Effect of strain on the energetics and kinetics of dissociation ofSb4on Ge(001)

Abstract

A comprehensive search for the precursor dissociation of antimony tetramers on Ge͑001͒ with strain was carried out using first-principles calculations. In contrast to previous theoretical studies on Si͑001͒ ͓Phys. Rev. Lett. 97, 046103 ͑2006͔͒ and in agreement with recent experiments, we reveal a square intermediate anisotropy dissociation pathway across the surface dimer row, where the dissociation energetics and kinetics can be qualitatively altered by the strain and lead to divergent dissociation pathways and patterns with substratedimer-bond breaking due to the weak interactions between Ge-Ge and Sb-Ge bonds.It has long been known that molecular chemisorption on solid surfaces often involves intermediate precursor states and several competing dynamical processes such as dissociation, diffusion, and desorption. 1 A typical example is the reaction of group-V elements ͑e.g., As, Sb, and Bi͒ with Si and Ge surfaces. 2-18 For Sb 4 on Si͑001͒, the three-dimensional ͑3D͒ clusters can convert to flat tetramers that can then split into pairs of dimers. Scanning tunneling microscopy ͑STM͒ measurements 2-4 and density-functional theory ͑DFT͒ calculation 14 revealed a two-stage reaction process involving two distinct pathways, along and across the surface dimer row via a rhombus intermediate state. Similar but distinct reaction behavior is also observed for Sb 4 on Ge͑001͒ where STM measurements identified a pathway involving a twodimensional ͑2D͒ flat square intermediate state across the surface dimer row. 5 Such processes have attracted considerable attention because they play a key role in the epitaxial growth of Ge/Si heterostructures. [15][16][17][18] In this Brief Report, we present a comprehensive search on the dissociation energetics and kinetics of Sb 4 on Ge͑001͒ surface with biaxial strain using DFT calculations. They show sensitive dependence on the strain state of the substrate: in the absence of an external strain, Sb 4 dissociates via a square intermediate state with a bond-twisting assisted rigid rotation mechanism for the first-stage conversion and a substrate-dimer-bond-breaking assisted piecewise rotation dissociation pathway across the dimer row for the secondstage conversion. While with an applied strain, the energetics and kinetics can be qualitatively altered, leading to distinct reaction pathways and patterns due to the weak interactions between Ge-Ge and Sb-Ge bonds. For comparison, we also performed calculations for Sb 4 on Si͑001͒. In stark contrast to the case of Sb 4 on Ge͑001͒, the external strain has little effect on the dissociation behavior on Si͑001͒ due to the strong interactions between Sb-Si and Si-Si bonds.The reported calculations are carried out using VASP code 19 with ultrasoft pseudopotentials 20 and the generalized gradient approximation ͑GGA͒. 21 An energy cutoff of 200 eV for the plane-wave basis set is used. The supercell size is set to XYZ =16ϫ 32ϫ 35.72 Å 3 with ten layers of Ge in the Z direction and one layer of hydrogen to passivate the bottom Ge layer. The XY plane corr...

Compressive-Strain-Facilitated Fast Oxygen Migration with Reversible Topotactic Transformation in La0.5Sr0.5CoOx via All-Solid-State Electrolyte Gating

“…This is consistent with the observation that a relatively low V th is needed to drive the transition from B-LSCO to P-LSCO because it is an exothermic reaction and consumes energy. It is known that the conversion rate between the two states of the reaction can be evaluated by the Arrhenius equation where D 0 is the prefactor, E a the energy barrier, k B the Boltzmann constant, and T the temperature. Therefore, the ratio of the conversion rate for the transition between B-LSCO and P-LSCO can be expressed as .…”

Magic Monatomic Linear Chains for Mn Nanowire Self-Assembly on Si(001)

“…1, we show five possible dimer or dimerlike structures PM, PP, and TT on the dimer rows and HH and MM on the trough. Here the dimers PM and TT are well defined for Si, Ge, and Bi on Si(001) [19][20][21][22][23][24], and an MM-type dimer has been used to describe the structure of group III elements Al and Ga on Si(001) [25][26][27]. However, among them, only the PM dimer is more stable than the P site ad-Mn.…”

Adsorption and dynamics of group IV, V atoms and molecular oxygen on semiconductor group IV (0 0 1) surfaces

“…Scanning tunneling microscope (STM) experiments have shown that initially the group V atoms group (Sb and Bi) are adsorbed in the form of Sb 4 tetramers, Bi 4 tetramers and Bi 2 dimers [110][111][112][113]. In the case of Sb 4 on Si(0 0 1) and Ge(0 0 1), the 3D Sb 4 clusters can convert to flat tetramers, which can subsequently [114][115][116][117]. The activation energy for the A → B transformation of the separate Sb ad-dimer on the Si(0 0 1) surface was found to be 1.0 eV [114][115][116][117].…”

“…In the case of Sb 4 on Si(0 0 1) and Ge(0 0 1), the 3D Sb 4 clusters can convert to flat tetramers, which can subsequently [114][115][116][117]. The activation energy for the A → B transformation of the separate Sb ad-dimer on the Si(0 0 1) surface was found to be 1.0 eV [114][115][116][117]. The two-stage A → B transformation (rotation) pathway, which is characterized by two transition states, and the local minimum between them was obtained for the Sb addimer on the Si(0 0 1) surface by using slab geometry and general gradient approx imation (GGA) calculations [116].…”