Standard Thermal Evaporation Research Articles

Thermally robust optical properties of the wafer-scale [formula omitted]-Sb[formula omitted]O[formula omitted] films

As a molecular crystal, the wafer-scale Sb2O3 films were deposited successfully by standard thermal evaporation deposition and their optical behaviours have been investigated in detail. XRD reveals that the as-deposited Sb2O3 films have a cubic phase (α-Sb2O3) with a lattice constant of about 11.16Å . In a further step, the thermal stability of lattice vibrations and optical constants of the as-deposited α-Sb2O3 films have been investigated by Raman and ellipsometric spectra at various temperatures from 200 to 600K. The temperature-dependent frequencies, intensities, and widths of the first-order Raman-active modes have a linear trend without phase transitions in the temperature range, which is confirmed by the temperature-dependence of optical constants (ϵr and ϵi) and optical band gap (Eg= 4.3∼4.4eV) extracted from the ellipsometric spectra. In addition, theoretical calculations were performed to clarify the physical mechanisms of dielectric constants and electronic transitions. The thermally robust crystalline structure and optical properties are very helpful for the α-Sb2O3 based (opto)electronic devices.

Thermo-plasmonic gold nanofilms for simple and mass-producible photothermal neural interfaces.

In recent years, photothermal stimulation methods using plasmonic metal nanoparticles have emerged as non-genetic optical techniques in neuromodulation. Although nanoparticle-based photothermal stimulation shows great potential in the excitation and the inhibition of neural activity, the complex synthesis processes of the nanoparticles and the lack of large-area deposition methods can be limiting factors for the development of photothermal neural devices. In this paper, we propose a plasmonic gold nanofilm, fabricated by a standard thermal evaporation process, as a simple and mass-producible photothermal neural interface layer for microelectrode array (MEA) chips. The absorption of the gold nanofilm at near infrared wavelengths is optimized to maximize the photothermal effect by varying the thickness and microstructure of the gold nanofilm. With the optimized conditions, a significantly strong photothermal effect is applied on MEAs without affecting the neural signal recording capability. Finally, primary rat hippocampal neuronal cultures are used to show that the photothermal neural inhibition using the gold nanofilm is as effective as that using the plasmonic nanoparticles. Due to the greater simplicity and versatility of the fabrication process, the plasmonic gold nanofilm can provide a promising solution for the mass production of photothermal platforms.

A comparative study of hydrogen- and hydroxyl-related pentacene defect formation in thin films prepared by Langmuir-Blodgett technique and thermal evaporation

The process of pentacene defects formation in aqueous environment was studied. Pentacene thin films (∼10 nm) covered platinum electrodes were prepared either by the Langmuir–Blodgett (LB) technique or by the standard thermal evaporation in high vacuum. Voltammograms were taken in various acidic and basic environments, results are discussed with the aim to extract the information about the dynamics of hydrogen- and hydroxyl-related defects formation in the above-mentioned thin films. Obtained data confirm that LB films immersed in aqueous environment are prone to more expressive defect formation (e.g., two orders higher for dihydropentacene) as obvious for thermally evaporated films. A possible explanation of this fact resides in a hypothetic existence of energetically more favourable sites for hydrogen bonding from aqueous environment on both the pentacene and pentacenequinone molecules comprised in films prepared by the LB technique. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Epitaxial ZnMnO/ZnO Coaxial Nanocable

Zn0.96Mn0.04O/ZnO coaxial nanocables were prepared in two steps: ZnO nanowires were synthesized by standard thermal evaporation, followed by depositing Zn0.96Mn0.04 onto the surface of prepared ZnO nanowires using an ultrahigh-vacuum radio frequency magnetron-sputtering system. X-ray diffraction and X-ray photoelectron spectroscopy analysis reveal that Mn is incorporated well into the wurtzite ZnO without forming any Mn oxide. High resolution transmission electron microscopy images demonstrate that both ZnO and Zn0.96Mn0.04 layers are single-crystalline, and epitaxial growth is achieved between them, which predicts high carrier mobility and spin injection efficiency. Magnetic property measurements show that the Zn0.96Mn0.04/ZnO nanocables are ferromagnetic with a Curie temperature higher than 350 K.

Four-probe electrical-transport measurements on single indium tin oxide nanowires between1.5 and 300 K

Single-crystalline indium tin oxide (ITO) nanowires (NWs) were grown by the standard thermalevaporation method. The as-grown NWs were typically 100–300 nm in diameter and a fewµm long. Four-probe submicron Ti/Au electrodes on individual NWs were fabricated by theelectron-beam lithography technique. The resistivities of several single NWs have beenmeasured from 300 down to 1.5 K. The results indicate that the as-grown ITONWs are metallic, but disordered. The overall temperature behavior of resistivitycan be described by the Bloch–Grüneisen law plus a low-temperature correctiondue to the scattering of electrons off dynamic point defects. This observationsuggests the existence of numerous dynamic point defects in as-grown ITO NWs.

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.

Room‐temperature ferromagnetism of ZnO/Zn0.96Mn0.04O core‐shell nanowimble

AbstractZnO/Zn0.96Mn0.04O core‐shell nanowimbles were prepared in two steps: ZnO nanowimbles were synthesized by the standard thermal evaporation method, followed by depositing Zn0.96Mn0.04O onto the surface of the prepared ZnO nanowimble using an ultrahigh‐vacuum radio‐frequency magnetron sputtering system. The scanning electron microscopy images show that the morphology, the alignment and the uniformity of ZnO/Zn0.96Mn0.04O core‐shell nanowimbles are maintained as for the as‐prepared uncoated ZnO nanowimble, and the thickness of the magnetic Zn0.96Mn0.04O layer is about 20 nm. The XRD analysis reveals that Mn is incorporated well into the wurtzite ZnO without forming Mn oxide. The magnetic property measurement shows that the ZnO/Zn0.96Mn0.04O nanowimble is in the ferromagnetic state at room temperature. The coercive field turns out to be as large as 109 Oe and 153 Oe at 300 K and 10 K, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Charge trapping and interface characteristics of thermally evaporated HfO2

Charge trapping and interface characteristics of hafnium oxide (HfO2) films, grown by standard thermal evaporation, were investigated. High frequency capacitance–voltage and conductance measurements were carried out at various temperatures on aluminum gate metal–oxide–semiconductor capacitors, annealed at 450°C. A hysteresis below 30mV was observed. Electrical data show, that charge trapping in HfO2 initially increases with decrease in temperature while it shows a turnaround phenomenon when the temperature is decreased further. Interface state density distribution observed at low temperatures suggests that charge-trapping behavior of these films is mostly due to shallow traps at the interface.

Electrical Characteristics of Thermally Evaporated HfO2

The electrical characteristics of hafnium oxide films, grown by standard thermal evaporation of hafnium while adding oxygen at constant partial pressure during evaporation, were investigated for the first time. The dielectric constant as measured by the capacitance-voltage technique is estimated to be in the range of 18-25. Metal oxide semiconductor (MOS) capacitors using as dielectric and annealed at 450°C show a hysteresis below 30 mV. A low leakage current density of A/cm2 at 1 V and reduced bulk oxide charges were also observed. The interface state density and low-temperature charge trapping behavior of these films were also investigated. Observed characteristics indicate that films deposited by standard thermal evaporation are suitable for MOS device applications. © 2004 The Electrochemical Society. All rights reserved.

Thermally Evaporated ZrO[sub 2

The characteristics of zirconium oxide (ZrO 2 ) films, grown by standard thermal evaporation of zirconium while adding oxygen at constant partial pressure during evaporation, were investigated for the first time. The physical thickness (t p h y s in A) and electrical thickness of the as-grown and annealed samples were studied. The dielectric constant as measured by the capacitance-voltage (C-V) technique is estimated to be around 36. C-V measurements taken at 100 kHz show a low hysteresis of ∼30 mV and the maximum capacitance seems to flatten out for the lower physical thickness, which might indicate presence of an interfacial oxide/silicate layer.

Strong impact of x-ray radiation associated with electron beam metallization of diamond devices

Electron-beam evaporation of metal contact is commonly used in the fabrication of semiconductor devices. We have observed that device irradiation by x-ray photons, which are generated by electrons striking the metal (titanium or gold) to be evaporated, has a strong impact on the characteristics of diamond devices used for radiation detection. It results in an improvement of the detector charge collection efficiency by a factor of 1.5 with respect to nonirradiated devices (standard thermal evaporation). Thermally stimulated current measurements showed that this effect is related to deep trap filling by free carriers generated in diamond by x-ray photons impinging the device during e-beam evaporation. Trap filling results in an increase of the free carrier drift distance before trapping. Study of contact annealing and the thermal stability of trap filling showed that charge detrapping at temperatures above 200 °C annihilates the observed detector sensitivity improvement.

Thermally and photo-induced irreversible changes in the optical properties of amorphous Ge xSe 100- x films

Films of amorphous Ge x Se 100- x were prepared by plasma-enhanced chemical vapour deposition (PECVD) using the hydrides GeH 4 and H 2Se as precursor gases and by standard thermal evaporation. The optical bandgap obtained from a Tauc plot showed a maximum ( E g = 2.27 eV) at the stoichiometric composition ( x = 33) for the PECVD films. The bandgap values of the virgin evaporated films were much lower in the range x = 40 to 75, the difference being due to the incorporation of hydrogen in the PECVD films, detected in IR and Raman spectra. Thermal annealing and illumination by bandgap light of the evaporated films induced irreversible bleaching. The PECVD films showed a more complex behaviour of the optical shift upon annealing due to the loss of hydrogen. An IR and Raman investigation demonstrated that the changes in the optical transparency are accompanied by an increase of ordering in the local structure.