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1.
Ultramicroscopy ; 253: 113799, 2023 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-37364403

RESUMO

The design of metal-organic interfaces with atomic precision enables the fabrication of highly efficient devices with tailored functionality. The possibility of fast and reliable analysis of molecular stacking order at the interface is of crucial importance, as the interfacial stacking order of molecules directly influences the quality and functionality of fabricated organic-based devices. Dark-field (DF) imaging using Low-Energy Electron Microscopy (LEEM) allows the visualization of areas with a specific structure or symmetry. However, distinguishing layers with different stacking orders featuring the same diffraction patterns becomes more complicated. Here we show that the top layer shift in organic molecular bilayers induces measurable differences in spot intensities of respective diffraction patterns that can be visualized in DF images. Scanning Tunneling Microscopy (STM) imaging of molecular bilayers allowed us to measure the shift directly and compare it with the diffraction data. We also provide a conceptual diffraction model based on the electron path differences, which qualitatively explains the observed phenomenon.

2.
ACS Nano ; 2022 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-36449748

RESUMO

Clean oxide surfaces are generally hydrophilic. Water molecules anchor at undercoordinated surface metal atoms that act as Lewis acid sites, and they are stabilized by H bonds to undercoordinated surface oxygens. The large unit cell of In2O3(111) provides surface atoms in various configurations, which leads to chemical heterogeneity and a local deviation from this general rule. Experiments (TPD, XPS, nc-AFM) agree quantitatively with DFT calculations and show a series of distinct phases. The first three water molecules dissociate at one specific area of the unit cell and desorb above room temperature. The next three adsorb as molecules in the adjacent region. Three more water molecules rearrange this structure and an additional nine pile up above the OH groups. Despite offering undercoordinated In and O sites, the rest of the unit cell is unfavorable for adsorption and remains water-free. The first water layer thus shows ordering into nanoscopic 3D water clusters separated by hydrophobic pockets.

3.
Sci Rep ; 12(1): 14497, 2022 08 25.
Artigo em Inglês | MEDLINE | ID: mdl-36008433

RESUMO

Biomimicking native tissues and organs require the development of advanced hydrogels. The patterning of hydrogel surfaces may enhance the cellular functionality and therapeutic efficacy of implants. For example, nanopatterning of the intraocular lens (IOL) surface can suppress the upregulation of cytoskeleton proteins (actin and actinin) within the cells in contact with the IOL surface and, hence, prevent secondary cataracts causing blurry or opaque vision. Here we introduce a fast and efficient method for fabricating arrays consisting of millions of individual nanostructures on the hydrogel surface. In particular, we have prepared the randomly distributed nanopillars on poly(2-hydroxyethyl methacrylate) hydrogel using replica molding and show that the number, shape, and arrangement of nanostructures are fully adjustable. Characterization by atomic force microscopy revealed that all nanopillars were of similar shape, narrow size distribution, and without significant defects. In imprint lithography, choosing the appropriate hydrogel composition is critical. As hydrogels with imprinted nanostructures mimic the natural cell environment, they can find applications in fundamental cell biology research, e.g., they can tune cell attachment and inhibit or promote cell clustering by a specific arrangement of protrusive nanostructures on the hydrogel surface.


Assuntos
Nanoestruturas , Poli-Hidroxietil Metacrilato , Hidrogel de Polietilenoglicol-Dimetacrilato/química , Hidrogéis/química , Microscopia de Força Atômica , Nanoestruturas/química , Poli-Hidroxietil Metacrilato/química
4.
Nanoscale ; 14(26): 9507-9515, 2022 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-35749122

RESUMO

Potential applications of 2D metal-organic frameworks (MOF) require the frameworks to be monophase and well-defined at the atomic scale, to be decoupled from the supporting substrate, and to remain stable at the application conditions. Here, we present three systems meeting this elusive set of requirements: M-TCNQ (M = Ni, Fe, Mn) on epitaxial graphene/Ir(111). We study the systems experimentally by scanning tunneling microscopy, low energy electron microscopy and X-ray photoelectron spectroscopy. When synthesized on graphene, the 2D M-TCNQ MOFs are monophase with M1(TCNQ)1 stoichiometry, no alternative structure was observed with slight variation of the preparation protocol. We further demonstrate a remarkable chemical and thermal stability of TCNQ-based 2D MOFs: all the studied systems survive exposure to ambient conditions, with Ni-TCNQ doing so without any significant changes to its atomic-scale structure or chemical state. Thermally, the most stable system is Fe-TCNQ which remains stable above 500 °C, while all the tested MOFs survive heating to 250 °C. Overall, the modular M-TCNQ/graphene system combines the atomic-scale definition required for fundamental studies with the robustness and stability needed for applications, thus we consider it an ideal model for research in single atom catalysis, spintronics or high-density storage media.

5.
Nat Commun ; 11(1): 1856, 2020 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-32312971

RESUMO

The realization of complex long-range ordered structures in a Euclidean plane presents a significant challenge en route to the utilization of their unique physical and chemical properties. Recent progress in on-surface supramolecular chemistry has enabled the engineering of regular and semi-regular tilings, expressing translation symmetric, quasicrystalline, and fractal geometries. However, the k-uniform tilings possessing several distinct vertices remain largely unexplored. Here, we show that these complex geometries can be prepared from a simple bitopic molecular precursor - 4,4'-biphenyl dicarboxylic acid (BDA) - by its controlled chemical transformation on the Ag(001) surface. The realization of 2- and 3-uniform tilings is enabled by partially carboxylated BDA mediating the seamless connection of two distinct binding motifs in a single long-range ordered molecular phase. These results define the basic self-assembly criteria, opening way to the utilization of complex supramolecular tilings.

6.
Nanoscale ; 10(37): 17520-17524, 2018 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-30207344

RESUMO

We employ low-energy electron beam irradiation to induce both n- and p-doping in a graphene layer. Depending on the applied gate voltage during the irradiation, either n- or p-doping can be achieved, and by setting an appropriate irradiation protocol, any desired doping levels can be achieved.

7.
J Vis Exp ; (127)2017 09 14.
Artigo em Inglês | MEDLINE | ID: mdl-28994785

RESUMO

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, their high cost production and/or incompatibility with microfabrication technologies, due to the use of pre-deposited catalyst-seeds and/or high processing temperatures exceeding 900 °C, represent a drawback for a widespread use of these methods. Here, however, we report the synthesis of ZnO rods via a non-catalyzed vapor-solid mechanism enabled by using an aerosol-assisted chemical vapor deposition (CVD) method at 400 °C with zinc chloride (ZnCl2) as the precursor and ethanol as the carrier solvent. This method provides both single-step formation of ZnO rods and the possibility of their direct integration with various substrate types, including silicon, silicon-based micromachined platforms, quartz, or high heat resistant polymers. This potentially facilitates the use of this method at a large-scale, due to its compatibility with state-of-the-art microfabrication processes for device manufacture. This report also describes the properties of these structures (e.g., morphology, crystalline phase, optical band gap, chemical composition, electrical resistance) and validates its gas sensing functionality towards carbon monoxide.


Assuntos
Óxido de Zinco/química , Aerossóis , Catálise
8.
Sci Rep ; 7(1): 563, 2017 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-28373676

RESUMO

Graphene field effect transistors are becoming an integral part of advanced devices. Hence, the advanced strategies for both characterization and tuning of graphene properties are required. Here we show that the X-ray irradiation at the zero applied gate voltage causes very strong negative doping of graphene, which is explained by X-ray radiation induced charging of defects in the gate dielectric. The induced charge can be neutralized and compensated if the graphene device is irradiated by X-rays at a negative gate voltage. Here the charge neutrality point shifts back to zero voltage. The observed phenomenon has strong implications for interpretation of X-ray based measurements of graphene devices as it renders them to significantly altered state. Our results also form a basis for remote X-ray tuning of graphene transport properties and X-ray sensors comprising the graphene/oxide interface as an active layer.

9.
ACS Appl Mater Interfaces ; 8(48): 33335-33342, 2016 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-27934171

RESUMO

We present a new method for vapor deposition of columnar ZnO structures in the form of rods on various substrates without the need for substrate modification with catalyst seed particles and at relatively low temperatures compared to other vapor deposition methods. These structures are used for the photodegradation of stearic acid (C18H36O2) and the photoactivated detection of gases such as carbon monoxide (CO), ethanol (C2H6O), toluene (C7H8), and nitrogen dioxide (NO2) at room temperature, showing improved selectivity compared to tests performed in themoactivated mode.

10.
Colloids Surf B Biointerfaces ; 123: 951-8, 2014 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-25465753

RESUMO

Cysteine and homocysteine play a crucial role in many biological functions but abnormal levels of these amino acids may lead to various forms of pathogenesis. Therefore, selective and easy-to-use methods for the detection of cysteine and homocysteine are essential for the early diagnosis of developing diseases. In this paper we report on a rapid, straightforward and highly selective method for the detection of cysteine (Cys) and homocysteine (Hcy) which uses a CuO/ZnO nanocomposite as a dual colorimetric and fluorometric assay. The presence of Cys and Hcy in a solution of these nanorods (NRs) induces a change in its color from light blue to dark grey which is visible to the naked eye. This is accompanied by a blue shift in the absorption spectra from 725 nm to 650 nm and a decrease in the intensity of CuO/ZnO nanocomposite emission. These changes are ascribed to the reduction of Cu(II) to Cu(0), and the oxidation of cysteine (homocysteine) and subsequent formation of the disulfide bond. This novel assay method does not respond to any other amino-acid which is present in living organisms; therefore the selective determination of cysteine (homocysteine) with a lower analyte limit of 40 µM (4.8 µg mL(-1)) can be carried out in aqueous solutions without the need for any sophisticated instrumentation, fluorophore molecules or complicated procedures.


Assuntos
Cobre/química , Cisteína/química , Homocisteína/química , Nanocompostos/química , Óxido de Zinco/química , Colorimetria , Fluorescência
11.
Chem Commun (Camb) ; 50(69): 9973-6, 2014 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-25033949

RESUMO

Metal coordination assemblies of the symmetric bi-functional 4,4'-di-(1,4-buta-1,3-diynyl)-benzoic acid are investigated by scanning tunnelling microscopy on metal surfaces. The formation of long-range ordered, short-range disordered and random phases depends on the competition between the convergent and divergent coordination motifs of the individual functional groups and is crucially influenced by the substrate.

12.
Nanotechnology ; 25(18): 185601, 2014 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-24739598

RESUMO

Synthesis of graphene by chemical vapor deposition is a promising route for manufacturing large-scale high-quality graphene for electronic applications. The quality of the employed substrates plays a crucial role, since the surface roughness and defects alter the graphene growth and cause difficulties in the subsequent graphene transfer. Here, we report on ultrasmooth high-purity copper foils prepared by sputter deposition of Cu thin film on a SiO2/Si template, and the subsequent peeling off of the metallic layer from the template. The surface displays a low level of oxidation and contamination, and the roughness of the foil surface is generally defined by the template, and was below 0.6 nm even on a large scale. The roughness and grain size increase occurred during both the annealing of the foils, and catalytic growth of graphene from methane (≈1000 °C), but on the large scale still remained far below the roughness typical for commercial foils. The micro-Raman spectroscopy and transport measurements proved the high quality of graphene grown on such foils, and the room temperature mobility of the graphene grown on the template stripped foil was three times higher compared to that of one grown on the commercial copper foil. The presented high-quality copper foils are expected to provide large-area substrates for the production of graphene suitable for electronic applications.

13.
Nano Lett ; 14(2): 563-9, 2014 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-24471471

RESUMO

Dye-sensitized solar cells constitute a promising approach to sustainable and low-cost solar energy conversion. Their overall efficiency crucially depends on the effective coupling of the photosensitizers to the photoelectrode and the details of the dye's energy levels at the interface. Despite great efforts, the specific binding of prototypical ruthenium-based dyes to TiO2, their potential supramolecular interaction, and the interrelation between adsorption geometry and electron injection efficiency lack experimental evidence. Here we demonstrate multiconformational adsorption and energy level alignment of single N3 dyes on TiO2 anatase (101) revealed by scanning tunnelling microscopy and spectroscopy. The distinctly bound molecules show significant variations of their excited state levels associated with different driving forces for photoelectron injection. These findings emphasize the critical role of the interfacial coupling and suggest that further designs of dye-sensitized solar cells should target a higher selectivity in the dye-substrate binding conformations in order to ensure efficient electron injection from all photosensitizers.

14.
J Am Chem Soc ; 134(14): 6072-5, 2012 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-22458838

RESUMO

The formation of extended two-dimensional metal-organic coordination networks (2D-MOCNs) showing high adaptability to surface step edges and structural defects is revealed by scanning tunneling microscopy. Rod-like 4,4'-di-(1,4-buta-1,3-diynyl)-benzoic acid (BDBA) and iron atoms assemble into extended 2D-MOCNs on Au(111) and Ag(100) surfaces. Independent from the chosen substrate and its surface symmetry the MOCN grows continuously over multiple surface terraces through mutual in-phase structure adaptation of network domains at step edges as well as on terraces. The adaptability of the MOCNs is mainly ascribed to the high degree of conformational flexibility of the butadiynyl functionality of the ligand. Despite their flexibility, the MOCNs exhibit considerable robustness against annealing at high temperatures. The findings show that mesoscale self-assembled functional architectures with a high degree of substrate error tolerance can be realized with metal coordination networks.

15.
J Nanosci Nanotechnol ; 9(10): 5887-90, 2009 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-19908470

RESUMO

We report on an alternative approach for the fabrication of metallic nanostructures: a selective growth on silicon substrates patterned by local anodic oxidation using atomic force microscopy. Our method represents a maskless, four-step process which combines a top-down and bottom-up approach. The dimensions of both the oxide lines and metallic elements can be controlled during the technological process. In this paper we demonstrate the preparation of gallium and cobalt structures on silicon substrates but this method can be extended to other combinations of metals and substrates enabling thus the fabrication of ordered nanostructures of various compositions and properties on locally oxidized surfaces.

16.
Nanotechnology ; 19(47): 475606, 2008 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-21836281

RESUMO

In this paper the growth of Ga droplets on a vicinal Si(111) surface is discussed. We report that the droplet size can be controlled down to the sub-100 nm range by carefully chosen deposition conditions. In addition, the dependence of the droplet size on deposition time is not monotonic, but shows self-limiting behaviour: with increasing amount of Ga on the surface the droplets stop increasing in lateral dimension and, instead, additional droplets of the same size are formed on the surface. Further, in the case of deposition at 300 °C substrate temperature it has been found that the growth proceeds in cycles. Thus, not only the size but also the droplet concentration can be controlled. In this way, non-ordered arrays of metallic droplets with a very narrow size distribution can be grown.

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