Effects of interactions with the surface on the orientation of the mesogenic monoazacrown-substituted phthalocyanine films

In this paper, the effect of interaction with the substrate surface on the orientation of films' molecules of substituted liquid crystalline phthalocyanines M(II)Pc (M = Cu, Ni, Zn) having monoazacrown ether moieties on the periphery containing long alkyloxyphenyl N-pivotal groups is studied. The phthalocyanine derivatives demonstrate thermotropic mesophase behaviour and show Col_h mesophases over a wide temperature range. The preferential orientation of the phthalocyanine films deposited on glass, silicon and NaCl substrates as well as between two of those substrates is studied by polarized Raman spectroscopy at different temperatures. These phthalocyanines form homeotropically aligned films on the surface of NaCl substrate, whereas planar alignment with a random distribution of the column directors occurs on the glass slides.     

Structural change of Langmuir-Blodgett film of tetra-neopentoxy phthalocyanine zinc during heat treatment

Langmuir-Blodgett (LB) films of tetra-neopentaxy phthalocyanine zinc (TNPPcZn) were prepared and annealed at a selected temperature. Their optical spectra and optical constants were measured and the structural changes of the films were studied by X-ray diffraction. The arrangement of molecules in the TNPPcZn LB film is changed from disorder to order due to increase of the dimer when the films are annealed at the temperature range of 363 to 433 K. When the annealing temperature is increased further from 433 K to the 573 K, the film undergoes a reorganization in which the orientation of phthalocyanine rings are transformed formed from perpendicular to the substrate surface into parallel to the substrate surface, because the dimers are destroyed owing to the segregation of the neopentoxy and the monomers are recovered.     

The anisotropic gas response behavior of LB films of an amphiphilic asymmetrically substituted phthalocyanine

1,4-Di(2-hydroxyethoxy)-9,10,16,17,23,24-hexapentyloxy phthalocyanine (asy-Pc) has been deposited as well-ordered Langmuir–Blodgett (LB) films on a glass substrate and glass-bearing interdigital electrodes. The molecular orientation of the asy-Pc LB films has been characterized by polarized UV-vis absorption spectra and in-plane dichroism has been observed. The LB films show good room temperature response to NO₂ gas and the recovery is almost complete. It has been found that the magnitude of the response increases with increasing gas concentration and is also dependent upon the LB dipping direction relative to the arms of the electrodes, consistent with conduction being favored along the axes of the stacks of asy-Pc molecules.     

Surface characterization of the monolayer and Langmuir–Blodgett films of tetra-tert-butyl-copper phthalocyanine

The relaxation and hysteresis phenomena of the tetra-tert-butyl-copper phthalocyanine (ttb-CuPc) monolayer were investigated. The monolayer was then transferred to a hydrophilic glass surface to prepare one monolayer of Langmuir–Blodgett (LB) films. The uniformity, stability and molecular arrangement of the LB films were studied by measurements of dynamic contact angle (DCA), and were compared with the information obtained by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results show that the monolayer of ttb-CuPc is generally stable. The limiting area of a molecule is smaller than those reported in the literature, which is attributed to the aggregation of ttb-CuPc molecules into multilayer domains. The advancing and receding contact angles of water on these LB films are much smaller than those on a homogeneous film prepared by vacuum deposition. The wettability analysis on the LB films suggests that ttb-CuPc molecules are not arranged uniformly and continuously, and the LB film of ttb-CuPc contains a high ratio of exposed glass substrate. The surface morphology inspected by TEM and AFM shows the formation of separated domains of ttb-CuPc molecules, which is consistent with the surface condition evaluated from the surface wettability.     

Optical characterization of electron beam evaporated chloroindium phthalocyanine thin films

In present study, the optical properties of chloroindium phthalocyanine (ClInPc) thin films prepared by electron beam evaporation have been investigated. The optical characteristics of the prepared thin films have been determined using spectrophotometric measurements of the absorbance, transmittance and reflectance at normal incidence in the spectral range 300–1,100 nm. Surface morphology of thin films is studied using field emission scanning electron microscopy. The absorption spectra recorded in UV-Visible region for the deposited films show two well defined intense absorption bands of phthalocyanine molecule; namely the Q-band and the Soret (B-band). The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region have been performed to determine the optical band gap energy and type of the electronic transition, which reveals the probability of direct and indirect transitions. Moreover, by studying the absorption coefficient spectra just below the fundamental absorption edge, the width of band tails of localized states (Urbach energy), steepness parameter and width of the defect states have been evaluated. The obtained results of this novel grown ClInPc thin films support the desirable feature for the optoelectronic devices.     

Molecular orientation analysis of a single-monolayer Langmuir-Blodgett film on a thin glass plate by infrared multiple-angle incidence resolution spectrometry

Molecular orientation analysis in a single monolayer deposited on a glass substrate has been a difficult matter, since the glass substrate absorbs infrared rays so strongly that the measurements of infrared spectra are difficult to perform, and the single monolayer is not suitable for X-ray diffraction analysis because no periodical structure is available. When a thin glass is used as the substrate, in particular, the infrared analysis becomes more difficult, since optical fringes appear strongly on the absorption spectra due to the multiple reflections in the glass. In the present study, infrared multiple-angle incidence resolution spectrometry (MAIRS) has been employed to remove the fringes from the spectra of single- and five-monolayer Langmuir-Blodgett (LB) films of cadmium stearate deposited on a thin glass plate. The MAIRS in-plane spectra gave quantitatively reliable infrared transmission spectra for both films with little fringes, which made it possible for the first time to analyze the molecular orientation in the single-monolayer LB film on glass. As a result, it has been revealed that the molecule in the single-monolayer LB film on thin glass exhibits a significantly larger molecular tilt angle than those prepared on other substrates such as gold and germanium.     

Morphology, structural and optical characterization of electron beam evaporated bromoaluminium phthalocyanine (BrAlPc) thin films

Bromoaluminium phthalocyanine (BrAlPc) thin films have been deposited onto pre-cleaned glass substrates by electron beam evaporation technique. Thin films have been characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and optical absorption (UV–Vis) spectra. XRD studies of BrAlPc thin film deposited at room temperature shows the indication of the α-phase. FESEM images have shown that the most of particles are spherical in shape with an average size about 26–34 nm. Using UV–Visible spectra over the wavelength range 300–800 nm, the optical band gap, absorption coefficient and extinction coefficient of BrAlPc thin films are evaluated. The optical absorption measurements of thin films show that the absorption mechanism is due to direct transition.     

Electrical and optical properties of one-dimensional metallophthalocyanine (M?=?Fe) thin films grown by thermal evaporation

Semiconducting molecular materials based on iron phthalocyanine and diamine ligands have been successfully used to prepare thin films by a thermal evaporation technique. The samples were deposited on corning glass substrates and crystalline silicon wafers and were characterized by FT-IR, UV–Vis, SEM and EDS. The optical parameters have been investigated using spectrophotometric transmission measurements in the 200–1,150 nm wavelength range. The UV–VIS spectra of the films show two well defined absorption bands, namely, the Soret and the Q-band. The values of the optical band gap E_g (direct transitions) calculated from the absorption spectra, ranged between 3.30 and 4.38 eV. The effect of temperature on the conductivity of the films was also evaluated and the electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.04–0.64 eV, were calculated from Arrhenius plots.     

Thickness dependence of structural, electrical and optical properties of sprayed ZnO:Cu films

ZnO:Cu thin films have been deposited by spray pyrolysis techniques within two different (450 °C and 500 °C) substrate temperatures. The structural properties of ZnO:Cu thin films have been investigated by X-ray diffraction techniques. The X-ray diffraction spectra showed that ZnO:Cu thin films are polycrystalline with the hexagonal structure and show a good c-axis orientation perpendicular to the substrate. The most preferential orientation is along the (002) direction for all spray deposited ZnO:Cu films together with orientations in the (100) and (101) planes also being abundant. Some parameters of the films were calculated and correlated with the film thickness for two different substrate temperatures. The optical properties of ZnO:Cu thin films have been investigated by UV/VIS spectrometer and the band gap values were found to be ranging from 3.29 eV to 3.46 eV.     

Preparation of poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester Langmuir-Blodgett bulk hetero junctions on indium tin oxide

Mono-layers of aggregated Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) molecules were obtained by using solutions of P3HT, PCBM and P3HT-PCBM mixture without stabilizers such as stearates in chloroform at an air-water interface. 1 to 10 cycle-lifted LB films of P3HT and PCBM were successfully transferred to cleaned bare indium-tin-oxide coated glass substrate by vertical lifting method excluding the first 1 to 2 cycle layer. The dependence of P3HT and PCBM film thickness on the transfer cycles has been explained by the molecular sizes, where four edge-on P3HT molecular and six PCBM molecular stacking which result in thickness was taken into account. Work functions of deposited LB-layers were consistent with those of the ordinary casted films. P3HT and PCBM LB-layers showed optical activity in both infra-red (IR) and visible absorption regions of the spectrum. P-polarized IR absorption owing to C=C and C=O stretching vibrations observed in LB-layered films clearly indicate the enhancement of the orientation of these bonds perpendicular to the substrate surface in contrast to the spin-coated one. Visible optical absorption intensity was increased well in proportion with the lift cycle-numbers of both P3HT and PCBM LB films. The photovoltaic characteristics have been observed in the devices fabricated with P3HT (5 cycles-layer)/PCBM (5 cycles-layer) LB hetero structure as an active layer of the solar cells. The surface pressure of LB compression for the mixture of P3HT and PCBM, that is, bulk hetero mixtures, has also been well built up to 30 mN/m.     

Influence of substrate temperature on crystalline copper aluminium oxide thin films synthesized through chemical spray pyrolysis (CSP) technique

Copper aluminium oxide (CuAlO₂) of well ordered crystalline films were deposited on to glass substrates with Cu/Al ratio r = 0.8 at the substrate temperatures of 250, 300, 350, 400 and 450 °C. Films which were characterized had a thickness of the order of few micrometers. Films deposited at the optimized deposition temperature (450 °C) revealed well-crystalline CuAlO₂ phase with XRD peak at 2θ = 31.7° corresponds to (006) reflection. The peak positions of the core level XPS spectra, confirm the presence of delafossite CuAlO₂ phase. The optical transmission of 80 % has been observed in the visible spectrum. The obtained band gap energy is 4.1 eV. From the observed results it was evidenced that the substrate temperature has strong influence on the structural and optical properties of the spray pyrolysed copper aluminium oxide films.     

Optical characterization of organic material bromoindium phthalocyanine thin films grown by electron beam evaporation

This paper presents the optical properties of organic material bromoindium phthalocyanine (BrInPc) thin films grown by electron beam evaporation technique. The paper describes the optical characteristics of BrInPc thin films, which have been determined using spectrophotometric measurements of the absorbance, transmittance and reflectance at normal incident of light in the spectral range 300–1,100 nm. The optical band gap energy and type of the electronic transition have been determined by analysis of spectral behavior of absorption coefficient, which reveals the probability of both direct and indirect transitions. Other optical constants, such as refractive index, extinction coefficient, complex dielectric constant and optical conductivity of thin films have been evaluated. Moreover, the width of band tails of localized states (Urbach energy), steepness parameter and width of the defect states have been determined by studying the absorption coefficient spectra just below the fundamental absorption edge.     

Properties of cu-doped low resistive ZnSe films deposited by two-sourced evaporation

Two-sourced evaporation technique is used to prepare hard ZnSe films by controlling the evaporation rates of both Zn and Se at substrate temperature of 400 °C. The films are doped with Cu by immersion in the Cu(NO₃)₂-H₂O solution for different periods of time. The XRD has not shown a drastic change in the film structure while the electrical resistivity of the deposited film dropped from 10⁹ Ω-cm to about 1.6 Ω-cm for solution immersed films after heat treatment. Optical properties of deposited and doped films, such as film thickness, absorption coefficient and optical band gap have been calculated from the normal transmission spectra in the range of 300-2200 nm.The optical results show a decrease of the transmission and an increase of the refractive index and a slight shift in the optical band gap. Chemical composition of the Cu is determined by using absorption of immersed films. The composition of Cu is also compared with the composition detected by electron microprobe analyzer (EMPA).     

ZnTe薄膜特性研究

用真空共蒸发法在室温下制备了ZnTe:Cu多晶薄膜.用XRD表征薄膜结构,刚沉积未掺Cu和适度掺Cu的薄膜为立方结构,高度(111)择优,重掺Cu的为立方和六方混合相.室温时薄膜的形貌和光能隙取决于掺Cu浓度和退火温度,并通过透射光谱的测量计算出光能隙.重掺Cu的薄膜具有反常电导温度关系.     

Substrate temperature influence on ZnS thin films prepared by ultrasonic spray

ZnS thin films were deposited by ultrasonic spray technique. The starting solution is a mixture of 0.1 M zinc chloride as source of Zn and 0.05 M thiourea as source of S. The glass substrate temperature was varied in the range of 250 °C-400 °C to investigate the influence of substrate temperature on the structure, chemical composition and optical properties of ZnS films. The DRX analyses indicated that ZnS films have nanocrystalline hexagonal structure with (002) preferential orientation and grain size varied from 20 to 50 nm, increasing with substrate temperature. The optical films characterization was carried out by the UV-visible transmission. The optical gap and films disorder were deduced from the absorption spectra and the refractive indices of the films were determined by ellipsometric measurements. It is shown that the obtained films are generally composed of ZnO and ZnS phases with varied proportion, while at deposition temperature of 400 °C, they are near stoichiometric ZnS.     

Orientation study of iron phthalocyanine (FePc) thin films deposited on silicon substrate investigated by atomic force microscopy and micro-Raman spectroscopy

In this article, we present temperature and orientation study of iron phthalocyanine (FePc) thin films with different thickness deposited on silicon substrate. The organic thin films were obtained by the quasi-molecular beam evaporation. The micro-Raman scattering spectra of FePc thin layers were investigated in the spectral range 550–1,800 cm⁻¹ using 488-nm excitation wavelength. The Raman scattering and atomic force microscopy studies were performed at room temperature before and after annealing process. Annealing process of thin layers was carried out at 453 K for 6 h. From polarized Raman spectra using surface Raman mapping procedure the information on distribution of polymorphic phases of FePc layers has been carried out. Moreover, the obtained results showed the influence of the annealing process on the ordering of the molecular structure of thin films deposited on silicon substrate. For the very thin layers we did not observe the change of the polymorphic phase but only reordering of the thin layers and change of molecular structure to intermediate phase. Using atomic force microscopy method, we observed arrangement of the thin layers structure connected with the change of roughness of the thin layers after annealing process. The obtained results indicate that the structure of thin layer deposited on silicon substrate is strongly affected by the annealing process.     

Synthesis and properties of epitaxial SnO2 films deposited on MgO (100) by MOCVD

Epitaxial tin oxide (SnO₂) thin films have been prepared on MgO (100) substrates at 500-600 °C by metalorganic chemical vapor deposition method. Structural and optical properties of the films have been investigated in detail. The obtained films were pure SnO₂ with the tetragonal rutile structure. An in-plane orientation relationship of SnO₂ (110) [010]//MgO (200) [110] between the film and substrate was determined. Two variant structure of SnO₂ were analyzed. The structure of the film deposited at 600 °C was investigated by high-resolution transmission electron microscopy, and an epitaxial structure was observed. The absolute average transmittance of the SnO₂ film at 600 °C in the visible range exceeded 90%. The optical band gap of the film was about 3.93 eV.     

Ordered Langmuir-Blodgett films of a substituted lutetium bisphthalocyanine

High-quality LB multilayers have been prepared from the Lu(III) sandwich complex of 2,3,9,10,16,17,23,24-octa (n-butoxy)phthalocyanine (LuPc₂(OBu)₁₆). Surface pressure-area isotherms were characterized and indicate that a stable monolayer is formed corresponding to an area per molecule of 2.4 nm² at 30 mN m⁻¹. The LB films were highly birefringent, and polarized spectra gave dichroic ratios of 3.3 for the 670 nm absorption band and between 0.5 and 2.8 for infrared absorptions. The results indicate that the phthalocyanine rings were highly oriented perpendicular to the dipping direction but somewhat tilted from the substrate normal. The order was shown to be absent when (i) unsubstituted LuPc₂ was used for LB films, or (ii) the horizontal lifting method of film deposition was used, or (iii) the surface pressure was increased to 50 mN m⁻¹, causing a molecular rearrangement. The ordering was improved at 100 °C and finally lost at 280 °C by annealing on a hot stage. The d.c. electrical conductivity of LB films of LuPc₂(OBu)₁₆ was low (σ ≈ 2 × 10⁻⁷ Ω⁻¹ m⁻¹), in contrast with unsubstituted LuPc₂ (σ ≈ 10⁻¹ Ω⁻¹ m⁻¹) and showed no evidence for anisotropy. The findings are in broad agreement with related studies and illustrate some of the many factors involved in improving the structure of phthalocyanine LB films for possible applications.     

Preparation and characteristics of Y2O3-doped CeO2 film by r.f. magnetron sputtering

Properties and applications as a pH sensor of Y₂O₃-doped CeO₂ films prepared by r.f. magnetron sputtering were studied. The CeO₂-Y₂O₃ films exhibited higher electric conductivity than yttria-stabilized zirconia. Films deposited on an MgO single-crystal (100) substrate without substrate heating had a more dense structure. The microstructure of the samples deposited at a substrate temperature of 873 K was shown to be columnar by scanning electron microscope. X-ray diffraction studies showed that a (111) diffraction peak assigned to CeO₂ was much greater and the films exhibited preferential orientation to the (111) plane with increasing r.f. power or substrate temperature. The pH electrode was made by a double layer of Y₂O₃-doped CeO₂ and Cu/Cu₂O redox films deposited onto the MgO substrate. pH response was measured in various pH buffer solutions at room temperature. It showed good agreement with a nernstian response in the pH range 9–13.     

Modeling of fluorescence emission from cyanine-dye-impregnated Langmuir-Blodgett films deposited on the surface of an optical fiber

Fluorescence emission was collected from cyanine-dye-impregnated Langmuir-Blodgett (LB) films of cadmium arachidate deposited on the surface of a quartz multimode optical fiber. A Y-type fiber optic coupler system was used to allow remote, distal-end spectral excitation and collection as the fiber tip was repeatedly dipped into the LB trough. Built-up LB films of up to 400 LB layers were examined. Fluorescence emission intensities were modeled as a function of the number of layers, or LB film thickness, using a simplified theory based on planar thin film optics. The fit of theory to experiment was qualitatively satisfying, indicating that LB films of reasonable optical quality can be deposited on the surface of cylindrical optical fibers.