Sb Monolayer Research Articles

Quantum Spin-Quantum Anomalous Hall Insulators and Topological Transitions in Functionalized Sb(111) Monolayers

Electronic and topological behaviors of Sb(111) monolayers decorated with H and certain magnetic atoms are investigated by using ab initio methods. The drastic exchange field induced by the magnetic atoms, together with strong spin-orbit coupling (SOC) of Sb atoms, generates one new category of valley polarized topological insulators, called quantum spin-quantum anomalous Hall (QSQAH) insulators in the monolayer, with a band gap up to 53 meV. The strong SOC is closely related to Sb px and py orbitals, instead of pz orbitals in usual two-dimensional (2D) materials. Topological transitions from quantum anomalous Hall states to QSQAH states and then to time-reversal-symmetry-broken quantum spin Hall states are achieved by tuning the SOC strength. The behind mechanism is revealed. Our work is helpful for future valleytronic and spintronic applications in 2D materials.

Electronic Structure and Carrier Mobilities of Arsenene and Antimonene Nanoribbons: A First-Principle Study.

Arsenene and antimonene, i.e. two-dimensional (2D) As and Sb monolayers, are the recently proposed cousins of phosphorene (Angew. Chem. Int. Ed., 54, 3112 (2015)). Through first-principle calculations, we systematically investigate electronic and transport properties of the corresponding As and Sb nanoribbons, which are cut from the arsenene and antimonene nanosheets. We find that different from the 2D systems, band features of As and Sb nanoribbons are dependent on edge shapes. All armchair As/Sb nanoribbons keep the indirect band gap feature, while the zigzag ones transfer to direct semiconductors. Quantum confinement in nanoribbons enhances the gap sizes, for which both the armchair and zigzag ones have a gap scaling rule inversely proportional to the ribbon width. Comparing to phosphorene, the large deformation potential constants in the As and Sb nanoribbons cause small carrier mobilities in the orders of magnitude of 101–102 cm2/Vs. Our study demonstrates that the nanostructures of group-Vb elements would possess different electronic properties for the P, As, and Sb ones, which have diverse potential applications for nanoelectronics and nanodevices.

A voltammetric study of the underpotential deposition of cobalt and antimony on gold

This study reports on preliminary experiments which are required to define the experimental conditions for depositing CoSb3 thin films by the electrochemical atomic layer epitaxy (EC-ALE) method. The underpotential deposition (UPD) of cobalt and antimony on polycrystalline gold substrates has been investigated by means of cyclic voltammetry, anodic potentiodynamic scanning and coulometry. The UPD of Sb on Co-covered Au and of Co on Sb-covered Au have also been studied and compared to those obtained on bare Au substrate.The UPD potential values for both Co and Sb are reported in this paper, and owing to the flexibility of the EC-ALE equipment, new insights on the Co UPD on gold substrate are presented. This study shows that the subsequent alternate deposition of Co and Sb monolayers is feasible and thus that the EC-ALE method can be used to elaborate CoSb3 thin films.

Sb-modified growth of stacked Ge/Si(100) quantum dots

We report on the Sb induced modifications of the morphology of self assembled Ge/Si(100) quantum dot stacks in a Si matrix grown by a molecular beam epitaxy. It is shown that the size of the quantum dots in the stack and the Si spacer layer uniformity inside the stack are regulated by the amount of deposited Sb. We consider the thin Sb layer at the Ge/Si growth interface as a factor limiting the surface migration of Si and Ge ad-atoms. The surface diffusion coefficients of Si ad-atom on uncovered pyramid shaped Ge island and on a Ge island covered by a single monolayer of Sb are estimated to be 2.4μm2s−1 and 2.3×10−4μm2s−1 at a temperature of 600°C, correspondingly. Based on this remarkable reduction of surface diffusion the morphology of the surface can be preserved when the growth is continued after the single monolayer of Sb is at the surface.

Ab initio study of the adsorption of antimony and arsenic on the Si(110) surface

We have performed first principles total energy calculations to investigate the adsorption of Sb and As adatoms on the Si(110) surface using a (2 × 3) supercell. The energetics and atomic structures have been investigated in four atomic configurations. One structure is obtained by placing 1/3 of a monolayer (ML) of Sb (As) atoms on the Si(110) surface. The other three geometries are obtained by depositing 1 ML of Sb (As) atoms on the surface. In the first case the structure is formed by four trimers, in the second case the geometry is formed by zigzag atomic chains and in the third case the structure contains “microfacets”. The energetics results of the Sb adsorption show that for low coverage the tetrahedrons formed by the adsorption of 1/3 ML is the most stable configuration, while in the monolayer region the zigzag atomic chain is the most stable structure. However, the total energies of the trimer and microfacet structures are slightly higher, indicating that under some conditions, they may be formed. In an experimental report it has been suggested that the adsorption of 1/3 and 1 ML of Sb corresponds to the low and high coverage in the experiments of Zotov et al. [A. V. Zotov, V. G. Lifshifts, and A. N. Demidchik, Surf. Sci. 274, L583 (1992)]. On the other hand, our results of the As adsorption show that for low coverage, the tetrahedrons in the adsorption of 1/3 ML also give the most stable configuration. However, at the 1 ML coverage, a structure formed by microfacets is the most stable structure, in agreement with previous results.

Improvement of interface structure and magnetic properties of Co on Si (100) by surfactant (Sb) mediated growth

In this study thin Co films were grown on Si (100): (1) with one monolayer of Sb as surfactant and (2) without any surfactant. The Co film, its interface with the Si substrate and the behavior of the Sb surfactant layer were investigated during the growth by high-resolution Rutherford backscattering. By the use of Sb, the evaporated cobalt grows in a layer-by-layer mode and the mixing of Co and Si at the interface is strongly reduced. During the evaporation of Co, Sb floats on the surface for all Co coverages with some incorporation in the grown Co film only for higher coverages. The improvement of the interface quality is also reflected in the magnetic properties of the Co film.

High Quality InSb Films Grown on Si(111) Substrate via InSb Bi-Layer

The heteroepitaxial growth of InSb films via InSb bi-layer (Si(111)-2 × 2-InSb surface reconstruction) was studied. The InSb bi-layer was able to be prepared by 1 monolayer Sb adsorption onto Si(111)-√7 × √3-In surface reconstruction, as well as the results with 2 × 2-In or√3 × √3-In. The InSb film grown via the √7 × √3-In surface reconstruction was fully rotated by 30° with respect to Si substrate. Because by using the √7 × √3-In surface reconstruction with higher In coverage, the area covered by the InSb bi-layer increased, and the area covered by 2 × 1-Sb surface phase which caused by desorption of In atoms from the InSb bi-layer decreased. Due to the decrease of the InSb crystals without rotation, which have poor crystal quality and electric properties, the electric properties of the films improved than those of the samples grown via 2 × 2-In. The cross-sectional scanning transmission electron microscope image clearly showed that the InSb film grown via the √7 × √3-In surface reconstruction has lower dislocation density than the sample directly grown on Si(111) substrate. [DOI: 10.1380/ejssnt.2009.145]

Heteroepitaxial InSb films grown via Si(111)‐√7×√3‐In surface reconstruction

AbstractThe In‐Sb bi‐layer (Si(111)‐2×2‐InSb surface reconstruction) was able to be prepared by 1 monolayer Sb adsorption onto Si(111)‐√7×√3‐In surface reconstruction, as well as results with 2×2‐In and √3×√3‐In. By using the √7×√3‐In surface reconstruction with higher In coverage, the area covered in the In‐Sb bi‐layer increased, and the area covered by 2×1‐Sb surface phase which caused by desorption of In atoms from In‐Sb bi‐layer decreased. The heteroepitaxial growth of InSb films on a Si(111)substrate via the In‐Sb bi‐layer was carried out by using two‐step growth procedure. The grown InSb films rotated by 30° with respect to Si substrate. Due to the decrease of the area covered by the 2×1‐Sb surface phase, the InSb crystals without rotation, which has poor crystal quality and electric properties, disappeared. Consequently, the electric properties of the films improved than those of the sample grown via 2×2‐In. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface phase diagram and alloy formation for antimony on Au(110)

The authors have evaporated submonolayer to monolayer Sb films on the clean Au(110) surface and investigated the resultant Sb-induced reconstructions using low energy electron diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and surface x-ray diffraction. They discovered a sequence of reconstructions, namely, c(2×2), (3×3)R54.7°, (2−112), and p(5×6), with increasing coverage of Sb. The well-known (2×1) reconstruction of the clean Au(110) surface changes to c(2×2) at an Sb coverage of θ≈0.5 ML. At higher Sb coverages, there is a phase transition from c(2×2) to (3×3)R54.7°, with the (3×3)R54.7° pattern emerging at an Sb coverage of θ≈0.7 ML. Upon further deposition, the superstructure spots of the (3×3)R54.7° reconstruction each split into two, resulting in the (2−112) pattern at a coverage of θ≈0.8 ML. Finally, an Sb∕Au(110)-p(5×6) reconstruction emerges at coverages in excess of 1 ML. They have also studied the temperature dependence of the c(2×2) surface phase.

Effects of In and Sb mono-layers to form rotated InSb films on a Si(1 1 1) substrate

A new method for InSb heteroepitaxial growth on a Si substrate was introduced in our previous work, in which an InSb film was formed via an InSb bi-layer. In the present work, to study the effects of In and Sb individual layers on the InSb film quality, InSb was deposited onto an InSb bi-layer, In mono-layer, and Sb mono-layer on a Si substrate. It was found that both In and Sb layers (in other words, InSb bi-layer) were essential to form a fine InSb film.

Heteroepitaxial growth of rotated InSb films on a Si(1 1 1) substrate via 2×2-In surface reconstruction

The heteroepitaxial growth of InSb films via In-induced surface reconstructions such as 2×2-In and √3×√3-In on a Si(1 1 1) substrate was carried out by using a two-step growth procedure in an ultra-high vacuum (UHV) chamber. The samples were characterized by high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning tunneling microscopy (STM) and Hall measurements. The RHEED and XRD ( φ scan) patterns of the samples showed the existence of InSb crystals rotated by 30° with respect to Si substrate. From comparison between the growth of InSb films via 2×2-In and that via √3×√3-In, we found that the origin of the 30°-rotated InSb is due to the existence of the In–Sb bi-layer formed by 1 monolayer (ML) Sb deposition onto the In-induced surface reconstructions.

Microscopic and Electronic Structure of Semimetallic Sb and Semiconducting AlSb Fabricated by Nanoscale Electrodeposition: An in Situ Scanning Probe Investigation

The nanoscale electrocrystallization of pure Sb and the compound semiconductor AlSb on Au(111) has been studied by in situ scanning probe techniques (STM and STS) employing an ionic liquid electrolyte, {AlCl3-[C4mim]+Cl-} (1:1) containing SbCl3. The characteristic changes of the electronic structures with varying potentials have been probed for the first time by normalized differential conductance spectra, (dI/dU)/(I/U). In the underpotential deposition range of Sb the formation of two layers is observed. For the first monolayer a (square root 3 x square root 3)R30 degrees structure is determined from atomically resolved STM images. During the deposition and dissolution of the Sb monolayers characteristic wormlike or spinodal structures appear indicating surface alloying of antimony with the gold substrate. Under overpotential conditions two different Sb structures have been observed. If the deposition potential is continuously stepped to -0.1 V, Sb nanostripes form. On the other hand, randomly dispersed small clusters occur if the potential is jumped from 0.0 to -0.3 V vs Al/Al(III). Both modifications exhibit typical semimetallic behavior as shown by the STS spectra. At -1.1 V the cyclic voltammogram shows a clear reduction wave that is assigned to AlSb compound formation. Deposits in this potential range are characterized by a homogeneous distribution of clusters with diameters of approximately 20 nm. Conductance spectra of these clusters exhibit the main features of the electronic structure of the bulk semiconductor AlSb, with a band gap of 2.0 +/- 0.2 eV. Electrodeposition experiments on both sides of the compound deposition potential show a strong doping effect that is manifest in the corresponding conductance spectra.

Electronic structure of Sb monolayers on the Mo(110) surface

AbstractWe compare theory and experimental (LEED and EELS) studies of the atomic and electronic structure of adsorbed Sb layers on Mo(110). At half a monolayer coverage, Sb atoms occupy the “long‐bridge” (hollow) sites forming the (1 × 2) film structure. At this coverage, a dramatic decrease of surface density of states in vicinity of Fermi level results in a quasi dielectric state of the surface. With increasing coverage, direct lateral interaction between Sb atoms becomes increasingly important and leads to push‐out of some Sb atoms in the (2 × 3/2) surface unit cell from the adsorption sites that are favorable at lower coverages. Substantial overlap of orbitals of neighboring adatoms results in metallic state of adsorbed Sb film, as suggested from significant increase of DOS at Fermi level. In EEL spectra, the nonmetal to metal transition reveals itself also by appearance of the –7.8 eV peak, which may be explained by the interband transition from Sb s band to unoccupied p states above EF. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surfactant effect of Sb on the growth of MnSi1.7 layers on Si(0 0 1)

Deposition of one monolayer of Sb prior to the deposition of Mn at 600°C is observed to increase the MnSi1.7 island density by about two orders of magnitude as well as to change the crystalline orientation of the silicide grains. The preferential epitaxial orientation of MnSi1.7 grains grown by this process is determined to be MnSi1.7(100)[010]||Si(001)[100]. This growth procedure results in the silicide growth into the Si matrix. For comparison, the same deposition process carried out without Sb leads to silicide formation on top of the substrate surface. The observed morphological changes of the MnSi1.7 layers can be explained by a reduced surface diffusion of the Mn atoms on Si(001) in presence of the Sb monolayer. Additionally, lateral Si diffusion is considered to be nearly suppressed, which is responsible for the observed silicide growth into the substrate.

Structure and stability of Sb/Au(1 1 0)-c(2 × 2) surface phase

Adsorption of 0.5 monolayers (ML) of Sb on the Au(1 1 0) surface resulted in the formation of a c(2 × 2) surface reconstruction. Analysis of surface X-ray diffraction data by a direct method revealed the existence of an ordered substitutional surface alloy, with every other hollow site occupied by Au and Sb atoms. Quantitative conventional χ 2 refinement showed a contraction of 0.12 ± 0.03 Å in the spacing of the first Au layer to the second, an expansion of 0.13 ± 0.03 Å in the second-to-third layer distance, and an inward Sb displacement (rumpling) of 0.21 ± 0.04 Å. This surface phase proved to be extremely robust, with the long-range order of this arrangement remaining up to substrate temperatures of 900 K.

Passivation of Si(0 0 1) by the surfactant Sb and its influence on the NiSi 2 growth

The study reports on the Sb mediated growth of NiSi 2 on Si(0 0 1) in the temperature range from 350 to 600 °C. Reactive deposition of Ni onto Si(0 0 1) in this temperature interval without the surfactant Sb leads to the formation of NiSi 2 islands. The NiSi 2 grains have pyramidal shape and grow from the Si surface into the substrate. They have the so-called A-type orientation. Deposition of about one monolayer of Sb onto Si(0 0 1) prior to reactive deposition of Ni leads to a relocation of the NiSi 2 nucleation from the Si(0 0 1) surface to the artificially created Si buffer interface. In this case three types of NiSi 2 crystallites, which differ in their shape and orientation, grow embedded into the Si matrix.

Ab initiostudy of quasiperiodic monolayers on a fivefoldi−AlPdMnsurface

We present a structural model for quasiperiodic monolayers formed on the fivefold surface of an icosahedral AlPdMn quasicrystal, based on ab initio density functional calculations. As a starting point we have investigated the relative stability of unsupported triangular, square, and quasiperiodic monolayers. The unsupported quasiperiodic monolayers are shown to be unstable upon relaxation by interatomic forces. This result indicates the important role of the adsorbate/substrate interaction for the stabilization of a quasiperiodic layer. The structural model of a monolayer adsorbed on the fivefold surface has been constructed on the basis of a mapping of the potential-energy landscape of an isolated adatom on the $i\text{\ensuremath{-}}\mathrm{Al}\mathrm{Pd}\mathrm{Mn}$ substrate. The structure of a clean fivefold $i\text{\ensuremath{-}}\mathrm{Al}\mathrm{Pd}\mathrm{Mn}$ surface is well described by a $P1$ tiling, with the vertices of the tiling located in the centers of $B$ (Bergman) clusters and occupied by Pd atoms. The potential-energy mapping emphasizes the important role of the $P1$ skeleton for the stabilization of a quasiperiodic adlayer: adsorption at the vertices of the $P1$ tiling leads to high binding energies of $\ensuremath{\simeq}4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\text{atom}$. The midedge positions of the $P1$ tiling and Mn atoms exposed at the surface are identified as further favorable adsorption sites. Altogether this leads to a structural model of the quasiperiodic adlayer with atoms at the vertices and midedge positions of the $P1$ tiling, centered pentagonal motifs decorating the pentagonal tiles, and one additional atom in the center of the pentagonal star and of the boat tile. For this structure we calculate a surface coverage of $\ensuremath{\simeq}0.09\phantom{\rule{0.3em}{0ex}}\text{atoms}∕{\mathrm{\AA{}}}^{2}$ in perfect agreement with experiment. The diffraction pattern of the adlayer exhibits (pseudo)decagonal symmetry. The structural stability of a $2∕1$ approximant to this model has been tested for Sn, Bi, and Sb monolayers via relaxation by the Hellmann-Feynman forces from ab initio density function theory calculations. The skeleton of adsorbed monolayers based on the $P1$ tiling was found to be stable, although the atomic decoration inside the tiles is partially distorted, albeit without violating the overall symmetry.

Sb adsorption and desorption pathways on (2 × 1) and c(4 × 4) reconstructed Si(0 0 1) surfaces

The role of initial surface reconstruction on the kinetics of heteroepitaxial growth of Sb on Si(0 0 1) surface is elucidated. The adsorption and desorption of Sb, from the clean-(2 × 1) and c(4 × 4) reconstructions of Si(0 0 1) surface, is investigated by in situ auger electron spectroscopy (AES) and low energy electron diffraction (LEED). Sb is adsorbed at room-temperature (RT) onto clean-(2 × 1) and c(4 × 4) reconstructed Si(0 0 1) surfaces at a base pressure of 3 × 10 −11 Torr. At the very low flux rates adopted (0.06 monolayer/min), Sb grows epitaxially at RT and forms a (1 × 1) surface phase for coverages greater than 1.0 monolayer (ML) on both the (2 × 1) and c(4 × 4) surfaces. Residual thermal desorption studies done on these RT-adsorbed systems are observed to adopt different pathways. The ‘(2 × 1) case’ results in an intermediate novel 0.6-ML (8 × 4) phase, while the ‘c(4 × 4) case’ directly yields the 0.25-ML c(4 × 4) phase. The 0.25-ML Sb covered c(4 × 4) obtained from the Si(0 0 1)-c(4 × 4) phase is observed to be sharper than that obtained from the (2 × 1) reconstructed surface. Upon complete Sb desorption both the cases result in the clean Si(0 0 1)-(2 × 1) surface. The difference in desorption pathways is related to the Sb monolayer formation.

A Study of Recombination Centers Related to As–Sb Nanoclusters in Low-Temperature Grown Gallium Arsenide

Electronic traps in “low-temperature” GaAs (LT-GaAs) grown at 150°C were studied. The As-Sb clusters appearing in this material after annealing were located in a plane that contained a single Sb monolayer formed during growth. The diameter of the clusters was as large as 20 nm. For the purpose of measurement, Au-n-GaAs Schottky barriers were used, in which, for certain bias voltages, the space charge region enclosed the narrow LT-GaAs layer containing the plane of clusters. The bias-voltage dependence of the structure capacitance indicates that the majority of the electrons in this layer are captured by traps, whose energy level lies ∼0.5 eV below the bottom of the conduction band. The energy density of states at this energy is 1014 cm−2 eV−1, which sharply decreases towards the midgap. The existence of traps with activation energies of ∼0.5 eV for the thermal emission of electrons is confirmed by deep-level transient spectroscopy. The magnitude of the electroncapture cross section determined by this method is in the range 5 × 10−14−1 × 10−12 cm2. It is assumed that traps of this type are related to large As-Sb clusters.

A novel (8 × 4) superstructure as precursor to the c(4 × 4) phase during Sb/Si(0 0 1) desorption

The role of kinetics in the superstructure formation of the Sb/Si(0 0 1) system is studied using in situ surface sensitive techniques such as low energy electron diffraction, Auger electron spectroscopy and electron energy loss spectroscopy. Sb adsorbs epitaxially at room-temperature on a double-domain (DD) 2 × 1 reconstructed Si(0 0 1) surface at a flux rate of 0.06 ML/min. During desorption, multilayer Sb agglomerates on a stable Sb monolayer (ML) in a DD (2 × 1) phase before desorbing. The stable monolayer desorbs in the 600–850 °C temperature range, yielding DD (2 × 1), (8 × 4), c(4 × 4), DD (2 × 1) phases before retrieving the clean Si(0 0 1)-DD (2 × 1) surface. The stable 0.6-ML (8 × 4) phase here is a precursor phase to the recently reported 0.25-ML c(4 × 4) surface phase, and is reported for the first time.