Infrared Monitoring of Diamond Metalization

Abstract

The ultra-high-vacuum growth of thin chromium and aluminum films on single diamond crystals at various temperatures was monitored by means of infrared spectroscopy, which provides instant information on electronic and morphological properties of the produced metal films. In accordance with atomic force microscopy results, spectra for Al indicate a clear island-like growth in the beginning followed by a transition to a continuous layer. Cr growth results in much smoother films because of a special growth mechanism. Analysis of infrared spectra of both kinds of ultrathin metal layers yields a high DC conductivity well above 10(6) S/m starting from only a few nanometers thickness for sufficiently high substrate temperatures.

Impact of Metal-Optical Properties on Surface-Enhanced Infrared Absorption

“…On the basis of the analysis of the slope according to ref we conclude that the plasma frequencies of all nanoscaled materials are similar, except for iron. The same is obtained in literature: the values of the materials aluminum (77 700 cm –1 ), copper (66 000 cm –1 ), gold (67 900 cm –1 ), and silver (71 800 cm –1 ) are similar, whereas the value for iron (35 200 cm –1 ) points out a significantly lower plasma frequency. Note that for aluminum, there is a significant mismatch with other literature values (e.g., 119 000 cm –1 ) .…”

“…In literature, there are many publications available, reporting Drude parameters (electronic scattering rate ω τ , plasma frequency ω p , and dielectric background ε ∞ ) of metal films. It was found that for the very same material, these parameters dramatically vary for thin films as well as for different morphologies, as it was shown by Fahsold et al in the example of iron. For the analysis of the plasmonic properties of the nanoantenna arrays in the IR, it is important that in the range below 2000 cm –1, the metals under investigation can be well-described by the Drude model.…”

“…This nonideal morphology may strongly influence the plasma frequency. It is well-known that the thermal evaporation of aluminum results in a grainy morphology . As a result, the antenna consists of an effective conductive medium for high-enough filling factors that can be described by a Drude model but with an effective plasma frequency. , …”

“…The literature values for copper and iron , were taken from frequency dependent models in the spectral range of the plasmonic resonances. Frequency independent parameters from literature were used for gold, , silver, , and aluminum. , The values for aluminum especially strongly vary for different thicknesses and morphologies, respectively. A recent publication shows higher near-IR reflectance for copper than calculated with older textbook data.…”

Surface-Enhanced Infrared Spectroscopy Using Resonant Nanoantennas

“…For randomly grown island films, the distribution of particle size and distance broadens the infrared spectrum significantly; thus it looks like a smooth background in infrared transmittance. − The slope of that background is determined by the density of the particles and changes its sign at the percolation threshold; see Figure .…”