NOVELTY - An apparatus (100) for forming solar cell absorber on continuous workpiece (106), comprises a rapid thermal processing tool including a continuous and leak-free process gap through which the continuous workpiece travels. The process gap includes a top wall and a bottom wall such that there exists an aspect ratio of 1/50-1/1000. The top wall and the bottom wall are partitioned into two different temperature zones (Z1, Z2) separated by a buffer zone between temperature zones.    USE - For reacting precursor material disposed over a continuous workpiece that continuously feeds their portions through the apparatus to form a solar cell absorber for converting sunlight directly into electrical power, and radiation detector.    ADVANTAGE - The apparatus provides a large degree of flexibility to optimize the absorber layer composition by optimizing the two reaction steps independent from each other. The continuous workpiece is moved at a predetermined speed through the buffer zone from the low temperature to high temperature zones of the thermal processing tool zone such that the rate of heating experienced by a portion of the continuous workpiece as it travels through buffer zone can be easily made greater than or equal to 10 degrees C/second by selecting the values for low temperature, high temperature, speed of continuous workpiece, and length of buffer zone. Thus apparatus provides flexibility and has ability to reach very high temperature rates at low cost, keeping the processing throughputs very high unique features.    DETAILED DESCRIPTION - An apparatus (100) used to react precursor material disposed over a continuous workpiece (106) that continuously feeds their portions through the apparatus to form a solar cell absorber, comprises a rapid thermal processing tool including a continuous and leak-free process gap through which the continuous workpiece travels. The process gap includes a top wall and a bottom wall such that there exists an aspect ratio of 1/50-1/1000. The top wall and the bottom wall are partitioned into two different temperature zones (Z1, Z2) separated by a first buffer zone between temperature zones. The first buffer zone includes several cavities within at least one of the top wall and the bottom wall that provide low thermal conductivity areas that together significantly inhibit transfer of thermal energy to the adjacent two different temperature zones while still maintaining the process gap, including the buffer zone, leak-free. The two different temperature zones include a first zone maintained at a first temperature range so that a section of the continuous workpiece is subjected to the first temperature range as the section of the continuous workpiece travels through the first zone; and a second zone maintained at a second temperature range so that the section of the continuous workpiece is subjected to the second temperature range as the section of the continuous workpiece travels through the second zone, where the second temperature range is higher than the first temperature range. Each of the top wall and the bottom wall include several cavities that provide low thermal conductivity areas that together significantly inhibit transfer of thermal energy to the adjacent two different temperature zones. The apparatus further includes a moving mechanism to move the portions of the continuous workpiece through the first and second zones, and the first buffer zone at a predetermined speed, where at the predetermined speed a heating rate on that portion of the continuous workpiece within the first buffer zone is at least 10 degrees C/second; a temperature controller that maintains a temperature differential between the first process zone and the second process zone of at least 300 degrees C. The first buffer zone has a length of less than 10 (preferably 1-5)% of the length of the second process zone. An INDEPENDENT CLAIM is included for reacting precursor material disposed over a continuous workpiece, which forms in a sheet that is continuously fed, involving feeding the sheet through a process gap that is leak-free; heating each portion of the sheet in a first zone of the process gap maintained at a first temperature range; heating each portion of the sheet at a second higher temperature range; and passing each portion of the sheet through a first buffer zone of the process gap that connects the first zone to second zone, where the buffer zone includes cavities of low thermal conductivity that together significantly inhibit transfer of thermal energy from the second zone to the first zone while still maintaining the process gap, including the buffer zone, leak-free.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the apparatus to react precursor material disposed over a continuous workpiece that continuously feeds their portions through the apparatus to form a solar cell absorber.    Apparatus (100)    First port (103)    Second port (104)    Workpiece (106)    Gaps (111)    Gas inlet (113)    Temperature zones. (Z1-Z3)