Abstract Copper was deposited onto the tungsten emitter of a probe-hole field emission microscope with magnetic deflection. The emitter was kept at a constant temperature between 300 and 900 K. Simultaneously the voltage changes necessary to maintain the emission current from a particular region of the emitter constant were recorded. The variations in the work function, corresponding to various amounts of adsorbed copper, were determined at different substrate temperatures for the (211), (111), (110) and (100) planes. It was found that changes in substrate temperature do not affect the work function variations, with exception of the (100) case for which a strong dependence was observed. On this plane the work function increases at temperatures between 300 and 550 K and decreases when the temperature varies between 600 and 900 K. Since an increase in the work function is observed for rough crystal planes such as (211) and (111) whereas a decrease is typical of the smooth (110) plane, it is proposed that the phenomena observed on the (100) plane can be accounted for by the transition from a rough low temperature phase to a smooth high temperature phase. The transition takes place at approximately 550 K.