We have developed a self-wrapping flexible cuff electrode for recording electrical activity on the descending contralateral movement detector (DCMD) neuron of the locust. First, a gold film is sputtered onto a monoaxially oriented polycarbonate membrane. Then, the resulting bilayer film is cut into individual strips parallel to the machine direction of the polycarbonate film. Thermally shrinking the polycarbonate at 155 0 C actuates the curl. This method can be used to fabricate controlled diameters between 50-250 µm; diameter is controlled by thickness of the two layers and the temperature and duration of the heat shrinking process. The cuffs are selfclosing, and do not require suturing for attachment to a nerve. The cuffs are carefully unrolled, a gold film deposited, and a plasmadeposited, ion-sensitive resist applied. A stencil mask is then used to define the metallization lines by 50 kV He + ion beam proximity lithography. Ion milling transfers the resist pattern to the metal film. Conformality of the resist and large depth-of-field of the lithography are key to high resolution patterning on these non-flat substrates. The dielectric overcoat is a layer of exposed resist, which simplifies the opening of the contact windows, and provides excellent biocompatibility.
In atom beam lithography, a beam of kilo-electron-volt helium atoms illuminates a stencil mask and transmitted beamlets transfer the mask pattern to resist on a substrate. It shares the advantages of masked ion beam lithography but is immune to charging artifacts that limit resolution and pattern fidelity. This paper describes a high-brightness source of energetic He atoms, where He+ ions are extracted from a multicusp ion source, focused by two-stage accelerating optics, and neutralized by charge-transfer scattering in a differentially pumped, He-filled cell. Since scattering angles are extremely small, the straight line trajectories of scattered atoms are essentially tangent to the (possibly curved) trajectories of the parent ions. Space-charge repulsion prevents the ion beam crossing over; instead, it converges to a waist of minimum cross section before diverging further downstream. Atom trajectories produced by a cell placed in the region of intense space charge near the waist are strongly affected by the curvature of ion trajectories within the cell. The flaring of the ion beam due to space charge can be used to increase the width of the atom beam, although to the detriment of resolution. In this paper, the authors study a configuration where the cell is placed in the converging ion beam as far as practicable from the ion-beam waist. The atom beam then converges to a crossover, which becomes the virtual source seen by the mask. The source diameter and angular flux density initially increase with increasing cell pressure but saturate at higher pressures; the respective saturation values at 50 keV are 125 μm (2σ) and 8.7 × 1017 particles/s sr. Under these conditions, the beam diameter is ∼2.5 cm, 7 m from the source. A practical system for subnanometer printing is discussed with 0.2 nm (2σ) penumbral blur and 1.25 × 1013 particles/s cm2 flux density over a 1 cm circular field.
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