R. I. G. Uhrberg's research while affiliated with Linköping University and other places

Publications (183)

Article
Full-text available
Atomic and electronic structure investigations of the substitutional Au2Sn surface alloy formed on Au(111) are presented. Low energy electron diffraction and scanning tunneling microscopy (STM) reveal a structure with a local 3×3 periodicity with a superimposed modulation resulting in a 26×3 unit cell. STM images show a striped structure that resem...
Article
Full-text available
Various elements (Ge, Sn, Pb, Sb, and Bi) form well-ordered two-dimensional surface alloys on Ag(111). One out of three Ag atoms in the surface layer is replaced in an ordered fashion to form a periodicity. These surface alloys play an important role as model systems and have been utilized particularly in studies of Rashba split of surface bands. I...
Article
Full-text available
Engineering tunable graphene-semiconductor interfaces while simultaneously preserving the superior properties of graphene is critical to the graphene-based devices for electronic, optoelectronic, biomedical and photoelectrochemical applications. Here, we demonstrate this challenge can be surmounted by constructing a novel atomic Schottky junction v...
Article
Full-text available
Inspired by the unique properties of graphene, research efforts are broadened to investigations of various other two-dimensional materials with the aim to explore their properties for future applications. Our combined experimental and theoretical study confirms the existence of a binary honeycomb structure formed by Ag and Te on Ag(111). Low energy...
Article
Full-text available
Group V element analogues of graphene have attracted a lot of attention recently due to their semiconducting band structures and several other interesting properties predicted by theoretical investigations in the literature. In this study, we present atomic and electronic structure data of an arsenic (As) layer on Ag(1 1 1). Low-energy electron dif...
Preprint
Inspired by the unique properties of graphene, the focus in the literature is now on investigations of various two-dimensional (2D) materials with the aim to explore their properties for future applications. The group IV analogues of graphene, i.e., silicene, germanene and stanene have been intensively studied in recent years. However, their semi-m...
Preprint
Group V element analogues of graphene have attracted a lot attention recently due to their semiconducting band structures, which make them promising for next generation electronic and optoelectronic devices based on two-dimensional materials. Theoretical investigations predict high electron mobility, large band gaps, band gap tuning by strain, form...
Article
The stacking order of multilayer graphene significantly influences its electronic properties. The rhombohedral stacking sequence is predicted to introduce a flat band, which has high density of states and the enhanced Coulomb interaction between charge carriers, thus possibly resulting in superconductivity, fractional quantum Hall effect and many o...
Article
Full-text available
Low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and photoelectron spectroscopy have been used to study an ordered structure formed by Ge atoms deposited onto the Au(111) surface. Based on a careful analysis of STM images and LEED patterns, we propose a new unit cell for the atomic structure of the Ge layer. Core level d...
Article
Full-text available
We report a study of structural and electronic properties of a germanium layer on Al(111) using scanning tunneling microscopy (STM), low energy electron diffraction and core-level photoelectron spectroscopy. Experimental results show that a germanium layer can be formed at a relatively high substrate temperature showing either (3×3) or (√7×√7)R±19....
Data
Detailed information of the (3×3) and (√7×√7) models.
Article
Full-text available
Silicene, the two-dimensional (2D) allotrope of silicon, has very recently attracted a lot of attention. It has a structure that is similar to graphene and it is theoretically predicted to show the same kind of electronic properties which have put graphene into the focus of large research and development projects worldwide. In particular, a 2D stru...
Article
Full-text available
In the case of graphene, hydrogenation removes the conductivity due to the bands forming the Dirac cone by opening up a band gap. This type of chemical functionalization is of utmost importance for electronic applications. As predicted by theoretical studies, a similar change of the band structure is expected for silicene, the closest analogue to g...
Research
By analyzing LEED and STM results, we have obtained a detailed structure determination of “2√3” silicene on Ag(111). Due to strain, the silicene layer exhibits a quasi-periodic long-range modulation resulting in a hexagonal like superstructure with a lattice constant ~3.7 times larger than that of a 2√3 unit cell. The homogeneous coverage of the Ag...
Article
Full-text available
Silicene, the two-dimensional (2D) allotrope of silicon has very recently attracted a lot of attention. It has a structure that is similar to graphene and it is theoretically predicted to show the same kind of electronic properties which has put graphene into the focus of large research and development projects world-wide. In particular, a 2D struc...
Article
Full-text available
We have investigated sub-monolayer coverages of Sn on the Ag/Ge(111) 3×3 surface. It was found that ≈ 0.45 monolayer (ML) resulted in a new, well-defined, reconstruction with a 33×33 periodicity. The periodic structure of the surface atoms was verified by low-energy electron diffraction and scanning tunneling microscopy. The electronic structure wa...
Article
Full-text available
This study focuses on the electronic structure of a 6 × 6 surface which is formed by 0.2 monolayer of Ag on top of the Ag/Ge(111) surface. The 6 × 6 periodicity was verified by low energy electron diffraction. Angle resolved photoelectron spectroscopy was employed to study the electronic structure along the and high symmetry lines of the 6 × 6 surf...
Article
The geometric symmetry of the surface plays an important role for the spin-oribit-induced spin texture of two-dimensional electronic states. This article reviews the peculiar Rashba spins induced by a C3 symmetry, including the completely spin polarized surface states with the polarization vector oriented perpendicular to the surface, i.e. a direct...
Article
Full-text available
We report a study of the atomic and electronic structures of the ordered Ag2Ge surface alloy containing ⅓ monolayer of Ge. Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES) data reveal a symmetry breaking of the expected √3 × √3 periodicity, which is established for ot...
Article
Full-text available
The Ag/Ge(111)√3×√3 surface together with Ag/Si(111)√3×√3 constitutes a set of surfaces that is ideally suited for fundamental studies related to low dimensional physics. We here focus on the atomic and electronic structures of the two-dimensional √3×√3 superstructure induced by Ag on Ge(111), a surface that is significantly less studied than the S...
Article
Full-text available
The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. So far, however, such devices have not been realized due to the difficulty to polarize the valleys, which is an indispensable step to activate this degree of freedom. H...
Article
There is an increasing interest in two-dimensional (2D) surface alloys as model systems for studies of various physical phenomena. We have formed a binary In/Pb surface alloy on Ge(111) by evaporating 0.8 monolayer (ML) of In on the Pb/Ge(111) surface with 1.33 ML of Pb. A highly ordered 3x3 periodicity is formed after annealing at a temperature sl...
Article
It is found that 1/3 monolayer (ML) of Sn forms a surface alloy with 2/3 ML of Ag on Ag(111). This highly ordered alloy layer shows a sqrt[3]×sqrt[3] structure. By employing experimental and theoretical tools (scanning tunneling microscopy [STM], angle resolved photoelectron spectroscopy, low-energy electron diffraction, and density functional theo...
Article
Full-text available
The existence of a highly ordered, two-dimensional, Sn/Ag alloy on Si(111) is reported in this study. We present detailed atomic and electronic structures of the one atomic layer thick alloy, exhibiting a 2×2 periodicity. The electronic structure is metallic due to a free-electron-like surface band dispersing across the Fermi level. By electron dop...
Article
Full-text available
The electronic and atomic structures of a well-ordered 3×3 periodicity of a binary Sn/Ag overlayer on Ge(111) have been studied. The ordered binary overlayer was formed by depositing 0.75 monolayer of Sn on an Ag/Ge(111) 3×3 surface. Annealing at 330 °C resulted in a low-energy electron diffraction pattern that exhibited sharp spots. A detailed ele...
Chapter
Full-text available
Metal adsorbates on semiconductor surfaces provide two-dimensional structures that are of fundamental importance to studies of various physical phenomena. Among others, silver (Ag) is an example of a metallic adsorbate that can induce several 2D structures on elemental semiconductor surfaces. For instance, one monolayer (ML) of Ag on Si(111), i.e.,...
Article
Core level spectroscopy measurements have been made on Si substrates with coverages of around one monolayer of As, Ga and GaAs. The interfaces were formed on on-axis Si(100) and Si(111) substrates using molecular beam epitaxy. Results are also presented for an arsenic monolayer on a single-domain Si(100) surface prepared by cutting the crystal off-...
Chapter
Full-text available
Metallic overlayers on semiconductor surfaces have been studied for both pure scientific and technological reasons, and have attracted a lot of attention during several decades. The studies have mostly been based on single metallic species on the Si and Ge surfaces, while binary overlayers have not been given similar attention so far. The reason co...
Article
The bonding at the interface between CaF2 and Si(111) has been investigated using core-level photoemission spectroscopy. The results are discussed in terms of various structural models of the interface. The stable interface has a depletion of fluorine from the interface resulting in strong Si - Ca bonding.
Article
Full-text available
The Si􏰁111􏰂 surface with an average coverage of slightly more than one monolayer of Sn, exhibits a 2􏰑3 􏰕2􏰑3 reconstruction below 463 K. In the literature, atomic structure models with 13 or 14 Sn atoms in the unit cell have been proposed based on scanning tunneling microscopy 􏰁STM􏰂 results, even though only four Sn atoms could be resolved in the un...
Article
Full-text available
With a Tl coverage of one monolayer, a 2􏰕1 reconstruction is formed on the Si􏰁001􏰂 surface at room temperature. In this study, low-temperature angle-resolved photoelectron spectroscopy 􏰁ARPES􏰂 data reveal four surface state bands associated with this Tl induced reconstruction. Calculated surface state dispersions, obtained using the “pedestal+valle...
Article
The Si 2p and Ge 3d core levels are investigated on the c(4×2) reconstructed surfaces of Si(001) and Ge(001), respectively. Calculated surface core-level shifts are obtained both with and without final state effects included. Significant core-level shifts are found within the four outermost atomic layers. A combination of the theoretical results an...
Article
The electronic structure of H/Ge(111)1×1 was investigated using angle-resolved photoelectron spectroscopy. Spectra were measured along the high-symmetry lines of the 1×1 surface Brillouin zone. In the Γ¯-K¯-M¯ direction, two surface states, labeled a and a' , were found in the lower and upper band-gap pockets. The a and a' surface states are associ...
Article
We have performed a detailed study of the formation and the atomic structure of a √3 × √3 surface on Si/Ge(1 1 1) using both scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Both experimental methods confirm the presence of a √3 × √3 periodicity but unlike the Sn/Ge(1 1 1) and the Sn/Si(1 1 1) surfaces, the Si/Ge(1 1...
Article
The influence of substrate orientation on the morphology of graphene growth on 6H-SiC(0 0 0 1) was investigated using low-energy electron and scanning tunneling microscopy (LEEM and STM). Large area monolayer graphene was successfully furnace-grown on these substrates. Larger terrace widths and smaller step heights were obtained on substrates with...
Article
The influence of substrate orientation on the morphology of graphene growth on 6H-SiC(0001) was investigated using low-energy electron and scanning tunneling microscopy (LEEM and STM). Large area monolayer graphene was successfully furnace-grown on these substrates. Larger terrace widths and smaller step heights were obtained on substrates with a s...
Article
The surface electronic structure of Ge(111)c(2×8) was studied by experimental techniques [low-energy electron diffraction, scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES)] and theoretical band-structure calculations. Bias-dependent STM images exhibit two different types of adatoms (AT,AR) and rest atoms (R...
Article
Full-text available
The polarization vector of the Rashba spin, which must be parallel to the two-dimensional (2D) plane in an ideal system, is found to change abruptly and definitely to the direction perpendicular to the surface at the K point of the Brillouin zone of a real hexagonal system, the Tl/Si(111)-(1x1) surface. This finding obtained experimentally by angle...
Article
The electronic structure of a single domain Si􏰁110􏰂-􏰁16􏰕2􏰂 surface has been investigated by high-resolution angle-resolved photoelectron spectroscopy and scanning tunneling microscopy 􏰁STM􏰂. Four semiconducting surface states with flat dispersions, whose binding energies are 0.2, 0.4, 0.75, and 1.0 eV, were observed in the bulk band gap and more th...
Article
The relation between annealing temperature and surface photovoltage (SPV) shifts on the Si(111)7×7 surface of lightly n-doped substrates has been studied by core-level and valence-band photoelectron spectroscopies at 100 K. The SPV shift was found to depend strongly on the annealing temperature and the photon flux. Between 900 and 1150 °C the magni...
Article
Variable temperature photoemission studies in the literature have revealed the presence of a surface state above the Fermi level on clean Ge􏰁001􏰂. We present photoemission and low energy electron diffraction results from Ge􏰁001􏰂 obtained between 185 and 760 K. Our measurements show a peak above the Fermi level with a maximum intensity at a sample t...
Article
We have investigated the surface electronic structure of the Tl induced surface by using angle-resolved photoelectron spectroscopy. Three semiconducting surface states were observed in the gap of the bulk band projection. Of these three states, the one, whose binding energy is approximately 0.3 eV, hardly disperses. Regarding the two other states,...
Article
The electronic and atomic structure of Si􏰁001􏰂 with 0.5 and 1 ML of lithium have been studied experimen- tally using angle resolved ultraviolet photoelectron spectroscopy, Si 2p core level spectroscopy, and low energy electron diffraction. Experimental surface state dispersions are compared with recent theoretical results in the literature and with...
Article
Full-text available
Recent results for the arsenic termination of the Ge(111), Si(111) and Si(100) surfaces are reviewed. Arsenic interaction with the Ge(111) and Si(111) surfaces has been found to result in the replacement of the outer Ge (Si) layer with an As layer. This arrangement has a 1 × 1 symmetry and the calculated positions of the As atoms are very close to...
Article
We have investigated the electronic structures of the so-called Eu- and Ca-induced Si􏰁111􏰂-􏰁5􏰕1􏰂 surfaces by using angle-resolved photoelectron spectroscopy 􏰁ARPES􏰂 and low-energy electron diffraction 􏰁LEED􏰂. The LEED patterns of these surfaces indicate that the periodicities of both surfaces are actually 􏰁5􏰕4􏰂. In the ARPES study, seven surface st...
Article
The atomic and electronic structures of the Ag/Si(111)3×3 surface are currently under debate. By employing angle-resolved valence-band spectroscopy, the surface band dispersions around the Kmacr point of the Ag/Si(111)3×3 surface have been investigated in detail. Contrary to a recent study, we conclude that the S2 and S3 surface state bands do not...
Article
The coverage-dependent valence state of Tl adsorbed on a Si􏰁111􏰂-􏰁7􏰕7􏰂 surface and the coverage depen- dence of the charge states of surface Si atoms have been investigated by high-resolution core-level photoelec- tron spectroscopy. Although two different reconstructions were observed in low-energy electron diffraction at different coverages, a 􏰁1􏰕...
Article
The atomic and electronic structures of the Si(001)-c(4 x 4) surface have been studied by scanning tunneling microscopy (STM) and density functional theory (DFT). To explain the experimental bias dependent STM observations, a modified mixed ad-dimer reconstruction model is introduced. The model involves three tilted Si dimers and a carbon atom inco...
Article
We have studied hydrogen adsorption on the Ge(111) c(2×8) surface using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES). We find that atomic hydrogen preferentially adsorbs on rest atom sites. The neighbouring adatoms appear higher in STM images, which clearly indicates a charge transfer from the rest atom...
Article
The surface structures of the (quasi-)one-dimensional reconstructions induced by the adsorption of Eu on Si(111) have been investigated by low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Different phases were observed in LEED depending on the Eu coverage. The lowest coverage phase has a (3×2) period...
Article
The adsorption and reaction processes of physisorbed oxygen molecules on a Si(111)-(7×7) surface have been investigated using time-resolved O 1s core-level photoemission measurements at 45 K. Physisorbed oxygen molecules are only observed at 45 K and lower temperatures on a Si(111)-(7×7) surface. At the dosage when the dangling bonds are saturated...
Article
The electronic structures of the Eu∕Si(111)-(3×2) and (2×1) surfaces have been investigated by angle-resolved photoelectron spectroscopy. On the (3×2) surface, we identify six surface states in the gap and a pocket of the bulk band projection. Among the five surface states observed in the bulk band gap, the dispersions of three of them agree well w...
Article
Adsorption of atomic hydrogen has been studied by scanning tunneling microscopy (STM) and photoelectron spectroscopy with a focus on the different adsorption sites provided by the Si(111) 7×7 surface. At low temperature, the hydrogen atoms adsorb preferentially on adatoms while at elevated temperatures the rest atoms are the first to become hydroge...
Article
A sqrt[21]×sqrt[21] reconstruction has been formed by adding either K or Cs atoms on the Ag∕Si(111)sqrt[3]×sqrt[3] surface at 120K. The electronic structures of these surfaces have been studied by angle-resolved valence band and core-level spectroscopy. In similarity with Ag or Au adatoms, the presence of K or Cs adatoms on Ag∕Si(111)sqrt[3]×sqrt[3...
Article
In this review, we present a series of photoemission studies performed on the so-called metal induced Si(111)-(3×1) surface, which is one of the most well known 1D structure formed on a Si(111) surface. Three different kinds of metals have been used as adsorbate, K, Ca, and Ag.On the K/Si(111)-(3×1) surface, five surface components were observed in...
Article
We have investigated the initial oxidation stage of an Si(111)-(7×7) surface using valence-band photoemission measurements. As the oxygen exposure increases, the intensities of the dangling bond states of adatoms (S1) and rest atoms (S2) decrease. Among the four oxygen-induced states, three originate from the orbitals of adsorbed oxygen species, an...
Article
We have investigated the metastable oxygen species adsorbed on a Si(111)-(7×7) surface at room temperature using real time valence-band and core-level photoemission measurements. The dosage- and time-dependent changes in the intensity of the metastable 3.8 eV peak observed in the valence-band spectra were different from those of the metastable O 1s...
Article
High-resolution photoemission provides important information about the electronic and atomic structure of surfaces. To make full use of the high-energy resolution that is available at many synchrotron radiation facilities, it is important to lower the phonon induced broadening by reducing the sample temperature. Another equally important factor is...
Article
The electronic structure of the Ca/Si(111)-(3×2) surface has been investigated by angle-resolved photoelectron spectroscopy. Five surface states, none of which crosses the Fermi level, were observed in the bulk band gap, and one surface state was observed in a bulk band pocket. The dispersion features of three of the surface states in the band gap...
Article
The electronic structure of the Ca/Si(111)-(3×2) surface has been investigated by angle-resolved photo-electron spectroscopy. Five surface states, none of which crosses the Fermi level, were observed in the bulk band gap, and one surface state was observed in a bulk band pocket. The dispersion features of three of the surface states in the band gap...
Article
We have investigated the electronic structure of the Ca/Si(111)-(2×1) surface using angle-resolved photoelectron spectroscopy. Two semiconducting surface states were clearly observed in the bulk band gap, and one was found in a pocket of the bulk band projection. Qualitatively, the dispersions of the two surface states observed in the band gap agre...
Article
The 6 × 6 and √39×√39 phases of Ag/Ge(1 1 1) have been studied by scanning tunneling microscopy (STM). Surface atomic structures of the 6 × 6 and the √39×√39 phase are proposed in terms of additional Ag adatoms on top of a √3×√3 layer described by the honeycomb-chain-trimer (HCT) model. By varying the STM tip bias, the reconstruction can be changed...
Article
We have investigated the surface structure of the Ca/Si(1 1 1)-(3 × 2) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Weak ×2 streaks were observed in LEED at 300 K. After cooling the sample to 100 K, ×2 spots, which originate from both (3 × 2) and c(6 × 2) periodicities, appeared. By...
Article
Using high-resolution core-level photoemission measurements, we show that two different metastable species exist on a Si(111)-(7×7) surface, instead of only one as suggested in the literature. One metastable species has a finite lifetime and is composed of both molecular and atomic oxygen. The other one, which is formed by atomic oxygen only, is st...
Article
A small amount of Au atoms deposited at room temperature transforms the Ag/Ge(1 1 1)√3×√3 surface into a √39×√39 surface. The presence of the Au atoms leads to downward shifts and modifications of the surface state bands compared to the initial √3×√3 surface. Further deposition of Au on the √39×√39 surface changes it into a 6 × 6 periodicity. At th...
Article
An evolution of an apparent 3×3 low-energy electron diffraction (LEED) pattern has been observed for the Sn1−xSix/Si(1 1 1) surface alloy. The origin of this additional diffraction has been investigated in detail by scanning tunneling microscopy (STM). The 3×3 diffraction, which appears after annealing, is associated with the arrangement of the Sn...
Article
The 6×6 and √39×√39 phases on Ag/Ge(1 1 1) have been studied by scanning tunneling microscopy (STM). Four types of 6×6 configurations are found which all consist of a √3×√3 layer with six extra Ag adatoms per 6×6 unit cell. These reconstructions show either mirrored or complementary relations. We observe interesting transitions between the differen...
Article
We have investigated the geometric structure of the Ca/Si(1 1 1)-(2×1) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. A clear (2×1) periodicity was observed in LEED after annealing the (7×1) phase formed at room temperature in LEED. In the Si 2p core-level spectra, three surface compo...
Article
We have investigated the geometric structure of the so-called Ca/Si(111)-(5×1) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. In LEED, dim extra spots besides the ×5 spots were observed after cooling the sample to 100 K. The positions of these dim spots reveal that this phase has a ×2...
Article
The surface structures of different Ca/Si(111) surfaces were studied by low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Five different phases were observed in LEED depending on the Ca coverage. The lowest coverage phase has both (3×2) and c(6×2) periodicities, and the highest coverage phase has a (2...
Article
The α-√3×√3, β-√3×√3, and 6×6 surfaces of Au/Si(111) have been studied by angle-resolved photoelectron spectroscopy (ARPES). The α-√3×√3 surface shows four surface state bands, one of which is a dispersing metallic band. Except for one nondispersing band near the Fermi level, the β-√3×√3 surface shows surface bands that are similar to those of α-√3...
Article
The initial adsorption stage of oxygen on a Si(111)-(7×7) surface has been investigated using real time high-resolution core-level measurements at 100 K. Among the six O 1s components observed on an O2 exposed Si(111) surface, the three components, whose intensities saturate at the same dosage, have the same lifetime. These results lead to a conclu...
Article
The , and 6×6 phases of Ag/Si(1 1 1) have been studied by angle-resolved photoemission and low-energy electron diffraction. The Ag/Si(1 1 1) surface has an intrinsic semiconducting character with two fully occupied, dispersing surface state bands. We find that only one of the additional surface bands on the surface is metallic in contrast to the tw...
Article
The phase transition of a metallic In chain structure on Si(111) was investigated by high-resolution photoemission. Core-level spectra clearly elucidate that the symmetry breaking at low temperature occurs only within the inner parts of the In chains. In the valence bands, the transition is accompanied by the formation of pseudogaps of 80–150 meV a...
Article
The structure of the K/Si(111)-(3 × 1) surface was studied by high-resolution core-level photoelectron spectroscopy. Five surface components were observed in the Si 2p core-level spectra. Compared to the bulk component, three components are shifted to lower and two to higher binding energies. The two components with the lowest binding energies are...
Article
We have observed the initial stage of oxygen adsorption on a Si(111)-(7×7) surface using scanning tunneling microscopy. Among the bright sites observed after exposing the surface to oxygen in occupied state images, there are differences in the bias dependence of the brightness. Taking into account the local density of states of the oxygen-adsorbed...