Helium Desorption Research Articles

Field desorption of helium and neon from tungsten and iridum

The first complete crystallographic distribution of helium and neon field adsorbed on tungsten and iridium surfaces has been determined using field desorption mass spectromatry. At 80 K He+ is removed from tungsten at high work function areas. The absence of He+ in other regions indicates that either helium is not adsorbed, or that it is removed from the surface as a WHe3+ molecular ion during field evaporation of the substrate, which is required for He+ detection. Helium adsorbed on iridium at 80 K may form IrHe3+ and neon IrNe2+ near prominent zone lines. The absence of ion species in specific crystallographic regions of iridium and tungsten suggests care when interpreting atom probe results in certain metallurgical applications.

Analysis of thermal-desorption spectra using a computer graphics system

A computer graphics system has been programmed to allow experimental thermal-desorption spectra to be matched visually with the sum of up to twelve theoretical first-order desorption peaks. The system allows the resulting theoretical spectrum to be stored for later recovery or plotted along with the experimental spectrum using an X–Y plotter. The temperatures and amplitudes of the chosen theoretical peaks and the rms difference between the theoretical and experimental spectra are available for either display or printout. Analysis of a series of helium desorption spectra showed that peak temperatures could be determined to within ±0.8%, and that the main limitations were attributable to temperature uncertainties and noise in the experimental spectra.

The kinetics of the desorption of helium implanted into a Nickel (100) crystal

Abstract The thermal desorption spectrum for helium implanted into a nickel (100) crystal has been measured under several temperature-time programs. These measurements indicate that for a particular peak in the spectrum, the desorption rate, d n ( t , T )/dt, obeys a first order desorption equation with temperature dependent parameters.

Nitrogen and helium diffusion in polystyrene

Abstract A study was made of the temperature dependence of the rate of nitrogen and helium desorption from gas-filled polystyrene films in the range 100–410°K. Considerable differences in the desorption regularities for nitrogen and helium were observed. In the range 190–380°K the diffusion of nitrogen is described by the Arrhenius law with the parameters D 0 =21 × 10 −5 cm 2 /sec and E =5·3 kcal/mole. At temperatures above 380°K there is a marked change in the diffusion parameters owing to the process of glass transition. The regularities of helium desorption are only slightly dependent on film thickness in the range 45–320 μm. This is explained by permeation of the gas through defects with dimensions comparable to those of helium atoms.

Radiation damage in tungsten: Its influence on the trapping and subsequent thermal desorption of helium

Abstract Desorption spectra of various doses of 160eV helium ions injected into a damaged polycrystallinc tungsten target are described. Conclusions derived from these are applied to the interpretation of spectra obtained for the injection of helium (at different energies and doses) into an undamaged target, and are shown to be consistent with the spectral variations observed. Experiments are described in which a damaged target was partially annealed prior to the injection of 160 eV helium, with the result that the desorption spectra were modified in such a way as to reveal new information about certain trapping sites and release processes in tungsten.

Field adsorption and desorption of helium and neon

Pulsing the atom-probe FIM in the presence of the imaging gases He or Ne reveals the adsorption of these noble gases on the surface of tips of W, Fe, Ir and Rh at temperatures as high as 78°K. A minimum field is necessary for the adsorption; for He 2.0 V A ̊ is required at 21 °K and 3.3 V A ̊ at 78°K, while with Ne, adsorption at 78 °K occurs between 2.3 and 5.0 V A ̊ only. Field desorption of the noble gas ions appears to require the simultaneous field evaporation of the tip metal atoms, which sometimes form various metal-noble gas molecular ions. The binding of the noble gas atoms is almost entirely due to the polarization energy 1 2 αF 2 . Field desorption appears possible only through the catalytic action of multiply charged metal ions. These effects suggests some reservations in the interpretation of all field evaporation data previously obtained in the presence of the image gas.

On the stabilization of radiation damage by rare gas atoms

A study on zirconium nitride was performed to assess the effect of radiation damage by heavy ions at cryogenic and elevated temperatures. Cross-sectional transmission electron microscopy, grazing incidence X-ray diffraction, nanoindentation, and helium desorption studies were used to assess the damage and its effects. Xenon and krypton were used as heavy ions at 300 keV to displacement damage as high as 200 dpa. Implants were cryogenic, 350 °C, 580 °C, and 800 °C. Amorphization was not observed at low temperatures nor was bubble formation observed at elevated temperatures, however, defect migration was observed at elevated temperatures. Nanoindenter results showed the onset of defect saturation. Helium release studies were performed to show the effect of increasing damage by Xe to 40 dpa.

Composite Diffusion Mechanisms and Diffusional Anisotropy of Helium in Beryl, Aquamarine, Quartz, and Related Glasses

The rates of desorption of helium from several types of beryl, from aquamarine, and from quartz have been measured using a mass-spectrometer-type leak detector of high sensitivity. The rates measured on beryl or aquamarine slabs cut perpendicularly and parallel to the hexagonal axis of symmetry at 680°C are very different but conform to the appropriate solution of the diffusion equation. Diffusion through the channels present in the beryl crystal structure is probably the controlling process at this temperature. The extent of anisotropy, the conformance to the ideal curve shape, and the sample to sample reproducibility correlate with the quality of the various beryls investigated. At low temperatures relatively little helium is evolved and the process does not conform to the solution of the diffusion equation mentioned above, probably because grain boundaries of various dimensions furnish the preferred diffusion paths. Fused beryl and quartz yield very anomalous (nonconforming) rate curves while crystalline quartz is intermediate between the glasses and the crystalline beryls. Defect diffusion is probably of considerable importance in these cases. Results obtained on a beryl powder indicate that surface desorption is negligibly small in comparison to bulk and defect diffusion.

Reduction of Warm-Up Rate within a Dewar System by Helium Desorption

Reduction of Warm-Up Rate within a Dewar System by Helium Desorption

Specific Heat of Ferrites at Liquid Helium Temperatures

The specific heat of lithium, cobalt, magnesium, and nickel ferrite has been measured from 1.8\ifmmode^\circ\else\textdegree\fi{}K to 5\ifmmode^\circ\else\textdegree\fi{}K using a calorimetric technique similar to that used by Clement. A "heat switch" was used to cool the samples rather than a helium exchange gas, thereby avoiding helium desorption effects. In all cases the specific heat $C$ could be described by the relation $C={\ensuremath{\alpha}}_{M}{T}^{\frac{3}{2}}+\ensuremath{\beta}{T}^{3}$, where $T$ is the temperature and ${\ensuremath{\alpha}}_{M}$ and $\ensuremath{\beta}$ are constants. The Debye temperatures were computed from $\ensuremath{\beta}$ and were in good agreement with values obtained at liquid nitrogen temperatures. The ${T}^{\frac{3}{2}}$ temperature dependence verifies the spin-wave theory for these compounds although the values of ${\ensuremath{\alpha}}_{M}$ were consistently larger than anticipated from observed values of the Curie temperatures. Possible explanations for this are discussed. An extra term proportional to ${T}^{\ensuremath{-}2}$ was observed for cobalt ferrite and this was identified as the nuclear contribution to the specific heat. From the magnitude of this term the magnetic field at the nucleus of the cobalt ion was evaluated and found to be approximately 410 koe.