Polyimide Langmuir-Blodgett Films Research Articles

Alignment of Liquid Crystal on the Conductive Pyrolyzed Polyimide Langmuir–Blodgett Films

Abstract Highly conductive pyrolyzed polyimide Langmuir–Blodgett (LB) films showed good aligning properties for a twisted nematic liquid crystal. Static and dynamic alignment properties of the LB films were similar to those of rubbed polyimide films on ITO electrodes.

Highly conductive Langmuir-Blodgett films prepared by the pyrolysis of polymide

The structure and electrical transport properties of the Langmuir-Blodgett (LB) films of polyimide are described. The highly conductive LB films were obtained by the pyrolysis of polyimide LB films at 1000°C in vacuum or under nitrogen atmosphere. The films showed the conductivity of as high as 300 S/cm, depending on the thickness of the precursor films. The surface of the film was smooth and uniform revealed by SEM. The films were stable under ambient conditions over months.

Scanning tunneling microscopy study of a polyimide Langmuir–Blodgett film

The microscopic molecular structure of a polyimide Langmuir–Blodgett (LB) film monolayer was studied by scanning tunneling microscopy (STM) and molecular simulation. An STM image of a polyimide monolayer on graphite showing the polymer chains was observed for the first time. The STM image directly indicated that the alignment direction of the polymer chains of polyimide is parallel to the deposition direction of the LB film. In order to investigate the microscopic interpretation of the molecular structure theoretically, molecular dynamics calculations of the optimum polyimide structure on graphite were carried out. The polyimide chain on graphite has a zigzag structure with bends at the ether-bonded oxygen atoms. The distance between oxygen atoms at successive bends is 17.8 Å and the bend angle is about 119 deg. These values are in fair agreement with the STM image. Therefore, it was confirmed that the STM image can be interpreted as showing the individual molecular chains of the polyimide monolayer.

ポリイミドＬＢ膜の電子伝導

ポリイミドＬＢ膜の電子伝導

Preparation and Photocurrent Properties of Tin Dioxide Electrode Modified by Polyimide Lagmuir-Blodgett Films Possessing Tetraphenylporphyrin Unit

Polyimide Langmuir-Blodgett (LB) film containing tetraphenylporphyrin (TPP) unit was newly prepared on the surface of tin dioxide electrode by “Precursor method” (Electrode I), and the generation of photocurrent was measured by the wet system. The photocurrent spectrum obtained was very similar in shape to the absorption spectrum of the LB film. The quantum efficiency of the electrode modified by one layer of the polyimide LB film was 0.178, and the values decreased with increasing the number of layers. The long term stability of the photocurrent of Electrode I was compared with that of the electrode possessing the monomeric TPP LB film prepared from a 1:1 mixture of monoamino-TPP and stearic acid (Electrode II). These two electrodes were stable under the irradiation of monochromatic light of 430 nm, while in the case of the direct irradiation of the xenon lamp, Electrode I kept the same level of the initial photocurrent for a long time, but Electrode II decreased to 50% within one hour. The absorption spectra indicated that both LB films did not come off from the surface of the electrodes during the photocurrent measurements. The decrease of the photocurrent of Electrode II was explained by the hydrophobicity of the surface of the LB film possessing the long alkyl chain and by the diffusing effect of the reducing agent in the electrolyte solution.

Electrical properties of MIM junctions with ultra-thin polyimide Langmuir-Blodgett films

The electrical properties of metal insulator metal (MIM) junctions with an ultrathin polyimide (PI) Langmuir-Blodgett (LB) film are examined at a temperature from 20 to 300 K. For Al/PI/Al junctions, native aluminum oxide makes a significant contribution to the electrical resistance of Al/PI/Al junctions with an electrical resistance as high as 10/sup 9/ Omega mm/sup 2/, even when the number of deposited layers is zero. For Au/PI/Au junctions, the I-V characteristic shows the existence of metallic pathways when the number of deposited layers n is <30, while the I-V characteristic shows the electrical conduction mechanism ruled by the tunneling theory when n is >or=30. From the experimental results, it is concluded that PI ultrathin LB films become good electrical insulating barriers when the deposited LB films have a thickness of more than 12 nm. Breakdown voltage of the PI layers sandwiched between both aluminum electrodes and gold electrodes are also investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Highly Conductive Langmuir–Blodgett Films of Pyrolytic Polyimide

Abstract Highly conductive Langmuir–Blodgett (LB) films were obtained by the pyrolysis of polyimide LB films at 1000 °C in vacuum or under nitrogen atmosphere. The films showed the conductivity of as high as 300 S/cm, depending on the thickness of the film. The highest conductivity so far obtained was 600 S/cm. The film was stable under ambient conditions over months.

Electrical properties of polyimide Langmuir-Blodgett films deposited on noble metal electrodes

The authors have examined the electrical properties of ultrathin insulating layers of polyimide (PI) deposited on a base of Au electrodes by using tunnel junctions with structures of Au/PI/(Pb-Bi) and Au/PI/Au. For Au/PI/Au junctions, ultrathin PI Langmuir-Blodgett films having good electrical insulating properties were obtained when the number of deposited layers was greater than about 30. It was found that the I-V characteristic of electrically insulating Au/PI/Au junctions was explained by a model on Simmons' tunnelling theory (1963), assuming that application of the top Au electrode resulted in a reduction of the PI layer thickness. For Au/Pi/(Pb-Bi) junctions, typical I-V characteristics of tunnel junctions were obtained at a temperature below the critical temperature of a superconducting Pb-Bi alloy, when the number of deposited layers was 27. It was concluded that the I-V characteristic was governed by the tunnelling conduction mechanism based on the Bardeen-Cooper-Schrieffer (BCS) theory.

Electrical Transport Properties of Josephson Junctions Using Polyimide Langmuir-Blodgett Films

Using thermally stable ultrathin polyimide (PI) Langmuir-Blodgett films, we made tunnel junctions having structures of Nb/PI/(Pb–Bi) and Au/PI/(Pb–Bi). Then we examined the electrical transport properties of the junctions. Here, Nb and Pb-Bi are superconducting electrodes, and Au is a base-(noble metal) electrode. For Nb/PI/(Pb–Bi) junctions, it was found that an inherent oxide layer formed on a base-Nb electrode makes a significant contribution to the electrical conduction through the PI layer and that a typical current-voltage (I-V) characteristic based on the ideal Josephson junction was obtained even when the number of deposited PI layers was zero. For Au/PI/(Pb–Bi) junctions, typical I-V characteristics of tunnel junctions were obtained at a temperature below the critical temperature of a Pb–Bi superconducting alloy only when the number of deposited layers was 27.

The preparation of high quality y-type polyimide Langmuir-Blodgett films

This paper describes a method which we have developed to prepare high quality polyimide Langmuir-Blodgett films. The key was to achieve good Y-type deposition of the polyamic acid Langmuir films from which the polyimide films are derived. It was found to be important to control two factors carefully: the time between preparation of the spreading solution and its use, and the pressure- annealing time of the Langmuir film. The characterization of the films, which involved liquid crystal alignment properties, Fourier transform IR, scanning electron microscopy, and scanning tunneling microscopy, showed that the structural integrity was much higher for the Y-type films. Also the degree of polymer chain alignment within each layer was again much higher for the Y-type films.

Photosensitive polyimide Langmuir-Blodgett films derived from 4-(17-octadecenyl)pyridine and polyamic acid

Thermally stable and photosensitive Langmuir-Blodgett (LB) films have been developed from polyamic acid (PA) and 4-(17-octadecenyl)pyridine (ODP). Fine patterns are easily fabricated with these LB films. From experiments using model compounds it has been found that the double bond in ODP is necessary for a cross- linking reaction to occur. The normalized thickness saturates around 40% for LB films irradiated in air or under flowing nitrogen conditions. It also saturates around 40% for LB films with higher molecular weight PA. By Fourier transform IR spectroscopy and gel permeation chromatography (GPC) measurements it has been found that this saturation is not due to a side reaction of the photosensitive agent nor is it due to main chain polymer degradation. It may be due to a scission between the main chain and the side-chain which contains the photosensitive group. Although the sensitivity has not been improved by using a high molecular weight polymer, it has been found that higher molecular weight polymers have the advantage of uniformity of the film after imidization.

Electrical properties of polyimide Langmuir-Blodgett films sandwiched between superconducting electrodes: detection of microwaves

We have examined the electrical properties of ultrathin insulating layers of cadmium arachidate (C 20), polyamic acid long alkyl amine salts (PAA) and polyimide (PI) by using tunnel junctions with structures of (Pb-Bi)/PAA (or C 20)/(Pb-Bi), Au/PI/(Pb-Bi) and Au/PI/Au. Typical current-voltage ( I-V) characteristics of weakly coupled superconductors were obtained for (Pb-Bi)/PAA (or C 20)/(Pb-Bi) junctions with one, two or three deposited layers at a temperature below the critical temperature of a Pb-Bi alloy. On the contrary, typical I-V characteristics of tunnel junctions were obtained for Au/PI/(Pb-Bi) and Au/PI/Au junctions, when the number of deposited layers is greater than about 30. Finally, we concluded that the efficiency of detecting microwaves is excellent in (Pb-Bi)/PAA (or C 20)/(Pb-Bi) junctions, although bridging filaments exist in the PAA (or C 20) Langmuir-Blodgett (LB) layers, and that the PI LB layers become good electrical insulating spacers when the thickness of deposited layers is more than about 11 nm.

Application of polyimide Langmuir-Blodgett films to deep UV resists

The preparation of Langmuir-Blodgett (LB) films based on a photosensitive polyimide precursor 2 and their application to deep UV resists have been studied. LB films fabricated from a mixed monolayer of polyimide precursor 2-octadecyl alcohol-benzoin ethylether (molar ratio, 3:3:1) were found to act as negative working resists with a resolution of 0.5 μm space and 1.0 μm line, a sensitivity of 100 mJ cm -2 and good plasma etching resistance. They are promising for application as KrF and ArF excimer laser resists corresponding to 16 and 64 Mbit dynamic random access memories.

Electrochemical Behavior of Polyimide Langmuir–Blodgett Films

Abstract The redox reaction of the polyimide LB films themselves was examined by means of cyclic voltammetry. Both their cathodic and anodic current peaks decreased with potential cycling, and no peaks were observed after a few tens of sweeps, whereas the redox reaction was reversible in the case of polyimide cast films.

Evaluation of Defects of Polyimide Langmuir–Blodgett Films by Electrochemical Method

Abstract The defects of the polyimide LB films deposited on glassy carbon electrodes were examined by means of cyclic voltammetry of the redox couple of potassium ferri- and ferrocyanide in aqueous solution. The degree of defects of the polypyromellitimide LB films was apparently less than that of the cadmium arachidate LB film. The polyimide derived from aliphatic tetracarboxylic acid afforded the ten-layer LB films possessing no detectable defects.

Electrical Properties of Polyimide Langmuir-Blodgett Films and fabrication of tunnel junctions

Thermally stable multilayer films of polyimide were prepared on noble metal base electrodes by using the Langmuir-Blodgett technique. Here, the monolayer thickness of the multilayer polyimide Langmuir-Blodgett films was about 0.4 nm. We have examined the electrical properties of Au/PI/Au and Au/PI/Pb-Bi tunnel junctions.For Au/PI/Au junctions, it was found that we could get ultrathin polyimide Langmuir-Blodgett films having a good electrical insulating property when the number of deposited polyimide layers is greater than about 30. The electrical conduction mechanism through polyimide Langmuir-Blodgett films was concluded to be ruled by the well-known tunneling theory.For Au/PI/Pb-Bi junctions, typical I-V characteristics of tunnel junctions were obtained at a temperature below the critical temperature of a superconductitg Pb- Bi alloy, when the number of deposited polyimide Langmuir-Blodgett films was 27. It was also concluded that the electrical conduction mechanism through Polyimide Langmuir Blodgett films was ruled by the B. C. S. theory.From thses experimental results descrided above, we found that polyimide Langmuir-Blodgett films were very useful electrical insulating materials, having a thickness of less than several tens of nm.

Alignment control of ferroelectric liquid crystals with polyimide Langmuir-Blodgett films.

The alignment of a ferroelecric liquid crystal on polyimide LB (Langmuir-Blodgett) films was investigated. Among the samples examined, a polyimide prepared from p-phenylenediamine and 3, 3′, 4, 4′, biphenyl tetracarboxylic dianhydride was the best material in order to obtain high orientation of ferroelectric liquid crystal molecules. When the conformation of the main chain of polymer molecule was linear, the higher ordering of the liquid crystal molecule was achieved.

Molecular photodiodes consisting of polyimide Langmuir–Blodgett films possessing electron acceptor, photo-sensitizer, and electron donor units

Molecular photodiodes possessing high efficiency for light–electricity conversion are constructed from polyimide Langmuir–Blodgett films consisting of electron acceptor, photo-sensitizer, and electron donor units.

Alignment of Ferroelectric Liquid Crystals on the Polyimide Langmuir-Blodgett Films: Application to LCDs

Alignment of Ferroelectric Liquid Crystals on the Polyimide Langmuir-Blodgett Films: Application to LCDs