Ultrafast spectroscopy of materials and devices

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What happens when light is absorbed in a material? If electrons in the material are excited to higher energy levels, do they break free and move around inside the material or do they get stuck somehow? When they finally get back to their original state in the material, do they get rid of their excess energy by emitting light or by shaking the atoms around them in the material? And how long does it take for them to do all that? These are the types of questions scientists ask when trying to understand the nature of new materials that may someday find their way into the latest electronic devices. Many fundamental processes in materials such as charge carrier photogeneration, transport, relaxation and recombination occur over very fast time scales much shorter than a billionth of a second (less than a nanosecond). In addition, the characteristic energy scales associated with a given process can vary greatly between different material systems. In order to better understand such ultrafast processes in materials and to study their effect in device structures, it is therefore essential to use ultrafast spectroscopic techniques that can excite and probe samples over a wide range of wavelengths and length scales with sub-picosecond time resolution (i.e., less than a thousandth of a nanosecond, which is the same amount of time it takes light to travel only a third of a millimeter!) In the Ultrafast Spectroscopy Lab and Ultrafast Nanotools Lab, we use a variety of advanced laser sources to study ultrafast phenomena in materials and devices, providing valuable insight into the nature of new materials and the ultimate switching speeds and response times of devices. We explore ultrafast carrier dynamics and transport in semiconductors, organic semiconductors, and nanomaterials, and explore how intense light interacts with materials. Ultrafast carrier dynamics in materials over nanometer length scales and even in single molecules will be explored using leading-edge scanning probe instruments coupled to an ultrafast laser source in the new Ultrafast Nanotools Lab, which is unique in the world.