Phthalocyanine Langmuir-Blodgett Films Research Articles

Langmuir-Blodgett films of phthalocyanines

The type of molecular packing developed within Langmuir-Blodgett (LB) film assemblies of phthalocyanines is shown to be dependent upon the choice of substituents on the ring system. Phthalocyanine derivatives cited in this paper include examples which possess two features which favour self-assembly; amphi-philic character and thermotropic liquid crystal behaviour. These materials show excellent monolayer and deposition behaviour. The LB films are well ordered and undergo structural reorganization at the molecular level on heating. Preliminary data from gas sensing experiments suggest that a film of one of these compounds shows a selective response to NO2 vapour.

Study on the stability of a copper phthalocyanine Langmuir-Blodgett film gas-sensitive element

The stability of an asymmetrically substituted copper phthalocyanine (AsyCuPc) Langmuir-Blodgett (LB) film gas-sensitive element which showed good selective sensitivity to NH 3 in air was inspected by an aging test on the device. The reasons leading to the change in response characteristic with time are discussed. It is indicated that the change in gas-sensing response of the AsyCuPc LB film probably arises from the variation in film structure due to the influence of some external factor such as environmental temperature and vibration.

U-shaped distribution of interface states in metal-(Langmuir-Blodgett) Si structures with phthalocyanine Langmuir-Blodgett films

A considerable part of the effort aimed at practical applications of Langmuir-Blodgett (LB) films is based on metal-insulator-semiconductor structures with an incorporated LB layer as the insulator. In accordance with this trend the present communication deals with a study of the metal-LB-Si structures with thin copper tetra-4- t-butylphthalocyanine films deposited by the conventional LB technique onto silicon substrates (ϱ ≈ 5 Ω cm). The experimental methods used were deep-level transient spectroscopy in a charge-modification mode and a feedback charge C-U method. The analysis of the results indicates the existence of energy states at the LB-Si interface. The states form a continuous U-shaped spectrum in the gap of the semiconductor. The high density of the states (about 10 12eV −1 cm −2) is typical of the “wet” technologies to which LB deposition belongs.

A gas-humidity sensor fabricated with phthalocyanine Langmuir-Blodgett film

Langmuir-Blodgett films of a symmetrically substituted copper phthalocyanine were deposited onto planar interdigital gold microelectrode arrays designed specially with a heating resistor. Measurements on this device showed that it could be used as a humidity sensor at room temperature, and as a gas sensor when it was heated by heating the resistor. Either as a humidity or gas sensor, it exhibits high sensitivity, rapid response and good stability. It has excellent selectivity to NH 3 as a gas sensor.

Structural study of spin coated and LB films of monomeric and oligomeric phthalocyanines

The Langmuir monolayer and Langmuir-Blodgett (LB) deposition behaviour of asymmetrically substituted 1,4-bis(6-hydroxyhexyl)−8,11,15,18,22,25-hexa-octylphthalocyanine ( 1) and a phthalocyanine dimer ( 2) and trimer ( 3) have been investigated. The materials were also deposited onto glass by the spin coating (SC) technique. The spin coated films were exceptionally smooth, even and free from crystallites. X-ray reflectivity measurements reveal varying degrees of order. Unpolarized UV-visible absorption spectra of the films deposited by the two techniques were closely similar. The LB technique has the advantage of introducing some degree of anisotropic ordering of the molecules within the films of the monomer and dimer whereas the SC method has the advantage of convenience.

Low temperature studies of substituted copper phthalocyanine Langmuir-Blodgett films

Molecules of copper phthalocyanine were specially substituted for better adherence and alignment in ultra thin films prepared by the Langmuir-Blodgett (LB) technique. The basic pressure-area isotherms and the optical absorption spectroscopic studies suggest that the LB films were deposited as monolayers. The layers were transferred onto quartz substrates predeposited with interdigitated platinum electrodes. The AC and DC characteristics within a temperature range of 77 K to 300 K. provided quantitative information on the transport properties of the thin films. The results verify the previously established power-law dependence of the conductivity on the frequency.

Fluorescence hole-burning spectroscopy of phthalocyanine Langmuir-Blodgett films

Low-temperature fluorescence and fluorescence excitation spectra of H2-tetra-4-tert-butyl phthalocyanine Langmuir-Blodgett films consisting of well-ordered phthalocyanines in domains and off-domain phthalocyanine molecules in random-oriented positions were measured. Persistent spectral hole burning was applied to study the role of fast excited energy transfer from domains to off-domain molecules.

Resonance Raman Scattering in Langmuir-Blodgett Films of a New Phthalocyanine

Abstract In this paper we present the results of Raman and optical spectroscopy measurements on Langmuir-Blodgett layers of a new phthalocyanine derivative. In particular we studied the eventual differences between Raman spectra obtained using the SERS advantage and those obtained without it. Furthermore the effects of resonance with the electronics states of the Q-band were studied. Finally, we made a preliminary investigation of the sensitivity of the samples to laser light.

Gas Sensing Device Based on Phthalocyanine LB Films

Abstract An investigation of the electrical conductivity of films consisting of multilayers of tetra-t−butyl-substituted copper phthalocyanine (TTBCuPc) films exposed to various levels of nitrogen oxides in air (within the ppm range) was carried out. The TTBCuPc films were deposited, using the Langmuir-Blodgett (LB) technique, onto glass substrates. Gold interdigital electrodes (ca. 2μm thick, 100 μm wide and 100 μm spaced) were evaporated on the top of the films. High reproducibility and reasonable sensitivity of the sensors to the nitrogen oxide at a relatively low temperature (313 K) suggest that TTBCuPc may be a viable material for gas sensing devices.

Photophysical properties of the phthalocyanine Langmuir-Blodgett films studied by hole burning spectroscopy

The hole burning method was applied to the study of the photophysical properties of H 2-tetra-4-tert-butyl phthalocyanine (H 2-TTBPc) Langmuir-Blodgett film. The fluorescence spectra of this film together with the hole profile and the holewidth temperature dependence are presented. The influence of the fast excited state energy transfer on the presented results is discussed.

Role of central metal in phthalocyanine Langmuir-Blodgett films studied by hole burning

The persistent spectral hole burning technique was applied to the fluorescence spectra of free base tetra-4- tert-butyl phthalocyanine and chlor-aluminium tetra-4- tert-butyl phthalocyanine multilayer Langmuir-Blodgett films. Resonant zero phonon holes were burnt into the O-O fluorescence band near 700 nm at 4.2 K. A set of red shifted off-resonant holes is explained as due to localized molecular vibrational states. For both free base and central metal phthalocyanine Langmuir-Blodgett films the structure of the hole burned spectra indicates a photophysical hole burning mechanism.

Experimental studies on substituted copper phthalocyanine Langmuir-Blodgett films

Using the Langmuir-Blodgett (LB) technique, novel copper bis(3-hydroxypropyloxy-hexaisopentyloxy)phthalocyanine molecules were deposited on quartz substrates. It is argued on the basis of pressure-area isotherms that films are deposited as monolayers. Optical absorption spectroscopy suggests that the deposited films were uniform. A.c. measurements were performed on LB films in a planar configuration at different temperatures. The power-law dependence of the conductivity on frequency is explained in terms of electronic conduction through hopping over a coulombic barrier 0.66 eV high. The Debye relaxation time is estimated to be of the order 811 µs at room temperature.

Nonlinear grating behavior of phthalocyanine Langmuir–Blodgett films

Optical second-harmonic generation was observed from nickel tetracumylphenoxy phthalocyanine films deposited on quartz by the Langmuir-Blodgett (L-B) technique. The L-B films consist of microcrystallites, i.e., phthalocyanine aggregates, which have a preferred in-plane orientation with respect to the deposition direction. The L-B films also display characteristics of a nonlinear grating with the same periodicity and groove depth over the entire surface. This is to our knowledge the first time that such nonlinear grating behavior has been observed from an organometallic multilayer film.

The characterization of two copper phthalocyanine Langmuir-Blodgett films and their gas-sensitive properties

The monolayer and deposition behaviour of a symmetrically substituted copper tetra-4-(2, 4-di-t-amylphenoxy) phthalocyanine (tapCuPc) and an asymmetrically substituted copper [tri-4-(2, 4-di-t-amylphenoxy)-mono-4-(-2-methoxyethoxy)]phthalocyanine (AsyCuPc) were investigated. The results on monolayer behaviour and spectroscopic characterization of the LB films show that both CuPc molecules in a monolayer at the air-water interface and the LB films are stacked and inclined. The gas-sensitive properties show that the responding speed of AsyCuPc LB film is faster than that of tapCuPc LB film.

Interaction between copper tetra-4(2,4-di tert-amylphenoxy) phthalocyanine Langmuir-Blodgett films as a gas-sensitive sensor and NH 3

Copper tetra-4-(2,4-di tert-amylphenoxy)phthalocyanine (tapCuPc) Langmuir-Blodgett (LB) films were deposited onto planar interdigital microelectrode arrays and the process of the interaction between the tapCuPc LB films and NH 3 was studied. The process of the interaction resulted in a large increase in the conductance of the LB film. The results of response and recovery processes were given when the tapCuPc LB films were exposed to 100 ppm NH 3 gas in air. It was suggested that the response process of the interaction between the tapCuPc LB films and NH 3 can be described by the relation I = I. 1−exp(− t/ τ), and the recovery process of the tapCuPc LB film may be described by the relation I = I exp(− t/ τ 1). The two relations are in approximate agreement with the response and recovery curves measured in the experiment. From the two relations we can obtain that the response and recovery times are 32s and 13 min respectively; the adsorption and the desorption probabilities are 3.12 × 10 -2 s -1 and 1.28 × 10 -3 s -1 respectively. The gas-sensitive sensor consisting of the tapCuPc LB film can detect NH 3 gas down to 2 ppm in air.

The effect of film-forming conditions for tapCuPc Langmuir-Blodgett films on morphology and properties

The dependence of morphology and properties on film-forming conditions is described for the symmetrically substituted copper tetra-4-(2, 4-di- t-amylphenoxy) phthalocyanine (tapCuPc) Langmuir-Blodgett (LB) films. The effects of LB film-forming conditions (such as the surface pressure, pH value and the concentrations of spreading solutions) on film quality were studied with the help of a UV-visible spectrophotometer and a transmission electron microscope. Transmission electron microscopy photographs of the surface morphology of tapCuPc LB films show that a smooth and homogeneous surface structure can be obtained under optimum film-forming conditions.

Substituted silicon phthalocyanine Langmuir-Blodgett film and its possible use in electronic devices

This paper summarizes the preparation of Langmuir-Blodgett (LB) films of a substituted silicon phthalocyanine, namely tetra-4- tert.-butyl-phthalocyaninato-silicon dichloride (ttb-PcSiCl 2), and its possible use in electronic devices. We describe how high quality ttb-PcSiCl 2 LB films which exhibit mechanical and thermal stability can be successfully deposited. The aggregation in the floating film is much reduced and the molecules are stacked edge on to the substrate with a preferred orientation perpendicular to the dipping direction. These are two distinct types of possible use for this film in electronic devices whose performance is enhanced by the incorporation of a few monolayers of ttb-PcSiCl 2: (1) the phthalocyanine layers take an “active” part in photovoltaic devices and gas-sensitive structures; (2) the layers play a “passive” role in metal-organic chemical-vapour-deposited (MOCVD) ZnSe/LB film and MOCVD InP/LB film metal insulator/semiconductor structures.

An optical sensor for nitrogen dioxide based on a copper phthalocyanine Langmuir—Blodgett film

A copper phthalocyanine Langmuir—Blodgett film has been incorporated in an optical gas sensor which exploits the phenomenon of surface plasmon resonance. For the detection of nitrogen dioxide, a significant improvement over previous work is demonstrated. The use of an ultra-thin layer of nickel to protect the underlying silver layer is also reported.

Characterization of copper phthalocyanine Langmuir-Blodgett films

Asymetrically substituted copper phthalocyanine (as-CuPc) Langmuir-Blodgett (LB) films are prepared on metal-coated quartz substrates and the electronic behaviour of sandwich structures of metal/CuPc LB film/metal are studied under normal laboratory ambients. The results show that CuPc films are very stable and reproducible. D.c. measurements produce ohmicI(V) characteristics while the a.c. conductance shows a power-law dependence on the frequency.

Phthalocyanine Langmuir-Blodgett film microsensors for halogen gases

Microsensors for halogen gases fabricated by Langmuir-Blodgett films of phthalocyanine [(C 6H 13) 3SiOSiPcOGePcOH] (where Pc is the phthalocyanato dianion) and planar microelectronic technologies are evaluated. The sensor incorporates a micro heater and a diode to control the temperature of the film. The gas concentration is measured by the conductance change. The film temperature effects on sensitivity, rise and decay times, as well as pulsed operation have been studied experimentally. The Cl 2 sensor reaches a sensitivity peak at 130 °C and the conductivity of the film changes from 10 -10 to 10 -6 mho cm -1 in 111 ppm pre-mixed Cl 2/N 2 mixture. The response and recovery times are about 1 min at 130 °C. For the I 2 sensor, the peak response is at 20 °C and the conductivity changes from 10 -9 to 10 -8 mho cm -1 for 40 ppm I 2 in air. The response and recovery times are about 20 s.