrochemical impedance spectroscopy. Upon annealing, those films further increased in impedance, suggesting improved corrosion protection compared to unannealed films. When soaking in water, films that contained high loading levels of coalescing agent (Dipropylene glycol monomethyl ether, DPM) in the topcoat formulation resulted in a visible whitening of the basecoat and a decrease in coating resistance. Characterization of the whitened layer by FT-IR indicated the presence of coalescent in the basecoat, suggesting that coalescent migrated from the topcoat into the primer basecoat. Annealing studies were performed to reduce uptake and reverse or inhibit water whitening.

Melting of solid nanoscale films with free surfaces

In the framework of the mean-field Landau theory and the Lindemann melting criterion, a novel method has been applied to study the properties of thin solid films. A novel profile of the order parameter in thin solid films of nanoscale thicknesses has been obtained. In terms of this method, it was shown that surface ordering of thin solid films affects their physical properties. A dependence of the order parameter on the reduced film thickness was obtained. It was shown that the melting temperature of a thin film with free surfaces decreases with decreasing film thickness. Nevertheless, it was found that there was no depression of the melting point due to the reduced thickness of films at least down to 15 nm. The results are in good agreement with available experimental data.

Shear strength determination using the nanoscratch technique and its application to thin solid films

Reliable measurement of mechanical properties of thin solid films has been challenging, despite widespread usage of thin films in applications such as semiconductor, magnetic storage, and microelectromechanical systems. Some of the challenges include instrument limitations and inadequacy of theoretical models to obtain quantitative prediction of thin film properties. In this article, we propose a technique to extract the shear strength of thin films from nanoscratch experiments using a contact mechanics analysis of a sliding sphere. Based on the stress field analysis by Hamilton, the stress status around the contact point is obtained at the initiation of yield, and is used to establish a direct correlation between contact pressure/surface traction and shear strength. Nanoscratch experiments were also performed on an extremely thin diamond carbon overcoat used in supersmooth magnetic storage disks, and the shear strength was successfully obtained using the proposed technique. These results were comparable with hardness values reported in the literature, assuming Tabor’s empirical relation (hardness ≈ 3*yield strength) and Tresca yield criterion. Finally, a finite element model was developed to simulate a rigid sphere sliding over a deformable solid to further verify the validit yo f the proposed model. The finite element analysis confirmed that the calculation results from the proposed relation are in good agreement with experimentally measured bulk property values of shear strength.

Mechanical Fatigue Measurement via a Vibrating Cantilever Beam for Self-Supported Thin Solid Films

In this paper, we develop a novel experimental apparatus, referred to as the resonant frequency device, and establish methodology to measure the fatigue properties of thin solid films. Arranging thin-film strips of our specimens into the mechanical setting of a cantilever beam and using state-of-the-art piezo actuators to generate oscillation at the clamp of the cantilever, we create a system suitable for studying the material properties of the cantilever, such as Young's modulus, fatigue and possibly, loss tangent. Deformation of the cantilever is our controlled variable in the present study, and measured with fiber-optic probes pointed at the specimen and at the piezo driver. Stress is calculated from relative deformation of the cantilever specimen with respect to the piezo actuator via a photograph of the cantilever under vibration with a curve fitting method. A LabView computer program is developed for the fatigue tests to accurately count number of cycles applied on the specimens, and a feedback mechanism is adopted to maintain displacement during the tests. Here, we present our experimental setup, procedure and theoretical models for material-property extraction. For small displacement, the two-dimensional Euler–Bernoulli beam theory is adopted. With large displacement, the system behaves as the Duffing oscillator due to geometrical nonlinearity. In addition, some experimental observations of the piezo actuators and fiber optics are reported. The method is applied to evaluate the fatigue properties of nanolayered copper-niobium composites and significant increase in the fatigue endurance limit compared to the constituent materials in the bulk form is noted.

Synthesis, Fluorescence and Photoisomerization Studies of Azobenzene‐Functionalized Poly(alkyl aryl ether) Dendrimers

A series of azobenzene-functionalized poly(alkyl aryl ether) dendrimers have been synthesized and their photochemical and photophysical properties in solution and as thin films have been investigated. Although the photochemical behavior of the azodendrimers in solution indicated that the azobenzene units behave independently, very similar to the constituent monomer azobenzene unit, the properties of thin solid films of the dendrimers were distinctly different. The azodendrimers, AzoG1, AzoG2, and AzoG3 were observed to form stable supercooled glasses, which showed long-wavelength absorption and red emission characteristics of J-aggregates of the azobenzene chromophores. Reversible photoinduced isomerization of the azodendrimers in the glassy state is described.

Structure and properties of C60–Pd films formed by electroreduction of C60 and palladium(ii) acetate trimer: evidence for the presence of palladium nanoparticles

The composition, surface morphology, structure, and electrochemical properties of thin solid films of the polymer, C60–Pd, were studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and energy dispersive X-ray fluorescence (EDXRF) as well as being examined by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) with selective area diffraction (SAD) and by cyclic voltammetry (CV), respectively. The C60–Pd films were deposited onto Au or Pt electrodes by electroreductive co-polymerization of C60 and the palladium(II) acetate trimer, [Pd(ac)2]3, in a mixed acetonitrile–toluene (4∶1, v/v) solution of 0.1 M tetra(n-butyl)ammonium perchlorate under multicyclic voltammetry or potentiostatic conditions. The structure and composition of the C60–Pd films were dependent on the relative concentration of the polymer precursors, i.e., C60 and [Pd(ac)2]3, in the solution for electropolymerization. That is, in films grown in solutions with a high [Pd(ac)2]3∶C60 ratio, (–C60–Pd–)n polymeric chains were separated by the Pd nanoclusters. These films were relatively smooth and uniform. In contrast, films electropolymerized in solutions with a low [Pd(ac)2]3∶C60 ratio were rough, porous and much less uniform. The presence of the Pd nanoclusters in the C60–Pd film influenced the electrode processes of probing redox species dissolved in solution. That is, electro-oxidation of an N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPDA) electrochemical redox probe was partially inhibited at the electrode coated by the C60–Pd film with a relatively low Pd nanocluster content. In contrast, electro-oxidation of TMPDA was effectively mediated by the C60–Pd film containing appreciable amounts of dispersed Pd nanoclusters.

Dielectric properties of thin solid films formed on silicon

We report on the measurement of the frequency-dependent complex permittivity, ɛ(ω)=′ɛ(ω)-iɛ″(ω), over the frequency range, 30 MHz to 6 GHz, of silicon wafers and of thin dielectric films formed on silicon. Measurements, as a function of temperature and time treatments, were obtained by means of an HP Network Analyzer and dielectric probe and the resulting ɛ′(ω)andɛ″(ω)plots for the silicon wafers are shown to have a Debye-type [1] profile, thereby indicating that the associated polarization mechanism is of the orientational variety.

Composition and properties of thin solid films on porous silicon surface

Research has been done on the composition and properties of natural thin film surface porous silicon (PS) coating as well as polymetacrylic acid films precipitated from water solution on the PS surface. Additional AES, elipsometric, TSDC methods have been applied to study surface films that play a decisive role in light-emitting properties of PS. The studies were done on the composition of real surface PS films containing pure silicon mixture of silicon oxides SiO λ and carbon atoms as well as the uncontrolled impurities of Cl, F, N, Fe. The research has been carried out on the precipitation of PMA polymer films that can be used for protecting PS surface from atmospheric vapours and gases and also the influence of PMA films on the spectrum of PS photoluminescence has been studied.

Size Effects on the Thermodynamic Properties of Thin Solid Films

Size Effects on the Thermodynamic Properties of Thin Solid Films

Raman-based measurements of optical properties of thin solid films: application to amorphous diamond

The potentialities of Raman spectroscopy to measure optical properties of thin solid films are considered. A new approach based on the analysis of interference-induced modification of the Raman scattering from the substrate material together with the normal reflection coefficient is proposed. It is shown that the method provides the absorption coefficient and refractive index of the film bulk with high spatial resolution and accuracy, and it can be applied to various transparent thin films. The developed approach is used to measure optical properties of amorphous diamond films deposited onto crystalline silicon. In the case of the amorphous diamond films deposited with a mass-separated ion beam, a straightforward correlation between the absorption coefficient and Raman spectra is obtained, which can be also used to estimate the optical properties. For the films deposited with pulsed cathodic arc discharge, such a relation appears to be more complex, which possibly indicates extensive variations of the sp 2 clusterization in the latter deposition method.

Vibrational spectra and thin solid films of a bi(propylperylenediimide)

The synthesis, the fabrication of thin solid films and the optical spectra of a member of a new series of bis-perylene materials—the bi(propylperylenediimide),N′,N′″-dipropyl-N,N″-bi[perylene-3,4:9,10-bis(dicarboximide)] (Pr2)—are reported. The objective of the present research effort is to provide the fundamental spectroscopic characterization of the ground electronic state and the methods for the fabrication of submicron thin solid films of these new materials which are being tested for performing elementary electrical functions of electronic devices. Pr2 is a high molecular weight perylene dye and the molecular organization formed in vacuum evaporated nanometric films is one of the key elements determining the electrical and optical properties of thin solid films. The spectroscopic techniques used in the study of fundamental vibrational modes were transmission and reflection–absorption infrared spectroscopy (RAIRS). The inelastic scattering was investigated using out-of-resonance excitation (FT-Raman), resonance Raman scattering (RRS) and surface-enhanced resonance Raman scattering (SERRS) on silver island films. The vibrational assignment of characteristic wavenumbers was assisted with semi-empirical quantum mechanical calculations.

Experimental determination of the thermo-optic properties of zirconium dioxide coatings

An experimental determination of optical constants and thermal optical properties of thin solid films is described in which the test element is a zirconium dioxide film coated onto the end face of a multimode fused silica optical fibre. Refractive index and thermal optic coefficient of the thin films for wavelengths between 700 nm and 900 nm were experimentally measured from the reflectance spectrum. The change in reflectance for the test element was measured as a function of temperature. The use of the results in the design of a thin-film fibre optic temperature sensor is discussed.

Optical properties of thin solid films of lead sulfide

The technique of electroless chemical deposition was used for preparation of thin solid films of lead sulfide (PbS). The thin solid PbS films were deposited on a glass substrate previously coated with a very thin layer of Cu2S. The optimal temperature of deposition was between 343 and 363 K. The thickness of these films was controlled by changing the concentration of the reaction solutions and the deposition time.The optical properties of these thin solid films of different thickness were determined by means of near infrared spectroscopy, Raman spectroscopy and visible spectroscopy.

Boundary lubrication and shear properties of thin solid films of dioctadecyl dimethyl ammonium chloride (TA 100)

The friction and shear strength behaviour of thin films of a surfactant dioctadecyl dimethyl ammonium chloride (TA100) has been extensively studied. These films were of different types, such as Langmuir-Blodgett (LB), hexane-retracted, self-assembly and 'melt'; they were deposited on clean soda-lime glass and sapphire flats. The frictional force required to slide spheres of soda-lime glass and sapphire on these flats was measured. The parameters investigated were (i) the contact pressure (in the range of 100-1900 MPa) between the sliding sphere and the flat, (ii) the number of friction cycles (up to 104), (iii) the substrate temperature (range: 290-380 K), and (iv) the sliding velocity (range: 0.01-0.3 mm s-1). If was found that even a single monolayer of LB film of this material causes a dramatic reduction of the friction between a glass slider and a coated glass flat: for a dean glass sphere sliding on a clean glass slide, the coefficient of dynamic friction was 0.9, whereas it dropped to a low value of 0.05-0.06 when there was a single monolayer on it. On the g)ass, films of TA100 have been shown to be considerably more durable and tenacious than those of stearic acid; even after 10000 to-and-fro friction cycles on a single track, the coefficient of dynamic friction remained at a low value of approximately 0.06. The various results obtained by varying different parameters have been satisfactorily explained using Eyring's shear flow model.