Deposition and nonlinear optical properties of transition metal nitride/oxide thin films

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Nontechnical description: The interaction of light with matter is of high scientific and technological interest. Light is an electromagnetic wave and the electric field may interact with the charges present in the material to produce separation of the positive and negative charge centers resulting in the appearance of an electric field within the body of the material. When the intensity of the light is low, then the induced electric field is also very small and proportional (linear) to the applied field. However, when intense light such as that from a laser is used then it is possible that a very high (nonlinear) response may be obtained. This intense response to the externally applied electric field depends on the structure and composition of the material and can be used to generate light of a different color, or to modulate the propagation of light through the material via an intensity dependent refractive index. For example, it is highly desirable to be able to protect sensors and the naked human eye from high intensity light such as lasers. While the military implications of such materials are obvious, the benefits can affect many areas of everyday life. Most of the materials known to have a nonlinear response are cut from large crystals or are liquids and are not suitable to cover large areas reproducibly such as those needed for the application described before. In this project, the research team study a new class of nonlinear optical materials that are based on thin films that can be deposited reliably and reproducibly on large surface areas including complex geometries and even optical fibers with atomic scale precision. The project is training of two graduate students in an area of high technological importance. Technical description: Nonlinear materials in thin film form are highly desirable for on chip fast all-optical switching devices, frequency conversion and optical limiting applications as conventional nonlinear optical materials are not suitable for integration with the contemporary semiconductor industry process flow. This project seeks to address this shortage by designing and investigating novel nonlinear optical materials based on rational principles. The materials investigated are based on titanium and tantalum nitride seeded dielectric thin films where the at% of titanium-nitrogen or tantalum-nitrogen bonding in the film volume can be used to control the value of the nonlinear index of refraction and film transparency. The maturation of ALD as a thin film deposition technique allows the formation of such structures with atomic level thickness control, through a single deposition process by just controlling parameters such as the process temperature and the precursor delivery temperature. This project includes design of seeded materials with tunable composition, as well as the adaptation of optical techniques such as Z-scan and ultrafast pump-probe to investigate these novel, ultrathin structures. The proposed activity and the interdisciplinary research team seek to combine and transfer knowledge between the electronics materials and nonlinear optics communities. Such cross pollination is expected to advance the state of the art in both fields, with the goal to enrich the materials toolkit available for on chip fast all-optical switching, frequency conversion and optical limiting applications. The main outcome for this proposal is to provide detailed understanding of the physics governing a new class of semiconductor compatible nonlinear optical materials that may address the technological need for novel, well-characterized materials to aid in the realization of new device paradigms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.