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Skyrmion imaging and electrical detection via topological Hall (TH) effect are two primary techniques for probing magnetic skyrmions, which hold promise for next-generation magnetic storage. However, these two kinds of complementary techniques have rarely been employed to investigate the same samples. We report the observation of nanoscale skyrmions in SrIrO3/SrRuO3 (SIO/SRO) bilayers in a wide temperature range from 10 to 100 K. The SIO/SRO bilayers exhibit a remarkable TH effect, which is up to 200% larger than the anomalous Hall (AH) effect at 5 K, and zero-field TH effect at 90 K. Using variable-temperature, high-field magnetic force microscopy (MFM), we imaged skyrmions as small as 10 nm, which emerge in the same field ranges as the TH effect. These results reveal a rich space for skyrmion exploration and tunability in oxide heterostructures.

Magnetic properties of [Co(0.4 nm)/Pt(0.7 nm)]5 multilayers are tailored by controlling the sputtering voltage during the growth of cobalt layers by a facing target cathode. It is shown that increasing sputtering voltage up to 150 V leads to an improved crystalline texture and this results in larger magnetic anisotropies and out-of-plane coercive fields. At a higher cathode voltage of 540 V however crystalline texture quality slightly worsens and this is accompanied by a decrease in the effective anisotropy. Using facing target cathode sputtering, the crystalline structure of the multilayers can be controlled without applying any heat treatment and this can be used to optimize the magnetic properties of Co/Pt multilayers for specific applications.

In this chapter, some other members of the scanning probe microscopy family are briefly described. All probe microscopes are based upon probing tips, but some tips are rather different from standard STM tips. Methods such as scanning near-field optical microscopy (SNOM), scanning ion conductance microscopy (SICM) or photoemission microscopy with scanning aperture (PEMSA), are based on tips with apertures, where light, ions or electrons can pass through. The scanning near-field acoustic microscope (SNAM) is the acoustic analogue of the SNOM. Other methods essentially depend on a standard STM feedback and measure outcoming radiation, as in the case of STM with inverse photoemission (STMiP), or measure the influence of incoming light on the tunneling current, as in the case of laser STM (LSTM), or measure the temperature of the tip, as in the case of scanning thermal microscopy (SThM), or perform measurements in an electrolyte, as in the case of electrochemical STM (ECSTM). In scanning noise microscopy (SNM), the noise of the tunneling current is measured at a compensated thermovoltage. In scanning capacitance microscopy (SCM), the capacitance between probing tip and sample is measured. In scanning potentiometry microscopy (SPotM), the electrical potential, which depends on the resistivity of the sample, is measured. In scanning spreading resistance microscopy (SSRM), the spreading resistance is monitored. Finally, scanning tunneling atom probe (STAP) is an example of the combination of STM with a time-of-flight mass spectrometer, where the mass of single ions from the probing tip can be analyzed.

This chapter reviews the principles and contrast mechanisms of the spin-polarized scanning tunneling microscope (SP-STM) and magnetic exchange force microscope (MExFM) and the application of these instruments to explore spin spirals and skyrmions in materials with Dzyaloshinkii-Moriya interaction.

Magnetic properties of [Co(0.4 nm)/Pt(0.7 nm)] 5 multilayers are tailored by controlling the sputtering voltage during growth of cobalt layers by a facing target cathode. It is shown that increasing sputtering voltage up to 150 V leads to an improved crystalline texture and this results in larger magnetic anisotropies together with increased out-of-plane coercive fields. At a higher cathode voltage of 540 V, however, crystalline texture quality slightly worsens and this is accompanied by a decrease in the effective anisotropy. Using facing target cathode sputtering, the crystalline structure of the multilayers can be controlled without applying any heat treatment and this can be utilized to optimize the magnetic properties of Co/Pt multilayers for specific applications.

High-quality epitaxial Pt _lms are usually grown by molecular beam evaporation (MBE) techniques, where the deposited atoms reach the substrate with typical thermal energies. To obtain a good epitaxial growth, the substrate is kept at elevated temperatures ranging between few hundred to thousand degrees. While the epitaxial quality improves at higher substrate temperatures, above a critical temperature Volmer-Weber growth mode starts and causes a rough _lm morphology. Here, we use a new type of facing target cathode (FTC) to grow Pt onto Al2O3 (0001) substrates. In contrast to conventional sputtering sources, FTC sources provide adatoms with lower kinetic energies, but higher growth rates compared to MBE. In this study, the crystal structure of Pt films is compared for different substrate temperatures. Using FTC, at Pt films with low strain and a morphology that is either nanocrystalline or highly epitaxial could be grown through proper choice of substrate temperature.

High-quality epitaxial Pt films are usually grown by molecular beam evaporation (MBE) techniques, where the deposited atoms reach the substrate with typical thermal energies. To obtain a good epitaxial growth, the substrate is kept at elevated temperatures ranging between few hundred to thousand degrees. While the epitaxial quality improves at higher substrate temperatures, above a critical temperature Volmer-Weber growth mode starts and causes a rough film morphology. Here, we use a new type of facing target cathode (FTC) to grow Pt onto Al 2 O 3 (0001) substrates. In contrast to conventional sputtering sources, FTC sources provide adatoms with lower kinetic energies, but higher growth rates compared to MBE. In this study, the crystal structure of Pt films is compared for different substrate temperatures. Using FTC, flat Pt films with low strain and a morphology that is either nanocrystalline or highly epitaxial could be grown through proper choice of substrate temperature.

Research in new quantum materials requires multi-mode measurements spanning length scales, correlations of atomic-scale variables with macroscopic function, and spectroscopic energy resolution obtainable only at millikelvin temperatures, typically in a dilution refrigerator. In this article, we describe a multi-mode instrument achieving μeV tunneling resolution with in-operando measurement capabilities of scanning tunneling microscopy (STM), atomic force microscopy (AFM), and magnetotransport inside a dilution refrigerator operating at 10 mK. We describe the system in detail including a new scanning probe microscope module design, sample and tip transport systems, along with wiring, radio-frequency (RF) filtering, and electronics. Extensive benchmarking measurements were performed using superconductor-insulator-superconductor (SIS) tunnel junctions, with Josephson tunneling as a noise metering detector. After extensive testing and optimization, we have achieved less than 8 μeV instrument resolving capability for tunneling spectroscopy, which is 5-10 times better than previous instrument reports and comparable to the quantum and thermal limits set by the operating temperature at 10 mK.

A class of artifacts manifesting as soft magnetic components are revealed from magnetometry measurements of rare earth-transition metal (TbFe) thin films prepared by magnetron sputtering. They are not inherent to TbFe, but are a direct result of the manner in which the substrates are mounted prior to sample fabrication, with a material deposited at the substrate sides giving rise to a significant magnetic moment. The authors find the same artifacts to also be present in rare earth-free [Co/Pt] multilayers. Trying to supress the appearance of this type of artifact has an influence on the coercivity and, in some cases, on the shape of the reversal curves. Care needs to be taken during fabrication to ensure reliable and reproducible samples so that sensitive magnetic parameters, such as coercivity and compensation points, can be extracted accurately and that data are not misinterpreted for even more complex systems. This type of artifact is not limited to samples prepared by sputtering but can extend to other conventional thin-film deposition methods.

We report on the design and first tests of a novel instrument aimed at combining the benefits of scanning force microscopy with those of X-ray spectroscopy. For this we built an instrument combining a scanning transmission X-ray microscope with a beam-deflection atomic force microscope in a coaxial geometry. This allows to combine X-ray absorption spectroscopy and high resolution topography in-situ. When replacing the conventional scanning probe tip by a coaxially shielded tip the instrument will allow detection of the photoelectrons produced by resonant X-ray absorption. This could yield spectroscopic information with a spatial resolution approaching the values achievable with atomic force microscopy.

Manipulation experiments have been performed with single molecules of the hydrocarbon propene on a copper(211) surface at 7 K. Depending on the location of the methyl group, propene forms two enantiomorphous pairs of different adsorbate states. Beyond repositioning of the molecules via vertical and lateral manipulations with the STM tip, conversions between the different adsorbate geometries were observed. The role of inelastically tunneled electrons and the electric field in the junction between tip and surface are discussed as origins of adsorbate mode conversion. Copyright © 2010 John Wiley & Sons, Ltd.

Pumped up: Propene molecules form chiral complexes when adsorbed on a copper surface. Inelastically scattered tunneling electrons from the tip of a scanning tunneling microscope induce rotation or diffusion of the adsorbate on the surface. Higher tunneling currents can lead to conversion of the adsorbate into the opposite enantiomer.

This article describes the design of a versatile ultrahigh vaccum (UHV) low temperature scanning force microscope system. The system allows scanning probe microscopy measurements at temperatures between 6 and 400 K and in magnetic fields up to 7 T. Cantilevers and samples can be prepared in UHV and transferred to the microscope. We describe some technical details of our system and present first measurements performed at different temperatures and in various scanning force microscopy operation modes. We demonstrate distortion free and calibrated images at temperatures ranging from 8 to 300 K, atomic resolution on NaCl at 7.6 K and various magnetic force microscopy images of vortices in high transition temperature superconductors. It is demonstrated that our instrumentation reaches the thermodynamically determined sensitivity limit. Using standard cantilevers force gradients in the 10−6N/m range, corresponding forces of about 10−15N can be measured.

A single propene molecule, located in the junction between the tip of a scanning tunneling microscope (STM) and a Cu(211) surface can be dehydrogenated by inelastic electron tunneling. This reaction requires excitation of the asymmetric C-H stretching vibration of the ═CH(2) group. The product is then identified by inelastic electron tunneling action spectroscopy (IETAS).

Magnetic domains of BaFe 12 O 19 have been imaged with a scanning tunneling microscope with a flexible, magnetic tip. We have found that Co and Fe thin films evaporated on a silicon tip, integrated with a cantilever, can give a high lateral resolution of less than 100 nm. We have observed domains 2 μm wide and domain walls 270 nm wide. Changes in the contrast along the domain wall have been observed. We explain the data using existing models.

Impressed by the high resolution and easy operation of the new generation scanning tunneling microscopes (STMs), we built a pocket‐size high‐stability atomic force microscope (AFM) with deflection measurement by tunneling. It was our aim to reach high mechanical and thermal stability of the tunnel junction as well as full compatibility with our existing STM system. Our first AFM scanhead, designed for large scan ranges up to 15 μm, stably measured an artificial grid structure on SiO2, reproducibly showing details of less than 1 nm in size. On this well‐defined sample we compared constant force with variable deflection measurements.

The parallel operation of SFMs has potential in several areas of nanoscale science and technology, such as data storage, lithography, high-speed/large-scale imaging and molecular and atomic manipulation. Minne et al. presented the parallel operation of a 1D array of cantilevers, where the parallel acquisition of images was demonstrated [448]. Ten cantilevers with integrated piezoresistive sensors and zinc-oxide (ZnO) actuators were operated in parallel, with each cantilever scanning a rectangular area of 200 µm x 2 mm A total area of 2 mm x 2 mm of a memory cell in an integrated circuit was imaged in this way. These scan areas are adapted to the needs of the semiconductor industry, where integrated circuit chips of 100 mm2 are common Each cantilever provided a resolution in the nm range with a bandwidth of 20 kHz. The microscope produces such a large amount of data that it is difficult to handle using today’s processing capabilities. These results clearly show new perspectives for microscopy, where large, complex structures are to be investigated on the nanometer scale. Furthermore, new avenues have been opened up in SFM lithography, where patterns on an area of 1 cm2 have been written with line widths in the micron range [448].

Scanning tunneling microscopy (STM) was invented by Binnig and Rohrer (see Fig. 2.1) [2,9]. Using the combination of a coarse approach and piezoelectric transducers, a sharp, metallic probing tip is brought into close proximity with the sample. The distance between tip and sample is only a few angstrom units, which means that the electron wave functions of tip and sample start to overlap. A bias voltage between tip and sample causes electrons to tunnel through the barrier. The tunneling current is in the range of pA to nA and is measured with a preamplifier.1 This signal is the input signal of the feedback loop, which is designed to keep the tunneling current constant during (x, y)-scanning. The output signal is amplified (high voltage amplifier) and connected to the z-piezo. According to the feedback output voltage and the sensitivity of the piezo (typically nm/V) the tunneling tip is moved backwards or forwards and the tunneling current is kept constant during acquisition of the image. This operation mode is called constant current mode.

Summary form only given. The bit size in magnetic recording has reached the resolution limit of presently available magnetic force microscopes. The next generation of magnetic force microscopes are expected to measure the magnetic field quantitatively, obtain a lateral resolution below 10 nm, and achieve a complete separation between topographical and magnetic information.

Magnetic domains of BaFe12O19 have been imagined with a scanning tunneling microscope having a flexible, magnetic tip. We have found that Co thin films evaporated on a silicon tip, integrated with a cantilever, can give high lateral resolution, below 50 nm. Therefore, we have been able to image domains and domain walls simultaneously. We have observed domains of 1.9 μm width and domain walls of 270 nm width. We explained the data using existing models.

Piezoelectric quartz tuning forks have been employed as the force sensor in a dynamic mode scanning force microscope operating at temperatures down to 1.7 K at He-gas pressures of typically 5 mbar. An electrochemically etched tungsten tip glued to one of the tuning fork prongs acts as the local force sensor. Its oscillation amplitude can be tuned between a few angstroms and tens of nanometers. Quality factors of up to 120000 allow a very accurate measurement of small frequency shifts. Three calibration procedures are compared which allow the determination of the proportionality constant between frequency shift and local force gradient based on the harmonic oscillator model and on electrostatic forces. The calibrated sensor is then used for a study of the interaction between the tip and a HOPG substrate. Force gradient and dissipated power can be recorded simultane-ously. It is found that during approaching the tip to the sample considerable power starts to be dissipated although the force gradient is still negative, i.e. the tip is still in the attractive regime. This observation concurs with experiments with true atomic resolution which seem to require the same tip-sample separation.

Piezoelectric quartz tuning forks are investigated in view of their use as force sensors in dynamic mode scanning probe microscopy at temperatures down to 1.5 K and in magnetic fields up to 8 T. The mechanical properties of the forks are extracted from the frequency dependent admittance and simultaneous interferometric measurements. The performance of the forks in a cryogenic environment is investigated. Force-distance studies performed with these sensors at low temperatures are presented.

A set of reference samples for comparing the results obtained with different magnetic force microscopes (MFM) has been prepared. These samples consist of CoNi/Pt magneto-optic multilayers with different thicknesses. The magnetic properties of the multilayer are tailored in such a way that a very fine stripe domain structure occurs in remanence. On top of this intrinsic domain structure, bits were written thermomagnetically using different laser powers. These samples have been imaged in six different laboratories employing both home-built and commercial magnetic force microscopes. The resolution obtained with these different microscopes, tips and measurement methods varies between 30 and 100 nm. ; Full-text of this article is not available in this e-prints service. This article was originally published in Journal of magnetism and magnetic materials, published by and copyright Elsevier.

We currently develop a novel type of scanning x-ray microscope. This instrument will combine the chemical specificity of x-ray absorption spectroscopy with the very high spatial resolution of scanning probe microscopy . In a fundamentally new instrumental approach, the instrument can be used as a conventional scanning transmission x-ray microscope (STXM), as a conventional scanning probe microscope (SPM) or in a mode combining these two techniques. In the latter case, the sample is placed in the focus generated by the fresnel zone plate of the STXM. The SPM-tip placed downstream acts as as a local detector of the emitted photoelectrons. Simulations and experiments have shown that the use of shielded SPM-tips is crucial to obtain a strongly increased chemical resolution. In contrast to similar projects underway at other synchrotrons we use a coaxial geometry. This should greatly enhance the flux density and reduce background signals caused by straylight illuminating the tip.

We employ a template-directed self-assembly process to arrange nanospheres as small as 20 nm in a polymer resist template with regular hole arrays with periods down to 42 nm produced using extreme ultraviolet interference lithography. To demonstrate magnetic probe recording employing magnetic tips, an array of magnetic caps with perpendicular magnetic anisotropy was then created by depositing Co/Pt multilayer films on 60 nm nanospheres, arranged on a square lattice with 100 nm period. The magnetic nanocaps can be switched individually in a controlled fashion, with recognition of a successful switching event realized by measurement of a force-distance curve.

Wrong handedness? No problem! K.-H. Ernst et al. describe in their Communication on page 4065 ff. how the chirality of single adsorbates can be switched into the opposite enantiomeric state. By using inelastically tunneling electrons from the tip of a scanning tunneling microscope in an ultra-high vacuum, certain molecular vibrations are excited that, in turn, cause different actions such as hopping, rotation, and chirality conversion at the surface.

The origin of the exchange bias (EB) effect has been traced back to the existence of pinned uncompensated spins (UCS) in the antiferromagnet (AFM) or at its interface. However, the understanding of the underlying mechanism is still clouded by contradictory reports: For example, both a parallel as well as an antiparallel orientation of the UCS relative to the magnetization direction of the ferromagnet (FM) were reported for similar FM/AFM systems. Here different magnetization histories in magnetometry and magnetic force microscopy measurements are used advantageously to demonstrate the co-existence of pinned UCS that are parallel and antiparallel to the cooling field in metallic (IrMn) and oxidic (CoO) EB systems. We further conclude that the EB effect is mainly a result of pinned interfacial UCS, which are antiparallel to the FM spins.

We report on a method to reproducibly batch fabricate single-crystal silicon cantilevers with dimensions an order of magnitude smaller than conventional cantilevers, i.e., with lengths between 10 and 35μm, a width of 4μm, and a thickness of 0.2μm. The cantilevers are attached to support chips specially tailored for use in a scanning force microscope. The resonance frequencies are0.2 – 2 MHz, the spring constants about 0.05−1N∕m, and the quality factors 1.5−3.0×104. The resulting thermal force noise is 1−2×10−16N∕Hz at room temperature in vacuum. These cantilevers allow an enhancement of the measurement speed of more than one order of magnitude, and 2−5× better force sensitivity. After annealing in ultrahigh vacuum and measuring at liquid helium temperature, the thermal force noise of these cantilevers is expected to be further reduced down to 10−18N∕Hz.

A metal ball supported by a nanometric filiform neck, made by surface diffusion in vacuum, has the potential to be used as an oscillating force detector in scanning force microscopy. Although in most cases, the oscillator is extremely fragile and does not survive the transport from one vacuum chamber to the other, there still remains the possibility that it can be used if fabricated and utilized in situ. With the aim of characterizing the oscillator without breaking the vacuum, we have made a scanning tunneling/force microscope (STM, SFM) with a heating filament for fabrication of the oscillator in a scanning electron microscope (SEM). The formation of the oscillator was observed with the SEM, and then, the tip of the STM/SFM was used for the application of force to verify its feasibility as an oscillator.

We use a high‐vacuum low‐temperature scanning tunneling microscope to study the Abrikosov vortex lattice in NbSe2 at 2.7 K. Vortex lattices imaged with a ferromagnetic Ni tip in an external field show a higher vortex density than lattices imaged with a nonmagnetic tip in the same field. The additional field induced by the Ni tip can be extracted from the vortex density and is found to be about 10 mT, independent of the external field. In zero external field, the Ni tip generates vortices with a density corresponding to 10 mT. The scanning motion of the Ni tip neither affects single vortices, nor the complete vortex lattice. We attribute this to the homogeneity of the tip stray field.

In the last 10 years forces in scanning probe microscopy (SPM) have been an interesting topic with continuing progress. The recently achieved true atomic resolution in dynamic force microscopy in ultrahigh vacuum (UHV) allows a comparison of scanning force microscopy (SFM) with scanning tunneling microscopy (STM) on Si(111)7x7 surfaces. The range of atomic resolution by SFM coincides with the stable tunneling range of STM. Wide area images of a quality comparable to STM have been obtained with a cleaned Si tip on stepped areas of the Si(111)7x7 and on surfaces of ionic crystals. The Magnetic Force Microscope yields new information on the magnetic domain structure of thin magnetic layers and on single flux lines and their pinning in high temperature superconductors. New visions to extend today’s SFM devices to create new sensors and detectors (nano-age mechanics) are discussed.

We have fabricated ultra-small, -fast, and -sensitive single-crystal silicon cantilevers, allowing at least a factor of 10 improvement in sensitivity and a factor of 20-50 enhancement in speed. Two methods allowing a good control of lever length and a miniaturized support chip were developed. These ultra-small cantilevers have excellent mechanical properties and are suitable for use in scanning force microscopes.