For the predeposition heat treatment of a semiconducting device, gallium atoms are to be diffused into silicon at a temperature of 1150°c for 2.5 h. if the required concentration of ga at a position 2 μm below the surface is 8 x 10^23 atoms/m^3, compute the required surface concentration of ga. assume the following: (i) the surface concentration remains constant (ii) the background concentration is 2 x 10^19 ga atoms/m^3 (iii) preexponential and activation energy values are 3.74 x 10^-5 m^2/s and 3.39 ev/atom, respectively. express your answer in atoms/m3 to three significant figures.

Determine the time of the day and month of the year at which the peak sensible cooling load occurs for a top floor, north-eastern corner room of an office building in durban for the following conditions: floor area: 8 x 8 x 3 m east and north walls: 115 mm face brick (outside), 20 mm air space, 115 mm ordinary brick (inside) with 15 mm plaster roof construction: suspended plasterboard ceiling, 450 mm air space, 150 mm concrete, 75mm screed, waterproofing no heat transfer across other surfaces window area 3x 1,5 m high in north wall only. ordinary glass with venetian blinds. lights and occupants : from 07: 00 to 18: 00 average light density: 25 w/m2 number of occupants : 5 seated, light office work room temperature 24°c