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1.
Nanoscale ; 2020 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-32348391

RESUMO

Focused Electron Beam Induced Deposition (FEBID) for magnetic tip fabrication is presented in this work as an alternative to conventional sputtering-based Magnetic Force Microscopy (MFM) tips. FEBID enables the growth of a high-aspect-ratio magnetic nanorod with customized geometry and composition to overcome the key technical limitations of MFM probes currently on the market. The biggest advantage of these tips, in comparison with CoCr coated pyramidal probes, lies in the capability of creating sharp ends, nearly 10 nm in diameter, which provides remarkable (topographic and magnetic) lateral resolution in samples with magnetic features close to the resolution limits of the MFM technique itself. The shape of the nanorods produces a very confined magnetic stray field, whose interaction with the sample is extremely localized and perpendicular to the surface, with negligible in-plane components. This effect can lead to a better analytical and numerical modelling of the MFM probes and to an increase in the sensitivity without perturbing the magnetic configuration of soft samples. Besides, the high-aspect ratio achievable in FEBID nanorod tips makes them magnetically harder than the commercial ones, reaching coercive fields higher than 900 Oe. According to the results shown, tips based on magnetic nanorods grown by FEBID can be eventually used for quantitative analysis in MFM measurements. Moreover, the customized growth of Co- or Fe-based tips onto levers with different mechanical properties allows MFM studies that demand different measuring conditions. To showcase the versatility of this type of probe, as a last step, MFM is performed in a liquid environment, which still remains a challenge for the MFM community largely due to the lack of appropriate probes on the market. This opens up new possibilities in the investigation of magnetic biological samples.

2.
Adv Mater ; 32(1): e1905504, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31736228

RESUMO

2D hexagonal boron nitride (hBN) is a wide-bandgap van der Waals crystal with a unique combination of properties, including exceptional strength, large oxidation resistance at high temperatures, and optical functionalities. Furthermore, in recent years hBN crystals have become the material of choice for encapsulating other 2D crystals in a variety of technological applications, from optoelectronic and tunneling devices to composites. Monolayer hBN, which has no center of symmetry, is predicted to exhibit piezoelectric properties, yet experimental evidence is lacking. Here, by using electrostatic force microscopy, this effect is observed as a strain-induced change in the local electric field around bubbles and creases, in agreement with theoretical calculations. No piezoelectricity is found in bilayer and bulk hBN, where the center of symmetry is restored. These results add piezoelectricity to the known properties of monolayer hBN, which makes it a desirable candidate for novel electromechanical and stretchable optoelectronic devices, and pave a way to control the local electric field and carrier concentration in van der Waals heterostructures via strain. The experimental approach used here also shows a way to investigate the piezoelectric properties of other materials on the nanoscale by using electrostatic scanning probe techniques.

3.
Nano Lett ; 19(8): 5459-5468, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31369278

RESUMO

We introduce scanning-probe-assisted nanowire circuitry (SPANC) as a new method to fabricate electrodes for the characterization of electrical transport properties at the nanoscale. SPANC uses an atomic force microscope (AFM) to manipulate nanowires to create complex and highly conductive nanostructures (paths) that work as nanoelectrodes, allowing connectivity and electrical characterization of other nano-objects. The paths are formed by the spontaneous cold welding of gold nanowires upon mechanical contact, leading to an excellent contact resistance of ∼9 Ω/junction. SPANC is an easy to use and cost-effective technique that fabricates clean nanodevices. Hence, this new method can complement and/or be an alternative to other well-established methods to fabricate nanocircuits such as electron beam lithography (EBL). The circuits made by SPANC are easily reconfigurable, and their fabrication does not require the use of polymers and chemicals. In this work, we present a few examples that illustrate the capabilities of this method, allowing robust device fabrication and electrical characterization of several nano-objects with sizes down to ∼10 nm, well below the current smallest size able to be contacted in a device using the standard available technology (∼30 nm). Importantly, we also provide the first experimental determination of the sheet resistance of thin antimonene flakes.

4.
ACS Nano ; 12(10): 10171-10177, 2018 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-30207692

RESUMO

The future of 2D flexible electronics relies on the preparation of conducting ultrathin films of materials with mechanical robustness and flexibility in a simple but controlled manner. In this respect, metal-organic compounds present advantages over inorganic laminar crystals owing to their structural, chemical, and functional diversity. While most metal-organic compounds are usually prepared in bulk, recent work has shown that some of them are processable down to low dimensional forms. Here we report the one-pot preparation, carried out at the water-air interface, of ultrathin (down to 4 nm) films of the metal-organic compound [Cu2I2(TAA)] n (TAA= thioacetamide). The films are shown to be homogeneous over mm2 areas, smooth, highly transparent, mechanically robust, and good electrical conductors with memristive behavior at low frequencies. This combination of properties, as well as the industrial availability of the two building blocks required for the preparation, demonstrates their wide range potential in future flexible and transparent electronics.

5.
Methods Mol Biol ; 1814: 3-17, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29956223

RESUMO

Exploring the limits of spatial resolution has been a constant in the history of atomic force microscopy imaging. Since its invention in 1986, the AFM has beaten the barrier of resolution continuously, thanks to technical developments, miniaturization of tips, and implementation of new imaging modes. The double helix structure of DNA has been always at the horizon of resolution. Today, this milestone has been reached, not only imaging DNA but also its close relative double-stranded RNA. Here, we provide a comprehensive description of the methods employed and the steps required to image the helical periodicity of these two nucleic acids with the sample immersed in a buffer solution.


Assuntos
Imageamento Tridimensional , Microscopia de Força Atômica/métodos , Ácidos Nucleicos/metabolismo , DNA/metabolismo , RNA de Cadeia Dupla/metabolismo
6.
Adv Mater ; 30(21): e1705645, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29659059

RESUMO

Molecular wires are essential components for future nanoscale electronics. However, the preparation of individual long conductive molecules is still a challenge. MMX metal-organic polymers are quasi-1D sequences of single halide atoms (X) bridging subunits with two metal ions (MM) connected by organic ligands. They are excellent electrical conductors as bulk macroscopic crystals and as nanoribbons. However, according to theoretical calculations, the electrical conductance found in the experiments should be even higher. Here, a novel and simple drop-casting procedure to isolate bundles of few to single MMX chains is demonstrated. Furthermore, an exponential dependence of the electrical resistance of one or two MMX chains as a function of their length that does not agree with predictions based on their theoretical band structure is reported. This dependence is attributed to strong Anderson localization originated by structural defects. Theoretical modeling confirms that the current is limited by structural defects, mainly vacancies of iodine atoms, through which the current is constrained to flow. Nevertheless, measurable electrical transport along distances beyond 250 nm surpasses that of all other molecular wires reported so far. This work places in perspective the role of defects in 1D wires and their importance for molecular electronics.

7.
Chem Soc Rev ; 47(3): 982-1021, 2018 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-29210397

RESUMO

Phosphorene, an emerging two-dimensional material, has received considerable attention due to its layer-controlled direct bandgap, high carrier mobility, negative Poisson's ratio and unique in-plane anisotropy. As cousins of phosphorene, 2D group-VA arsenene, antimonene and bismuthene have also garnered tremendous interest due to their intriguing structures and fascinating electronic properties. 2D group-VA family members are opening up brand-new opportunities for their multifunctional applications encompassing electronics, optoelectronics, topological spintronics, thermoelectrics, sensors, Li- or Na-batteries. In this review, we extensively explore the latest theoretical and experimental progress made in the fundamental properties, fabrications and applications of 2D group-VA materials, and offer perspectives and challenges for the future of this emerging field.

8.
Adv Mater ; 30(2)2018 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-29076558

RESUMO

Antimonene, defined in sensu stricto as a single layer of antimony atoms, is recently the focus of numerous theoretical works predicting a variety of interesting properties and is quickly attracting the attention of the scientific community. However, what places antimonene in a different category from other 2D crystals is its strong spin-orbit coupling and a drastic evolution of its properties from the monolayer to the few-layer system. The recent isolation of this novel 2D material pushes the interest for antimonene even further. Here, a review of both theoretical predictions and experimental results is compiled. First, an account of the calculations anticipating an electronic band structure suitable for optoelectronics and thermoelectric applications in monolayer form and a topological semimetal in few-layer form is given. Second, the different approaches to produce antimonene-mechanical and liquid phase exfoliation, and epitaxial growth methods-are reviewed. In addition, this work also reports the main characterization techniques used to study this exotic material. This review provides insights for further exploring the appealing properties of antimonene and puts forward the opportunities and challenges for future applications from (opto)electronic device fabrication to biomedicine.

9.
Angew Chem Int Ed Engl ; 56(46): 14389-14394, 2017 11 13.
Artigo em Inglês | MEDLINE | ID: mdl-28945952

RESUMO

Antimonene, a novel group 15 two-dimensional material, is functionalized with a tailormade perylene bisimide through strong van der Waals interactions. The functionalization process leads to a significant quenching of the perylene fluorescence, and surpasses that observed for either graphene or black phosphorus, thus allowing straightforward characterization of the flakes by scanning Raman microscopy. Furthermore, scanning photoelectron microscopy studies and theoretical calculations reveal a remarkable charge-transfer behavior, being twice that of black phosphorus. Moreover, the excellent stability under environmental conditions of pristine antimonene has been tackled, thus pointing towards the spontaneous formation of a sub-nanometric oxide passivation layer. DFT calculations revealed that the noncovalent functionalization of antimonene results in a charge-transfer band gap of 1.1 eV.

10.
Angew Chem Int Ed Engl ; 55(46): 14345-14349, 2016 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-27529687

RESUMO

We report on a fast and simple method to produce highly stable isopropanol/water (4:1) suspensions of few-layer antimonene by liquid-phase exfoliation of antimony crystals in a process that is assisted by sonication but does not require the addition of any surfactant. This straightforward method generates dispersions of few-layer antimonene suitable for on-surface isolation. Analysis by atomic force microscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy confirmed the formation of high-quality few-layer antimonene nanosheets with large lateral dimensions. These nanolayers are extremely stable under ambient conditions. Their Raman signals are strongly thickness-dependent, which was rationalized by means of density functional theory calculations.

11.
Adv Mater ; 28(30): 6515, 2016 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-27493072

RESUMO

On page 6332, J. Gómez-Herrero, F. Zamora, and co-workers describe the isolation of antimonene, a new allotrope of antimony that consists of a single layer of atoms. They obtain antimonene flakes by the scotch tape method; these flakes are highly stable in ambient conditions and even when immersed in water. The 1.2 eV gap calculated in this study suggests potential applications in optoelectronics.

12.
Adv Mater ; 28(30): 6332-6, 2016 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-27272099

RESUMO

Antimonene fabricated by mechanical exfoliation is highly stable under atmospheric conditions over periods of months and even when immersed in water. Density functional theory confirms the experiments and predicts an electronic gap of ≈1 eV. These results highlight the use of antimonene for optoelectronics applications.

13.
Nanoscale ; 8(23): 11818-26, 2016 Jun 09.
Artigo em Inglês | MEDLINE | ID: mdl-26876486

RESUMO

Double-stranded (ds) RNA mediates the suppression of specific gene expression, it is the genetic material of a number of viruses, and a key activator of the innate immune response against viral infections. The ever increasing list of roles played by dsRNA in the cell and its potential biotechnological applications over the last decade has raised an interest for the characterization of its mechanical properties and structure, and that includes approaches using Atomic Force Microscopy (AFM) and other single-molecule techniques. Recent reports have resolved the structure of dsDNA with AFM at unprecedented resolution. However, an equivalent study with dsRNA is still lacking. Here, we have visualized the double helix of dsRNA under near-physiological conditions and at sufficient resolution to resolve the A-form sub-helical pitch periodicity. We have employed different high-sensitive force-detection methods and obtained images with similar spatial resolution. Therefore, we show here that the limiting factors for high-resolution AFM imaging of soft materials in liquid medium are, rather than the imaging mode, the force between the tip and the sample and the sharpness of the tip apex.


Assuntos
Microscopia de Força Atômica , RNA de Cadeia Dupla/química , Fenômenos Mecânicos
14.
Small ; 11(36): 4731-6, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26150330

RESUMO

In this work, the use of magnetic force microscopy (MFM) to acquire images of magnetic nanostructures in liquid environments is presented. Optimization of the MFM signal acquisition in liquid media is performed and it is applied to characterize the magnetic signal of magnetite nanoparticles. The ability for detecting magnetic nanostructures along with the well-known capabilities of atomic force microscopy in liquids suggests potential applications in fields such as nanomedicine, nanobiotechnology, or nanocatalysis.


Assuntos
Magnetismo , Microscopia de Força Atômica/métodos , Nanoestruturas/química , Nanotecnologia/métodos , Ar , Animais , Meios de Contraste/química , Humanos , Nanopartículas de Magnetita/química , Nanomedicina/métodos , Tamanho da Partícula , Succímero/química , Água
15.
Bioinformatics ; 31(17): 2918-20, 2015 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-25931516

RESUMO

UNLABELLED: Scanning probe microscopy (SPM) is already a relevant tool in biological research at the nanoscale. We present 'Flatten plus', a recent and helpful implementation in the well-known WSxM free software package. 'Flatten plus' allows reducing low-frequency noise in SPM images in a semi-automated way preventing the appearance of typical artifacts associated with such filters. AVAILABILITY AND IMPLEMENTATION: WSxM is a free software implemented in C++ supported on MS Windows, but it can also be run under Mac or Linux using emulators such as Wine or Parallels. WSxM can be downloaded from http://www.wsxmsolutions.com/. CONTACT: ignacio.horcas@wsxmsolutions.com.


Assuntos
Pesquisa Biomédica , Proteínas de Ciclo Celular/química , Proteínas Cromossômicas não Histona/química , DNA/química , Processamento de Imagem Assistida por Computador/métodos , Microscopia de Varredura por Sonda/métodos , Software , Algoritmos , Proteínas de Ciclo Celular/ultraestrutura , Proteínas Cromossômicas não Histona/ultraestrutura , DNA/ultraestrutura , Humanos , Aumento da Imagem
16.
Nanotechnology ; 20(38): 385709, 2009 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-19713587

RESUMO

The interplay between local mechanical strain energy and lateral frictional forces determines the shape of carbon nanotubes on substrates. In turn, because of its nanometer-size diameter, the shape of a carbon nanotube strongly influences its local electronic, chemical, and mechanical properties. Few, if any, methods exist for resolving the strain energy and static frictional forces along the length of a deformed nanotube supported on a substrate. We present a method using nonlinear elastic rod theory in which we compute the flexural strain energy and static frictional forces along the length of single walled carbon nanotubes (SWCNTs) manipulated into various shapes on a clean SiO(2) substrate. Using only high resolution atomic force microscopy images of curved single walled nanotubes, we estimate flexural strain energy distributions on the order of attojoules per nanometer and the static frictional forces between a SWCNT and SiO(2) surface to be a minimum of 230 pN nm(-1).

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