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Register a new userFlux dependent 1.5 MeV self-ion beam induced sputtering from Gold nanostructured thin films
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J. Ghatak
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We discuss four important aspects of 1.5 MeV Au2+ ion-induced flux dependent sputtering from gold nanostrcutures (of an average size 7.6 nm and height 6.9 nm) that are deposited on silicon substrates: (a) Au sputtering yield at the ion flux of 6.3x10^12 ions cm-2 s-1 is found to be 312 atoms/ion which is about five times the sputtering yield reported earlier under identical irradiation conditions at a lower beam flux of 10^9 ions cm-2 s-1, (b) the sputtered yield increases with increasing flux at lower fluence and reduces at higher fluence (1.0x10^15 ions cm-2) for nanostructured thin films while the sputtering yield increases with increasing flux and fluence for thick films (27.5 nm Au deposited on Si) (c) Size distribution of sputtered particles has been found to vary with the incident beam flux showing a bimodal distribution at higher flux and (d) the decay exponent obtained from the size distributions of sputtered particles showed an inverse power law dependence ranging from 1.5 to 2.5 as a function of incident beam flux. The exponent values have been compared with existing theoretical models to understand the underlying mechanism. The role of wafer temperature associated with the beam flux has been invoked for a qualitative understanding of the sputtering results in both the nanostructured thin films and thick films.
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We report a direct observation of segregation of gold atoms to the near surface regime due to 1.5 MeV Au2+ ion impact on isolated gold nanostructures deposited on silicon. Irradiation at fluences of 6x10^13, 1x10^14 and 5x10^14 ions cm-2 at a high beam flux of 6.3x1012 ions cm-2 s-1 show a maximum transported distance of gold atoms into the silicon substrate to be 60, 45 and 23 nm, respectively. At a lower fluence (6x1013 ions cm-2) transport has been found to be associated with the formation of gold silicide (Au5Si2). At a high fluence value of 5x10^14 ions cm-2, disassociation of gold silicide and out-diffusion lead to segregation of gold to defect - rich surface and interface region.
Enhanced diffusion of gold atoms into silicon substrate has been studied in Au thin films of various thicknesses (2.0, 5.3, 10.9 and 27.5 nm) deposited on Si(111) and followed by irradiation with 1.5 MeV Au2+ at a flux of 6.3x10^12 ions cm-2 s-1 and fluence up to 1x10^15 ions cm-2. The high resolution transmission electron microscopy measurements showed the presence of gold silicide formation for the above-mentioned systems at fluence greater than equal to 1x1014 ions cm-2. The maximum depth to which the gold atoms have been diffused at a fluence of 1x10^14 ions cm-2 for the cases of 2.0, 5.3, 10.9 and 27.5 nm thick films has been found to be 60, 95, 160 and 13 nm respectively. Interestingly, at higher fluence of 1x1015 ions cm-2 in case of 27.5 nm thick film, gold atoms from the film transported to a maximum depth of 265 nm in the substrate. The substrate silicon is found to be amorphous at the above fluence values where unusually large mass transport occurred. Enhanced diffusion has been explained on the basis of ion beam induced, flux dependent amorphous nature of the substrate, and transient beam induced temperature effects. This work confirms the absence of confinement effects that arise from spatially confined structures and existence of thermal and chemical reactions during ion irradiation.
We report a direct observation of dramatic mass transport due to 1.5 MeV Au2+ ion impact on isolated Au nanostructures of an average size 7.6 nm and a height 6.9 nm that are deposited on Si (111) substrate under high flux (3.2x10^10 to 6.3x10^12 ions cm-2 s-1) conditions. The mass transport from nanostructures found to extend up to a distance of about 60 nm into the substrate, much beyond their size. This forward mass transport is compared with the recoil implantation profiles using SRIM simulation. The observed anomalies with theory and simulations are discussed. At a given energy, the incident flux plays a major role in mass transport and its re-distribution. The mass transport is explained on the basis of thermal effects and creation of rapid diffusion paths at nano-scale regime during the course of ion irradiation. The unusual mass transport is found to be associated with the formation of gold silicide nanoalloys at sub-surfaces. The complexity of the ion-nanostructure interaction process has been discussed with a direct observation of melting (in the form of spherical fragments on the surface) phenomena. The transmission electron microscopy, scanning transmission electron microscopy and Rutherford backscattering spectroscopy methods have been used.
We report on an XPS study of AlN thin films grown on Si(100) substrates by ion beam sputter deposition (IBSD) in reactive assistance of N+/N2+ ions to unravel the compositional variation of their surface when deposited at different substrate temperatures. The temperature of the substrate was varied as room temperature (RT), 100oC and 500oC. The binding energy of Al-2p, N-1s and O-1s core electrons indicate the formation of 2H polytypoid of AlN. The increase in concentration of AlN with substrate temperature during deposition is elucidated through detailed analysis with calculated elemental atomic concentrations (at. %) of all possible phases at the film surface. Our results show that predominate formation of AlN as high as 74 at. % is achievable using substrate temperature as the only process parameter. This high fraction of AlN in thin film surface composition is remarkable when compared to other growth techniques. Also, the formation of other phases is established based on their elemental concentrations.
The plasmonic properties of vacuum evaporated nanostructured gold thin films having different types of nanoparticles are presented. The films with more than 6 nm thickness show presence of nanorods having non cylindrical shape with triangular base. Two characteristics plasmon bands have been recoreded in absorption spectra. First one occurs below 500 nm and other one at higher wavelength side. Both the peaks show dependence on the dielectric property of surroundings. The higher wavelength localized surface plasmon resonance (LSPR) peak shifts to higher wavelength with an increase in the nanoparticle size, surface roughness and refractive index of the surrounding (Methylene Blue dye coating). This shows that such thin films can be used as sensor for organic molecules with a refractive index sensitivity ranging from 250 - 305 nm/RIU (Refractive Index Unit).
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