| 31. |
- Lin, Ke, et al.
(författare)
-
Reorientation dynamics in liquid alcohols from Raman spectroscopy
- 2012
-
Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 43, s. 82-88
-
Tidskriftsartikel (refereegranskat)abstract
- Polarized Raman spectroscopy has been employed to study the reorientational, or more specifically the translational relaxation dynamics, of alcohol molecules in pure liquids and aqueous solutions. It is found from the spectral width measurements that alcohol molecules in pure liquids have typically translational relaxation times on the order of picoseconds, following the order methanol < ethanol < i-propanol < n-propanol. Temperature-dependent measurements show that hydrogen-bonding (HB) and hydrophobic interactions control the translational motion. The hydrophobic interaction reduces the relaxation time more apparently in view of the –CH3 group than the skeleton motion. For alcohol–water mixtures, the increaseofwater concentration generally slows down the relaxation process in a non-monotonic behavior. However, the trend stops at a certain point and the motion of alcohol molecules becomes faster when the alcohol concentration further drops. Different mechanisms have been proposed to interpret these observations, which might be helpful to gain deeper insight into the HB networks of alcohols with water. Our study strongly illustrates that Raman spectroscopy can be applied to the study of fast translational motion of molecules in HB systems.
|
|
| 32. |
- Lin, Ke, et al.
(författare)
-
The Microscopic Structure of Liquid Methanol from Raman Spectroscopy
- 2010
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:10, s. 3567-3573
-
Tidskriftsartikel (refereegranskat)abstract
- The microscopic Structure of liquid methanol has been systematically investigated with Raman spectroscopy in a temperature range of 15-55 degrees C. The unbonded free -OH stretching vibrational hand has been observed at similar to 3660 cm(-1) in pure liquid. With the aid of depolarization measurements and theoretical calculations, four featured spectral components have been unambiguously identified and assigned to four well-defined vibrational modes of Clusters in chain or ring forms. Furthermore, the Cluster size distribution and its temperature dependence have been derived from the spectral fittings for the first time, which lead to the conclusion that the trimer, tetramer, and pentamer are the dominant Clusters ill liquid methanol, taking Up more than 50% of total Clusters.
|
|
| 33. |
- Lin, Lili, et al.
(författare)
-
Elastic and inelastic electron transport in metal-molecule(s)-metal junctions
- 2013
-
Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 47, s. 167-187
-
Forskningsöversikt (refereegranskat)abstract
- An overview of studies on-elastic and inelastic electron transport properties of molecular junction devices is presented. The development of the experimental fabrication and characterization of molecular junctions as well as the corresponding theoretical modeling is briefly summarized. The functions of molecular devices are generally governed by the intrinsic structure-property relationships, and strongly affected by various environment factors including temperature, solvent and intermolecular interactions. Those detailed structural and environmental information could be probed by a powerful tool of inelastic electron tunneling spectroscopy, for which the theoretical modeling becomes particularly important. With many successful examples, it is demonstrated that the combination of theoretical simulations and experimental measurements can help not only to understand the electron-phonon interaction, but more importantly also to accurately determine the real configurations of molecules inside the junctions.
|
|
| 34. |
- Lin, Lili, et al.
(författare)
-
First-principles investigations on the anisotropic charge transport in 4,4 '-bis((E)-2-(naphthalen-2-yl)vinyl)-1,1 '-biphenyl single crystal
- 2014
-
Ingår i: Theoretical Chemistry accounts. - : Springer Science and Business Media LLC. - 1432-881X .- 1432-2234. ; 133:9, s. 1551-
-
Tidskriftsartikel (refereegranskat)abstract
- We applied the master equation method to investigate the anisotropic transport property of the 4,4'-bis((E)-2-(naphthalen-2-yl)vinyl)-1,1'-biphenyl molecular crystal based on first-principles calculation. It is found that the hole mobility has the largest value along the [100] direction, while electrons have the best transport property along the [010] direction. The anisotropic transport property was found to have close relationship with the charge transfer integral which is determined by the molecular stacking network in the crystals as well as the intermolecular frontier orbital overlap. In addition, the effect of the charge carrier density and the electronic field on the charge transport was also studied, and little effect was found except that the density is larger than 0.01 and the electronic field is increased to 1.0 x 106 V/cm. The kinetic Monte Carlo simulation method has also been used to study the anisotropic charge transport property, and consistent results were obtained as with the master equation method.
|
|
| 35. |
- Lin, Li-Li, et al.
(författare)
-
Assignments of Inelastic Electron Tunneling Spectra of Semifluorinated Alkanethiol Molecular Junctions
- 2011
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:41, s. 20301-20306
-
Tidskriftsartikel (refereegranskat)abstract
- The peculiar experimental inelastic electron tunneling spectra of a series of hexadecanethiol molecular junctions have finally been reproduced by first-principles simulations. It is found that the debated spectral profile around 0.38 eV indeed originated from the C-H stretching vibration associated with at least two terminal methylene groups close to the sulfur atom. The intensity of this spectral peak becomes dominant, as observed in the experiments when the molecule is titled -40 degrees relative to the normal of the electrode surface, which is due to the opening of a new tunneling pathway bypassing the end sulfur atom. The dependence of this strong vibrational feature on the titled angle of the molecule is predicted with the help of the concept of effective coupling energy. The degree of the fluorination on the inelastic electron tunneling spectrum of hexadecanethiol molecules has also been discussed in detail.
|
|
| 36. |
- Lin, Li-Li, et al.
(författare)
-
Determination of the Configuration of a Single Molecule Junction by Inelastic Electron Tunneling Spectroscopy
- 2010
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:11, s. 5199-5202
-
Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations for inelastic electron tunneling spectroscopy (IETS) of a single 1,3-propanedithiol molecule covalently bound to gold electrodes are presented. Inelastic electron tunneling spectra of the single molecule junction with different contact geometries and molecular orientations at the interface are simulated. It is demonstrated that the delicate variation in the configuration of the single molecule junction caused by separating the two electrodes call result in significant changes in the inelastic electron tunneling spectral profile of the junction. The two Most probable configurations of the molecular junction formed in the experiment (Nano Lett. 2008, 8, 1673) are theoretically identified, and the experimental IET spectra are correctly assigned.
|
|
| 37. |
- Lin, Li-Li, et al.
(författare)
-
Formation and electronic transport properties of bimolecular junctions based on aromatic coupling
- 2010
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 22:32, s. 325102-
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic first-principles study on conductance-voltage characteristics of bi-(quasi) oligo(phenylene ethynylene)-monothiol molecular junctions reported by Wu et al (2008 Nat. Nanotechnol. 3 569) is presented. The so-called ortho-and para-conformations of the bimolecular junction are considered. Our calculation indicates that the bimolecular junction prefers to take the ortho-conformation because of its lower energy. The simulation supports the experimental findings that aromatic coupling between two molecules is strong enough to induce the formation of molecular junctions. By comparing with experimental results, structure parameters for a probable bimolecular junction are determined. The underlying mechanism for formation of the bimolecular junction and its electron transport is discussed.
|
|
| 38. |
- Lin, Li-Li, et al.
(författare)
-
Inelastic Electron Tunneling Spectroscopy of Gold-Benzenedithiol-Gold Junctions : Accurate Determination of Molecular Conformation
- 2011
-
Ingår i: ACS NANO. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 5:3, s. 2257-2263
-
Tidskriftsartikel (refereegranskat)abstract
- The gold benzenedithiol gold junction is the classic prototype of molecular electronics. However, even with the similar experimental setup, it has been difficult to reproduce the measured results because of the lack of basic information about the molecular confirmation inside the junction. We have performed systematic first principles study on the inelastic electron tunneling spectroscopy of this classic junction. By comparing the calculated spectra with four different experimental results, the most possible conformations of the molecule under different experimental conditions have been successfully determined. The relationship between the contact configuration, and the resulted spectra is revealed. It demonstrates, again that one should always combine the theoretical and experimental inelastic electron tunneling spectra to determine the molecular conformation in a junction. Our simulations have also suggested that in terms of the reproducibility and stability, the electromigrated nanogap technique is much better than the mechanically controllable break junction technique.
|
|
| 39. |
- Lin, Lili, et al.
(författare)
-
Theoretical insights into the charge transport in perylene diimides based n-type organic semiconductors
- 2012
-
Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 13:11, s. 2763-2772
-
Tidskriftsartikel (refereegranskat)abstract
- We employed a tunneling enabled hopping model to investigate the charge transport properties for four n-type organic semiconductors perylene diimides compounds. The molecular parameters are calculated by density functional theory and the transport is modeled by kinetic Monte Carlo simulation. It is found that the substitutions at the bay positions of the perylene core have large influences on the charge transport properties through modifications in molecular conformation, the charge reorganization energy as well as the stacking networks in the crystals. The temperature dependence of the mobility shows typical "band-like", in agreement with the recent experiment, but we ascribe it to be the characteristic of nuclear tunneling effect for a localized charge, not by a delocalized band. The largest charge mobility is calculated to be 16.96 cm(2)/V s for the cyano substitution, in good comparison with the experimental value of 6 cm(2)/V s.
|
|
| 40. |
- Lin, Lili
(författare)
-
Theoretical Modeling of Intra- and Inter-molecular Charge Transport
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on theoretical study of charge transportproperties in molecular systems. The understanding of the transportprocess and mechanism in molecular systems is essential forthe design of new functional molecular materials and molecularelectronic devices. The molecular junctions and organic molecularcrystals have been used as the model systems to highlight the usefulnessof theoretical modelling. A molecular junction is a system that consists ofone or several molecules sandwiched between two electrodes.The charge transport in molecular junctions is a very complex processthat is affected by the interaction between molecules and electrodes,the surroundings, as well as electron-electron (e-e) andelectron-phonon (e-p) couplings. When the molecule-electrode couplingis strong, the transport process can be very quick. If the e-p couplingis weak, the inelastic tunneling has only negligible contributions to thetotal current and the elastic electron tunneling plays the dominant role.Furthermore, the hopping process becomes dominant in the case of strong e-pcoupling, for which the geometric relaxation of the molecule needsto be considered. In this thesis, we have examined these three kinds oftransport processes separately. The first studied system is a molecular junction consisting of aromaticallycoupled bimolecules. Its elastic electron tunneling property is simulatedusing Green's functional theory at density functional theory level.The dependence of the conductance of bimolecular junctions on the vertical distances,horizontal distances and the tilt angles has been systematically studied. Theinelastic electron tunneling spectra (IETS) of molecular junctions have beencalculated for several systems that were experimentally measured with conflictingresults and controversial assignments. Our calculations provide the reliableassignments for the experimental spectra and revealed unprecedented detailsabout the molecular conformations within the junctions under different conditions.It demonstrates that a combined theoretical and experimental IETS study is capableof accurately determining the structure of a single molecule inside the junction.The hopping process is a dominant charge transfer process in organic molecularcrystals. We have studied the charge transport ability of four kinds of n-typeorganic semiconductor materials to find out the related structure-to-propertyrelationship. It is done by adopting the quantum charge transfer rate equationcombined with the random walk approach.
|
|
