A source of gas, vapor, metal, and carbon ions based on a low-pressure hollow-cathode discharge

A compact source of gas, vapor, metal, and carbon ions based on a cold-hollow-cathode reflective discharge has been developed, in which a 6-mm-diameter flat target (Cu, Mo, W, C) is installed on the bottom of the cold cathode insulated from it. The density of the ion flow from cathode plasma reaches 100 mA/cm² at an accelerating voltage of up to 10 kV and a discharge current of 0.2-0.5 A. Vapors produced during ion sputtering of the target are ionized in the cathode and anode cavities. A beam containing ions of the plasma-producing gas and vapor is extracted throug h the channel in the reflector cathode. A fraction of the vapor of the sputtered target, the flow of which is sufficient for growing layers at a rate of ∼0.03 nm/s at a distance of 10 cm from the emission channel under the action of an ion beam, is extracted together with ions. The fraction of metal ions in the extracted beam is 0.05-0.10. The total current of the ion beam is 20-30 mA.     

Characterization of plasma ion source utilizing anode spot with positively biased electrode for stable and high-current ion beam extraction

The operating conditions of a rf plasma ion source utilizing a positively biased electrode have been investigated to develop a stably operating, high-current ion source. Ion beam characteristics such as currents and energies are measured and compared with bias currents by varying the bias voltages on the electrode immersed in the ambient rf plasma. Current-voltage curves of the bias electrode and photographs confirm that a small and dense plasma, so-called anode spot, is formed near an extraction aperture and plays a key role to enhance the performance of the plasma ion source. The ion beam currents from the anode spot are observed to be maximized at the optimum bias voltage near the knee of the characteristic current-voltage curve of the anode spot. Increased potential barrier to obstruct beam extraction is the reason for the reduction of the ion beam current in spite of the increased bias current indicating the density of the anode spot. The optimum bias voltage is measured to be lower at higher operating pressure, which is favorable for stable operation without severe sputtering damage on the electrode. The ion beam current can be further enhanced by increasing the power for the ambient plasma without increasing the bias voltage. In the same manner, noble gases with higher atomic number as a feedstock gas are preferable for extracting higher beam current more stably. Therefore, performance of the plasma ion source with a positively biased electrode can be enhanced by controlling the operating conditions of the anode spot in various manners.     

A source of broad electron beams with a self-heated hollow cathode for plasma nitriding of stainless steel

The principle of operation and characteristics of a broad electron beam source based on the discharge with a self-heated hollow cathode and widened anode part are described. The source is intended for the ion nitriding of metals in the electron beam plasma. The influence of the current density (1–7 mA/cm²) and ion energy (0.1–0.3 keV) on the nitriding rate of the 12X18H10T austenitic stainless steel is studied. It is shown that the maximal nitriding rate is reached by the combining of the minimal bias voltage across the samples (100 V) and maximal ion current density, which ensures the dynamic oxide layer sputtering on the sample surface. The electron source, in which electrons are extracted through a stabilizing grid in the direction normal to the axis of the hollow cathode, ensures the radially divergent electron beam formation with a 700-cm² initial cross section, a current of up to 30 A, and initial electron energy of 0.1–0.5 keV. The source stably operates at nitrogen-argon mixture pressures of up to 3 Pa.     

Novel plasma immersion ion implantation and deposition hardware and technique based on high power pulsed magnetron discharge

A novel plasma immersion ion implantation technique based on high power pulsed magnetron sputtering (HPPMS) discharge that can produce a high density metal plasma is described. The metal plasma is clean and does not suffer from contamination from macroparticles, and the process can be readily scaled up for industrial production. The hardware, working principle, and operation modes are described. A matching circuit is developed to modulate the high-voltage and HPPMS pulses to enable operation under different modes such as simultaneous implantation and deposition, pure implantation, and selective implantation. To demonstrate the efficacy of the system and technique, CrN films with a smooth and dense surface without macroparticles were produced. An excellent adhesion with a critical load of 59.9 N is achieved for the pure implantation mode.     

A high-voltage power supply of the diagnostic neutral beam injector of the Alcator-Cmod tokamak

A diagnostic neutral beam injector for ensuring the active spectroscopic diagnostics of plasma parameters in the Alcator-Cmod tokamak (Massachusetts Institute of Technology (MIT), Boston, United States) is designed and manufactured at the Institute of Nuclear Physics (Novosibirsk). The energy of fast atoms of the diagnostic injector is determined by the output voltage level of the high-voltage power supply and can vary from 20 to 55 keV. The ion source of the diagnostic neutral beam injector generates proton beams with an equivalent current of up to 7 A. The accelerated protons after the neutralization on a gas target produce streams of neutral particles—fast atoms with an equivalent current of up to 4 A. The diagnostic neutral beam injector is capable of producing 100% energy-modulated fast hydrogen atomic beams, and this is ensured by operation of the high-voltage power supply under the corresponding law. The high-voltage power supply is based on modules consisting of high-frequency transformers and diode rectifiers placed in a sealed tank filled with insulating gas SF₆. The output voltage is smoothly regulated from 20 to 55 kV by IGBT inverters with a pulse-width control energizing the primary windings of the step-up high-frequency transformers. The high-voltage power supply allows the multiple-breakdown operation mode of the load with voltage recovering as the specified time passes after the breakdown. The rated power of the high-voltage power supply is 450 kW. A functional diagram and design of the high-voltage power supply are given.     

The effect of gas mixing and biased disc voltage on the preglow transient of electron cyclotron resonance ion source

The effect of gas mixing and biased disc voltage on the preglow of electron cyclotron resonance ion source plasma has been studied with the AECR-U type 14 GHz ion source. It was found that gas mixing has a significant effect on the preglow. The extracted transient beam currents and efficiency of the heavier species increase, while the currents and efficiency of the lighter species decrease when gas mixing is applied. The effect of the biased disc was found to be pronounced in continuous operation mode in comparison to preglow. The data provide information on the time scales of the plasma processes explaining the effects of gas mixing and biased disc. The results also have implications on production of radioactive ion beams in preglow mode for the proposed Beta Beam neutrino factory.     

Surface plasma source with anode layer plasma accelerator

Proposed plasma generation system can be used for high current negative ion beam production and for directed deposition by flux of sputtered neutrals and negative ions. The main mechanism of negative ion formation in surface plasma sources is the secondary emission from low work function surface bombarded by a flux of positive ion or neutrals. The emission of negative ions is enhanced significantly by introducing a small amount of cesium or other substance with low ionization potential. In the proposed source are used positive ions generated by Hall drift plasma accelerator (anode layer plasma accelerator or plasma accelerator with insulated channel, with cylindrical or race track configuration of emission slit). The target-emitter is bombarded by the ion beam accelerated in crossed ExB fields. Negative ions are extracted from the target surface with geometrical focusing and are accelerated by negative voltage applied between emitter and plasma, contacting with the plasma accelerator. Hall drift ion source has a special design with a space for passing of the emitted negative ions and sputtered particles through the positive ion source.     

Alloy liquid metal ion sources and their application in mass separated focused ion beams

For special purposes like writing ion implantation or ion mixing in the micrometer- or sub-micrometer range different ion species are needed. Therefore alloy liquid metal ion sources (LMISs) are used. The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of a FIB column. Different source materials like Au(73)Ge(27), Au(82)Si(18), Au(77)Ge(14)Si(9), Co(36)Nd(64), Er(69)Ni(31), and Er(70)Fe(22)Ni(5)Cr(3) were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass and emitter temperature. The alloy LMISs discussed above have been used in the Rossendorf FIB system IMSA especially for writing implantation to fabricate sub-micrometer pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi(2) micro-structures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell time was used for radiation damage investigations in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume-loss method. Especially this technique was used for the fabrication of various kinds of micro-tools.     

Ion beam sputtering: an improved method of metal coating SEM samples and shadowing CTEM samples

An apparatus to ion beam sputter-coat SEM samples has recently become available. The equipment uses a small saddle-field ion source to sputter deposit metals on to samples. This eliminates the surface artefacts seen at high magnifications on samples coated by diode sputtering. Ion beam sputtering has also been used to shadow samples for CTEM and has been found to result in a grain size of 1.2 nm. This technique isolates the specimens from the high-energy plasma and thus little or no heating of the sample occurs. The removal of the SEM samples from the high-energy plasma and the use of diffusion pump vacuum conditions to prevent contamination are suggested as reasons for the improved coating quality over diode sputtering.     

Production of a highly charged uranium ion beam with RIKEN superconducting electron cyclotron resonance ion source

A highly charged uranium (U) ion beam is produced from the RIKEN superconducting electron cyclotron resonance ion source using 18 and 28 GHz microwaves. The sputtering method is used to produce this U ion beam. The beam intensity is strongly dependent on the rod position and sputtering voltage. We observe that the emittance of U(35+) for 28 GHz microwaves is almost the same as that for 18 GHz microwaves. It seems that the beam intensity of U ions produced using 28 GHz microwaves is higher than that produced using 18 GHz microwaves at the same Radio Frequency (RF) power.     

Investigation of ISIS and Brookhaven National Laboratory ion source electrodes after extended operation

Linac4 accelerator of Centre Europe?en de Recherches Nucle?aires is under construction and a RF-driven H(-) ion source is being developed. The beam current requirement for Linac4 is very challenging: 80 mA must be provided. Cesiated plasma discharge ion sources such as Penning or magnetron sources are also potential candidates. Accelerator ion sources must achieve typical reliability figures of 95% and above. Investigating and understanding the underlying mechanisms involved with source failure or ageing is critical when selecting the ion source technology. Plasma discharge driven surface ion sources rely on molybdenum cathodes. Deformation of the cathode surfaces is visible after extended operation periods. A metallurgical investigation of an ISIS ion source is presented. The origin of the deformation is twofold: Molybdenum sputtering by cesium ions digs few tenths of mm cavities while a growth of molybdenum is observed in the immediate vicinity. The molybdenum growth under hydrogen atmosphere is hard and loosely bound to the bulk. It is, therefore, likely to peel off and be transported within the plasma volume. The observation of the cathode, anode, and extraction electrodes of the magnetron source operated at BNL for two years are presented. A beam simulation of H(-), electrons, and Cs(-) ions was performed with the IBSimu code package to qualitatively explain the observations. This paper describes the operation conditions of the ion sources and discusses the metallurgical analysis and beam simulation results.     

A Universal Ion Source

A model of an ion source based on a glow discharge in crossed fields for obtaining a drop-free stationary beam with a controlled Ti-to-N component ratio is described. A two-stage process of producing a gas–metal plasma takes place in a two-chamber device. The external ring-shaped chamber is the plasma source of a radially converging gas ion beam entering the internal chamber, in which metal vapors are produced by means of controllable sputtering of an isolated target electrode, and a gas–metal plasma is obtained for extraction of a mixed ion beam. A ion beam with an energy of 40 keV and a current of 6 mA at a Ti-to-N ratio of 0.8 is extrtacted. The model is designed for studying processes related to the obtainment of nonseparated beams of mixed composition and their use in technology.     

Fast ion beam-plasma interaction system

A device has been constructed for the study of the interaction between a fast ion beam and a target plasma of separately controllable parameters. The beam of either hydrogen or helium ions has an energy of 1-4 keV and a total current of 0.5-2 A. The beam energy and beam current can be varied separately. The ion source plasma is created by a pulsed (0.2-10-ms pulse length) discharge in neutral gas at up to 3 x 10(-3) Torr. The neutrals are pulsed into the source chamber, allowing the neutral pressure in the target region to remain less than 5 x 10(-5) Torr at a 2-Hz repetition rate. The creation of the source plasma can be described by a simple set of equations which predict optimum source design parameters. The target plasma is also produced by a pulsed discharge. Between the target and source chambers the beam is neutralized by electrons drawn from a set of hot filaments. Currently under study is an unstable wave in a field-free plasma excited when the beam velocity is nearly equal to the target electron thermal velocity (v(beam) approximately 3.5 x 10(7) cm/s, Te = 0.5 eV).     

Development of a radio-frequency ion beam source for fast-ion studies on the large plasma device

A helium ion beam source (23 kV/2.0 A) has been constructed for studying fast-ion physics in the cylindrical magnetized plasma of the large plasma device (LAPD). An inductive RF source produces a 10(19) m(-3) density plasma in a ceramic dome. A multi-aperture, rectangular (8 cm × 8 cm) three-grid system extracts the ion beam from the RF plasma. The ion beam is injected at a variety of pitch angles with Alfve?nic speeds in the LAPD. The beam current is intense enough to excite magnetic perturbations in the ambient plasma. Measurements of the ion beam profile were made to achieve an optimum beam performance and a reliable source operation was demonstrated on the LAPD.     

Development of a low-energy and high-current pulsed neutral beam injector with a washer-gun plasma source for high-beta plasma experiments

We have developed a novel and economical neutral-beam injection system by employing a washer-gun plasma source. It provides a low-cost and maintenance-free ion beam, thus eliminating the need for the filaments and water-cooling systems employed conventionally. In our primary experiments, the washer gun produced a source plasma with an electron temperature of approximately 5 eV and an electron density of 5 × 10(17) m(-3), i.e., conditions suitable for ion-beam extraction. The dependence of the extracted beam current on the acceleration voltage is consistent with space-charge current limitation, because the observed current density is almost proportional to the 3∕2 power of the acceleration voltage below approximately 8 kV. By optimizing plasma formation, we successfully achieved beam extraction of up to 40 A at 15 kV and a pulse length in excess of 0.25 ms. Its low-voltage and high-current pulsed-beam properties enable us to apply this high-power neutral beam injection into a high-beta compact torus plasma characterized by a low magnetic field.     

Pulsed Nano-Electrospray Ionization: Characterization of Temporal Response and Implementation with a Flared Inlet Capillary

The temporal response of pulsed nano-electrospray ionization mass spectrometry (nano-ESI-MS) was studied and its influence on ion formation and detection was characterized. Rise and decay times for the mass resolved ion current were determined to be 20 ± 3 msec and 61 ± 5 msec, respectively, which led to a maximum pulse rate of 12 Hz. Pulsed nano-ESI operation was demonstrated from a multi-sprayer source controlled by a high voltage pulsing circuit constructed in-house. The desired source mode of operation (e.g. pulsing or continuous) can be realized solely by controlling the voltage applied to each sprayer.     

A high voltage pulse power supply for metal plasma immersion ion implantation and deposition

We describe the design and implementation of a high voltage pulse power supply (pulser) that supports the operation of a repetitively pulsed filtered vacuum arc plasma deposition facility in plasma immersion ion implantation and deposition (Mepiiid) mode. Negative pulses (micropulses) of up to 20 kV in magnitude and 20 A peak current are provided in gated pulse packets (macropulses) over a broad range of possible pulse width and duty cycle. Application of the system consisting of filtered vacuum arc and high voltage pulser is demonstrated by forming diamond-like carbon (DLC) thin films with and without substrate bias provided by the pulser. Significantly enhanced film∕substrate adhesion is observed when the pulser is used to induce interface mixing between the DLC film and the underlying Si substrate.     

Ion beam-sputtered and magnetron-sputtered thin films on cytoskeletons: A high-resolution tem study

A comparison of ion beam-sputtered and magnetron-sputtered thin platinum (Pt) and tungsten (W) films was made. Cytoskeletons from detergent extracted glioma cells grown on gold grids were coated with Pt or W at thicknesses of 1, 1.5, and 2.5 nm. Transmission electron micrographs were taken at high magnification and the granularity of the metal films was evaluated both on the Formvar film and the filaments of the cytoskeleton. In order to make a comparison between the two deposition methods, the metal deposition rate must be equal when corresponding thicknesses are made. Since ion beam sputtering generally is a slower process than magnetron sputtering, an increased target to specimen distance was necessary with the latter technique. This resulted in a coarser granularity of the W films as compared with the ion beam sputtered. The Pt, however, showed no marked difference between the two techniques at equal deposition rates. The study also demonstrated that varying the deposition rate caused differences in the granularity of the magnetron-sputtered Pt and W films, even if the voltage of the target was kept constant. Decreasing the target to specimen distance which increased the deposition rate resulted in a finer granularity of both the Pt and the W films. At the highest deposition rate the granularity of both the Pt and W films was comparable with the granularity of the ion beam-sputtered films.     

SURFACE INTEGRITY AND REMOVAL RATE OF SILICON SPUTTERED WITH FOCUSED ION BEAM

This paper investigates the micromachinability of (100) silicon by focused gallium ion beam sputtering at normal incident angle. Effect of the beam parameters (dose, aperture and accelerating voltage) and the beam scanning parameters (pixel spacing, dwell time, retracing time and scanning type) on the surface integrity and material removal rate were studied. Statistical models derived from factorial experiments were used to predict the sputtered depths and material removal rates of silicon. The sputtering depth increased with higher accelerating voltage, more ion dose, shorter pixel spacing, and longer dwell time. Similar trends were found for predicting the material removal rate. A surface roughness in the range 2-5 nm was achieved, and was found to be linearly dependent on the pixel spacing.