Table of contents

The 12th International Workshop on Desorption Induced by Electronic Transitions (DIET XII) took place from 19–23 April 2009 in Pine Mountain, Georgia, USA. This was the 12th conference in a strong and vibrant series, which dates back to the early 1980s. DIET XII continued the tradition of exceptional interdisciplinary science and focused on the study of desorption and dynamics induced by electronic excitations of surfaces and interfaces. The format involved invited lectures, contributed talks and a poster session on the most recent developments and advances in this area of surface physics.

The Workshop International Steering Committee and attendees wish to dedicate DIET XII to the memory of the late Professor Theodore (Ted) Madey. Ted was one of the main pioneers of this field and was one of the primary individuals working to keep this area of science exciting and adventurous. His overall contributions to surface science were countless and his contributions to the DIET field and community were enormous. He is missed and remembered by many friends and colleagues throughout the world.

The papers collected in this issue cover many of the highlights of DIET XII. Topics include ultrafast electron transfer at surfaces and interfaces, quantum and spatially resolved mapping of surface dynamics and desorption, photon-, electron- and ion-beam induced processes at complex interfaces, the role of non-thermal desorption in astrochemistry and astrophysics and laser-/ion-based methods of examining soft matter and biological media.

Although the workshop attracted many scientists active in the general area of non-thermal surface processes, DIET XII also attracted many younger scientists (i.e., postdoctoral fellows, advanced graduate students, and a select number of advanced undergraduate students). This field has had an impact in a number of areas including nanoscience, device physics, astrophysics, and now biophysics. We believe that this special issue of Journal of Physics: Condensed Matter will help foster further progress in the study of DIET processes. Since the field remains vibrant and exciting, the workshop series will continue with DIET XIII. Professor Richard Palmer (University of Birmingham, UK) will chair DIET XIII in the UK in early summer 2012.

We gratefully acknowledge financial support from SPECS, HIDEN Analytical, BRUKER, The United States National Science Foundation, Georgia Institute of Technology and The State University of New Jersey, Rutgers.

The role of diffraction in electron-stimulated desorption (DESD) is demonstrated experimentally and described theoretically. Specifically, initial state effects in DESD of Cl ⁺ from Si(111)-(1 × 1):Cl and Si(111)-(7 × 7):Cl are examined and a theoretical treatment that includes spherical-wave effects and multiple scattering of low-energy incident electrons is presented. Although contributions from complicated defect configurations such as SiCl₂ and SiCl₃ cannot be ruled out, comparison of the experimental data with theory indicates that Cl ⁺ desorption from Si(111)-(1 × 1):Cl and Si(111)-(7 × 7):Cl surfaces may be dominated by monochloride terminal sites. The initial states probably contain significant Si 3s and/or Si–Cl σ-bonding character. In the Si(111)-(7 × 7):Cl case, these excitations favor a propensity for Cl ⁺ desorption from the unfaulted, rather than faulted, zones of the 7 × 7 reconstructed rest atom area. This propensity may be related to increased screening and hole localization in the Si–Si backbonds within the faulted region. Finally, introducing Debye–Waller factors into each scattering path accounts for much of the experimentally observed DESD width broadening at room temperature.

The precise calibration of thermally driven processes in scanning tunnelling microscope (STM) manipulation experiments, especially at room temperature and above, is necessary to uncover an accurate picture of non-thermal dynamical processes such as desorption induced by electronic transitions, driven by the STM current. Here we probe the displacement (the sum of desorption and diffusion) of chlorobenzene molecules chemisorbed on the Si(111)-7 × 7 surface, induced both by the STM electrical current and by heat. We also establish truly passive imaging inspection parameters. The activation energy for pure thermal displacement is 580 ± 20 meV, possibly associated with excitation to a physisorbed precursor state. STM induced displacement shows a marked decrease with increasing temperature, once the thermal effects are removed.

Low energy electron induced dissociation in multilayer films of nitromethane (CD₃NO₂) was investigated by high resolution electron energy loss spectroscopy (HREELS) and by the electron stimulated desorption (ESD) of neutral species. HREELS measurements show that the lowest electronic states of the condensed molecule are very similar to those seen in the gas phase. Desorbed neutrals were detected using combined non-resonant multi-photon ionization at 355 nm and time of flight mass spectrometry. The most intense signals detected were those of CD₃ ⁺ and NO ⁺ and are attributed primarily to the desorption of CD₃ and NO₂ fragments following molecular dissociation via low-lying electronic excited states of nitromethane (the detected NO ⁺ being the result of the dissociative ionization of NO₂). By varying the time delay between the incident electron pulse and the ionizing laser pulse, it is possible to measure the kinetic energy distributions of desorbing fragments. The kinetic energy distributions above ∼ 5 eV appear invariant with incident electron energy, indicating that the same desorption process (dissociation via low-lying electronic states) operates at all the studied incident energies. Nevertheless, measurements of neutral yields as functions of incident electron energy demonstrate that excitation of the dissociative electronic states also proceeds via previously identified transient negative ions. At energies less than ∼ 5 eV, contributions from dissociative electron attachment are also observed in the yield of CD₃ and other neutral fragments.

The aim of this work is to characterize desorption induced by electronic transition processes that affect the reflectivity of TiO₂-capped multilayer mirrors used in extreme ultraviolet (EUV) lithography. A low energy electron beam is employed to mimic excitations initiated by EUV radiation. Temperature programmed desorption, x-ray photoelectron spectroscopy, and low energy ion scattering are used to analyze the surface reactions. Carbon film growth on the TiO₂(011) crystalline surface is measured during 10–100 eV electron bombardment in benzene or methyl methacrylate vapor over a wide range of pressures and temperatures near 300 K. Low energy secondary electrons excited by EUV photons contribute substantially to the carbon accumulation on clean TiO₂ cap layers. For benzene on clean TiO₂, secondary electron effects dominate in the initial stages of carbon accumulation, whereas for C-covered TiO₂, direct excitations appear to dominate. We report on the adsorption energy, the steady-state coverage of the molecules on the surface and the cross sections for electron-stimulated dissociation: all key parameters for understanding and modeling the processes relating to the EUV lithography mirrors.

The electron-stimulated desorption (ESD) yields and energy distributions (ED) for neutral cesium atoms have been measured from cesium layers adsorbed on a gold-covered tungsten surface as a function of electron energy, gold film thickness, cesium coverage and substrate temperature. The measurements have been carried out using a time-of-flight method and surface ionization detector in the temperature range 160–300 K. A measurable ESD yield for Cs atoms is observed only after deposition of more than one monolayer of gold and cesium on a tungsten surface at a temperature T = 300 K, which is accompanied by the formation of a CsAu semiconductor film covered with a cesium atom monolayer. The Cs atom ESD yield as a function of incident electron energy has a resonant character and consists of two peaks, the appearance of which depends on both electron energy and substrate temperature. The first peak has an appearance threshold at an electron energy of 57 eV and a substrate temperature of 300 K that is due to Au 5p_3/2 core level excitation in the substrate. The second peak appears at an electron energy of 24 eV and a substrate temperature of 160 K. It is associated with a Cs 5s core level excitation in the Cs adsorbed layer. The Au 5p_3/2 level excitation corresponds to a single broad peak in the ED with a maximum at a kinetic energy of 0.45 eV at a substrate temperature T = 300 K, which is split into two peaks with maxima at kinetic energies of 0.36 and 0.45 eV at a substrate temperature of 160 K, associated with different Cs atom ESD channels. The Cs 5s level excitation leads to an ED for Cs atoms with a maximum at a kinetic energy of ∼ 0.57 eV which exists only at T < 240 K and low Cs concentrations. The mechanisms for all the Cs atom ESD channels are proposed and compared with the Na atom ESD channels in the Na–Au–W system.

The dynamics of electron-induced reactions in condensed trifluoroiodomethane (CF₃I) were studied under ultrahigh vacuum conditions. Seven CF₃I radiolysis products (C₂F₆, C₂F₅I, C₂F₃I, CF₂I₂, C₂F₄I₂, CFI₃ and C₂F₃I₃) were identified using temperature-programmed desorption experiments conducted after irradiation with 4 eV electrons. Although C₂F₆ formation at energies above 4 eV is ascribed to electron-induced electronic excitation followed by prompt dissociation of the C–I bond to form radicals that dimerize, the formation of the other six radiolysis products at low sub-ionization incident electron energies is attributed to dissociative electron attachment (DEA) because of the observed resonance peaks in the radiolysis product yields as functions of incident electron energy (∼2 to ∼ 7 eV). All seven CF₃I electron-induced reaction products were also identified following irradiation with 500 eV electrons. While dissociative electron attachment and/or electron impact excitation may play an important role in the high-energy radiation-induced synthesis of the high-yield product C₂F₆, a dramatic enhancement of up to ∼ 2 × 10⁴ in product yield per electron at 500 eV relative to that at 4 eV for some products suggests, however, that DEA is not the dominant mechanism for the high-energy radiation-induced synthesis of those products.

The interaction of low-energy multiply charged Ar^{q +} (q ≤ 7) ions with a solid Ne surface is experimentally studied. Desorption of very large cluster ions Ne_n ⁺ (n > 100) is observed. The size distribution of smaller (n = 1–3) cluster ions depends strongly on the charge state of the incident ion, whereas that of larger (n > 7) cluster ions exhibits no dependence on the charge state, indicating that desorption of large cluster ions is due to kinetic sputtering. The potential sputtering yield is estimated by analyzing the size distribution of the desorbed cluster ions. The results suggest that the ion desorption mechanism, which is known as desorption induced by electronic transitions, can also be applied to explain the present results.

Slow highly charged ions (HCIs) carry a large amount of potential energy that can be dissipated within femtoseconds upon interaction with a surface. HCI–insulator collisions result in high sputter yields and surface nanofeature creation due to strong coupling between the solid's electronic system and lattice. For HCIs interacting with Al oxide, combined experiments and theory indicate that defect mediated desorption can explain reasonably well preferential O atom removal and an observed threshold for sputtering due to potential energy. These studies have relied on measuring mass loss on the target substrate or probing craters left after desorption. Our approach is to extract highly charged ions onto the Al oxide barriers of metal–insulator–metal tunnel junctions and measure the increased conductance in a finished device after the irradiated interface is buried under the top metal layer. Such transport measurements constrain dynamic surface processes and provide large sets of statistics concerning the way individual HCI projectiles dissipate their potential energy. Results for Xe^{q +} for q = 32, 40, 44 extracted onto Al oxide films are discussed in terms of postirradiation electrical device characteristics. Future work will elucidate the relationship between potential energy dissipation and tunneling phenomena through HCI modified oxides.

The scattering of low energy alkali ions is used to probe the atomic and electronic structures of Au nanoclusters grown onto an untreated silicon (111) wafer. Charge-state-resolved time-of-flight spectra were collected for 2 keV ⁷Li ⁺ and ³⁹K ⁺ as a function of Au coverage. The shapes of the spectra are interpreted in terms of the shadow cones formed by incoming Li ⁺ and K ⁺ . The differences in neutralization are interpreted in terms of the ionization potentials. The results indicate that nanoclusters displaying quantum size effects are formed upon the initial Au deposition, and they evolve to multilayer nanoclusters after a critical coverage has been reached. When sufficient Au is deposited, a thick film is formed with the properties of the bulk metal.

We have made Na ⁺ and He ⁺ ions incident on the surface of solid state tunnel junctions and measured the energy loss due to atomic displacement and electronic excitations. Each tunnel junction consists of an ultrathin film metal–oxide–semiconductor device which can be biased to create a band of hot electrons useful for driving chemical reactions at surfaces. Using the binary collision approximation and a nonadiabatic model that takes into account the time-varying nature of the ion–surface interaction, the energy loss of the ions is reproduced. The energy loss for Na ⁺ ions incident on the devices shows that the primary energy loss mechanism is the atomic displacement of Au atoms in the thin film of the metal–oxide–semiconductor device. We propose that neutral particle detection of the scattered flux from a biased device could be a route to hot electron mediated charge exchange.

Laser induced desorption of CO adsorbed on platinum nanoparticles on an epitaxial alumina support grown on NiAl(110) is reported for nanosecond laser excitation at λ = 355 nm. The nominal amount of platinum deposited was 0.1 nm, resulting in platinum particles with an average diameter of a few nanometres. The laser fluence was systematically varied between 6.4 and 25.5 mJ cm ^{− 2} per pulse. Fourier transform infrared reflection absorption spectra have been recorded as a function of CO coverage, the laser fluence and the number of photons impinging on the surface. Laser desorption is observed, in contrast to the case for experiments on Pt(111) for the same laser wavelength. For laser fluences below 12.7  mJ cm ^{− 2} per pulse, a cross section of (1.1 ± 0.2) × 10 ^{− 19} cm² can be estimated from the measurements. At elevated fluences a second desorption channel occurs with a cross section more than an order of magnitude larger, scaling linearly with the laser fluence. In all cases desorption ends at a critical coverage beyond which no desorption occurs and which depends on the laser fluence. Laser induced particle morphology changes are observed for higher laser fluences which are not apparent for bare particles. A model implying energy pooling within adsorbates at hot spots and even spillover between the metal nanoparticles and the oxidic support is discussed. Implications for the design of photocatalysts with possible use in chemical solar energy conversion are pointed out.

Nanosecond laser induced photoreactions of N₂O adsorbed on Ag(111) have been studied by temperature programmed desorption (TPD) and mass-selected, angle-dependent time-of-flight (MS-TOF) measurements of neutral desorbing particles. N₂O molecules in the first monolayer are thermally inert but photo-dissociate into N₂ + O, or photodesorb molecularly or dissociatively, at photon energies above 3.5 eV. We have found that TOF spectra of photodesorbed N₂ as well as of N₂O measured at hν = 4.7 eV consist of two velocity components. The desorption flux of the fastest component of N₂O peaks ∼ 25° off the surface normal, whereas the others are directed in the surface normal. Origins and photo-excitation as well as photodesorption mechanisms of the N₂O and N₂ signals are discussed.

We report results of laser desorption from water ice surfaces using XUV pulses from the free-electron laser in Hamburg (FLASH). This XUV to soft x-ray FEL provides femtosecond pulses at 20–200 eV photon energy with pulse energies up to 100 µJ. The interaction of this intense soft x-ray radiation with ice (H₂O, D₂O) adsorbed on highly oriented pyrolytic graphite (HOPG) yields the desorption of various ions, particularly H ⁺ (D ⁺ ), O ⁺ , O₂ ⁺ and others. For H ⁺ and O ⁺ ions linear desorption yields are observed, while for O₂ ⁺ a highly nonlinear desorption yield with n = (2.5 ± 0.2) is found. Kinetic energies of 1.8 eV, 559 meV and 390 meV for H ⁺ , O ⁺ , and O₂ ⁺ , respectively, account for only a small part of the available excess energy.

A natural TiO₂ anatase crystal, cut to exhibit its (010) surface, was cleaved by breaking off one of its corners. The resulting sample exhibited a small, flat area ca. 2 mm² in size with a (101) orientation as confirmed by LEED. The evolution of the surface morphology was monitored with UHV-STM. After one sputtering/annealing cycle the surface is characterized by periodic ridges that run parallel to the [010] direction. The ridges are ∼ 3 nm high and 10–15 nm wide and have a spacing of 30 nm. Interestingly, -oriented step edges are not observed, despite them having the lowest formation energy. The ridges flatten with repeated sputter/annealing cycles. After a total of three cycles a flat surface is achieved, which exhibits trapezoidal terraces that are typical for anatase (101). The importance of preparing such a pristine surface for understanding the surface structure and chemistry of TiO₂ anatase is discussed.

The observation of periodic responses after absorption of ultrashort laser pulses in condensed media and at solid interfaces is a common phenomena in various time-resolved spectroscopic methods using laser pulses shorter than the period of the coherently excited vibrations. Normally these signals have to be separated from strong slowly decaying backgrounds related to the creation of nonequilibrium carriers. The recording normally requires either a small period of time or lacks temporal resolution to obtain the good signal-to-noise ratio necessary for the observation of the vibrations. The standard method used for the analysis of the data is a curve-fitting routine to the time-domain data. However, the disadvantage is the necessity to estimate the number of spectral components before fitting. This paper will introduce under which conditions linear prediction and singular value decomposition in combination with an iterative nonlinear fitting in the time and spectral domain may extract an unknown number of spectral components including amplitude, lifetime, frequency and phase. Such information is essential to unambiguously evaluate the dominant optical excitation process, the phase of the initial displacement, the symmetry of the excited vibrational mode and the specific vibration generation process.

Surface science has been an area of continuous interest during the last decades. In recent years, we have witnessed both the development of surface techniques to a high degree of accuracy and their application to an ever growing range of new phenomena. The outcome has been the appearance and development of promising scientific topics, which have attracted a lot of interest. This special issue presents a collection of eleven invited articles covering both the current status and recent developments of surface science techniques, and several selected subjects of current interest. Obviously, the selection does not pretend to be exhaustive, which would exceed the possibilities of a single special issue, but it rather concentrates on a few important topics. The first paper by Woodruff [1] reviews the status of investigations related to the structure of surfaces and their future development. Low-energy electron microscopy, a technique which is being used to analyze more and more systems showing fascinating physical properties, is the subject of the next article written by Altman [2]. Optical properties of surfaces are reviewed by McGilp [3], and Benedek and co-workers [5] provide an overview of recent advances in the study of surface vibrations. The rest of the articles in this issue deal with more specific topics and recent experimental advances. Thiele reviews thin films evolution [4], and Wulfhekel and Gao the analysis of magnetic properties with scanning tunneling microscopy [6]. Next, the surface science of quasicrystals is reviewed in a paper by McGrath and co-workers [7]. Three articles study different aspects of the interaction of molecules with surfaces: the properties of adsorbed complex molecules by Grill [8]; an analysis of components of future molecular devices by Trevethan and co-workers [9]; and finally atomic interconnects and molecule logic gates by Joachim and co-workers [10]. The final paper by Hasegawa deals with the properties of one-dimensional metals grown on semiconductor surfaces [11].

The editor is grateful to all the invited authors for their contributions to this special issue of Journal of Physics: Condensed Matter.

References

[1] Woodruff D P 2010 J. Phys.: Condens. Matter22 084016

[2] Altman M S 2010 J. Phys.: Condens. Matter22 084017

[3] McGlip J F 2010 J. Phys.: Condens. Matter22 084018

[4] Thiele U 2010 J. Phys.: Condens. Matter22 084019

[5] Benedek G, Bernasconi M, Chis V, Chulkov E, Echenique P M, Hellsing B and Toennies J P 2010 J. Phys.: Condens. Matter22 084020

[6] Wulfhekel W and Gao C L 2010 J. Phys.: Condens. Matter22 084021

[7] McGrath R, Smerdon J A, Sharma H R, Theis W and Ledieu J 2010 J. Phys.: Condens. Matter22 084022

[8] Grill L 2010 J. Phys.: Condens. Matter22 084023

[9] Trevethan T, Shluger A and Kantorovich L 2010 J. Phys.: Condens. Matter22 084024

[10] Joachim C, Martrou D, Rezeq M, Troadec C, Jie D, Chandrasekhar N and Gauthier S 2010 J. Phys.: Condens. Matter22 084025

[11] Hasegawa S 2010 J. Phys.: Condens. Matter22 084026

A brief survey is presented of the methods of quantitative surface structure determination and some of the main phenomena that have been established, and their associated trends. These include surface relaxation and reconstruction of clean surfaces and the structures formed by atomic and molecular adsorbates. Examples include the surfaces of semiconductors, oxides and metals. Future challenges, concerned with complexity and precision, are discussed.

Low energy electron microscopy (LEEM) and spin polarized LEEM (SPLEEM) are two powerful in situ techniques for the study of surfaces, thin films and other surface-supported nanostructures. Their real-time imaging and complementary diffraction capabilities allow the study of structure, morphology, magnetism and dynamic processes with high spatial and temporal resolution. Progress in methods, instrumentation and understanding of novel contrast mechanisms that derive from the wave nature and spin degree of freedom of the electron continue to advance applications of LEEM and SPLEEM in these areas and beyond. We review here the basic imaging principles and recent developments that demonstrate the current capabilities of these techniques and suggest potential future directions.

Optical techniques for probing surface and interface structure are introduced and recent developments in the field are discussed. These techniques offer significant advantages over conventional surface probes: all pressure ranges of gas–condensed matter interfaces are accessible and liquid–liquid, liquid–solid and solid–solid interfaces can be probed, due to the large penetration depth of the optical radiation. Sensitivity and discrimination from the bulk are the two challenges facing optical techniques in probing surface and interface structure. Where instrumental improvements have resulted in enhanced sensitivity, conventional optical techniques can be used to characterize heterogeneous adsorbed layers on a substrate, often with sub-monolayer resolution. Nanoscale lateral resolution is possible using scanning near-field optics. A separate class of techniques, which includes reflection anisotropy spectroscopy, and nonlinear optical probes such as second-harmonic and sum-frequency generation, uses the difference in symmetry between the bulk and the surface or interface to suppress the bulk contribution. A perspective is presented of likely future developments in this rapidly expanding field.

In the present contribution we review basic mathematical results for three physical systems involving self-organizing solid or liquid films at solid surfaces. The films may undergo a structuring process by dewetting, evaporation/condensation or epitaxial growth, respectively. We highlight similarities and differences of the three systems based on the observation that in certain limits all of them may be described using models of similar form, i.e. time evolution equations for the film thickness profile. Those equations represent gradient dynamics characterized by mobility functions and an underlying energy functional.

Two basic steps of mathematical analysis are used to compare the different systems. First, we discuss the linear stability of homogeneous steady states, i.e. flat films, and second the systematics of non-trivial steady states, i.e. drop/hole states for dewetting films and quantum-dot states in epitaxial growth, respectively. Our aim is to illustrate that the underlying solution structure might be very complex as in the case of epitaxial growth but can be better understood when comparing the much simpler results for the dewetting liquid film. We furthermore show that the numerical continuation techniques employed can shed some light on this structure in a more convenient way than time-stepping methods.

Finally we discuss that the usage of the employed general formulation does not only relate seemingly unrelated physical systems mathematically, but does allow as well for discussing model extensions in a more unified way.

Recent studies of the surface dynamics of Al(001) and Cu(111) based on density functional perturbation theory have substantiated the existence of subsurface optical phonon resonances of all three polarizations, thus confirming early predictions of the embedded-atom method. The hybridization of the shear-vertical optical resonance with the longitudinal acoustic phonon branch accounts for the ubiquitous anomalous acoustic resonance as an intrinsic feature of metal surfaces. The DFPT calculation of the phonon-induced surface charge density oscillations shows that helium atom scattering spectroscopy (HAS) can indeed probe subsurface resonances. This opens new perspectives to HAS for the measurement of subsurface phonon dispersion curves in thin films, as proved by recent HAS studies on Pb and Fe ultrathin films on copper. After discussing these recent advances, this paper briefly reviews other important trends of surface dynamics expressed in recent years.

Most ferromagnetic and antiferromagnetic substances show a simple collinear arrangement of the local spins. Under certain circumstances, however, the spin configuration is non-collinear. Scanning tunneling microscopy with its potential atomic resolution is an ideal tool for investigating these complex spin structures. Non-collinearity can be due to topological frustration of the exchange interaction, due to relativistic spin–orbit coupling or can be found in excited states. Examples for all three cases are given, illustrating the capabilities of spin-polarized scanning tunneling microscopy.

The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.

Intramolecular manipulation of single molecules on a surface with a scanning tunnelling microscope enables the controlled modification of their structure and, consequently, their physical and chemical properties. This review presents examples of intramolecular manipulation experiments with rather large molecules, driven by directional, i.e. chemical or electrostatic, forces between tip and molecule. It is shown how various regimes of forces can be explored and characterized with one and the same manipulation of a single molecule by changing the tip–surface distance. Furthermore, different deposition techniques under ultrahigh vacuum conditions are discussed because the increasing functionality of such molecules can lead to fragmentation during the heating step, making their clean deposition difficult.

We discuss challenges involved in modelling different components of molecular devices and give several examples that demonstrate how computer modelling evolved over the last few years to become a comprehensive tool for designing molecules, predicting their adsorption and diffusion at surfaces, simulating atomic force microscopy imaging and manipulation of atoms and molecules at insulating surfaces and studying electron conduction in prototype molecular devices. We describe some of the computational techniques used for modelling adsorption, diffusion, imaging and manipulation of organic molecules at surfaces and challenges pertaining to these studies, give several examples of applications and discuss further prospects for theoretical modelling of complex organic molecules at surfaces.

The scientific and technical challenges involved in building the planar electrical connection of an atomic scale circuit to N electrodes (N > 2) are discussed. The practical, laboratory scale approach explored today to assemble a multi-access atomic scale precision interconnection machine is presented. Depending on the surface electronic properties of the targeted substrates, two types of machines are considered: on moderate surface band gap materials, scanning tunneling microscopy can be combined with scanning electron microscopy to provide an efficient navigation system, while on wide surface band gap materials, atomic force microscopy can be used in conjunction with optical microscopy. The size of the planar part of the circuit should be minimized on moderate band gap surfaces to avoid current leakage, while this requirement does not apply to wide band gap surfaces. These constraints impose different methods of connection, which are thoroughly discussed, in particular regarding the recent progress in single atom and molecule manipulations on a surface.

Several examples are known in which massive arrays of metal atomic chains are formed on semiconductor surfaces that show quasi-one-dimensional metallic electronic structures. In this review, Au chains on Si(557) and Si(553) surfaces, and In chains on Si(111) surfaces, are introduced and discussed with regard to the physical properties determined by experimental data from scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES) and electrical conductivity measurements. They show quasi-one-dimensional Fermi surfaces and parabolic band dispersion along the chains. All of them are known from STM and ARPES to exhibit metal–insulator transitions by cooling and charge-density-wave formation due to Peierls instability of the metallic chains. The electrical conductivity, however, reveals the metal–insulator transition only on the less-defective surfaces (Si(553)–Au and Si(111)–In), but not on a more-defective surface (Si(557)–Au). The latter shows an insulating character over the whole temperature range. Compared with the electronic structure (Fermi surfaces and band dispersions), the transport property is more sensitive to the defects. With an increase in defect density, the conductivity only along the metal atomic chains was significantly reduced, showing that atomic-scale point defects decisively interrupt the electrical transport along the atomic chains and hide the intrinsic property of transport in quasi-one-dimensional systems.

Using first-principles calculations, we present a comprehensive study on the atomic and electronic structures of metal adatoms (noble metals Ag, Au, Cu and alkali metals Li, Na, K) adsorbed on a –Ag (hereafter -Ag) surface. We found that adsorption of noble and alkali adatoms can induce significant structural changes in the topmost Ag layer. The most striking and interesting results are the immersion of the noble and Li adatoms into the substrate Ag layer and the finding of the most stable configurations with three adatoms incorporating into or being adsorbed on the surface dependent on their atomic radii. We also found that the almost empty two-dimensional free-electron-like band s₁ and its band folding s₁^* of the original surface band s₁ of the -Ag surface split into a gap at the surface Brillouin zone (SBZ) boundary with adsorption of an adatom. The two surface bands gradually move downwards and the s₁ band is gradually filled with an increase of coverage. The s₁ band is fully occupied with the largest band gap ∼ 0.25 eV between the s₁ and s₁^* bands at the critical coverage of 0.14 monolayers (ML) [three adatoms in a –Ag (hereafter -Ag) unit cell], which corresponds to the most stable adsorption phase. Although the adsorption configurations are different, both the noble and alkali adatom adsorptions give rise to similar electronic structures at low coverages, indicating a free-electron-like character of the adsorption surfaces.

Adsorption of NH₃ molecules on Si(111)-(7 × 7) has been studied by scanning tunneling microscopy. We find that the dissociative adsorption is site-selective and exhibits two adsorption structures resulting from different reaction channels: and . To explain the dissociation processes, an adsorption model for these reactions is given. Furthermore, the evolution of the local electronic structures is investigated by means of atomically resolved scanning tunneling spectroscopy to clarify the effect of different fragments on the surface states. Finally, we discuss the adsorption position of H atoms from the NH₃ dissociation.

We present the results of a systematic study of the influence of carbon surface oxidation on Dubinin–Astakhov isotherm parameters obtained from the fitting of CO₂ adsorption data. Using GCMC simulations of adsorption on realistic VPC models differing in porosity and containing the most frequently occurring carbon surface functionalities (carboxyls, hydroxyls and carbonyls) and their mixtures, it is concluded that the maximum adsorption calculated from the DA model is not strongly affected by the presence of oxygen groups. Unfortunately, the same cannot be said of the remaining two parameters of this model i.e. the heterogeneity parameter (n) and the characteristic energy of adsorption (E₀). Since from the latter the pore diameters of carbons are usually calculated, by inverse-type relationships, it is concluded that they are questionable for carbons containing surface oxides, especially carboxyls.

The density functional calculations have been performed to study the Nb(001) and α-Nb₅Si₃(001) surfaces as well as the interface properties of Nb(001)/α-Nb₅Si₃(001). The surface energy of the Nb(001) surface is about 2.25 J m ^{− 2}. The calculated cleavage energies of bulk Nb₅Si₃ are 5.103 J m ^{− 2} and 5.787 J m ^{− 2} along (001) planes with the breaking of Nb–Si and Nb–NbSi bonds, respectively. For the Nb(001)/α-Nb₅Si₃(001) models, the Nb atoms in the interface region initially belonging to body centered cubic metal Nb are twisted to the position of the Nb atom layer in Nb₅Si₃ and the interlayer distance is similar to that of bulk Nb₅Si₃ after being fully relaxed. The ideal work of adhesion of the Nb(001)/Nb₅Si₃(001) interface is calculated and compared to those of bulk Nb and Nb₅Si₃. The results show that the bulk Nb₅Si₃ has the largest work of adhesion, the bcc Nb ranks second and the interface ranks last. Moreover, the Nb–Si bond is weaker than Nb–NbSi and Nb–Nb bonds in the interface, which means that the Nb–Si bond in the interface is the most possible site for the micro-crack generation when the stress is applied quasi-statically along the [001] direction. The densities of states, Mulliken population and overlap population of the Nb(001)/α-Nb₅Si₃(001) interface are also analyzed.

The thermodynamics and mechanics of the surface of a deformable body are studied here, following and refining the general approach of Gibbs. It is first shown that the 'local' thermodynamic variables of the state of the surface are only the temperature, the chemical potentials and the surface strain tensor (true thermodynamic variables, for a viscoelastic solid or a viscous fluid). A new definition of the surface stress is given and the corresponding surface thermodynamics equations are presented. The mechanical equilibrium equation at the surface is then obtained. It involves the surface stress and is similar to the Cauchy equation for the volume. Its normal component is a generalization of the Laplace equation. At a (body–fluid–fluid) triple contact line, two equations are obtained, which represent: (i) the equilibrium of the forces (surface stresses) for a triple line fixed on the body; (ii) the equilibrium relative to the motion of the line with respect to the body. This last equation leads to a strong modification of Young's classical capillary equation.

An analysis of the differences observed between the Si KLV Auger spectra of the Si/Ge(001)-2 × 1 interface and pure Si indicates that the electronic structure of the interface is characterized by a reduction in the local p DOS at the Si sites and a transfer of p valence charge from Si to Ge. As a result, the screening of core-ionized Si sites at the interface is significantly shifted towards s screening compared with the situation for pure Si. It is possible that there is an increase in the on-site electron correlation energy, U_P, for Si sites at the interface as compared with pure Si.

Singly charged buckminsterfullerene anions, C₆₀⁻, are subject to a strong intramolecular Jahn–Teller (JT) effect. When such ions interact with other C₆₀⁻ ions in a solid through a cooperative JT effect, they will be subject to an additional interaction. There are a number of different mechanisms that can cause this interaction. However, in the molecular field approximation, all can be modelled phenomenologically in terms of a symmetry-lowering interaction written in terms of a linear combination of electronic operators for the h modes involved in the intramolecular JT effect. We will consider the combined effect of this distortion and the intramolecular JT effect. We will analyse the lowest adiabatic potential energy surface, and calculate the energies of the resultant vibronic states. The results are shown to have a complicated dependence on the particular combination of h modes chosen, and the energies of the resultant vibronic states cannot easily be deduced from the form of the potential alone.