Oscillatory Mass Transport in Vapor-Liquid-Solid Growth of Sapphire Nanowires

Oh, Sang Ho; Chisholm, Matthew F.; Kauffmann, Yaron; Kaplan, Wayne D.; Luo, Weidong; Rühle, M.; Scheu, Christina

doi:10.1126/science.1190596

Cited by 181 publications

(195 citation statements)

References 27 publications

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“…The calculations show that an Al termination of the oxide, both at the surface and at the metal-oxide interface, is thermodynamically preferred for the α-Al 2 O 3 ð0001Þ over the considered O 2 pressure range. This is consistent with experiment [22,23] as well as with previous DFT studies [11] including DFT molecular dynamics (MD) simulations of the α-Al 2 O 3 =Al interface [12].…”

supporting

confidence: 80%

Mechanism for Limiting Thickness of Thin Oxide Films on Aluminum

2014

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A first-principles account of the observed limiting thickness of oxide films formed on aluminum during oxidizing conditions is presented. The results uncover enhanced bonding of oxygen to thin alumina films in contact with metallic aluminum that stems from charge transfer between a reconstructed oxide-metal interface and the adsorbed molecules. The first-principles results are compared with the traditional CabreraMott (CM) model, which is a classical continuum model. Within the CM model, charged surface oxygen species and metal ions generate a (Mott) potential that drives oxidation. An apparent limiting thickness is observed as the oxidation rate decreases rapidly with film growth. The present results support experimental estimates of the Mott potential and film thicknesses. In contrast to the CM model, however, the calculations reveal a real limiting thickness that originates from a diminishing oxygen adsorption energy beyond a certain oxide film thickness. Oxidation of metals has tremendous impact on society, and corrosion alone costs the U.S. trillions of dollars each year [1]. Under controlled conditions, however, oxidation plays an important role; thin oxides are used as catalysts, sensors, dielectrics, and corrosion inhibitors. For the latter purpose, metals such as aluminum and rhodium are preferred, as they develop protective oxide layers that inhibit bulk oxidation. Owing to its importance, there have been numerous experimental and theoretical efforts concerning the fundamental understanding of oxidation processes and, especially, the initial growth.The seminal work of Cabrera and Mott (CM) of the mid20th century still remains the key theoretical model for growth of thin oxides on metals, see Fig. 1 [2]. According to CM, electrons from the Fermi level of the metal substrate (ϵ F ) traverse the developing oxide film (with a band gap of E g ) by either tunneling or thermionic emission to acceptor levels (φ a ) of oxygen species, thereby, forming different types of anions (O 2− 2 , O − 2 , O 2− , O − ) on the oxide surface. The negative anions and the positive counterpart at the metal-oxide interface generate an electric potential, called the Mott potential (V M ), which effectively lowers the energy barriers for migration of cations and/or anions through the oxide. This leads to a high oxidation rate even at low temperatures. As the oxide thickness increase, the additional effect of the Mott potential diminishes, and the oxidation process effectively stops at an apparent limiting thickness. It could be noted that although the original CM model discusses charge transfer through tunneling or thermionic emission, the actual transfer is probably defect or polaron mediated. However, this issue is not addressed in the present Letter.Oxidation of aluminum is the prototypical process owing to the simple but versatile electronic structure of aluminum when discussing thin film growth, and this system has played a central role in the establishment of the CM model [3,4]. Recently, Zhou et al. [5,6] showed that the th...

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confidence: 80%

Mechanism for Limiting Thickness of Thin Oxide Films on Aluminum

2014

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“…From meticulous experiments [115,118] and molecular dynamics simulations [119][120][121], it appears that the rate limiting mechanism for non-reactive and dissolutive spreading kinetics is friction at the triple junction, where order in the liquid at the solidliquid interface plays a key role in defining this parameter. Order in the liquid at solid-liquid interfaces has been theoretically analyzed [122][123][124][125][126][127][128][129] and experimentally observed [130][131][132][133][134][135], and will be discussed below in terms of adsorption.…”

Section: Thin Film Stabilitymentioning

confidence: 99%

A review of wetting versus adsorption, complexions, and related phenomena: the rosetta stone of wetting

et al. 2013

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This paper reviews the fundamental concepts and the terminology of wetting. In particular, it focuses on high temperature wetting phenomena of primary interest to materials scientists. We have chosen to split this review into two sections: one related to macroscopic (continuum) definitions and the other to a microscopic (or atomistic) approach, where the role of chemistry and structure of interfaces and free surfaces on wetting phenomena are addressed. A great deal of attention has been placed on thermodynamics. This allows clarification of many important features, including the state of equilibrium between phases, the kinetics of equilibration, triple lines, hysteresis, adsorption (segregation) and the concept of complexions, intergranular films, prewetting, bulk phase transitions versus ''interface transitions'', liquid versus solid wetting, and wetting versus dewetting.

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“…While most analyses of NW growth kinetics are based on post-growth characterization and static analyses of complete NWs, recent progress has been made experimentally by insitu growth characterization [39][40][41][42][43] and ex situ study of NWs with markers inserted during growth [23,44], and dynamic modelling [45][46][47]. For a more complete understanding of growth one should understand in detail the dependence of the basic control parameters (i.e.…”

Section: Introductionmentioning

confidence: 99%

Advances in the theory of III–V nanowire growth dynamics

Krogstrup¹,

Jørgensen²,

Johnson³

et al. 2013

J. Phys. D: Appl. Phys.

127

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Nanowire (NW) crystal growth via the vapour-liquid-solid mechanism is a complex dynamic process involving interactions between many atoms of various thermodynamic states. With increasing speed over the last few decades many works have reported on various aspects of the growth mechanisms, both experimentally and theoretically. We will here propose a general continuum formalism for growth kinetics based on thermodynamic parameters and transition state kinetics. We use the formalism together with key elements of recent research to present a more overall treatment of III-V NW growth, which can serve as a basis to model and understand the dynamical mechanisms in terms of the basic control parameters, temperature and pressures/beam fluxes. Self-catalysed GaAs NW growth on Si substrates by molecular beam epitaxy is used as a model system.

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Oscillatory Mass Transport in Vapor-Liquid-Solid Growth of Sapphire Nanowires

Cited by 181 publications

References 27 publications

Mechanism for Limiting Thickness of Thin Oxide Films on Aluminum

Mechanism for Limiting Thickness of Thin Oxide Films on Aluminum

A review of wetting versus adsorption, complexions, and related phenomena: the rosetta stone of wetting

Advances in the theory of III–V nanowire growth dynamics

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