کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5375628 | 1504308 | 2008 | 14 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Ultrafast dynamics of heat flow across molecules
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی تئوریک و عملی
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
An ultrafast flash thermal conductance apparatus is used to study heat flow through aliphatic and aromatic molecules arranged in self-assembled monolayers (SAMs). The apparatus consists of a thin metal film which can be flash-heated by many hundreds of degrees in â¼1Â ps using a femtosecond pulse. Heat flow from the metal surface into the SAM molecules is detected using vibrational sum-frequency generation (SFG) spectroscopy. The SAMs studied were alkanethiolates (AT) ranging from C6 to C24, benzenethiolate (BT) and benzylmercaptide (BMT). SFG in the CH-stretch region selectively probes transitions of the terminal methyl groups of AT and the CH moiety at the 4-position of the phenyl ring of BT and BMT (opposite the thiolate-surface bond). The SFG signal is sensitive to temperature-jump induced thermal disorder of the SAM and also to vibrational frequency shifts induced by the changing intramolecular vibrational populations. The SFG probe functions as a thermometer, and this thermometer is â¼1.5Â Ã
thick with a response time of â¼1Â ps. In the AT chains, a study of the length dependence is used to determine the rate heat flows across the metal-SAM interface and the rate of heat flow through the AT chains. The interface thermal conductance is 220Â GWÂ mâ2Â sâ1. The AT molecular conductance is 50Â pWÂ Kâ1 or 0.3Â eVÂ sâ1Â Kâ1. Heat flow through the AT chains is ballistic with a velocity of 1Â km/s. Heat flow into BMT is slower than in BT because BMT has one additional methylene linker group. The BT and BMT structures evidence a thermally-initiated surface rearrangement occurring in a few tens of picoseconds. These SAMs are strained and the phenyl rings cannot adopt the most stable staggered herringbone structure. After the T-jump, the SAM molecules have enough freedom to relax into more favorable configurations.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemical Physics - Volume 350, Issues 1â3, 23 June 2008, Pages 31-44
Journal: Chemical Physics - Volume 350, Issues 1â3, 23 June 2008, Pages 31-44
نویسندگان
Zhaohui Wang, David G. Cahill, Jeffrey A. Carter, Yee Kan Koh, Alexei Lagutchev, Nak-Hyun Seong, Dana D. Dlott,