Denoising diffusion probabilistic models, or diffusion models, have been successfully used for generating images, audio, and music. This work aims to investigate the potential of employing diffusion models to develop a motif composed by human composers to arouse specific emotions. To achieve this, a dataset consisting of melodies and their corresponding emotion label is constructed for training the diffusion model. The model is conditioned on the user-generated motif and a label displaying the desired emotion category, which opens up an opportunity for human composers to collaborate with computer technology in the field of music composition.