A timed scratch steers crystal growth in semiconductor films
Researchers changed the arrangement of crystals in solution-processed semiconductor films by choosing when to initiate their formation. A mechanical scratch in the wet film separated nucleation from subsequent growth. The peer-reviewed experiments and model connect solvent evaporation to the final structure, with aligned films carrying charge more effectively in an illustrative transistor system.
Science··Midday
A scratch starts crystals at a chosen moment
Researchers steered the crystalline arrangement of semiconductor films by scratching their wet surface at a chosen point during coating. The peer-reviewed study in Nature Communications separated the formation of a stable crystal nucleus from subsequent growth. The film was deposited by spinning and then heated to continue growth. Crystal regions were large after early initiation, aligned after intermediate initiation and small after late initiation.[1]
Evaporation sets the growth conditions
As solvent evaporates, the concentration of dissolved material changes the critical size required for a stable nucleus. The formation barrier at the scratch tip differs from those on a flat interface and within the liquid. A model combined this changing concentration with transport of material to growing crystals. Tests covered perovskites, organic semiconductors and an inorganic salt, and imaging found that induced and spontaneous nuclei followed the same growth framework after formation.[1]
Aligned domains carry charge more readily
In illustrative perovskite transistors, aligned films reached a charge-carrier mobility of 2.6 square centimetres per volt-second. The value for large regions was 0.6, while films with small regions reached 0.2. Boundaries affected transport, with different results from local optical and whole-device measurements. The model assumes evaporation-controlled concentration and growth limited by material transport, including uniform evaporation across the surface. The experiments tested laboratory films rather than production-scale manufacturing or long-lived commercial devices.[1]
