Platinum-based transition metal dichalcogenides have been gaining renewed interest because of the development of a new method to synthesize thin film structures. Here, using first-principles calculation, we explore the electronic properties of PtX 2 (X = S, Se, and Te) with respect to film thickness. For bulk and layered structures (1 to 10 layers), octahedral 1T is the most stable. Surprisingly, we also find that the 3R structure has comparable stability relative to the 1T, implying possible synthesis of 3R. For a bulk 1T structure, PtS 2 is semiconducting with an indirect band gap of 0.25 eV, while PtSe 2 and PtTe 2 are both semi-metallic. Still, all their corresponding monolayers exhibit an indirect semiconducting phase with band gaps of 1.68, 1.18, and 0.40 eV for PtS 2 , PtSe 2 , and PtTe 2 , respectively. For the band properties, we observe that all these materials manifest decreasing/closing of indirect band gap with increasing thickness, a consequence of quantum confinement and interlayer interaction. Moreover, we discover that controlling the thickness and applying strain can manipulate van Hove singularity resulting to high density of states at the maximum valence band. Our results exhibit the sensitivity and tunability of electronic properties of PtX 2 , paving a new path for future potential applications.
NO dissociation on Cu(111) and Cu(2)O(111) surfaces is investigated using spin-polarized density functional theory. This is to verify the possibility of using Cu-based catalyst for NO dissociation which is the rate limiting step for the NO(x) reduction process. The dissociation of molecularly adsorbed NO on the surface is activated for both cases. However, from the reaction path of the NO-Cu(2)O(111) system, the calculated transition state lies below the reference energy which indicates the possibility of dissociation. For the NO-Cu(111) system, the reaction path shows that NO desorption is more likely to occur. The geometric and electronic structure of the Cu(2)O(111) surface indicates that the surface Cu atoms stabilize themselves with reference to the O atom in the subsurface. The interaction results in modification of the electronic structure of the surface Cu atoms of Cu(2)O(111) which greatly affects the adsorption and dissociation of NO. This phenomenon further explains the obtained differences in the dissociation pathways of NO on the surfaces.
We report results of our study on the adsorption of CO on CuPd surfaces with bulk stoichiometric and nonstoichiometric layers using density functional theory (DFT). We found that the presence of Pd atoms in the subsurface layer promotes the adsorption of CO. We also observed CO-induced Pd segregation on the CuPd surface and we attribute this to the strong CO-Pd interaction. Lastly, we showed that the adsorption of CO promotes Pd-Pd interaction as compared to the pristine surface which promotes strong Cu-Pd interaction. These results indicate that CO adsorption on CuPd surfaces can be tuned by taking advantage of the CO-induced segregation and by considering the role of subsurface Pd atoms.
We performed density functional theory (DFT) based calculations to investigate the interaction of CO2 and its dissociated species (CO and O) on Cu3 cluster supported on Cu(1 1 1) (Cu3/Cu(1 1 1)) surfaces. Similar investigations were conducted on Cu(1 1 1) for purpose of comparison. In general, adsorption of CO and O are stronger on the cluster region than on the terrace region of Cu3/Cu and on the flat Cu surface. CO2, on the other hand, is weakly adsorbed on the surfaces. With reference to CO2 dissociation on Cu(1 1 1), we found that the cluster lowers the activation barrier and provides a more stable adsorption of the dissociated species. The presence of co-adsorbed CO in the cluster, however, will increase the activation energy. The variation in the activation barrier with the amount of CO is influenced by the stability of the O atom from the dissociated CO2. We further found that the adsorption energy of O atom is a possible descriptor for CO2 dissociation on the cluster region. The Cu cluster supported on Cu surface could be a promising catalyst for CO2 related reactions based on the lower activation energy for CO2 dissociation on the system than on Cu(1 1 1).
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