Diffusion Pump Vacuum Research Articles

Safety interlock and remote computer monitoring for a diffusion-pumped vacuum system

A safety interlock system for a diffusion-pumped ultra-high vacuum chamber is presented. It controls and monitors vacuum system valves, diffusion pumps, liquid nitrogen filling, chilled water flow, and pressures in the chamber. The interlock system is interfaced with a phone dialer and a personal computer to provide remote monitoring and diagnostics of the vacuum system. This interlock prevents many operational errors and problems due to the power and liquid nitrogen failure.

PbO Reduction and Crucible Reactions of 70 wt% PbO · 30 wt% B2O3 Glass

AbstractSeventy wt% PbO · 30 wt% B2O3 glass was melted in Pt and graphite crucibles; PbO reduction and subsequent crucible reactions were empirically investigated as a function of temperature and oxygen partial pressure. This research was conducted at NASA to determine optimum processing conditions for subcentimeter glass hollow spheres to be used as inertial confinement fusion targets for a particle beam fusion accelerator at Sandia National Laboratories. The research enables selection of appropriate crucible materials and oxygen partial pressure-temperature combinations necessary to avoid phase separation from PbO reduction and/or crucible reactions. Phase separation from PbO reduction was not detected in glass samples melted in Pt crucibles under oxidizing atmospheres. Under reducing atmospheres from mechanical and diffusion pump vacuum, oxygen gas emissions were detected along with Pb-Pt compounds forming on Pt crucibles. With graphite crucibles, glasses contained lead-rich phases and CO2 gas bubbles. Experimental results were compared with the theoretical Pb-PbO stability boundary predicted on the basis of the standard free energy change of PbO reduction.

Nuclear resonance profiling of high dose implants of Al in Si

We have applied nuclear resonance profiling (NRP) techniques to determine the depth distribution of implanted Al into Si. For implantation of Al at 100 keV and at doses of up to 10 18 Al/cm 2, our results indicate that the depth distribution of Al implanted in an ultra-high vacuum (UHV) system (∼- −8 Torr) is independent of dose rate and target orientation. For a dose of 10 18 Al/cm 2 a single Al distribution was observed with an Al concentration of about 65% at peak while 85% of the implanted Al was retained in the Si target.On the other hand, the depth distribution of implanted Al in a diffusion pumped vacuum (DPV) system (∼- 10 −6 Torr) was greatly influenced by dose rates and target orientation. For high dose rate implantation (40–50 μA/cm 2) the depth distribution of Al appears to be bimodal or broadened and about 95% of the implanted Al is retained in the Si target. A peak Al concentration of up to 75% could be obtained.

A mass spectrometer study of the reaction of erbium with the residual gases in a vacuum coating unit and with heavy water

A quadrupole gas analyser was used to study the gases inside a conventional diffusion-pumped vacuum evaporator prior to and following the evaporation of erbium. Studies have also been done on the effects of admitting heavy water (D 2O) to the system. It has been found that erbium at the evaporation source reduces H 2O and D 2O to produce H 2 and D 2 respectively and that CO in the vacuum is converted to CH 4 in the presence of H 2O. Various deuterated forms of CH 4 occur in the presence of H 2O and D 2O. An explanation is given of why vacuum-deposited films of erbium are frequently contaminated by ErH 2 in the presence of water even though Er 2O 3 is thermodynamically much more stable than ErH 2.

Gettering of Impurities during High Dose Implantation of Al or Cr into Si and the Resulting Effect on Structure and Composition

ABSTRACTThis paper presents strong evidence for carbon and oxygen gettering during high dose implantation of Cr and Al into Si by implanted ions or Si atoms. Rutherford Backscattering (RBS) and Auger Electron Spectroscopy (AES) experiments of Cr and Al implanted Si samples in a diffusion pumped vacuum (DPV) system (≃ 10−6 Torr) clearly indicate that the incorporation of carbon or oxygen occurs preferentially and depends on the surface composition which is controlled by the dose of implantation and by sputteripg.The implantation of Cr and Al in a DPV system (≃ 10−6 Torr) results in a large increase in the concentration and retention of implanted atoms compared to implantation in a UHV system (≃ 10−8 Torr). For implantation in a DPV system, the Cr distribution broadens up to a factor of two. For Al a bimodal or broadened distribution could be observed by nuclear resonance profiling (NRP).

The Influence of Implantation Conditions and Target Orientation in High Dose Implantation of Al+ into Si

ABSTRACTWe report the preliminary results of a study to determine the dependence of the near surface composition and structure on total dose, dose rate, vacuum condition and substrate orientation for Al implantation into Si (111) and Si (100) with doses up to 2 × 10l8 ions/cm2. Our studies include the results of Rutherford Back Scattering (RBS), Auger Electron Spectroscopy (AES) and x-ray diffraction measurements on samples implanted with a 100 keV energy in a diffusion pumped vacuum (DPV) system (10−6 Torr) with and without a LN2 trap and in an ultra high vacuum (UHV) system (2–4) x 10−8 Torr.Results of high dose rate (50 μA/cm2 ) implantation into Si (111) in an untrapped DPV system indicate that Al segregates with a preferred (111) orientation. For a dose of 1 × 1018 ions/cm2 the surface is Al-rich to a depth of 2500Å while for lower doses the surface is silicon-rich. A carbon build-yp occurred for samples prepared by low dose rate (5 μA/cm2 ) implantation. However, no Al segregation could be observed for doses of less than 1018 ions/cm2 . A similar behavior has been observed for Si (100) except that Al segregation occurs with a polycrystalline structure. Moreover, the segregated Al is present at depths greater than the projected range.When implantation was carried out in a DPV system with a LN2 trap, no carbon peaks could be observed by RBS regardless of the dose rate. For these conditions, as well as for the implantation of Al in an UHV system, we find Al segregation with a polycrystalline structure independent of the dose rates and target orientations we used. Al is observed at a depth greater by a factor of two than the expected value from the Rpcalculations. The Al depth penetration increases with the dose of implantation.

Study of Near Surface Structure and Composition for High Dose Implantation of Cr+ into Si

ABSTRACTThe dependence of the implanted layer composition on total dose, dose rate and target chamber environment for Cr+ implanted Si have been studied by means of Rutherford Back Scattering (RBS) and Auger Electron Spectroscopy (AES). Implantation of Cr+ for doses up to 2 × 1018 ions/cm2 and a fixed dose rate and energy were carried out in an ultra high vacuum (UHV) system as well as in a diffusion pumped vacuum (DPV) system. For the former, the maximum Cr concentration was about 42%. On the other hand, implantation of Cr in a DPV system resulted in a much higher peak concentration (86%) and retention.Both the RBS and AES results positively demonstrate the existence of extensive surface carbon for a Si-rich surface and a chromium oxide layer for the Cr-rich surface. This result suggests that the interaction of oxygen or carbon occurs preferentially and depends on the surface composition.No surface compositional variation could be observed by the RBS experiments for Cr implanted in a UHV system for different dose rates. In contrast, for implantation in a DPV system, higher concentrations can be achieved for lower dose rates.

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

SUMMARYAn 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.

Operation and maintenance of a diffusion-pumped vacuum system

Operation and maintenance of a diffusion-pumped vacuum system

Operation and maintenance of a diffusion-pumped vacuum system

Sources of contamination in a diffusion-pumped vacuum system are detailed. Means of minimizing these are described. Proper pumping procedures are suggested, with particular stress placed on the use of dry N2 purge gas.

A new apparatus for crystal growth from the melt under very high vacuum conditions

This paper describes new equipment for high purity crystal growth from the melt and presents some experimental results which characterize the quality of the apparatus under operating conditions. Although primarily designed for electron beam float zone growth of metal crystals, the machine provides all necessary mechanical and electrical requirements for crystal growth by pedestal pulling, Czochralski technique or Bridgman method utilizing either electron beam-, r.f.- or resistance-heating. Contamination of the mechanical parts of the equipment by evaporating materials is prevented by a liquid nitrogen cooled cooper baffle which surrounds the energy source-melt assembly. Since this baffle simultaneously acts as a heat shield, outgassing of environmental parts is minimized. Standard conflat flange feedthroughs are used and all parts are bakable which makes the apparatus suitable for UHV operation. In conjunction with a 6 inch diffusion pump vacuum station the system was operated in the very high vacuum range (ultimate pressure 1.5 × 10−8 torr. The linearity of the drive system is better than 1% and the noise amplitude under operating conditions can be kept below two times the background noise level which is ∼ 2 μm rms.

Computer Control of Van de Graaff Accelerator Vacuum Systems

The seven main diffusion-pump vacuum systems on our Tandem Van de Graaff accelerator are controlled by a Honeywell H610 digital control computer. Each system has a local control panel with a hardwire protection shutdown system but no recovery capability. Control is normally left to the computer, which, through analog and digital inputs, senses trouble and secures the system according to the difficulty. The computer then recovers the systems completely or to the level of the difficulty. The computer operators’ console includes control buttons to enable/disable the securing function or the recovery function for a system. An alarm typewriter informs the operator of any action that the computer has taken, including which inputs are out of limit. An Adage AGT-10 display system shows each vacuum system and the status of each input. This takes the place of the usual remote indication panel.

818. Investigation of the influence of ozone on the stability of DC-704 in a diffusion pump vacuum system: J. Farrell, Rep NASA-CR-897770, June 1967, 41 pages (Sci tech aerospace reps, 5 (24), 4475, N67-40550).

818. Investigation of the influence of ozone on the stability of DC-704 in a diffusion pump vacuum system: J. Farrell, Rep NASA-CR-897770, June 1967, 41 pages (Sci tech aerospace reps, 5 (24), 4475, N67-40550).

Evaluating explosions in diffusion-pumped vacuum systems: G J Farrell and H J O'Neill,Res/Develop, Jan 1967, 50–53

A versatile, inexpensive electrospray interface has been constructed and installed on an external source Fourier transform mass spectrometer with a quadrupole ion guide. This interface is readily interchangeable with FAB and MALDI sources, with the main time requirement for changing being the pump-down time. A heated capillary, two skimmers and a set of Einzel lenses are used to deliver ions to the quadrupole ion guide. SIMION (Idaho National Engineering Laboratory, Idaho Falls, Idaho) was used to model ion trajectories and determine optimal dimensions. Five stages of pumping are employed, using mechanical, turbomolecular and cryopumps. A solenoid-driven shutter on the final lens blocks neutrals after injection of the ion packet.Kinetic energy distributions of both small and large biomolecular ions were investigated. For large (104–105 Da), highly charged species, the kinetic energy distributions were quite favorable to trapping, with sharp peaks at less than 10 eV. Thus a 50 ms ion accumulation time is sufficient to obtain spectra of lysozyme with high S/N ratio. Distributions for smaller ions tended to be somewhat wider and peaked at higher energies. The spectra obtained to date illustrate the ability of the instrument to handle biomolecules ranging from bradykinin to bovine serum albumen.

An electric discharge as a trap for diffusion-pump vacuum systems: R O Adams,US At Energy Comm, RFP-572, 1965, 9 pages.

An electric discharge as a trap for diffusion-pump vacuum systems: R O Adams,US At Energy Comm, RFP-572, 1965, 9 pages.

379. Cadmium trap for obtaining high vacuum in a mercury-diffusion pumping system: Lu Ti-ren et al, Acta Phys Sinica, 21 (6), June 1965, 1170–1174, (in Chinese)

We have used a nonrefrigerated cadmium trap in a 2-stage glass mercury diffusion pump vacuum system. Experiments show that the cadmium trap is capable of isolating mercury vapour effectively, as high vacua of 10-5-10-7 mmHg is attainable in an evacuated container. Systematic investigations of the effect of the cadmium film under various conditions on the ultimate pressure were carried out. It is found that newly evaporated cadmium films are most effective for that purpose, while after exposure in air of 10-2 mm Hg, the ultimate pressure does not change appreciably, and that had the cadmium film been exposed to the atmosphere, it would be one order higher than before. Improvement on the ultimate vacuum can be effected by decreasing the cadmium trap temperature and utilizing two or more cadmium traps in series as well as through bake-out of the evacuated container. When such measures are put in force, an ultra-high vacuum of 10-9 mm Hg is obtained in our test.

An electric discharge as a trap for diffusion pump vacuum system

An electric discharge as a trap for diffusion pump vacuum system

351. An electric discharge as a trap for diffusion pump vacuum systems: R O Adams, Rep RFP-572, 1965, Rocky Flats Div, Dow Chemical Co, Golden, Colorado

351. An electric discharge as a trap for diffusion pump vacuum systems: R O Adams, Rep RFP-572, 1965, Rocky Flats Div, Dow Chemical Co, Golden, Colorado

Mercury vapor hazards in vacuum laboratories

Mercury vapor concentrations have been measured with ultraviolet absorption spectrometer in several vacuum laboratories, following accidents involving mercury spillage or the release of mercury vapor. The results suggest that condensed vapor from damaged diffusion-pumped vacuum systems may cause far more dangerous contamination that has hitherto been suspected. Hazards resulting from spilt liquid mercury appear to be much less, although not negligible. The relative effectiveness of various decontamination procedures is discussed.

CADMIUM TRAP FOR OBTAINING HIGH VACUUM IN A MERCURY-DIFFUSION PUMPING SYSTEM

We have used a nonrefrigerated cadmium trap in a 2-stage glass mercury diffusion pump vacuum system. Experiments show that the cadmium trap is capable of isolating mercury vapour effectively, as high vacua of 10 -5 -10 -7 mmHg is attainable in an evacuated container. Systematic investigations of the effect of the cadmium film under various conditions on the ultimate pressure were carried out. It is found that newly evaporated cadmium films are most effective for that purpose, while after exposure in air of 10 -2 mm Hg, the ultimate pressure does not change appreciably, and that had the cadmium film been exposed to the atmosphere, it would be one order higher than before. Improvement on the ultimate vacuum can be effected by decreasing the cadmium trap temperature and utilizing two or more cadmium traps in series as well as through bake-out of the evacuated container. When such measures are put in force, an ultra-high vacuum of 10 -9 mm Hg is obtained in our test.