Kalevi Kokko

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Verified

Kalevi verified their affiliation via an institutional email.

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• PhD
• Professor Emeritus at University of Turku

Most electronic and photonic devices include ohmic metal–semiconductor junction(s), of which contact resistivity needs to be minimized for best efficiency of the devices. Interface defects in the junction usually degrade the junction’s performance, thus cleaning and passivation of semiconductor surface is crucial during contact fabrication. For sil...

Gold (Au) segregation at Pt grain boundaries (GBs) plays an important role in the properties of Pt-based alloys. It was reported that close-packed GBs and open GBs exhibit different segregation behaviors, and their origin is still unclear. Based on the density functional theory as implemented in the exact muffin-tin orbitals method and the full cha...

Current transport in polysilicon is a complicated process with many factors to consider. The inhomogeneous nature of polysilicon with its differently shaped and sized grains is one such consideration. We have developed a method that enhances existing resistivity models with a 2-D extension that incorporates the grain size distribution using a Voron...

Current transport in polysilicon is a complicated process with many factors to consider. The inhomogeneous nature of polysilicon with its differently shaped and sized grains is one such consideration. We have developed a method that enhances existing resistivity models with a two-dimensional extension that incorporates the grain size distribution u...

Polycrystalline silicon (poly‐Si) has been and still is a pivotal material, particularly in the electronics and solar energy industries. Controlling crystallization is one of the challenges, e.g., in producing poly‐Si films for radio frequency applications. Since film growth by deposition is a random process, producing a specific grain size distrib...

Polycrystalline silicon (poly-Si) is an excellent material for use in microelectronic devices, both in electrical and mechanical applications. Its mechanical and electrical properties are widely adjustable, its processing technology is compatible with existing microcircuit manufacturing technology, and its availability and recyclability are at a hi...

Polycrystalline silicon (poly-Si) significantly expands the properties of the ICT miracle material, silicon (Si). Depending on the grain size and shape and grain boundary structure, the properties of poly-Si exceed what single-crystal (c-Si) and amorphous (a-Si) silicon can offer, especially for radio frequency (RF) applications in microelectronics...

Ultrahigh vacuum (UHV) environment has been widely used in surface science, but UHV technology has been often considered too complex and expensive methodology for large-scale industrial use. Because the preparation of atomically smooth and clean Si surfaces has become relevant to some industrial processes, we have re-addressed the question if UHV c...

Manufacturing a low‐resistive Ohmic metal contact on p‐type InP crystals for various applications is a challenge because of the Fermi‐level pinning via surface defects and the diffusion of p‐type doping atoms in InP. Development of wet‐chemistry treatments and nanoscale control of p‐doping for InP surfaces is crucial for decreasing the device resis...

Germanium is an excellent material candidate for various applications, such as field effect transistors and radiation detectors/multijunction solar cells, due to its high carrier mobilities and narrow bandgap, respectively. However, the efficient passivation of germanium surfaces remains challenging. Recently, the most promising results have been a...

Properties of oxidized InP surfaces, which are known to cause less electrical and optical losses than other III-V oxides, are relevant to develop the passivation of current and future applications of III-V crystals (e.g., lasers, detectors). We report that a proper low-temperature (< 400 ℃) gas exposure with NH3 or O2 enables beneficial modificatio...

FinEstBeAMS is an atmospheric and materials science beamline located at the 1.5 GeV storage ring of the MAX IV Laboratory in Lund, Sweden. It offers a very wide photon energy range 4.5-1300 eV and radiation with different polarization characteristics. The beamline has three end stations installed at two branch lines. The new solid state end station...

High-k dielectrics Al2O3 and HfO2 are widely used in combination with Si to produce electronic components and solar cells. A negative fixed charge is known to appear at Si/high-k material interface after high-temperature annealing, yet the formation mechanism of the negative charge is poorly understood. In this work, we investigate the parameters a...

Low temperature treatments to control the Si-interface properties become more and more relevant to the broad Si-based electronics and photonics technology when the back-end-of-line processing is developed and the integration of hybrid materials on the Si platform increases. In this work we have investigated effects of NH3 nitridation of three diffe...

Growing SiO2 layer by wet-chemical oxidation of Si surfaces before growth of another insulating film(s) is a used method to passivate Si interfaces in applications (e.g., solar cell, photodiode) at low temperatures (LT) below 450 °C. We report on potential of LT ultrahigh-vacuum (UHV) treatments combined with the wet-chemical oxidation, by investig...

To enable accurate molecular dynamics simulations of iron–chromium alloys with surfaces, we develop, based on density-functional-theory (DFT) calculations, a new interatomic Fe–Cr potential in the Tersoff formalism. Contrary to previous potential models, which have been designed for bulk Fe–Cr, we extend our potential fitting database to include no...

Properties of Ge oxides are significantly different from those of widely used Si oxides. For example, the instability of GeOx at device junctions causes electronic defect levels that degrade the performance of Ge-containing devices (e.g., transistors and infrared detectors). Therefore, the passivating Si layers have been commonly used at Ge interfa...

In this paper we continue to develop our structural optimization algorithm built earlier on a numerical platform, the Genetic Hybrid Algorithm (GHA). Our goal now is to extend our algorithm to oxides, find an effective way to search for the known global minimum, alpha-quartz as a test case, and report our results and findings for this system. We st...

III-V semiconductor - oxide interfaces have attracted huge interest due to their substantial potential in electronic applications. However, due to the extreme complexity of the modeling of the interfaces, there are only few ab initio studies of these interfaces. Several model interfaces of native InPO4 oxides are designed in this study. It is shown...

To enable accurate molecular dynamics simulations of iron-chromium alloys with surfaces, we develop, based on density-functional-theory (DFT) calculations, a new interatomic Fe-Cr potential in the Tersoff formalism. Contrary to previous potential models, which have been designed for bulk Fe-Cr, we extend our potential fitting database to include no...

The close similarity of silicon and germanium, isoelectronic group-IV elements, makes the integration of Ge layers on Si substrates suitable for technology development, but the atomic and electronic structures of Si1−xGex surfaces are still an open issue, in particular, for the alloy systems where Si is deposited on the Ge substrate. In this study,...

Negative static charge and induced internal electric field have often been observed in the interfaces between silicon and high‐κ dielectrics, for example Al2O3 and HfO2. The electric field provides either beneficial (e.g., field‐effect passivation) or harmful (e.g., voltage instability) effect depending on the application. Different intrinsic and e...

The adsorption of oxygen on bcc Fe–Cr(100) surfaces with two different alloy concentrations is studied using ab initio density functional calculations. Atomic-scale analysis of oxygen–surface interactions is indispensable for obtaining a comprehensive understanding of macroscopic surface oxidation processes. Up to two chromium atoms are inserted in...

Control of interfacial physicochemical properties associated with device materials to minimize the impact of point defects on device performance has been a dominant theme in the semiconductor industry. Control of the density of such defects for silicon has been well established for metal oxide-semiconductor field-effect device applications through...

Recently, Theophilou (J. Chem.Phys {\bf 149} 074104 (2018)) showed that a set of spherically symmetric densities determines uniquely the external potential in molecules and solids. Here, spherically symmetric Kohn-Sham-like equations are derived. The spherical densities can be expressed with radial wave functions. Expression for the total energy is...

Low-temperature (LT) passivation methods (<450 °C) for decreasing defect densities in the material combination of silica (SiO x ) and silicon (Si) are relevant to develop diverse technologies (e.g., electronics, photonics, medicine), where defects of SiO x /Si cause losses and malfunctions. Many device structures contain the SiO x /Si interface(s),...

Using a hydrogen molecule as a test system we demonstrate how to compute the effective potential according to the formalism of the new density functional theory (DFT), in which the basic variable is the set of spherically averaged densities instead of the total density, used in the traditional DFT. The effective potential together the external pote...

Using scanning tunneling microscopy, x-ray photoelectron spectroscopy, and low-energy electron diffraction, we have studied clean and Ni-containing Si(1 0 0) surfaces and shown that the Ni contamination can easily appear at the Si(1 0 0) during its annealing at high temperature (1230 °C) because of migration of this impurity from heated parts of th...

Abstract The thermodynamic ordering transformation of tetragonal FeNi system is investigated by the Exact Muffin-Tin Orbitals (EMTO) method. The tetragonal distortion of the unit cell is taken into account and the free energy is calculated as a function of long-range order and includes the configurational, vibrational, electronic and magnetic contr...

We studied the magnetic phase diagram of the rare-earth manganites series Gd1−xCaxMnO3 (GCMO) over the full concentration range based on density functional theory. GCMO has been shown to form solid solutions. We take into account this disordered character by adapting special quasi-random structures at different concentration steps. The magnetic pha...

Density functional alloy theory is used to accurately describe the three core effects controlling the thermodynamics of random Cu-Au alloys. These three core effects are exchange correlation (XC), local lattice relaxations (LLRs), and short-range order (SRO). Within the real-space grid-based projector augmented-wave (GPAW) method based on density f...

We implement a Becke fuzzy cells type space partitioning scheme for the purposes of exchange-correlation within the GPAW projector augmented-wave method based density functional theory code. Space partitioning is needed in the situation where one needs to treat different parts of a combined system with different exchange-correlation functionals. Fo...

X-ray photoelectron spectroscopy (XPS) is one of the most used methods in a diverse field of materials science and engineering. The elemental core-level binding energies (BE) and core-level shifts (CLS) are determined and interpreted in the XPS. Oxidation is commonly considered to increase the BE of the core electrons of metal and semiconductor ele...

Silica phases, SiOx forming at surfaces of various silicon crystals, e.g., Si wafers, nanowires, and nanoparticles via Si oxidation are key building blocks of diverse applications in the fields of electronics, medicine, and photonics for instance. The Si oxidation has been established to produce amorphous SiOx films, and the resulting oxide/silicon...

InAs crystals are emerging materials for various devices like radio-frequency transistors and infrared sensors. Control of oxidation-induced changes is essential for decreasing amounts of the harmful InAs surface (or interface) defects because it is hard to avoid the energetically favored oxidation of InAs surface parts in device processing. We hav...

Our understanding of bias-dependent scanning-tunneling-microscopy (STM) images is complicated not only by the multiplicity of the surface electronic structure, but also the manifold tunneling effects in probing semiconductor surfaces having directional dangling- and covalent-bond orbitals. Here we present a refined interpretation of empty-state STM...

We studied for the first time the magnetic phase diagram of the rare-earth manganites series Gd(1-x)Ca(x)MnO3 (GCMO) over the full concentration range based on density functional theory. GCMO forms a solid solution and we take into account its disorder by adapting special quasi random structures at different concentration steps. The magnetic phase...

We implement a Becke fuzzy cells type space partitioning scheme for the purposes of exchange-correlation within the GPAW projector augmented-wave method based density functional theory code. Space partitioning is needed in the situation where one needs to treat different parts of a combined system with different exchange-correlation functionals. Fo...

Oxidation treatment creating a well-ordered crystalline structure has been shown to provide a major improvement for III-V semiconductor/oxide interfaces in electronics. We present this treatment's effects on InSb(111)B surface and its electronic properties with scanning tunneling microscopy and spectroscopy. Possibility to oxidize (111)B surface wi...

Since oxide materials like Sr2FeMoO6 are usually applied as thin films, we studied the effect of biaxial strain, resulting from the substrate, on the electronic and magnetic properties and, in particular, on the formation energy of point defects. From our first-principles calculations, we determined that the probability of forming point defects, li...

Oxygen vacancies can be of utmost importance for improving or deteriorating physical properties of oxide materials. Here, we studied from first-principles the electronic and magnetic properties of oxygen vacancies in the double perovskite Sr₂FeMoO₆ (SFMO). We show that oxygen vacancies can increase the Curie temperature in SFM...

We use three gradient level and two nonlocal density functional approximations to study the thermodynamic properties of Cu-Au compounds. It is found that a well-designed gradient level approximation (quasi non-uniform approximation, QNA) reproduces the experimental equilibrium volumes and the formation energies of L12 and L10 phases. On the other h...

Since oxide materials like Sr$_2$FeMoO$_6$ are usually applied as thin films, we studied the effect of biaxial strain, resulting from the substrate, on the electronic and magnetic properties and, in particular, on the formation energy of point defects. From our first-principles calculations, we determined that the probability of forming point defec...

Effects of magnesium (Mg) alloying of GaxIn1−xAs(100) semiconductor surfaces have been investigated by low-energy electron diffraction, scanning tunneling microscopy/spectroscopy, and responsivity analysis of an infrared-detector component. In particular, the formation of an unusual Mg-induced (2 × 1) structure on GaAs(100) surfaces is found when d...

Oxygen vacancies can be of utmost importance for improving or deteriorating physical properties of oxide materials. Here, we studied from first-principles the electronic and magnetic properties of oxygen vacancies in the double perovskite Sr2FeMoO6 (SFMO). We show that oxygen vacancies can increase the Curie temperature in SFMO, although the total...

Crystalline oxide phases on InSb(111)B revealed with scanning tunneling microscopy and spectroscopy

Kullback–Leibler and relative Fisher information functionals are applied in studying deviation from local density approximation. The reduced density gradient s and the local kinetic energy parameter α are key ingredients of these new locality descriptors. The relative Kullback–Leibler information density contains extra knowledge as it is negative w...

Control of defect densities at insulator/GaxIn1−xAs interfaces is essential for optimal operation of various devices like transistors and infrared detectors to suppress, for example, nonradiative recombination, Fermi-level pinning, and leakage currents. It is reported that a thin InOx interface layer is useful to limit the formation of these defect...

III-V semiconductors are prominent alternatives to silicon in metal oxide semiconductor devices. Hafnium dioxide (HfO2) is a promising oxide with a high dielectric constant to replace silicon dioxide (SiO2). The potentiality of the oxide/III-V semiconductor interfaces is diminished due to high density of defects leading to the Fermi level pinning....

The FinEstBeaMS beamline is under construction at the 1.5 GeV storage ring of the MAX IV Laboratory at Lund, Sweden. It has been designed to cover an unusually wide energy range from ultraviolet (4.3 eV) to soft X-rays (1000 eV) but experiments will also be possible at the Mg and Al Kα energies. Instead of having two different insertion devices and...

Hydrogen, carbon, and oxygen are common unintentional impurities of Al(x)Ga(1-x)N crystals. This impurity structure and its interplay with Mg impurities in Al(x)Ga(1-x)N semiconductors are relevant to develop the p-type nitride crystals for various devices (e.g, LEDs, transistors, gas sensors), but are still unclear. Here we have investigated Mg-do...

Epitaxial Bi-containing III–V crystals (III-V1-xBix) have attracted increasing interest due to their potential in infrared applications. Atomic-scale characterization and engineering of bulk-like III-V1-xBix properties (e.g., Bi incorporation and defect formation) are challenging but relevant to develop applications. Toward that target, we report h...

Ab initio total-energy calculations, based on the exact muffin-tin orbitals method, are used to determine the equilibrium chemical configuration of alloy as a function of disorder and temperature. The transition from a substitutionally disordered face-centred-cubic crystallographic phase to an ordered phase is monitored using the coherent potential...

First-principles calculations have been performed to study the effect of C on the stacking fault energy (SFE) of paramagnetic g-Fe and FeeCreNi austenitic steel. In these systems, the local magnetic structure is very sensitive to the volume in both fcc and hcp structures, which emphasizes the importance of the magnetovolume coupling effect on the S...

Semilocal density functional approximations occupy the second rung of the Jacob's ladder model and are thus expected to have certain limits to their applicability. A recent study [Y. Zhang, G. Kresse, and C. Wolverton, Phys. Rev. Lett. 112, 075502 (2014)] hypothesizes that the formation energy, being one of the key quantities in alloy theory, would...

Titanium is a strong, corrosion resistant metal with low mass density, making it ideal for various purposes, including aviation and medical applications. In the present work, the elastic properties of titanium have been investigated using the first principles Exact Muffin-Tin Orbitals method. The focus of our study is the anisotropic elasticity of...

Strong Fermi-level pinning (FLP) near the valence-band maximum on n-type Ge surfaces has been a long-standing challenge in semiconductor physics, and the nature of this phenomenon has been heavily debated for years. Here, we report a systematic synchrotron-based photoemission study of atomically well-defined Ge(100) surfaces and interfaces to eluci...

We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the...

We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the...

The oxidation of GaSb(100) surface has been widely studied because it affects the functionality of various devices. However even initial stages of the oxygen incorporation are not completely understood. To clarify this issue, we have investigated the oxidized GaSb(100) surfaces, which have been recently probed by scanning tunneling microscopy and s...

A novel simple method to produce a high-quality interface between semiconductor (e.g., Ge or III-V) and dielectric film (i.e., SiO2) is suggested. A nonoxygen element is deposited directly on an oxidized substrate at T ≥ 300 °C, leading to semiconductor reduction and dielectric film growth. As a result, the formed interface is atomically abrupt and...

Fe–Al is one of the best corrosion resistant alloys at high temperatures. The flip side of Al addition to Fe is the deterioration of the mechanical properties. This problem can be solved by adding a suitable amount of third alloying component. In the present work, we use ab initio calculations based on density functional theory to study the elastic...

Iron-chromium alloys, the base components of various stainless steel grades, have numerous technologically and scientifically interesting properties. However, these features are not yet sufficiently understood to allow their full exploitation in technological applications. In this work, we investigate segregation, precipitation, and phase separatio...

A recently developed theoretical framework of performing self-consistent orbital-free (OF) density functional theory (DFT) calculations at Kohn-Sham DFT level accuracy is tested in practice. The framework is valid for spherically symmetric systems. Numerical results for the Beryllium atom are presented and compared to accurate Kohn-Sham data. These...

First-principles alloy theory is used to establish the $\gamma$-surface of Fe-Cr-Ni alloys as function of chemical composition and temperature. The theoretical stacking fault energy (SFE) versus chemistry and temperature trends agree well with experiments. Combining our results with the recent plasticity theory based on the $\gamma$-surface, the st...

Interstitials (carbon and nitrogen) are crucial alloying elements for optimizing the mechanical performance of the twinning-induced plasticity (TWIP) steels in terms of the stacking fault energy (SFE). First-principles calculations have been performed to study the effect of interstitial-induced lattice expansion on the SFE. Comparing the prediction...

TiO2/AlInP junctions are used to construct the antireflection coatings for solar cells and to passivate III–V nanostructure surfaces. The thickness of AlInP epilayer affects light absorption and appropriate Al composition determining further the energy barrier for carriers. We report on reducing the AlInP thickness by dry etching down to 10 nm with...

Oxidation of semiconductor surfaces is known to cause defect states at oxide-semiconductor interfaces of various devices. In contrast, effects of the semiconductor interaction with non-oxygen elements at such junctions are still unclear. We present evidence for the interrelationship between a metal (non-oxygen)-semiconductor reaction and formation...

GaAs1-xBix alloys have useful properties for many optoelectronic applications. Although the crystal growth by molecular beam epitaxy is influenced by kinetics, it is also important to understand the thermodynamics of the alloys. The Gibbs formation energies and the immiscibility curve of the totally disordered GaAs1-xBix (0 ≤ x ≤ 1) are determined...

Atomic-scale knowledge and control of oxidation of GaSb(100), which is a potential interface for energy-efficient transistors, are still incomplete, largely due to an amorphous structure of GaSb(100) oxides. We elucidate these issues with scanning-tunneling microscopy and spectroscopy. The unveiled oxidation-induced building blocks cause defect sta...

Atomic structure of the Sr-adsorbed Si(100)(1 × 2) surface has been investigated by scanning tunneling microscopy (STM) and ab initio calculations. This surface reveals rows of Sr atoms between unbuckled Si dimer rows as well as an abundance of vacancy defects in the metal rows. The density of such defects can be minimized by the optimization of gr...

Segregation, precipitation, and phase separation in Fe-Cr systems is investigated. Monte Carlo simulations using semiempirical interatomic potential, first-principles total energy calculations, and experimental spectroscopy are used. In order to obtain a general picture of the relation of the atomic interactions and properties of Fe-Cr alloys in bu...

The In 3d5/2 photoelectron spectroscopy peak has been widely used to determine the interface structures of In-containing III–V device materials (e.g., oxidation states). However, an unclear parameter affecting the determination of the energy shifts and number of the core-level components, and therefore, the interpreted interface structure and compo...

Atomic-scale understanding and processing of the oxidation of III–V compound–semiconductor surfaces are essential for developing materials for various devices (e.g., transistors, solar cells, and light emitting diodes). The oxidation-induced defect-rich phases at the interfaces of oxide/III–V junctions significantly affect the electrical performanc...

The pre-oxidized crystalline (3×1)-O structure of InAs(100) has been recently found to significantly improve insulator/InAs junctions for devices, but the atomic structure and formation of this useful oxide layer are not well understood. We report high-resolution photoelectron spectroscopy analysis of (3×1)-O on InAs(100) and InSb(100). The finding...

In orbital-free density functional theory, only a Schrödinger-like equation has to be solved for the square root of the electron density. In this equation, however, there is an extra potential in addition to the Kohn-Sham potential, the so-called Pauli potential. Cusp relations are now presented for this Pauli potential for spherically symmetric sy...

Atomic structure of interfaces between oxide layers and semiconductors is usually challenging to probe because of its buried nature. Here, we present a synchrotron photoemission approach to unveil the interface structure of BaO/Si(100), a prototype model of crystalline-oxide/semiconductor junctions, and demonstrate that such interface outspreads ov...

Short-range correlations in Ag-Au and Ag-Pd alloys are investigated by analyzing the ab initio total energy of face centered cubic (fcc) based random AgcAu1-c, and AgcPd1-c. Since the information on the atomic interactions is incorporated in the energetics of alloys it is possible with a suitable model, Bethe-Peierls-Weiss model is used in the pres...

GaAs1 − xBi x alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to Bi clustering at certain Bi compositions. Using ab initio calculations, we show that there is no thermodynamical driving force for the formation of sma...

The exothermic nature of oxidation causes nearly all semiconductor applications in various fields like electronics, medicine, photonics, and sensor technology to acquire an oxidized semiconductor surface part during the application manufacturing. The significance of understanding and controlling the atomic scale properties of oxidized semiconductor...

Synthesis of layered SnO with a monocrystalline structure on a semiconductor substrate is demonstrated using a vacuum deposition method as well as diffraction, microscopy, and spectroscopy characterization.

Bismuth (Bi) induced c(4 × 4) surface structure of the GaAs(100) substrate, i.e., the GaAs(100)c(4 × 4)-Bi surface has been studied with synchrotron-radiation photoelectron spectroscopy and ab initio calculations. The surface was prepared by combining molecular beam epitaxy and in-situ electron diffraction methods, and then the sample was transferr...

In our previous study [Phys. Rev. B 86, 201104 (2012)] we introduced the so called quasi-non-uniform gradient-level exchange-correlation approximation (QNA) and demonstrated it's strength in producing highly accurate equilibrium volumes for metals and their alloys within the density-functional theory. In this paper we extend the scheme to include t...

The synthesis of novel functional crystalline films on semiconductor substrates calls for atomic-level knowledge and controlling of the initial stages of interface or junction formation. Technologically relevant epitaxial oxide films can be grown on Si(100) surfaces modified by submonolayer alkaline earth adsorbates, e.g., barium (Ba) and strontium...

Growing a crystalline oxide film on III-V semiconductor renders possible approaches to improve operation of electronics and optoelectronics heterostructures such as oxide/semiconductor junctions for transistors and window layers for solar cells. We demonstrate the growth of crystalline barium oxide (BaO) on GaAs(100) at low temperatures, even down...

We determine the interface energy and the work of separation of the Fe/Cr2O3 interface using first-principles density functional theory. Starting from different structures, we put forward a realistic interface model that is suitable to study the complex metal-oxide interaction. This model has the lowest formation energy and corresponds to an interf...

Ab initio alloy theory, formulated within the exact muffin-tin orbitals method in combination with the coherent-potential approximation, is used to determine the elastic properties of Ni-Fe alloys with Fe:Ni ratio 1:3. The interplay between magnetic and chemical effects is investigated by computing the lattice parameters and the single- and polycry...

Clean and metal-adsorbed (100) surfaces of group-IV semiconductors, such as Si and Ge, often exhibit electronically and structurally similar reconstructions. However, the fundamental bulk properties of group-IV materials can have an impact on particular features of such systems, which are related, e.g., to final-state relaxation in photoemission an...