Thermal Evaporation In High Vacuum Research Articles

Defect states in pentacene thin films prepared by thermal evaporation and Langmuir–Blodgett technique

We investigate defect states in pentacene thin films (PTFs) prepared by two different deposition techniques: standard thermal evaporation in high vacuum and the Langmuir–Blodgett (LB) technique. Time domain capacitance–voltage (C–V) and charge deep-level transient spectroscopy (DLTS) techniques were employed. C–V measurements indicate that Schottky barrier structures on both types of PTFs exhibit a common behavior: the thinner the PTF, the closer the measured C–V curve to the ideal shape for the Schottky barrier. Charge DLTS measurements show a peak with an activation energy of about 0.70eV above Ev and an attempt-to-escape frequency of 3×1014s−1 for PTFs deposited by thermal evaporation. For PTFs prepared by LB technique two deep-levels with activation energies of 0.20eV and 0.21eV, and an attempt-to-escape frequencies of 2×107s−1 and 2×106s−1, respectively, are found. The amplitude of the charge DLTS signals increases with decreasing PTF sample thickness for both deposition techniques. The observed defects can not be removed by annealing in vacuum. The origin of defects responsible for the measured charge DLTS spectra is discussed.

Investigating aluminum thin films properties by stochastic analysis

AbstractIn this article, we investigate about stochastic properties of a thin film such as aluminum thin film that is formed by thermal evaporation in high vacuum. So we prepare thin films with different thicknesses on glass surfaces in high vacuum chamber with 10−6 torr. Then, we use Atomic Force Microscopy (AFM), for determining the height fluctuations of aluminum thin films in different growth stages and use an inverse method that utilizes data from AFM to construct a simple equation that governs the stochastic process and a relation between stochastic parameters such as roughness, correlation and Markov length, drift, and diffusion coefficients during the growth process. Also we show that aluminum thin films, during growth by evaporating in high vacuum chamber, have a mono fractal behavior in small distances(little than 100 nm) on the surfaces. Copyright © 2008 John Wiley & Sons, Ltd.

Structure and mechanical properties of Cu–Ag nanocomposite films

Metal–metal nanocomposites are studied to answer the questions of their formation mechanism, morphological development and related physical properties. The films were prepared by combinatorial co-deposition of Cu and Ag in a wide composition interval using thermal evaporation in high vacuum. Films close in composition to the eutectic have grain size below 10 nm and display strong <111> texture. Nanoindentation data show that Cu–Ag nanocomposite films have a maximum of hardness reaching 4 GPa around 20 at.% of Ag, four times greater than either of the building components. The composition dependence of the Young's modulus obeys the rule of mixtures, while their H/ E ratio values are about 0.02 and practically constant in 10–60, at.% Ag content range.

4-Amino-2,2,6,6-tetramethylpiperidin-1-oxyl radical (ATEMPO)

The title compound, C9H19N2O, was studied in the context of nitroxide radicals bearing amino or hydr­oxy groups as candidates for obtaining thin films of mol­ecular magnets by thermal evaporation in high vacuum on various substrates; the knowledge of its crystal structure is useful for checking the nature and quality of the films. In the crystal structure ATEMPO radicals are linked by weak inter­molecular N—H⋯O hydrogen bonds to form infinite chains running along [010]. Structural features of the radical are similar to those reported for clathrates or adducts involving ATEMPO: the piperidine ring has a chair conformation and the N—O. bond length is 1.2870 (13) A.

Influence of the central metal atom on the nonlinear optical properties of MPcs solutions and thin films

Third order nonlinear optical susceptibility ( χ 〈3〉) of metallophthalocyanines (MPcs, where M = Co, Cu, Zn, Mg) thin films and solutions was investigated by standard backward degenerate four wave mixing (DFWM) method at 532 nm. Third harmonic generation (THG) measurement at 1064 nm performed on MPcs thin films is also discussed. MPcs thin films were grown by conventional thermal evaporation in high vacuum and solution were dissolved in tetrahydrofuran (THF), in which the studied materials are soluble. In the case of microscopic nonlinearity, we calculated the second order hyperpolarizability ( γ) for MPcs solutions. We found that the χ 〈3〉 and the γ values are affected by the nature of the central metal atom. We also found that the χ DFWM 〈 3 〉 value is larger than that measured via THG experiment. The variation in χ 〈3〉 values occurs due to the different resonance contributions.

Conductivity of the thin film phase of pentacene

We investigated the morphological, structural and transport properties of pentacene thin films (20 nm) grown by high vacuum thermal evaporation on patterned substrates with different interelectrodes distances. X-ray diffraction and atomic force microscopy show a structure in the so called ‘‘thin film phase’’ with 1–2 lm sized grains. By means of in situ electrical measurements we found for these films a resistivity value of q = 4.7 ± 0.2 · 10 4 Xm, that is an order of magnitude lower than the value reported to date in literature for single crystals of pentacene. This value is not affected by the presence of grain boundaries. The resistivity is further reduced by a factor 8.9 ± 0.7, 14 ± 1, 2.3 ± 0.3 upon exposure to oxygen, nitrogen and ambient air, respectively.

Epitaxial pentacene films grown on the surface of ion-beam-processed gate dielectric layer

The following research describes the process of fabrication of pentacene films with submicron thickness, deposited by thermal evaporation in high vacuum. The films were fabricated with the aforementioned conditions and their characteristics were analyzed using x-ray diffraction, scanning electron microscopy, polarized Raman spectroscopy, and photoluminescence. Organic thin-film transistors (OTFTs) were fabricated on an indium tin oxide coated glass substrate, using an active layer of ordered pentacene molecules, which were grown at room temperature. Pentacene film was aligned using the ion-beam aligned method, which is typically employed to align liquid crystals. Electrical measurements taken on a thin-film transistor indicated an increase in the saturation current by a factor of 15. Pentacene-based OTFTs with argon ion-beam-processed gate dielectric layers of silicon dioxide, in which the direction of the ion beam was perpendicular to the current flow, exhibited a mobility that was up to an order of magnitude greater than that of the controlled device without ion-beam process; current on/off ratios of approximately 106 were obtained. Polarized Raman spectroscopy investigation indicated that the surface of the gate dielectric layer, treated with argon ion beam, enhanced the intermolecular coupling of pentacene molecules. The study also proposes the explanation for the mechanism of carrier transportation in pentacene films.

Surface Morphology and Sensing Property of NiO-WO3 Thin Films Prepared by Thermal Evaporation

WO3 and NiO-WO3 thin films of various thicknesses were deposited on anAl2O3-Si (alumina-silicon) substrate using high vacuum thermal evaporation. Afterannealing at 500oC for 30 minutes in air, the crystallanity and surface morphology of WO3and NiO-WO3 thin films were investigated using X-ray diffraction (XRD) and ScanningElectron Microscopy (SEM). It is observed that the WO3 thin films were resulted in cracksbetween the polycrystalline grains and the grain growth was increased with increasingthickness causing deteriorated sensing characteristics of the films. On the other hand, anoptimum deposition of NiO on WO3 thin film has inhibited the grain growth and improvedthe sensitivity of the films. The inhibition is limited to a certain thickness of WO3 and NiOcontent (mol %) of inclusion and below or above this limitation the grain growth could notbe suppressed. Moreover, the deposition sequence of NiO and WO3 is also playing asignificant role in controlling the grain growth. A probable mechanism for the control ofgrain growth and improving the sensing property has been discussed.

Electrical Effect in Organic Thin-Film Transistors Using Polymerized Gate Insulators by Vapor Deposition Polymerization (VDP)

We report that the organic thin film transistors were fabricated by the organic gate insulators transistor with vapor deposition polymerization (VDP) processing. In order to form polyimide as a gate insulator, vapor deposition polymerization process was also introduced instead of spin-coating process, where polyimide film was co-deposited by high-vacuum thermal evaporation from 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 4,4′-oxydianiline (ODA), and cured at 150 °C for 1 hour followed by 200 °C for 1 hour. Details on the explanation of organic thin-film transistors (OTFTs) electrical characteristics of 6FDA-ODA as gate insulators fabricated thermal co-deposition method.

The behavior of WO3 thin film on NiO addition

Thin films of tungsten oxide and nickel oxide were deposited on <TEX>$Al_2O_3/Si-substrate$</TEX> by high vacuum thermal evaporation. The properties of microstructure and crystallinity were analyzed by SEM and XRD respectively. <TEX>$WO_3$</TEX> films without addition of NiO showed polycrystalline structure after annealing at <TEX>$500^{\circ}C$</TEX> for SO min. There were the cracks between the polycrystalline grains and the crack width was increased with the thickness of <TEX>$WO_3$</TEX> films. The cracks in the <TEX>$WO_3$</TEX> films could be controlled by an optimum deposition of NiO on <TEX>$WO_3$</TEX> films and either less or more than the optimum addition fails to suppress the cracks. A process mechanism to suppress the crack has been discussed.

Thermal Evaporation법에 의해 제조된 WO3박막과 NiO-WO3박막의 전기적 특성에 관한 연구

본 연구는 <TEX>$WO_3$</TEX> 박막과 <TEX>$NiO-WO_3$</TEX> 박막을 고진공 저항가열식 thermal evaporation 법으로 (100) n형의 실리콘 단결정 기판 위에 증착시켰고, 막의 결정성 증진을 위하여 공기 중 <TEX>$500^{\circ}C$</TEX>에서 30분 동안 열처리하였다. 박막의 결정성 및 결정구조를 분석하기 위해서 X선 회절분석기를 사용하였고, 표면 및 단면 관찰을 위해서는 주사전자현미경을 이용하였다. 그리고 화학 조성 결합에너지는 XPS를 이용하였다. 순수 <TEX>$WO_3$</TEX> 박막의 결정 크기는 <TEX>$500^{\circ}C$</TEX>에서 30분 동안 공기중 열처리에 의해서 <TEX>$0.6{\mu}m$</TEX>로 성장하였고 <TEX>$WO_3$</TEX> 박막의 두께가 증가할수록 거의 변화 없이 일정하였다. 반면, NiO가 첨가된 <TEX>$WO_3$</TEX> 박막 두께별 결정크기는 각각 <TEX>$0.12{\mu}m,\;0.28{\mu}m,\;0.32{\mu}m$</TEX>및 <TEX>$0.43{\mu}m$</TEX>로 순수 <TEX>$WO_3$</TEX> 박막에 비해 치밀한 표면을 형성하였고, 최대 5배정도 성장이 억제되었다. 가스감도 측정은 대기 중에서의 센서 저항 값을 기준으로 측정가스 저항 값의 비율 <TEX>$(R_{NOx}/R_{air})$</TEX>로 가스감도를 나타내었다. 전기적 성질은 MFC로 NOx가스 5ppm을 일정히 유지시켰고, Multimeter로 계측하여 컴퓨터에 자동 계측되는 시스템을 사용하였다. 순수 <TEX>$WO_3$</TEX>박막보다는 <TEX>$NiO-WO_3$</TEX> 박막이 우수한 NOx 감도특성을 보였고 센서의 작동온도는 <TEX>$250^{\circ}C$</TEX>에서 우수한 감도를 나타내었다. [ <TEX>$WO_3$</TEX> ] and <TEX>$NiO-WO_3$</TEX> thin films were deposited on a Si (100) substrate by using high vacuum thermal evaporation. The effects of various film thicknesses on the surface morphology <TEX>$WO_3$</TEX> and <TEX>$NiO-WO_3$</TEX> thin films were investigated. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the deposited films. The results suggest that as <TEX>$WO_3$</TEX> thin films became thick, their grain grew up to a <TEX>$0.6{\mu}m$</TEX>. On the other hand, NiO-doping to <TEX>$WO_3$</TEX> thin films inhibited the grain growth five times less than undoped <TEX>$WO_3$</TEX> thin films. This results show that NiO doping inhibited the grain growing of <TEX>$WO_3$</TEX> thin films. Also, the variation of NOx sensitivity <TEX>$(R_{NOx}/R_{air})$</TEX> to the thickness of <TEX>$WO_3$</TEX> and <TEX>$NiO-WO_3$</TEX> thin films were measured according to the thickness change of thin films and the working temperature of sensor in 5ppm NOx gas. As a result, <TEX>$NiO-WO_3$</TEX> thin films showed more excellent properties than <TEX>$WO_3$</TEX> thin films for NOx sensitivity.

Spectroscopic Ellipsometry of the Optical Functions of Some Widely Used Organic Light Emitting Diodes (OLEDs) Materials.

AbstractIn this work, optical functions of some widely used OLEDs materials 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), tris (8-hydroxyquinoline) aluminum (Alq3), (N,N′-di(naphthalene-1-yl)-N,N′- diphenylbenzidine (NPB),poly(3,4,-ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) and indium tin oxide (ITO)) were studied using spectroscopic ellipsometry (SE) in the spectral range from 1.55 eV to 4.1 eV (wavelength range of 300 nm to 800 nm). The samples were prepared either by thermal evaporation in high vacuum or spin-coating of thin films onto glass substrates. For determination of the optical functions of ITO, commercial ITO glass was used. Measurements at different incident angles were performed to determine whether the samples can be considered isotropic. The SE data were modeled using an oscillator model (Lorentz for semiconducting and Lorentz-Drude for conducting materials). The absorption spectra were also measured, and the comparison with the data determined by SE is given.

Flexible Pentacene/PMMA Thin-Film Transistors Fabricated on Aluminium Foil Substrates

AbstractPentacene thin-film transistors (TFT) were fabricated on aluminum foils using polymethyl methacrylate (PMMA) as gate dielectric. In such structure, the aluminum substrate acts as the gate electrode itself. A bottom gate inverted structure was used to study the influence of the dielectric and the aluminum substrate on the device performance.Pentacene thin-films were deposited by thermal evaporation in high-vacuum at deposition rates around 3 Ås-1 and three different substrate temperatures (30, 60 and 90°C). The maximum process temperature achieved was 170°C, corresponding to the baking of polymethyl methacrylate. The TFTs exhibit field-effect mobility values of ∼ 10-3 cm2V-1s-1 and threshold voltage values around –15 V. The influence of the dielectric and the substrate temperature on the pentacene structure and device field-effect mobility is discussed.

Organic Thin-Film Transistors Based on Vapor-Deposition Polymerized Gate Insulators

In this study, we demonstrated that organic thin-film transistors (OTFTs) can be fabricated by using organic gate insulators using a vapor deposition polymerization (VDP) process. We found that electrical output characteristics in our organic thin-film transistors using a staggered-inverted top-contact structure show a saturated slope in the saturation region and a subthreshold nonlinearity in the triode region. The field-effect mobility, threshold voltage, and on-off current ratio of OTFTs using 4,4'-oxydiphthalic anhydride[ODPA]-4,4'-oxydianiline[ODA] and 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride[6FDA]-[ODA] as gate insulators with a thickness of 0.45 µm were about 0.13–0.5 cm2/Vs, -7 V, and 104, respectively. To form polyimide as a gate insulator, the VDP process was also introduced instead of a spin-coating process, in which a polyimide film was codeposited by the high-vacuum thermal evaporation of ODPA and ODA, 6FDA and ODA, and cured at 150°C for 1 h followed by 200°C for 1 h after codeposition. To explain the differences in the electrical characteristics caused by the insulators, the morphology of pentacene on the polyimide from ODPA-ODA was compared with that from 6FDA-ODA, respectively.

Morphological, structural and electrical characterization of nanostructured vanadium–tin mixed oxide thin films

Thin films made by a mixing of vanadium and tin oxides have been obtained by high vacuum thermal evaporation. A detailed, electrical, morphological and structural characterization has been performed on all deposited films. In particular, transmission electron microscopy observations allow us to confirm the realization of a thin film made by nanosized crystalline grains of vanadium oxide and tin oxide homogeneously arranged. The Hall effect measurements together with scanning tunnelling spectroscopy gives the surface density of electronic states and the electrical charge transport mechanism of our metal-oxide films as a function of surrounding atmosphere. In this way, the dopant effect of adsorbed oxygen on metal-oxide thin films was monitored. The obtained results allows us to conclude that the nanostructured vanadium–tin mixed oxide thin films is suitable for gas sensing applications.

P‐110: Organic TFT Using Polymerized Gate Insulators by Vapor‐Deposition Polymerization

AbstractIn this paper, it was demonstrated that the organic thin‐film transistors were fabricated with the organic gate insulator with vapor deposition polymerization (VDP) processing. The saturated slop in the saturation region and the subthreshold nonlinearity in the triode region were clearly observed in the electrical output characteristics in our organic thin film transistors using the staggered‐inverted top‐contact structure. Field effect mobility, threshold voltage, and on‐off current ratio in 0.45 μm thick gate dielectric layer were about 0.5 cm2/Vs, −5 V, and 105 A/A, respectively. In order to form polyimide as a gate insulator, vapor deposition polymerization process was also introduced instead of spin‐coating process, where polyimide film was co‐deposited by high‐vacuum thermal evaporation from 6FDA and ODA followed by curing.

Pentacene thin-films obtained by thermal evaporation in high vacuum

Pentacene thin-films were obtained by thermal evaporation in high vacuum of a pure (98%) commercially available source. All the samples were grown at room temperature (25 °C) and high deposition rates (>20 Å/s) on Corning glass substrates. The microstructure of the pentacene thin-films evidences the coexistence of thin-film and bulk triclinic crystalline phases. The optical absorption edge close to 1.7 eV, together with the high optical absorption in the visible range, make pentacene a promising candidate for low cost solar cells. Doping series of samples were obtained by dipping pieces cut from the same pentacene sample into a solution of iodine in acetonitrile for different times (<1 h). Thereby, room temperature dark conductivity changes from 3×10 −7 to 4×10 −5 Ω −1 cm −1. Finally, glass/SnO/pentacene/Al and glass/ZnO:Al/pentacene/Au structures were fabricated showing rectifying characteristics with on/off ratios of approximately 3 orders of magnitude.

An Organic Electrophosphorescent Device Driven by All-Organic Thin-Film Transistor using Polymeric Gate Insulator

In this paper, we demonstrate that the organic electrophosphorescent device is driven by the organic thin film transistor with spin-coated photoacryl gate insulator. It was found that electrical output characteristics in our organic thin film transistors using the staggered-inverted top-contact structure showed the non-saturated slope in the saturation region and the sub-threshold nonlinearity in the triode region, where we obtained the maximum power luminance that was about 90 cd/m². Field effect mobility, threshold voltage, and on-off current ratio in 0.45 µm thick gate dielectric layer were 0.17 cm²/Vs, -7 V and 106, respectively. In order to form polyimide as a gate insulator, vapor deposition polymerization process was also introduced instead of spin-coating process, where polyimide film was co-deposited by high-vacuum thermal evaporation from 4,4'-oxydiphthalic anhydride (ODPA) and 4,4'-oxydianiline (ODA) and cured at 150°C for 1hr. It was also found that field effect mobility, threshold voltage, on-off current ratio, and sub-threshold slope with 0.45 µm thick gate dielectric films were 0.134 cm²/Vs, -7 V and 106 AA, and 1 V/decade, respectively.

Temperature Dependence of the Electrical Resistivity of Polymerized C60 Thin Films

ABSTRACTHighly conducting thin films of C60 were deposited by thermal evaporation in high vacuum on single crystal silicon substrates. The microstructure of the films was characterized by using Atomic Force Microscopy, and laser Raman spectroscopy. The films were polymerized by uv irradiation. The dc electrical resistivities of the as-deposited and uv-polymerized films were measured as functions of temperature between 295 and 17K by the four-probe technique. We present results on the effects of uv-irradiation on the surface microstructure and the temperature dependence of the electrical resistivity of these films.

Semiconducting polymers based on tetraizoindole

The growing interest in the production of electronic devices are able to detect very small amounts of cellular second-messengers as NO or for monitoring gases as NO 2, O 2, CO 2, Cl 2 or other toxic gases. The metal-complex tetraizoindoles (metal phthalocyanines, MePcs) were previously shown as potential sensor materials for nitrogen oxide-sensing devices. The synthesis of nickel phthalocyanines (NiPcs), copper polyphthalocyanines (CuPcs) and aliphatic amines-condensed CuPc derivatives are described. Three new aliphatic amine-condensed CuPc derivatives as n-type organic semiconductors were obtained using an original technique conventionally used for aromatic derivatives synthesis. NiPc and aliphatic amine-substituted CuPc derivatives were deposited onto glass substrates by a high-vacuum thermal evaporation technique. Microscopic studies (interference) show that thin films of vapor-deposited MePcs had a thickness of 89–220 nm. The optical properties of MePc thin films have been examined by UV–Vis and IR spectrometry and the effect of NO x upon optical properties is in course. The sensor could be prepared by deposition of MePc thin films on a substrate with IPID (in-plane interdigitated) electrodes for the detection of NO 2. The final goal of this paper was to extend both the knowledge on the synthesis of organic metal-complex tetraizoindoles and their potential use as semiconductors in NO x sensing devices.