Methods for depositing a molybdenum metal film over a dielectric surface of a substrate by a cyclical deposition process are disclosed. The methods may include: providing a substrate comprising a dielectric surface into a reaction chamber; depositing a nucleation film directly on the dielectric surface; and depositing a molybdenum metal film directly on the nucleation film, wherein depositing the molybdenum metal film includes: contacting the substrate with a first vapor phase reactant comprising a molybdenum halide precursor; and contacting the substrate with a second vapor phase reactant comprising a reducing agent precursor. Semiconductor device structures including a molybdenum metal film disposed over a surface of a dielectric material with an intermediate nucleation film are also disclosed.