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1.
Hydrogenation-induced metal-semiconductor transitions usually occur in simple systems based on rare earths and/or magnesium, accompanied by major reconstructions of the metal host (atom shifts >2 A). We report on the first such transition in a quaternary system based on a transition element. Metallic LaMg2Ni absorbs hydrogen near ambient conditions, forming the nonmetallic hydride LaMg2NiH7 which has a nearly unchanged metal host structure (atom shifts <0.7 A). The transition is induced by a charge transfer of conduction electrons into tetrahedral [NiH4]4- complexes having closed-shell electron configurations. 相似文献
2.
Lanier CH Rondinelli JM Deng B Kilaas R Poeppelmeier KR Marks LD 《Physical review letters》2007,98(8):086102
The structure of the (sqrt[5] x sqrt[5])R26.6 degrees reconstruction of LaAlO3 (001) has been determined using transmission electron diffraction combined with direct methods. It has a lanthanum oxide termination with one lanthanum vacancy per surface unit cell. Density functional calculations indicate that charge compensation occurs by a fractional number of highly delocalized holes, and that the surface contains no oxygen vacancies and the holes are not filled with hydrogen. The reconstruction can be understood in terms of expulsion of the more electropositive cation from the surface and increased covalency. 相似文献
3.
For many decades it has been assumed that an adsorbate centered above a metal surface and with a net negative charge should increase the work function of the surface. However, despite their electronegativity, N adatoms on W[100] cause a significant work function decrease. Here we present a resolution of this anomaly. Using density functional theory, we demonstrate that while the N atom carries a negative charge, of overriding importance is a reduction in the surface overspill electron density into the vacuum, when that charge is engaged in bonding to the adatom. This novel interpretation is fundamentally important in the general understanding of work function changes induced by atomic adsorbates. 相似文献
4.
We present and discuss density functional theory calculations addressing the electronic structure and energetics of isolated oxygen ad-atoms at the (001) surfaces of PbTiO3 (PTO) and LaMnO3 (LMO) cubic perovskites. Both AO- and BO2-type of surface terminations are considered for each perovskite. Difference electron density analysis has been carried out for each surface to probe local electronic charge redistribution upon oxygen adsorption. Our results show that the (001) surfaces of the two perovskites behave quite differently towards oxygen adsorption. In the case of the PTO (001) surfaces, the adsorbate oxygen atom was found to form a peroxide-type molecular species along with a surface lattice oxygen atom on both PbO- and TiO2-terminated surface facets. On the other hand, the most stable oxygen adsorption site for the LMO (001) surfaces corresponds to the one expected from a natural continuation of the perovskite lattice. Moreover, the dissociative adsorption of molecular oxygen varies from being only slightly exothermic on the PTO (001) facets to being highly exothermic on the LMO (001) facets. The AO-terminated facets, in general, showed a stronger binding to the adsorbed oxygen. 相似文献
5.
贾国荣 《原子与分子物理学报》2017,34(6)
运用密度泛函理论(DFT)方法,研究了异构体C60O[6,6]与C60O[5,6]之间的重排反应机理。结果显示: 它们之间的反应路径是经过一个过渡态没有中间体的一步反应。C60O[6,6] 转化成C60O[5,6]的反应能垒是42.7 kcal*mol-1,在反方向,C60O[5,6]转化成C60O[6,6]的反应能垒是47.3 kcal*mol-1,同时,扫描出氧原子在富勒烯C60(Ih)表面的势能面(PEC),以详细显示异构体C60O[6,6]与C60O[5,6]之间的重排反应机理。 相似文献
6.
运用密度泛函理论(DFT)方法,研究了异构体C60O[6,6]与C60O[5,6]之间的重排反应机理。结果显示: 它们之间的反应路径是经过一个过渡态没有中间体的一步反应。C60O[6,6] 转化成C60O[5,6]的反应能垒是42.7 kcal*mol-1,在反方向,C60O[5,6]转化成C60O[6,6]的反应能垒是47.3 kcal*mol-1,同时,扫描出氧原子在富勒烯C60(Ih)表面的势能面(PEC),以详细显示异构体C60O[6,6]与C60O[5,6]之间的重排反应机理。 相似文献
7.
Xuemin WangChangle Sheng Yuyin WangLiping Peng Weidong Wu Yongjian Tang 《Physica B: Condensed Matter》2011,406(14):2777-2782
The adsorption of oxygen atoms on Mg3Nd (0 0 1) surface was studied based on density function theory (DFT), in which the exchange-correlation potential was chosen as the generalized gradient approximation (GGA) in the Perdew and Wang (PW91). The most preferred adsorption position was at the top-hollow site. Upon the optimization on top-hollow site with different coverage, it was found that the adsorption energy decreased with oxygen coverage. The density of states analysis showed that obvious charge transfer took place between O atom and the nearest Nd atom and chemical bond formed between O atom and the nearest Nd atom after O adsorption. The result of surface energy as a function of chemical potential change of oxygen indicated the clean Mg3Nd (0 0 1) surface was easy to adsorb oxygen and form 1.00 ML surface. 相似文献
8.
合成了 4种茜素黄R稀土配合物 ,通过对元素分析、红外光谱、紫外光谱和核磁共振氢谱的分析 ,确定它们的组成为 :Na[REL2 ]·2H2 O(RE =Sm ,Eu ,Tb ,Y ,NaHL =茜素黄R)。红外光谱表明 :配体以羧羰基的氧与稀土离子以单齿配位 ;配体的酚羟基离解 ,脱去质子后羟基氧与稀土离子配位 ;即酚氧和羧羰基的氧与稀土离子形成一个六元螯合环。配体的吸收峰 398nm在形成配合物后移于 35 1~ 35 5nm ,发生了较大位移 ,这说明稀土离子与配体成键 ;配合物IR在 4 15~ 4 35cm-1之间出现的新吸收峰归属为RE—O键的伸缩振动 ,佐证了配合物的形成 ;硝基中的氧和偶氮的氮原子未参与配位 ;IR还说明有两个水分子配位于稀土离子。紫外灯下可以看到Eu(Ⅲ )的配合物很强的红色荧光 ;荧光光谱测定 :Na[EuL2 ]·2H2 O有两个荧光发射峰分属于Eu的 5D0 → 7F1和5D0 → 7F2 跃迁。 相似文献
9.
The adsorption of oxygen on a (110)Ag surface is investigated by means of Auger electron spectroscopy, LEED and low energy helium ion scattering (IS). With LEED two ordered structures, i.e. (3×1) and (2×1) were observed at oxygen exposures of 1700 L and 7000 L respectively. The oxygen signal observed by AES and IS increases monotonically with oxygen exposure. The signals can be related to absolute coverage by comparison with Δφ measurements and by the use of the LEED data. With this calibration and with theoretical scattering cross-sections the IS measurements allow the position of the adsorbed oxygen to be estimated. The observation of a strong azimuthal anisotropy of the IS signal, e.g. a large oxygen signal if the plane of scattering is parallel to the [110] direction and a relatively small oxygen signal in the [100] direction, leads to the conclusion that the oxygen is adsorbed in a bridge position between two Ag atoms of the [110] surface channels, its centre being slightly below the centres of the Ag atoms. 相似文献
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12.
Scott P. Price Xiao Tong Claron Ridge Vladimir Shapovalov Zhenpeng Hu Paul Kemper Horia Metiu Michael T. Bowers Steven K. Buratto 《Surface science》2011,605(9-10):972-976
We use ultra-high vacuum scanning tunneling microscopy (UHV–STM) to probe, at the atomic level, the structure of mass-selected isolated V1, V2, VO and VO2 clusters deposited on rutile TiO2(110) by ion soft landing. All four species interact differently with the TiO2 surface and the ultimate binding site and configuration strikes a balance between the gas-phase structure and the ligation of this cluster by the TiO2 surface. Our results show that vanadium atoms prefer to bind in the upper threefold hollow sites on the surface and have a slight tendency to pair along the [1–10] direction, while vanadium dimers bind to the surface oriented along the [001] direction exclusively. VO clusters bind with the vanadium atom in the upper threefold hollow site and with the oxygen atom bound to an adjacent fivefold coordinated Ti atom (5c-Ti). The VO2 cluster also binds with the vanadium atom in the upper threefold hollow site and with both oxygen atoms bound to adjacent 5c-Ti atoms or with only one oxygen bound to the surface and the other directed out of the plane of the surface. 相似文献
13.
The displacement of an oxygen atom in pure alpha quartz is studied via first-principles molecular dynamics. The simulations show that when an O atom in a Si-O-Si bridge is moved away from its original equilibrium position, a new stable energy minimum can be reached. Depending on the spin state and charge Q of the system, this minimum can give rise to either a threefold oxygen (singlet ground state and Q=+1) or to an unsaturated Si atom carrying a dangling bond (triplet state). In the latter case, the hyperfine parameters associated with the 29Si dangling bond are in rather good agreement with electron paramagnetic resonance/electron nuclear double resonance experiments. 相似文献
14.
The adsorption of one cesium atom on a (110) gallium arsenide surface is investigated by means of a molecular-orbital method. Several surface deformations are considered. The values obtained for the extraction energy of one electron, the net charge of cesium atom, and the adsorption energy, allow to infer that the cesium atom is placed above the surface in neighbourhood of a gallium atom. 相似文献
15.
?. Kadero?lu Z. Aydu?an B. Alkan M. ?akmak 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(3):359-363
The atomic and electronic properties of the adsorption of tert-butanol
[(CH3)3OH] molecule on the Si(001)-(2×1) surface have been
studied by using the ab-initio density functional theory (DFT) based
on pseudopotential approach. We have found that tert-butanol bonded the Si(001) surface by oxygen atom, cleaving
a O–H bond and producing a Si-H bond and tert-butoxy surface species. We
have also investigated the influence of chemisorption of tert-butanol on the
electronic structure of the clean Si(001)-(2×1) surface. Two occupied
surface states situated entirely below the bulk valence band maximum have
been identified, which means that the clean Si(001)-(2×1)surface was passivated by the chemisorption of tert-butanol. In order
to explain
the nature of the surface components we have also plotted the total and partial
charge densities at the [`(K)]\bar{K} point of the surface Brillouin zone (SBZ). 相似文献
16.
The surface structures of twenty-two high Miller Index crystal faces of platinum were studied in ultrahigh vacuum (uhv) when clean and in the presence of a monolayer of chemisorbed oxygen or carbon by low-energy electron diffraction (LEED). Besides the low Miller index planes [the (001), (011), and (111)], only a few of the surfaces [the (112), (113), (133), (122) and (012)] were stable under all conditions of the experiments. The stable surfaces are characterized by a very high density of periodic steps of one atom in height or a complete lack of steps. The other platinum crystal faces restructure as the surface composition is changed. Some of the surface structures that are stable in uhv and in oxygen reconstruct in the presence of carbon while others are stable when clean and when carbon covered but restructure when covered with oxygen. In addition to the one atom high step-terrace configuration there are atomically clean surface structures with multiple height steps and structures in “hill and valley” configuration consisting of large facet planes detectable by LEED. The implications to heterogeneous catalysis of the observed stability and restructuring of the various crystal planes in changing reaction conditions are discussed. 相似文献
17.
LaTiO3 是一种典型的强关联电子材料, 其(110) 薄膜为通过晶格对称性、应变等的设计调控外延结构的物理性质提供了新的机会. 本文研究了SrTiO3(110) 衬底表面金属La 和Ti 沉积所引起的微观结构变化, 进而利用电子衍射信号对分子束外延薄膜生长表面阳离子浓度的灵敏响应, 发展了原位、实时、精确控制金属蒸发源沉积速率的方法, 实现了高质量LaTiO3(110) 薄膜的生长和对阳离子化学配比的精确控制. 由于LaTiO3中Ti3+ 3d 电子的库仑排斥作用, 氧原子层截止的(110) 表面更容易实现极性补偿, 因此生长得到的薄膜表面暴露出单一类型的氧截止面. 相似文献
18.
The electron terms are constructed for oxygen dimer ions at large ion-atom distances taking into account a certain scheme of summation of electron momenta on the basis of a hierarchy of various ion-atom interactions. Because the number of interaction types exceeds that in the Hund scheme, a realistic hierarchy of interactions and corresponding quantum numbers of the diatomic ion are outside the Hund coupling scheme. Electron terms are evaluated for the oxygen dimer ion in the case where the ground and first excited states of an atom and an ion belong to the respective valence electron shells p4 and p3 and correspond to the range of separations that determine the cross sections of resonant charge exchange in plasma. These electron terms allow us to calculate the partial and average cross sections for resonant charge exchange involving an oxygen ion and atom in the ground and first excited states in the range of collision energies of interest for oxygen plasmas. The specific features of electron terms of the oxygen ion dimer and the cross section of electron transfer are analyzed. 相似文献
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20.
Using DMol and the discrete variational method within the framework of the density functional theory,we study the alloying effects of Nb,Ti,and V in the [100](010) edge dislocation core of NiAl.We find that when Nb(Ti,V) is substituted for Al in the center-Al,the binding energy of the system reduces 3.00 eV(2.98 eV,2.66 eV).When Nb(Ti,V) is substituted for Ni in the center-Ni,the binding energy of the system reduces only 0.47 eV(0.16 eV,0.09 eV).This shows that Nb(Ti,V) exhibits a strong Al site preference,which agrees with the experimental and other theoretical results.The analyses of the charge distribution,the interatomic energy and the partial density of states show that some charge accumulations appear between the impurity atom and Ni atoms,and the strong bonding states are formed between impurity atom and neighbouring host atoms due mainly to the hybridization of 4d5s(3d4s) orbitals of impurity atoms and 3d4s4p orbitals of host Ni atoms.The impurity induces a strong pinning effect on the [100](010) edge dislocation motion in NiAl,which is related to the mechanical properties of the NiAl alloy. 相似文献