Metal reconstructed

A breakdown of the structural results by type of surface shows results for nearly 50 clean, unreconstructed metal surfaces and about 10 alloys and reconstructed metal surfaces. The structures of about 65 atomic overlayers on metal surfaces have been determined, some 40 of these involving chalcogen atoms. Just over 20 molecular structures have been determined for metal surfaces, half of these being overlayers of undissociated carbon monoxide and the others various hydrocarbons. Turning to semiconductors, some 13 clean, usually reconstructed structures were determined, against nearly 10 atomic overlayer structures. In addition, about 15 insulator surface structures have been investigated. 

From the above it is evident that metal surfaces may be utilized as templates if certain conditions are met. If we consider reconstructed surfaces the reconstruction has to be stable during further deposition of material. The same holds for nanopatterns formed by deposition of thin films. Likewise vicinal surfaces may facet during the deposition of further material. This section will therefore be dedicated to the use of metal surfaces as growth templates. We use the classification of the systems that was estabhshed in Sect. 2 and begin with reconstructed metal surfaces. 

After having exploited the use of reconstructed metal surfaces and vicinal surfaces as templates we will now turn to metal films. Since it has been shown that the nanopatterns of the above mentioned surfaces are in many cases excellent templates for overlayer growth the same can be expected for nanostructured metal films. Indeed a number of such systems have been investigated in terms of their potential use as templates. As the first example we refer to the homoepitaxial growth of Ag on the reconstructed 2 ML thick Ag film on Pt(l 11) (see Fig. 10). Already in 1995 Brune et al. were able to show that further Ag deposition at 100 K on this specific surface leads to the ordered growth of Ag islands [169,170]. Later it was reasoned that the ordering occurs due to the confined nucleation of adatoms within the superstructure cells of the periodic surface dislocation network [171]. The same effect is also present for the deposition of mass select Ag7 clusters [172] and Fe film growth on 2 ML Cu on Pt(l 1 1) [170]. 

Furthermore, the moir pattern found for FeO thin films on Pt(l 11) has been used as a template for the growth of nanopatterned Fe layers [198]. This effect is believed to be due to the strain relief in the oxide layer resulting in domains with fee and hep stacking. Thus, the same mechanism as found for similarly reconstructed metal surfaces should be responsible for the template-controlled growth on metal film templates. Table 2 summarizes the results obtained for the template-controlled growth on the surfaces discussed in Sect. 4. 

A detailed study of N2O reduction on a variety of single-crystal Pt-group metal electrodes shows that N2O reduction current maxima occurred exactly at Claviher s Eq=o- Therefore the N2O reduction data have been used for obtaining the Eq values (Table 5). The importance of a local value of Eq=o has been emphasized, especially with respect to reconstructing metal surfaces such as Pt(lOO) and Pt(llO), which can be prepared in a variety of crystallographic states [5, 65-68]. 

Fig. 13 (a) Non-reconstructed and (b) reconstructed metal terminated (001) chalcopyrite surface. All distances are in Angstroms. Reprinted with permission from Ref. 30. Copyright (2012) American Chemical Society. 

Another important application area is the non-destructive defectoscopy of electronic components. Fig.2a shows an X-ray shadow image of a SMC LED. The 3-dimensional displacement of internal parts can only be visualized non-destructively in the tomographic reconstmction. Reconstructed cross sections through this LED are shown in Fig.2b. In the same way most electronic components in plastic and thin metal cases can be visualized. Even small electronic assemblies like hybrid ICs, magnetic heads, microphones, ABS-sensors can be tested by microtomograpical methods. 

Perhaps the most fascinating detail is the surface reconstruction that occurs with CO adsorption (see Refs. 311 and 312 for more general discussions of chemisorption-induced reconstructions of metal surfaces). As shown in Fig. XVI-8, for example, the Pt(lOO) bare surface reconstructs itself to a hexagonal pattern, but on CO adsorption this reconstruction is lifted [306] CO adsorption on Pd( 110) reconstructs the surface to a missing-row pattern [309]. These reconstructions are reversible and as a result, oscillatory behavior can be observed. Returning to the Pt(lOO) case, as CO is adsorbed patches of the simple 1 x 1 structure (the structure of an undistorted (100) face) form. Oxygen adsorbs on any bare 1 x 1 spots, reacts with adjacent CO to remove it as CO2, and at a certain point, the surface reverts to toe hexagonal stmcture. The presumed sequence of events is shown in Fig. XVIII-28. 

Kolb D M 1996 Reconstruction phenomena at metal-electrolyte interfaces Prog. Surf. Sc/. 51 109... 

In the first reconstruction [27] of road slabs contaminated with CL, silicon iron anodes were embedded in a layer of coke breeze as shown in Fig. 19-4a or the current connection was achieved with noble metal wires in a conducting mineral bedding material. Slots were ground into the concrete surface for this purpose at spacings of about 0.3 m (see Fig. 19-4b). This system is not suitable for vertical structures. 

Since then, STM has been established as an insttument fot foteftont research in surface physics. Atomic resolution work in ultrahigh vacuum includes studies of metals, semimetals and semiconductors. In particular, ultrahigh-vacuum STM has been used to elucidate the reconstructions that Si, as well as other semiconducting and metallic surfaces undergo when a submonolayer to a few monolayers of metals are adsorbed on the otherwise pristine surface. ... 

In 1985 Car and Parrinello invented a method [111-113] in which molecular dynamics (MD) methods are combined with first-principles computations such that the interatomic forces due to the electronic degrees of freedom are computed by density functional theory [114-116] and the statistical properties by the MD method. This method and related ab initio simulations have been successfully applied to carbon [117], silicon [118-120], copper [121], surface reconstruction [122-128], atomic clusters [129-133], molecular crystals [134], the epitaxial growth of metals [135-140], and many other systems for a review see Ref. 113. 

We shall first review the basic principles of VASP and than describe exemplary applications to alloys and compounds (a) the calculation of the elastic and dynamic properties of a metallic compound (CoSi2), (b) the surface reconstruction of a semiconducting compound (SiC), and (c) the calculation of the structural and electronic properties of K Sbi-j, Zintl-phases in the licpiid state. 

H = di(Z—iy di are the potential parameters I is the orbital quantum number 3 characterizes the spin direction Z is the nuclear charge). Our experience has show / that such a model potential is convenient to use for calculating physical characteristics of metals with a well know electronic structure. In this case, by fitting the parameters di, one reconstructs the electron spectrum estimated ab initio with is used for further calculations. 

Over the past 10 years it has been demonstrated by a variety of in situ and ex situ techniques187,188 485 487 488 534 that flame-annealed Au faces are reconstructed in the same way as the surfaces of samples prepared in UHV,526-534 and that the reconstructed surfaces are stable even in contact with an aqueous solution if certain precautions are taken with respect to the potential applied and the electrolyte composition 485,487,488 A comprehensive review of reconstruction phenomena at single-crystal faces of various metals has been given by Kolb534 and Gao etal.511,513... 

Kolb and Franke have demonstrated how surface reconstruction phenomena can be studied in situ with the help of potential-induced surface states using electroreflectance (ER) spectroscopy.449,488,543,544 The optical properties of reconstructed and unreconstructed Au(100) have been found to be remarkably different. In recent model calculations it was shown that the accumulation of negative charges at a metal surface favors surface reconstruction because the increased sp-electron density at the surface gives rise to an increased compressive stress between surface atoms, forcing them into a densely packed structure.532... 

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