Pulsed Electron Beam Deposition Research Articles

Growth of group III nitride films by pulsed electron beam deposition

We have grown group III nitride films on Al 2O 3 (0 0 0 1), 6H–SiC (0 0 0 1), and ZnO ( 0 0 0 1 ¯ ) substrates by pulsed electron beam deposition (PED) for the first time and investigated their characteristics. We found that c-plane AlN and GaN grow epitaxially on these substrates. It has been revealed that the growth of GaN on atomically flat 6H–SiC substrates starts with the three-dimensional mode and eventually changes into the two-dimensional mode. The GaN films exhibited strong near-band-edge emission in their room temperature photoluminescence spectra. We also found that the use of PED allows us to reduce the epitaxial growth temperature for GaN down to 200 °C.

Dynamics of a pulsed-electron beam induced plasma: application to the growth of zinc oxide thin films

Spatial and temporal distributions of species emitted from ablation of zinc oxide target by a pulsed-electron beam are studied by the complementary use of optical emission spectroscopy and camera fast imaging. We show that the slowest electrons produced by the accelerating tube in the pulsed-electron beam deposition (PED) system interact with the plasma plume and involve a further excitation of the neutrals species. The velocities of atoms and ions are found to be similar to those obtained in the well-known pulsed-laser deposition (PLD) process while the plasma temperature and the electron density are lower. The low absorption of the electron beam by the expanding plasma compared with that experienced in PLD leads to a higher removal of ablated material and consequently to a higher deposition rate ten times greater than in PLD. The PED ZnO films grown at room temperature on silicon substrate are constituted by the stacking of small aggregates without large macroscopic droplets. These results are in agreement with the ICCD images recorded at long time delays from the electron impact which do not evidence bright trails correlated with the propagation of slow and large particles.

Synthesis and optical properties of CeO2 nanocrystalline films grown by pulsed electron beam deposition

The nanocrystalline cerium dioxide (CeO2) thin films were deposited on soda lime (SLG) and Corning glass by pulsed e-beam deposition (PED) method at room temperature. The structure of the produced CeO2 thin films was investigated by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and micro Raman spectroscopy. The surface topography of the films was examined by atomic force microscopy (AFM). Film thickness and growth morphologies were determined with FEG-SEM from the fracture cross sections. XPS studies gave a film composition composed of +4 and +3 valent cerium typical to nanocrystalline ceria structures deficient in oxygen. The ceria films were polycrystalline in nature with a lattice parameter (a) of 0.542 nm. The Raman characteristics of the source material and the films deposited were very similar in character. Raman lines for thin film and bulk CeO2 was observed at 465 cm−1. The optical properties of the CeO2 films were deduced from reflectance and transmittance measurements at room temperature. From the optical model, the refractive index was determined as 1.8–2.7 in the photon energy interval from 3.5 to 1.25 eV. The optical indirect band gap (Eg) of CeO2 nanocrystalline films was calculated as 2.58 eV.

Pulsed electron beam deposition of oxide thin films

In this work we studied the pulsed electron beam deposition (PED) method using a channel-spark discharge as the electron source. In order to estimate the potential of the PED method, thin films of zinc oxide, zirconium tin titanate, barium strontium titanate and biocompatible oxides were grown and investigated taking into account two important points: the surface morphology and the film composition. We showed that PED leads to films free from micrometre size droplets and by a careful optimization of the beam parameters it is possible to drastically reduce the density and size of nanoparticulates. In fact, by studying the relationships between the discharge parameters, electron beam characteristics and surface morphology of films we evidenced that a decrease in the beam energy leads to a drastic reduction in the nanoparticulate density. The composition of the various oxide thin films investigated in this work is close to that of the target, as in the case of pulsed laser deposition, even in the case of complex oxide compounds. Hence, smooth and dense thin films preserving the composition of the bulk target can be obtained by the PED method. The study by fast imaging of the expansion of the plasma plume produced by the pulsed electron beam interaction with the target indicates that the kinetic energy of the species emitted by the target is roughly in the 10–50 eV range.

Hardness of zirconium diboride films deposited on titanium substrates

The study was aimed at the hardness determination of thin ZrB 2 films produced on pure titanium substrate by pulsed laser deposition and electron beam deposition techniques. The former method allows the deposition of dense crystalline films, being textured preferentially along the (1 1 0) direction, whereas the electron beam deposition allows the production of compact X-ray amorphous films. The thickness of the films was about 200 and 500 nm, respectively. Vickers hardness values obtained by microindentation technique are close to those of bulk ZrB 2 ceramics. Pulsed laser deposited ZrB 2 films are harder ranging from 21 to 27 GPa than the electron beam deposited films ranging from 19 to 23 GPa. An increase in the substrate preheating temperature leads to a decrease in hardness value.

Pulsed electron beam deposition of highly oriented thin films of polytetrafluoroethylene

Thin films of polytetrafluoroethylene (PTFE) were deposited by pulsed electron deposition (PED) technique. The transmission electron microscopy (TEM) image of the RT fabricated (20 Å thick) film on carbon coated copper grid shows crystalline nature. Infrared spectra show one to one correspondence between PED ablated film and the PTFE bulk target. The asymmetrical and symmetrical –CF 2– stretching modes were observed at 1220 and 1156 cm −1, respectively. The –CF 2– wagging and bending modes occur at 644 and 512 cm −1, respectively. X-ray diffraction patterns of the film deposited at room temperature (RT) show oriented film along (1 0 0) plane of hexagonal structure and the crystalline nature is retained up to 300 °C on vacuum annealing. The room temperature fabricated film shows smooth and pin hole free surface whereas post-annealing brings discontinuity, roughness and pin holes.

Potential of pulsed electron-beam deposition for nanomaterial fabrication: Spatial distribution of deposited materials

Pulsed electron-beam deposition (PED) is a recently developed pulsed energy ablation/deposition technique with distinct advantages for its cost effectiveness, nature of the electron-material interactions, and large-scale production. By the proper control of the ablation/deposition parameters, one can produce high purity quantum dots and thin films in situ in vacuum chamber. Further, PED can also be used for unique material syntheses by introducing reactive gases in the chamber. However, little systematic work has been done to demonstrate PED’s potential applications except for few on film and nanoparticle fabrications. Particular efforts are made here to study the spatial variations of the deposited materials.

Er-doped ZnO films grown by pulsed e-beam deposition

Erbium (Er)-doped ZnO thin films were grown on fused silica(SiO2) substrates by pulsed electron-beam deposition (PED) and analysed by Rutherford backscatteringspectrometry (RBS), ultraviolet–visible absorption, and photoluminescence (PL). Subsequent annealingat 700 °C produces remarkable effects on the optical properties of Er-doped films. Under 325 nmexcitation, a dramatic increase of deep-level emission from 450 to 680 nm was observed fromannealed Er-doped ZnO films. Under 488 nm excitation, the PL spectrum of annealedEr-doped ZnO films revealed sharp and well-resolved Stark-splitting peaks in both thegreen emission of transition and the red emission of transition of Er3+ ions, which suggests that the Er ions have been incorporated inside the crystalline ZnOgrains after thermal annealing.

Novel Vapor Phase biodegradable coatings for controlled drug delivery systems

AbstractThe synthesis of nano-functionalized drug particles or drug particles with nanoscale biodegradable polymeric coatings has wider ranging applications in sustained release drug delivery systems. An important area of application includes delivery of drugs, such as proteins, peptides, and glucocorticoids via the inhalation process. The advantages of this method include, rapid absorption by the body and lack of metabolic degradation effects which is typically by some drugs during oral delivery. Here we discuss the novel pulsed laser and pulsed electron method to synthesize nanoscale biodegradable coatings of poly lactic acid (PLA) onto antiasthmatic drugs. In pulsed laser method a pulsed excimer laser ablates a thin layer of polymer which is deposited onto 1 -5 micron drug particles which are fluidized in the gas chamber. The control of the thickness, conformation and the chemistry of the nanoscale coating process will be discussed in detail. Applications of this methodology to delivery of anti asthamtic drugs and insulin will be discussed. The effect of polymer coating chemistry, molecular weight, hydrophobicity, and thickness on the sustained release characteristics will be discussed. A unique method for depositing the PLA films, pulsed electron beam deposition (PED) was used to deposit the films. This technique was tried done to overcome the difficulties like low absorption co-efficient of UV-laser. Method proved to be promising for producing smooth films and offers a better thickness control of the deposition. The RMS roughness and other morphological characteristics of PED deposited films were superior over the conventional laser ablated films.

Characterization of CdTe nanoparticles fabricated by pulsed electron deposition technique at different ablation parameters

AbstractCadmium Telluride (CdTe) is a front‐runner photovoltaic (PV) material because it has already attained efficiencies above 16%. The fabrication of CdTe nanoparticles has aroused considerable interest because of their potential application as active layer in organic/inorganic hybrid solar cells. They can also be used for sensitisation of wide band gap semiconductors. In this work, we explore pulsed electron beam deposition (PED) technique to fabricate CdTe nanoparticles. Two ablation parameters, namely background gas pressure and electron energy, were varied to investigate their effects on the nanoparticle formation. Optical transmission measurements and SEM indicate that we have deposited CdTe nanocrystalline films exhibiting quantum confinement effects. From AFM, these films are as smooth as the Si substrate. In addition to the smooth film, larger nanoparticles with diameters varying from 40 nm to 500 nm were also deposited on the substrate. They contribute to the absorption onset at the bulk band gap energy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancing low-field magnetoresistance of La 0.67 Ca 0.33 MnO 3 films deposited on anodized aluminium-oxide membranes

In this paper we report a new method to fabricate nanostructured films. La0.67Ca0.33MnO3 (LCMO) nanostructured films have been fabricated by using pulsed electron beam deposition (PED) on anodized aluminium oxide (AAO) membranes. The magnetic and electronic transport properties are investigated by using the Quantum Design physics properties measurement system (PPMS) and magnetic properties measurement system (MPMS). The resistance peak temperature (Tp) is about 85 K and the Curie temperature (Tc) is about 250 K for the LCMO film on an AAO membrane with a pore diameter of 20 nm. Large magnetoresistance ratio (MR) is observed near Tp. The MR is as high as 85% under 1 T magnetic field. The great enhancement of MR at low magnetic fields could be attributed to the lattice distortion and the grain boundary that are induced by the nanopores on the AAO membrane.

The effect of grain boundaries on magnetic and transport properties in colossal magnetoresistance particle film

La0.67Ca0.33MnO3 grain films have been grown by pulsed electron beam deposition technology,and their magnetic and electronic transport properties investigated in detail.The influence of grain boundaries on the physical properties of La0.67Ca0.33MnO3 grain films were studied.Grain boundaries weaken the coupling between grains,resulting in a cluster spin glass state.The metal-insulator transition temperature (Tp) was shifted far below the ferromagnetic-paramagnetic transition temperature (Tc).At low temperatures,the electron transportation indicates a weak localization behavior,and under low magnetic fields,the intrinsic magnetoresisance effect is screened by the influence of grain boundaries.

High Quality<tex>$rm SmBa_2rm Cu_3rm O_7hbox -delta$</tex>Thin Films on<tex>$rm SrTiO_3$</tex>

We for the first time report a successful fabrication of a high-J/sub C/ SmBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(SmBCO) thin film (/spl sim/240 nm thickness) on SrTiO/sub 3/ (100) substrate by the pulsed electron beam deposition (PED) process. For this study, we systematically investigated the effect of processing parameters, including substrate temperature (Ts), ambient oxygen pressure (PO/sub 2/), and target-to-substrate distance, on superconducting properties, including critical temperature (T/sub C/) and critical current density (J/sub C/), of PED-processed SmBCO films. The highest J/sub C/ value of 1.37 MA/cm/sup 2/ at 77 K in self field was obtained from an optimally processed sample using Ts of 900/spl deg/C (corresponding to real substrate temperature of 810/spl deg/C), PO/sub 2/ of 15 mTorr, and target-to-substrate distance of 9 cm, evidencing that this process is a potential alternative to the PLD process.

Growth of ZnO films on C-plane (0 0 0 1) sapphire by pulsed electron deposition (PED)

Thin films of ZnO on C-plane (0 0 0 1) sapphire (α-Al 2O 3) substrates were grown by pulsed electron beam deposition (PED). Intense electron pulses, approximately 0.8 J/70 ns pulse produced by a channelspark pulsed electron source at a rate of 10 Hz were used to ablate sintered polycrystalline ZnO targets at an oxygen pressure of 15 mTorr. During growth, the sapphire substrate temperature was maintained at 700 °C. A 15 min growth produced a 250 nm film, as measured by a Dektak profilometer. Measurements by X-ray diffraction indicate c-axis oriented films. Cathodoluminescence (CL) data show strong band edge emission. Optical absorption data indicate a sharp band edge with clearly visible exciton absorption at room temperature, and resolved A and B excitons at 77 K. Thus, pulsed electron beam deposition of ZnO films is shown to be a viable technique for producing high quality ZnO films.

Pulsed-electron-beam deposition of transparent conducting SnO2 films and study of their properties

Transparent conducting films of SnO2 are grown on single-crystal R-Al2O3 substrates by the pulsed electron beam deposition (PED) technique, and their electrical, optical, and microstructural properties are compared with the films grown by pulsed-laser deposition (PLD). In PED, the pulsed electron beam used for ablation is generated by a channel-spark system with discharge voltage of 12 kV, current ∼1 kA, and pulse duration of ∼100 ns. The PED films are highly oriented, show good epitaxy, and are highly transparent with transmittance of ∼80% in the visible and IR range. The measured band gap is close to 3.9 eV. It is shown that the PED film properties compare well with those of PLD films, with the Sn119 Mossbauer spectroscopy showing comparable local environments in the two.

Oxide scale growth on MCrAlY bond coatings after pulsed electron beam treatment and deposition of EBPVD-TBC

Thin layers restructured by surface melting to approximately 30-μm depth on MCrAlY coatings were produced using the large-area pulsed electron-beam GESA facility. With a beam diameter of up to 10 cm, it is possible to treat large surface areas, with just a few overlapping electron beam pulses. The high cooling rates lead to nanocrystalline structures at the sample surface. Their oxidation properties were studied at 950°C in air. As the surface treatment leads to smooth surfaces, with an R A<1.5 μm, even on formerly rough low-pressure plasma spray (LPPS) samples, the samples can subsequently be coated directly with electron beam physical vapor deposition (EBPVD) thermal barrier coatings (TBC). The growth of the thermally grown oxide (TGO) on such samples was also studied at 950°C in air for up to 5000 h and compared to that of samples without the TBC. The treated samples appeared to have a strongly enhanced oxidation resistance without spinel formation in the α-Al 2O 3 oxide scale.

Deposition of MBa2Cu3O7-x thin films by channel-spark method

Channel-spark pulsed electron beam deposition (CS), a new deposition method based on a simple and inexpensive system, has been used for preparation of high-quality GdBa2Cu3O7-x, Gd1-xEuxBa2Cu3O7-x and YBa2Cu3O7-x thin films epitaxially grown on NdGaO3 and SrTiO3 substrates. Typical critical temperatures for zero DC resistance lie in the intervals 87-89 K for Y-based films and 91.0-92.6 K for Gd- and GdEu-based ones. The transition widths for the best films are less than 0.5 K. The critical current densities reach the values of 3*106 A cm-2 at 77 K, zero field.

Technique for studying dynamic tensile failure in liquids: application to glycerol

A new experimental technique has been developed for the study of the dynamic tensile strength of liquids. The liquid is confined between a solid plate and a stretched aluminized Mylar film. Pulsed electron beam deposition in the plate generates a stress wave which traverses the liquid and gives a high tensile stress during reflection at the Mylar-covered free surface. Interferometric analysis of the motion of the Mylar film provides a sensitive measure of the stress-wave-liquid interaction. The technique has been used to determine a dynamic tensile strength for glycerol at room temperature of 0.6±0.1 kbar from 5 to 23 kbar/μsec. No variation of tensile strength with stress rate was found.