Historical research guide · 0452 · 2005
Analysis of Ni-hydride thin film after surface plasmons generation by laser technique
V. Violante · E. Castagna · C. Sibilia · S. Paoloni · F. Sarto
In one minute
Vittorio Violante and colleagues at ENEA Frascati and Rome’s Sapienza took a sputtered nickel film, loaded it with hydrogen in forty minutes of ordinary-water electrolysis, then shone a helium-neon laser at it through a lens coupler so the light would hand its energy to surface plasmons — the collective sloshing of the metal’s own electrons across its surface. Two things followed. The angle at which the film swallowed the laser light moved and broadened, which says the electronic structure of the metal had changed and a hydride phase had formed. Then, after three hours under the beam, a secondary-ion mass spectrometer found the copper impurity in the film carrying the wrong isotopes: the copper-63 to copper-65 ratio had shifted by 1360 per cent, the heavier isotope now the abundant one, while the un-loaded control film kept the natural ratio. The team read that as the signature of a nuclear process in condensed matter triggered electrodynamically, by plasmons, and asked for it to be repeated.
Connection
Chapter 12 is about getting nuclear work out of ordinary matter by changing its electromagnetic environment rather than by heat and pressure, and this is one of the experiments that puts an instrument on the exact object the theory needs: the surface plasmon on a loaded hydride. Violante’s team excites that plasmon deliberately with a laser and then goes looking downstream for a nuclear fingerprint — which is the same causal chain Widom and Larsen write down as equations.
From the source
Surface plasmons — quanta of the collective oscillation of the electrons on a metal surface — cannot be excited by simply shining light on a smooth surface, because a photon and a plasmon cannot satisfy energy and momentum conservation at the same time there. The paper uses the attenuated total reflection method with a lens coupler, which bends the light line until it crosses the plasmon dispersion curve; deliberate roughness or a grating does the same job by adding a wave-vector increment. The resonance shows up as a minimum in reflected intensity at an incidence angle beyond the total-reflection angle, and only p-polarised light works, because s-polarised light gives the same field on both sides of the interface and produces no charge displacement.Sections 2 and 3, Equations 20 to 27, Figures 4 to 7
The paper states the link between the surface plasmon and vacuum energy in one line: the change in zero-point energy of the surface plasmon oscillator system corresponds precisely to the classical image potential energy, so an external point charge induces exactly the polarisation charge density a set of surface plasmons would. A strong local electric field enhancement arises whenever the plasmons are excited, and the authors note it can be derived classically or quantum-mechanically.Section 1, Introduction, with references 2 and 3
The optical constants are tabulated for four metals at 632 nanometres. Nickel has a complex dielectric function of about minus 9 plus 14i, a plasmon propagation length along the surface of 3.8 micrometres, a penetration depth of about 0.4 micrometres into the dielectric and about 0.03 micrometres into the metal — silver, by comparison, propagates about 88 micrometres. Those numbers set how far the excited surface layer extends, and they are what make the effect a surface-and-near-surface phenomenon rather than a bulk one.Table 2.1
After forty minutes of electrolysis in one molar lithium sulphate in light water, at 10 to 30 milliamps, the reflectance minimum of the nickel film shifts in angle and its half-height width increases. The authors attribute both to the change in the electronic band structure of the metal caused by the electrons hydrogen adds to the lattice, and conclude on that optical evidence alone that a hydride phase had been created. The blank and the loaded film were sputtered in the same run, so they differ only by the loading.Section 6, Experimental results, Figure 11
Both films were then held under the helium-neon beam at the reflectance-minimum angle for about three hours and analysed by secondary-ion mass spectrometry, with copper chosen as the marker because it has only two isotopes and no overlapping masses. The blank shows copper-63 more abundant, as nature has it. The loaded film shows the ratio changed by 1360 per cent, with copper-65 the abundant isotope. The shift held at more than ten separate points on the sample and persisted 200 ångströms down, half the film thickness, which rules out a surface or substrate artefact; the authors also rule out nickel-hydride mass overlap, since the greater abundance of nickel-62 over nickel-64 would have pushed mass 63 up more than mass 65.Section 7, SIMS analysis, Figures 12 to 14
What to watch: the authors call the result a clear signature of a low-energy nuclear reaction occurring in condensed matter under the electrodynamic trigger of plasmons-polaritons, and propose that the local electromagnetic field the plasmons create is also what carries energy from the composite nucleus into the lattice, by acting on the decay process. They then say plainly that the result should be considered preliminary and must be repeated to separate the role of the electrolysis from the role of the laser. The measurement that would settle it is the one they name: cross-analysis by secondary-ion mass spectrometry and neutron activation analysis on films where loading and illumination are varied one at a time.Section 8, Conclusions
The way in
https://doi.org/10.1142/9789812701510_0035How to cite it
V. Violante, E. Castagna, C. Sibilia, S. Paoloni, F. Sarto (2005) Analysis of Ni-hydride thin film after surface plasmons generation by laser technique doi:10.1142/9789812701510_0035