A delivery device for thin-film material deposition has at least first, second, and third inlet ports for receiving a common supply for a first, a second and a third gaseous material, respectively. Each of the first, second, and third elongated emissive channels allow gaseous fluid communication with one of corresponding first, second, and third inlet ports. The delivery device can be formed from apertured plates, superposed to define a network of interconnecting supply chambers and directing channels for routing each of the gaseous materials from its corresponding inlet port to a corresponding plurality of elongated emissive channels. The delivery device comprises a diffusing channel formed by a relief pattern between facing plates. Also disclosed is a process for thin film deposition. Finally, more generally, a flow diffuser and a corresponding method of diffusing flow is disclosed.