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Register a new userPreparation of Silver and Silver-backing self-supported thin targets by high vacuum evaporation
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We have produced in the Nuclear Physics Center in Lisbon thin film self-supported targets of Ag, LiF/Ag and CaF$_2$/Ag by a high vacuum resistance evaporation method. The production setup, materials, methods, characterization and results are described.
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Thin uniform arsenic targets suitable for high-fidelity cross section measurements in stacked-target experiments were prepared by electrodeposition of arsenic on titanium backings from aqueous solutions. Electrolytic cells were constructed and capable of arsenic deposits ranging in mass from approximately 1 to 29 mg (0.32-7.22 mg/cm$^2$, 0.57-12.62 $mu$m). Examination of electrodeposit surface morphology by scanning electron microscopy and microanalysis was performed to investigate the uniformity of produced targets. Brief studies of plating growth dynamics and structural properties through cyclic voltammetry were also undertaken. An alternative target fabrication approach by vapor deposition was additionally conducted. We further introduce a non-destructive characterization method for thin targets by neutron activation, which is independent of neutron flux shape, environmental factors, and source geometry, while correcting for any potential scatter or absorption effects.
Self Supporting isotopically enriched $^{116}$Sn (~380 microgram/cm$^2$), $^{124Sn}$ (~400 microgram/cm$^2$) and $^{112}$Sn (1.7 mg/cm$^2$), $^{120}$Sn (1.6 mg/cm$^2$) have been prepared using resistive heating and Mechanical rolling methods respectively at Variable Energy Cyclotron Centre(VECC). Preparation of enriched targets with small amount of material, selection of releasing agent for thin targets and separation of deposited material in solvent were among the several challenges while fabrication of thin targets .These targets has been successfully used in Nuclear Physics Experiments at VECC.
Noble gas permeabilities and diffusivities of Kapton, butyl, nylon, and Silver Shield are measured at temperatures between 22C and 115C. The breakthrough times and solubilities at 22C are also determined. The relationship of the room temperature permeabilities to the noble gas atomic radii is used to estimate radon permeability for each material studied. For the noble gases tested, Kapton and Silver Shield have the lowest permeabilities and diffusivities, followed by nylon and butyl, respectively.
We have used the two-step growth technique, quench condensing followed by an anneal, to grow ultra thin films of silver on glass substrates. As has been seen with semiconductor substrates this process produces a metastable homogeneous covering of silver. By measuring the in situ resistance of the film during growth we are able to see that the low temperature growth onto substrates held at 100 Kelvin produces a precursor phase that is insulating until the film has been annealed. The transformation of the precursor phase into the final, metallic silver film occurs at a characteristic temperature near 150K where the sample reconstructs. This reconstruction is accompanied by a decrease in resistance of up to 10 orders of magnitude.
Light-matter interaction at the atomic scale rules fundamental phenomena such as photoemission and lasing, while enabling basic everyday technologies, including photovoltaics and optical communications. In this context, plasmons --the collective electron oscillations in conducting materials-- are important because they allow manipulating optical fields at the nanoscale. The advent of graphene and other two-dimensional crystals has pushed plasmons down to genuinely atomic dimensions, displaying appealing properties such as a large electrical tunability. However, plasmons in these materials are either too broad or lying at low frequencies, well below the technologically relevant near-infrared regime. Here we demonstrate sharp near-infrared plasmons in lithographically-patterned wafer-scale atomically-thin silver crystalline films. Our measured optical spectra reveal narrow plasmons (quality factor $sim4$), further supported by a low sheet resistance comparable to bulk metal in few-atomic-layer silver films down to seven Ag(111) monolayers. Good crystal quality and plasmon narrowness are obtained despite the addition of a thin passivating dielectric, which renders our samples resilient to ambient conditions. The observation of spectrally sharp and strongly confined plasmons in atomically thin silver holds great potential for electro-optical modulation and optical sensing applications.
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