Vibrational excitation in collisions involving oxygen ion beams
Inelastic energy losses in oxygen ion beams collisions with neutral molecules, determining vibrational transition probabilities
Cosby, P. C.↗
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Ion-beam texturing of materials
Xenon ion-beam source is used to create microscopically-rough surface texture by sputter-etching surface while simultaneously sputter depositing lower yield material onto surface.
Hudson, W. R.↗
Ion Beam Sputtered Coatings of Bioglass
The ion beam sputtering technique available at the NASA-Lewis was used to apply coatings of bioglass to ceramic, metallic, and polymeric substrates. Experiments in vivo and in vitro described investigate these coatings. Some degree of substrate masking was obtained in all samples although stability and reactivity equivalent to bulk bioglass was not observed in all coated samples. Some degree of stability was seen in all coated samples that were reacted in vitro. Both metallic and ceramic substrates coated in this manner failed to show significantly improved coatings over those obtained with existing techniques. Implantation of the coated ceramic substrate samples in bone gave no definite bonding as seen with bulk glass; however, partial and patchy bonding was seen. Polymeric substrates in these studies showed promise of success. The coatings applied were sufficient to mask the underlying reactive test surface and tissue adhesion of collagen to bioglass was seen. Hydrophilic, hydrophobic, charged, and uncharged polymeric surfaces were successfully coated.
Hench, Larry L.↗
Making AlN(x) Tunnel Barriers Using a Low-Energy Nitrogen-Ion Beam
A technique based on accelerating positive nitrogen ions onto an aluminum layer has been demonstrated to be effective in forming thin (<2 nm thick) layers of aluminum nitride (AlN(x)) for use as tunnel barriers in Nb/Al-AlN(x)/Nb superconductor/insulator/ superconductor (SIS) Josephson junctions. AlN(x) is the present material of choice for tunnel barriers because, to a degree greater than that of any other suitable material, it offers the required combination of low leakage current at high current density and greater thermal stability. While ultra-thin AlN films with good thickness and stoichiometry control are easily formed using techniques such as reactive molecular beam epitaxy and chemical vapor deposition, growth temperatures of 900 C are necessary for the dissociative adsorption of nitrogen from either nitrogen (N2) or ammonia (NH3). These growth temperatures are prohibitively high for the formation of tunnel barriers on Nb films because interfacial reactions at temperatures as low as 200 to 300 C degrade device properties. Heretofore, deposition by reactive sputtering and nitridation of thin Al layers with DC and RF nitrogen plasmas have been successfully used to form AlN barriers in SIS junctions. However, precise control over critical current density Jc has proven to be a challenge, as is attaining adequate process reproducibility from system to system. The present ion-beam technique is an alternative to the plasma or reactive sputtering techniques as it provides a highly controlled arrival of reactive species, independent of the electrical conditions of the substrate or vacuum chamber. Independent and accurate control of parameters such as ion energy, flux, species, and direction promises more precise control of film characteristics such as stoichiometry and thickness than is the case with typical plasma processes. In particular, the background pressure during ion-beam nitride growth is 2 or 3 orders of magnitude lower, minimizing the formation of compounds with contaminants, which is critical in devices the performance of which is dictated by interfacial characteristics. In addition, the flux of incoming species can be measured in situ using ion probes so that the dose can be controlled accurately. The apparatus used in the present ion-beam technique includes a vacuum chamber containing a commercial collimated- ion-beam source, a supply of nitrogen and argon, and an ion probe for measuring the ion dose. Either argon or nitrogen can be used as the feed gases for the ion source, depending on whether cleaning of the substrate or growth of the nitride, respectively, is desired. Once the Nb base electrode and Al proximity layer have been deposited, the N2 gas line to the ion beam is vented and purged, and the ion-source is turned on until a stable discharge is obtained. The substrate is moved over the ion-beam source to expose the Al surface layer to the ion beam (see figure) for a specified duration for the formation of the nitride tunnel barrier. Next, the Nb counter-electrode layer is deposited on the nitride surface layer. The Nb/Al- AlN(x)/Nb-trilayer-covered substrate is then patterned into individual devices by use of conventional integrated-circuit processing techniques.
Kaul, Anupama↗
ITO/InP solar cells: A comparison of devices fabricated by ion beam and RF sputtering of the ITO
This work was performed with the view of elucidating the behavior of indium tin oxide/indium phosphide (ITO/InP) solar cells prepared by RF and ion beam sputtering. It was found that using RF sputter deposition of the ITO always leads to more efficient devices than ion beam sputter deposition. An important aspect of the former technique is the exposure of the single crystal p-InP substrates to a very low plasma power prior to deposition. Substrates treated in this manner have also been used for ion beam deposition of ITO. In this case the cells behave very similarly to the RF deposited cells, thus suggesting that the lower power plasma exposure (LPPE) is the crucial process step.
Coutts, T. J.↗
Ion beam applications research. A summary of Lewis Research Center Programs
A summary of the ion beam applications research (IBAR) program organized to enable the development of materials, products, and processes through the nonpropulsive application of ion thruster technology is given. Specific application efforts utilizing ion beam sputter etching, deposition, and texturing are discussed as well as ion source and component technology applications.
Banks, B. A.↗
The influence of stray magnetic fields on ion beam neutralization
An experimental investigation is described of a comparison between the ion beam neutralization characteristics of a local neutralizer (within approximately 5 cm of the beam edge) and those associated with a distant one (approximately 1 meter away from the thruster). The influence of magnetic fields in the vicinity of the neutralizer cathode orifice which are either parallel or normal to the neutralizer axis is assessed. The plasma property profiles which reflect the influence of the magnetic fields are measured. The results suggest that magnetic fields at the region of a neutralizer cathode orifice influence its ability to couple to the ion beam. They reveal that there is a potential jump from the neutralizer cathode orifice to the plasma which exists close to the orifice. This potential drop is found to increase as the axial component of magnetic flux density increases. A magnetic field perpendicular to the neutralizer axis induces a potential rise a few centimeters downstream from the neutralizer cathode.
Feng, Y.-C.↗
Numerical Simulations of Virtual Anodes in Ion Beams Emissions in Space
Standard theories have shown that when the current density in a one-dimensional electron or ion beam exceeds a critical value, a potential hump will show up. This hump will behave as a virtual electrode to the beam particles. Measurements have demonstrated the existence of virtual cathodes and anodes. Results are presented of particle-in-cell simulations of ion beam emissions in space.
Ion Beam Plasma Ionization Particles↗
Characterization of ion beam modified ceramic wear surfaces using Auger electron spectroscopy
An investigation of the surface chemistry and morphology of the wear surfaces of ceramic material surfaces modified by ion beam mixing has been conducted using Auger electron spectroscopy and secondary electron microscopy. Studies have been conducted on ceramic/ceramic friction and wear couples made up of TiC and NiMo-bonded TiC cermet pins run against Si3N4 and partially stabilized zirconia disc surfaces modified by the ion beam mixing of titanium and nickel, as well as ummodified ceramic/ceramic couples in order to determine the types of surface changes leading to the improved friction and wear behavior of the surface modified ceramics in simulated diesel environments. The results of the surface analyses indicate that the formation of a lubricating oxide layer of titanium and nickel, is responsible for the improvement in ceramic friction and wear behavior. The beneficial effect of this oxide layer depends on several factors, including the adherence of the surface modified layer or subsequently formed oxide layer to the disc substrate, the substrate materials, the conditions of ion beam mixing, and the environmental conditions.
Wei, W.↗
Electromagnetic ion beam instabilities - Hot beams at interplanetary shocks
This paper considers Vlasov instabilities driven by a very hot ion beam streaming parallel to a magnetic field. The linear theory of electromagnetic instabilities driven by such a beam in a homogeneous, collisionless, nonrelativistic plasma is used. Numerical solutions of the full linear dispersion equation for bi-Maxwellian distribution functions are presented. If the thermal speed of the beam is greater than its drift speed, the two dominant modes are the right-hand and left-hand resonant ion beam instabilities. The parametric dependencies of the threshold drift speeds and growth rates for both modes are presented. In particular, the thresholds are shown to be sensitive functions of the beam temperature anisotropies. Arguments are presented that these two modes are driven by the suprathermal ion component at interplanetary shocks, and that the growth of these modes is sufficient to account for the amplitudes of MHD-like waves observed at such shocks.
Gary, S. P.↗
A new model for the ion beams in the plasma sheet boundary layer
A new model is proposed for the ion beams frequently observed in the plasma sheet boundary layer. The model assumes injection of magnetosheath plasma onto closed tail field lines. The plasma then expands along the field lines and is convected towards the earth. Particle simulations of the expansion process are used to calculate properties of these beams. The expansion produces beams of ions at energies of up to a few tens of k(B)T(e), which are consistent with the observed energies of the beams.
Whelan, T.↗
Investigation of ion-beam machining methods for replicated x-ray optics
The final figuring step in the fabrication of an optical component involves imparting a specified contour onto the surface. This can be expensive and time consuming step. The recent development of ion beam figuring provides a method for performing the figuring process with advantages over standard mechanical methods. Ion figuring has proven effective in figuring large optical components. The process of ion beam figuring removes material by transferring kinetic energy from impinging neutral particles. The process utilizes a Kaufman type ion source, where a plasma is generated in a discharge chamber by controlled electric potentials. Charged grids extract and accelerate ions from the chamber. The accelerated ions form a directional beam. A neutralizer outside the accelerator grids supplies electrons to the positive ion beam. It is necessary to neutralize the beam to prevent charging workpieces and to avoid bending the beam with extraneous electro-magnetic fields. When the directed beam strikes the workpiece, material sputters in a predicable manner. The amount and distribution of material sputtered is a function of the energy of the beam, material of the component, distance from the workpiece, and angle of incidence of the beam. The figuring method described here assumes a constant beam removal, so that the process can be represented by a convolution operation. A fixed beam energy maintains a constant sputtering rate. This temporally and spatially stable beam is held perpendicular to the workpiece at a fixed distance. For non-constant removal, corrections would be required to model the process as a convolution operation. Specific figures (contours) are achieved by rastering the beam over the workpiece at varying velocities. A unique deconvolution is performed, using series-derivative solution developed for the system, to determine these velocities.
Drueding, Thomas W.↗
Radiological physics characteristics of the extracted heavy ion beams of the bevatron.
Studies of the depth-ionization properties and the biological effects of heavy ion beams produced at the bevatron have extended work previously done with less energetic beams from other sources. Results indicate that heavy ion beams are suitable for tumor therapy, studies relating to space biology, and fundamental radiobiology.
Tobias, C. A.↗
Adaptation of ion beam technology to microfabrication of solid state devices and transducers
It was found that ion beam texturing of silicon surfaces can be used to increase the effective surface area of MOS capacitors. There is, however, a problem with low dielectric breakdown. Preliminary work was begun on the fabrication of ion implanted resistors on textured surfaces and the potential improvement of wire bond strength by bonding to a textured surface. In the area of ion beam sputtering, the techniques for sputtering PVC were developed. A PVC target containing valinomycin was used to sputter an ion selective membrane on a field effect transistor to form a potassium ion sensor.
Topich, J. A.↗
The electromagnetic ion beam instability upstream of the earth's bow shock
The linear theory of the electromagnetic ion beam instability for arbitrary angles of propagation has been studied. The parameters considered in the theory are typical of the solar wind upstream of the earth's bow shock when a 'reflected' proton beam is present. Maximum growth occurs for propagation parallel to the ambient magnetic field B, but this instability also displays significant growth at wave-vectors oblique to B. Oblique, unstable modes seem to be the likely source of the compressive magnetic fluctuations recently observed in conjunction with the 'diffuse' ion population. An energetic ion beam does not directly give rise to linear growth of either ion acoustic or whistler mode instabilities.
Gary, S. P.↗
Scanning-electron-microscopy observations and mechanical characteristics of ion-beam-sputtered surgical implant alloys
An electron bombardment ion thruster was used as an ion source to sputter the surfaces of orthopedic prosthetic metals. Scanning electron microscopy photomicrographs were made of each ion beam textured surface. The effect of ion texturing an implant surface on its bond to bone cement was investigated. A Co-Cr-W alloy and surgical stainless steel were used as representative hard tissue implant materials to determine effects of ion texturing on bulk mechanical properties. Work was done to determine the effect of substrate temperature on the development of an ion textured surface microstructure. Results indicate that the ultimate strength of the bulk materials is unchanged by ion texturing and that the microstructure will develop more rapidly if the substrate is heated prior to ion texturing.
Weigand, A. J.↗
Electromagnetic ion beam instabilities. II
The results of Gary et al. (1984) on the properties of the right-hand resonant and nonresonant electromagnetic ion beam instabilities for relatively cool beam temperatures are extended. In particular, the parametric dependence of the real frequency at maximum growth of these modes is examined. It is demonstrated that the right-hand resonant ion beam instability can have maximum growth at frequencies near the ion-cyclotron frequency if the beam main component relative drift speed is about twice the Alfven speed and at least one of two conditions holds: that the ion beta or the beam main component relative temperature are sufficiently small, or the perpendicular-to-parallel beam temperature ratio is sufficiently large. These results support the identification of the right-hand resonant instability as the source of the large amplitude magnetic fluctuations observed upstream of slow shocks in the earth's magnetotail.
Gary, S. P.↗
Normal incidence reflectance of ion beam deposited SiC films in the EUV
Results are presented from an experimental investigation of the normal-incidence reflectance at 58.4, 92.0, and 121.6 nm wavelength of 30- and 80-nm-thick SiC films produced by ion-beam deposition on unheated 5 x 5-cm microscope slides. The films were deposited in the 2-m evaporator described by Bradford et al. (1969) with chamber base pressure 1 microtorr, operating pressure 40 microtorr, and a 50-62-mA 750-eV Ar ion beam; the reflectance measurements were obtained in the reflector-monochromator system described by Osantowski (1974). Reflectances of over 30 percent were found at 92 and 121.6 nm, almost equal to those of polished CVD films of SiC and degrading only slightly after aging for 4 months. It is suggested that ion-beam deposition may be the best low-temperature technique for coating EUV optics for space astronomy.
Keski-Kuha, Ritva A. M.↗