Combined Scanning Force Microscopy Research Articles

Revisiting the switching characteristics and electroresistance effect in ferroelectric thin film towards an optimized hybrid switching strategy

Combining scanning force microscopy characterization and theoretical modeling, in this work, we performed an in-depth study on the electrical/mechanical switching and electroresistance effect in a BaTiO3 thin film. Correlations of the tip load (bias/force and loading time), the switched polarization magnitude, the surface potential, and the tunnel electroresistance are revealed for both electrical and mechanical switching. It is found that electrical switching (with a maximum bias of 4 V) leads to larger saturated switched polarization and sharper switched domain than mechanical switching (with a maximum force of 6600 nN). Meanwhile, mechanical switching exhibits generally smaller surface potential of the switched domain and a more significant tunnel electroresistance effect. However, the load time-dependence of performance is also more serious for mechanical switching. The different characteristics between electrical and mechanical switching are attributed to the charge injection and the switched domain size, which are believed to further affect the surface potential and the tunnel electroresistance of the thin film. At the end, an optimized hybrid switching strategy, which combines tip force and bias, is proposed and shown to be able to achieve complete polarization reversion, low charge injection, high switch speed, and strong tunnel electroresistance effect.

Micrometer‐sized DNA–Single‐Fluorophore–DNA Supramolecule: Synthesis and Single‐Molecule Characterization

The synthesis of single-fluorophore-bis(micrometer-sized DNA) triblock supramolecules and the optical and structural characterization of the construct at the single-molecule level is reported. A fluorophore-bis(oligodeoxynucleotide) triblock is synthesized via the amide-coupling reaction. Subsequent protocols of DNA hybridization/ligation are developed to form the supramolecular triblock structure with lambda-DNA fragments on the micrometer length scale. The successful synthesis of the micrometer-sized DNA-single-fluorophore-DNA supramolecule is confirmed by agarose gel electrophoresis with fluorescence imaging under UV excitation. Single triblock structures are directly imaged by combined scanning force microscopy and single-molecule fluorescence microscopy, and provide unambiguous confirmation of the existence of the single fluorophore inserted in the middle of the long DNA. This type of triblock structure is a step closer to providing a scaffold for single-molecule electronic devices after metallization of the DNAs.

Combined scanning force microscopy and scanning tunneling spectroscopy of an electronic nanocircuit at very low temperature

The authors demonstrate the combination of scanning force microscopy and scanning tunneling spectroscopy in a local probe microscope operating at very low temperature (60mK). This local probe uses a quartz tuning fork ensuring high tunnel junction stability. They performed the spatially resolved spectroscopic study of a superconducting nanocircuit patterned on an insulating substrate. Significant deviations from the theoretical prediction are observed.

Ethane-Bridged Zinc Porphyrin Dimers in Langmuir−Shäfer Thin Films: Structural and Spectroscopic Properties

This work reports on the structural and spectroscopic properties of ethane-bridged Zn porphyrin dimers (1) in Langmuir-Schäfer (LS) thin films by combining scanning force microscopy (SFM) with film balance, UV-vis absorption, fluorescence, and nanosecond laser flash photolysis measurements. Results show that depending on the surface pressure the Langmuir films of pure 1 can be arranged in two different condensed phases, whereas SFM of the LS films shows characteristic fractal networks constituted by nanoscopic aggregates. The spectral findings agree with a picture in which 1 is apparently present in the anti conformation but aggregated in a sort of H-type structure whose optical features resemble those of the syn conformer. This type of structure is not responsive to light stimuli. By diluting 1 in arachidic acid the porphyrin aggregation is significantly minimized with 1 exhibiting almost exclusively the anti conformation. As a result the LS films become photoresponsive, showing fluorescence emission and triplet-triplet transient absorption.

Combining scanning force microscopy with nanoindentation for more complete characterisation of bulk and coated materials

The mechanical properties of thin films as well as bulk materials can be measured by a variety of different techniques, with nanoindentation being one of the most recent developments in this growing field. By using a depth-sensing indentation method it is possible to obtain quantitative values for the hardness and modulus, and thus gain better insight into the response of a material to controlled deformation at such small scales. However, the calculation of such values from conventional load-displacement curves can prove inaccurate owing to the effects of pile-up and sink-in which invariably occur during the indentation of many types of material and which seriously affect the calculation of residual contact area. This paper addresses the problem and suggests the use of scanning force microscopy (SFM) as a complimentary tool which allows the true residual contact area to be measured. In addition, some experimental results are presented for a variety of bulk and coated materials, these confirming the use of the SFM for obtaining significant additional information concerning the true response of a material to instrumented indentation at a nanometric scale, e.g., elastic/plastic deformation, cracking, phase transformation, pile-up/sink-in effects, etc.

Cantilever probes for SNOM applications with single and double aperture tips

In this paper we introduce a cantilever-based probe concept combining scanning force microscopy (SFM) and scanning near-field optical microscopy (SNOM). Microstructure technology processes are used to fabricate probes with hollow-metal aperture tips of less than 60 nm aperture size integrated in the very end of a cantilever. Probe characterization revealed reproducible optical and mechanical properties for both SFM and SNOM applications. The dependence of the optical transmission of aperture tips on their aperture size was investigated as a function of the polarization state. To determine the lateral resolution in the optical transmission-mode polarization-dependent measurements on micro-fabricated test samples, e.g. grid-like structures, were performed. Preliminary results of the investigation of Garnet samples in a near-field Faraday microscope set-up are presented.

Combined Scanning Force Microscopy and Electrochemical Quartz Microbalance in-Situ Investigation of Specific Adsorption and Phase Change Processes at the Silver/Halogenide Interface

Specific adsorption of halogenides and silver halogenide phase formation was investigated by the combination of electrochemical quartz microbalance measurements (EQMB), topographical in-situ scanning force microscopy (SFM), and in-situ lateral force microscopy (LFM). In-situ LFM can be employed to monitor specific adsorption and, more generally, chemical conversion reactions in submonolayers of atomic species which are inaccessible to topological imaging by SFM. Reorganization of the electrochemical double layer during specific adsorption caused nanotribological changes. Hydrated anions in the outer Helmholtz plain are not locally bonded to a specific site and give low LFM friction values. Specifically adsorbed anions and ion pairs, on the other hand, impede the lateral cantilever translation, resulting in increased friction. EQMB measurements yielded data corresponding to the formation of up to one monolayer of specifically adsorbed cation−halogenide ion pairs. Anodic dissolution of silver to AgO- and th...

Nanostructural characterization of thin-film transistors using a combination of scanning force microscopy and transmission electron microscopy

The nanostructure and morphology of MoTa films deposited on glass substrates as gate metals are studied by combined scanning force microscopy and plan-view transmission electron microscopy (TEM). Hydrogenated amorphous silicon bottom-gate thin-film transistors (TFTs) are used to investigate whether the deposition of each subsequent layer of metal or dielectric is a conformal process. The improvement in the electron mobility of TFTs is discussed in relation to the surface roughness of the bottom-gate metal. The conformability of the nanometer-scale multilayered structure of the TFTs is confirmed by means of cross-sectional TEM. The electron mobility of the TFTs increase with a decrease in the surface roughness of the bottom-gate metal. The improvement in the TFT performance indicates that the smooth surface of the bottom-gate metal is the key factor.

Trapping and Imaging Molecular Dynamics by Combining Scanning Force Microscopy with Topology

Trapping and Imaging Molecular Dynamics by Combining Scanning Force Microscopy with Topology

A look at membrane patches with a scanning force microscope

We combined scanning force microscopy with patch-clamp techniques in the same experimental setup and obtained images of excised membrane patches spanning the tip of a glass pipette. These images indicate that cytoskeleton structures are still present in such membrane patches and form a strong connection between the membrane and the glass wall. This gives the membrane patch the appearance of a tent, stabilized by a scaffold of ropes. The lateral resolution of the images depends strongly on the observed structures and can reach values as low as 10 nm on the cytoskeleton elements of a (inside-out) patch. The observations suggest that measurements of membrane elasticity can be made, opening the way for further studies on mechanical properties of cell membranes.