Two‐photon lithography has been used to create a three‐dimensional metallic structure for the first time. A porous gel filled with AgNO3 solution was laser irradiated in a multi‐photon process that allowed silver nanocrystals to be written only on the interior of the gel, resulting in the macroscopic three‐ dimensional spiral shown in the Figure.

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N CERTAIN electron multiplication devices, it is advanta-I geous to use the glass surface itself as the secondary emitting element or dynode. Adams' has listed the requirements for such glasses; one of the properties necessary for stable performance of the device is that the glass possess electronic conductivity. The glasses commonly used in devices are based on lead silicate compositions, and the glass surface must be reduced to render it electronically conducting.* It is logical, therefore, that semiconducting glasses which show bulk electronic conductivity be evaluated. Results for such glasses are reported herein.The secondary yield, S, was determined in the usual manner, making all current measurements in the target circuit.' The electron beam was incident perpendicular to the surface of the target. The collector was roughened and coated with graphite to reduce the error resulting from creation of secondary electrons at the collector by high-energy back-scattered electrons. Experiments were performed in a vacuum of torr. Platinum was used as a reference for the system, and the values obtained for S,, and E, , (maximum yield and primary electron energy where this yield occurs) were identical to literature values? Charging of the glass surface was minimized by using small primary currents ( lo-'' A) for short periods (2 to 3 s ) . Stable, reproducible values were thus attained.The As-Se-Te glasses were prepared by melting the pure elements in evacuated fused SiOJ ampoules at 850°C and then, after being crushed and resealed, melted again. X-ray diffraction showed that the samples were amorphous. The preparation of the 80V20,-20P20, glass was described previously.5The samples were ground and polished to a thickness of 1 mm.Thin samples are desired because the change in potential of the surface depends on the capacitance of the material.The secondary yield curves of the glasses are shown in Fig. 1. A curve for soda-lime silicate glass is included as a reference. The data are summarized in Table I. The significant results noted are:( 1 ) Although the resistivity of the chalcogenide samples changes greatly when they are doped with Te, they differ only slightly in 8," and E, m.