Beam Evaporation Research Articles

Surface enhanced Raman scattering by organic and inorganic semiconductors formed on laterally ordered arrays of Au nanoclusters

This work is devoted to the investigation of surface-enhanced Raman scattering by vibrational modes of cobalt phthalocyanine ultrathin films and CuS nanocrystals prepared using by organic molecular beam vapor deposition and the Langmuir–Blodgett technique, respectively, on laterally ordered arrays of Au nanoclusters formed by electron beam lithography on Si and GaAs substrates.The surface-enhanced Raman scattering study of cobalt phthalocyanine films demonstrates the strong dependence of Raman intensity of vibrational modes in cobalt phthalocyanine on the laser excitation wavelength as well as on the size and period of Au nanoclusters. By tuning the optical resonance conditions a maximal enhancement factor of 2×104 is achieved. The investigation of surface-enhanced Raman scattering by cobalt phthalocyanine deposited on laterally ordered arrays of paired Au nanoclusters (dimers) reveals anisotropic enhancement with respect to polarization of the scattered light parallel or perpendicular to the dimer axis.

A Microfabricated Propofol Trap for Breath-Based Anesthesia Depth Monitoring

This paper reports a golden microtrap chip for anesthetic depth monitoring. The chip selectively captures the propofol (2,6-diisopropylphenol) compound, which is a widely used substance for anesthesia, by filtering out the other species found in human breath. The fabricated silicon-glass chip is 12 mm on each side and consists of an array of high aspect ratio parabolic reflectors inside its 7 mm × 7 mm × 0.24 mm cavity. The interior surfaces of the chip are coated with an electroplated gold layer having a surface roughness of around 6.82 nm, which is an order of magnitude higher than a gold layer deposited by electron (e)-beam evaporation. Uncoated and e-beam gold-coated chips are unable to trap propofol and other compounds found in human breath. In contrast, silicon-glass chips coated with Tenax TA (2,6 diphenylene oxide), a gas adsorbing polymer, captures propofol among other volatiles present in human breath. Only devices coated with an electroplated gold layer demonstrate selective affinity for the target compound propofol. For the same propofol concentration, these golden microtraps show consistent capture efficiency with less than 8% variation in the trapped propofol amount while tested with different human breath samples. These microfabricated chips have the potential to accurately quantify the amount of propofol present in human breath samples without incorporating the gas chromatography column into the testing setup, resulting in faster analysis and reduced cost and complexity.

Copper Nanowires Preparation and Field Electron Emission Properties

Copper (Cu) nanowires films are deposited on the molybdenum film-coated Al2O3 ceramic substrates by using the electron beam vapor deposition technique. The films were characterized by optical microscopy, scanning electron microscope , x-ray diffraction spectrum and energy dispersive spectrum. The surface morphology show that the Cu nanowires have excellent length-to-diameter ratio of 300, and each Cu nanowires diameter is uniform. The field electron emission measurements of Cu nanowires films were also carried out showing the turn on field as low as 2.5 V/μm and the average current density of 0.10 mA/cm2 at electric field of 10.8 V/μm were obtained from a broad uniform emission screen over 3.0 cm2.

Effects of high magnetic field on the microstructure and magnetic properties of Fe80Ni20 thin films with different thickness values

Fe80Ni20 thin films with different thickness values are prepared by the molecular beam vapor deposition technique, respectively, in the cases with applying no magnetic field and with applying a 6 T magnetic field perpendicular to the surface of substrates. Film property studies show that as film thickness value increases, the coercive force in-plane decreases, which is in accordance with Neel theory, and that the squareness ratio first quickly increases, and then slowly decreases. The 6 T magnetic field restrains coalescence and abnormal growth of grains, and reduces surface roughness. Therefore, with 6 T magnetic field applied during the film preparation, the coercive force of thin film is less and the squareness ratio is larger than that with no magnetic field applied. The thin films are anisotropic in-plane with applying no magnetic field, but isotropic with applying a 6 T magnetic field.

A new approach to understand liquid injection into atmospheric plasma jets

Infrared images are used to characterize the atmospheric plasma and the influence of liquid injection into it. In the infrared spectral range low energies of rotational vibrational transitions can be captured which are emitted by hot liquid vapors. These vapor streams enable the qualification of the injection depth. High speed shadowgraphy is used to prove the correlations between vapor cloud and drop atomization behavior. In addition the combustion of organic liquids like ethanol and pentanol can be seen directly with an increase of emitted radiation. A direct correlation between vapor cone and liquid properties can be made. Lower Ohnesorge numbers lead to more focused vapor beams.

Effects of high magnetic field on the structure evolution, magnetic and electrical properties of the molecular beam vapor deposited FexNi1−x (0.3≤x

Nanocrystalline FexNi1−x (in at%, x=0.74, 0.6, 0.55, and 0.3) thin films were prepared on a 25°C quartz substrate by using a molecular beam vapor deposition method with and without a 6T magnetic field. The microstructure of the thin films was characterized by energy dispersive x-ray spectroscopy, x-ray diffractometry and transmission electron microscopy. The magnetic and electrical properties of the thin films were examined by a vibrating sample magnetometer and four-point probe method. Results show that the thicknesses of these films with different compositions are 50, 90, 80, and 150nm, correspondingly. The crystallinity of FexNi1−x (x=0.74 and 0.6) thin films is enhanced, and the γ 〈111〉 orientation degree of the FexNi1−x (x=0.55 and 0.3) thin films increases under a 6T magnetic field. The grain refinement and defect decrease under 6T magnetic field are affirmed by TEM. A 6T magnetic field can help the thin films transform from anisotropy to isotropy. The soft magnetic properties of the FexNi1−x (x=0.74, 0.6, 0.55, and 0.3) thin films are enhanced, and their resistivities decrease under a 6T magnetic field.

Observing electronic structures on ex‐situ grown topological insulator thin films

Abstractmagnified imageTopological insulators represent a new state of quantum matter recently discovered with insulating bulk but conducting surface states formed by an odd number of Dirac fermions. In this Letter, we report our recent progress on the study of electronic structures of ex‐situ grown topological insulator thin films by angle resolved photoemission spectroscopy (ARPES). We successfully obtained the topological band structures of molecular beam epitaxial HgTe and vapor–solid grown Bi2Te3 thin films after proper surface cleaning procedures. This new development will not only enable us to study more topological insulators that cannot be measured by conventional in‐situ ARPES technique (e.g. by cleaving or growing samples in‐situ), but also open the door to directly characterize the electronic properties of topological insulators used in functional devices. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Field Electron Emission from Hydrogen Plasma Treated Nano-ZnO Thin Films

A nano-Zno films are deposited on the Mo film/ceramic substrates by using the electron beam vapor deposition technique. Then a hydrogen plasma treated method is used to improve the characteristics of ZnO thin films by microwave plasma chemical vapor deposition system. Effects of process parameters on morphologies and structures of the ZnO thin films are detected and analysed by field emission scanning electron microscopy, X-ray diffraction spectrum and energy dispersive spectrum. The experimental result indicates that the hydrogen plasma treated techniques can essentially reduce the surface resistance and improve the field emission current density of the nano-ZnO thin films. For the hydrogen plasma treated sample, its field emission current density can increased more than three times at 2.2 V/microm electric field condition.

Photoluminescence of Er-doped ZnO nanoparticle films via direct and indirect excitation

Photoluminescence (PL) of Er-doped ZnO nanoparticle films was studied. The films were grown on silicon (100) or fused silica substrates using e -beam evaporation and subsequently annealed at 700 °C in air for an hour. PL was measured at two excitation wavelengths, 325 and 514.5 nm. The 325 nm was used for exciting the host semiconductor ZnO while 514.5 nm was used for directly exciting Er 3+ ions in the ZnO host. Er 3+ luminescence was observed from annealed films using either indirect (325 nm) or direct (514.5 nm) excitations. It has been found that the indirect excitation is significantly more efficient than the direct excitation in producing 1.54 μm photoluminescence. With indirect excitation, the Er 3+ luminescence observed is attributed to energy transfer from ZnO host to the Er 3+ ions doped. Energy transfer from e-h pairs resulting from ZnO host excitation may provide efficient routes for exciting Er 3+ ions inside nano-crystalline particles of the films.

Compositional analysis and depth profiling of thin film CrO2 by heavy ion ERDA and standard RBS: a comparison

Chromium dioxide (CrO 2 ) thin film has generated considerable interest in applied research due to the wide variety of its technological applications. It has been extensively investigated in recent years, attracting the attention of researchers working on spintronic heterostructures and in the magnetic recording industry. However, its synthesis is usually a difficult task due to its metastable nature and various synthesis techniques are being investigated. In this work a polycrystalline thin film of CrO 2 was prepared by electron beam vaporization of Cr 2 O 3 onto a Si substrate. The polycrystalline structure was confirmed through XRD analysis. The stoichiometry and elemental depth distribution of the deposited film were measured by ion beam nuclear analytical techniques heavy ion elastic recoil detection analysis (ERDA) and Rutherford backscattering spectrometry (RBS), which both have relative advantage over non-nuclear spectrometries in that they can readily provide quantitative information about the concentration and distribution of different atomic species in a layer. Moreover, the analysis carried out highlights the importance of complementary usage of the two techniques to obtain a more complete description of elemental content and depth distribution in thin films. Heavy ion elastic recoil detection analysis (ERDA) and Rutherford backscattering spectrometry (RBS) both have relative advantage over non-nuclear spectrometries in that they can readily provide quantitative information about the concentration and distribution of different atomic species in a layer. ► Thin films of CrO 2 have been grown by e-beam evaporation of Cr 2 O 3 target in vacuum. ► The composition was determined by heavy ion—ERDA and RBS. ► HI-ERDA and RBS provided information on the light and heavy elements, respectively.

Influence of growth parameters on the microstructures of erbium films deposited on Si(111) substrates

Erbium films were grown on single crystal Si(111) substrates by electron beam vapor deposition. The microstructures of the erbium films were systematically investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Results indicate that the surface morphologies and microstructures of the erbium films with Si as substrates are susceptible to the substrate temperatures when the deposition rates are fixed. The pure erbium films with columnar grains were obtained at temperatures below 200 °C, but in the films grown at temperatures higher than 350 °C, some pinholes that are composed of erbium silicides were found. The pinholes have triangular shapes which is in accordance with the geometry of the underlying Si(111) substrate. The films grown at a substrate temperature equal or greater than 450 °C have cracks which would be formed due to the different shrinkage degree of erbium and silicon when the substrate temperature was cooled down to room temperature. The films grown at 200 °C show the (002) preferred orientation, which is consistent to the prediction by the theory of surface energy minimization. The deposition rate and deposition time are considered as factors to affect the reaction of the erbium film and the silicon substrate.

Directed assembly in epitaxial zinc oxide films on focused ion beam modified sapphire substrates

A new method for directed self-assembly using focused ion beam (FIB) and physical vapor deposition is presented. The high resolution and site-specific patterning capabilities of FIB are coupled with the self-assembly process in heteroepitaxial thin film growth. An efficient FIB-induced damage mechanism is exploited to pattern amorphous regions in sapphire substrates which direct the subsequent assembly of a sputter-deposited zinc oxide film. This novel approach allows for the fabrication of in-plane nano- to microscale heterostructures comprising epitaxial regions with high strain and defect density that are separated by regions of randomly oriented (in-plane) grains with much lower strain and defect density.

Structural and optical studies of thick freestanding GaN films deposited by Hydride vapor phase epitaxy

Thick freestanding films or bulk GaN substrates with very low background impurity levels (≤1×1015/cm3) and high crystalline quality are required for a number of electronic device applications. Low pressure chemical vapor and molecular beam epitaxy techniques can systematically deposit films with low residual impurity concentrations. However, their typical slow growth rate prevents their utilization for substrate growth. The hydride vapor phase epitaxy deposition technique can achieve hundreds of microns per hour growth rate, but these films have typically high free carrier concentration (≥3×1017/cm3). It is crucial to verify if this method can reproducibly deliver thick freestanding GaN films of high crystalline quality with exceptionally low free carrier concentration. Low temperature photoluminescence and room temperature Raman scattering experiments carried out on a number of samples indicate that they have high crystalline quality and uncommonly low donor background levels. Reduced concentration of uncompensated shallow donors verified by low temperature electron paramagnetic resonance was confirmed by detailed high sensitive SIMS analyses. In addition, it was verified by X-ray diffraction analysis that relatively low dislocation densities can be achieved.

Fabrication of ${\rm Gd}_{1}{\rm Ba}_{2}{\rm Cu}_{3}{\rm O}_{\rm x}$ Coated Conductors for HTS Cables

We have been fabricating Gd1Ba2Cu3Ox (GdBCO) coated conductors (CCs) on textured clad-type substrates by using pulsed laser deposition (PLD) method for high temperature superconducting (HTS) power cables. In this project, numerous numbers of CCs are required for fabricating a 66 kV class, 3-in-One HTS cable and for the evaluation of its properties. In order to achieve this, it is important to ensure the stable production and the high-throughput manufacturing. In this work, we have newly installed a high power laser of 300 W for the PLD equipment, which has 1.66 times higher power than the previous one. As a result, the stability of manufacturing and the production rate were greatly improved. In addition, we have adopted a wide tape approach using 30 mm width substrates to increase the throughput. Moreover, we have optimized deposition condition for a seed layer by electron beam (EB) evaporation method, then the maximum Ic value for a short sample has achieved 497 A/cm at 77 K in the self-field. With this improved process, long GdBCO tapes with high Ic have been successfully fabricated.

Fabrication and Characterization of Solid Oxide Fuel Cell Electrolyte Films by Electron Beam Vapor Deposition

Thin films of SDC for SOFC electrolyte were prepared using electron beam deposition technique. The influence of annealing temperature, substrate temperature and e-beam gun power on the structure and surface morphology of the thin films was examined. It was found that the SDC thin films annealed at 800 degrees C consisted of a single cubic phase and the main crystal structure of the thin films represented those of evaporated electrolyte powders. The crystal orientation of the SDC films increased with substrate temperature and decreased with e-beam gun power. The higher XRD peak intensity was observed for the SDC films deposited on NiO-YSZ substrate compared with those on SiO2 substrate due to the polycrystalline structure of the NiO-YSZ substrate. A good adhesion to the substrate and a columnar structure were observed by the fractured cross-sectional view of the SDC films on NiO-YSZ anode substrate. Electrical conductivity of SDC film with 5 microm thickness was observed to be 2.31 x 10(-3) Sm(-1) at 800 degrees C.

Diffusion Monte Carlo calculation of rate of elastic transmission of a helium vapor beam through a slab of superfluid helium

Diffusion Monte Carlo calculation of rate of elastic transmission of a helium vapor beam through a slab of superfluid helium

Growth of Large Grain Polycrystalline Silicon Thin Film on Soda-lime Glass at Low Temperature for Solar Cell Applications

ABSTRACTHigh quality polycrystalline silicon (poly-Si) thin film solar cell was successfully fabricated on soda-lime glass substrates by electron beam (Ebeam) evaporation at low processing temperature. The initial poly-Si seed layer (p+-type 0.5 μm thick) was grown via the aluminum induced crystallization (AIC) method at 450 °C. Prominent interdiffusion and Si crystallization have been observed. X-ray diffraction (XRD) shows that (111) is the dominating crystalline orientation. Post annealing at 450 °C for six hours has produced densely packed Si grains with dimension of more than 10 μm in the plane of the film. Non-destructive Raman spectroscopy reveals the remarkable crystalline improvement for samples after thermal treatment. After removing the top diffused Al by chemical means, an absorber layer (p-type) of 0.9 μm thick was subsequently deposited onto the seed layer by Ebeam evaporation at 500 °C. Transmission electron microscopy (TEM) confirmed good homo-epitaxial growth. Without breaking the high vacuum, an n-type amorphous Si (a-Si) layer (0.7 μm thick) was coated onto the absorber layer to form p-n junction. The corresponding I-V characteristics suggest that our low temperature processing technique is applicable for production of poly-Si thin film solar cell on low cost substrates.

Preparation of Scandia-Stabilized Zirconia Electrolyte Thin Films for Intermediate Temperature-Solid Oxide Fuel Cells by Electron Beam Vapor Deposition

Thin films of scandia-stabilized zirconia (ScSZ) for a solid oxide fuel cell (SOFC) electrolyte were prepared using electron beam vapor deposition. The effects of annealing temperature, substrate temperature, and e-beam gun power on the structure and surface morphology of the thin films were examined. It was found that the ScSZ thin film samples annealed at approximately 1000 °C consisted of a single cubic phase. The crystal orientation of the ScSZ films increased with substrate temperature and with e-beam gun power. A good adhesion to the substrate and a columnar structure were observed from the fractured cross-sectional view of the ScSZ films on a NiO-YSZ anode substrate. The ionic conductivity of the ScSZ film with 2.5 µm thickness was observed to be 9.46×10-3 S cm-1 at 700 °C with the conduction activation energy of 0.82 eV. The results in this study showed that the crystallite size of the ScSZ thin films and thus the electrochemical properties can be improved by optimizing e-beam deposition conditions and annealing temperature.

Preparation of Scandia-Stabilized Zirconia Electrolyte Thin Films for Intermediate Temperature-Solid Oxide Fuel Cells by Electron Beam Vapor Deposition

Thin films of scandia-stabilized zirconia (ScSZ) for a solid oxide fuel cell (SOFC) electrolyte were prepared using electron beam vapor deposition. The effects of annealing temperature, substrate temperature, and e-beam gun power on the structure and surface morphology of the thin films were examined. It was found that the ScSZ thin film samples annealed at approximately 1000 °C consisted of a single cubic phase. The crystal orientation of the ScSZ films increased with substrate temperature and with e-beam gun power. A good adhesion to the substrate and a columnar structure were observed from the fractured cross-sectional view of the ScSZ films on a NiO-YSZ anode substrate. The ionic conductivity of the ScSZ film with 2.5 µm thickness was observed to be 9.46×10-3 S cm-1 at 700 °C with the conduction activation energy of 0.82 eV. The results in this study showed that the crystallite size of the ScSZ thin films and thus the electrochemical properties can be improved by optimizing e-beam deposition conditions and annealing temperature.

Electroluminescence of double-doped diamond thin films

A new electroluminescence device is fabricated by microwave plasma chemical vapour deposition system and electron beam vapour deposition system. It is comprised of highly doped silicon/diamond/boron/nitrogen-doped diamond/indium tin oxide thin films. Effects of process parameters on morphologies and structures of the thin films are detected and analysed by scanning electron microscopy, Raman spectrometer and x-ray photoelectron spectrometer. A direct-current (DC) power supply is used to drive the electroluminescence device. The blue light emission with a luminance of 1.2 cd-m−2 is observed from this double-doped diamond thin film electroluminescence device at an applied voltage of 105 V.