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Ion beam surface modification is typically carried out in a laboratory environment where the processing rate is not a big concern. Nevertheless, it is interesting to consider the possibilities that might allow substantial increase (orders of magnitude) in the processing rate, possibly for industrial application. Here we consider two possible approaches to very large scale ion beam surface modification – the use of very broad beam vacuum arc ion sources and the use of ion sources that have been developed to provide intense neutral beams as part of the world controlled fusion research effort. These sources can provide beam intensities in the tens of amperes range, and quasi-dc operation has been demonstrated. A third possibility is scale-up of the Plasma Immersion Ion Implantation approach, and some relevant work has been done along these lines. These approaches to giant ion beam surface modification systems, and the implied parameters and features of such systems, as well as the highly related concern of the necessary accompanying electrical systems, are briefly considered here.

Since the initial reported outbreak of coronavirus disease 2019 (COVID-19), many unique case reports have been published in the medical literature. Here we report a complicated clinical course of a young patient with COVID-19 who presented initially with recurrent autoimmune hemolytic anemia (AIHA). He subsequently developed bilateral pulmonary emboli, and ultimately succumbed to encephalitis and cryptococcemia in the context of being treated with high dose immunosuppression for the AIHA. Combining immunosuppression with active COVID-19 infection presents some truly challenging diagnostic and management scenarios which this case summarizes and highlights very well. Based on this case, we propose some strategies on how to approach these difficult decisions while also recognizing the significant gaps that exist in such an evolving topic. Lastly, this case also represents a potentially novel presentation of secondary fungal infection of the central nervous system (CNS) related to COVID-19.

Nanocomposites formed by metal nanoparticles self-assembled in an insulator matrix are of great technological importance. Applications include surface enhanced Raman spectroscopy based biosensors, optical devices, photovoltaic cells, and more. Self-assembling of nanocomposites using low energy ion implantation offers a fast and low cost process. We report here on our work on nanocomposites formed by very low energy ion implantation of gold and platinum nanoparticles into Poly(methyl methacrylate) (PMMA), with description of the nanoparticle evolution as a function of implantation dose. The Au-PMMA and Pt-PMMA nanocomposites were characterized by transmission electron microscopy, thus determining the nanoparticle density, their size distribution, and the distance between particles as a function of implantation dose. A comparison between Au-PMMA and Pt-PMMA reveals substantial differences in the formation processes of the nanoparticles. The results provide insight into basic nanoparticle formation processes, as well as crucial information important for design applications. In addition, the tunneling decay length ξ and the electron affinity e of the implantation-modified PMMA were obtained using a new and simple approach.

The goal of this study was to determine the critical ion-radiation conditions under which heavy ion beams can induce DNA double-strand breaks. Helium, nitrogen and argon-ion beams in the energy range of 20 eV to 2 keV were used to irradiate naked DNA plasmid pGFP to fluences of 1, 2 and 4 × 1015 ions/cm2. The topological forms of DNA were subsequently analyzed using gel electrophoresis. The DNA forms were changed from the original supercoiled to damaged relaxed and linear forms, depending on the ion mass, energy, fluence and inertia. We found ion energy and fluence thresholds above which direct double-strand breaks can occur. The threshold is discussed in terms of the areal ion-energy density and the cross-section.

Under physiological conditions, the opening and closing of the leaflets of an implanted artificial heart valve (AHV) affects the blood components and therefore may cause various complications to the patient such as hemolysis or platelet activation. In this paper, a computational fluid model is presented. The regional distribution of flow shear stress in an AHV is analyzed using computational fluid dynamics and AHV performance is evaluated in terms of the variation of flow velocity and pressure when blood passes the leaflets in the aortic valve. The results suggest that for the design of a mechanical AHV, the maximum opening angle and internal orifice diameter should be increased to improve the fluid structure interaction and decrease the possibility of damage to blood components. Finally, the fluid stress distribution of the AHV leaflet structure was calculated and analyzed under pulsating flow conditions.

Acoustic cavitation, especially transient cavitation, in solutions is accompanied by a number of physical and chemical effects. Due to high temperature and pressure conditions inside bubbles at their collapse, excitation of various species as well as formation of radicals occurs in solution [1-4]. Water molecules excited by megasonic irradiation typically dissociate to hydrogen and hydroxyl radicals (H• and OH•) [5]. The hydroxyl radical is a strong oxidant while the hydrogen radical has reducing properties. In presence of O2 in the solution, H• reacts with O2 to form hydroperoxyl (HO2•) radicals, which act as a reducing as well as a (weak) oxidizing agent [6]. Dissociation of hydroperoxyl radicals result in the formation of superoxide anion radicals (O2•-) as follows [6]

There is special interest in the incorporation of metallic nanoparticles in a surrounding dielectric matrix for obtaining composites with desirable characteristics such as for surface plasmon resonance, which can be used in photonics and sensing, and controlled surface electrical conductivity. We have investigated nanocomposites produced by metal ion implantation into insulating substrates, where the implanted metal self-assembles into nanoparticles. The nanoparticles nucleate near the maximum of the implantation depth profile (projected range), which can be estimated by computer simulation using the TRIDYN code. TRIDYN is a Monte Carlo simulation program based on the TRIM (Transport and Range of Ions in Matter) code that takes into account compositional changes in the substrate due to two factors: previously implanted dopant atoms, and sputtering of the substrate surface. Our study show that the nanoparticles form a bidimentional array buried a few nanometers below the substrate surface. We have studied Au/PMMA (polymethylmethacrylate), Pt/PMMA, Ti/alumina and Au/alumina systems. Transmission electron microscopy of the implanted samples show that metallic nanoparticles form in the insulating matrix. These nanocomposites have been characterized by measuring the resistivity of the composite layer as a function of the implantation dose. The experimental results are compared with a model based on percolation theory, in which electron transport through the composite is explained by conduction through a random resistor network formed by the metallic nanoparticles. Excellent agreement is found between the experimental results and the predictions of the theory. We conclude in that the conductivity process is due only to percolation (when the conducting elements are in geometric contact) and that the contribution from tunneling conduction is negligible.

Ion implantation provides an important technology for the modification of material surface properties. The vacuum arc ion source is a unique instrument for the generation of intense beams of metal ions as well as gaseous ions, including mixed metal–gas beams with controllable metal:gas ion ratio. Here we describe our exploratory work on the application of vacuum arc ion source-generated ion beams for ion implantation into polymer textile materials for modification of their biological cell compatibility surface properties. We have investigated two specific aspects of cell compatibility: (i) enhancement of the antibacterial characteristics (we chose to use Staphylococcus aureus bacteria) of ion implanted polymer textile fabric, and (ii) the “inverse” concern of enhancement of neural cell growth rate (we chose Rat B-35 neuroblastoma cells) on ion implanted polymer textile. The results of both investigations were positive, with implantation-generated antibacterial efficiency factor up to about 90%, fully comparable to alternative conventional (non-implantation) approaches and with some potentially important advantages over the conventional approach; and with enhancement of neural cell growth rate of up to a factor of 3.5 when grown on suitably implanted polymer textile material.

This paper provides a confirmation of the effectiveness of the recently suggested ab initio approach to the theoretical prediction of phase transformations which may be induced in metallic alloys by metal plasma immersion and ion implantation processing. The approach is based on an assumption that at certain concentrations of the implanted species, the relaxation of the exited electronic state of the implanted structure should be accompanied by the rearrangement of atoms leading to the formation of a new phase. Recently, on the basis of density functional theory calculations of the energetic characteristics of the electronic subsystems of the implanted Mg–Ag system, it was predicted that concentrations of the implanted Ag ions within the range from ∼18 to 23 at% Ag, favor transition to the phase e′-Ag17Mg54. Our transmission electron microscopy observations and electron diffraction analysis of the Mg-based alloy subjected to the implantation of Ag ions at dose of ∼5×1015 ion/cm2 confirmed that the formati...

We have explored the suitability and characteristics of interface tailoring as a tool for enhancing the adhesion of hydrogen-free diamond-like carbon (DLC) thin films to silicon substrates. DLC films were deposited on silicon with and without application of an initial high energy carbon ion bombardment phase that formed a broad Si–C interface of gradually changing Si:C composition. The interface depth profile was calculated using the TRIDYN simulation program, revealing a gradient of carbon concentration including a region with the stoichiometry of silicon carbide. DLC films on silicon, with and without interface tailoring, were characterized using Raman spectroscopy, scanning electron microscopy, atomic force microscopy and scratch tests. The Raman spectroscopy results indicated sp3 -type carbon bonding content of up to 80%. Formation of a broadened Si:C interface as formed here significantly enhances the adhesion of DLC films to the underlying silicon substrate.

We have explored the effects of atmospheric environment on Kelvin force microscopy (KFM) measurements of potential difference between different regions of test polycrystalline diamond surfaces. The diamond films were deposited by microwave plasma-assisted chemical vapor deposition, which naturally produces hydrogen terminations on the surface of the films formed. Selected regions were patterned by electron-beam lithography and chemical terminations of oxygen or fluorine were created by exposure to an oxygen or fluorine plasma source. For KFM imaging, the samples were mounted in a hood with a constant flow of helium gas. Successive images were taken over a 5-h period showing the effect of the environment on KFM imaging. We conclude that the helium flow removes water molecules adsorbed on the surface of the samples, resulting in differences in surface potential between adjacent regions. The degree of water removal is different for surfaces with different terminations. The results highlight the importance of taking into account the atmospheric environment when carrying out KFM analysis. © 2012 Wiley Periodicals, Inc.

WOS: 000301521200008, Biodegradable polymers are widely used in biomedical and tissue engineering applications due to their biocompatibility and hydrolysis properties in the body. However, their low surface energy and lack of functional groups to interact with the cellular environment have limited their applications for in vivo studies. Ion beam modification is a convenient method for improving the surface properties of polymeric materials for functional biomedical applications. In the work described here, vacuum arc metal ion implantation was used to modify the composition of the near-surface region of three kinds of polymers-poly(L-lactide), poly(D, L-lactide-co-glycolide), and poly(L-lactide/caprolactone)-chosen as representative of biodegradable polymers. X-ray photoelectron spectroscopy analysis was used to characterize the chemical effects of these polymers after implantation with C and with Au, and the results were compared with untreated control samples. We find that oxidation behavior is brought about for certain implantation fluences, resulting in improved surface hydrophilicity.

The authors present here a summary of their investigations of ultrathin films formed by gold nanoclusters embedded in polymethylmethacrylate polymer. The clusters are formed from the self-organization of subplantated gold ions in the polymer. The source of the low energy ion stream used for the subplantation is a unidirectionally drifting gold plasma created by a magnetically filtered vacuum arc plasma gun. The material properties change according to subplantation dose, including nanocluster sizes and agglomeration state and, consequently also the material electrical behavior and optical activity. They have investigated the composite experimentally and by computer simulation in order to better understand the self-organization and the properties of the material. They present here the results of conductivity measurements and percolation behavior, dynamic TRIM simulations, surface plasmon resonance activity, transmission electron microscopy, small angle x-ray scattering, atomic force microscopy, and scanning...

In this work PMMA was deposited on glass substrate, nanolithographed using Atomic Force Microscopy (AFM) and doped with gold using very low energy ion implantation. Samples with different geometries were prepared in order to identify anisotropic resistivity due to an anisotropic surface morphology. One of the samples was fabricated with parallel lines along the substrate length and the second one with parallel lines perpendicular to it. The PMMA with gold implanted presented resistivities in the range 7.7 x 10-8 Ω.m to 0.23 Ω.m. For any PMMA surface morphology the resistivity decreased when the gold dose increased. The anisotropic factor for both morphologies described above presented a prominent peak for a dose of 1.15 x 1016 atoms/cm2. Finally, a new sample of PMMA with gold implanted dose of 1.15 x 1016 atoms/cm2 was prepared and an I-V curve was obtained, showing clearly that the material is a semiconductor.

Low-energy ion beam biotechnology has seen rapid development worldwide in recent years. This is an important expansion of studies on ion beam modification of solid materials, vastly different from and more complex than the latter. Among other novelties, we have focused our interest on ion beam bombardment effects on plant and bacterial cell envelopes and tried to understand mechanisms involved in ion beam-induced gene transfer. Through a comprehensive investigation, we have discovered ion beam-induced formation of nanocrater-like structures in the cell envelope, a general phenomenon of ion beam bombardment of cells; these structures may act as pathways for exogenous macromolecule transfer. We have also quantitatively obtained abnormally great penetration depth and sputtering of ions in the cell envelope. All these results are significantly advantageous for ion beam processing of biological cells.

We review some novel developments of the electrostatic plasma lens and some new plasma devices based on the plasma-optical idea of magnetic insulation of electrons and equipotentialization along magnetic field lines. The plasma lens configuration of crossed electric and magnetic fields provides an attractive and simple method in establishing a stable plasma discharge at low pressure and has been used to develop some cost-effective low-maintenance plasma devices for ion cleaning, surface activation, and polishing of substrates prior to film deposition. Recent embodiments of these devices use permanent magnets and possess considerable flexibility with respect to spatial configuration.

A quantum mechanical approach is developed to calculate the surface-induced electrical conductivities of very thin metallic films with isotropic and anisotropic surfaces. Two particular cases are analyzed with this formalism: (1) films with isotropic surfaces and (2) films with anisotropic surfaces which have different morphological properties along two orthogonal directions. It is shown that, depending on the differences between these morphological properties, the surface-induced resistivities can be different along these directions. In order to investigate the validity of these predictions we have fabricated Pt films, with thickness in the 0.90 ≤ d ≤ 11.10 nm range, with very different morphological properties along two orthogonal directions. Measuring the electrical resistivities of these films, we have found different resistivities along these directions. We show that this anisotropic resistivity can be well explained by our theoretical approach.

We describe a concept for spacecraft propulsion by means of an energetic ion beam, with the ion source fixed at the spacecraft starting point (e.g., a lunar-based ion beam generator) and not onboard the vessel. This approach avoids the substantial mass penalty associated with the onboard ion source and power supply hardware, and vastly more energetic ion beam systems can be entertained. We estimate the ion beam parameters required for various scenarios, and consider some of the constraints limiting the concept. We find that the "ion beam sail' approach can be viable and attractive for journey distances not too great, for example within the Earth-Moon system, and could potentially provide support for journeys to the inner planets.

A specialized bioengineering ion beam line has recently been completed at Chiang Mai University to meet rapidly growing needs of research and application development in low-energy ion beam biotechnology. This beam line possesses special features: vertical main beam line, low-energy (30 keV) ion beams, double swerve of the beam, a fast pumped target chamber, and an in-situ atomic force microscope (AFM) system chamber. The whole beam line is situated in a bioclean environment, occupying two stories. The quality of the ion beam has been studied. It has proved that this beam line has significantly contributed to our research work on low-energy ion beam biotechnology.

A program in ion beam bioengineering has been established at Chiang Mai University (CMU), Thailand, and ion beam induced transfer of plasmid DNA molecules into bacterial cells (Escherichia coli) has been demonstrated. However, a good understanding of the fundamental physical processes involved is lacking. In parallel work, onion skin cells have been bombarded with Ar+ ions at energy 25 keV and fluence1–2 × 1015 ions/cm2, revealing the formation of microcrater-like structures on the cell wall that could serve as channels for the transfer of large macromolecules into the cell interior. An in-situ atomic force microscope (AFM) system has been designed and installed in the CMU bio-implantation facility as a tool for the observation of these microcraters during ion beam bombardment. Here we describe some of the features of the in-situ AFM and outline some of the related work.

Platinum thin films with thickness in the range of 0.4–12nm were formed by filtered vacuum arc plasma deposition on a substrate with anisotropic roughness. The electrical resistivity was measured in directions parallel and perpendicular to the surface modulation as a function of film thickness, and the resistivity was found to be anisotropic with the degree of anisotropy increasing with decreasing film thickness. The very small thickness of the films calls for a quantum model for film resistivity, and it is shown that the measured resistivity can be interpreted as due to quantum electron scattering by the thin film anisotropic surface roughness.

We report electrical resistivity measurements of platinum and gold thin films over a range of film thickness d(1.3 ≤ d ≤ 11.7 nm ), together with associated measurements of the film morphological and crystallographic grain size. The resistivity results are compared to predictions of the Fuchs–Sondheimer and the Mayadas–Shatzkes models, based on the electron mean free path and crystallographic grain size, and the agreement is not satisfactory. We describe an alternative model based on elastic electron scattering with morphological granularity (grain structure as measured on the film surface) and film surface roughness, and good agreement is obtained with the experimental results. This suggests that electron scattering by morphological granularity and surface roughness plays an important role in determining the electrical resistivity of thin metal films.

Made available in DSpace on 2018-12-11T16:41:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-06-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Chinese Hamster Ovary (CHO) cell cultures were grown on surfaces lithographed with periodic 3D hexagonal microcavity array morphology. The range of microcavity size (inscribed circle diameter) was from 12 μm to 560 μm. CHO cells were grown also on flat surfaces. The characterization was performed with respect to cell growth density (number of nuclei per unit area) by fluorescence optical microscopy and evaluated by correlation function analysis. We found that optimum microcavity radius was 80 μm, concerning to the maximum cell growth density, being even greater than the growth density on a flat (unstructured) substrate of the same material. This finding can be important for optimization of biotechnological processes and devices. Institute of Physics University of São Paulo, C.P. 66318 Pharmacy School UFOP Federal University of Ouro Preto Botucatu Medical School UNESP São Paulo State University Lawrence Berkeley National Laboratory, 1 Cyclotron Road Botucatu Medical School UNESP São Paulo State University CNPq: CNPq-157021/2011-4

The formation of a new phase of composition Mg 54 Al 28 Ag 18 was observed as a result of plasma immersion ion implantation of Ag into the compound Mg 17 Al 12 . The new structure was characterized using a micro-beam diffraction technique. It was found that the implantation-induced phase transition occurs when the retained dose of the implanted ions is within the range of about 10 15 –10 16 ions/cm 2 . The implanted system has been studied theoretically by means of density-functional electronic structure calculations and a new ab initio approach has been developed to evaluate the specific concentrations of the implanted ions that might cause the phase transition effect in the implanted matrix. The theoretically estimated values of concentrations are in good agreement with experimental observations.

Ion beam bombardment of biological material has been recently applied for gene transfer in both plant and bacterial cells. A consistent physical mechanism for this significant result has not yet been developed. A fundamental question about the mechanism is the possible formation of pathways due to ion bombardment that are responsible for the gene transfer. We have carried out investigations of the effects of low-energy bombardment by both gaseous and metallic ion species of onion skin cells on their surface microstructure. Our experimental results reveal evidence demonstrating that the formation of micro-crater-like structures on the plant cell envelope surface is a general phenomenon consequent to ion bombardment, no matter what ion species, under certain ion beam conditions. The micro-craters are about 0.1–1 μm in size (diameter) and a few tens of nanometers in depth. The micro-crater formation process seems to be unrelated to the chemical composition of and rapid water evaporation from the cell envelope, but is associated with the special microstructure of the cell wall.

We describe the results of experimental investigations of factors restricting the maximum compression of multi-aperture heavy-ion beams focused by a high-current electrostatic plasma lens. We show that, under optimal conditions of the lens operation for which all negative factors are removed or suppressed, the compression of the ion beam is determined only by its initial emittance.

The vacuum arc ion source has evolved over the past 20 years into a standard laboratory tool for the production of high current beams of metal ions, and is now used in a number of different embodiments at many laboratories around the world. The primary application of this kind of source has evolved to be ion implantation for material surface modification. Another important use is for injection of high current beams of heavy metal ions into the front ends of particle accelerators, and much excellent work has been carried out in recent years in optimizing the source for reliable accelerator application. The source also provides a valuable tool for the investigation of the fundamental plasma physics of vacuum arc plasma discharges. As the use of the source has grown and diversified, at the same time, the ion source performance and operational characteristics have been improved in a variety of different ways also. Here we review the growth and status of vacuum arc ion sources around the world and summarize some of the applications for which the sources have been used.

We have fabricated diamond microstructures using silicon molds into which microcrystalline diamond was deposited by plasma assisted chemical vapor deposition. Prior to diamond deposition the silicon molds were seeded with the diamond powder of two different grain sizes, 14 and 1μm. Scanning electron microscopy and atomic force microscopy were used to view and characterize the resultant diamond microstructures. Analysis of the diamond replicas indicates better reproduction fidelity for the 14μm diamond powder, and a surface roughness of 20 nm.

Mechanisms responsible for current oscillations at the ion branch of the probe characteristic are investigated experimentally and theoretically. A comparison between experiment and theory shows that the oscillations in a hollow-cathode discharge in a longitudinal magnetic field are most likely related to the onset of helical instability.

The interaction between ion beam and biological cells has been studied to apply ionbeam- induced mutation to breeding of crops and gene transfer in cells. Formation of micro-craters has been observed after ion bombardment of plant cells and they are suspected to act as pathways for exogenous macromolecule transfer in the cells. A technique of in-situ atomic force microscopy (AFM) in the ion beam line is being developed to observe ion bombardment effects on cell surface morphology during ion bombardment. A commercial AFM is designed to place inside the target chamber of the bioengineering ion beam line at Chiang Mai University. In order to allow the ion beam to properly bombard the sample without the risk of damaging the scanning tip and affecting normal operation of AFM, geometrical factors have been calculated for tilting the AFM with 35 degree from the normal. In order to avoid vibrations from external sources, mechanical designs have been done for a vibration isolation system. Construction and installation of the in-situ AFM facility to the beam line have been completed and are reported in details.

Vacuum arc plasma can be formed using particularly uncomplicated hardware, providing a means for laboratory scale formation of dense and highly-ionized metal plasma. The simplicity and versatility of the approach has led to its widespread use in recent times for both fundamental and technological applications. When embodied in a plasma gun configuration, the source can provide a valuable tool for plasma deposition of metal and metal-containing thin films, including in plasma immersion configurations. When embodied in an ion source configuration, high current beams of metal ions can be formed, and such beams have found good use for ion implantation and particle accelerator injection. Here we briefly review vacuum arc plasma guns and ion sources, outlining some of the hardware embodiments that have been developed at Berkeley and used for various materials modification applications.

A vacuum arc ion source based metal ion implantation facility is built and in operation at TUBITAK (The Scientific and Technical Research Council of Turkey), Izmir, Turkey and a surface modification research and development program is being carried out here. The system is similar to the one in Lawrence Berkeley Laboratory, which was first built and developed by Brown et al. The broad-beam ion source can be repetitively pulsed at rates up to ∼50 pulses per second and the extracted ion beam current can be up to ∼1 A peak or ∼10 mA time averaged. The ion source extraction voltage can be increased up to 110 kV. Additionally, mixed metal and gas ion beams were generated by a magnetic field, which was obtained through a magnet coil located in front of anode plate and by adding gas in the discharge region. This modified system was used to form buried layers of mixed metal–gas species such as Ti+N (on 316 SS and Ti alloy samples) and Zr and W (316 SS and Ti alloy samples, respectively) of which their hardness, coefficient of friction and wear volumes were measured and their RBS results were obtained. The anodic electrochemical tests showed that the corrosion resistance of Ti implanted 304 SS samples was increased with the dose. Micro structures of Ti implanted surfaces of 304 SS samples were examined with SEM before and after the corrosion tests and the results showed that the pittings were formed mostly in the areas where implanted Ti concentration was less. Recently, the system is equipped with TOF for measuring the charge state distribution of ions. R&D work is planned for the purpose of forming tribologically enhanced materials for industrial applications by using ion implantation, PVD coating, plasma nitriding and their combinations. The results showed that the hardness and performance of ion implanted (with various metals and N) PVD coated cutting inserts increased remarkably. The use of ion implantation techniques in modifying the properties of textile and other materials and optimising the performance of textile and other industrial machine parts and tools is also being investigated and some of the results are presented in this work.

We have developed a code STOPPO which can be used to modify the more-widely used ion implantation codes to more accurately predict the mean nuclear and electronic stopping power, preferential sputtering and range of heavy ions in monatomic target materials. In our simulations an effective atomic number and effective atomic mass are introduced into conveniently available analytical stopping cross-sections and a better fitting function for preferential sputtering yield is carefully evaluated for each ion implantation. The accuracy of the code confirmed experimentally by comparison with measured Rutherford backscattering spectrometry (RBS) concentration profiles for 130 keV Zr ions implanted into Be to fluences of 1 × 1017, 2 × 1017 and 4 × 1017 ions/cm2. We find a steady increase in the mean nuclear and electronic stopping powers of the target; the increase in nuclear stopping power is much greater than the increase in electronic stopping power.

Ion bombardment of living cellular material is a novel subfield of ion beam surface modification that is receiving growing attention from the ion beam and biological communities. Although it has been demonstrated that the technique is sound, in that an adequate fraction of the living cells can survive both the vacuum environment and energetic ion bombardment, there remains much uncertainty about the process details. Here we report on our observations of onion skin cells that were subjected to ion implantation, and propose some possible physical models that tend to support the experimental results. The ion beams used were metallic (Mg, Ti, Fe, Ni, Cu), mean ion energy was typically 30 keV, and the implantation fluence was in the range 10 14 –10 16 ions/cm 2 . The cells were viewed using Atomic Force Microscopy, revealing the formation of microcrater-like structures due to ion bombardment. The implantation depth profile was measured with Rutherford backscattering spectrometry and compared to the results of the TRIM, T-DYN and PROFILE computer codes.

Low-energy ion beam bombardment of biological materials for genetic modification purposes has experienced rapid growth in the last decade, particularly for the direct DNA transfer into living organisms including both plants and bacteria. Attempts have been made to understand the mechanisms involved in ion-bombardment-induced direct gene transfer into biological cells. Here we summarize the present status of the application of low-energy ions for genetic modification of living sample materials.

Formation of intermetallic compounds within the Mg matrix as a result of implantation of Ag by plasma immersion ion implantation technology was investigated. Transmission electron-microscopy studies of the implanted samples revealed the appearance of nanoparticles of binary phase Mg-Ag. A model based on the classical mechanisms of propagation of accelerated ions through the metal matrix was suggested for the explanation of the experimental observations. Ab initio calculations of the electronic sub-systems proved to be helpful in providing theoretical prediction of the structural changes, which may be induced in the implanted system.

A simple hollow cathode “cold wall” dc gaseous ion source with magnetic field was investigated. Parameters of the plasma and ion beam were measured as a function of magnetic field. The extracted ion current shows a nonmonotonic behavior as function of magnetic field strength but the magnetic field distribution had only little influence on the current-voltage characteristics and on all other derived plasma and beam parameters. Analysis of our experimental conditions indicates that the observed nonmonotonic behavior is associated with a change in the ratio of electron Larmor radius to cathode sheath thickness.

Summary form only given, as follows. There is a need for an alternative to traditional vacuum ion optic systems for the case of high-current beams, particularly for moderate energy (10-100 keV) heavy ion beam manipulation, when space charge forces are large. The axially-symmetric electrostatic plasma lens provides an attractive and unique alternative. Use of a plasma lens in this way was successful demonstrated by a series of experiments. Here we briefly review the plasma lens fundamentals, peculiarities of focusing heavy ion beams, and summarize some recent developments (experiments, computer simulations, theory). We show that there is a very narrow range of low magnetic field for which the optical properties of the lens improve markedly. This opens up possibilities for creation of a new-generation compact lens based on permanent magnets. The first experimental results obtained at Kiev and Berkeley about the operation of a permanent magnet plasma lens for manipulating wide aperture high-current heavy ion beams will be presented and summarized.

The authors describe a method for the measurement of secondary electron emission coefficients and demonstrate the use of this approach for the measurement of secondary electron yields for titanium, copper, and carbon ions incident upon an aluminum target. The method is time-resolved in that a series of measurements can be obtained within a single ion beam pulse of several hundred microseconds duration. The metal ion beams were produced with a vacuum arc ion source, and the ratio of secondary electron current to incident ion current was determined using a Faraday cup with fast control of the electron suppressor voltage. The method is relatively simple and readily applied and is suitable for measurements over a wide parameter range. The secondary yields obtained in the present work are of relevance to the measurement of ion current and implantation dose in plasma immersion ion implantation.

This study investigates the depth of ion penetration in plant cell wall material. Based on the biological structure of the plant cell wall, a physical model is proposed which assumes that the wall is composed of randomly orientated layers of cylindrical microfibrils made from cellulose molecules of C6H12O6. With this model, we have determined numerical factors for ion implantation in the plant cell wall to correct values calculated from conventional ion implantation programs. Using these correction factors, it is possible to apply common ion implantation programs to estimate the ion penetration depth in the cell for bioengineering purposes. These estimates are compared with measured data from experiments and good agreement is achieved.

We have fabricated platinum thin films by metal plasma ion deposition on silicon substrates. The roughness of these films has been measured by a scanning tunneling microscope (STM) and we have determined the growth dynamics critical exponents.

A cathodic arc plasma source equipped with a curved magnetic duct to filter macro-particles was used to study plasma transport through the duct. The optimal duct bias, at which the magnetic duct produces the maximum plasma output, for titanium cathodic arc plasma at 50, 100 and 150 A arc current was determined and the parametric effects of the arc current and guiding magnetic field on the optimal duct bias were investigated. The optimal bias decreased as the guiding magnetic field increased from 100 to 400 G and was almost independent of the guiding magnetic field when it was between 400 and 600 G, the upper limit for our equipment. The optimal duct bias at 400 G guiding magnetic field decreased with increasing arc current. Our results indicate that the optimal duct bias is related not only to the structure of the plasma source, but is also influenced by many other factors including cathode material and other plasma properties.

Recent developments in the field of ion beam bioengineering, for example our own work demonstrating ion beam-induced transfer of exogenous macromolecules into the interior cell region, have underscored the need for a better understanding of the effects of ion bombardment on the cell wall material. We describe here, our investigations of ion beam sputtering of plant cell wall material and ion beam-induced damage to the cell wall. The presently available ion implantation simulation programs are not adequate, and experimental results are not available, either. We have indirectly estimated the surface sputtering yield of plant cell wall composed of C6H12O6-compound by remodeling the cell wall material so as to use partial mass densities and surface binding energies in the available ion implantation programs. For bombardment with a 30-keV Ar-ion beam, the sputtering yield from the cell wall is estimated to be approximately 10 atoms/ion, which is somewhat greater than the value predicted by direct program simulation, but in good agreement with experimental results. We have also performed electron microscopy on the ion-bombarded cell walls. The micrographs show novel microcrater-like structures on the cell wall subsequent to ion bombardment, which could be the ion beam-generated pathways for exogenous macromolecule transfer.

The goal of the work described here was to study ion beam interactions with bacteria and thus develop an understanding of the mechanisms involved in ion bombardment-induced direct gene transfer into bacterial cells. Ar ion beams at an energy of 26 keV and fluences ranging from 5×10 14 to 4×10 15 ions/cm 2 were used to bombard bacterial cells of Escherichia coli strain DH5α. The bacteria were able to survive the low-temperature and low-pressure treatment conditions for at least a few hours. The ion bombardment created novel crater-like structures on the surface of the bacterial cell envelope, as observed by scanning electron microscopy. Four variously sized DNA plasmids carrying the ampicillin resistance gene were transferred and expressed in E. coli cells bombarded with ion fluences of 1×10 15 and 2×10 15 ions/cm 2 . The dependence of the DNA transfer on the plasmid DNA size, ion fluence and incubation time all suggests that the ion beam-induced surface crater-like structures provide the pathway for the mechanism that is responsible for the ion beam-induced DNA transfer.

Carbon and titanium plasmas are used to investigate the effects of duct bias on the plasma transport through the magnetic duct of a cathodic-arc plasma source as a function of the magnetic-field strength and arc current so as to determine the optimal duct bias, at which the magnetic duct produces the maximum efficiency for plasma transport. The influence of the guiding magnetic field and arc current on the optimal duct bias is investigated. The optimal duct bias increases with the plasma density for carbon plasma, while the relationship is the opposite for the titanium plasma. The carbon-plasma behavior can be explained by a plasma-diffusion model presented in this paper, since the electron-ion collision frequency /spl nu//sub ei/ is less than the electron-cyclotron frequency /spl nu//sub c,e/. On the other hand, in a titanium plasma, /spl nu//sub ei/ is larger than /spl nu//sub c,e/, so this model is inaccurate. Our result shows that different kinds of plasmas have different transport behavior through the magnetic duct and thus, the duct parameters must be carefully chosen in order to achieve the optimal transport efficiency.

Characteristics of plasmas formed by repetitively-pulsed electrical discharges in sodium chloride and barium chloride saline solutions are reported. Spectroscopic observations in conjunction with an analysis of the voltage and current behavior of the discharge lead to a model in which the liquid is vaporized and ionized to form a plasma containing excited water fragments H* and OH* as well as ions and neutrals from the salt. For typical conditions under which plasma is formed, the plasma density is estimated to be of order 10/sup 12/ cm/sup -3/ and the electron temperature about 4 eV.

We have investigated the electrostatic charging effects of dielectric substrate materials during plasma immersion ion implantation. The results demonstrate that the time-dependent surface potential (negative) may be reduced in magnitude due to the charging effect of the dielectric surface, leading in turn to a reduction in the energy of the incident ions and a broadening of the implanted ion energy spectrum. The charging effect is greater during the plasma immersion bias pulse rise-time, and the electrostatic potential charging may be as large as 75% of the total applied (pulse) potential. This is due to abundant charge movement both of ions and secondary electrons, and has been confirmed by computer simulation. The plasma sheath capacitance has a small influence on the surface potential, via the bias pulse rise-time. Processing parameters, for example voltage, pulse duration, plasma density, and pulse rise-time, have a critical influence on the charging effects. Short pulse duration, high pulse frequency and low plasma density are beneficial from the viewpoint of maximizing the implantation ion energy.

AISI D3 tool steel was ion implanted with zirconium and the improvement in surface tribological properties investigated. The Zr ion implantation was done using a metal vapor vacuum arc (Mevva) broad-beam ion source, with a mean ion energy of 130 keV and at doses of 3.6×10 16 , 5×10 16 and 1×10 17 ions/cm 2 . Wear, friction and hardness of the implanted samples were measured and compared to the performance of unimplanted steel. The wear resistance was increased by about a factor of two, the friction remained about the same or was possibly increased by a small amount and the near-surface hardness was improved by a factor of five or more by the ion implantation. We also investigated the effect on the Zr implantation profile of the multi-component energy distribution of the ion beam.

We report on an experimental study of an ion source based on a Penning discharge with a cold hollow cathode in crossed electric and magnetic fields. The minimum vacuum chamber operating pressure was 3 × 10(-5) Torr for argon and 5 × 10(-5) Torr for hydrogen. The use of a hollow cathode allowed decreasing the discharge operating voltage down to 350 V at a discharge current of ~100 mA. At a discharge current of 100 mA and beam accelerating voltage of 2 kV, the ion current was 2.5 mA for argon and 8 mA for hydrogen, and the ion beam on-axis current density 170 and 450 μA/cm(2), respectively. The current-voltage characteristics of the discharge and the radial ion beam current density distribution were measured. The influence of pressure on the discharge parameters and their time stability was investigated.