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1.
ACS Nano ; 2018 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-30499656

RESUMO

Quasi-one-dimensional (quasi-1D) materials enjoy growing interest due to their unusual physical properties and promise for miniature electronic devices. However, the mechanical exfoliation of quasi-1D materials into thin flakes and nanoribbons received considerably less attention from researchers than the exfoliation of conventional layered crystals. In this study, we investigated the micromechanical exfoliation of representative quasi-1D crystals, TiS3 whiskers, and demonstrate that they typically split into narrow nanoribbons with very smooth, straight edges and clear signatures of 1D TiS3 chains. Theoretical calculations show that the energies required for breaking weak interactions between the two-dimensional (2D) layers and between 1D chains within the layers are comparable and, in turn, are considerably lower than those required for breaking the covalent bonds within the chains. We also emulated macroscopic exfoliation experiments on the nanoscale by applying a local shear force to TiS3 crystals in different crystallographic directions using a tip of an atomic force microscopy (AFM) probe. In the AFM experiments, it was possible to slide the 2D TiS3 layers relative to each other as well as to remove selected 1D chains from the layers. We systematically studied the exfoliated TiS3 crystals by Raman spectroscopy and identified the Raman peaks whose spectral positions were most dependent on the crystals' thickness. These results could be used to distinguish between TiS3 crystals with thickness ranging from one to about seven monolayers. The conclusions established in this study for the exfoliated TiS3 crystals can be extended to a variety of transition metal trichalcogenide materials as well as other quasi-1D crystals. The possibility of exfoliation of TiS3 into narrow (few-nm wide) crystals with smooth edges could be important for the future realization of miniature device channels with reduced edge scattering of charge carriers.

2.
ACS Omega ; 3(4): 4141-4147, 2018 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-30023886

RESUMO

A main challenge in understanding the structure of a cell membrane and its interactions with drugs is the ability to chemically study the different molecular species on the nanoscale. We have achieved this for a model system consisting of mixed monolayers (MLs) of the biologically relevant phospholipid 1,2-distearoyl-sn-glycero-phosphatidylcholine and the antibiotic surfactin. By employing nano-infrared (IR) microscopy and spectroscopy in combination with atomic force microscopy imaging, it was possible to identify and chemically detect domain formation of the two constituents as well as to obtain IR spectra of these species with a spatial resolution on the nanoscale. A novel method to enhance the near-field imaging contrast of organic MLs by plasmon interferometry is proposed and demonstrated. In this technique, the organic layer is deposited on gold and ML graphene substrates, the latter of which supports propagating surface plasmons. Plasmon reflections arising from changes in the dielectric environment provided by the organic layer lead to an additional contrast mechanism. Using this approach, the interfacial region between surfactin and the phospholipid has been mapped and a transition region is identified.

3.
Opt Express ; 25(14): 16574-16588, 2017 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-28789160

RESUMO

Synchrotron radiation-based nano-FTIR spectroscopy utilizes the highly brilliant and ultra-broadband infrared (IR) radiation provided by electron storage rings for the infrared spectroscopic characterization of samples at the nanoscale. In order to exploit the full potential of this approach we investigated the influence of the properties of the radiation source, such as the electron bunch shape and spectral bandwidth of the emitted radiation, on near-field infrared spectra of silicon-carbide (SiC). The adapted configuration of the storage ring optics enables a modification of the transverse electron bunch profile allowing an increase of the measured near-field signal amplitude. Additionally, the decay of the signal amplitude due to the decreasing storage ring current is also eliminated. Further options for improving the sensitivity of nano-FTIR spectroscopy, which can also be applied to other broadband radiation sources, are the adaption of the spectral bandwidth to the wavelength range of interest or the use of polarization optics. The sensitivity enhancement emerging from these options is verified by comparing near-field spectra collected from crystalline SiC samples. The improvement in sensitivity by combining these approaches is demonstrated by acquiring nano-FTIR spectra from thin organic films, which show weak resonances in the IR-regime.

4.
Opt Express ; 24(2): 1154-64, 2016 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-26832499

RESUMO

Nanoscale plasmonic phenomena observed in single and bi-layers of molybdenum disulfide (MoS(2)) on silicon dioxide (SiO(2)) are reported. A scattering type scanning near-field optical microscope (s-SNOM) with a broadband synchrotron radiation (SR) infrared source was used. We also present complementary optical mapping using tunable CO(2)-laser radiation. Specifically, there is a correlation of the topography of well-defined MoS(2) islands grown by chemical vapor deposition, as determined by atomic force microscopy, with the infrared (IR) signature of MoS(2). The influence of MoS(2) islands on the SiO(2) phonon resonance is discussed. The results reveal the plasmonic character of the MoS(2) structures and their interaction with the SiO(2) phonons leading to an enhancement of the hybridized surface plasmon-phonon mode. A theoretical analysis shows that, in the case of monolayer islands, the coupling of the MoS(2) optical plasmon mode to the SiO(2) surface phonons does not affect the infrared spectrum significantly. For two-layer MoS(2), the coupling of the extra inter-plane acoustic plasmon mode with the SiO(2) surface transverse phonon leads to a remarkable increase of the surface phonon peak at 794 cm(-1). This is in agreement with the experimental data. These results show the capability of the s-SNOM technique to study local multiple excitations in complex non-homogeneous structures.

6.
Opt Express ; 22(15): 17948-58, 2014 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-25089414

RESUMO

We describe the application of scattering-type near-field optical microscopy to characterize various semiconducting materials using the electron storage ring Metrology Light Source (MLS) as a broadband synchrotron radiation source. For verifying high-resolution imaging and nano-FTIR spectroscopy we performed scans across nanoscale Si-based surface structures. The obtained results demonstrate that a spatial resolution below 40 nm can be achieved, despite the use of a radiation source with an extremely broad emission spectrum. This approach allows not only for the collection of optical information but also enables the acquisition of near-field spectral data in the mid-infrared range. The high sensitivity for spectroscopic material discrimination using synchrotron radiation is presented by recording near-field spectra from thin films composed of different materials used in semiconductor technology, such as SiO2, SiC, SixNy, and TiO2.

7.
Opt Express ; 21(3): 2913-9, 2013 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-23481749

RESUMO

We demonstrate scanning near-field optical microscopy with a spatial resolution below 100 nm by using low intensity broadband synchrotron radiation in the IR regime. The use of such a broadband radiation source opens up the possibility to perform nano-Fourier-transform infrared spectroscopy over a wide spectral range.


Assuntos
Aumento da Imagem/instrumentação , Microscopia , Nanotecnologia/instrumentação , Espectroscopia de Infravermelho com Transformada de Fourier/instrumentação , Síncrotrons/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento
9.
Opt Express ; 19(24): 23867-77, 2011 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-22109411

RESUMO

The influence of surface plasmons on the magneto-optic activity in a two-dimensional hexagonal array is addressed. The experiments were performed using hexagonal array of circular holes in a ferromagnetic Ni film. Well pronounced troughs are observed in the optical reflectivity, resulting from the presence of surface plasmons. The surface plasmons are found to strongly enhance the magneto-optic response (Kerr rotation), as compared to a continuous film of the same composition. The influence of the hexagonal symmetry of the pattern on the coupling between the plasmonic excitations is demonstrated, using optical diffraction measurements and theoretical calculations of the magneto-optic and of the angular dependence of the optical activity.


Assuntos
Membranas Artificiais , Nanoestruturas/química , Níquel/química , Ressonância de Plasmônio de Superfície/métodos , Luz , Campos Magnéticos , Teste de Materiais , Refratometria , Espalhamento de Radiação
10.
Small ; 7(21): 3096-100, 2011 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-21916008

RESUMO

The transmission of light through a metallic film stack on a transparent substrate, perforated with a periodic array of cylindrical holes/nanocavities, is studied. The structure is fabricated by using self-assembled nanosphere lithography. Since one layer in the film stack is made of a ferromagnetic metal (iron), exposure of the structure to a solution containing iron oxide nanoparticles causes nanoparticle accumulation inside the nanocavities. This changes the dielectric constant inside the nanocavities and thus affects the light transmission. Simulations are in good agreement with experiment, and show large sensitivity of the response to the amount of iron oxide nanoparticles deposited. This could be used in various sensor applications.


Assuntos
Compostos Férricos/química , Luz , Nanopartículas Metálicas/química , Magnetismo , Microscopia Eletrônica de Varredura , Ressonância de Plasmônio de Superfície
11.
Langmuir ; 26(5): 3549-54, 2010 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-20104920

RESUMO

Fabrication of tailored nanomaterials with desired structure and properties is the greatest challenge of modern nanotechnology. Herein, we describe a wet chemical method for the preparation of large area metal nanoring arrays. This method is based on self-assembly of polystyrene sphere template on a flat substrate and wicking/reducing metal precursor into the interstices between the template and the substrate. In this article, platinum, gold, and copper nanorings were fabricated by applying 505 nm polystyrene spheres onto highly oriented pyrolytic graphite (HOPG) and Si(100) substrates, followed by reducing the templated metal salt with NaBH(4). AFM images reveal formation of arrays of metal nanorings comprising metal nanoparticles with the average ring height of 5.7 +/- 0.8 nm and diameter of 167.3 +/- 8.9 nm. XPS confirms that these structures are metallic.

12.
Small ; 5(3): 400-6, 2009 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-19148886

RESUMO

A fast and cheap, large-area (>1 cm(2)), high-coverage fabrication technique for periodic metallic split-ring resonator metamaterials is presented, which allows control of inner- and outer-ring diameters, gap angles, as well as thickness and periodicity. This method, based on shadow nanosphere lithography, uses tilted-angle-rotation thermal evaporation onto Langmuir-Blodgett-type monolayers of close-packed polystyrene nanospheres. Excellent agreement of the process parameters with a simplified model is demonstrated. Pronounced, tunable optical metamaterial resonances in the range of 100 THz are consistent with simulations.


Assuntos
Nanosferas/química , Simulação por Computador , Nanotecnologia/métodos , Óptica e Fotônica , Espectroscopia de Infravermelho com Transformada de Fourier , Propriedades de Superfície
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