Vacuum Evaporation-condensation Research Articles

Preparation of 82Se thin films with trigonal hexagonal crystal structure for in-beam nuclear structure experiments

We report a novel approach in producing and characterizing enriched isotopic selenium-82 (82Se) thin films with trigonal hexagonal crystal structure (t-82Se), the most thermodynamically stable form of the element. The obtained t-82Se thin films are used as targets in accelerator based nuclear structure experiments. Several 82Se thin films with thicknesses around 5 mg/cm2 (10.4 μm) were deposited on 5 mg/cm2 (3 μm) tantalum (Ta) foils by vacuum evaporation-condensation method. The condensed 82Se films exhibit unstable amorphous structure (a-82Se), therefore were converted to t-82Se by means of an appropriate vacuum heat treatment developed in the target laboratory of IFIN-HH. After the thermal treatment, the microstructure, morphology and composition of the 82Se films were evaluated before and after the vacuum thermal treatment using Fourier Transform Raman Spectroscopy (FT-Raman), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) techniques. Furthermore, an in-beam γ-spectroscopy experiment performed at the 9-MV tandem accelerator of IFIN-HH confirmed that the thermally treated t-82Se films possess high durability and high purity with no detectable contamination and no mass loss.

Recovery of pure lead and preparation of nano-copper from waste glass diodes via a clean and efficient technology of step-by-step vacuum evaporation-condensation

Waste glass diodes, generated vastly with discarded printed circuit boards, are rich in metal resources while carriers of hazardous heavy metals. They require proper treatment to recover metals and avoid heavy metal contamination, but relevant research is insufficient currently. Thus, an environmentally-friendly and efficient technology of step-by-step vacuum evaporation-condensation was proposed in this study to recover lead and prepare nano-copper particles. A heat transfer model was established to guide the evaporation process with the purpose of effective treatment and energy-saving. According to the model, metal materials and the heating equipment could reach the endpoint of the set temperature T1 almost simultaneously when T1 ≥ 600 ℃. In the first step, 99.94% of lead was separated when evaporating at 800 ℃ for 1 h. Condensation products of pure lead were collected centrally, which eliminated the Pb contamination caused by its migration. The second step was optimized by the response surface methodology, and optimal operation parameters were determined as 1250 ℃ and 3 h. Under these conditions, 91.71% of copper was evaporated and transformed into nano-copper particles ranging from 20 nm to 200 nm. In short, this study firstly provided an effective approach for the treatment of waste glass diodes and their high-value-added reuse.

Production of Granulated Relite by High-Speed Electron-Beam Evaporation

The conditions of high-speed vacuum evaporation–condensation for producing granulated relite (a eutectic alloy of tungsten monocarbide and semicarbide) using electron-beam process have been studied. When the material is deposited onto cooled surfaces, the deposition products can be refined by removal of metallic and nonmetallic impurities depending on their vapor pressures.

Preparation of 10Be targets by high vacuum evaporation–condensation

10Be targets in the form of BeO on thin C backings were prepared by high-vacuum evaporation–condensation. Starting from a solution of Be(NO 3) 2 in nitric acid, solid BeO was prepared by heat treatment at 773 K , in air, which was subsequently evaporated from a Re crucible mounted in a micro-evaporation module. Typically 200– 400 μg of BeO was evaporated in one run, resulting in a target spot of 3 mm diameter and 100– 200 μg/cm 2 thickness.

Preparation of radioactive targets for tandem accelerator experiments by high vacuum evaporation–condensation

Radioactive thin film targets have been prepared by high vacuum evaporation–condensation in the hot-lab facility of the University of Munich. Targets made by this technique are of high density and excellent smoothness, being well suited for experiments aimed at the production and spectroscopy of fission fragments. Cold crucible electron beam heating is the preferred method for evaporation of actinide isotopic material of sufficient abundance, for instance 230Th, 232Th, 233U, 235U, 238U and 239Pu. Exotic isotopes, which are available only in submilligram quantities, are processed in a micro-evaporator module consisting of a chimney-type crucible heated by low-tension electron bombardment. This set-up is characterised by a high collection efficiency and was used for the production of 244Pu and 10Be targets.

Characterization of thin films by X-ray transmission measurements

We have used synchrotron radiation in order to determine the mass densities and the elemental composition of single and multilayered solid films. Soft X-rays were used to measure the spectral transmittance in a certain photon energy range, i.e. between 50 eV and 10 keV, and the local transmission profile at discrete photon energies within this range. To give an example, we present some results obtained for an optical filter which is to be used in the focal plane PN CCD-camera of ESAs XMM (X-ray Multi Mirror) astronomy satellite. Moreover, we established a laboratory set-up for transmittance measurements using the discrete line radiation emitted from a solid target X-ray source. Thus, we are able to control layer thicknesses of thin films produced by vacuum evaporation condensation. We describe the compact X-ray test facility, and give the obtained performance data of the filters.

Preparation of 180Ta targets by high vacuum evaporation-condensation

A method for the routine preparation of enriched 180Ta thin film targets by evaporation-condensation of submilligram quantities of Ta 2O 5 onto thin C backings is described.

Note on the variation of isotope abundance ratios of metallic lithium during the vacuum evaporation-condensation process

The variation of isotope ratios during the vacuum evaporation-condensation process of 150 mg metallic lithium have been analyzed. The 6 Li 7 Li isotope ratio shows a time dependence consistent with that predicted by Rayleigh's formula.

Targets with magnetic properties

Various multilayer targets with ferromagnetic matter as a middle layer for TF (transient magnetic field) measurements were prepared using rolling and vacuum evaporation-condensation techniques. The compatibility of different backing materials with the condensed ferromagnetic matter was investigated. The influence of the substrate temperature on the magnetic properties was analyzed as well. Ferromagnetic Fe layers consisting of separated segments of domain size were prepared by vacuum evaporation-condensation through suitable mesh masks. For NMR-ON (nuclear magnetic resonance on oriented nuclei) experiments and for studies of the circular magnetic X-ray dichroism rolled foils of highly diluted ferromagnetic alloys were needed. The preparation of such impurity systems by means of an electron beam source in high vacuum is described. The diluting process strongly depends on the relative vapor pressures of the two metals.

Preparation of ductile Zr from ZrO 2

Ductile Zr was prepared without making use of the Van Arkel-De Boer purification procedure. Bomb reduction of K 2[ZrF 6] with Na and subsequent high-vacuum electron-beam melting yields pure Zr metal suitable for further processing to nuclear accelerator targets by vacuum evaporation-condensation as well as by cold rolling. Methods for the conversion of ZrO 2, the standard chemical inventory form of enriched Zr isotopes, to K 2[ZrF 6] were also investigated and are described in some detail.

Heavy-ion irradiation damage in carbon stripper foils

Slackened carbon stripper foils of about 4 μg/cm 2, produced by vacuum evaporation-condensation and used for heavy ion stripping in the terminal of the Munich MP tandem, were investigated in order to get more information about irradiation damages. Electron diffraction and electron transmission muscope investigations related with theoretical considerations revealed a clear picture of the irradiation damage mechanism in carbon stripper foils. Due to these results it can be predicted, how the crystallographic structure of a carbon foil should be constituted in order to show best stripper performance.

Ferromagnetic gadolinium foils for transient field experiments

Ferromagnetic Gd-foils were prepared in a thickness range of 100 μg/cm 2 to 8 mg/cm 2 using vacuum evaporation-condensation techniques. Diffusion barriers had to be found, because the ferromagnetic structure cannot be achieved below 700-K substrate temperature. Thick layers (0.5–20 mg/cm 2) of Al, Si, Ag, and Au had to be evaporated on both sides of the Gd-foils to be used as target, recoil stopper or just heat conductor.

210Pb targets for nuclear spectroscopy

The preparation of metallic 210Pb targets by vacuum evaporation condensation is described. Lead-210, which is highly radioactive, is available as nitrate in 3M HNO 3. Solid Pb(NO 3) 2 is extracted from this solution and subjected to a reductive evaporation procedure. A special-shaped evaporation crucible yields a collection efficiency of 2.8 mg/cm 2 per milligram of employed material.

Preparation of phosphorus targets using the compound phosphorus nitride

Commercially available phosphorus nitride (P 3N 5) shows a high oxygen content. Nevertheless, this material is attractive for use as phosphorus targets in experiments where red phosphorus would disappear due to its high vapor pressure and where a metal partner in the phosphite must be excluded due to its high atomic number. Methods are described to produce phosphorus nitrite targets by vacuum evaporation condensation.

Structure studies of carbon foils with the aim to improve the ability for heavy-ion stripping

Slackened carbon stripper foils of 3 to 5 μg/cm 2 produced by vacuum evaporation-condensation were graphitized by annealing at about 3300 K with a pulsed laser beam (1.06 μm). An average crystal size of 10 nm was measured by electron diffraction. The texture of the 002-plane is parallel to the surface of the foil as known from slightly annealed carbon foils. Radiation damages caused by high doses of heavy ions dramatically change the crystal structure. Electron diffraction patterns reveal newly formed graphite crystals with their 002-plane perpendicular to the texture. Compared to carbon foils of the same kind, but not graphitized, a lifetime prolongation of a factor of two was achieved for such foils tested in the terminal of the Munich MP tandem. The slope of the curve for heavy-ion transmission through carbon stripper foils varies for foils of the same kind and for different ion-beam conditions.

Preparation of Nuclear Accelerator Targets by Vacuum Evaporation

In many cases an accelerator target for physical or chemical research work has to be prepared in form of a uniform, as far as possible self supporting thin film of thickness 0.1-10 ?m. Typical target materials are stable or radioactive isotopes for nuclear physics and nuclear chemistry experiments, mixtures of different elements for material analysis with ion beams as well as single crystal samples for special solid state physics applications. A powerful method to prepare thin film nuclear accelerator targets is the procedure of vacuum evaporation-condensation. In the present paper the physical and technological background of this method is discussed and the construction of suitable evaporation systems and related equipment is displayed. Different sublimation techniques including resistance-, induction- and electron beam heating as well as ion beam sputtering are described considering their specific benefits and disadvantages. Particular attention is paid to the collection efficiency of these various techniques in view of the low abundance and high cost of isotopically enriched target material. Since in many cases a target backing severely disturbs the actual measurement, emphasis is also given to procedures yielding unsupported high purity targets. In addition, special techniques for preparation, handling and storage of chemical reactive targets and of radioactive targets are discussed. Finally the preparation of single crystal thin film targets is briefly mentioned as well as target preparation by chemical vapour deposition, which in a physical sense is closely related to the vacuum evaporation-condensation method.