Translational and rotational energy measurements of desorbed water molecules in their vibrational ground state following 157 nm irradiation of amorphous solid water

Water ice is the major solid component in a variety of astrophysical environments, e.g., cold and dense molecular clouds. Photodesorption plays a dominant role in consuming ice in such cold regions. In this study, photodesorption of vibrationally ground-state H₂O(v = 0) from amorphous solid water has been investigated at 157 nm. Using a resonance-enhanced multiphoton ionization technique, the translational and rotational energy distributions of photodesorbed H₂O(v = 0) were measured, i.e., Boltzmann distributions at 1800 and 300 K, respectively. These energies are in good accordance with those predicted by classical molecular calculations for water photodesorption due to a kick-out mechanism following absorption of a single photon; hot H atom released by photodissociation of H₂O in ice transfers enough momentum to another H₂O molecule to kick it off the surface. Desorption of D₂O(v = 0) following 193 nm photoirradiation of a D₂O/H₂S mixed ice was investigated to provide further direct evidence for the operation of a kick-out mechanism. The other desorption mechanisms were also discussed in the context of possible photodesorption of vibrationally excited H₂O.     

Effect of Low Pressure Nitrogen–Oxygen (N<Subscript>2</Subscript>/O<Subscript>2</Subscript>) Plasma Treatment on Surface Properties of Polypropylene Films

In this paper the effect of plasma treatment by using mixed gas (N₂/O₂) on surface properties of a Polypropylene PP films were investigated as a function of O₂ content and treatment time. Results obtained by using Fourier Transform infrared spectrometer (FTIR), contact angle measurement and scanning electron microscopy (SEM). It is found that plasma treatment can change chemical structure of polymer surfaces partially. SEM images revealed distinct changes in topography of PP due to O₂/N₂ plasma treatment. Finally wettability and surface energy before and after treatment investigated in different conditions.     

Charge exchange of medium energy H and He ions emerging from solid surfaces

Charge exchange of medium energy H and He ions emerging from clean solid surfaces is studied extensively using a toroidal electrostatic analyzer with an excellent energy resolution. The charge distributions of He ions scattered from sub-monolayers near a surface are non-equilibrated, resulting in a surface peak even for poly-crystal solids. By solving simultaneous rate equations numerically, we derive electron capture and loss cross sections for Ni and Au surfaces. Based on a free electron gas model, non-equilibrated He⁺ fractions dependent on emerging angle reveals uniform electronic surfaces for metals and corrugated surfaces for Si and graphite with covalent bonds. It is also found that equilibrium charge fractions of H⁺ are independent of surface materials (Z₂) and in contrast equilibrium He⁺ fractions depend pronouncedly on Z₂. The data obtained are compared with semi-empirical formulas.     

Secondary electron yields from the entrance and exit surfaces of thin carbon foils induced by penetration of H+, H0 and H+2 projectiles (1.2 MeV/u)

We report experimental work on secondary electron emission from both entrance (γ_b) and exit (γ_f) surfaces of thin carbon foils traversed by H⁺, H⁰ and H⁺₂ projectiles (1.2 MeV/u). Secondary electron coefficients γ_b and γ_f, were measured simultaneously. The results are discussed in the framework of a semiempirical model for kinetic emission of target electrons from solid surfaces.     

Investigation of plasma exposed W–1% La2O3 tungsten in a high ion flux,low ion energy,low carbon impurity plasma environment for the International Thermonuclear Experimental Reactor

Previous investigations of tungsten for the International Thermonuclear Experimental Reactor (ITER) were focusing on using energetic ion beams whose energies were over 1 keV. This study presents experimental results of exposed W–1% La₂O₃ in high ion flux (10²² m^–2), low ion energies (about 110 eV) steady-state deuterium plasmas at elevated temperatures (873–1250 K). The tungsten samples are floating during plasma exposure. Using a high-pressure gas analyzer, the residual carbon impurities in the plasma are found to be about 0.25%. No carbon film is detected on the surface by the EDX analysis after plasma exposure. An infrared pyrometer is also used as an in situ detector to monitor the surface emissivities of the substrates during plasma exposure. Using the scanning electron microscopy, microscopic pits of sizes ranging from 0.1 to 5 μm are observed on the plasma exposed tungsten surfaces. These pits are believed to be the results of erupted deuterium gas bubbles, which recombine underneath the surface at defect locations and grain boundaries, leading to substrate damage and erosion loss of the substrate material. Low temperature plasma exposure of a tungsten foil indicates that deuterium gas (D₂) is trapped inside the substrate. Macroscopic blisters are observed on the surface. The erosion yield of the W–1% La₂O₃ increases with temperature and seems to saturate at around 1050 K. Scattered networks of bubble sites are found 5 μm below the substrate surface. High temperature plasma exposure appears to reduce the population as well as the size of the pits. The plasma exposed W–1% La₂O₃ substrates, exposed above 850 K, retain about 10¹⁹ D/m², which is two orders of magnitude less than those retained by the tungsten foils exposed at 400 K.     

X-ray impact induced desorption of gases from surfaces

Measurements of gases released from 302 stainless steel and gold surfaces before and after discharge cleaning were made in ultrahigh vacuum using X-rays with an energy distribution typical of a tungsten bremsstrahlung spectrum. Similar measurements were also made for Al₂O₃ surfaces which had not been discharge cleaned. For the non-discharge-cleaned surfaces of stainless steel, Al₂O₃, and gold the predominant gas species observed mass spectrometrically was CO₂. For some stainless steel and Al₂O₃ surfaces CO and O₂ were also readily observed. Mean quantum yields for CO, O₂ and CO₂ release from such stainless steel surfaces, for example, ranged from < 6 × 10^?5 to 9 × 10^?4 molecules per photons in the bremsstrahlung spectrum characteristic for 50 keV electron energy. After discharge cleaning a decrease in the mean quantum yields was observed for the stainless steel and gold surfaces.     

Electron- and photon-induced desorption

The process of electron and photon induced desorption as a quantum effect (that is, as opposed to thermal effects) has now been firmly established. Considerable data exists on electron induced desorption in the low energy range of approximately 0–200 eV. It now seems certain that these low energy electrons interaction directly with the adsorbed gas species and that desorption effects are fairly independent of the substrate material. Results from several laboratories showing the similarity of data for carbon monoxide adsorption and desorption on different metals will be discussed as a typical system. True photodesorption has now been established but is based on very much fewer experimental results. Our most recent data seem to indicate that the photodesorption process involves first absorption by the substrate with desorption occurring via a secondary process. Thus, the photodesorption process is very much substrate dependent. Recent results obtained on a number of different substrate materials will be discussed and the possible mechanism considered.     

Cosmic ion bombardment of the icy moons of Jupiter

A large number of experiments have been performed in many laboratories in the world with the aim to investigate the physico-chemical effects induced by fast ions irradiating astrophysical relevant materials. The laboratory in Catania (Italy) has given a contribution to some experimental works. In this paper I review the results of two class of experiments performed by the Catania group, namely implantation of reactive (H⁺, C⁺, N⁺, O⁺ and S⁺) ions in ices and the ion irradiation induced synthesis of molecules at the interface between water ice and carbonaceous or sulfurous solid materials. The results, discussed in the light of some questions concerning the surfaces of the Galilean moons, contribute to understand whether minor molecular species (CO₂, SO₂, H₂SO₄, etc.) observed on those objects are endogenic i.e. native from the satellite or are produced by exogenic processes, such as ion implantation.The results indicate that:

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C-ion implantation is not the dominant formation mechanism of CO₂ on Europa, Ganimede and Callisto.

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Implantation of sulfur ions into water ice produces hydrated sulfuric acid with high efficiency such to give a very important contribution to the sulfur cycle on the surface of Europa and other satellites.

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Implantation of protons into carbon dioxide produces some species containing the projectile (H₂CO₃, and O-H in poly-water).

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Implantation of protons into sulfur dioxide produces SO₃, polymers, and O₃ but not H-S bonds.

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Water ice has been deposited on refractory carbonaceous materials: a general finding is the formation of a noteworthy quantity of CO₂. We suggest that this is the primary mechanism to explain the presence of carbon dioxide on the surfaces of the Galilean satellites.

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Water ice has been deposited on refractory sulfurous materials originating from SO₂ or H₂S irradiation. No evidence for an efficient synthesis of SO₂ has been found.

     

Study of surface activation of PET by low energy (keV) Ni and N ion implantation

Polyethyleneterephthalate (PET) has been modified by 100 keV Ni⁺ and N⁺ ions using metal ion from volatile compound (MIVOC) ion source to fluence ranging from 1 × 10¹⁴ to 1 × 10¹⁶ ions/cm². The increasing application of polymeric material in technological and scientific field has motivated the use of surface treatment to modify the physical and chemical properties of polymer surfaces. When a material is exposed to ionization radiation, it suffers damage leading to surface activation depending on the type. The surface morphology was observed by atomic force microscopy (AFM). That show the roughness increases with fluence in both the cases. The Ni particles as precipitation in PET were observed by cross-section transmission electron microscopy (XTEM). The optical band gap (E_g) deduced from absorption spectra; was calculated by Tau’c relation. Raman spectroscopy shows quantitatively the chemical nature at the damage caused by the Ni⁺ and N⁺ bombardment. The ration of I_D/I_G shows graphite-like structure is formed on the surface. A layer of hydrogenated amorphous carbon is formed on the surface, which has confirmed by XPS results also.     

The chemical interaction of hydrogen discharges with non metals

The impurity ions in an r.f. discharge have been directly extracted and then both energy and mass analysed. A variety of surfaces have been exposed to the plasma including borosilicate glass, alumina and carbon. In each case a large variety of species were produced initially, due to desorption of impurities from the surface. After some hours exposure to the plasma many of these species decayed away and relatively simple ion mass spectra were observed. The principal species with oxide surfaces were OH⁺, OH⁺₂ and OH⁺₃ and the corresponding OD⁺, OD⁺₂, OD⁺₃ in a deuterium plasma. Two other major impurities were mass 28 and 29. These are attributed to CO⁺ and COH⁺. When the carbon sample was exposed to the plasma the main species observed were CH⁺₃, CH⁺₄ and the series C₂H⁺₂ to C₂H⁺₆.     

The influence of sodium vapour on the wetting of UO2-stainless steel 1.4970 (liquid) and its interpretation using scanning auger spectroscopy

The influence of sodium vapour on the contact angle and the wetting properties in the system UO₂ -liquid steel at the liquidus temperature of the steel ($\text{T= 1690}$ K) was measured using the sessile drop technique. The contact angle was 111.5° and the surface energy of steel 1.16 J/m².The surfaces and the interface of the system were investigated using scanning Auger spectroscopy and showed the presence of sodium at the interface (UO₂-stainless steel 1.4970) and its absence from the surfaces of the steel and UO₂. It can be concluded that sodium vapour does not influence the surface energy of UO². Using the known value for the surface energy of UO₂, the interfacial energy of 1.35 J/m² is obtained. The temperature for a wetting angle 0° was calculated to be 2380 K.     

Effect of 4MeV electron beam irradiation on carbon films

Pulsed KrF excimer laser is used to deposit tetrahedral amorphous carbon (ta-C) thin films on Si (1 1 1) single crystal substrates at room temperature under vacuum ∼10⁻⁶ mbars. The pristine deposited films are then irradiated by 4 MeV electron beam at doses varying from 1000 to 4000 cGy. Analysis through AFM illustrates that the irradiation of electron has induced cluster formation on the film surface and increased the surface roughness. Optical properties (n, α and Tauc optical band gap) measured by spectroscopic ellipsometry and electrical resistivity measured by four probe technique are found to depend strongly on electron dose. High electron doses cause significant alteration in order/disorder or sp² states in the film which is the main cause of modifying band gap in the carbon films. The electrical conductivity of the films also increases by increasing electron dose which is due to tunneling of charge carriers through neighbouring conductive chains. The present electron irradiation process at varying electron doses proved to be successful to modulate the optical and electrical properties of carbon films.     

Density functional theory study of H,C and O chemisorption on UN(001) and(111) surfaces

We performed density functional theory calculations of H, C, and O chemisorption on the UN(001) and(111) surfaces using the generalized gradient approximation(GGA) and the Hubbard U parameter and revised Perdew-Burke-Ernzerhof(RPBE) exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorption energies vs. distance of molecules from UN(001) and UN(111) surfaces have been optimized for four symmetrical chemisorption sites, respectively. The results show that the Hollow, N-top, and Hollow adsorption sites are the most stable sites for H, C, and O atoms with chemisorption energies of 13.06,25.50 and 27.34 kJ/mol for UN(001) surface, respectively. From the point of adsorbent(UN(001) and UN(111)surfaces in this paper), interaction of O with the chemisorbed surface is of the maximum magnitude, then C and H, which are in agreement with electronegativities of individual atoms. For the UN(001) surface, U-N bond lengths change relatively little( 9%) as a result of H chemisorption, however C and O chemisorptions result in remarkable changes for U-N bond lengths in interlayer( 10%). Electronic structure calculations indicate that Bridge position is equivalent with Hollow position, and the most stable chemisorption position for H, C,and O atoms are all Bridge(or Hollow) position for the UN(111) surface. Calculated electronic density of states(DOSs) demonstrate electronic charge transfer between s, p orbitals in chemisorbed atoms and U 6d, 5f orbitals.     

Surface oxidation of Zircaloy-4 at 600 K by adsorbed oxygen, nitric oxide, and sulfur dioxide

Understanding and controlling the formation of surface oxides on Zircaloy-4 (Zry-4) surfaces in the presence of nitrogen or sulfur at high temperatures is of interest in applications where this alloy serves as a structural material. In this article we monitor the adsorption of gases on Zry-4 surfaces at 600 K using Auger electron spectroscopy. We find that sulfur dioxide (SO₂), nitric oxide (NO), and isotopic oxygen (¹⁸O₂) all result in the formation of surface oxides. The presence of sulfur on the surface is reflected both in an increase in the intensity of the overlapping [Zr(MNV) + S(LMM)] feature and its shift toward higher kinetic energies. On the other hand, since oxide formation results in shifts of the Zr(MNV) Auger transition toward lower energies, opposite to what the presence of sulfur does, we also obtain useful information from the Zr(MNN) transition. Although exposure to oxygen results in the largest oxygen concentration near the surface, all the three adsorbates shift the Zr(MNN) feature by about 1.5-2.0 eV, indicative of surface oxidation.     

Characterization of 316 stainless steel surfaces used in BWR recirculation piping

The effect of surface treatments such as sandblasting, acid pickling, and electropolishing on surface topography and composition has been investigated for 316 nuclear grade stainless steel. The build-up of radioactive cobalt-60 on sandblasted surfaces is much higher compared to that on acid pickled surfaces. Compared to sandblasted surfaces, acid pickling produces smooth surfaces and also generates grain boundary grooves, which can be effectively removed by subsequent electropolishing. Sandblasting produces rough and textured surfaces. Electropolishing of such surfaces reduces the roughness but does not produce as smooth a surface as a pickled surface. The techniques used in the surface analyses were scanning electron microscopy (SEM), X-ray energy spectroscopy (XES), and Auger electron spectroscopy (AES).     

The iodine-induced strain rate sensitivity of Zircaloy fuel rod cladding

The strain rate sensitivities and failure times characteristic of iodine-induced stress corrosion cracking of Zircaloy fuel rod cladding are important because they can be related to certain power ramping rates which may increase fuel rod failure probabilities. The CCSCC model developed in this paper approximates these failure characteristics by simulating the transition from the slower (less observable) non-corrosive creep cracking (CC) regime to the faster (more observable) stress corrosion cracking (SCC) regime. Components of the CCSCC model include: ZrI₄ production by chemical reaction between Zircaloy and iodine; diffusion of the ZrI₄ to the crack tip; chemisorption, embrittlement, and damage accumulation at the crack tip; and crack initiation times and growth rates.Results indicate that the Zr-I₂ SCC process is dominated by competition between chemical reaction and material creep rate phenomena, rather than by stress thresholds or by the requirement that a complete monolayer of ZrI₄ form on the exposed Zircaloy surface at the crack tip. Failure times are dominated by the time required to initiate active crack growth. The SCC process is apparently not limited by diffusion kinetics on the time scale of laboratory experiments. Conflicting results were found concerning the chemical reaction rate at the crack tip.     

Adsorption behaviour of H2 and CO on inconel 600 surfaces under laser-induced thermal desorption

Laser-induced thermal desorption (LITD) has been used to determine the desorption energy of CO and H₂ on Inconel 600 surfaces. Isothermal curves have been measured between 300 K and 450 K., which give a value of 71 kJ mol for H₂/Inconel 600. In the case of the CO adsorption a rapidly growing chromium oxide layer at the surface due to the laser shots was found by monitoring the surface composition changes in between by Auger electron spectroscopy (AES). From experimental recoverage times and equilibrium coverages, values ranging between 92 and 82 kJ mol were derived for the desorption energy of CO/Inconel 600. The variation of the desorption energy is correlated with the oxidation degree of the Inconel surface.     

Sputtering of silicon carbide coatings by low-energy hydrogen ions

Various types of silicon carbide coatings made by reactive ion-plating have been bombarded with a 3.0 keV H⁺₃ ion beam at temperatures around 500°C. The sputtering yield in stoichiometric samples (i.e. Si : C = 1 : 1) at 500°C was $\text{1.15 × 10}{}^{\mathrm{?2}}$ atoms/H⁺. As the stoichiometry deviates from this point, the sputtering yield has larger values. The temperature dependence of the sputtering yield in stoichiometric samples was negligible below 600°C. No surface topography changes occurred in stoichiometric samples even at a high fluence of $\text{2 × 10}{}^{20}\text{H}{}^{\mathrm{+}}\text{/cm}{}^2$, while severe erosion took place in non-stoichiometric samples. By Auger electron spectroscopy (AES), carbon exists on the surface in the form of carbide in stoichiometric SiC before and after bombardment, while it exists in the form of graphite in carbon rich samples, which suggests that the bound state of carbon in the form of carbide should correspond to the low sputtering yield in stoichiometric SiC coatings. The surface stoichiometry changes due to hydrogen bombardment were observed by AES, where the carbon population increases in stoichiometric SiC, while it decreases in carbon rich samples, which was supported as well by the results from electron probe X-ray microanalysis.     

Laser sputtering: Part I. On the existence of rapid laser sputtering at 193 nm

Irradiation, i.e.bombardment, with 193 nm laser pulses having an energy fluence of 2.5 $\text{J}\text{cm}{}^2$ and a duration of ~12 ns leads to rapid sputtering with Au, Al₂O₃, MgO, MgO. Al₂O₃, SiO₂, glass and LaB₆, relatively slow sputtering with MgF₂ and diamond, and mainly thermal-stress cracking with W. Scanning electron microscopy (SEM) suggests that the mechanism for the sputtering of Au in either vacuum or air is one based on the hydrodynamics of molten Au, while an SEM-derived surface temperature estimate confirms that thermal sputtering (which might have been expected) is not possible. SEM with W shows that the near total lack of material removal is due to the thermal-stress cracking not leading to completed exfoliation, together with the surface temperature being too low for either hydrodynamical or thermal processes. Corresponding SEM with Al₂O₃ shows, in the case of specimens bombarded in vacuum, topography of such a type that all mechanisms except electronic ones can be ruled out. The topography of Al₂O₃ or other oxides bombarded in air through a mask is somewhat different, showing craters as for vacuum bombardments but ones which have a cone-like pattern on the bottom.