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The interfaces between metal oxides and liquids represent the next frontier in the study of oxide chemistry. In this work, (110)-oriented rutile TiO2 wafers were annealed in oxidative atmospheres and immersed in aqueous KCl solutions of pH 3, 6, and 11. Topographic imaging of the TiO2 wafers was carried out in solution via atomic force microscopy using the frequency-modulation force detection technique. Crystalline terraces of 100 nm in width were observed with no sign of solution-induced etching. In a pH-6 solution, ridges parallel to the [001] axis with trenches in between were observed and assigned to the rows of oxygen anions protruding from the surface plane to the solution. Individual anions were further resolved in the ridges, revealing atomic-size protrusions located on the (1 × 1) meshes of the (110) truncation. The topography in an acidic solution (pH 3) was similar to that observed in a neutral solution and could be interpreted as protruding oxygen anions covered partially by protons. In a basic solution with pH 11, qualitatively different features were observed; atomic-size swellings formed a p(2 × 1) superstructure covering the surface, which was hypothesized to be Ti–OH− on five-fold coordinated Ti cations in the surface plane. These results show the feasibility of advanced atomic force microscopy for probing metal-oxide surfaces submerged in liquids. [ABSTRACT FROM AUTHOR]

We observed the fourth-order and third-order optical responses in the time domain on a TiO2 (110) surface covered with trimethyl acetates. Coherent vibrations assignable to near-surface phonon modes were present at 179, 191, 359, 440, 507, 609, and 823 cm-1 in the fourth-order responses. The amplitude and phase of each mode were determined with different azimuths and polarizations of pump and probe light pulses. Vibrational assignments and possible mechanisms to excite the vibrations were discussed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Frequency-modulation AFM (FM-AFM) was applied for imaging a Co-porphyrin on mica. • Organic solvent molecules coordinating to individual porphyrins were visualized. • Layered structure of hexanol liquid was recognized on mica. Abstract Adsorption of 5,10,15,20-tetraphenyl-21 H ,23 H -porphyrin cobalt (CoTPP) on mica immersed in organic solvents of 1-hexanol, 1-chlorohexane, and 1-phenyloctane was examined. Flat-lying CoTPP molecules were recognized in topographic images observed by atomic force microscopy. The topographic height of individual porphyrins fluctuated by 0.2 nm in a time scale of 10 s. The height fluctuation was ascribed to two states with and without a solvent molecule trapped in the axial ligand position of the CoTPP. In imaging in phenyloctane, adsorbed CoTPPs were removed by adding 1-hexylamine to the imaging solution. Hexylamine ligands would have occupied the axial position of CoTPP to hinder adsorption. In addition, two-dimensional distribution of force pushing the tip was observed in hexanol to show a layered liquid structure parallel to the mica surface. [ABSTRACT FROM AUTHOR]

Rutile titanium dioxide (TiO 2 ) (110)-(1 × 1) surfaces prepared in ultrahigh vacuum (UHV) were removed from the UHV, immersed in Hank's buffered salt solution (HBSS), and then re-introduced to the UHV to be examined for an atomic-level study of the osteoconductivity of TiO 2 . X-ray photoelectron spectroscopy (XPS) showed the adsorption of phosphate ions and divalent Ca ions from the HBSS. The density of the phosphate ions increased with the immersion time for up to 1 min and remained constant with further immersion time up to 1 week. Unlike in the case of the phosphate ions, the density of the Ca ions decreased with the immersion time after reaching the maximum value at 1 min immersion. Consequently, calcium phosphate was not formed on the (1 × 1) surface in the 1-week immersion. Scanning tunneling microscopy revealed molecule-sized spots covering the surfaces immersed for 1 min and longer. On the basis of density analysis by XPS, the spots were hypothesized to represent phosphate ions. Phosphate ions on the (1 × 1) surface are unable to undergo arrangement needed to facilitate the epitaxial growth of the brushite. [ABSTRACT FROM AUTHOR]

Rutile titanium dioxide (TiO 2 ) (110) surfaces annealed in air were examined by frequency modulation atomic force microscopy (FM-AFM), X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) techniques. The terraces separated by monatomic steps showed an atomically irregular appearance in the obtained FM-AFM images, while the surface produced a (1 × 1) LEED pattern that indicated atomic ordering of the top few surface layers. Subsequent annealing in atmospheric-pressure O 2 produced several ten-nanometre-sized pits with irregular shapes on the terraces. Molecule-sized spots were recognised on the subsequently O 2 -annealed surface. Half-order spots along the 〈001〉 directions emerged in the LEED pattern. We propose the rutile substrate covered with hydroxylated amorphous TiO 2 of monatomic thickness as the structure of the air-annealed surface. The amorphous TiO 2 was dehydroxylated by subsequent O 2 annealing and was transformed into the thermodynamically stable rutile structure. The molecule-sized spots were attributed to hydroxyl (OH) and hydroperoxyl (OOH) groups that were produced on the area with the (1 × 1) structure. A part of the OH and OOH groups were arranged in a (2 × 1) structure and produced the half-order spots in the LEED pattern. [ABSTRACT FROM AUTHOR]

Atomically-flat MgO(100) surfaces were prepared by sputtering and annealing. Noncontact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) were used to characterize the MgO(100) surfaces. The NC-AFM images revealed the presence of point defects on an atomically-resolved surface. The surface potential at these point defects, as well as features such as step edges and deposited Ba nanoparticles were mapped using KPFM. The Kelvin images show that the surface potential increases at the point defects and at the step edges. On the other hand, a decrease in the potential was found over Ba nanoparticles which can be explained by electron charge transfer from the Ba to the MgO. [ABSTRACT FROM AUTHOR]

Water contact angles on three types of Si(1 1 1) and (0 0 1) surfaces were measured in nitrogen gas atmosphere without exposing them to air; the surfaces were prepared to be (I) cleaned and reconstructed, subsequently (II) atomic hydrogen (H) terminated, or (III) thinly oxidized in an ultrahigh vacuum (UHV) chamber. The surfaces were characterized by Auger electron spectroscopy and atomic force microscopy. The H-terminated Si surfaces showed as less hydrophilic with a water contact angle of about 37° on the (1 1 1) and about 60° on the (0 0 1) surface, respectively. The clean and oxidized surfaces showed as super-hydrophilic with the angles less than 6°. To quantitatively evaluate the contact angles on the super-hydrophilic surfaces, an optical interference fringe method was used under an optical microscope in air. The most super-hydrophilic surface was the oxidized Si(1 1 1) surface. The reactivity of the Si surfaces and their degree of hydroxyl group termination to the Si surfaces responsible for water wettability were discussed. [ABSTRACT FROM AUTHOR]

Abstract: A TiO2(110)-(1×1) surface was prepared in an ultra-high vacuum, transported in laboratory air, and observed with a scanning tunneling microscope (STM) operated in a vacuum of 10−4 Pa. Empty state images showed atomically flat terraces separated by single-height steps, on which 5-fold-coordinated surface Ti atoms were observed as spots arranged in a rectangular lattice. The Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 (N3) dye was adsorbed on the TiO2 surface by immersing the TiO2 wafer into an acetonitrile solution of the dye. In the empty state images, individual N3 molecules were observed as oval particles protruding by 0.6nm from the TiO2 surface. The oval shape elongated to the [1 0] directions was attributed to electron tunneling from tip to unoccupied states localized at the two carboxyl groups bound to the TiO2 surface. [Copyright &y& Elsevier]

The charge transfer from a nanometer-sized transition metal particle to a catalyst support is thought to affect reactions over the metal surface. We propose the application of Kelvin probe force microscope, which is extension of the atomic force microscope, to observe the charge transfer particle-by-particle. Our recent results on Na adatoms, C1 adatoms, Pt adatoms and particles, and particles evaporated on TiO2(110) are reviewed. [ABSTRACT FROM AUTHOR]

We present a noncontact atomic force microscopy (NC-AFM) image of a mixed monolayer composed of propiolate (HC&z.tbnd6;CCOO−) and formate (HCOO−) molecules prepared on a TiO2(1 1 0)-(1×1) surface. An isolated former molecule can be regarded as a needle with a single-atom diameter perpendicular to the surface. The height difference between the propiolate and formate in the NC-AFM image was smaller than the physical height difference. A simple simulation that employed van der Waals forces between the tip and monolayer-covered surface reproduced the experimental topography. [Copyright &y& Elsevier]

The feasibility of noncontact atomic force microscopy (NC-AFM) in single-molecule analysis is experimentally demonstrated. Carboxylates (RCOO−) with different R’s were identified molecule-by-molecule on the TiO2(1 1 0) substrate. The constant frequency-shift topography exhibited a good correlation with the physical topography of the carboxylates with R&z.dbnd6;H, CH3, C(CH3)3 and C&z.dbnd6;CH. The molecule-dependent topography was interpreted with the van der Waals force pulling the tip into the adsorbates. The constant frequency-shift topography of a series of fluorine-containing acetates (R&z.dbnd6;CH3, CHF2, and CF3) revealed that the intramolecular electric polarization perturbs the tip–molecule force through electrostatic couplings. [Copyright &y& Elsevier]

Low frequency vibrational spectra of submonolayer N3 dye (Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2) adsorbed on TiO2 (110) were reported by using fourth-order coherent Raman spectroscopy, which is interface-sensitive vibrational spectroscopy. Most of the peaks observed in the experiment were at the same frequency as that of Raman and infrared spectra of the dye and TiO2. Two interfacial modes at 640 and 100 cm-1 and one resonantly enhanced phonon at 146 cm-1 appeared in addition to the pure TiO2 and N3 spectra. Adsorption of N3 dye on TiO2 contributed to the enhancement of 100 and 146 cm-1 mode. The results not only reported interfacial low-frequency vibrations of TiO2 (110) with N3 dye adsorption but also suggested the coupling between the surface vibrations of TiO2 and charge transfer between N3 dye and TiO2 on the surface. [ABSTRACT FROM AUTHOR]

Over a hundred years an atomistic point of view has been indispensable to explore fascinating properties of various materials and to develop novel functional materials. High-resolution microscopies, rapidly developed during the period, have taken central roles in promoting materials science and related techniques to observe and analyze the materials. As microscopies with the capability of atom-imaging, field ion microscopy (FIM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) can be cited, which have been highly evaluated as methods to ultimately bring forward the viewpoint of reductionism in materials science. On one hand, there have been difficulties to derive useful and practical information on large (micro) scale unique properties of materials using these excellent microscopies and to directly advance the engineering for practical materials. To make bridges over the gap between an atomic scale and an industrial engineering scale, we have to develop emergence science step-by-step as a discipline having hierarchical structures for future prospects by combining nanoscale and microscale techniques; as promising ways, the combined microscopic instruments covering the scale gap and the extremely sophisticated methods for sample preparation seem to be required. In addition, it is noted that spectroscopic and theoretical methods should implement the emergence science.Fundamentally, the function of microscope is to determine the spatial positions of a finite piece of material, that is, ultimately individual atoms, at an extremely high resolution with a high stability. To define and control the atomic positions, the STM and AFM as scanning probe microscopy (SPM) have successfully demonstrated their power; the technological heart of SPM lies in an atomically sharpened tip, which can be observed by FIM and TEM. For emergence science we would like to set sail using the tip as a base. Meanwhile, it is significant to extend a model sample prepared for the microscopies towards a microscale sample while keeping the intrinsic properties found by the microscopies.In this study we present our trial of developing microscopic combined instruments among FIM, field emission microscopy (FEM), STM, AFM and scanning electron microscopy (SEM), in which we prepared and characterized the tips for the SPM, and in addition, the sample preparation to take a correlation between nanoscale and microscale properties of functional materials. Recently, we developed a simple sample preparation method of a rutile single crystal TiO2 covered with an epitaxially-grown monolayer of SiO2 by annealing the crystals in a furnace at high temperatures in air; the crystal samples were placed into a quartz container in the furnace [1]. The vapor of SiO evaporated from the quartz container were adsorbed on the crystal while the crystal surfaces being fully oxidized in air. The SiO2-TiO2 composite systems are promising to protect catalytic TiO2 performance; the photo-catalytic activity is kept by coating with hard and stable SiO2 layers and to extend the lifetime of water super-hydrophilicity even in dark, though understanding of their properties is insufficient due to the lack of techniques to fabricate a well-characterized system on a nanoscale to conduct control experiments. The SiO2 overlayers were observed by low energy electron diffraction (LEED) in vacuum and frequency-modulation (FM) AFM in water [1,2], and water contact angles (WCA) were measured [2]. Although the WCA measurement seems a classic characterization, this method possesses a high potential to make a bridge by controlling the environmental conditions. We will discuss the details. [ABSTRACT FROM PUBLISHER]

The work function of an atomically flat TiO2(1 1 0) surface was mapped with a lateral resolution of several nanometers by using a Kelvin probe force microscope. Islands crystallized on an extended terrace exhibited larger work functions than those of the terrace itself. The increment of the work function was dependent on the size of each island; a small island presented an enhanced increment. Laterally oriented electric dipole moments are proposed on single-height steps terminating the islands to interpret the size-dependent increment of the work function. [Copyright &y& Elsevier]

Low coverages of 4,4″-diamino- p -terphenyl (DAT) molecules deposited on a Si(001)-(2 × 1) surface in ultrahigh vacuum at room temperature were observed by scanning tunneling microscopy (STM). The linear framework of DAT, consisting of a central benzene ring, two phenyl rings (terphenyl) and two amino groups at both ends, mostly lay down laterally on the surface. The majority of DATs were tilted at about 17° with respect to the direction of a Si dimer row on the surface, though a variety of DAT configurations with different angles was found by STM. The histograms of the tilted angles showed that the most frequent angle was 17°. The apparent height of DAT tilted at 17° looked hollow at the center and lower than that of other configurations of DAT in STM images. This indicates that the DAT tends to take a double arched shape at the tilted angle of 17° in a stable conformation with butterfly-like bonding through the central benzene ring to a Si dimer as well as through the two amino groups bonded to respective Si atoms on the dimer row. [ABSTRACT FROM AUTHOR]

Abstract: Local interaction imaging of cleaved InAs surface (110) using a high aspect ratio (HAR) SiGe quantum dot (QD) probe was demonstrated by frequency-modulation mode noncontact atomic force microscopy under atmospheric pressure. The local contrast image with pronounced brightness is mainly attributed to no contact potential difference between the HAR SiGe-QD probe apex and the sample surface, and low frequency-change of the HAR SiGe-QD probe. [Copyright &y& Elsevier]

Abstract: The lateral distribution of Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 (N3) dye molecules on a titanium dioxide (TiO2) surface was examined by using a scanning tunneling microscope. Pivalate ((CH3)3CCOO−) -covered rutile TiO2(110) surfaces were immersed in acetonitrile containing the N3 dye. The N3 molecules which replaced the pivalates were observed as protrusions embedded in the pivalate monolayer. A two-dimensional radial distribution function indicated that the adsorbed N3 molecules tended to be aggregated. Trapping of an N3 molecule in the solution by a preadsorbed N3 molecule was proposed as a driving force for the aggregation. The hydrogen bonds between the carboxyl groups of two N3 molecules contribute to the trapping. [Copyright &y& Elsevier]