Detection of Percolation in Hermetic Single-Device Human Implants by Ion Beam Analysis (IBA)*

Percolation of bodily fluids into medical implants limits device lifetimes to less than a week in permanent glucose sensors for diabetics. Rutherford Backscattering Spectrometry (RBS) can detect C, O, Na from these fluids. But the RBS detection limit, \textbf{D}$^{\mathrm{\mathbf{min}}}$, is inadequate for low Z elements in higher Z substrates. With 2 MeV $^{4}$He$^{2+}$, \textbf{D}$^{\mathrm{\mathbf{min}}}$ of C in Si is $\sim$ 5 ML. The 4.265 $\pm$ 0.05 MeV $^{12}$C($\alpha $,$\alpha )^{12}$C Nuclear Resonance Analysis (NRA) reduces \textbf{D}$^{\mathrm{\mathbf{min,\thinspace C\thinspace }}}_{\mathrm{\mathbf{Si}}}$ to $\sim$ 0.05 ML. Next, NRA combined with channeling can lower \textbf{D}$_{\mathrm{\mathbf{min}}}$ by 20-50, with \textbf{D}$^{\mathrm{\mathbf{min,\thinspace C\thinspace }}}_{\mathrm{\mathbf{Si}}}$ \textless 0.002 ML for C. Thirdly, geometry, such as the tilt angle of the \textless 111\textgreater axis with the Si(100) surface almost doubles the sampled depth, reducing \textbf{D}$^{\mathrm{\mathbf{min,\thinspace C\thinspace}}}_{\mathrm{\mathbf{Si}}}$ by 1.7. Low \textbf{D}$^{\mathrm{\mathbf{min,Na}}}$ is needed as mobile Na ions destroys electronic sensors. In this work, \textbf{D}$^{\mathrm{\mathbf{min,Na}}}$ is increased using $^{4}$He$^{2+}$ near 4.68 MeV, by a factor 1.44. C, O and Na from blood and saline are studied.