Lattice misfit

Precipitate microstructures are important for the strength and hardness of many alloys [196-210]. A number of experimental [211-228] and theoretical [220,229-247] investigations have shown that the development of precipitate morphologies is influenced by elastic interactions (El) resulting from a lattice misfit between matrix and precipitates and from an externally applied elastic strain. 

Fig. 12. STM image (10 x 10 nm2) of a densely-packed Pb monolayer on Ag(lll), showing the individual Pb atoms as well as the Moire pattern due to the lattice misfit between monolayer and substrate. Deposition from 0.5 M NaC104 + 0.1 M Na2HCit+ 1 mM Pb (N03)2 at -0.44 V vs. SCE [48],...

Ikemiya et al. [445] have investigated both the atomic structure and growth of electrodeposited Te films on Au(lOO) and Au(lll) with large lattice misfits. Deposition was performed in sulfuric acid solutions using in situ AFM. On both substrates, bulk-deposited Te films were formed according to the Stranski-Krastanov mechanism. Their atomic structures changed with the increasing film thickness. 

The literature in this field is almost unduly preoccupied with lattice mismatch, so it seems appropriate to make a comment before proceeding. In this Datareview, I use the Matthew s convention [1] to compute the misfit. This convention gives a misfit which is simply related to the number of dislocations the film needs to accommodate the misfit. In practice, coherent epitaxy is never achieved for misfits larger than about 2%, so computation of a misfit may not be terribly meaningful. Lattice misfits to the nitride semiconductors for the materials discussed in this paper are given in TABLE 1. 

In the following, structural aspects of substrate surfaces and Me UPD overlayers obtained by in situ GIXS, STM and AFM are discussed. UPD systems without and with different crystallographic Me-S lattice misfit are presented. 

This UPD system is characterized by a significant positive Me-S lattice misfit (do.Tl = 0.3400 nm, doAg - 0.2890 nm) and by the formation of two T1 monolayers in the UPD range. Cyclic voltammograms and l E) isotherms of the system Ag(M/)/Pb, H, CIO4, measured with the FTTL technique [3.105], are presented in Figs. 3.3 and 3.10, respectively. The electrosorption valency was found to be = z = 1 in the entire UPD range (Fig. 3.12b). This means that cosorption or competitive adsorption processes of anions can be excluded in this system. 

Independent of the Me UPD system (chemical nature of Me and S, crystallographic orientation of S, Me-S lattice misfit), thermodynamic and structural results... 

In systems with significant Me-S lattice misfit, the 2D Meads overlayers and/or 2D Me-S surface alloys formed in the UPD range have a different structure in comparison with the 3D Me bulk phase, and contain considerable internal strain (cf. Section 3.4). Thus, the nucleation and growth kinetics in the OPD range will be strongly influenced by the internal strain energy of 2D Me UPD phases. 

In the case of a strong Me-S interaction, the structure and orientation of a Me deposit on top of Me UPD modified S according to the Frank-van der Merwe (cf. Fig. 1.1b) or Stranski-Krastanov mechanisms (cf. Fig. 1.1c) strongly depend on the substrate structure. Independently of crystallographic Me-S lattice misfit, distinct correlations between the epitaxy of a condensed 2D Meads phase and/or 2D Me-S surface alloy phase and the epitaxy of a 3D Me bulk phase can be expected. 

In absence of Me-S lattice misfit, the structure of growing 3D Me layers usually continues that of the condensed and commensurate 2D Meads overlayer and or 2D Me-S surface alloy formed in the UPD range at high For low AEi. The structure of a 3D Me film is usually in complete registry with the structure of the modified substrate surface SQikl) [hkl] II Me(M0 [hkl], where (hkl) and [hkl] are the Miller indices and crystallographic directions, respectively. 

In presence of significant Me-S lattice misfit, the epitaxy of isolated 3D Me crystallites or compact 3D Me films is strongly determined by the structure of internally strained 2D Meads overlayer and/or 2D Me-S surface alloy formed in the UPD range at high F or low AEi. The misfit between the lattice parameters of the 2D Meads phase and/or 2D Me-S surface alloy phase and the 3D Me bulk phase is mainly removed by misfit dislocations. The initial strain disappears after depositing a certain thickness of the 3D Me bulk phase. Usually, a thickness of n Me monolayers where 2 < < 20 is necessary to adjust the 3D Me bulk lattice parameters [4.58, 4.59]. If an incommensurate structure of a 2D Meads overlayer is formed in the UPD range, this structure will also be reflected epitaxially in 3D Me crystallites and ultrathin 3D Me films. 

This system is characterized by a strong Me-S interaction and a significant positive Me-S lattice misfit (rfo.Pb > < o.Ag)- Ag(lOO) and (111) substrates are modified by compressed 2D hep Pbads overlayers, which are higher order commensurate or incommensurate, at relatively low AE (cf. Section 3.4). 

This system is characterized by a strong Me-S interaction and a significant negative Me-S lattice misfit (do.Cu < o.Au)-... 

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