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# ss_1 - 3 Wafers of silicon are used to make semiconductor...

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Unformatted text preview: 3. Wafers of silicon are used to make semiconductor devices. The density of silicon is 2.33 g/cm3 and its atomic weight is 28.086 g/mole. Estimate how many Si atoms are contained in a single- crystal wafer 500 pm thick and 15 cm in diameter. If this wafer is uniformly doped (lightly alloyed) with 1016 phosphorus atoms per cubic centimeter, what is the atomic fraction of phosphorus in silicon? 7' gooh'o' cm \ r S x \o’zcm V‘C“ \B _*'+ W66” \D 2.4. Aluminum foil used for storing food weighs about 0.3g/in2. Estimate how many atoms are contained in one square inch of aluminum foil. Estimate the volume per aluminum atom and, from this, determine a dimension characteristic of a single aluminum atom. Compare your estimate value to the tabulated atomic radius for aluminum. L6 907,1)! in} SW W M mks Q1%L%2X\ / é.‘+0 MID-u mot—.3 7. Tantalum and depleted uranium (the uranium left over once the radioactive isotopes are removed) are typically used in penetrators of armor-piercing artillery shells, and these penetrators can often pierce several inches of steel protecting a tank or other armored vehicle. By considering the momentum of a penetrator, brieﬂy describe why Ta and U are preferred for this application rather than, for example, a high-strength steel or an aluminum alloy. 3 'S : E} 4:3 En ”"61 l/w fee, 1' WC 7) f0: \qog ﬁI/CME §)R\: ?.% K/Ch ._ \Jm' £3 MOMRDTUM: F: \“M " RSSoMQZﬁW. blips r“7 ZMxpxU; m RLEZA‘VaW TD PM ES. S‘UCE @LLFzZN-ad’zw\u W7 \3 ix MM; (35» m gum 2M m mw mm as No mwm, ...
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