Situ Scanning Tunneling Microscopy Research Articles

Strain- and Electron Doping-Induced In-Plane Spin Orientation at Room Temperature in Single-Layer CrTe2.

Ferromagnets with a Curie temperature surpassing room temperature (RT) are highly sought after for advancing planar spintronics. The ultrathin CrTe2 is proposed as a promising two-dimensional (2D) ferromagnet with a Curie temperature above 300 K. However, its single-layer film is highly susceptible to specific external perturbations, leading to variable magnetic features depending on the environment. The magnetic ordering of single-layer CrTe2 remains a topic of debate, and experimental confirmation of ferromagnetic order at RT is still pending. In our study, we utilized molecular beam epitaxy to create a single-layer 1T-CrTe2 on bilayer graphene, demonstrating ferromagnetism above 300 K with in-plane magnetization through superconducting quantum interference devices (SQUID) measurements. Our density functional theory (DFT) calculations suggest that the ferromagnetic properties stem from epitaxial strain, which increases the distance between adjacent Cr atoms within the layer by about 1.6% and enhances the Cr-Te-Cr angle by approximately 1.6°. Due to its interaction with the graphene substrate, the magnetic moment transitions from an out-of-plane to an in-plane orientation, while electronic doping exceeds 1.5 e/u.c. Combining DFT calculations with in situ scanning tunneling microscopy (STM) characterizations allowed us to determine the configuration of the CrTe2 single layer on graphene. This discovery presents the first experimental proof of ferromagnetic order in single-layer CrTe2 with a Curie temperature above RT, laying the groundwork for future applications of CrTe2 single-layer-based spintronic devices.

Effect of 2-Mercapto-1-methylimidazole on the Electrodeposition of Nickel on an Ordered Au(111) Electrode.

A nickel film electroplated onto a metal substrate can be used as a catalyst for water splitting and a magnetic material for spin valves. Although the nucleation and growth of Ni on Au(111) have already been examined with in situ scanning tunneling microscopy (STM), the current study provides new insights of the structure of the first layer of Ni on an ordered Au(111) electrode in 0.1 M KSO4 + 1 mM H2SO4 + 10 mM NiSO4 (pH 3). Prolonged STM scanning of the Ni monolayer on a Au(111) electrode revealed interfacial mixing to produce a surface alloy, initially assuming segregated Ni domains and later transforming them to a homogeneous Ni/Au phase. The formation of the Ni/Au(111) surface alloy affected the structure of the subsequent bulk Ni deposition. The inclusion of 2-mercapto-1-methylimidazole (MMI) in the deposition bath incurred Ni deposition at a less negative potential and a faster rate, resulting in an overall 5.3 times more Ni deposited on the Au electrode in potentiodynamic experiments. MMI molecules were adsorbed on the Ni deposit to prevent Ni dissolution in the Au(111) electrode. MMI could catalyze the presumed rate-determining step from Ni2+ to Ni+ en route to the metallic Ni. The resultant Ni film with MMI had a 3D texture without a preferred crystal orientation on the Au electrode, as opposed to a layer type growth of Ni on Au(111) without MMI.

In Situ Characterization of Atomic-Scale Surface Restructuring of Copper Electrodes Under CO2 Electroreduction Conditions

The electrochemical CO2 reduction reaction (CO2RR) by copper-based heterogeneous catalysts has attracted widespread attention due to its potential social, economic, and environmental benefits, as it utilizes electricity from renewable sources to transform CO2 into value-added chemicals, thus closing the carbon cycle[1]. However, because the energy efficiency, selectivity and lifetime of CO2RR on Cu are still far away from those required at industrially conditions, a knowledge-based catalyst design to optimization of the catalytic system is urgently needed. The reactivity and selectivity of CO2RR depends on the catalyst material as well as on surface and interfacial structure/composition and the nanoscale morphology of the catalyst[2]. With the development of in situ and operando characterization techniques, the fundamental understanding of the structure-reactivity/selectivity relationships of catalysts under reaction conditions can be obtained. Here we monitor the CO-induced surface reconstruction of Cu(100) electrodes during CO2RR in 0.1M KHCO3 solution by in situ scanning tunneling microscopy (STM), surface X-ray diffraction (SXRD), and Raman spectroscopy. In situ STM images during step-wise potential changes show reversible cluster formation. The nanosized clusters start to appear at a potential ≤ -0.2 V vs. RHE and slowly disappear once the potential is changed back to more positive potentials, the clusters slowly disappear. However, the formation of Cu nanocluster leads to an irreversible modification of the surface structure on the molecular level. According to our previous research [3],freshly prepared Cu(100) electrodes are covered by a well-ordered (bi)carbonate adlayer in the double layer regime. After a potential excursion to the range of cluster formation, a disordered adlayer phase with only short-range order is observed in STM images, which can be explained by the presence of Cu adatoms and surface vacancies that remain on the electrode after dissolution of the nanoclustersIn the in situ SXRD studied, crystal truncation rods (CTRs) were recorded at different potentials from the double layer (0 V) to the CO2RR (-1.1 V) regime and then back to 0 V. Quantitative analysis based on a surface adatom/vacancy pairs model exhibits a clear increase in the surface defects density at potentials ≤ -0.2 V and a change in the defects coverage of ≈ 4%. After increasing the potential back to 0 V, the coverage of these defects decreases only slightly, indicating that some Cu adatoms remain on the surface. These results are in good agreement with our STM studies. The vertical expansion of the topmost atomic Cu layer exhibits a distinctly different potential dependence. This surface relaxation is not related to cluster formation, but can be attributed to changes in the type of chemisorbed species on the surface.To identify the adsorbate species on copper surface, in situ surface-enhanced Raman was employed. In the double layer range, bidentate carbonates and (bi)carbonate anions are dominant surface species. Below -0.04 V, the characteristic bands of carbonate become weak or disappear. In the meantime, new bands assigned to adsorbed carboxylate or carboxyl groups emerge, which can be attributed to the first reduction intermediates of CO2[4]. These bands disappear at potential below -0.34 V. Adsorbed CO appears on the surface starting from -0.24 V in the same potential range as the Cu nanocluster. In the reverse potential scan back to more positive values, only weak carbonate bands reappear and formate bands remain constant up to 0.26 V. These observed behavior suggests that some intermediates are formed irreversibly, in accordance with the irreversible changes in the molecular structure of the adlayer.[1] S. Nitopi et. al., Chem. Rev. 2019, 119(12), 7610–7672[2] Y. Y. Birdja at. al, Nature Energy 2019, 4, 732–745[3] R. Amirbeigiarab et. al., Angew. Chemie Int. Ed. 2022, 61 (46), No. e202211360[4] W. Shan et. al., ACS Nano 2020, 14(9), 11363–11372

The spatial structures of iron oxide formed on an ordered Pt(111) electrode in pH 3 sulfate and chloride media

Platinum (Pt) electrodes modified with iron (Fe) have been used as electrocatalysts to split water, to reduce oxygen, and to oxidize methanol. The current study employed cyclic voltammetry and in situ scanning tunneling microscopy (STM) to probe the redox chemistry and spatial structure of an iron hydroxide thin film adsorbed on an ordered Pt(111) electrode in pH 3 sulfate solution (1 mM H2SO4 + 0.1 M K2SO4) containing 10 mM FeSO4. The Pt(111) electrode was pretreated with the conventional annealing-and-quenching method, which resulted in a sub-monolayer native oxide. After this native oxide was stripped off, the adsorption of Fe2+ ions and the reduction of oxygen concurred to yield an ordered FeOH film on the Pt(111) electrode. In situ STM imaging revealed a unique spoke – wheel (SW) structure between 0.1 and -0.1 V (vs. Ag/AgCl). As opposed to the hexagonal FeO(111) bilayer structure observed on Pt(111) in the vacuum, a distorted hexagonal adlattice was seen with this SW pattern. Shifting the potential positively and negatively resulted in transformations of the SW structure into distorted moiré patterns. The same STM experiment performed with Fe2(SO4)3 led to a disordered film, indicating that ferrous, not ferric, ions were orderly adsorbed on the Pt(111) electrode. The role of anion in the formation of the FeOH film on the Pt(111) electrode was also conducted in pH 3 chloride solution (1 mM HCl + 0.1 M KCl + FeCl2).

Electrochemical interfaces between Au(100) and deep eutectic solvents: An in situ scanning tunneling microscopy study

Deep eutectic solvents (DESs) are promising electrolytes for electrochemical fields due to their excellent properties. Electrochemical behaviors of Au(100) electrode in two choline chloride-based DESs ethaline and reline with different hydrogen bond donor molecules have been investigated by cyclic voltammetry and in situ scanning tunneling microscopy (STM). Cyclic voltammograms present three pairs of current peaks for Au(100) electrodes in the two DESs. On the basis of the results of in situ STM, the three pairs of current peaks are assigned to the formation and lifting of Au(100) surface reconstruction, adsorption and desorption of chloride ions, and phase transition of chloride ion adlayer. Compared with Au(111), one extra current peak and the corresponding (√5 × √5)R26.6° ordered adlayer of chloride ions were observed for Au(100) electrode. An order-order phase transition of chloride ion adlayer was observed in ethaline, while an order-disorder phase transition was observed in reline. Furthermore, no Au islands was observed on Au(100) surface in ethaline after the lifting of reconstruction when the potential is moved positively and gradually. However, gold nanowires could form and stably exist on Au(100) surface, which are different from that formed on Au(111) surface in reline. Our results provide detailed insights into the interfacial structures between Au(100) electrode and DESs on the atomic scale that hydrogen bond donor molecules and the surface crystallography of the electrode interface could significantly affect the arrangement of gold atoms of the electrode surface and chloride ions in the innermost Stern plane.

Thickness-Dependent Evolutions of Surface Reconstruction and Band Structures in Epitaxial β-In2Se3 Thin Films.

Ferroelectric materials have received great attention in the field of data storage, benefiting from their exotic transport properties. Among these materials, the two-dimensional (2D) In2Se3 has been of particular interest because of its ability to exhibit both in-plane and out-of-plane ferroelectricity. In this article, we realized the molecular beam epitaxial (MBE) growth of β-In2Se3 films on bilayer graphene (BLG) substrates with precisely controlled thickness. Combining in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) measurements, we found that the four-monolayer β-In2Se3 is a semiconductor with a (9 × 1) reconstructed superlattice. In contrast, the monolayer β-In2Se3/BLG heterostructure does not show any surface reconstruction due to the interfacial interaction and moiré superlattice, which instead results in a folding Dirac cone at the center of the Brillouin zone. In addition, we found that the band gap of In2Se3 film decreases after potassium doping on its surface, and the valence band maximum also shifts in momentum after surface potassium doping. The successful growth of high-quality β-In2Se3 thin films would be a new platform for studying the 2D ferroelectric heterostructures and devices. The experimental results on the surface reconstruction and band structures also provide important information on the quantum confinement and interfacial effects in the epitaxial β-In2Se3 films.

Adsorption of 2-Mercapto-1-methylimidazole on the (√3 × 22) Reconstructed and (1 × 1) Phases of an Ordered Au(111) Electrode under Potential Control

The self-assembled monolayers (SAMs) of organosulfur compounds bearing an imidazole (Im) functional group can form hydrogen bonds with others and tailor specific interfacial structures used for CO2 reduction, biosensing, and corrosion prevention. The current study employed cyclic voltammetry and in situ scanning tunneling microscopy (STM) to address the adsorption and structure of 2-mercapto-1-methylimidazole (MMI) on the reconstructed and unreconstructed Au(111) electrodes as a function of potential. The adsorbed MMI molecule assumed the unprotonated form, allowing its S- and N-ends to bind with the Au electrode at a positive potential. Molecular resolution STM images showed an ordered Au(111)–(√21 × √21)R10.9°–MMI structure. The Au–N bond could weaken and be broken at a negative potential, leading to a disordered MMI adlayer. This restructuring event was coupled with the protonation of the Im group. These processes resulted in a sharp peak, which shifted negatively by 60 mV with an increase of 1 pH unit. MMI admolecules were desorbed at a more negative potential to unveil a pitted Au surface, resulting from etching of MMI adsorption. This feature supports the S–Au–S motif for MMI adsorbed to the Au(111) electrode, irrespective of the initial Au surface structure. The effect of MMI as an additive to the deposition bath of Ni was also explored.

Unconventional Electrochemical Behaviors of Cu Underpotential Deposition in a Chloride-Based Deep Eutectic Solvent: High Underpotential Shift and Low Coverage.

The (5 × 5) Moiré pattern resulting from coadsorption of Cu atoms and chloride ions on the Au(111) electrode is one of the most classical structures for underpotential deposition (UPD) in electrochemical surface science. Although two models have been proposed to describe the pattern, the details of the structure remain ambiguous and controversial, leading to a question that remains to be answered. In this work, we investigate the UPD behaviors of Cu on the Au(111) electrode in a chloride-based deep eutectic solvent ethaline by in situ scanning tunneling microscopy (STM). Benefiting from the properties of the ultraconcentrated electrolyte, we directly image not only Cu but also Cl adlayers by finely tuning tunneling conditions. The structure is unambiguously determined for both Cu and Cl adlayers, where an incommensurate Cu layer is adsorbed on the Au(111) surface with a Cu coverage of 0.64, while the Cl coverage is 0.32 (only half of the expected value); i.e., the atomic arrangement of the observed (5 × 5) Moiré pattern in ethaline matches neither of the models proposed in the literature. Meanwhile, STM results confirm the origin of the cathodic peak in the cyclic voltammogram, which indicates that the underpotential shift of Cu UPD in ethaline indeed increases by ca. 0.40 V compared to its counterpart in a sulfuric acid solution, resulting in a significant deviation from the linear relation between the underpotential shift and the difference in work functions proposed in the literature. The unconventional electrochemical behaviors of Cu UPD reveal the specialty of both the bulk and the interface in the chloride-based deep eutectic solvent.

Submonolayer and Monolayer Sn Adsorption and Diffusion Behavior on Oxidized Nb(100)

Current efforts to produce brighter beams of charged particles are focused on developing Nb3Sn-coated superconducting radio frequency (SRF) cavities for use in superconducting accelerator facilities. The growth mechanisms driving the formation of Nb3Sn films on preexisting Nb SRF cavities are not, however, fully understood. In order to understand the complex interplay between metallic Sn and the oxidized Nb surface leading to Nb3Sn alloy formation, we have examined how the structural and chemical composition of an oxidized Nb(100) single crystal influences Sn adsorption and diffusion behavior at submonolayer and monolayer Sn coverages. Sn was deposited on an NbO surface and annealed at temperatures relevant to Nb3Sn growth procedures before analysis via in situ scanning tunneling microscopy (STM). Experimental data, along with supporting simulated STM and calculated binding energies obtained using density functional theory, revealed the influence of Sn coverage and annealing temperatures on thermodynamic and kinetically driven diffusion pathways, preferred binding sites, novel Sn adlayer structures, and how the underlying NbO substrate evolves to accommodate Sn diffusion. This newly realized understanding of the interfacial chemical interactions between adsorbed Sn and the Nb surface sites is essential to develop predictive growth models for Nb3Sn films for use in future SRF cavities.

Over- and underpotential deposition of copper from a deep eutectic solvent: Pt(1 1 1) single crystal versus polycrystalline Pt substrates

• Deposition/dissolution of Cu on Pt from ethaline occur in one-electron reactions. • A full (1x1) monolayer of Cu adatoms is formed on Pt(111) in ethaline. • No voltammetric signals of Cu UPD were observed for Pt(poly) in ethaline. • Surface structure determines the mechanism and rate of Cu OPD at the initial stages. • Cu OPD on Pt(111) and Pt(poly) in ethaline occurs via 2D and 3D growth, respectively. Deep eutectic solvents (DESs) attract ever greater interest as nonaqueous media for the electrodeposition of metals and alloys. This work investigates the initial stages of Cu electrodeposition from DES representing a mixture of choline chloride and ethylene glycol (ChCl:EG) with a (1:2) molar ratio that contains CuCl or CuCl 2 salts. These studies were performed by means of cyclic voltammetry and scanning probe microscopy on single-crystalline Pt(111) and polycrystalline Pt(poly) electrodes. Additional experiments on Cu deposition were carried out using an aqueous Cl - -rich solution (3 M NaCl + 0.01 M CuCl). The process of Cu underpotential deposition (UPD) on the surface of Pt(111) in DES is observed for the first time. It is proposed that a complete (1x1) monolayer of Cu adatoms is formed at potentials more positive than the onset of overpotential deposition (OPD). The comparison of results for Pt(111) and Pt(poly) in ChCl:EG (1:2) and in the aqueous 3 M NaCl solution confirms that the surface morphology and (co)adsorption of solution components play an important role in the Cu UPD process. In DES, as well as in the aqueous solutions containing CuCl, Cu OPD occurs via the reduction of Cu(I) ions. The Cu(I)/Cu(II) redox transition was observed at significantly more positive potentials. We conclude on the basis of voltammetry and in situ scanning tunneling microscopy (STM) data that the mechanism of Cu electrodeposition in DES is determined by the surface structure. STM data demonstrate the layer-by-layer growth of a two-dimensional Cu deposit on Pt(111), while the resulting Cu deposit on Pt(poly) is characterized by a grain-like morphology. We also demonstrate that the mechanism of Cu OPD affects the initial deposition rate under conditions of diffusion limitations.

The adsorption and electropolymerization of terthiophene on Au(1 1 1) electrode – Probed by in situ STM

• In situ STM imaging terthiophene molecule adsorbed on an ordered Au(1 1 1) electrode in sulfuric and perchloric acid. • Dominant effect of potential control on the adsorption and oxidation of terthiophene admolecule. • Terthiophene admolecules accompanied by bisulfate anions to form highly ordered adlattices. • Revelation of adsorption configuration and spatial arrangement of TT on Au(1 1 1) electrode. • STM visualization of oligothiophenes produced by anodization. In situ scanning tunneling microscopy (STM) was used to examine terthiophene (TT) adsorbed on an ordered Au(1 1 1) electrode in 0.1 M H 2 SO 4 and HClO 4 , as a model system to gain a fundamental understanding of the effects of potential control on the coadsorption of anion and the oxidation of a thiophene - bearing entity. TT was irreversibly adsorbed onto an Au(1 1 1) bead crystal from a dosing solution made of ethanol at room temperature. The cyclic voltammogram (CV) recorded with this sample in 0.1 M H 2 SO 4 showed a series of well-defined peaks, resulting from the restructuring of the TT adlayer, coupled with anion coadsorption and the phase transition of the Au(1 1 1) electrode. In contrast, the CV obtained in 0.1 M HClO 4 was mostly featureless before TT admolecules were irreversibly oxidized at E > 0.7 V (vs Ag/AgCl). TT molecule was adsorbed most horizontally on Au(1 1 1) electrode in H 2 SO 4 , but displaced by bisulfate anion at positive potential. Anodization of this TT/Au(1 1 1) electrode triggered the oxidation and subsequent coupling of TT monomers to yield oligothiophenes, whose internal structures and dimensions were revealed by STM in pH1 and 5 sulfate media. The as – produced oligothiophenes appeared as winding ribbons spanning ∼ 200 and ∼ 40 Å in pH 5 and 1 sulfate media. Their internal structures, particularly the trans and cis conformations of neighboring thiophenes units, were visualized by molecular resolution STM.

The Underpotential Deposition of Lead and its Effect on Carbon Monoxide Adsorption on Pt(111) Electrode

In situ scanning tunneling microscopy (STM) was used to examine the spatial structures of lead (Pb) adatom and carbon monoxide (CO) molecule adsorbed onto an ordered Pt(111) electrode in 0.1 M perchloric acid (HClO4) containing 1 mM Pb(ClO4)2 under potential control. Ordered Pb structures were not seen until the potential was made more negative to 0 V (vs Ag/AgCl), where a quasi-square array (√7 × √57) was seen. Shifting the potential more negative substantiated Pb deposition, which triggered restructuring of the Pb adlayer into (√21 × √21)R11° and (3 × 2√3)rect (θ = 0.62 and 0.67) at −0.1 V. Pb adatom reduced the poisoning effect of CO on the Pt(111) electrode by blocking the adsorption of CO and by forcing CO molecule to asymmetric sites. An ordered (√7 × 3)—Pb + CO structure was imaged at 0 V in 0.1 M HClO4 + 1 mM Pb(ClO4)2, from which the surface coverage and binding sites of CO molecule were inferred.

Local Chiral Inversion of Thymine Dimers by Manipulating Single Water Molecules.

Water, as one of the most important and indispensable small molecules in vivo, plays a crucial role in driving biological self-assembly processes. Real-space detection and identification of water-induced organic structures and further capture of dynamic dehydration processes are important yet challenging, which would help to reveal the cooperation and competition mechanisms among water-involved noncovalent interactions. Herein, introduction of water molecules onto the self-assembled thymine (T) structures under ultrahigh vacuum (UHV) conditions results in the hydration of hydrogen-bonded T dimers forming a well-ordered water-involved T structure. Reversibly, a local dehydration process is achieved by in situ scanning tunneling microscopy (STM) manipulation on single water molecules, where the adjacent T dimers connected with water molecules undergo a local chiral inversion process with the hydrogen-bonding configuration preserved. Such a strategy enables real-space identification and detection of the interactions between water and organic molecules, which may also shed light on the understanding of biologically relevant self-assembly processes driven by water.

The Effects of Potential and pH on the Adsorption of Guanine on the Au(111) Electrode.

The adsorption of nucleobase at a gold electrode has been a model system to study the interaction between biomolecule and metal, which is relevant to the development of sensors and molecular electronics. The current study has employed in situ scanning tunneling microscopy (STM) and voltammetry to investigate the adsorption configuration and spatial structure of guanine (G) on a well-defined Au(111) electrode in perchloric acid (HClO4) and neutral phosphate buffer solution (PBS) containing 50 μM G. Potential control had a profound effect on the adsorption of the G molecule on the Au(111) electrode. No adsorption of G was observed at a potential more negative than 0 V in HClO4 and -0.2 V (versus Ag/AgCl) in PBS; shifting potential positively triggered a rapid adsorption of G to yield a well-ordered G array. Different spatial structures of G admolecules were imaged with STM in HClO4 and PBS, suggesting that ions in the electrolyte were important in this adsorption event. Shifting potential positively caused a more compact G adlayer with molecules adopting a tilted orientation. Meanwhile, G molecules continued to deposit on the Au(111) electrode leading to a multilayer G film. These processes were reversible to the potential modulation. G admolecules on the Au(111) electrode could be irreversibly oxidized in 0.1 M PBS, which resulted in a prominent peak at 0.74 V in the voltammogram. This oxidation process could be used to analyze the G molecule in a sample.

Operando Stability Studies of Ultrathin Single-Crystalline IrO2(110) Films under Acidic Oxygen Evolution Reaction Conditions

The anodic corrosion behavior of 50 A thick single-crystalline IrO2(110) films supported on slightly bulk-reduced TiO2(110) single crystals is studied during acidic water splitting by a unique combination of operando techniques, namely, synchrotron-based high-energy X-ray reflectivity (XRR) and surface X-ray diffraction (SXRD) together with highly sensitive inductively coupled plasma mass spectrometry (ICP-MS). Corrosion-induced structural and morphological changes of the IrO2(110) model electrode can be followed on the atomic scale by operando XRR and SXRD that are supplemented with ex situ scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), whereas with ICP-MS, the corrosion rate can be quantified down to 1 pg·cm-2·s-1 with a time resolution on the second scale. The operando synchrotron-based X-ray scattering techniques are surprisingly sensitive to Ir corrosion of about 0.10 monolayer of IrO2(110) in ∼26 h, i.e., 0.4 pg·cm-2·s-1. The present study demonstrates that single-crystalline IrO2(110) films are much more stable than hitherto expected. Although the dissolution rate is very small, ICP-MS experiments reveal a significantly higher dissolution rate than the operando high-energy XRR/SXRD experiments. These differences in dissolution rate are suggested to be due to the different modi operandi encountered in ICP-MS (dynamic) and operando XRR/SXRD experiments (steady state), a fact that may need to be considered when hydrogen production is coupled to intermittent energy sources such as renewables. (Less)

A STM view of the reorientation of cytosine adsorbed on the Au(111) – (1 × 1) electrode in sulfuric and perchloric acids

The adsorption of cytosine (C) on gold electrode has been studied to gain a fundamental understanding of the interaction between biomolecule and metal entity, which has important ramifications in the modern research on biological surface science. The characteristics of tautomerization and acid-base equilibrium of C at Au(111) electrode are intriguing and challenging to the modern study of electrified interface. Although this system has been studied by using in situ scanning tunneling microscopy (STM) and vibrational spectroscopy, many critical issues such as intermolecular interaction, substrate structure, and concentration of C are yet to be explored. High-resolution STM was used in the current study to probe the structure of C adsorbed on an Au(111) electrode in sulfuric and perchloric acids as a function of potential and [C]. C molecules arranged differently on the Au(111) – (1 × 1) substrate in 0.1 M H2SO4 and HClO4 containing 1 mM C, indicating that anion was coadsorbed with C admolecule. Adsorbed C was protonated at the negative potential, but deprotonated at the positive potential. Meanwhile, C admolecule reoriented from horizontal to upright configuration, as inferred from the ordered structures observed at different potentials. The surface coverage of C on Au(111), evaluated from the ordered structures, increased with more positive potential and grew into a multilayer film in 1 mM C in these acids.

Revisiting the Formation of the (√67 × √67)R12.2° Bilayer Oxide on Ni3Al(111) by In Situ STM—Surprises Regarding Oxygen Volume Diffusion

The Ni3Al(111) surface was imaged by in situ scanning tunneling microscopy (STM) during growth of the (√67 × √67)R12.2° bilayer oxide. Following reported growth protocols in the literature, the sur...

The adsorption of anionic [Ptx(CO)y]n− clusters on an Au(111) electrode and its oxidative conversion to an atomic Pt adlayer

Fabricating platinum film can be a promising approach to remedy the high-cost and scarcity of Pt, and opens up an avenue for studying the electrochemical property of a unique Pt entity. The current report describes Pt-carbonyl cluster denoted as [Ptx(CO)y]n− adsorbed onto an ordered Au(111) substrate from an aqueous PtCl62− solution saturated with carbon monoxide (CO). This Pt+CO cluster was converted into CO-capped metallic Pt adlayer by exposing to O2 and N2. This transformation manifested in the drastic changes of the Au(111) surface structure, where the striped and honeycomb structures were converted into (√7 × √7)R19.1° and (2 × 2) - CO structures, as revealed by in situ scanning tunneling microscope (STM). The chemical composition of the Au(111)-supported Pt-carbonyl cluster was characterized by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV), which resulted in a 47/73 (Pt/CO) ratio. This Pt-carbonyl cluster was accompanied with counter cations La3+, indicating that it was anionic. The XPS and stripping voltammetry results indicate a [Pt47(CO)73]5- cluster, whose CO molecules could be stripped off to produce an ordered smooth Pt metallic adlayer, making it possible to study the electrocatalytic properties of a well-organized Pt thin film.

4,4'-Bipyridine Adsorption on Sb(111) from Ionic Liquid- in Situ STM and EIS Study

Room-temperature ionic liquids (RTIL) draw a lot of attention in modern electrochemical research due to their high stability under applied electrode potential, the wide electrochemical window and dual usability as a solvent and an electrolyte RTILs have become very attractive. Molecular self-assembly at solid surfaces, resulting in the formation of nanostructures with well-controlled properties and functionality presents multiple prospective applications in science and technology [2], e.g., the smart tailoring of the structural properties of the functionalized electrodes attracts a lot of attention due to an ability to trigger the specific electrochemical processes.In this study, the in situ scanning tunnelling microscopy (STM) and impedance spectroscopy methods have been applied to study the structure and adsorption properties of the electrochemically polished Sb(111) single crystal electrode | EMImBF4, and EMImBF4 + X% 4,4'-bipyridine (x= 1; 2; 5), interface.During the measurements, atomically flat areas have been observed on the in situ STM images of Sb(111) single crystal electrode surface in EMImBF4 and atomic resolution was obtained. The in situ STM data show that there is no quick surface reconstruction process. The surface structure is stable within the potential region investigated (-0.8 — -0.1 vs. Ag/AgCl|EMImBF4) as it has been shown for inactive electrolyte solutions [3].Additionally, the influence of electrode potential on the adsorption kinetics of 4,4'-bipyridine on Sb(111) has been demonstrated. Within the region of maximal adsorption, the capacitance pits in the differential capacitance vs. electrode potential curves have been observed, depending on the 4,4'-bipyridine concentration [4]. The influence of electrode potential (E) on the adsorption kinetics of 4,4'-BiPy on Sb(111) has been demonstrated. From the in situ STM data it has been found that 4,4’-BP adsorbs in a form of a stripe pattern on antimony single crystal electrodes.AcknowledgementsThis work was supported by Estonian Research Council grants PUT PSG249 and RSG676, and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).

Tuning the length/width aspect ratio of epitaxial unidirectional silicide nanowires on Si(110)-16 × 2 surfaces

The reactive deposition epitaxy growth of self-organized cobalt silicide nanowires (NWs) on clean Si(110) surfaces has been investigated by in situ scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) as well as by scanning electron microscopy (SEM). Half a monolayer of cobalt was deposited on the Si(110) surfaces at ∼600 °C substrate temperature. Following cobalt deposition, the substrates have been annealed for different durations. Cobalt forms aligned cobalt disilicide nanowires upon reaction with the silicon substrate, following the twofold substrate symmetry. With increasing duration of annealing, the NWs have been found to grow with larger aspect ratio (length/width), eventually producing narrower NWs. These self-organized unidirectional NWs of sub-hundred nanometer width and ∼4–7 nm height produce a Schottky barrier with the silicon substrate and are expected to find applications in nanoelectronic devices.