Scanning Force Microscopy Probe Research Articles

A novel scanning force microscopy probe with thermal-electrical actuation and piezo-resistive sensing

This work presents a novel scanning force microscopy probe with electro-thermal actuation and piezo-resistive detection. The fabricated probe of 270 × 58 × 2.5 μm3 can generate a force between 1.05 μN and 16.52 μN with a resolution of nano-newton, and can detect the nanometer-scale deflection. The minimum detectable output signal of the probe could be down to 20 μV and the sensitivity reaches 4.92 mV μm−1. This is a straight-forward technique for characterizing the mechanical properties of micro/nano-structures and devices.

Interfactant action of an amphiphilic polymer upon directing graphene oxide layer formation on sapphire substrates

Quality assured surface pre-treatment may greatly enhance adhesive interactions and, thus, the performance and durability of material joints. This holds true as well for substrates used in coating processes as for adherents introduced into bonding processes. Wettable polymeric wetting agents—shortly called polymeric interfactants—contribute to modifying surfaces and governing the properties of interphases. This is demonstrated for amphiphilic polymers directing the adsorption of graphene oxide (GO) nano-sheets from aqueous dispersion on alumina surfaces. In this contribution, contact angle measurements as well as X-ray photoelectron spectroscopy and scanning force microscopy investigations are applied for the characterization of thin films. GO is adsorbed either from a buffered dispersion on pristine aluminum oxide surfaces or on alumina modified with a few nanometers thin layer of a polymeric interfactant. Laterally extended nanoparticles and GO nano-sheets are preferentially found on interfactant layers whereas on pristine aluminum oxide smaller adsorbates dominate. The driving forces directing the GO attachment are discussed using a phenomenological model based on polymer/substrate interactions governing the sticking probabilities of GO nano-sheets with different sizes.

A single probe for imaging photons, electrons and physical forces

The combination of complementary measurement techniques has become a frequent approach to improve scientific knowledge. Pairing of the high lateral resolution scanning force microscopy (SFM) with the spectroscopic information accessible through scanning transmission soft x-ray microscopy (STXM) permits assessing physical and chemical material properties with high spatial resolution. We present progress from the NanoXAS instrument towards using an SFM probe as an x-ray detector for STXM measurements. Just by the variation of one parameter, the SFM probe can be utilised to detect either sample photo-emitted electrons or transmitted photons. This allows the use of a single probe to detect electrons, photons and physical forces of interest. We also show recent progress and demonstrate the current limitations of using a high aspect ratio coaxial SFM probe to detect photo-emitted electrons with very high lateral resolution. Novel probe designs are proposed to further progress in using an SFM probe as a STXM detector.

Atomic-Scale Imaging of the Surface Dipole Distribution of Stepped Surfaces.

Stepped well-ordered semiconductor surfaces are important as nanotemplates for the fabrication of 1D nanostructures. Therefore, a detailed understanding of the underlying stepped substrates is crucial for advances in this field. Although measurements of step edges are challenging for scanning force microscopy (SFM), here we present simultaneous atomically resolved SFM and Kelvin probe force microscopy (KPFM) images of a silicon vicinal surface. We find that the local contact potential difference is large at the bottom of the steps and at the restatoms on the terraces, whereas it drops at the upper part of the steps and at the adatoms on the terraces. For the interpretation of the data we performed density functional theory (DFT) calculations of the surface dipole distribution. The DFT images accurately reproduce the experiments even without including the tip in the calculations. This underlines that the high-resolution KPFM images are closely related to intrinsic properties of the surface and not only to tip-surface interactions.

Current distribution and Hall potential landscape towards breakdown of the quantum Hall effect: a scanning force microscopy investigation

We present line- and area-scans of the Hall potential landscape of a two-dimensional electron system (2DES) in narrow (AlGa)As-based Hall bars under quantum Hall (QH) conditions, obtained by low-temperature scanning force microscopy. For several magnetic field values B in the regime of the QH plateau with Landau level filling factor , we measured the evolution of the Hall potential profiles and of the longitudinal voltage drop along the Hall bar as a function of increasing voltage/current bias, leading finally to the electrically induced breakdown of the quantum Hall effect (QHE). Basically two types of evolution were observed: for the low B-field side of the QHE plateau, two distinct Hall potential drops appear close to the two edges of a cross section, equally distributed at low bias but continuously developing to an asymmetrical distribution with increasing bias. At high bias, a steady increase of the longitudinal voltage drop is observed, accompanied by a rising slope of the Hall potential drop in the bulk. For the upper B-field side of the QH plateau, the Hall voltage drops are broadly distributed across the whole cross section, and the distribution remains almost unchanged until the bias reaches a critical value where the Hall potential profile changes rather abruptly, enhancing locally the Hall field. Beyond this, with further increase of the bias, a steep rise of the longitudinal voltage drop is detected. These findings are naturally explained in the microscopic picture of the QHE, based on the self-consistent evolution of the compressible and incompressible landscape inside the 2DES with increasing bias.

Nanostructure characterization by a combined x-ray absorption/scanning force microscopy system

A combined x-ray transmission and scanning force microscope setup (NanoXAS) recently installed at a dedicated beamline of the Swiss Light Source combines complementary experimental techniques to access chemical and physical sample properties with nanometer scale resolution. While scanning force microscopy probes physical properties such as sample topography, local mechanical properties, adhesion, electric and magnetic properties on lateral scales even down to atomic resolution, scanning transmission x-ray microscopy offers direct access to the local chemical composition, electronic structure and magnetization. Here we present three studies which underline the advantages of complementary access to nanoscale properties in prototype thin film samples.

Metrology and microscopic picture of the integer quantum Hall effect

Since 1990, the integer quantum Hall effect has provided the electrical resistance standard, and there has been a firm belief that the measured quantum Hall resistances are described only by fundamental physical constants--the elementary charge e and the Planck constant h. The metrological application seems not to rely on detailed knowledge of the microscopic picture of the quantum Hall effect; however, technical guidelines are recommended to confirm the quality of the sample to confirm the exactness of the measured resistance value. In this paper, we give our present understanding of the microscopic picture, derived from systematic scanning force microscopy investigations on GaAs/(AlGa)As quantum Hall samples, and relate these to the technical guidelines.

Synthesis and aggregation behaviour of amphiphilic block copolymers with random middle block

The effect of microstructure on the aggregation behaviour of symmetrical di- and triblock copolymers P(BMA)-b-P(MAA) and P(BMA)-b-P(BMA-co-MAA)-b-P(MAA) with a molecular weight of 40,000 g/mol was studied. The critical micelle concentration, hydrodynamic radius and morphology of the micelles were determined by fluorescence spectroscopy, dynamic light scattering and scanning force microscopy (SFM). Whereas no effect of the microstructure on the critical micelle concentration could be detected, the hydrodynamic radius decreased from di- to triblock copolymer from 53 to 36 nm. The decrease of about 32% corresponds to the length of the random middle block within the triblock copolymer so that the reduction in hydrodynamic radius was caused by a complete orientation of the random middle block at the core corona interface. Finally, the SFM investigation showed that dehydration of micelles on a substrate is accompanied by formation of a physisorbed monolayer with a thickness of 2 nm on which the micelles are deposited.

Initiation of Sliding of an Elastic Contact at a Nanometer Scale Under a Scanning Force Microscope Probe

A contact between a scanning force microscope Si3N4 probe and a flat surface of similar material is created. The low roughness of surfaces and their mechanical properties allow generating a nanoscopic elastic contact governs by an extended Hertz theory (DMT theory). The behavior of the initiation of sliding is investigated by submitting the contact to lateral sinusoidal displacements whose amplitude increases from zero to a few nanometers. The lateral force generated by the displacement is analyzed by a lock-in amplifier and the in-phase and out-of-phase components are recorded as a function of the displacement amplitude. Experimental results are compared to the Mindlin and Savkoor theories, which describe the initiation of sliding of macroscopic elastic contact. A relatively good agreement between our experiments and these theories is observed. For our particular experimental conditions, i.e., Si3N4 probe sliding on a similar material, the Mindlin’s model gives a slightly better agreement than the Savkoor’s model. This study shows that macroscopic concepts remain valid at the nanoscale, at least for the particular case studied here.

Evaporation based micro pump integrated into a scanning force microscope probe

A micro pump was integrated into a scanning force microscope probe for circulating liquid through its hollow cantilever and tip. The interior cross section of the cantilever was 2.25μm×3.75μm. All fluidic parts were made of SiO2, while the tip apex was made of Si3N4. The key fabrication techniques were silicon wafer bonding and wet-oxidation. The pumping mechanism was relying on the enhanced evaporation at an enlarged water/air interface at the exit of the microchannel. Capillary forces continuously wetted this interfacial area, thus drawing the liquid through the system. At room temperature, a pump rate of 11pls−1 was experimentally evaluated. The observed temperature dependence of the pump rate could be qualitatively understood by a plain model calculation.

SFM studies of carbon ion induced damages in plasmid DNA

In this study we present for the first time detailed scanning force microscopy (SFM) investigations of carbon ion induced damages in plasmid DNA in order to obtain information about the biological effectiveness of particle radiation. For this purpose, we have combined SFM and gel electrophoresis measurements in a dose range between D = 0 Gy and 5000 Gy. After irradiation with C ions, the percentage of double-strand breaks (DSBs) increases drastically, i.e. from initially 0% for D = 0 Gy to 38% for D = 5000 Gy. Increasing the dose over the total range is accompanied by a shortening of the average fragment length from L = 1100 nm to L = 575 nm. In addition to our experiments, the average numbers of induced DSBs per irradiated plasmid and per broken plasmid have been calculated from the SFM measurements. The most important among the numerous results is that a significant amount of plasmids has suffered more than two DSBs for all applied doses, indicating multiple DSBs. The number of DSBs per broken plasmid increases from approximately 1.7 after irradiation with a dose of D = 250 Gy to 3.2 after exposure to the highest dose of D = 5000 Gy. The results provide experimental data for the spatially correlated production of DSBs after carbon irradiation, that are relevant to the understanding of its biological effectiveness.

Magnetic force microscopy sensors using iron-filled carbon nanotubes

Probes for magnetic force microscopy (MFM) were prepared by pinning iron-filled multiwall carbon nanotubes to conventional scanning force microscopy probes. These nanotube MFM probes reveal a great potential for high spatial resolution of both topography and magnetic stray field. The ends of the high aspect ratio iron nanowires within the nanotubes can be considered as stationary effective magnetic monopole moments which opens the possibility of quantitative stray field measurements in a straightforward manner. The carbon shells around the iron nanowires provide wear resistance and oxidation protection.

Self-organized nanofibers from a giant nanographene: effect of solvent and deposition method

We describe the synthesis of the to-date largest soluble nanographene molecule containing 132 carbons in its core and the Scanning Force Microscopy investigation on its self-organization into supramolecular fibers. This alkylated polycyclic aromatic hydrocarbon can grow from solution on solid substrates into fibrils with a length of several micrometers and a cross section of about 16 nm. Making use of different solvents and deposition methods it was possible to achieve a control over the interplay between dewetting and intermolecular π–π stacking, promoting the formation of thermodynamically favoured regular fibrils on mica. On the other hand, under kinetically controlled film growth the formation of ordered supramolecular arrangements at surfaces was hampered. These fibril nanostructures may be useful in the future for the fabrication of molecular nanowires.

Self-Supported Particle-Track-Etched Polycarbonate Membranes as Templates for Cylindrical Polypyrrole Nanotubes and Nanowires: An X-ray Scattering and Scanning Force Microscopy Investigation

Self-supported particle-track-etched polycarbonate membranes with nearly perfect cylindrical pores are used for the preparation of similarly perfect cylindrical polypyrrole nanowires and nanotubes. A complete investigation of the structural properties that result at different stages of the preparation route of polypyrrole nanowires and nanotubes is based on a combination of real and reciprocal space techniques. Nanoporous membranes with nominal pore size ranging from 5 to 150 nm and pore density up to 10(9) pores/cm(2) made from 21-microm-thick polycarbonate films are used. Polypyrrole nanotubes or nanowires are synthesized inside the pores. A real-space picture of the nanomaterial results from scanning force microscopy (SFM) on ultrathin sections made in two directions to obtain structures in the sample surface as well as perpendicular to the surface. From a model-based fit to the small-angle and ultra-small-angle X-ray scattering (SAXS/USAXS) data, the geometric pore structure is obtained and compared to values determined with scanning electron microscopy (SEM). Nanopores, nanowires, and nanotubes are described by uniform solid cylinders or hollow tubes, which are oriented highly parallel to each other and exhibit a small size distribution. Below a critical pore diameter, solid nanowires are produced whereas above this limit hollow nanotubes result.

Injection-moulded scanning force microscopy probes

This paper presents the first production and demonstration of thermoplastic scanning forcemicroscopy cantilevers with integrated tips fabricated via injection moulding. Theirimaging resolution, clarity, and accuracy are equal to conventional silicon-typeparts. The tips exhibit acceptable wear and are ready for use upon removal fromthe injection mould. This work shows the ability to economically mass-produceSFM probes with arbitrary shapes and features, as well as tailorable physical andchemical properties, which until now were limited by the properties of silicon andintegrated-circuit processing technology used to make current commercial SFM probes.

Influence of the solvent on the aggregation of a poly(3-hexylthiophene)–quinquethiophene-S,S-dioxide blend at surfaces: an SFM study

We describe a study on the morphology of thin films processed from equiweight solution blends of the electron donor regioregular poly(3-hexylthiophene) (P3HT) with the electron acceptor 3″-methyl,4″-hexyl-2,2′:5′,2″:5″,2‴:5‴,2′‴-quinquethiophene-1″,1″-dioxide (T5HOM). Spin-coated films supported on a glass/ITO/PEDOT : PSS substrate have been prepared with systematic variation of the type of solvent. Scanning Force Microscopy investigations revealed that, depending on the solvent type, different kinds of complex phase segregated morphologies on the sub-micrometer scale can be obtained. The formation of either lateral or vertical phase segregated structures is primarily governed by the different tendency of the two molecular systems to self-aggregate in the given solvent. A minor role can also be ascribed to an interfacial recognition phenomenon. Among the different architectures obtained, phase separated T5OHM crystals with sizes of hundreds of nanometers embedded in a P3HT grainy amorphous matrix seems to be the most suitable candidate for photovoltaic applications.

Probing the Limits of the Derjaguin Approximation with Scanning Force Microscopy

We have measured the interaction force between a silicon nitride scanning force microscopy (SFM) probe and the basal plane of highly oriented pyrolitic graphite as a function of pH and ionic concentration in aqueous solutions. Forces in the range +/- 50 pN were reconstructed from measured signals using dynamical analysis of the cantilever. We modeled the force-separation data using a flat plate electric double-layer interaction and assumed the Derjaguin approximation to adapt the flat plate geometry for the SFM probe shape. Measured forces were well modeled by the theory at high ionic concentrations (10 and 100 mM), where Debye lengths were 3.0 and 0.96 nm, respectively. The theory failed to model forces at a lower ionic concentration (1 mM), where the Debye length was 9.6 nm. To investigate this, we calibrated the SFM probe geometry using blind reconstruction and obtained an apex radius of 7 nm. This value suggested that failure of the theory was due to an invalidation of the Derjaguin approximation at long Debye lengths, where the characteristic length scale for the interaction was larger than the size of the SFM probe. The errors were reduced by replacing the Derjaguin approximation with a surface element integration. The result experimentally demonstrates the limitations of the Derjaguin approximation for predicting interactions of nanoscale colloids.

Correction of systematic errors in scanning force microscopy images with application to ion track micrographs

Scanning force microscopy (SFM) is capable of imaging surfaces with resolution on a nanometer scale. This method therefore plays an important role in characterizing radiation-induced defects in solids complementing methods like transmission electron microscopy, small-angle X-ray scattering and optical spectroscopy, to name a few. In particular, the SFM inspection of ionic single-crystals irradiated with energetic heavy ions revealed minute hillocks. The aim to determine the size and shape of these ion tracks as a function of parameters such as energy loss gives rise to critically analyze the interaction between SFM probe tip and sample in order to recognize and take into account systematic errors. Such errors originate especially from the finite size of the sensor tip. This work presents both an uncomplicated model of the SFM imaging process and its experimental verification allowing one to quantify the influence of the tip geometry on the recorded micrographs and correct the resulting data accordingly. For this purpose, a computer program was developed, which is able firstly to determine the tip geometry by means of the known geometry of a calibration standard. Secondly, using this tip geometry, the program reproduces the original sample topography containing the radiation damage structures under study. This is illustrated representatively for artificially generated images and also for a sample micrograph recorded on the surface of U-irradiated CaF 2 to prove the efficiency of the suggested procedures. Afterwards, an existing set of images showing the calibration standard 2D200 (NANOSENSORS) is used to classify the average tip shape. Due to the fact that no large variations in this shape occur, the procedure of imaging the calibration standard for each measurement can be replaced by using this average tip for reconstruction. The article concludes with the elimination of systematic errors in existing data sets of hillock diameters recorded on LiF, CaF 2 and LaF 3 after irradiation with swift heavy ions.

Nanoscale dispensing of liquids through cantilevered probes

Nanoscale dispensing is a novel technique to deposit material and create structures at dimensions of 100 nm and below. It has great flexibility in feature shape and choice of deposited material. Due to its potential low cost and lack of time consuming steps, it represents an interesting complementary tool to standard lithographic processes. The key feature of nanodispensing is deposition of liquids through an apertured scanning force microscopy probe tip. In the first experiments, liquid is manually loaded into a hollow pyramidal probe tip. Upon contact of the tip and the substrate, liquid at the end of the tip is transferred to the substrate surface. Moving the sample during contact allows to write features with sizes that can be as small as 100 nm and below, largely dependent on the aperture diameter. This approach is novel, and has recently been demonstrated in our laboratory for the first time, with feature sizes still well above 1 μm.

TEM and SFM investigation of nitrided Ti–1Al–1Mn alloy for medical applications

Investigations of the microstructure and mechanical properties of nitrided Ti–1Al–1Mn alloy were performed. The microstructural analyses were carried out using light microscopy, scanning electron microscopy and transmission electron microscopy (TEM). Phase identifications and chemical compositions of the bulk material and the layers were determined by electron diffraction as well as by energy-dispersive X-ray spectrometry. Scanning force microscopy (SFM) was applied for the alloy surface topography analysis. Microhardness and Young’s modulus measurements as well as scratch tests were performed. The investigations revealed a clear correlation between the nitriding process temperature, surface topography, microstructure, and mechanical properties of the alloy investigated.