  Sub-{\mu}m thin samples are essential for spectroscopic purposes. The
development of flat micro-jets enabled novel spectroscopic and scattering
methods for investigating molecular systems in the liquid phase. However
characterization of the temperature of these ultra-thin liquid sheets in vacuum
has not been systematically investigated. Here we present a comprehensive
temperature characterization of two methods producing sub-micron flatjets,
using optical Raman spectroscopy: colliding of two cylindrical jets and a
cylindrical jet compressed by a high pressure gas. Our results reveal the
dependence of the cooling rate on the material properties and the source
characteristics, i.e. nozzle orifice size,flowrate, pressure. We show that
materials with higher vapour pressures exhibit faster cooling rates which is
illustrated by comparing the temperature profile of liquid water and ethanol
flatjets. In a sub-{\mu}m liquid sheet, the temperature of the water sample
reaches around 268 K and the ethanol around 253 K.
