. The Bell System technical journal . ing surfaces with respect to which a depth can be measured. It is S. Tolansky, Multiple-Beam Interferometry of Surfaces and Films, Oxford, atat the Clarendon Press, 1948. INTERFERENCE MEASUREMENT OF THIN SURFACE LAYERS 1211 also advisable to use plane-parallel samples to facilitate the lapping of al)Ovel at a small angle. For lapping, the sample is waxed with its back side to the face of ashort steel cylinder. The face is cut at a small angle. Angles of ° ° are practical. The cylinder is placed in a jig, in svich a position thatapproximately half o
. The Bell System technical journal . ing surfaces with respect to which a depth can be measured. It is S. Tolansky, Multiple-Beam Interferometry of Surfaces and Films, Oxford, atat the Clarendon Press, 1948. INTERFERENCE MEASUREMENT OF THIN SURFACE LAYERS 1211 also advisable to use plane-parallel samples to facilitate the lapping of al)Ovel at a small angle. For lapping, the sample is waxed with its back side to the face of ashort steel cylinder. The face is cut at a small angle. Angles of ° ° are practical. The cylinder is placed in a jig, in svich a position thatapproximately half of the sample surface projects above the plane ofthe jig (Fig. 1). A short grind on a slightly rough glass plate using aline abrasive with water gives usable bevels. For a shiny finish just thelight degree of roughness of the glass is important. The use of a lappingmachine with a vulcanized fiber plate and fine abrasive gives a bettersurface finish, but the ridge is not as sharp. A ° bevel could be obtainedonly on a glass Fig. 1 — Jig for lapping a bevel. MARKING OF p-TYPE OR n-TYPE SURFACE LAYERS In a sample with a p-type or n-type surface layer the junction is ex-posed within the bevel. The next step is to detect and mark the junc-tion. The sample is fixed on a microscope stage which allows a micrometercontrolled movement in two directions (Fig. 2 shows a Wilder microm-eter cross slide). The sample is oriented in such a way that the ridgeis parallel to one direction of movement (y-direction). One or two linesof aquadag are applied to the surface of the sample, perpendicular tothe ridge. The acjuadag should be diluted with water in such a proportionas to achieve a thin film w^hich is non reflecting. A needle is fixed to the base of the stage with a suitable linkage leav-ing a vertical degree of freedom. The needle is brought into contact withthe surface of the sample outside the acjuadag. Thus, the sample can bemoved under the needle while the needle maintains c
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