Excitation and deexcitation of the Si-H stretching mode in a Si [electronic resource] : H with picosecond free electron laser pulses
- Published:
- Upton, N.Y. : Brookhaven National Laboratory, 1995. and Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
- Physical Description:
- pages Th4.16 : digital, PDF file
- Additional Creators:
- Brookhaven National Laboratory and United States. Department of Energy. Office of Scientific and Technical Information
- Access Online:
- www.osti.gov
- Summary:
- Hydrogen in amorphous and crystalline silicon has been the topic of intense theoretical and experimental investigations for more than one decade. To better understand how the Si-H bonds interact with the Si matrix and how they can be broken, it would be useful to excite selectively these bonds and monitor the energy flow from the Si-H bonds into the bulk Si modes. One attractive way of exciting the Si-H modes selectively is with an infrared laser tuned to a Si-H vibrational mode. Unfortunately, up to now, this type of experiment had not been possible because of the lack of a laser producing intense, ultrashort pulses that are tunable in the mid infrared. In this presentation, we report the first measurement where a 1 picosecond long laser pulse was used to excite the Si-H stretching modes near 2000 cm⁻¹ and another identical laser pulse was used to measure the deexcitation from that specific vibrational mode. The laser was the Stanford free electron laser generating ∼1 ps-long pulses, tunable in the 5 μm region and focussed to an intensity of ∼1 GW/cm². The pump-probe measurements were performed in transmission at room temperature on several 2 μm thick a-Si:H films deposited on c-Si. Samples with predominant Si-H₁ modes, predominant Si-H{sub n>1} modes and with a mixture of modes were prepared. The laser was tuned on resonance with either of these modes. Immediately after excitation, we observe a bleaching of the infrared absorption, which can be attributed to excitation of the Si-H mode. Beaching is expected since, as a result of anharmonicity, the detuning between the (E₃ - E₂) resonance and the (E₂ - E₁) resonance is larger than the laser bandwidth. Note that despite the anharmonicity, it should be possible to climb the vibrational ladder due to power broadening.
- Subject(s):
- Note:
- Published through SciTech Connect., 12/31/1995., "bnl--61982-absts.", " conf-9508156--absts.", "DE96002729", ": Contract N00014-92-J-4063", "Contract N00014-94-1-1024", 17. international free electron laser conference, New York, NY (United States), 21-25 Aug 1995., and Xu, Z.; Fauchet, M.; Rella, C.W.
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