Possible Pathways of CVD Processes Leading to III–V Semiconductors via a Two‐Dimensional Growth

Himmel, Hans‐Jörg

doi:10.1002/cphc.200400643

Cited by 7 publications

(10 citation statements)

References 34 publications

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“…Group 13–15 binary hydrides, [HMYH] n , together with their substituted analogues, hold the promise for acting as precursors for group 13–15 semiconducting nanomaterials 1. 2 Structural characteristics of the higher oligomeric cages of the hydrides are known to differ from their valence isoelectronic carbon analogues. The combination of 12 five‐membered rings and a variable number of six‐membered rings,3 familiar from fullerenes4 and carbon nanotubes,5 does not apply, since the five‐membered rings would require the presence of MM and YY bonds.…”

Section: B3lyp/tzvp Calculated Total Energies and Gibbs Free Energiesmentioning

confidence: 99%

Cages and Needles of Group 13–15 Binary Hydrides

et al. 2006

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Group 13-15 binary hydrides, [HMYH] n , together with their substituted analogues, hold the promise for acting as precursors for group 13-15 semiconducting nanomaterials. [1,2] Structural characteristics of the higher oligomeric cages of the hydrides are known to differ from their valence isoelectronic carbon analogues. The combination of 12 five-membered rings and a variable number of six-membered rings, [3] familiar from fullerenes [4] and carbon nanotubes, [5] does not apply, since the five-membered rings would require the presence of MÀM and YÀY bonds. This structural problem can be avoided by replacing the 12 pentagons with six squares, as postulated for boron nitride cages.[6] Previous theoretical studies on [HMYH] n structures where n 16, have led to the conclusion that needleshaped structures with three adjacent squares at each end are thermodynamically favored for all group 13-15 pairs. [7,8] Very recently, the existence of perhydrogenated fullerenes, that is, the fulleranes, has been predicted, where partial endo-hydrogenation significantly stabilizes the cages.[9] In the theoretical study reported herein, we demonstrate that application of the structural motifs of the fulleranes for group 13-15 binary hydrides produces stable "in-out" isomeric cages without adjacent squares.We compared the needle-shaped structures with tetrahedral cages for group 13-15 binary hydrides [HMYH] n , (M= B, Al, Ga; Y = N, P, As). The curvature of the cages flattens as a function of the size of the cage, making large exo-hydrogenated cage structures unfavorable due to distortion from the optimal sp 3 hybridization. The problem with large structures can be overcome by partial endo-hydrogenation, which has been demonstrated to produce very stable C 80 H 80 and C 180 H 180 fulleranes with stabilities improving as a function of the size of the cage.[9] This "in-out" isomerism originates from puckering of the hexagons and hence applies for group 13-15 binary hydrides, as well. Since the six squares, necessary for cage closure, cannot participate in the puckering, the "in-out" isomerism requires the presence of atoms that are not a part of a square. The smallest tetrahedral cage meeting the requirement is the T d -symmetric [HMYH] 16 (Figure 1 a). Here, the atoms that basically could become endo-hydrogenated are the four connecting each set of three squares. Due to its small size, however, the repulsions between the endo-hydrogens would destabilize the cage. The next tetrahedral cage in the series is the Tsymmetric [HMYH] 28 , which already has sufficient space for endo-hydrogenation. A particularly favorable species is obtained by endo-hydrogenation of every other atom at the distance of two MÀY bonds from each square atom (Figure 1 b).We optimized the compounds shown in Figure 1 at the B3LYP/TZVP level of theory. The stabilities of the cages compared to the isomeric needles (Figures 1 c-1 d) are given in Figure 2, showing total energies and Gibbs free energies (T = 298.15 K) per HMYH unit relative to the previously reported...

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Section: B3lyp/tzvp Calculated Total Energies and Gibbs Free Energiesmentioning

confidence: 99%

Cages and Needles of Group 13–15 Binary Hydrides

et al. 2006

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“…Substitution of bromide by hydrogen results in the exothermic generation of both “handled” cages and “balustrade” ladder compounds. These compounds provide a viable alternative to the 2D structures theoretically considered by Himmel . Further theoretical and experimental studies in this direction are highly desirable and expected to be very promising.…”

Section: Discussionmentioning

confidence: 97%

“…8 It is argued that cross-linking reactions play a role in this conversion. 8 Possible pathways of formation of 2D AlN structures were considered in detail by Himmel 9 using theoretical methods.…”

Section: Introductionmentioning

confidence: 99%

Aluminum−Nitrogen Rings and Cages with Organic Handles: A Theoretical Study

2009

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The structures and stability of monomeric and oligomeric compounds resulting from the elimination of 2 mol of HBr from the AlBr(3)en complex have been studied theoretically at the B3LYP/LANL2DZ(d,p) level of theory. Two series of the ring and cage oligomer compounds were considered: imino [AlBrNCH(2)CH(2)NH(2)](n), n = 1-4, 6 (I(n)), and isomeric amido [AlBrNHCH(2)CH(2)NH](n), n = 1-3 (A'(n)), species. In all cases the amido isomers are 95-295 kJ mol(-1) more stable compared to their imino counterpairs. Intramolecular donor-acceptor interactions play an important role in the stabilization of the structure. Possible pathways of the polymerization have also been explored. Although the generation of the oligomers via HBr elimination in the gas phase is predicted to be thermodynamically unfavorable, operation of such reactions in the condensed phase is feasible. Substitution of bromine by hydrogen makes H(2) elimination reactions thermodynamically favorable. This opens a perspective for the synthesis of novel ladder-type oligomers with a continuous (AlN)(n) core supported by C(2)H(4) balustrade and imino cages with C(2)H(4) handles.

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“…They found that the formation of the [RGaNR′] 4 tetramer and [RGaNR′] 6 hexamer species is thermodynamically favorable in the gas phase at temperatures up to 720 K (R = H, R′ = CH 3 ) and 920-940 K (R = H, CH 3 , R′ = H). In a recent study on the possible pathways of CVD processes leading to III-V semiconductors, Himmel [18] simulated a two-dimensional growth of solid AlN under CVD conditions and proposed several intermediates. Based solely on the free energy calculations (kinetic factors are ignored), it is argued that higher Al n N n H m clusters can preferentially be formed at the surface and not in the gas phase at temperatures used in a CVD process.…”

Section: Decomposition Reactionsmentioning

confidence: 99%

Thermodynamic Stability of Small Ga_nN_n Clusters as Intermediates in GaN CVD

Tafipolsky

Schmid

2007

Chemical Vapor Deposition

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Small stoichiometric, as well as some nonstoichiometric, gallium nitride clusters of the type Ga n N m (n + m ≤ 8) are investigated by density functional theory (DFT), MP2, and coupled cluster, CCSD(T), calculations. The lowest energy structures of the stoichiometric clusters and the corresponding products after the loss of a nitrogen molecule have been determined. It is shown that, above room temperature, they are unstable against the loss of nitrogen molecules and therefore are even less stable than the bulk material. Thus, these clusters can be ruled out as direct intermediates for the formation of bulk GaN. This has been ignored up to now and is of crucial importance for the decomposition mechanism of single-molecule precursor systems. It is argued that the azide group can stabilize a tetrahedral arrangement of four gallium atoms around the N atom, and a nonstoichiometric gallium nitrogen cluster like gallium azide, GaN 3 , can play an important role as an intermediate during the formation of bulk GaN in CVD.

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Possible Pathways of CVD Processes Leading to III–V Semiconductors via a Two‐Dimensional Growth

Cited by 7 publications

References 34 publications

Cages and Needles of Group 13–15 Binary Hydrides

Cages and Needles of Group 13–15 Binary Hydrides

Aluminum−Nitrogen Rings and Cages with Organic Handles: A Theoretical Study

Thermodynamic Stability of Small Ga_nN_n Clusters as Intermediates in GaN CVD

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Possible Pathways of CVD Processes Leading to III–V Semiconductors via a Two‐Dimensional Growth

Cited by 7 publications

References 34 publications

Cages and Needles of Group 13–15 Binary Hydrides

Cages and Needles of Group 13–15 Binary Hydrides

Aluminum−Nitrogen Rings and Cages with Organic Handles: A Theoretical Study

Thermodynamic Stability of Small GanNn Clusters as Intermediates in GaN CVD

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Thermodynamic Stability of Small Ga_nN_n Clusters as Intermediates in GaN CVD