Cesium Sputter Ion Source Research Articles

Extraction of SiN− ions from source of negative ions by cesium sputtering

We investigated the production of SiN− ions from a source of negative ions by cesium sputtering (SNICS) ion source. Currents up to 17μA were obtained by optimizing the operation parameters such as the cathode voltage, ionizer current, temperature of the cesium reservoir and fine turning the focussing system. Damage and damage annealing of low energy SiN− implanted in silicon are also studied and reported in this presentation.

Iron acceleration with a simple iron gas-covered cathode in a tandem accelerator

Using a simple iron gas-covered cathode with hydrogen in cesium sputter ion source, we obtained 10 μA positive iron ion currents of Fe 3+ and Fe 2+ in tandem accelerator operation.

Cluster-ion implantation: An approach to fabricate ultrashallow junctions in silicon

Cluster-ion implantation in combination with two-step annealing is effective in making ultrashallow junctions. We have demonstrated the use of heavy atom–boron cluster ions to effectively reduce the boron energy for shallow-junction formation. SiB, SiB2, and GeB cluster ions have been used to produce 2 keV boron for low-energy ion implantation. We have generated the SiB, SiB2, and GeB cluster ions using the source of negative ions by cesium sputtering ion source. Shallow junctions have been made by SiB, SiB2, and GeB cluster ions implanted into Si substrates at 1×1015/cm2 with energies at 6.88, 8.82, and 15 keV, respectively. We also discussed the benefit of a 550 °C preannealing before a 1000 °C, 10 s rapid thermal annealing.

Operation of the Relativistic Heavy Ion Collider Au− ion source

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is beginning its second year of operation. A cesium sputter ion source injecting into a tandem Van de Graaff provides the gold ions for RHIC. The ion source is operated in the pulsed beam mode and produces a 500-μs-long pulse of Au− with a peak intensity of 290 μA at the entrance of the tandem. After acceleration in the tandem and post-stripping, this results in a beam of Au+32 with an intensity of 80 μA and an energy of 182 MeV. Over the last several years, a series of improvements have been made to increase the intensity of the pulsed beam from the ion source. Details of the source performance and improvements will be presented. In addition, an effort is under way to provide other beam species for RHIC collisions.

Negative cesium sputter ion source for generating cluster primary ion beams for secondary ion mass spectrometry analysis

A cesium sputter ion source has been used to generate novel cluster and monoatomic primary ion beams for secondary ion mass spectrometry (SIMS). The source produces a variety of primary ion beam species with sufficient flux to be usable for both organic surface analysis and semiconductor depth profiling. The primary focus of this work is on the generation and use of carbon and carbon-containing cluster primary ion beams for SIMS. Stability of the sputter ion source is a few percent over 20 min, has useful lifetimes of weeks to months, and produces total primary ion beam currents for C2− ions, measured at the sample, of >1 μA at an extraction voltage of 10 kV. Larger cluster ions (Cx−x=4–10 and CsCx−x=2–8) are produced with tens of nA of beam current. Due to the divergence of the source, focused beam operation gives current densities under optimal conditions of 0.4–0.5 mA/cm2. Cluster bombardment studies of organic films using carbon clusters Cx−x=1–10 indicate that large enhancements (up to a factor of 800) in the secondary ion yield for characteristic molecular ions from organic samples can be obtained with the larger cluster ions. The signal enhancement can also be utilized in microfocus operation of the source for organic secondary ion imaging studies. For favorable organic samples, cluster bombardment with Cx−, x>6 shows little evidence of degradation of the sample from the accumulation of primary beam-induced damage. This effect can be potentially utilized for depth profiling of organic thin films and for further enhancements in sensitivity for organic SIMS analysis. Depth profiling of low energy As implants in silicon with the CsC6− primary ion demonstrates that as much as a factor of 6 improvement in apparent depth resolution can be obtained compared to profiles obtained under standard conditions using Cs+ bombardment. The flexibility of the source to produce monoatomic primary ion beams from virtually any target material is also being exploited to prepare low energy in situ ion implant standards for quantitative SIMS analysis.

Low-energy biomedical GC–AMS system for 14C and 3H detection

The use of accelerator mass spectrometry (AMS) in biomedical research will require the development of cost-effective, laboratory-sized AMS systems that can be used in conjunction with gas and liquid phase separation techniques. This paper describes a prototype GC–AMS system designed for the detection of 14C and 3H in organic samples. The entire AMS system including the injector, ion source, tandem accelerator, and high-energy analyzer is approximately 3.5 m wide, 1.5 m high and 1 m deep. Also described are methods for converting gas chromatograph (GC) effluent to gaseous CO 2 for 14C-labeled compounds. A gas-fed cesium (Cs) sputter ion source converts the CO 2 into C − for injection into the AMS accelerator, allowing on-line analysis of 14C-labeled biological samples with AMS.

Production of Ce negative ions in a Cs sputter ion source

We have developed a new technique for stable production of lanthanide negative ions in a cesium sputter ion source without damage to the ionizer. Lanthanide elements sticking to a cesium ionizer deteriorate an ionization efficiency of the ionizer because of their characteristics such as low vapor pressures and low work functions. We have resolved the problem to make a sputter cathode that has a predrilled double layer structure. Cerium oxide powder pressed in the cathode pellet was covered by tungsten and drilled. Using this cathode, we achieved smaller solid angle emission of the sputtered lanthanide elements from the bottom of the drilled hole, and most of them could pass through the center hole of the ionizer. As a result, damage to the ionizer decreased, and stable operation of the ion source was successfully achieved with a cerium oxide beam current of 600 nA for 24 h continuous operation. The technique was applied for production of other rare earth ions.

The Leibniz-Labor AMS facility at the Christian-Albrechts University, Kiel, Germany

The AMS facility of the Leibniz-Labor für Altersbestimmung und Isotopenforschung of the Christian-Albrechts Universität is based on a 3 MV Tandetron from High Voltage Engineering Europa (HVEE) with a single cesium sputter ion source and a separator/recombinator for simultaneous injecton of the three isotopic carbon beams. The AMS system is similar to those at the Woods Hole Oceanographic Institution, USA, and the University of Groningen, The Netherland, but it has some new features based on experience at these two facilities. These include improved vacuum seals, beam diagnostics, X-ray and background suppression as well as a more reliable system control through a PLC-unit with a serial line to the main system computer. The open system design of the beam optics allows significant horizontal and vertical movement of the ion beams without loss to the walls of the system. This leads to plateaus in the response of the isotope beams and ratios to changing values of various ion optical elements. Combined with highly stable power supplies, this gives reproducible measurements. The acceptance tests, e.g., showed that Poisson counting statistics at 0.15% and 0.22% respectively, determined the statistical uncertainty in the 14C12C ratios measured for the individual samples of two test series. Strong discrimination of unwanted ions results in low background count rates in the detector, equivalent to an apparent age of 75000 years at present, in spite of the open architecture. Routine measurements since late January 1996 (to late May 1996) have dated 127 unknown samples, mostly foraminifera. The prototype of the carbonate to CO2 conversion system and the graphite system used for the measurements are also described.

Radium, actinides, and their molecular negative ions from a cesium sputter ion source

The negative ions of the isotopes 226Ra, 231Pa and 244Pu, produced by a Cs sputter ion source, have been observed for the first time using the IsoTrace heavy element AMS system. The properties of these negative ions have been compared with those of Th and U, and the electron affinities of all these elements (Ra, Th, Pa, Th and Pu) have been found to be similar and greater than 50 meV. Some molecular negative ions of these elements, in particular carbides and oxides, have also been measured. It was found that di-carbide is generally a profitable molecule form for measuring Ra, Th and Pa, while mono-oxide is more efficient for measuring U and Pu.

Size distribution of atomic clusters formed by energetic-heavy-ion sputtering.

A cesium sputter ion source is used to produce cluster beams of various materials. The size distributions of these clusters have been studied. The dependence of the cluster yields on the structure of the substrate used has also been studied for carbon.

High energy carbon cluster beams

Carbon cluster beams with mega-electronvolt energies have been accelerated in the Orsay MP tandem accelerator. In a conventional cesium sputter ion source, negative beams of C − 8, C − 9 and C − 12 cluster ions were produced and injected into the accelerator with a terminal voltage of 5.5 and 4 MV, respectively. Different charge exchange and decay processes in the terminal as well as in the beam line are described. Energy and time-of-flight measurements show that different carbon cluster ions can be formed, accelerated and transported far away from the accelerator and arrive intact at the experimental site.

A new AMS facility in Erlangen — status and first results

A new beamline for AMS measurements has been built at the Erlangen EN tandem accelerator. The main components at the low-energy side of the accelerator are a cesium sputter ion source and a 90° injection magnet. At the high-energy side, a 15° electrostatic sector field, a 55° analyzing magnet for the separation of Be and C isotopes, and a gas-filled ionization chamber are used. In 14C test measurements of charcoal, pit-coal and graphite samples, using a preliminary and simple ion source, the 14C events could be clearly separated from the background. The system will be completed with a newly developed high-current ion source, which is presently being installed, and with a 120° mass spectrometer, which will be used for measuring heavier ions such as 26Al, 36Cl, 90Sr and 129I.

The beam emittance of negative ion sources

A computer controlled emittance meter has been used to measure the emittance of various beams produced by the three ion sources installed at the Strasbourg tandem injector: the direct extraction douplasmatron source, the Penning source and the cesium sputter ion source (model 860). The RMS emittance and the emittance enclosing 90% of the beam intensity were extracted and compared. The shape of emittance contours and the fractional intensity emittance were analyzed. For the three sources, an emittance value smaller than 5 π mm mrad MeV 1 2 was found for a beam intensity ranging from 500 to 2500 nA.

Memory Effects in an AMS System: Catastrophe and Recovery

A sample with a 14C concentration estimated to be greater than 30,000 Modern was inadvertently graphitized and measured in an AMS system. No measurable contamination of the cesium sputter ion source was observed. Simple cleaning procedures removed the contamination from the sample preparation system, with the exception of the reaction vessel in which the sample was graphitized. Sample cross-contamination factors were estimated for all of the preparation and measurement procedures.

Aspects of negative-ion generation and extraction from a refocus geometry cesium sputter negative-ion source. II

The basic parameters of the refocus geometry cesium sputter ion source for the production of negative ions from a low-sputtering material (carbon) and a high-sputtering material (copper) have been measured. The question of the influence of sample temperature on the negative-ion generation process has been addressed. Negative-ion yields from carbon samples are found to be weakly dependent on temperature over a range from 26° to 400 °C, while those from copper samples are found to be essentially independent of temperature over a range of 26° to 200 °C. The results of these investigations indicate that (1) sample temperature does not strongly influence negative formation in these sources, and (2) the maximum negative-ion yields for a given sample are dependent on both cesium-ion energy and positive-ion current. In addition to these data, the negative-ion extraction optics of the source are briefly discussed and cursory estimates of the probabilities for negative-ion formation presented.