A Density Functional Theory Study on the Effect of Ge Alloying on Hydrogen Desorption from SiGe Alloy Surfaces

Abstract

We have used density functional theory to investigate hydrogen desorption from SiGe alloy surfaces, and the effect of Ge alloying on the kinetics of hydrogen desorption via the prepairing and interdimer mechanisms. We find that the calculated activation barriers of the prepairing mechanism are affected by the surface atom bonded to the desorbing hydrogen atoms. On the other hand, our calculations show that the activation barrier for hydrogen desorption via the 2H interdimer mechanism is affected by all four surface atoms of the two neighboring dimers. For the 4H interdimer mechanism, we have shown that the activation barrier for hydrogen desorption is not significantly higher than the endothermicity of hydrogen desorption. We also find that the calculated activation barriers of the interdimer mechanisms are generally lower than those of the prepairing mechanism. In addition, our calculations show that surface Ge atoms on neighboring dimers on SiGe alloy surfaces have a minor effect on the calculated activation barriers of both the prepairing and interdimer mechanisms, which indicates that the effect of Ge alloying on hydrogen desorption is local in nature. We also discuss the effects of cluster size and constraints on the calculated reaction energies and activation barriers of hydrogen desorption via the two mechanisms.

Ab Initio Study of H2 Associative Desorption on Ad-Dimer Reconstructed Si(001) and Ge(001)-(2×1) Surfaces

“…As stated previously, although the trends predicted by semilocal GGA-DFT functionals about the H 2 desorption from the Si(001)-(2×1) surface or SiGe surface alloys are correct, ,, they can also underestimate the desorption barriers and reaction energies, thus leading to a limited agreement with experiments . To overcome these limitations and to have an accurate picture of the desorption barriers and reaction energies of the Si and Ge systems studied in this work, we performed the calculations using the HSE hybrid functional, which includes an exact short-range Fock exchange term .…”

“…In the H2 interdimer adsorption pathway, , the H 2 molecule dissociates over two clean Si neighboring dimers, ending with two H atoms at the same side of the dimers. In the H4 mechanism, , the adsorption occurs on two neighboring Si dimers, which are both already covered on one side with hydrogen atoms, so that adsorption results in a pair of fully saturated dimers. In our case, the interdimer H 2 desorption pathway corresponds to the H2 mechanism, as we considered that only two Si or Ge surface atoms are previously saturated with hydrogen atoms.…”

“…28 For SiGe alloy surfaces, Ge neighboring atoms (either in the bulk or on neighboring dimers) have a minimal effect on the intradimer H 2 desorption. 16 For the interdimer desorption mechanism, previous calculations show a wide range of desorption barriers (1.9−3.1 eV), depending on the number of H atoms considered and on the size of the cluster model used to represent the corresponding semiconductor surface (see, e.g., refs 6, 29−31).…”

“…There have been numerous experimental and theoretical studies on H 2 adsorption, dissociation, and further desorption from the dimerized Si(001)-(2×1) surface. ,− Also, to a lesser extent, the effect of Ge on H 2 desorption from Si(001) has motivated a number of experimental and theoretical studies on both Ge-covered Si(001)-(2×1) and SiGe alloy surfaces. ,− For H 2 desorption from the Si(001)-(2×1) surface, the mechanisms proposed in the literature involve the detachment of two H atoms from the same Si dimer (intradimer or “prepairing” mechanism) or from two different dimers (interdimer mechanism). , From a theoretical point of view, this latter mechanism involves different possibilities, depending on whether both dimers are fully passivated or not, i.e., with 2 or 4 H atoms (H2 or H4 reaction path mechanisms, respectively). , Experimental studies seem to support the interdimer mechanism, i.e., the recombinative desorption from two Si–H bonds on two adjacent dimers along a dimer row . For SiGe alloy surfaces, Ge neighboring atoms (either in the bulk or on neighboring dimers) have a minimal effect on the intradimer H 2 desorption . For the interdimer desorption mechanism, previous calculations show a wide range of desorption barriers (1.9–3.1 eV), depending on the number of H atoms considered and on the size of the cluster model used to represent the corresponding semiconductor surface (see, e.g., refs , − ).…”

Reversible Coordination of H2 by a Distannyne

“…The interaction of hydrogen with transition metals is a key process in organometallic chemistry. − Furthermore, reversible oxidative addition and reductive elimination reactions of H 2 with transition metal complexes constitute fundamental steps in many catalytic cycles. , Such processes have been widely studied not only in organometallic chemistry but also in surface chemistry − and hydrogenase enzymes , and in connection with their relevance to chemical hydrogen storage. , In effect, the binding, storage, and release of H 2 under mild conditions are of major importance, − but despite the investigations of several H 2 carrier species, e.g., amine borane, Mg, , or Al , systems, there have been relatively few instances where reversible absorption and release of hydrogen has been effected under mild conditions for main-group compounds. − Two examples involve the use of metal-free frustrated Lewis pair systems − and antiaromatic boron-containing organic rings . In addition, several main-group compounds have been shown to react with H 2 under ambient conditions to yield hydrides. − These include low-valent group 13 and 14 element compounds, which feature frontier orbitals with small energy separations and suitable symmetry to react with H 2 and whose reactivity can mimic that of transition metal complexes .…”