Growth of Oriented Au Nanostructures: Role of Oxide at the Interface

We report on the formation of oriented gold nano structures on Si(100) substrate by annealing procedures in low vacuum (\approx10-2 mbar) and at high temperature (\approx 975^{\circ} C). Various thicknesses of gold films have been deposited with SiOx (using high vacuum thermal evaporation) and without SiOx (using molecular beam epitaxy) at the interface on Si(100). Electron microscopy measurements were performed to determine the morphology, orientation of the structures and the nature of oxide layer. Interfacial oxide layer, low vacuum and high temperature annealing conditions are found to be necessary to grow oriented gold structures. These gold structures can be transferred by simple scratching method.Comment: 13 pages, 3 figures, Accepted in J. Appl. Phy

Dynamic and Static Transmission Electron Microscopy Studies on Structural Evaluation of Au nano islands on Si (100) Surface

Transmission electron microscopy (TEM) study on morphological changes in gold nanostructures deposited on Si (100) upon annealing under different vacuum conditions has been reported. Au thin films of thickness ~2.0 nm were deposited under high vacuum condition (with the native oxide at the interface of Au and Si) using thermal evaporation. In-situ, high temperature (from room temperature (RT) to 850\degreeC) real time TEM measurements showed the evaluation of gold nanoparticles into rectangular/square shaped gold silicide structures. This has been attributed to selective thermal decomposition of native oxide layer. Ex-situ annealing in low vacuum (10-2 mbar) at 850\degreeC showed no growth of nano-gold silicide structures. Under low vacuum annealing conditions, the creation of oxide could be dominating compared to the decomposition of oxide layers resulting in the formation of barrier layer between Au and Si.Comment: 15 pages, 4 figure

Nanodot to Nanowire: A strain-driven shape transition in self-organized endotaxial CoSi2 on Si (100)

We report a phenomenon of strain-driven shape transition in the growth of nanoscale self-organized endotaxial CoSi2 islands on Si (100) substrates. Small square shaped islands as small as 15\times15 nm2 have been observed. Islands grow in the square shape following the four fold symmetry of the Si (100) substrate, up to a critical size of 67 \times 67 nm2. A shape transition takes place at this critical size. Larger islands adopt a rectangular shape with ever increasing length and the width decreasing to an asymptotic value of ~25 nm. This produces long wires of nearly constant width.We have observed nanowire islands with aspect ratios as large as ~ 20:1. The long nanowire heterostructures grow partly above (~ 3 nm) the surface, but mostly into (~17 nm) the Si substrate. These self-organized nanostructures behave as nanoscale Schottky diodes. They may be useful in Si-nanofabrication and find potential application in constructing nano devices.Comment: 9 pages, 7 figure

RP-HPLC METHOD DEVELOPMENT AND VALIDATION FOR SIMULTANIOUS ESTIMATION AND FORCED DEGRADATION STUDIES OF LAMIVUDINE AND RALTEGRAVIR IN SOLID DOSAGE FORM

Objective: A stability indicating reverse phase high-performance liquid chromatography (RP-HPLC) method was developed and validated for the estimation of the combined tablet formulation of lamivudine (LAM) and raltegravir (RAL) in dosage forms and its API.Methods: Chromatographic separation was achieved on inertsil ODS C18 5 µm (4.6 X 150 mm) using a mobile phase (MP) consisting of a mixture of mixed orthophosphoric acid (OPA): acetonitrile (ACN) in the ratio 50:50 v/v which was determined at 242 nm respectively. Results: The assay of LAM and RAL was performed with tablets, and the % assay was found to be 100.12 and 99.89 which shows that the method is useful for routine analysis. The linearity of LAM and RAL was found to be linear with a correlation coefficient of 0.998 and 0.999, which shows that the method is capable of producing good sensitivity. The retention time of LAM and RAL was 1.99 min and 4.34 min respectively; linearity range was found to lie from 15 µg/ml to 75 µg/ml for LAM, 30 µg/ml to 150 µg/ml for RAL with a correlation coefficient of 0.999 respectively. Forced degradation studies were conducted in acidic, basic, thermal, photolytic and peroxide where all the degradation peaks were monitored.Conclusion: The proposed HPLC method was found to be simple, specific, precise, accurate, rapid and economical for simultaneous estimation of LAM and RAL in bulk and tablet dosage form. Thus the validated economical method was applied for forced degradation study of LAM and RAL tablet

Origin of Shifts in the Surface Plasmon Resonance Frequencies for Au and Ag Nanoparticles

Origin of shifts in the surface plasmon resonance (SPR) frequency for noble metal (Au, Ag) nanoclusters are discussed in this book chapter. Spill out of electron from the Fermi surface is considered as the origin of red shift. On the other hand, both screening of electrons of the noble metal in porous media and quantum effect of screen surface electron are considered for the observed blue shift in the SPR peak position.Comment: 37 pages, 14 Figures in the submitted book chapter of The Annual Reviews in Plasmonics, edited by Professor Chris D. Geddes. Springer Scinec

Evaluation of thermogravimetric analysis as a rapid tool for the detection of rhizobacteria biostimulants used in precision agriculture

Publication history: Accepted - 31 October 2020; Published online - 17 January 2021Six-week-old root samples were evaluated using high resolution (maximum resolution [MaxRes]) thermogravimetric analyses (TGA) of the cell wall compositions of Gram-positive (Bacillus mucilaginosus, Bacillus amyloliquefaciens, and Bacillus subtilis) and Gram-negative (Burkholderia sp., Rahnella aquatilis strain H 2.6, and R. aquatilis strain RC 2.5) root colonizing plant growth promoting rhizobacteria (PGPR) commercial inoculant strains (biostimulants) applied to pot grown wheat plants. TGA discriminated the strains within the two types of rhizobacterial cohorts and thus provided a rapid non-molecular means for the detection of PGPR inoculant biostimulants within hours of root sampling. The latter was due to the greater degree of definition of TGA fingerprints of individual thermal weight loss events occurring over a degradation range, and heightened the corresponding peak temperature divergences within strains of either type of bacteria themselves for their unequivocal identification. Confirmation of biostimulant rhizobacteria identity in concomitant root samples was achieved through either cultural methods or direct tissue PCR molecular protocols within 5 days and 2 days of sampling, respectively. The results suggested that MaxRes TGA could serve as a rapid, inexpensive stand-alone tool or as combinatorial utility alongside pyrolysis gas chromatography mass spectra, and Fourier transform infrared analytics for the early detection of PGPR biostimulants in precision farmingWe thank EU-BIOFECTOR (Grant Agreement No. 312117) funded by the European Commission within the 7th Framework Programme, and the Department of Agriculture, Environment and Rural Affairs (DAERA), Northern Ireland, UK for their Evidence and Innovation grant (activity 48125) to carry out the study at the Agri-Food & Biosciences Institute laboratories (AFBINI.GOV.UK

Temperature-dependent electron microscopy study of Au thin films on Si (100) with and without native oxide layer as barrier at the interface

Real time electron microscopy observation on morphological changes in gold nano structures deposited on Si (100) surfaces as a function of annealing temperatures has been reported. Two types of interfaces with the substrate silicon were used prior to gold thin film deposition: (i) without native oxide and on ultra-clean reconstructed Si surfaces and (ii) with native oxide covered Si surfaces. For a \approx 2.0 nm thick Au films deposited on reconstructed Si(100) surfaces using molecular beam epitaxy method under ultra high vacuum conditions, aligned four-fold symmetric nanogold silicide structures formed at relatively lower temperatures (compared with the one with native oxide at the interface). For this system, 82% of the nanostructures were found to be nano rectangles like structures with an average length \approx 27 nm and aspect ratio of 1.13 at \approx 700{\deg}C. For \approx 5.0 nm thick Au films deposited on Si (100) surface with native oxide at the interface, formation of rectangular structures were observed at higher temperatures (\approx 850{\deg} C). At these high temperatures, desorption of the gold silicide followed the symmetry of the substrate. Native oxide at the interface was found to act like a barrier for the inter-diffusion phenomena. Structural characterization was carried out using advanced electron microscopy methods.Comment: 27 pages, 7 figures, 1 Tabl

Nano scale phase separation in Au-Ge system on ultra clean Si(100) surfaces

We report on the formation of lobe-lobe (bi-lobed) Au-Ge nanostructures under ultra high vacuum (UHV) conditions (\approx 3\times 10^{-10} mbar) on clean Si(100) surfaces. For this study, \approx 2.0 nm thick Au samples were grown on the substrate surface by molecular beam epitaxy (MBE). Thermal annealing was carried out inside the UHV chamber at temperature \apprx 500{\deg}C and following this, nearly square shaped Au_{x}Si_{1-x} nano structures of average length \approx 48 nm were formed. A \approx 2 nm Ge film was further deposited on the above surface while the substrate was kept at a temperature of \approx 500{\deg}C. Well ordered Au-Ge nanostructures where Au and Ge residing side by side (lobe-lobe structures) were formed. In our systematic studies, we show that, gold-silicide nanoalloy formation at the substrate (Si) surface is necessary for forming phase separated Au-Ge bilobed nanostructures. Electron microscopy (TEM, STEM-EDS, SEM) studies were carried out to determine the structure of Au - Ge nano systems. Rutherford backscattering Spectrometry measurements show gold inter-diffusion into substrate while it is absent for Ge.Comment: 23 pages, 6 Figures, 1 Tabl