Varsha Bhattacharyya

Effect of nitrogen ion bombardment on copper-gold interface

Abstract A 60 nm film of copper was deposited on a gold foil and a 60 nm film of gold was deposited on a copper foil. Both films were subjected to N2+ ion bombardment at a dose of 5 × 1016 ions cm−2, at an accelerated voltage of 150 kV. Both the films were studied by means of Auger depth profiling. XPS and SEM observations were also taken when both gold and copper were consistently seen. It is observed that the interface is less disturbed when implantation is from the gold side. Secondly, copper forms metastable bonds with nitrogen bubbles are formed when the remains only as an interstitial in the gold matrix. It is observed that nitrogen bubbles are formed when the bombardment is from the copper side. This has been explained on the basis of radiation induced segregation of nitrogen at the grain boundaries, surfaces and interfaces.

Substrate dependence in the formation of TiO2 nanophases by dense electronic excitation

Irradiation by swift heavy ion (SHI) is an excellent tool for the nanostructuring of thin films. During SHI irradiation, the energy of the projectile is transferred to the target mainly via electronic energy loss (Se). If the value of Se is more than a threshold value Seth, then latent tracks are formed in the target and a large amount of deposited energy gets confined in narrow dimensions. This leads the system to a non-equilibrium state and it then relaxes dynamically by inducing nucleation of nanocrystallites along the latent tracks. In the present investigation, amorphous thin films of TiO2 are deposited on substrates of fused silica and that of single crystal sapphire. The films are then irradiated by a 100 MeV Au ion beam. Atomic force microscopy is employed for the surface study. The structural phase change induced by SHI irradiation is identified by glancing angle x-ray diffraction. Optical characterization is carried out by UV?vis absorption spectroscopy. Defects created during irradiation are studied by electron spin resonance spectroscopy studies. The role of a substrate in the SHI-induced nanocrystallization process is studied.

Effect of nitrogen ion bombardment at copper-alumina interface

Abstract A thin film of copper 60 nm thick was deposited on an alumina substrate. One piece of this film was subjected to bombardment of N + 2 ions of 40 keV energy at a dose of 5×10 16 ions cm −2 and the other piece of the same film was subjected to high power Q-switched laser pulses at a density of 2.4 J cm −2 ; in liquid nitrogen. The two samples were studied by XPS and SEM. It was observed that a drastic mixing in the neighbourhood of interface has taken place for the laser treated sample whereas in case of N + 2 bombardment the mixing at the interface was found to be less. It was observed that in the case of laser bombardment, there was preferential bond formation of copper with carbon deposited from inside the evaporation system. Further in the case of laser implantation, nitrogen did not penetrate beyond 30 nm and there exist two types of radiation induced segregations in both the cases giving rise to multiple peaks in the depth distribution of nitrogen.

Study of Swift Heavy Ion Irradiation Induced Nanophases of TiO2

Ion beam irradiation is a unique non-equilibrium technique for phase formation and material modification. Localized rise in temperature and ultra fast (~1012 s) dissipations of impinging energy make it an attractive tool for nanostructure synthesize. Dense electronic excitation induced spatial and temporal confinement of high energy in a narrow dimension leads the system to a highly non-equilibrium state and the system then relaxes dynamically inducing nucleation of nanocrystals along the latent track. In the present investigation, amorphous thin films of TiO2 are irradiated by 100 MeV Ag ion beam. These irradiated thin films are characterized by Atomic Force Microscopy (AFM), Glancing Angle X-ray Diffraction (GAXRD), Transmission Electron Microscopy (TEM) and UV-VIS absorption spectroscopy. AFM and TEM studies indicate formation of circular nanoparticles of size 10±2 nm in a film irradiated at a fluence of 1×1012 ions.cm-2. Nanophase formation is also inferred from the blueshift observed in UV-VIS absorption band edge.

Work function changes of W(110) with temperature and Sm adsorption using electron beam retarding potential technique

Abstract We have studied the work function changes (ΔΦ) of W(110) by Sm adsorption as a function of Sm thickness at room temperature and also that of the Sm-covered W(110) as a function of temperature. The work function change was monitored using the electron beam retarding potential technique in conjunction with low energy electron diffraction (LEED). It is found that the work function of W(110) decreases rapidly at lower dose (0.75 A) of Sm, touches a minima (ΔΦ=0.32 eV), then increases slightly and is saturated with further Sm dosing. Besides, it was also found that the work function of W(110) reduces by 0.3 eV at a particular dose of Sm with substrate temperature up to 523 K. These results show a strong dependence of the work function of W(110) on its temperature and adsorption of Sm and this can be used to advantage in the making of emitters.

Radiation-assisted interactions between gold and copper across a nickel barrier☆

Abstract Previously we had studied the effect of nitrogen bombardment on the interface of thin electrodeposited films of copper and gold. In practical applications thin films of nickel are used between as barrier layers. Extensive interdiffusion was observed between gold and copper layers under the influence of ion bombardment, without practically disturbing the nickel layer between. The resulting composition after bombardment from the copper side is discussed and a mechanism for the process is suggested.

Synthesis of embedded titanium dioxide nanoparticles by oxygen ion implantation in titanium films

Thin films of titanium of 100nm thickness are deposited on fused silica substrates. These films are implanted by oxygen ions with implantation energy of 60keV obtained from ECR based highly charged ion accelerator. The implanted films are later annealed in a tube furnace to establish nanophase formation. The post implanted annealed films are characterized by UV-Visible Spectroscopy and Glancing Angle X-ray Diffraction technique (GAXRD). The phase formed and particle size is determined by GAXRD. Nanoparticle formation is confirmed by the UV-VIS spectroscopic analysis that shows quantum size effects in the form of a blue shift in the band-gap energy of titanium-oxide.

The effects of the crystal structure of a thin barrier on radiation assisted interaction between Au and Cu thin films

Abstract 20 nm of iron, cobalt and nickel films were deposited on three samples of gold film substrates. 60 nm of copper film was deposited on these thin films of iron, cobalt and nickel. The samples thus prepared were bombarded by 150 keV N ions, and were studied by means of XPS, Auger depth profiling and scanning Auger imaging. It was observed that nickel proves to be a better barrier although copper diffuses into gold without involvement of nickel. Iron also acts as a barrier to a lesser extent whereas grains of cobalt (oriented with 0001 planes at right angles to the direction of implantation) collapse under bombardment.