Combined Scanning Probe Research Articles

Three-dimensional simulation of electron beam induced current collected by a nano-contact: Diffusion and collection analysis

Three-dimensional simulation is used to study the electron beam induced current collected by a nano-contact forming a nano-junction. For the calculation the surface recombination velocity is supposed to be either infinite or zero. The influence of the bulk diffusion length, energy of the incident electron beam, shape and size of the depletion zone beneath the nano-contact on the induced current collected by the nano-junction is studied. From the fit of the simulated data, the minority carrier effective diffusion length is extracted, and its variation with the electron beam energy is compared with experimental measurements obtained with the nano-EBIC (electron beam induced current) technique that we have developed by combining scanning probe microscopy and scanning electron microscopy. The effective diffusion length is an increasing function with electron beam energy up to a certain value beyond which it decreases. The simulation shows that the same behavior also occurs in the case of the conventional detection by a semi-infinite Schottky contact perpendicular to the electron beam. This is the first time, to our knowledge, that this behavior is pointed out.

Single-molecule protein arrays enabled by scanning probe block copolymer lithography

The ability to control the placement of individual protein molecules on surfaces could enable advances in a wide range of areas, from the development of nanoscale biomolecular devices to fundamental studies in cell biology. Such control, however, remains a challenge in nanobiotechnology due to the limitations of current lithographic techniques. Herein we report an approach that combines scanning probe block copolymer lithography with site-selective immobilization strategies to create arrays of proteins down to the single-molecule level with arbitrary pattern control. Scanning probe block copolymer lithography was used to synthesize individual sub-10-nm single crystal gold nanoparticles that can act as scaffolds for the adsorption of functionalized alkylthiol monolayers, which facilitate the immobilization of specific proteins. The number of protein molecules that adsorb onto the nanoparticles is dependent upon particle size; when the particle size approaches the dimensions of a protein molecule, each particle can support a single protein. This was demonstrated with both gold nanoparticle and quantum dot labeling coupled with transmission electron microscopy imaging experiments. The immobilized proteins remain bioactive, as evidenced by enzymatic assays and antigen-antibody binding experiments. Importantly, this approach to generate single-biomolecule arrays is, in principle, applicable to many parallelized cantilever and cantilever-free scanning probe molecular printing methods.

Watching domains grow: In-situ studies of polarization switching by combined scanning probe and scanning transmission electron microscopy

Ferroelectric domain nucleation and growth in multiferroic BiFeO3 films is observed directly by applying a local electric field with a conductive tip inside a scanning transmission electron microscope. The nucleation and growth of a ferroelastic domain and its interaction with pre-existing 71° domain walls are observed and compared with the results of phase-field modeling. In particular, a preferential nucleation site and direction-dependent pinning of domain walls are observed due to slow kinetics of metastable switching in the sample without a bottom electrode. These in situ spatially resolved observations of a first-order bias-induced phase transition reveal the mesoscopic mechanisms underpinning functionality of a wide range of multiferroic materials.

Prolonged Blinking with TERS Probes

Tip-enhanced Raman spectroscopy (TERS), an emerging technique combining scanning probe microscopy (SPM) and Raman spectroscopy, provides the sensitivity and selectivity necessary for chemical imaging with nanoscale resolution. We demonstrate that coating the fragile plasmonic structures used to enhance the electric field with a protective layer improves significantly its mechanical, chemical, and thermal stability without loss of the extreme optical enhancement that appears as a “blinking” phenomenon. This observation provides important information on the mechanism of blinking. The fact that TERS blinking from a polymer layer is preserved when the analyte is separated from the plasmonic nanostructure by a 3 nm thick coating proves that chemical enhancement and charge transfer do not play a significant role in the blinking. Rather, thermally activated diffusion appears to be the dominant mechanism. While extreme enhancement persists only for minutes for an unprotected silver-coated tip, it persists for tens of hours with plasmonic structures coated by an ultrathin layer of alumina (Al2O3), opening broader opportunities for the study of blinking and for chemical imaging and sensing based on plasmonic structures.

Combining scanning probe microscopy and x-ray spectroscopy

A new versatile tool, combining Shear Force Microscopy and X-Ray Spectroscopy was designed and constructed to obtain simultaneously surface topography and chemical mapping. Using a sharp optical fiber as microscope probe, it is possible to collect locally the visible luminescence of the sample. Results of tests on ZnO and on ZnWO4 thin layers are in perfect agreement with that obtained with other conventional techniques. Twin images obtained by simultaneous acquisition in near field of surface topography and of local visible light emitted by the sample under X-Ray irradiation in synchrotron environment are shown. Replacing the optical fibre by an X-ray capillary, it is possible to collect local X-ray fluorescence of the sample. Preliminary results on Co-Ti sample analysis are presented.

Combining Scanning Probe and Confocal Microscopy to Investigate the Biophysical Properties of the Primary Cilium

Primary cilia are non-motile specialised sensory organelles that protrude from the surface of epithelial cells. In the kidney, they are 200 nm in diameter and extend approximately 10 µm in length into the lumen of the nephron. Ciliary dysfunction is linked to autosomal dominant polycystic kidney disease, the most common of the inherited cystic diseases. The manner in which the cilium bends in response to fluid flow along the nephron and the mechanisms leading to the intracellular calcium release are widely debated. To gain insight into the mechanism of ciliary bending, we investigated the biophysical properties of the primary cilium. Here, a TCS SP5 Confocal Microscope (Leica, Wetzlar, Germany) was used to identify cells with a primary cilium and then position a cantilever in a Nanowizard II Atomic Force Microscope (JPK, Berlin, Germany) in the near vicinity of the cilium. We controllably probed individual primary cilia with the AFM cantilever tip to obtain a vertical deflection map in one plane. By probing primary cilia at different heights from the surface of the cell, we produced AFM deflection volume maps. This detailed probing of the mechanical response of the cilium is a mechanical analogue of the z-stack optical imaging employed in confocal microscopy. Thus, using our technique, we have quantified the rigidity of the primary cilium. Funded by BBSRC, EPSRC and JPK Instruments (Berlin, Germany)

Combined scanning probe and light scattering characterization of multi-stage self-assembly of targeted liposome-based delivery systems

The mean size and size distribution of a targeted nanoparticle delivery system (NDS) strongly influences the intrinsic stability and functionality of this molecular complex, affects its performance as a systemic drug delivery platform and ultimately determines its efficacy toward early detection and treatment of cancer. Since its components undergo significant reorganization during multiple stages of self-assembly, it is essential to monitor the size and stability of the complex throughout the NDS formulation in order to ensure its potency and manufacturability prior to entering clinical trials. This work combines scanning probe microscopy (SPM) and dynamic light scattering (DLS) techniques to obtain quantitative and reliable size measurements of the NDS, and to investigate how variations in the NDS formulation or self-assembly process impact the size, structure and functionality of the complex with various therapeutic and diagnostic agent payloads. These combined SPM and DLS methods, when implemented at an early stage of the NDS formulation, present a potential measurement approach to facilitate drug discovery and development, optimization and quality control during manufacturing of the NDS.

Highly Conductive Redox Protein–Carbon Nanotube Complex for Biosensing Applications

AbstractThe integration of redox proteins with nanomaterials has attracted much interest in the past years, and metallic single‐walled carbon nanotubes (SWNTs) have been introduced as efficient electrical wires to connect biomolecules to metal electrodes in advanced nano‐biodevices. Besides preserving biofunctionality, the protein–nanotube connection should ensure appropriate molecular orientation, flexibility, and efficient, reproducible electrical conduction. In this respect, yeast cytochrome c redox proteins are connected to gold electrodes through lying‐down functionalized metallic SWNTs. Immobilization of cytochromes to nanotubes is obtained via covalent bonding between the exposed protein thiols and maleimide‐terminated functional chains attached to the carbon nanotubes. A single‐molecule study performed by combining scanning probe nanoscopies ascertains that the protein topological properties are preserved upon binding and provides unprecedented current images of single proteins bound to carbon nanotubes that allow a detailed I–V characterization. Collectively, the results point out that the use as linkers of suitably functionalized metallic SWNTs results in an electrical communication between redox proteins and gold electrodes more efficient and reproducible than for proteins directly connected with metal surfaces.

NT-MDT - Integrated Solutions for Nanotechnology

The interest in graphene is continuously rising among science communities. Applied physicists, new material designers, and nanotechnology engineers are attracted by its unique properties such as electrical and thermal conductivity. Fundamental physicists are enchanted by the possibility of exploring quantum relativistic phenomena on 2-dimensional crystals that have a unusual electronic spectrum. In order to manipulate a single-atom-thin structure, one needs a reliable high precision tool. In this article two experimental examples are presented. The first one shows the advantages of the NTEGRA based atomic force microscopy (AFM) and how it can reveal the fine structure of graphene flakes. The second example shows how the NTEGRA combines scanning probe microscopy (SPM) with the Raman spectroscopy to become a NanoLaboratory with advanced analytical capability.

Toward Robust High Resolution Chemical Imaging

Abstract Resonant plasmon excitations at the surface of noble metals can localize and amplify an electromagnetic field in a very small volume and are the enabling element of surface enhanced optical microscopies. Tip enhanced Raman spectroscopy (TERS) combines scanning probe microscopy (SPM) with Raman spectroscopy, taking advantage of this enhancing mechanism. So far a 20 nm lateral resolution in chemical imaging of a surface has been achieved. So far a 20 nm lateral resolution in chemical imaging of a surface has been achieved.

Gold Nanostructures Fabricated on Si Substrates Covered with a Self-assembled Monolayer by Combining Scanning Probe Lithographic and Electroless Plating Processes

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High-resolution DNA melting analysis: advancements and limitations

Recent advances in fluorescent dyes, methods, instruments and software for DNA melting analysis have created versatile new tools for variant scanning and genotyping. High resolution melting analysis (HRM or HRMA) is faster, simpler, and less expensive than alternative approaches requiring separations or labeled probes. With the addition of a saturating dye before PCR followed by rapid melting analysis of the PCR products, the sensitivity of heterozygote scanning approaches 100%. Specificity can be increased by identifying common polymorphisms with small amplicon melting, unlabeled probes or snapback primers to decrease the sequencing burden. However, some homozygotes require mixing for identification. Furthermore, different heterozygotes may produce melting curves so similar to each other that, although they clearly vary from homozygous variants, they are not differentiated from each other. Nevertheless, the experimental return for minimal effort is great. This focus issue of Human Mutation includes a concise, timely review on high resolution melting, a comparison to denaturing gradient gel electrophoresis, integration with qPCR for copy number assessment, combined amplicon scanning and unlabeled probe genotyping from a single melting curve, and applications to the mitochondrial genome and to BRCA1.

A Microforce and Nanoforce Biomicroscope Device for In Vitro Mechanotransduction Investigation

This paper deals with the development of an open design platform for explorative cell mechanotransduction investigation. The produced setup combines scanning probe microscopy (SPM) techniques and advanced robotics approaches, allowing both prolonged observations and spatial measurements on biological samples. As a result, an enhanced force probing method based on scanning microscopy techniques and advanced robotics and automation approaches is integrated in this device. Visual and force feedback control is used to achieve automatic data acquisition and monitoring processes when high skills are required. Experimentation on the mechanical cell characterization under in vitro conditions on human adherent cervix epithelial Hela cells are presented to demonstrate the viability and effectiveness of the proposed setup.

Characterization of cellular mechanical behavior at the microscale level by a hybrid force sensing device

This paper deals with the development of an open design platform for characterization of mechanical cellular behavior. The resulting setup combines Scanning Probe Microscopy (SPM) techniques and advanced robotic approaches in order to carry out both prolonged observations and spatial measurements on biological samples. Visual and force feedback is controlled to achieve automatic data acquisition and to monitor process when high skills are required. The issue of the spring constant calibration is addressed using an accurate dynamic vibration approach. Experimentation on the mechanical cell characterization under in vitro conditions on human adherent Epithelial Hela cells demonstrates the viability and effectiveness of the proposed setup. Finally, the JKR (Johnson, Kendall and Roberts), the DMT (Derjaguin, Muller and Toporov) and Hertz contact theories are used to estimate the contact area between the cantilever and the biological sample.

Combined scanning probe and total internal reflection fluorescence microscopy

Combining scanning probe and optical microscopy represents a powerful approach for investigating structure–function relationships and dynamics of biomolecules and biomolecular assemblies, often in situ and in real-time. This platform technology allows us to obtain three-dimensional images of individual molecules with nanometer resolution, while simultaneously characterizing their structure and interactions though complementary techniques such as optical microscopy and spectroscopy. We describe herein the practical strategies for the coupling of scanning probe and total internal reflection fluorescence microscopy along with challenges and the potential applications of such platforms, with a particular focus on their application to the study of biomolecular interactions at membrane surfaces.

Electronic structure and morphology of organic/metal/organic junctions

We have investigated the electronic structures and morphologies of two organic–metal–organic junctions, relevant for organic bistable devices, photovoltaics, and light emitting devices. Combined photoemission spectroscopy and scanning probe measurements found that in a 3,4,9,10 perylenetetracarboxylic dianhydride bis-benzimidazole (PTCBI)/Ag/Cu-phthalocyanine (CuPc) junction, Ag undergoes a chemical reaction with PTCBI leading to a discontinuous film of Ag clusters. In contrast, Au forms a continuous metal film in the PTCBI/Au/CuPc junction with no observable chemistry occurring. Photoemission spectroscopy suggests that both heterojunctions exhibit barrierless charge recombination leading to very similar functional behavior when integrated in device structures despite significant chemical and morphological differences.

Modeling tip performance for combined STM-luminescence and aperture-SNOM scanning probe: Spatial resolution and collection efficiency

Finite-element simulations of the performance of the tip intended for use in combined aperture-SNOM and the scanning tunneling microscope (STM)-luminescence microscopy are presented. Tip geometry and the role of the opening in the protective metal coating were addressed. It is shown that the tip shape can affect transmittance for the excitation SNOM mode by nearly two orders of magnitude and the metal coating can enhance collection efficiency for the STM-luminescence mode. Desired tip configuration can be chosen based on the interplay between the improving collection efficiency and the deteriorating spatial resolution with increasing opening size.

Modification of single molecule fluorescence close to a nanostructure: radiation pattern, spontaneous emission and quenching

The coupling of nanostructures with emitters opens up ways for the realization of man-made subwavelength light emitting elements. In this article we present an overview of our recent progress in the modification of fluorescence when an emitter is placed close to a nanostructure. In order to control the wealth of parameters that contribute to this process, we have combined scanning probe technology with single molecule microscopy and spectroscopy. We discuss the enhancement and reduction of molecular excitation and emission rates in the presence of a dielectric or metallic nanoparticle and emphasize the role of plasmon resonances in the latter. Furthermore, we examine the spectral and angular emission characteristics of the molecule–particle system. The experimental findings are in excellent semi-quantitative agreement with the outcome of theoretical calculations. We show that the interaction of an emitter with a nanoparticle can be expressed in the framework of an optical nanoantennae and propose arrangements that could lead to the modification of spontaneous emission by more than 1000 times.

Combined Scanning Nanoindentation and Tunneling Microscope Technique by Means of Semiconductive Diamond Berkovich Tip

A combined Scanning Probe Microscope (SPM) - nanoindentation instrument enables submicron resolution indentation tests and in-situ scanning of structure surfaces. A newly developed technique is based on the scanning tunneling microscopy (STM) with integrated Berkovich diamond semiconductive tip. Diamond tips for a combined SPM were obtained using the developed procedure including the synthesis of the semiconductive borondoped diamond monocrystals by the temperature gradient method at high pressure - high temperature conditions and fabrication of the tips from these crystals considering their zonal structure. Separately grown semiconductive diamond single crystals were studied in order to find the best orientation of diamond crystals. Optimal scanning characteristics and experimental data errors were calculated by an analysis of the general functional dependence of the tunneling current from properties of the tip and specimen. Tests on the indentation and scanning of the gold film deposited on the silicon substrate employing the fabricated tips demonstrated their usability, acceptable resolution and sensitivity.

Nanolayer Patterning Based on Surface Modification with Extreme Ultraviolet Light

As predicted by Moore’s Law, [1] the feature size of semiconductor devices reached the 90 nm node in 2004. [2] Presently, research is focused on reaching 32 nm. [3] Unfortunately, standard UV lithography cannot be used at this scale. [3] Thus, several next-generation lithographic techniques have been proposed. [4–7] Work combining scanning probe lithography and self-assembly [8] has demonstrated that a hybridization of topdown and bottom-up techniques may be effective. [9] As photolithography using shorter-wavelength light, such as extreme UV or soft X-rays, is considered to be a leading next-generation lithography technology, a hybrid approach combining extreme UV lithography (EUVL) with bottom-up assembly could be used in the industrial production of microelectronic devices. Polymers have typically been used as templates for this type of hybrid patterning, [10,11] but thinner layers are required to continue to reduce feature sizes via EUVL. Nanolayers of small molecules on silicon consist of only a few atomic layers. As these systems are structurally simple and well ordered, a number of surface science studies have been performed to probe the behavior of these materials during the last several decades. [12] Therefore, they are well understood and are an excellent choice for studying EUV-induced surface modification at the atomic scale. EUV is normally used in the identification of chemical structures or the analysis of chemical environments, but an EUV-induced surface modification is clearly observed for a molecular nanolayer of Cl2 in this work. We report that EUV-induced surface modification can be used to pattern surfaces, resulting in a variety of possible functionalities. As surface modification originates from secondary electrons produced by EUV, it can also occur from primary electrons or photons with shorter wavelengths, suggesting that our concept could be extended to electron-beam (e-beam) and proximity X-ray lithographies.