Showing papers on "Indium tin oxide published in 2001"

Composition and Microstructure of Cobalt Oxide Thin Films Obtained from a Novel Cobalt(II) Precursor by Chemical Vapor Deposition

Abstract: The present work reports the synthesis and the characterization of cobalt oxide thin films obtained by chemical vapor deposition (CVD) on indium tin oxide (ITO) substrates, using a cobalt(II) β-diketonate as precursor. The complex is characterized by electron impact mass spectrometry (EI-MS) and thermal analysis in order to investigate its decomposition pattern. The depositions are carried out in a cold wall reactor in the temperature range 350−500 °C at different oxygen pressures, to tailor film composition from CoO to Co3O4. The crystalline nanostructure is evidenced by X-ray diffraction (XRD), while the surface and in-depth chemical composition is studied by X-ray photoelectron (XPS) and X-ray excited auger electron spectroscopy (XE-AES). Atomic force microscopy (AFM) is employed to analyze the surface morphology of the films and its dependence on the synthesis conditions. Relevant results concerning the control of composition and microstructure of Co−O thin films are presented and discussed.

Synthesis and characterization of a low bandgap conjugated polymer for bulk heterojunction photovoltaic cells

Abstract: Low optical bandgap conjugated polymers may improve the efficiency of organic photovoltaic devices by increasing the absorption in the visible and near infrared region of the solar spectrum. Here we demonstrate that condensation polymerization of 2,5-bis(5-trimethylstannyl-2-thienyl)-N-dodecylpyrrole and 4,7-dibromo-2,1,3-benzothiadiazole in the presence of Pd(PPh3)2Cl2 as a catalyst affords a novel conjugated oligomeric material (PTPTB), which exhibits a low optical bandgap as a result of the alternation of electron-rich and electron-deficient units along the chain. By varying the molar ratio of the monomers in the reaction and fractionation of the reaction product, two different molecular weight fractions (PTPTB-I and PTPTB-II, see Experimental section) were isolated, containing 5–17 and 13–33 aromatic units respectively, as inferred from matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Thin films of PTPTB-I and PTPTB-II exhibit an optical bandgap of 1.60 and 1.46 eV, respectively. Photoinduced absorption (PIA) and photoluminescence spectroscopy of blends of PTPTB-I and a methanofullerene (1-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]C61, PCBM) gave direct spectral evidence of the photoinduced electron-transfer reaction from PTPTB-I as a donor to the fullerene derivative as an acceptor. Thin PTPTB-I:PCBM composite films were sandwiched between indium tin oxide/poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonic acid) (ITO/PEDOT:PSS) and Al electrodes to prepare working photovoltaic devices, which show an open circuit voltage of 0.67 V under white-light illumination. The spectral dependence of the device shows an onset of the photocurrent at 1.65 eV (750 nm).

Electronic band structure of indium tin oxide and criteria for transparent conducting behavior

Abstract: Indium-based transparent conductors, notably indium tin oxide (ITO), have a wide range of applications due to a unique combination of visible light transparency and modest conductivity. A fundamental understanding of such an unusual combination of properties is strongly motivated by the great demand for materials with improved transparent conducting properties. Here we formulate conditions for transparent conducting behavior on the basis of the local density full-potential linear muffin-tin orbital electronic band structure calculations for Sn-doped ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ and available experimental data. We conclude that the position, dispersion, and character of the lowest conduction band are the key characteristics of the band structure responsible for its electro-optical properties. Further, we find that this lowest band is split with Sn doping due to the strong hybridization with dopant s-type states and this splitting contributes to both the decrease of the plasma frequency and the mobility of the carriers.

Indium tin oxide thin films grown on flexible plastic substrates by pulsed-laser deposition for organic light-emitting diodes

Abstract: Transparent conducting indium tin oxide (ITO) thin films were grown by pulsed laser deposition (PLD) on flexible polyethylene terephthalate (PET) substrates. The structural, electrical, and optical properties of these films were investigated as a function of substrate deposition temperature and background gas pressure. ITO films (200 nm thick), deposited by PLD on PET at 25 °C and 45 mTorr of oxygen, exhibit high optical transparency (∼87%) in the visible (400–700 nm) with a low electrical resistivity of 7×10−4 Ω cm. ITO films grown by PLD on PET were used as the anode contact in organic light-emitting devices. A luminous power efficiency of ∼1.6 lm/W was achieved at 100 cd/m2, slightly higher than that (∼1.5 lm/W) measured for the control device based on a sputter-deposited ITO on glass.

Surface electronic structure of plasma-treated indium tin oxides

Abstract: X-ray photoelectron spectroscopy (XPS) has been used to study the electronic structures of indium tin oxide (ITO) surfaces treated by O+, Ar+, and NHx+ plasmas. The XPS data show that there is a significant change in core level energies (In 3d5/2 O 1s, and Sn 3d5/2), in donor concentration (Sn4+), in valence band maximums (VBM), and in work functions on ITO surfaces being treated by O+ and NHx+ plasmas, compared with that of virgin and Ar+ plasma treated surfaces. Based on these experimental data, a surface band-bending theory is proposed. The theory explains that when Fermi energy of the plasma-treated surface is shifted towards the middle of the band gap: core levels will shift their energies to lower binding energies, VBM will bend upward, and work function will increase, as observed.

Fine tuning work function of indium tin oxide by surface molecular design: Enhanced hole injection in organic electroluminescent devices

Abstract: Characteristics of electroluminescent (EL) devices were improved dramatically using indium tin oxide (ITO) chemically modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By the use of reactive –COCl groups, ITO surfaces were modified quickly and the work function of the modified ITO was changed widely depending upon the permanent dipole moments introduced in the para- position of benzoyl chloride. We also compared the performance of the EL devices with ITO modified with different binding groups (–SO2Cl, –COCl, and –PO2Cl2) of p-chlorobenzene derivatives. Finally, we examined the correlation between the change in the work function and the performance of the EL devices by the chemical modification and found that the enormous increase in ITO work function up to 0.9 eV is possible using phenylphosphoryl dichloride with a CF3-terminal group in the para-position.

Order on disorder: Copper phthalocyanine thin films on technical substrates

Abstract: We have studied the molecular orientation of the commonly used organic semiconductor copper phthalocyanine (CuPC) grown as thin films on the technically relevant substrates indium tin oxide, oxidized Si, and polycrystalline gold using polarization-dependent x-ray absorption spectroscopy, and compare the results with those obtained from single crystalline substrates [Au(110) and GeS(001)]. Surprisingly, the 20–50 nm thick CuPC films on the technical substrates are as highly ordered as on the single crystals. Importantly, however, the molecular orientation in the two cases is radically different: the CuPC molecules stand on the technical substrates and lie on the single crystalline substrates. The reasons for this and its consequences for our understanding of the behavior of CuPC films in devices are discussed.

Low-resistance and high-transparency Ni/indium tin oxide ohmic contacts to p-type GaN

Abstract: The characteristics of Ni/indium tin oxide (ITO) ohmic contacts to p-type GaN (∼2×1017 cm−3) have been studied. The Ni/ITO (10 nm/250 nm) layers were prepared by thermal evaporation and rf magnetron sputtering, respectively. Although the as-deposited Ni/ITO contacts present rectified behavior, the linear current–voltage characteristics can be obtained. The contact resistance can be reduced significantly for the ITO/Ni/p-GaN samples after suitable rapid thermal process. The contact property of ITO/Ni/p-GaN shows lowest specific contact resistivity of 8.6×10−4 Ω cm2 and high transparency (above 80% for 450–550 nm) as the sample annealed at 600 °C in air. Possible mechanisms for the observed low contact resistance and high transparency will be discussed. The present process is compatible with the fabrication for the high-efficient GaN light-emitting devices.

Synthesis and Characterization of Indium Oxide Nanoparticles

Abstract: Nanoparticles of indium oxide, a transparent conducting oxide with a band gap close to GaN, were synthesized by pulsed laser ablation of a pure indium metal target. X-ray diffraction and transmission electron microscopy confirmed that nanocrystalline indium oxide particles with a mean diameter of 6.6 nm with a cubic crystal structure were formed. Photoluminescence spectroscopy shows a strong emission peak at 3.78 eV with a weak size dependence.

Mobility-Dependent Charge Injection into an Organic Semiconductor

Abstract: Measurements of charge injection from indium tin oxide (ITO) into the organic semiconductor, tetraphenyl diamine doped polycarbonate (PC:TPD), were carried out. The current injected at the contact was measured as a function of the hole mobility in the organic semiconductor, which was varied from 10(-6) to 10(-3) cm (2)/V x s by adjusting the concentration of the hole transport agent, TPD, in the PC host. These experiments reveal that the current injected at the contact is proportional to the hole mobility in the bulk. As a result, the ITO/PC:TPD contact is found to limit current flow in all samples, regardless of the hole mobility in PC:TPD.

Neutron diffraction study on the defect structure of indium--tin--oxide

Abstract: The defect structure of undoped and Sn-doped In2O3 (ITO) materials was studied by preparing powders under different processing environments and performing neutron powder diffraction. The effect of tin doping and oxygen partial pressure was determined. Structural information was obtained by analyzing neutron powder diffraction data using the Rietveld method. The results include positions of the atoms, their thermal displacements, the fractional occupancy of the interstitial oxygen site, and the fractional occupancies of Sn on each of the two nonequivalent cation sites. The tin cations show a strong preference for the b site versus the d site. The measured electrical properties are correlated with the interstitial oxygen populations, which agree with the proposed models for reducible (2SnIn•Oi″)x and nonreducible (2SnIn•3OOOi″)x defect clusters.

GaN metal-semiconductor-metal ultraviolet photodetectors with transparent indium-tin-oxide Schottky contacts

Abstract: Indium-tin-oxide (ITO) layers were deposited onto n-GaN films and/or glass substrates by electron-beam evaporation. With proper annealing, we found that we could improve the optical properties of the ITO layers and achieve a maximum transmittance of 98% at 360 nm. GaN-based metal-semiconductor-metal (MSM) photodetectors with ITO transparent contacts were also fabricated. A maximum 0.12-A photocurrent with a photocurrent to dark current contrast higher than five orders of magnitude during ultraviolet irradiation were obtained for a photodetector annealed at 600/spl deg/C. We also found that the maximum photo responsivity at 345 nm is 7.2 and 0.9 A/W when the detector is biased at 5 and 0.5 V, respectively.

Electrochemical Characterization of Self-Assembled Alkylsiloxane Monolayers on Indium−Tin Oxide (ITO) Semiconductor Electrodes

Abstract: Self-assembled monolayers (SAMs) of octyltrimethoxysilane (OTMS) were deposited onto indium−tin oxide (ITO) electrode surfaces. Contact angle measurements evidenced the hydrophobicity and homogeneity of the functionalized surface despite the intrinsic surface roughness of the polycrystalline ITO electrodes. The electrochemical properties of the OTMS monolayers were quantitatively analyzed in terms of resistance, dielectric thickness, diffusion constant, and defect area by cyclic voltammetry and impedance spectroscopy. It has been demonstrated that the alkylsiloxane monolayer acts as a diffusion barrier for ions in the electrolyte. Furthermore, a significant suppression of the charge transfer at the interface was observed, demonstrating the passivation effect of the monolayers against electrochemistry. In addition, the effect of alkyl chain length on the electrochemical properties was briefly analyzed by using octadecyltrimethoxysilane (ODTMS). The defect area of this self-assembled monolayer was reduced t...

Organic luminescent element

Abstract: An organic luminescent element includes a substrate, an anode, a cathode, at least one organic material layer interposed between the anode and the cathode, and a sealing film containing a ferroelectric material provided on the anode or the cathode on the organic material layer. Preferably, the organic luminescent element further includes a counter electrode provided on the sealing film. Preferably, the substrate is transparent, and the anode is composed of indium tin oxide.

Modification of Indium Tin Oxide for Improved Hole Injection in Organic Light Emitting Diodes

Abstract: Modification of indium tin oxide (ITO) electrode interface for improved hole injection in organic light emitting diodes (OLED) was investigated The injection efficiency measurements were carried out to characterize contact between ITO and the organic semiconductor triphenyldiamine (TDP) layer Coating of ITO with self-assembled ultrathin platinum (Pt) films as interface modification layers, dramatically enhances OLED efficiency and contact with TDP becomes nearly ohmic The surface morphology of ITO electrodes was investigated by atomic force microscopy (AFM)

Characteristics of Indium-Tin-Oxide/Silver/Indium-Tin-Oxide Sandwich Films and Their Application to Simple-Matrix Liquid-Crystal Displays

Abstract: We developed low-resistivity transparent conductive films having the structure of indium-tin-oxide/silver/indium-tin-oxide (ITO/Ag/ITO). The thin silver film was sandwiched by ITO films. Our goal was to study the characteristics of the sandwich films and the display characteristics of simple-matrix liquid-crystal displays (LCDs) fabricated using the sandwich film. The electrical and optical characteristics of the sandwich films depended greatly on the thickness of the ITO and silver layers. Low resistivity and high transmittance were obtained when the film structure had a thickness of ITO/Ag/ITO: 40 nm/15 nm/40 nm. The simple-matrix LCD fabricated using a sandwich of ITO/Ag/ITO exhibited 27%–48% reduction in the level of crosstalk compared to the conventionally available simple-matrix LCDs fabricated using a single-layer ITO film; thus, the display performance was improved.

Influence of Carrier Gas Conditions on Electrical and Optical Properties of Pb(Zr, Ti)O3 Thin Films Prepared by Aerosol Deposition Method

Abstract: Transparent Pb(Zr, Ti)O3 (PZT) thin films with over 1 µm thickness were deposited by the aerosol deposition method (ADM). The transparency of the PZT thin film deposited at room temperature strongly depended on the kinds of carrier gases and the particle flow velocity. The color of the film became black if He gas was used as a carrier gas, and became transparent using N2, O2 or air gases, which were difficult to electrically discharge during the impacting of particles. The transmittance values in the 0.5–0.8 µm wavelength region of as-deposited 2-µm-thick PZT thin films on indium tin oxide (ITO) substrate were 70–80%. After annealing at 600°C, the remanent polarizations and the coercive fields of PZT thin films were 36 µC/cm2 and 89 kV/cm, respectively. With increasing carrier gas velocity, the remanent polarization decreased and the coercive field increased.

Combinatorial fabrication and studies of intense efficient ultraviolet–violet organic light-emitting device arrays

Abstract: Arrays of ultraviolet–violet (indium tin oxide)/[copper phthalocyanine (CuPc)]/[4,4′-bis(9-carbazolyl)biphenyl (CBP)]/[2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4oxadiazole (Bu-PBD)]/CsF/Al organic light-emitting devices, fabricated combinatorially using a sliding shutter technique, are described. Comparison of the OLED electroluminescence and CBP photoluminescence spectra indicates that the emission originates from the bulk of that layer. In arrays of devices in which the thickness of the CuPc and Bu–PBD were varied, but that of CBP was fixed at 50 nm, the optimal radiance R was obtained at CuPc and Bu–PBD thicknesses of 15 and 18 nm, respectively. At 10 mA/cm2, R was 0.38 mW/cm2, i.e., the external quantum efficiency was 1.25%; R increased to ∼1.2 mW/cm2 at 100 mA/cm2.

A Modified Transparent Conducting Oxide for Flat Panel Displays Only

Abstract: To keep up with the current development trends of thin film transistor liquid-crystal display (TFT-LCD), two major requirements must be satisfied in the transparent conducting oxide (TCO)-meterial itself. First, there must be no etch residue after TCO patterning and good etch selectivity against low electrical resistivity metals. Second, there must be good chemical endurance of the TCO material to secure a good electrical signal that is transported from the controller to the TFT-LCD by way of contact between the TCO and the tape carrier package (TCP). To obtain a new TCO material to achieve the kind of trade-off behavior that a TCO film has, the method in which ZnO is alloyed into indium tin oxide (ITO) was studied. It was determined that the 2.0–4.0 wt% ZnO-alloyed ITO film (named ITZO) is desirable in order to obtain a well-defined patterning ability and the stable TCP-contact property simultaneously. It is concluded that ITZO film can replace ITO and IZO for the pixel electrodes of a TFT-LCD designed with specifications for high resolution and large display size.