2D Adlayer Research Articles

Highly Ordered Adlayer Formation of Water-Insoluble Nanographenes on Gold Using "Molecular Container"

Carbon materials such as graphene have been extensively studied for their application in electronic devices,electrocatalysis, and sensors. In contrast, polycyclic aromatic hydrocarbons (PAHs), the so-called nanographenes, are excellent materials for the creation of two-dimensional (2D) nanosheets.[1] The formation of adlayers on electrode surfaces is challenging because PAHs without peripheral substituents are used as 2D molecular templates and applications in conductance enhancement and organic field-effect transistors.[2] However, large PAHs tend to exhibit poor or no solubilities in organic solvents and water.To overcome this issue, in this study, we employed water-soluble micellar capsules consisting of V-shaped amphiphilic molecules. Characteristic electrochemical behaviors were observed in 0.1 M H2SO4 in the presence of the water-soluble capsules containing PAHs such as dicoronylene. Furthermore, under these conditions, PAHs were released from the capsules, resulting in the formation of a 2D adlayer of PAHs at the electrochemical interface. Finally, using electrochemical scanning tunneling microscopy (EC-STM), we demonstrate that our molecular containers based on the water-soluble molecular capsules allow the facile preparation of 2D PAH adlayers in addition to structurally controlling nanostructure formation on Au surfaces.In particular, dicoronylene molecules formed a highly ordered adlayer with c(4 x 8√3)rect adlattice.[3]

A Supramolecular Approach to the Preparation of Nanographene Adlayers Using Water‐Soluble Molecular Capsules

AbstractPolycyclic aromatic hydrocarbons (PAHs) are excellent building blocks for the creation of two‐dimensional (2D) nanosheets. However, large PAHs tend to exhibit poor or no solubility in organic solvents and water. To overcome this issue, we employed water‐soluble micellar capsules consisting of V‐shaped amphiphilic molecules. Characteristic electrochemical behavior was observed in 0.1 m H2SO4 in the presence of the water‐soluble capsules containing PAHs, such as ovalene, circobiphenyl, and dicoronylene. Furthermore, under these conditions, PAHs were released from the capsules, resulting in the formation of a 2D adlayer of PAHs at the electrochemical interface. Finally, using electrochemical scanning tunneling microscopy, we demonstrate that our molecular containers based on water‐soluble molecular capsules allow the facile preparation of 2D PAH adlayers in addition to structurally controlling nanostructure formation on Au surfaces.

A Supramolecular Approach to the Preparation of Nanographene Adlayers Using Water-Soluble Molecular Capsules.

Polycyclic aromatic hydrocarbons (PAHs) are excellent building blocks for the creation of two-dimensional (2D) nanosheets. However, large PAHs tend to exhibit poor or no solubility in organic solvents and water. To overcome this issue, we employed water-soluble micellar capsules consisting of V-shaped amphiphilic molecules. Characteristic electrochemical behavior was observed in 0.1 m H2 SO4 in the presence of the water-soluble capsules containing PAHs, such as ovalene, circobiphenyl, and dicoronylene. Furthermore, under these conditions, PAHs were released from the capsules, resulting in the formation of a 2D adlayer of PAHs at the electrochemical interface. Finally, using electrochemical scanning tunneling microscopy, we demonstrate that our molecular containers based on water-soluble molecular capsules allow the facile preparation of 2D PAH adlayers in addition to structurally controlling nanostructure formation on Au surfaces.

Creating a Nanospace under an h-BN Cover for Adlayer Growth on Nickel(111).

Heterostructures of two-dimensional (2D) atomic crystals have attracted increasing attention, while fabrication of the 2D stacking structures remains a challenge. In this work, we present a route toward formation of 2D heterostructures via confined growth of a 2D adlayer underneath the other 2D overlayer. Taking a hexagonal boron nitride (h-BN) monolayer on Ni(111) as a model system, both epitaxial and nonepitaxial h-BN islands have been identified on the Ni surface. Surface science studies combined with density functional theory calculations reveal that the nonepitaxial h-BN islands interact weakly with the Ni(111) surface, which creates a 2D nanospace underneath the h-BN islands. An additional h-BN or graphene layer can be grown in the space between the nonepitaxial h-BN islands and Ni(111) surface, forming h-BN/h-BN bilayer structures and h-BN/graphene heterostructures. These results suggest that confined growth under 2D covers may provide an effective route to obtain stacks of 2D atomic crystals.

Solutions of Polyoxometalates: Ionic Association and Oversaturation as the Factors Affecting Electrode Surface Modification

Solutions of polyoxometalates (POM) are widely applied for modification of electrode surfaces with 2D adlayers, multilayer compositions and rechargeable 3D films. All currently existing and future applications (sensors, electrochromic devices, electrocatalytic processes, molecular electronics) are related to operation in solutions. Correspondingly, wet fabrication techniques are preferable to adapt the material to operation medium from the very beginning. The majority of wet techniques involving oxoanions of tungsten, molybdenum, vanadium and some other transition metals utilize POM solutions. Even if the simplest oxocompounds are used as the starting components of acidic and neutral solutions, they always undergo complex transformations with formation of isopolyanins. Under these circumstances POMs become direct molecular precursors of substances responsible for functional properties of modified electrodes, and exact molecular characterization of these precursors should be considered as the principle research task. For heteropolycompounds synthesized beforehand, the main problems are (1) pH-induced transformations to lacunary anions and (2) association with solution cations. Both problems are closely related to more general problem of (3) multistep protonation. For majority of POMs, no data on protonation and association constants are available, and serious efforts (both experimental and computational) are typically required to characterize solutions properly [1, 2]. For isopolyanins, additional problem is (4) speciation resulting in coexistence of numerous anions under equilibrium or (more usually) in metastable solution equilibrating very slowly [3-6]. The latter is most typical for highly acidic solutions demonstrating ca. 2-3 orders formal oversaturation with respect to low soluble hydrated oxides. Just this unexpectedly high concentration of isopolyanions is favorable for immediate oversaturation with reduction products and subsequent nucleation of non-stoichiometric oxides with rather attractive rechargeable and electrochromic properties. Finally, general problem consists in (5) adsorption effects on ionic equilibria. Namely, additional protonation and/or ionic association can take place in POM adlayers formed at electrified interfaces of both ideally polarizable [1,2] and catalytically active [7,8] surfaces. Original results of electrochemical techniques, in situ Raman and UV-vis spectroscopy are presented to illustrate how the problems (1) – (5) can be solved, with illustrations related to importance of ionic speciation and its dynamics in solution for surface modification procedures.ReferencesP. A. Zagrebin, R. R. Nazmutdinov, E. A. Spector, M. I. Borzenko, G. A. Tsirlina, K. N. Mikhelson, Electrochimica Acta 55 (2010) 6064–6072.L. V. Pugolovkin, M. A. Naumova, A. A. Fedorova, M. I. Borzenko, G. A. Tsirlina, Electrochimica Acta 111 (2013) 292–298.M.I. Borzenko, G.N. Botukhova, G.A. Tsirlina, O.A. Petrii, Electrochimica Acta 53 (2008) 3854-3861.V.K. Laurinavichute, S.Yu.Vassiliev, L.M. Plyasova, I.Yu. Molina, A.A. Khokhlov, L.V. Pugolovkin, M.I. Borzenko, G.A. Tsirlina, Electrochimica Acta 54 (2009) 5439–5448.V. K. Laurinavichute, S.Yu.Vassiliev, A. A.Khokhlov, L. M. Plyasova, I. Yu. Molina, Ga. A.Tsirlina, Electrochimica Acta 56 (2011)3530-3536.V. K. Laurinavichyute, A. A. Khokhlov, A. V. Vannikov, G. A. Tsirlina, Electrochimica Acta 99 (2013) 102–107.O. V. Cherstiouk, A. N. Simonov, G. A. Tsirlina, Electrocatalysis 3 (2012) 230–237.G. Tsirlina, E. Mishina, E. Timofeeva, N. Tanimura, N. Sherstyuk, M. Borzenko, S. Nakabayashi, O. Petrii, Faraday Discuss. 140 (2008) 245–267.

Diffusion-Controlled Growth of Molecular Heterostructures: Fabrication of Two-, One-, and Zero-Dimensional C60 Nanostructures on Pentacene Substrates

A variety of low dimensional C60 structures has been grown on supporting pentacene multilayers. By choice of substrate temperature during growth the effective diffusion length of evaporated fullerenes and their nucleation at terraces or step edges can be precisely controlled. AFM and SEM measurements show that this enables the fabrication of either 2D adlayers or solely 1D chains decorating substrate steps, while at elevated growth temperature continuous wetting of step edges is prohibited and instead the formation of separated C60 clusters pinned at the pentacene step edges occurs. Remarkably, all structures remain thermally stable at room temperature once they are formed. In addition the various fullerene structures have been overgrown by an additional pentacene capping layer. Utilizing the different probe depth of XRD and NEXAFS, we found that no contiguous pentacene film is formed on the 2D C60 structure, whereas an encapsulation of the 1D and 0D structures with uniformly upright oriented pentacene is achieved, hence allowing the fabrication of low dimensional buried organic heterostructures.

Potentiostatic deposition of differently shaped Pt and PtBi nanoparticles

This article presents a comparative study of the deposition behaviors of Pt and PtBi nanoparticles on glassy carbon. Sea-urchin-like Pt nanoparticles and spherical PtBi nanoparticles were produced by potentiostatic deposition. Chronoamperometric characterizations show that the Pt electrodeposition corresponds to the mechanism for 3D progressive nucleation and growth. The sea-urchin-like morphology can be attributed to the effect of applied potential and the electroadsorption of hydrogen and trace Cl−. The PtBi electrodeposition fits well to the mechanism for 2D progressive nucleation at t/t max < 1.5, and there is a transition from 2D adlayer to 3D clusters at t/t max > 1.5. The spherical PtBi nanoparticles result from the three effects caused by bismuth co-electrodeposition: higher overpotential, strengthened affinity to Cl−, and improved hydrogen evolution. These results suggest that the adsorption of solution anions and cations on the deposit surface can be used to change the morphologies of the deposits.

In-situ STM observation of the phase transition of two-dimensional 2,5-distyrylpyrazine nanostructure adsorbed on Au(111) in an electrochemical environment

The phase transition of 2,5-distyrylpyrazine (DSP) adsorbed on Au(111) substrate was studied as a function of the substrate potential in 0.1 M HClO4, using an in situ scanning tunneling microscope (STM). Depending on the applied electric field, DSP formed three distinctly different, two-dimensionally^(2D) ordered, supramolecular nanostructures on the Au(111) surface. In the potential range of 0.55 V < E < 0.75 V, the DSP molecules formed a close-packed stripe pattern with the adlayer structure $$\left( {\begin{array}{*{20}c} { - 1} \\ 8 \\ \end{array} \begin{array}{*{20}c} 3 \\ 6 \\ \end{array} } \right)$$ . When the potential was reduced to 0.45 V < E < 0.55 V, a ridge-like pattern built from dimer subunits was observed, with the adlayer structure $$\left( {\begin{array}{*{20}c} 4 \\ { - 12} \\ \end{array} \begin{array}{*{20}c} 5 \\ 4 \\ \end{array} } \right)$$ . Further decreasing in the electrode potential to 0.2 V < E < 0.45 V caused the appearance of a herringbone-like pattern consisting of dimer subunits, with the adlayer structure $$\left( {\begin{array}{*{20}c} 9 \\ 3 \\ \end{array} \begin{array}{*{20}c} 0 \\ 9 \\ \end{array} } \right)$$ . The potential-induced phase transitions revealed the structure-determining role of substrate-adsorbate coordination and intermolecular interaction in forming the distinct 2D adlayer motifs.

EC-STM Investigation of Electrochemically Active 2D Adlayer Consisting of Metal Ions and a Bis(terpyridine) Derivative

Abstract Two-dimensional (2D) molecular assemblies of 4′,4′′′′-(1,4-phenylene)bis(2,2′:6′,2′′-terpyridine) (PTPy) with several metal ions were investigated in 0.1 M HClO4 by cyclic voltammetry and electrochemical scanning tunneling microscopy (EC-STM). An STM image revealed that a disordered adlayer was deposited when iron ions were used, whereas well-ordered PTPy and gold complex adlayers were clearly observed when the electrode potential was precisely controlled. We succeeded in the direct formation of electrochemically active adlayers and the determination of the dependence of the electrocatalytic activity of O2 on the metal ion present.

Structure and Morphology Modifications of Silver Surface in the Early Stages of Sulfide Growth in Alkaline Solution

Electrochemical scanning tunneling microscopy has been employed to investigate the growth mechanism of the 2D adlayer formed on Ag(111) surfaces in the potential range negative to 3D sulfide growth in HS–-containing alkaline aqueous solution. The results show that (2√3 × 2√3)R30°, (√3 × √3)R30°, and (√7 × √7)R19° superstructures are formed with potential-driven increasing uptake of sulfur up to saturation and that extraction of Ag adatoms from the terrace edges is induced by adsorption already at low surface coverage. Irreversible surface fragmentation is produced at the nanometer scale. It is concluded that S uptake occurs via a two-electron oxidative reaction forming S adatoms in the whole range of potential. No extracted Ag adatoms participate to the construction of the (2√3 × 2√3)R30° and (√3 × √3)R30° superstructures. However, the formation of the (√7 × √7)R19° saturated adlayer involves surface reconstruction and the immobilization of the Ag adatoms extracted from the terrace edges at lower potentia...

Intermolecular vs molecule–substrate interactions: A combined STM and theoretical study of supramolecular phases on graphene/Ru(0001)

The competition between intermolecular interactions and long-range lateral variations in the substrate–adsorbate interaction was studied by scanning tunnelling microscopy (STM) and force field based calculations, by comparing the phase formation of (sub-) monolayers of the organic molecules (i) 2-phenyl-4,6-bis(6-(pyridin-3-yl)-4-(pyridin-3-yl)pyridin-2-yl)pyrimidine (3,3'-BTP) and (ii) 3,4,9,10-perylene tetracarboxylic-dianhydride (PTCDA) on graphene/Ru(0001). For PTCDA adsorption, a 2D adlayer phase was formed, which extended over large areas, while for 3,3'-BTP adsorption linear or ring like structures were formed, which exclusively populated the areas between the maxima of the moiré structure of the buckled graphene layer. The consequences for the competing intermolecular interactions and corrugation in the adsorption potential are discussed and compared with the theoretical results.

Direct formation of a 2D redox-active adlayer based on a bisterpyridine derivative and Co2+ on a Au(111) electrode

The direct assembly of single component 4',4''''-(1,4-phenylene)bis(2,2' : 6',2''-terpyridine) (PTPy) and Co(2+) and PTPy mixed arrays was examined on a Au(111) surface by a simple immersion method. A redox active 2D adlayer consisting of a bisterpyridine derivative and cobalt ions was found to form directly on Au(111) from solution, suggesting that new nanostructures and/or adlayers with electrochemical activity can be precisely designed and controlled by selection of the metal ion and ligand.

Structure Formation and Annealing of Isophthalic Acid at the Electrochemical Au(111)−Electrolyte Interface

Using in situ scanning tunneling microscopy (STM) and electrochemical and thermal annealing procedures, we achieve for the first time long-range ordered chemisorbed adlayers of isophthalic acid (IA) at electrified Au(111)/0.1 M HClO4 interfaces. At room temperature, IA chemisorbs in a highly disordered manner at a positively charged surface due to the formation of strong bonds between one carboxylate group per molecule and the gold substrate. Upon electrochemical and thermal annealing, molecular rearrangement in the chemisorbed adlayer is promoted and a highly two-dimensional (2D) order is achieved. We present a comprehensive structural analysis of the chemisorbed and physisorbed adlayers of IA on Au(111), revealing the structure-determining role of substrate−adsorbate coordination and of intermolecular hydrogen bonds in forming distinct 2D adlayer motifs. The annealing strategies are expected to have general value in generating thermodynamically equilibrated molecular-scale architectures on electrified s...

Angle-resolved photoemission study of Fe on a vicinal Au (7 8 8) surface

The electronic and magnetic nature of Fe monatomic chains and two-dimensional (2D) adlayers grown by step decoration of a vicinal Au (7 8 8) surface has been investigated by angle-resolved photoemission spectroscopy (ARPES). By comparing the coverage dependence of ARPES spectra with bulk photoemission data and band structure calculations, we found that the Fe chains have a low ferromagnetic spin state or a nonmagnetic state, and that the 2D Fe adlayers have a high ferromagnetic spin state similar to the bulk Fe. We have succeeded in mapping out the band dispersion of the Fe chains and the 2D adlayers. The band dispersion of the monatomic chains derived from the ARPES measurement show a strong anisotropic feature reflecting a one-dimensional (1D) character. On the other hand, the ARPES spectra of the 2D adlayers show a finite energy dispersion even in the direction perpendicular to the steps, implying the break down of the 1D character. These results suggest that the electronic structures and the magnetism strongly depend on the dimensionality of the Fe adatom structures.

Molecular Dynamics study of Cu and Au 2D adlayers on the Cu 3Au(1 1 0) surface

We present Molecular Dynamics simulation results concerning the structural properties of Cu and Au 2D adlayers on the Cu 3Au(1 1 0) surface. We found that at low coverage the Cu adatoms occupy mainly dumbbell positions forming “pairs” with the Cu surface atoms, giving an incommensurate 1 × 4 aspect in the surface layer. It appears that this “pairing” stabilizes the surface preventing the location of Cu surface atoms at anti-sites. At higher coverage the Cu atoms reside at the four-fold adatom positions forming a well-ordered new type of “contracted” 2×1 Cu adlayer. Au deposition is characterized by wetting phenomena that take place very quickly already at low coverage and temperatures. Au segregation occurs via exchange diffusion with the Cu surface atoms, resulting in mixed and disordered surface and adlayer. It comes out that these phenomena persist even close to the order–disorder bulk transition temperature.

Electrodeposition of bismuth and silver phases in nanometer-sized zero-dimensional STM-formed cavities on gold(111)

Nanometer-sized zero-dimensional (0D) cavities, 5–10 nm in diameter and 3–4 atomic layers deep, were produced locally on a Au(111) surface in a nitrate electrolyte by applying short voltage pulses (80 ns, −2.8 V) to a scanning tunnelling microscope (STM) tip. In the system Au(111)/BiO +,NO 3 −, localised electrochemical underpotential deposition (upd) of 0D bismuth dots was observed in these nano-cavities by in-situ STM. This contrasted to the behaviour of the Au(111)/Ag +,NO 3 − system in which the 0D cavities remained unfilled in the entire upd range, and only were filled during layer-by-layer growth of Ag on the (111) terraces at overpotentials. The difference between the two systems are discussed in respect to the different and nearly equal atomic radii of the Bi/Au(111) and Ag/Au(111) adsorbate–substrate systems, respectively, and the influence of the anion adsorption on the stability of close-packed 2D ad-layers relative to the formation of 3D phases. 0D deposits can be generated when a sufficiently wide stability region for a dense monolayer existed so that concurrent growth of 2D (terraces) and 3D (bulk) phases were avoided.

1998 Alcan Award Lecture Surface electrochemistry - surface science with a joy stick

This lecture gives a review of thermodynamic, spectroscopic, STM and AFM imaging, and X-ray diffraction studies of molecular and ionic adsorption at Au(111) electrodes. In the first part, thermodynamics of adsorption of simple ions such as sulfate, chloride, bromide, and iodide will be discussed. At high coverages, anions adsorbed at a single crystal surface form ordered 2D adlayers. We show that the structure of these adlayers can be studied by STM and surface X-ray diffraction techniques. Next, the information concerning adsorption of simple ions is used to describe mixed adlayers formed by coadsorption of anions and metal adatoms. We demonstrate how to combine electrochemical experiments with in situ polarization-dependent Cu K-edge X-ray absorption spectroscopy to determine the composition and the structure of mixed films formed by deposition of Cu on Au(111) in the presence of SO42-. In the last part we review our efforts to describe coordination of organic molecules to gold electrodes. First, we will discuss adsorption of benzonitrile at the Au(111) electrode surface. We combine electrochemical methods with in situ infrared spectroscopy to describe (i) the energetics of molecular adsorption at the gold electrode surface, (ii) the character of the interaction of the adsorbed molecule with the metal substrate, and (iii) the influence of the electric field on the orientation of the adsorbed molecule. In the last section we describe surface aggregation phenomena. We apply AFM and STM to determine the structure of hemimicelles formed at the Au(111) electrode surface by adsorbed molecules of sodium dodecyl sulfate and we discuss the potential-controlled transformation of these hemimicelles into a condensed monolayer.Key words: surface electrochemistry, electrosorption, surface aggregation, gold electrodes, molecular adsorption, ionic adsorption.

Self-assembly of aromatic molecules over zeolite (0 1 0) surfaces: An AFM and semiempirical study

Self-assembly of pyridine base molecules, pyridine and b-picoline, were observed by atomic force microscopy (AFM) on (0 1 0) surfaces of natural zeolites, heulandite and stilbite, respectively. The molecular array structures of the self-assembled adlayers were determined from the AFM images, and they showed well-ordered, two-dimensional (quasi-) hexagonal lattice structures. Orientations of the molecules within the 2D adlayers were also estimated from the AFM images, and their energetics were calculated by means of a semiempirical molecular orbital method.

Surface spectroscopy studies of Pb monolayers on Si(111)

We have studied the adsorption process and the thermal desorption process of Pb on clean Si(111)7 × 7 substrates using LEED and AES. The growth kinetics follows a Stranski-Krastanov mode (2D adlayer + 3D islands). The adlayer is completed at one monolayer when deposited below the lead melting point. Upon heat treatment, three different surface phases resulting in a ( 3 × 3 ) R30 ° unit cell are identified. The last one, saturated at 1 ML, undergoes a reversible phase transition to a 1×1 structure. This phase transition is attributed to an order-order solid phase transition.

Interpretation of fractional-order Bragg reflections with zero intensity in LEED patterns

It is necessary to take into account the occurrence of disorder in 2D adlayers in order to interpret LEED patterns with zero-intensity fractional-order Bragg reflections. A computerized trial and error method is used in lattice gas and kinematic approximations, to model the structural features relevant to such diffraction data. A comprehensive application to the Cu(110)-S, Ni(110)-S and Pd(110)-S systems shows the possibilities of such a method to extend the field of qualitative interpretation of LEED patterns.