This licentiate thesis by Babak Bakhit explores the growth and properties of transition metal diboride thin films using magnetron sputtering with metal-ion irradiation. The research focuses on controlling the crystalline phase and stoichiometry of these materials, which are known for their high melting temperatures and suitability in extreme thermal and chemical environments. The thesis highlights the potential applications of transition metal diborides in aerospace, nuclear reactors, and advanced electronics due to their unique combination of hardness, thermal conductivity, and electrical properties. The work is supported by various research grants and contributes to the field of materials science by addressing challenges in film composition and proposing strategies to enhance both hardness and toughness of the films. The intended audience includes researchers and professionals in materials science and engineering.