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Electron-nuclear Dynamics in Noble Metal Nanoparticles
Başlık:
Electron-nuclear Dynamics in Noble Metal Nanoparticles
Yazar:
Senanayake, Ravithree Dhaneeka, author.
ISBN:
9780438123564
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (275 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-11(E), Section: B.
Advisors: Christine M. Aikens Committee members: Daniel Higgins; Ryszard Jankowiak; Bin Liu; Douglas McGregor.
Özet:
Thiolate-protected noble metal nanoparticles (~2 nm size) are efficient solar photon harvesters, as they favorably absorb within the visible region. Clear mechanistic insights regarding the photo-physics of the excited state dynamics in thiolate-protected noble metal nanoclusters are important for future photocatalytic, light harvesting and photoluminescence applications. Herein, the core and higher excited states lying in the visible range are investigated using the time-dependent density functional theory method for different thiolate-protected nanoclusters. Nonadiabatic molecular dynamics simulations are performed using the fewest switches surface hopping approach with a time-dependent Kohn-Sham (FSSH-TDKS) description of the electronic states with decoherence corrections to study the electronic relaxation dynamics. Calculations on the [Au25(SH)18]-1 nanocluster showed that relaxations between core excited states occur on a short time scale (2-18 ps). No semiring or other states were observed at an energy lower than the core-based S1 state, which suggested that the experimentally observed picosecond time constants could be core-to-core transitions rather than core-to-semiring transitions. Electronic relaxation dynamics on [Au 25(SR)18]-1 with different R ligands (R = CH3, C2H5, C3H7, MPA) [MPA = mercaptopropanoic acid] showed that all ligand clusters including the simplest SH model follow a similar trend in decay within the core states. In the presence of higher excited states, R= H, CH3, C2H 5, C3H7 demonstrated similar relaxations trends, whereas R=MPA showed a different relaxation of core states due to a smaller LUMO+1-LUMO+2 gap. Overall, the S1 state gave the slowest decay in all ligated clusters. An examination of separate electron and hole relaxations in the [Au25(SCH3)18]-1 nanocluster showed how the independent electron and hole relaxations contribute to its overall relaxation dynamics. Relaxation dynamics in the Au18(SH) 14 nanocluster revealed that the S1 state has the slowest decay, which is a semiring to core charge transfer state. Hole relaxations are faster than electron relaxations in the Au18(SH)14 cluster due its closely packed HOMOs. The dynamics in the Au38(SH) 24 nanocluster predicted that the slowest decay, the decay of S 11 or the combined S11-S12, S1-S 2-S6-S7 and S4-S5-S 9-S10 decay, involves intracore relaxations. The phonon spectral densities and vibrational frequencies suggested that the low frequency (25 cm-1) coherent phonon emission reported experimentally could be the bending of the bi-icosahedral Au23 core or the "fan blade twisting" mode of two icosahedral units. Relaxation dynamics of the silver nanoparticle [Ag25(SR)18]-1 showed that both [Ag25(SH)18]-1 and [Au 25(SH)18]-1 follow a common decay trend within the core states and the higher excited states.
A real-time TDDFT investigation on a set of linear gold nanowires Au m (m = 4, 6, 8, 10, 12) indicated that the longitudinal peak splits due to the involvement of interband transitions. Time-dependent occupation numbers and their Fourier transformed spectra revealed a dominant single particle transition (Sigman → Sigma n+1) in the longitudinal peaks that is coupled with less probable d-band transitions (d → Sigma). The transverse modes are constructed from a coupling of two or more single particle transitions with Sigman → product n character.
Notlar:
School code: 0100
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