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1.
Angew Chem Int Ed Engl ; 59(6): 2323-2327, 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-31765512

RESUMO

Organothiol monolayers on metal substrates (Au, Ag, Cu) and their use in a wide variety of applications have been extensively studied. Here, the growth of layers of organothiols directly onto muscovite mica is demonstrated using a simple procedure. Atomic force microscopy, surface X-ray diffraction, and vibrational sum-frequency generation IR spectroscopy studies revealed that organothiols with various functional endgroups could be self-assembled into (water) stable and adaptable ultra-flat organothiol monolayers over homogenous areas as large as 1 cm2 . The strength of the mica-organothiol interactions could be tuned by exchanging the potassium surface ions for copper ions. Several of these organothiol monolayers were subsequently used as a template for calcite growth.

2.
Nano Lett ; 19(6): 3634-3640, 2019 06 12.
Artigo em Inglês | MEDLINE | ID: mdl-31095394

RESUMO

X-ray diffraction is measured on individual bilayer and multilayer graphene single-crystals and combined with electrochemically induced lithium intercalation. In-plane Bragg peaks are observed by grazing incidence diffraction. Focusing the incident beam down to an area of about 10 µm × 10 µm, individual flakes are probed by specular X-ray reflectivity. By deploying a recursive Parratt algorithm to model the experimental data, we gain access to characteristic crystallographic parameters of the samples. Notably, it is possible to directly extract the bi/multilayer graphene c-axis lattice parameter. The latter is found to increase upon lithiation, which we control using an on-chip peripheral electrochemical cell layout. These experiments demonstrate the feasibility of in situ X-ray diffraction on individual, micron-sized single crystallites of few- and bilayer two-dimensional materials.


Assuntos
Grafite/química , Lítio/química , Nanoestruturas/química , Algoritmos , Nanoestruturas/ultraestrutura , Difração de Raios X , Raios X
3.
Langmuir ; 34(14): 4241-4248, 2018 04 10.
Artigo em Inglês | MEDLINE | ID: mdl-29565136

RESUMO

The structure of the solid-liquid interface formed by muscovite mica in contact with two divalent ionic solutions (SrCl2 and BaCl2) is determined using in situ surface X-ray diffraction using both specular and non-specular crystal truncation rods. The 0.5 monolayer of monovalent potassium present at the surface after cleavage is replaced by approximately 0.25 monolayer of divalent ions, closely corresponding to ideal charge compensation within the Stern layer in both cases. The adsorption site of the divalent ions is determined to be in the surface ditrigonal cavities with minor out-of-plane relaxations that are consistent with their ionic radii. The divalent ions are adsorbed in a partly hydrated state (partial solvation sphere). The liquid ordering induced by the presence of the highly ordered crystalline mica is limited to the first 8-10 Å from the topmost crystalline surface layer. These results partly agree with previous studies in terms of interface composition, but there are significant differences regarding the structural details of these interfaces.

4.
Nanoscale ; 10(1): 87-92, 2017 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-29210438

RESUMO

Understanding the physical properties of cholesterol-phospholipid systems is essential to gain a better knowledge of the function of each membrane constituent. We present a novel, simple and user-friendly setup that allows for the straightforward grazing incidence X-ray diffraction characterization of hydrated individual supported lipid bilayers. This configuration minimizes the scattering from the liquid and allows the detection of the extremely weak diffracted signal of the membrane, enabling the differentiation of the coexisting domains in DPPC:cholesterol single bilayers.


Assuntos
1,2-Dipalmitoilfosfatidilcolina/química , Colesterol/química , Bicamadas Lipídicas/química , Difração de Raios X
5.
Ultramicroscopy ; 182: 233-242, 2017 11.
Artigo em Inglês | MEDLINE | ID: mdl-28734230

RESUMO

A combined X-ray and scanning tunneling microscopy (STM) instrument is presented that enables the local detection of X-ray absorption on surfaces in a gas environment. To suppress the collection of ion currents generated in the gas phase, coaxially shielded STM tips were used. The conductive outer shield of the coaxial tips can be biased to deflect ions away from the tip core. When tunneling, the X-ray-induced current is separated from the regular, 'topographic' tunneling current using a novel high-speed separation scheme. We demonstrate the capabilities of the instrument by measuring the local X-ray-induced current on Au(1 1 1) in 800 mbar Ar.

6.
Sci Rep ; 7(1): 1615, 2017 05 09.
Artigo em Inglês | MEDLINE | ID: mdl-28487534

RESUMO

Electrochemical Atomic Layer Deposition (E-ALD) technique has demonstrated to be a suitable process for growing compound semiconductors, by alternating the under-potential deposition (UPD) of the metallic element with the UPD of the non-metallic element. The cycle can be repeated several times to build up films with sub-micrometric thickness. We show that it is possible to grow, by E-ALD, Cu2S ultra-thin films on Ag(111) with high structural quality. They show a well ordered layered crystal structure made on alternating pseudohexagonal layers in lower coordination. As reported in literature for minerals in the Cu-S compositional field, these are based on CuS3 triangular groups, with layers occupied by highly mobile Cu ions. This structural model is closely related to the one of the low chalcocite. The domain size of such films is more than 1000 Å in lateral size and extends with a high crystallinity in the vertical growth direction up to more than 10 nm. E-ALD process results in the growth of highly ordered and almost unstrained ultra-thin films. This growth can lead to the design of semiconductors with optimal transport proprieties by an appropriate doping of the intra metallic layer. The present study enables E-ALD as an efficient synthetic route for the growth of semiconducting heterostructures with tailored properties.

7.
J Am Chem Soc ; 139(12): 4532-4539, 2017 03 29.
Artigo em Inglês | MEDLINE | ID: mdl-28252295

RESUMO

The surface restructuring of Pt(111) electrodes upon electrochemical oxidation/reduction in 0.1 M HClO4 was studied by in situ grazing-incidence small-angle X-ray scattering and complementary scanning tunneling microscopy measurements. These methods allow quantitative determination of the formation and structural evolution of nanoscale Pt islands during potential cycles into the oxidation region. A characteristic ripening behavior is observed, where these islands become more prominent and homogeneous in size with increasing number of cycles. Their characteristic lateral dimensions primarily depend on the upper potential limit of the cycle and only slightly increase with cycle number. The structural evolution of the Pt surface morphology strongly resembles that found in studies of Pt(111) homoepitaxial growth and ion erosion in ultrahigh vacuum. It can be fully explained by a microscopic model based on the known surface dynamic behavior under vacuum conditions, indicating that the same dynamics also describe the structural evolution of Pt in the electrochemical environment.

8.
Langmuir ; 32(49): 12955-12965, 2016 12 13.
Artigo em Inglês | MEDLINE | ID: mdl-27951689

RESUMO

The solid-liquid interface formed by single terminated muscovite mica in contact with two different ionic solutions is analyzed using surface X-ray diffraction. Specular and nonspecular crystal truncation rods of freshly cleaved mica immersed in CsCl or RbBr aqueous solution were measured. The half monolayer of the surface potassium ions present after the cleavage is completely replaced by the positive ions (Cs+ or Rb+) from the solution. These ions are located in the ditrigonal surface cavities with small outward relaxations with respect to the bulk potassium position. We find evidence for the presence of a partly ordered hydration shell around the surface Cs+ or Rb+ ions and partly ordered negative ions in the solution. The lateral liquid ordering induced by the crystalline surface vanishes at distances larger than 5 Å from the surface.

9.
Rev Sci Instrum ; 87(11): 113705, 2016 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-27910601

RESUMO

We have developed a new instrument combining a scanning probe microscope (SPM) and an X-ray scattering platform for ambient-pressure catalysis studies. The two instruments are integrated with a flow reactor and an ultra-high vacuum system that can be mounted easily on the diffractometer at a synchrotron end station. This makes it possible to perform SPM and X-ray scattering experiments in the same instrument under identical conditions that are relevant for catalysis.

10.
Proc Natl Acad Sci U S A ; 113(34): 9521-6, 2016 08 23.
Artigo em Inglês | MEDLINE | ID: mdl-27503887

RESUMO

In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces.


Assuntos
Bicamadas Lipídicas/química , Proteolipídeos/química , Espectrometria por Raios X/métodos , Antraquinonas/química , Glicosídeos/química , Humanos , Fosfatidilcolinas/química , Albumina Sérica Humana/química , Soluções , Espectrometria por Raios X/instrumentação
11.
Chem Mater ; 28(11): 3727-3733, 2016 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-27346923

RESUMO

We employed operando anomalous surface X-ray diffraction to investigate the buried interface between the cathode and the electrolyte of a model solid oxide fuel cell with atomic resolution. The cell was studied under different oxygen pressures at elevated temperatures and polarizations by external potential control. Making use of anomalous X-ray diffraction effects at the Y and Zr K-edges allowed us to resolve the interfacial structure and chemical composition of a (100)-oriented, 9.5 mol % yttria-stabilized zirconia (YSZ) single crystal electrolyte below a La0.6Sr0.4CoO3-δ (LSC) electrode. We observe yttrium segregation toward the YSZ/LSC electrolyte/electrode interface under reducing conditions. Under oxidizing conditions, the interface becomes Y depleted. The yttrium segregation is corroborated by an enhanced outward relaxation of the YSZ interfacial metal ion layer. At the same time, an increase in point defect concentration in the electrolyte at the interface was observed, as evidenced by reduced YSZ crystallographic site occupancies for the cations as well as the oxygen ions. Such changes in composition are expected to strongly influence the oxygen ion transport through this interface which plays an important role for the performance of solid oxide fuel cells. The structure of the interface is compared to the bare YSZ(100) surface structure near the microelectrode under identical conditions and to the structure of the YSZ(100) surface prepared under ultrahigh vacuum conditions.

12.
J Appl Crystallogr ; 48(Pt 4): 1324-1329, 2015 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-26306093

RESUMO

BINoculars is a tool for data reduction and analysis of large sets of surface diffraction data that have been acquired with a two-dimensional X-ray detector. The intensity of each pixel of a two-dimensional detector is projected onto a three-dimensional grid in reciprocal-lattice coordinates using a binning algorithm. This allows for fast acquisition and processing of high-resolution data sets and results in a significant reduction of the size of the data set. The subsequent analysis then proceeds in reciprocal space. It has evolved from the specific needs of the ID03 beamline at the ESRF, but it has a modular design and can be easily adjusted and extended to work with data from other beamlines or from other measurement techniques. This paper covers the design and the underlying methods employed in this software package and explains how BINoculars can be used to improve the workflow of surface X-ray diffraction measurements and analysis.

13.
Langmuir ; 30(42): 12570-7, 2014 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-25263250

RESUMO

Stable layers of crown ethers were grown on muscovite mica using the potassium-crown ether interaction. The multilayers were grown from solution and from the vapor phase and were analyzed with atomic force microscopy (AFM), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, and surface X-ray diffraction (SXRD). The results show that the first molecular layer of the three investigated dibenzo crown ethers is more rigid than the second because of the strong interaction of the first molecular layer with the potassium ions on the surface of muscovite mica. SXRD measurements revealed that for all of the investigated dibenzo crown ethers the first molecule lies relatively flat whereas the second lies more upright. The SXRD measurements further revealed that the molecules of the first layer of dibenzo-15-crown-5 are on top of a potassium atom, showing that the binding mechanism of this layer is indeed of the coordination complex form. The AFM and SXRD data are in good agreement, and the combination of these techniques is therefore a powerful way to determine the molecular orientation at surfaces.

14.
Phys Chem Chem Phys ; 14(14): 4796-801, 2012 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-22361687

RESUMO

The structure and chemical composition of Pd nanoparticles exposed to pure CO and mixtures of CO and O(2) at elevated temperatures have been studied in situ by a combination of X-ray Diffraction and X-ray Photoelectron Spectroscopy in pressures ranging from ultra high vacuum to 10 mbar and from room temperature to a few hundred degrees celsius. Our investigation shows that under CO exposure, above a certain temperature, carbon dissolves into the Pd particles forming a carbide phase. Upon exposure to CO and O(2) mixtures, the carbide phase forms and disappears reversibly, switching at the stoichiometric ratio for CO oxidation. This finding opens new scenarios for the understanding of catalytic oxidation of C-based molecules.

15.
J Endod ; 37(5): 684-7, 2011 May.
Artigo em Inglês | MEDLINE | ID: mdl-21496671

RESUMO

INTRODUCTION: The aim of this study was to determine in anterior teeth, bicuspids, and molars (1) the accuracy of 3 different electronic apex locators (EALs) in detecting the apical foramen and (2) the accuracy of digital radiography in determining the working length (WL), compared with visible control under a microscope. METHODS: By using radiovideography (RVG), we measured the lengths of 120 root canals with 3 different EALs (Endex, ProPex II, and Root ZX) and compared them with the actual lengths. The accuracy of EALs and RVG was related to each dental category. An endodontic training kit (Pro-Train) was used during experimental procedures. RESULTS: Statistical analysis showed that the 3 EALs and RVG were less accurate in anterior teeth and molars than in bicuspids. The paired-sample t test showed no statistically significant difference between mesiodistal plane and buccolingual plane digital radiography in all groups. CONCLUSIONS: The 3 EALs tested were more accurate in detecting the apical foramen in bicuspids than in both molars and anterior teeth. Radiographic measurements were not reliable for determining WL in all dental groups in both radiographic planes.


Assuntos
Cavidade Pulpar/anatomia & histologia , Odontometria/instrumentação , Ápice Dentário/anatomia & histologia , Adulto , Dente Pré-Molar/anatomia & histologia , Cinerradiografia , Dente Canino/anatomia & histologia , Cavidade Pulpar/diagnóstico por imagem , Equipamentos e Provisões Elétricas/estatística & dados numéricos , Desenho de Equipamento , Humanos , Incisivo/anatomia & histologia , Microscopia/estatística & dados numéricos , Pessoa de Meia-Idade , Dente Molar/anatomia & histologia , Odontometria/estatística & dados numéricos , Radiografia Dentária Digital/estatística & dados numéricos , Preparo de Canal Radicular/instrumentação , Ápice Dentário/diagnóstico por imagem , Raiz Dentária/anatomia & histologia
16.
J Endod ; 36(12): 2003-7, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21092822

RESUMO

INTRODUCTION: This study compared (1) the accuracy of three different electronic apex locators (EALs) in detecting the apical foramen ex vivo under clinical conditions; (2) the accuracy of digital radiography and EALs in determining the working length (WL) with visible control under a microscope; and (3) the precision of #10, #15, and #20 K-files in electronic measurements. METHODS: The length of 101 extracted human teeth was measured with three different EALs (Endex [Osada Electric Co, Tokyo, Japan], ProPex II [Dentsply-Maillefer, Ballaigues, Switzerland], and Root ZX [J. Morita Co, Tustin, CA]), with radio videography (RVG) and compared with the actual length. An endodontic training kit (Pro-Train; Simit Dental, Mantova, Italy) was used during the experimental procedures. RESULTS: Statistical analysis showed that Endex and ProPex II were more accurate than Root ZX in determining the WL. The paired sample t test showed no statistically significant difference between the accuracy of the two radiographic planes examined. The t test showed no significant difference between the three different K-file sizes measurements. CONCLUSIONS: Endex and ProPex II were more accurate than Root ZX in determining the actual WL. Instrument sizes of hand files did not affect the accuracy of EALs. EALs showed to be more accurate in determining the WL than RVG.


Assuntos
Equipamentos Odontológicos , Cavidade Pulpar/anatomia & histologia , Odontometria/instrumentação , Radiografia Dentária Digital , Ápice Dentário/anatomia & histologia , Adulto , Cavidade Pulpar/diagnóstico por imagem , Humanos , Pessoa de Meia-Idade , Odontometria/métodos , Reprodutibilidade dos Testes , Preparo de Canal Radicular/instrumentação , Ápice Dentário/diagnóstico por imagem
17.
Nat Chem ; 2(9): 730-4, 2010 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-20729891

RESUMO

Atomic steps at the surface of a catalyst play an important role in heterogeneous catalysis, for example as special sites with increased catalytic activity. Exposure to reactants can cause entirely new structures to form at the catalyst surface, and these may dramatically influence the reaction by 'poisoning' it or by acting as the catalytically active phase. For example, thin metal oxide films have been identified as highly active structures that form spontaneously on metal surfaces during the catalytic oxidation of carbon monoxide. Here, we present operando X-ray diffraction experiments on a palladium surface during this reaction. They reveal that a high density of steps strongly alters the stability of the thin, catalytically active palladium oxide film. We show that stabilization of the metal, caused by the steps and consequent destabilization of the oxide, is at the heart of the well-known reaction rate oscillations exhibited during CO oxidation at atmospheric pressure.


Assuntos
Monóxido de Carbono/química , Paládio/química , Catálise , Cinética , Análise Numérica Assistida por Computador , Propriedades de Superfície , Difração de Raios X
18.
J Phys Chem B ; 110(11): 5586-94, 2006 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-16539501

RESUMO

The surface structure of dodecanethiolate self-assembled monolayers (SAMs) on Au(111) surfaces, formed from the liquid phase, have been studied by grazing incidence X-ray diffraction (GIXRD), scanning tunneling microscopy (STM), and electrochemical techniques. STM images show that the surface structure consists of (square root 3 x square root 3)-R30 degrees domains with only a few domains of the c(4 x 2) lattice. The best fitting of GIXRD data for the (square root 3 x square root 3)-R30 degrees lattice is obtained with alkanethiolate adsorption at the top sites, although good fittings are also obtained for the fcc and hcp hollow sites. On the basis of this observation, STM data, electrochemical measurements, and previously reported data, we propose a two-site model that implies the formation of incoherent domains of alkanethiolate molecules at top and fcc hollow sites. This model largely improves the fitting of the GIXRD data with respect to those observed for single adsorption sites and, also, for the other possible two-site combinations. The presence of alkanethiolate molecules adsorbed at the less favorable top sites could result from the adsorption pathway that involves an initial physisorption step which, for steric reasons, takes place at on top sites. Once the molecules are chemisorbed, the presence of energy barriers for alkanethiolate surface diffusion, arising mostly from chain-chain interactions, "freezes" some of them at the on top sites, hindering their movement toward fcc hollow sites. By considering the length of the hydrocarbon chain and the adsorption time, the two-site model could be a tool to explain most of the controversial results on this matter reported in the literature.

19.
Nat Mater ; 4(9): 688-92, 2005 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-16113682

RESUMO

Understanding the adsorption mechanisms of large molecules on metal surfaces is a demanding task. Theoretical predictions are difficult because of the large number of atoms that have to be considered in the calculations, and experiments aiming to solve the molecule-substrate interaction geometry are almost impossible with standard laboratory techniques. Here, we show that the adsorption of complex organic molecules can induce perfectly ordered nanostructuring of metal surfaces. We use surface X-ray diffraction to investigate in detail the bonding geometry of C(60) with the Pt(111) surface, and to elucidate the interaction mechanism leading to the restructuring of the Pt(111) surface. The chemical interaction between one monolayer of C(60) molecules and the clean Pt(111) surface results in the formation of an ordered sqrt[13] x sqrt[13]R13.9 degrees reconstruction based on the creation of a surface vacancy lattice. The C(60) molecules are located on top of the vacancies, and 12 covalent bonds are formed between the carbon atoms and the 6 platinum surface atoms around the vacancies. In-plane displacements induced on the platinum substrate are of the order of a few picometres in the top layer, and are undetectable in the deeper layers.


Assuntos
Materiais Revestidos Biocompatíveis/química , Fulerenos/química , Teste de Materiais/métodos , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Platina/química , Difração de Raios X/métodos , Adsorção , Materiais Revestidos Biocompatíveis/análise , Fulerenos/análise , Conformação Molecular , Nanoestruturas/análise , Platina/análise
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