The shapes of (111) oriented two-dimensional (2D) islands and facets, the latter being part of three-dimensional (3D) crystallites of Pb, were equilibrated at 104-520 K. Island sizes were in the range of 15-90 nm radius, facets typically at 100-270 nm radius. They were imaged by scanning tunneling microscopy to provide the exact outline of the bounding step. Increased step roughening with increasing temperature decreases the radius anisotropy of islands and facets in a consistent manner. Products of island/facet radius times local step curvature versus temperature were obtained experimentally, serving as the basis of absolute step and kink energies at 0 K. They are f 1 A (0)=128.3′0.3 meV. f 1 B (0) = 115.7′5.8 meV, and e k A =42.5 ′1.0 meV, e k B =60.6′1.6 meV, respectively. The combination of studying small 2D islands (unstable at high temperature) and large 2D facets allows measurements over a very large range of temperatures.

Scanning tunnelling microscopy has proven to be an extremely useful technique for imaging small crystallites equilibrated at elevated temperature. As an example, we review recent work on three-dimensional Pb crystallites of 1–2 μm diameter, supported on Ru(0 0 1). Large (1 1 1) facets and, depending on temperature, small (1 1 2) facets were observed in the top section of the crystallites. The temperature dependent facet anisotropy was analyzed to yield the absolute step free energies of Pb(1 1 1) vicinal steps. The vicinal region close to the (1 1 1) facet was studied in detail to determine the shape exponent, the step–step interaction energy and the constant of the dipole interaction potential. Boundary conditions of the evaluated vicinal region have been specified for proving the universality of shapes, characterized by the exponent of 3/2, which is clear evidence for the 1/x2 step interaction potential. The role of the activation barrier for facet growth or shrinkage is discussed in the context of attaining 3D equilibrium of crystallites. A comparative study of crystallites with defect-free and dislocated facets shows significant differences, providing direct evidence of the activation barrier. Reliable step–step interaction energies were obtained for dislocated crystallites. Extrapolating the temperature dependent total step interaction energy to 0 K yields for the first time values of the structure dependent dipole–dipole step interaction energies of A- and B-steps.

Equilibrated three-dimensional Pb crystallites, supported on Ru(001) and of about 1 mum diameter, were imaged by scanning tunnelling microscopy at 298-393 K. The top section of the crystallites exhibited large (111) facets and, depending on temperature, smaller (112) facets. The vicinal shapes close to (111) were analysed in detail to determine the critical shape exponent and the step-step interaction energy as well as the interaction constant of the potential. Analyzing the complete shape in sections of 1degrees or 3degrees azimuthal increments and averaging over all sections of one crystallite, we found a shape exponent of 1.490. The exponent is very close to the theoretically predicted universal value of 3/2 and as such clear evidence for the 1/x(2) step interaction potential. Several crystallites had dislocations threading the (111) facet. For those crystallites the step interaction energy was determined as 16 meV Angstrom(-2) at about 350 K, equivalent to a dipole interaction energy of 8.1 meV Angstrom(-2) at 0 K. The interaction constant for the dipole-dipole part of step interaction was found to be 115 meV Angstrom.

Three-dimensional crystallites of Pb, equilibrated at various temperatures and imaged by scanning tunneling microscopy at temperature, have provided the basis for a quantitative determination of absolute step free energies and kink formation energies of vicinal Pb(111) surfaces. The anisotropy of large (111) facets was evaluated as a function of temperature. Products of radius times local curvature for A- and B-steps of these facets were calculated and their dependence on temperature fitted by theoretical expressions. Absolute values of step energies at 0 K are f1A(0)=131 meV and f1B(0)=117 meV, with the corresponding kink energies of εkA=40.0 meV and εkB=60.3 meV.

A 1 mum diameter Pb crystallite, supported on Ru(001), was equilibrated and imaged by scanning tunneling microscopy at 298 K. The vicinal shapes close to the (111) facet at the top of the crystal were analyzed in detail to determine the critical shape exponent and the step-step interaction energy as well as the interaction constant of the potential. An average shape exponent of 1.47 and a step interaction energy of similar to32 meV/Angstrom(2) were obtained. The exponent is very close to the theoretically predicted universal value of 3/2 and as such provides clear evidence for a dominant 1/x(2) step interaction potential. The ratio of step free energy to step interaction energy for Pb at 298 K is similar to0.34.

Three-dimensional (3D) equilibrium crystal shapes (ECS) of Pb are utilized for the first time to determine absolute surface free energies via a quantitative evaluation of the measured ECS and published values of step free energies of vicinal (111) surfaces. 3D images of Pb crystallites are obtained by scanning tunneling microscopy at 323–393 K. Line scans through high symmetry 〈110〉 azimuths are transformed into an anisotropic relative surface free energy, γ(θ,T). The absolute surface free energy of Pb(111) is obtained from the limiting slopes, df(θ,T)/dtanθ, of the orientation dependent f(θ,T)=γ(θ,T)/cosθ at the boundaries of the (111) facet, located at θ=0°. This value is 25.7±1.4 meV/Å2 or 440±22 mJ/m2. Absolute surface free energies of other low-index orientations, such as (100), (110) etc. are calculated from the relative anisotropy of γ(θ)/γ(111). It is found that surface free energies of orientation (hkl), expressed in meV/atom, scale with the number of bonds broken in forming such a surface. Free energies of steps bounding other facets, such as (100), (110), (112), (113) and (221), are evaluated in the [011̄] zone, using the corresponding facet radii and the absolute surface free energies of those facets.

Three-dimensional relaxation of small crystallites was imaged in real time using variable-temperature scanning tunneling microscopy. The micron-sized Pb crystallites, supported on Ru(0001), were equilibrated at 500-550 K, and the volume-preserving shape relaxation was induced by a rapid temperature decrease to 353-423 K The (111) facet at the top of the crystallite grows by sequential peeling of single atomic layers, which shrink like circular islands. The rate of layer peeling slows dramatically as a new final state is reached.

The article describes the combination of a Besocke-type scanning tunneling microscope (STM) with a scanning electron microscope (SEM) in an ultrahigh vacuum (UHV) environment. The open design of the Besocke STM allows the SEM to be implemented as an add-on of a high resolution electron column and a secondary electron detector. The combined instrument is capable of atomic resolution imaging by STM and real time SEM imaging. SEM resolution down to about 80 nm was achieved. Simultaneous operation of STM and SEM is possible. The operation and performance of the combined instrument is illustrated by a variety of examples. Although the instrument is suitable for a wide range of applications where a combination of atomic resolution with lower magnification imaging is required, its operation in an UHV environment makes it particularly appropriate for the study of reactive metal surfaces.

The adsorption of CO on a Pt(1 1 0) surface was studied by X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD), and low energy electron diffraction (LEED). CO exposure during cooling the sample from 600 K to several final temperatures, Tf, resulted in CO layers of increasing coverage. For Tf>350 K, a disordered CO layer was obtained, characterized by a (1×1) LEED pattern, but also by an increasing intensity of inter-molecular scattering peaks in C 1s XPD with increasing CO coverage. This behavior appears to indicate a rising degree of short range order in the adlayer. A well-ordered (2×1)-CO pattern at a coverage of 1.0 was obtained for final temperatures below 300 K. XPD measurements provided evidence of 22° tilted CO molecules, with the projected tilt parallel to the [0 0 1] azimuth of the Pt(1 1 0) surface. The latter is consistent with a p2mg symmetry of the (2×1)-CO structure. A second well-ordered c(8×4)-CO pattern was prepared upon adsorption at T<240 K, which was characterized by an O 1s doublet, assigned to on-top and bridge adsorbed CO, at a total coverage of 1.09. The corresponding XPD C 1s intensity distribution, measured over a large solid angle, indicated tilted and perpendicular CO, and inter-molecular scattering peaks distinctly different from those of the (2×1)p2mg-CO layer. A structure model for the c(8×4)-CO layer was developed. Single scattering cluster calculations were performed for real space models of CO layers at low coverage, and for the high coverage (2×1)p2mg and c(8×4) layers. Good consistency between the experimental and theoretical C 1s angular intensity distributions was found, involving both tilted and perpendicular CO.

Equilibrium crystal shapes exhibit flat facets and rough vicinal surfaces, with transitions between them being either continuous or discontinuous, the latter recognizable by a sharp edge. In general, mixed repulsive/attractive step–step interactions may lead to continuous or discontinuous facet-to-vicinal transitions. In can be shown that the contact angle at the facet for a discontinuous transition is directly related to the ratio of the step interaction strengths. Alternatively, surface reconstruction of facets can also be responsible for sharp edges at the facet boundary. In this case the contact angle is related to the difference between surface free energies of the reconstructed and unreconstructed facet as well as the corresponding difference of step interaction energies. Fitting the experimental shapes by theoretical expressions can be used to extract the relevant surface and step free energies and also step interaction energies. Experimental examples of Pb and Au equilibrium shapes are evaluated and discussed. Step free energies of vicinal Au(1 1 1) and Au(1 0 0) surfaces, evaluated by both models, are 30 and 10 meV/Å2, respectively.

An investigation of acetic acid adsorption on Ni(110) at room temperature by LEED and X-ray photoelectron diffraction reveals a well-ordered c(2 × 2) acetate overlayer with a molecular coverage near 0.5. Large solid angle maps of angle-resolved C 1s and O 1s intensities from this layer show intense maxima due to electron forward scattering by nearby atoms, either of the same acetate or of neighboring acetate species. The data provide strong evidence for acetate in a bidentate configuration, bonded through both oxygen atoms to the surface and aligned along the [Formula: see text] surface azimuth. A real space model for the c(2 × 2) acetate layer has been derived and single scattering cluster calculations for this model layer have been carried out for C 1s and O 1s emissions. Allowing for changes in intramolecular bond length of the acetate relative to those in a Ni-acetate complex, good agreement between experimental and theoretical C 1s and O 1s distributions was obtained.

It is shown that exact images of the three-dimensional equilibrium shape of crystallites (ECS), recorded at several temperatures between 0.3 and 0.8 of the melting temperature of a solid, can be evaluated to yield absolute values of the surface and step free energies versus temperature, in addition to the formation energy of kinks. The essential input for this novel approach is the temperature variation of the size of a facet on the ECS and of the separation between the Wulff point and that particular facet. This approach promises access to surface free energies over a large temperature range and for well-defined low-index surface orientations.

Adsorbed layers of CO, methoxy (CH3O) and formate (HCOO) on a clean Ni(110) surface are investigated by angle-resolved X-ray photoelectron spectroscopy. Large solid angle stereographic projections of C1s or O1s core level intensity measured for these adsorbates at 85K show strong forward scattering enhancements that unambiguously and rather directly determine the molecular orientation, and in the case of CO, the order within the layer. CO in the (2×1) p2mg structure and methoxy are tilted by 20° and 30° relative to the normal, respectively, with the projection of the tilt in the 〈001〉 azimuth. Formate is bonded through oxygen in the bidendate configuration, aligned along the 〈110〉 azimuth. The O–C–O bond angle is determined as 124°. These results are in good agreement with previous data.