'spread onto' is a correct and usable phrase in written English.
It is used to describe distributing a substance onto a larger area. For example, "The chef carefully spread tomato sauce onto the pizza crust."
This mixture is spread onto a baking sheet and chilled.
Frosting is spread onto thoroughly cooled cakes, where it will cling.
Subtropical high pressure probably spread onto Gondwana, particularly the Australian and Antarctic sectors.
The antibody can be spread onto a catheter or stent, or applied around an incision or stitches.
Packets were cut open and seeds spread onto both asymbiotic (RM1) and symbiotic media (RM2).
50 μL of cells suspension was spread onto a coverslip and air dried for 30 min.
Bacterial suspension was spread onto the surface of the model pond and left for 30 min.
0.1 mL from each dilution was spread onto YM agar plates.
Then, the slurry was spread onto a piece of carbon coating Al foil substrate.
One hundred microliters of overnight cultures of each bacterium was spread onto LB agar plates.
GO solution was dropwise spread onto the water surface by using a glass syringe.
