A method controllably and sustainably creates an upwardly directed gradient of dropping temperatures in a wet treatment tank between a cooled and face down workpiece (e.g., an in-process semiconductor wafer) and a lower down heat source. A thermal fluid upwell containing thermally collapsible bubbles is then directed from the heat source to the face down workpiece. In one class of embodiments, bubble collapse energy release and/or bubble collapse locations are controlled so as to avoid exposing delicate features of the to-be-treated surface to damaging forces. In one class of embodiments the wet treatment includes ultra-cleaning of the work face. Cleaning fluids that are essentially free of predefined contaminates are upwelled to the to-be-cleaned surface and potentially contaminated after-flows are convectively directed away from the workpiece so as to prevent recontamination of the workpiece.