اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEffect of alkyl substituents on the adsorption of thienylenevinylene oligomers on the Si (100) surface
151
0
0.0
(
0
)
تأليف
Bruno Grandidier
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The adsorption of thienylenevinylene oligomers on the Si(100) surface has been investigated using scanning tunneling microscopy. The mode of substitution of the thiophene ring exerts a strong influence on the adsorption configurations and the images of the oligomer based on 3,4-dihexyl thiophene are highly voltage dependent. We discuss the influence of the alkyl chains on the adsorption process and on the appearance of the molecules in the STM images.
قيم البحث
اقرأ أيضاً
A pi-conjugated {C}3h-oligomer involving three dithienylethylene branches bridged at the meta positions of a central benzenic core has been synthesized and deposited either on the Si(100) surface or on the HOPG surface. On the silicon surface, scanni
ng tunneling microscopy allows the observation of isolated molecules. Conversely, by substituting the thiophene rings of the oligomers with alkyl chains, a spontaneous ordered film is observed on the HOPG surface. As the interaction of the oligomers is different with both surfaces, the utility of the Si(100) surface to characterize individual oligomers prior to their use into a 2D layer is discussed.
We present semiempirical tight binding calculations on thienylenevinylene oligomers up to the hexadecamer stage (n=16) and ab initio calculations based on the local density approximation up to n=8. The results correctly describe the experimental vari
ations of the gap versus size, the optical spectra, and the electrochemical redox potentials. We propose a simple model to deduce from the band structure of the polymer chain the electronic states of the oligomers close to the gap. We analyze the evolution of the gap as a function of the torsion angle between consecutive cells: the modifications are found to be small up to a ~30^{circ}; angle. We show that these oligomers possess extensive pi-electron delocalization along the molecular backbone which makes them interesting for future electronic applications such as molecular wires.
Several dissociated and two non-dissociated adsorption structures of the phenol molecule on the Si(001)-(2 times 1) surface are studied using density functional theory with various exchange and correlation functionals. The relaxed structures and adso
rption energies are obtained and it is found that the dissociated structures are energetically more favourable than the non-dissociated structures. However, the ground state energies alone do not determine which structure is obtained experimentally. To elucidate the situation core level shift spectra for Si 2p and C 1s states are simulated and compared with experimentally measured spectra. Several transition barriers were calculated in order to determine which adsorption structures are kinetically accessible. Based on these results we conclude that the molecule undergoes the dissociation of two hydrogen atoms on adsorption.
First-principles calculations using density functional theory based on norm-conserving pseudopotentials have been performed to investigate the Mg adsorption on the Si(001) surface for 1/4, 1/2 and 1 monolayer coverages. For both 1/4 and 1/2 ML covera
ges it has been found that the most favorable site for the Mg adsorption is the cave site between two dimer rows consistent with the recent experiments. For the 1 ML coverage we have found that the most preferable configuration is when both Mg atoms on 2x1 reconstruction occupy the two shallow sites. We have found that the minimum energy configurations for 1/4 ML coverage is a 2x2 reconstruction while for the 1/2 and 1 ML coverages they are 2x1.
We report a first-principles calculation that models the effect of iron (Fe) atoms on the adsorption of a tungsten (W) atom on W(100) surfaces. The adsorption of a W atom on a clean W(100) surface is compared with that of a W atom on a W(100) surface
covered with a monolayer of Fe atoms. The total energy of the system is computed as the function of the height of the W adatom. Our result shows that the W atom first adsorbs on top of the Fe monolayer. Then the W atom can replace one of the Fe atoms through a path with a moderate energy barrier and reduce its energy further. This intermediate site makes the adsorption (and desorption) of W atoms a two-step process in the presence of Fe atoms and lowers the overall adsorption energy by nearly 2.4 eV. The Fe atoms also provide a surface for W atoms to adsorb facilitating the diffusion of W atoms. The combination of these two effects result in a much more efficient desorption and diffusion of W atoms in the presence of Fe atoms. Our result provides a fundamental mechanism that can explain the activated sintering of tungsten by Fe atoms.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
