Silicide formation by Ar+ ion bombardment of Pd/Si

Palladium films, 45 nm thick, evaporated on to Si(111) were irradiated to various doses with 78 keV Ar⁺ ions to promote silicide formation. Rutherford backscattering spectroscopy (RBS) shows that intermixing has occurred across the Pd/Si interface at room temperature. The mixing behaviour is increased with dose which coincides well with the theoretical model of cascade mixing. The absence of deep RBS tails for palladium and the small area of this for silicon spectra indicate that short-range mixing occurs. From the calculated damage profiles computed with TRIM code, the dominant diffusion species is found to be silicon atoms in the Pd/Si system. It is also found that the initial compound formed by Ar⁺ irradiation is Pd₂Si which increases with dose. At a dose of 1×10¹⁶ Ar⁺ cm^–2, a 48 nm thickness of Pd₂Si was formed by ion-beam mixing at room temperature.     

Kinetics of ion-beam mixing at Ti-Si interfaces

Ion-beam mixing at Ti-Si interfaces induced by krypton ions has been studied as a function of fluence and temperature by means of sheet resistivity measurements and a 2 MeV⁴He⁺ Rutherford backscattering spectrometry. For mixing induced by 200 keV Kr⁺, substrate temperatures during irradiation between 30 and 400° C and with fluences ranging from 1.0×10¹⁵ to 7.5×10¹⁵ Kr⁺/cm², the amount of mixing has a linear fluence dependence at low fluences and square-root fluence dependence at high fluences. Above 100° C, the mixing is strongly temperature dependent. The activation energy for the temperature-dependent part is 0.115 eV. Also, 300 keV Kr⁺ ion mixing at room temperature with fluences ranging from 2.5×10¹⁶ to 1.0×10¹⁷ Kr⁺/cm² displays a linear fluence dependence in this fluence range and the formation of nonuniform Ti _x Si_1–x layers.     

Formation of Ni2Si silicide in Ni/Si bilayers by ion beam mixing

We have studied ion mixing in Ni-Si(1 1 1) bilayers using noble gas ions. Thin Ni films of 45 nm thickness, deposited on a Si (1 1 1) substrate, were irradiated with 175 keV Kr and 110 keV Ar ions at the same fluence of 4×10¹⁶ ions/cm² at room temperature. The formation of the mixing and the elemental depth profile were investigated by Rutherford backscattering spectrometry. In the Ar irradiated sample, there was no structural change. On the other hand, we have noted the formation of Ni₂Si for the sample irradiated with Kr ions. X-ray diffraction measurements confirmed the formation of the Ni₂Si phase. The surface morphology of the Kr irradiated sample was also studied by scanning electron microscopy.     

Effect of oxygen on the wettability of sapphire by liquid palladium

The surface tension of liquid palladium and the contact angle between liquid palladium and sapphire have been measured at 1833 K as a function of oxygen pressure by the sessile drop method. Oxygen acted as a surface-active element on the surface of liquid palladium and at the interface between liquid palladium and sapphire, resulting in the decrease of the surface tension and the contact angle. The work of adhesion calculated from their values increased with increasing oxygen pressure, and had a constant value above 400 Pa. The maximum excess concentration of oxygen was estimated to be 7.3×10^–6 mol m^–2 for the surface and 6.9×10^–6 mol m^–2 for the interface.     

Irradiation-induced gold silicide formation and stoichiometry effects in ion beam-mixed layer

The irradiation-induced silicide formation in ion beam-mixed layer of Au/Si(1 0 0) system was investigated by using 200 keV Kr⁺ and 350 keV Xe⁺ ions to fluences ranging from 8×10¹⁴ to 1×10¹⁶ ions/cm² at room temperature. The thickness of Au layer evaporated on Si substrate was ∼500 Å. Rutherford backscattering spectrometry (RBS) experiments were carried out to study the irradiation effects on the mixed layers. We observed that at the fluence of 1×10¹⁶ Kr⁺/cm² and starting from the fluence of 8×10¹⁴ Xe⁺/cm², a total mixing of the deposited Au layer with Si was obtained. RBS data corresponding to the fluences of 1×10¹⁶ Kr⁺/cm² and 8×10¹⁴ Xe⁺/cm² clearly showed mixed layers with homogenous concentrations of Au and Si atoms which can be attributed to gold silicides.The samples irradiated to fluences of 1×10¹⁶ Kr⁺/cm² and 1×10¹⁶ Xe⁺/cm² were also analyzed by X-ray photoelectron spectroscopy (XPS). The observed chemical shift of Au 4f and Si 2p lines confirmed the formation of gold silicides at the surface of the mixed layers. Au₂Si phase is obtained with Kr⁺ irradiation whereas the formed phase with Xe⁺ ions is more enriched in Si atoms.     

Ar+-induced mixing mechanisms in metal-metal bilayer systems

Ion-beam mixing in Al-Pd, Al-Cr, Pd-Cu, Ag-Cu and Ag-Fe bilayers has been studied using Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES) over an ion dose range between 1 × 10¹⁵ and 1 × 10¹⁶ Ar⁺ cm^–2 at room temperature. RBS and AES results show that the mixing efficiency of the light elements is higher than that of the heavy elements. The mixing efficiency of a heavy element is independent of the heat of mixing energy, while that of a light element has a close relation with the heat of mixing. The experimental results are discussed in terms of cascade mixing and thermal spike mixing.     

Comparison of corrosion behavior of zirconium bombarded with self-ion and molybdenum ion

In order to study the effects of zirconium and molybdenum ion bombardment on the aqueous corrosion behavior of zirconium, one group of specimens was implanted with zirconium ions with ions surface densities ranging from 1 × 10¹⁵ to 2 × 10¹⁷ ions/cm² at about 170 °C, using a metal vapor vacuum arc (MEVVA) source operated at an extraction voltage of 50 kV. The other group of specimens was bombarded with molybdenum ion with ions surface densities ranging from 1 × 10¹⁶ to 5 × 10¹⁷ ions/cm² at about 160 °C, using a MEVVA source operated at an extraction voltage of 40 kV. The valence states and depth distribution of elements in the surface of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), respectively. Polarization curves measurement was employed to evaluate the aqueous corrosion resistance of the zirconium samples in a 1N H₂SO₄ solution. It was found that the aqueous corrosion resistance of zirconium implanted with 5 × 10¹⁶ Zr ions/cm² is the best in first group samples. For molybdenum ion implantation, the aqueous corrosion resistance of samples declined with raising ions surface densities. The natural corrosion potentials of zirconium samples bombarded with self-ions are more negative than that of the as-received zirconium. While, as for molybdenum ion implantation, the results are opposite. Finally, the mechanisms of the corrosion behavior of the zirconium samples implanted with zirconium and molybdenum ions are discussed.     

Ion beam induced interface mixing of Ni on PTFE bilayer system studied by quadrupole mass analysis and electron spectroscopy for chemical analysis

We have investigated interfacial chemistry in a 100 nm Ni on PTFE (polytetrafluoroethylene) bilayer system induced by 120 MeV Au ions with fluences varying from 1 × 10¹² to 5 × 10¹³ ions/cm². In-situ quadrupole mass analysis (QMA) shows emission of Fluorine (F) and different fluorocarbons (C_xF_y) such as CF, CF₃, C₂F₃ etc. during irradiation. Electron spectroscopy for chemical analysis (ESCA) studies show that Ni reacts with chemically reactive species such as F⁻/F and C_xF_y ions or radicals emitted during irradiation forming NiF₂ and metal-polymer complexes (-CFNi-). Rutherford backscattering spectrometry (RBS) was used to analyze the atomic transport at the interface and strong interface mixing is observed at the ion fluence 5 × 10¹³ ions/cm². Atomic force microscopy (AFM) studies before and after irradiation show that surface roughness is increased from 6.9 to 12.4 nm with increasing fluence. Observed results have been explained on the basis of the chemical reactions taking place within molten ion tracks in the polymer and hot zones around the ion paths created in the Ni film. The studies show that swift heavy ion irradiation introduces strong chemical alteration in the system and induces chemical reactions within the ion track, which enhance ion beam mixing in Ni-PTFE bilayer systems.     

Mixing induced by swift heavy ion irradiation at Fe/Si interface

The present work deals with the mixing of metal and silicon by swift heavy ions in high-energy range. Threshold value for the defect creation in metal Fe calculated was found to be ∼ 40 keV/nm. A thin film of Fe (10 nm) was deposited on Si (100) at a pressure of 4 × 10⁻⁸ Torr and was irradiated with 95 MeV Au ions. Irradiation was done at RT, to a dose of 10¹³ ions/cm² and 1 pna current. The electronic energy loss was found to be 29.23 keV/nm for 95 MeV Au ions in Fe using TRIM calculation. Compositional analysis of samples was done by Rutherford backscattering spectroscopy. Reflectivity studies were carried out on the pre-annealed and post-annealed samples to study irradiation effects. Grazing incidence X-ray diffraction was done to study the interface. It was observed that ion beam mixing reactions at RT lead to mixing as a result of high electronic excitations.     

Physicochemical and catalytic properties of palladium supported on poly(o-methoxyaniline)

Palladium was introduced into a conjugated polymer poly(o-methoxyaniline) (POM) by reacting the powdered polymer with aqueous solution of PdCl₂ of low acidity (PdCl₂: 2.3 × 10⁻³ mol/dm³, HCl: 0.66 × 10⁻³ mol/dm³). Various Pd²⁺ complexes with Cl⁻, H₂O, OH⁻ ligands coexisted in this solution but predominated [PdCl₂(H₂O)₂] ones. Several techniques like X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron and Raman spectroscopy, extended X-ray absorption fine structure have been used to characterize the poly(o-methoxyaniline)-Pd systems. In particular, the state of Pd species in the Pd/POM of various content of palladium (2-8 wt.% Pd) and chemical changes in the polymer matrix induced by insertion of palladium were studied. The protonation and redox reactions involved on palladium incorporation resulted in palladium ions and Pd metal in the final samples. Metallic Pd produced due to spontaneous reduction of palladium ions by the polymer formed large crystalline particles 200-1000 nm in size. The Pd²⁺ species in the form of anionic complexes like [PdCl₄]²⁻ acted as the counterions at low content of palladium (2-4 wt.% Pd). At high palladium content (8 wt.% Pd), several atoms like Cl, N and/or O were identified by extended X-ray absorption fine structure (EXAFS) technique in the nearest environment of Pd atoms. The structural groups of POM (like N groups and/or OCH₃) as well as H₂O, OH⁻ molecules are, therefore, considered as probable species in the coordination sphere of palladium. The catalytic properties were studied for the as-prepared Pd/POM and the samples additionally reduced with aqueous solution of NaH₂PO₂. They were used in the hydrogenation of CC bonds in maleic acid (MAC) and CO groups in 2-ethylanthraquinone (eAQ) at 60 °C and atmospheric pressure of hydrogen using xylene-octanol-2 or water medium. The correlation between Pd/POM activities and the content of Pd metal was found. Activation of the as-prepared Pd/POM with NaH₂PO₂ improved their catalytic properties. Much higher and much stable activities were then obtained in both MAC and eAQ hydrogenation reactions.     

Ion irradiation induced modifications of nanostructured Ni–Mn–Sn ferromagnetic shape memory alloy thin films

Thin films of Ni–Mn–Sn ferromagnetic shape memory alloy, grown on Si substrate by DC magnetron sputtering were bombarded by 450 keV Ar^{+ 4} ions at different fluences ranging from 1 × 10¹⁴ to 3 × 10¹⁶ ions/cm² in order to investigate the effect of ion irradiation on characteristic transformation temperatures and thus on shape memory behavior. Temperature dependent resistivity measurements reveal the increase in martensitic transformation temperature (~ 100 K) upto a fluence of 1 × 10¹⁵ ions/cm², above which shape memory behavior degrades and completely loses its behavior at 3 × 10¹⁶ ions/cm², which is ascribed to the amorphization of Ni–Mn–Sn structure at a fluence of 3 × 10¹⁶ ions/cm² as evidenced from X-ray diffraction pattern. The diffuse rings in the electron diffraction pattern also confirmed the amorphization of the film at highest fluence. The temperature dependent magnetization measurements also show the increase in martensitic transformation temperature upto a fluence of 1 × 10¹⁵ ions/cm² in support of resistivity data. This work gives a possibility to acquire a better control on the properties of FSMA thin films using ion irradiation.     

A dilution refrigerator with large cooling power

A dilution refrigerator with sintered copper heat exchangers and a He³ circulation rate of 1.4 × 10⁻⁴ − 3 × 10⁻⁴ mole s⁻¹ is described. The cooling power at 15 mK is 1μW. Construction of the cryostat and the pumping system is discussed in detail. Heat transfer in the exchangers and in the mixing chamber is discussed and measurements of thermal contact between the mixing chamber and an outside load are presented.     

The impact of high-dose implantation into manganin on its thermo-resistance properties under high pressure

Using high-dose implantation into manganin of 253 MeV Kr ions (a surface dose of 2.5×10¹⁵ ion/cm²), as well as 250 keV Bi ions (a surface dose of 10¹⁷ ion/cm²) and 250 keV Kr ions (a surface dose of 10¹⁶ ion/cm²), the pressure and temperature sensitivities of manganin foil have been investigated. It was found that the pressure sensitivity of manganin increased (α=2.45×10⁻⁵ MPa⁻¹ before implantation and α_imp=4.60×10⁻⁵ MPa⁻¹ after complex implantation with 250 keV of Bi and Kr ions, the accuracy of estimation does not exceed 0.01×10⁻⁵ MPa⁻¹) and its temperature sensitivity remained appreciably reduced.     

Electrical and morphological properties of poly(3-hexyl thiophene) irradiated with 100 MeV silver ions

Poly(3-hexyl thiophene) has been prepared by a chemical oxidation process. The pristine polymer was irradiated with various fluences of (silver (Ag⁸⁺)) swift heavy ions viz. 10¹⁰, 10¹¹, and 10¹² ions/cm². All the samples, irradiated and without irradiation, have been characterized by various techniques such as surface electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), FT-IR and UV spectroscopy. The dc conductivity of all the samples has been investigated in 77-300 K. The room temperature conductivity of pristine samples is 2.39 × 10⁻⁸ which increases to 1.65 × 10⁻⁶ Ohm⁻¹ cm⁻¹ at the fluence of 10¹¹ ions/cm². The observed conduction mechanism for all the samples could be explained in terms of Mott's variable range hopping model.     

Effect of sulfide ions on the stress corrosion behaviour of Al-brass and Cu10Ni alloys in salt water

The stress corrosion cracking (SCC) behavior of Al-brass and Cu10Ni alloys was investigated in 3.5% NaCl solution in absence and in presence of different concentrations of Na₂S under open-circuit potentials using the constant slow strain rate technique. The results indicated that the Cu10Ni alloy is more susceptible to stress corrosion cracking than as-received Al-brass at strain rate of 3.5 × 10^–6 s^–1 in 3.5% NaCl in presence of high concentration of sulfide ions (1000 ppm). The sulfide ions (up to 500 ppm) has no effect on the stress corrosion cracking of the annealed Al-brass in 3.5% NaCl at two strain rates of 7.4 × 10^–6 and 3.5 × 10^–6 s^–1. The results support film rupture for Al-brass and sulfide stress corrosion cracking assisted with pitting corrosion for Cu10Ni at slip steps as the operating mechanisms.     

Studies on the optical band gap and cluster size of the polyaniline thin films irradiated with swift heavy Si ions

Polyaniline thin films prepared by RF plasma polymerisation were irradiated with 92 MeV Si ions for various fluences of 1×10¹¹, 1×10¹² and 1×10¹³ ions/cm². FTIR and UV-vis-NIR measurements were carried out on the pristine and Si ion irradiated polyaniline thin films for structural evaluation and optical band gap determination. The effect of swift heavy ions on the structural and optical properties of plasma-polymerised aniline thin film is investigated. Their properties are compared with that of the pristine sample. The FTIR spectrum indicates that the structure of the irradiated sample is altered. The optical studies show that the band gap of irradiated thin film has been considerably modified. This has been attributed to the rearrangement in the ring structure and the formation of CC terminals. This results in extended conjugated structure causing reduction in optical band gap.     

Structural damage studies in conducting indium-tin oxide (ITO) thin films induced by Au swift heavy ions (SHI) irradiation

Spray pyrolysis deposited indium-tin oxide (ITO) thin films were fabricated and irradiated using Au⁸⁺ swift heavy ions (SHI) (100 MeV energy), at different fluency doses ranging between 1×10¹¹ ions/cm² and 1×10¹³ ions/cm². After irradiation, significant changes have been observed in surface morphology and crystallographic structure pertaining to increase in grain size, change in surface roughness, crystallographic disorders of large crystallites, and noticed a net decrease in optical transmittance and electrical resistivity of these films.     

Wear resistance of TiN coatings implanted with Al and N ions

Titanium nitride (TiN) coatings were prepared on HS 6-5-2 high-speed steel cutting inserts and next implanted either with Al ions (fluence 2×10¹⁷ ions/cm²) or with Al and N ions (fluence (1+1)×10¹⁷ ions/cm²) on the rake face. Microhardness and friction coefficient of the implanted surfaces were examined. A noticeable increase of microhardness in Al implanted inserts has been observed.The elemental composition and structural properties of the surface layer were examined by glow discharge optical emission spectroscopy (GDOES) and gliding angle X-ray diffraction (XRD).The tests of turning of 40 H constructional steel with the cutting inserts have shown an improvement in the implanted inserts, especially marked in those implanted with Al+N.     

Phase formation and modification of corrosion property of nitrogen implanted Ti-Al-V alloy

In the present investigation, polished samples were implanted with nitrogen ion at an energy of 60 keV and implantation doses were 1×10¹⁶, 5×10¹⁶, 1×10¹⁷ and 6×10¹⁷ ions/cm². Glancing incidence X-ray diffraction was employed on the implanted specimens to understand the phases formed with increasing dose. The valence states of nitrogen, titanium and carbon on the sample surfaces were analyzed by X-ray photoemission spectroscopy. The corrosion resistance was examined by the electrochemical methods in a solution with pH=10 at room temperature in order to determine the optimum dose that can give good corrosion resistance in a simulated nuclear reactor condition. Scanning electron microscopy was used to observe the topographies of nitrogen-implanted Ti-Al-Zr after potentiodynamic measurement. It was found that implanted nitrogen dissolved in titanium matrix with increasing dose and the resultant nitrides such as TiN and Ti₂N precipitated. Implantation of nitrogen ions into the surface of Ti-Al-V alloy improves its corrosion resistance, and the increase of the corrosion resistance depends on the nitrogen dose employed; the maximum improvement of the corrosion resistance was observed at a dose of 1×10¹⁷ N⁺/cm².     

Hydrogen transport by group 5 metals: Achieving the maximal flux density through a vanadium membrane

Hydrogen transport by 100-μm-thick vanadium and palladium membranes was studied in the pressure range from 1 × 10^?8 to 4.5 × 10^?1 MPa at a temperature of 400°C. Both sides of the vanadium membrane were covered by 2 μm of palladium (Pd-V-Pd) for facilitating the dissociative absorption and associative desorption of H₂ molecules. At low pressures, hydrogen flux densities through vanadium and palladium membranes are nearly the same; at high pressures, the flux through the vanadium membrane becomes 16 times larger than the flux through the palladium membrane and attains a value of 2.4 scc cm^?2 s^?1. This flux of permeating hydrogen is larger than all values ever observed earlier for membranes made of group 5 metals or any other unsupported metal membranes.