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Understanding the interactions between a tip apex and a target atom or molecule is crucial for the manipulation of individual molecules with precise control by using scanning tunnelling microscopy (STM) and atomic force microscopy. Herein, we demonstrate the manipulation of target CO molecules on a Cu(111) substrate using a CO-functionalized W tip with atomic-scale accuracy. All experiments were performed in a home-built ultra-high vacuum STM system at 5 K. The CO-tip was fabricated by picking up a single CO molecule from a Cu(111) surface. In contrast to a metal tip, repulsive interactions occur between the CO-tip and the target CO molecule. This repulsive interaction promises perfect lateral hopping without any vertical hopping. Hopping events were directly monitored as sudden current drops in the simultaneously measured I-z curves. A larger barrier height between the CO-tip and the target CO (∼9.5 eV) was found from the slope of the I-z curve, which decreases the electron tunnelling probability between the tip and sample. Therefore, electron-driven manipulation cannot be a major trigger for the CO-CO repulsive manipulation. The CO-tip is able to manipulate only the target CO molecule, even when another CO molecule was located ∼0.5 nm away. Statistical measurements revealed that the nearest neighbour atop site is the energetically stable position after hopping. However, if the CO target has another CO molecule in a neighbouring position (denoted as a 'pair'), the target CO hops more than twice as far. This means that the CO-tip experiences a larger repulsive interaction from the pair. These observations of CO-tip manipulation are useful for the design of two-dimensional artificial molecular networks as well as for developing a better understanding of catalytic oxidation processes.

Normalized differential tunneling conductivities obtained with Fe-coated W tips show a spin-polarized peak around +0.8 V on ultrathin bct Mn films grown on Fe(001)-whiskers. This spin-polarized peak results in a clear magnetic contrast in spectroscopic images. Our normalization removes the influence of the tunneling probability and makes the spectroscopic curves most reliable for a derivation of the spin-resolved sample density of states (DOS) at positive voltages. From this analysis we conclude that the magnetic contrast in our spectroscopic maps is caused by a highly polarized DOS. Furthermore, a tip polarization of about 15% is found.

The control of atomically flat interfaces between iron (Fe) and insulating oxide films, such as the Fe/MgO(001) interface, is crucial for tunnel-magnetoresistance (TMR) devices. However, the realization of an ideal atomically flat and clean interface is rather difficult since iron easily binds to impurities such as oxygen. Atomic step defects and iron oxide at the interface could reduce TMR. In this study, the oxidization of an atomically flat and clean Fe(001)-whisker single crystal at different substrate and annealing temperatures was investigated with an ultrahigh-vacuum scanning tunneling microscope (STM). Annealing up to a temperature of 850 K was required to obtain ordered and atomically flat Fe(001)-p(1×1)O terraces after the oxidization with the coexistence of Fe–O nanoislands (∼1 nm in height, ∼50 nm in size). We found that the growth of such nanoislands, which enhances interface roughness, strongly depends on the substrate temperature (T S) during the oxidization. A T S lower than 300 K reduces the coverage by the nanoislands to less than 10%.

Single molecules have attracted much interest as new materials for future spin electronic devices; however, many open questions still remain. One of them is how the electronic local density of states (LDOS) of single molecules is affected when they are in contact with electrodes. We show a systematic study of the LDOS of π-conjugated phthalocyanine (H2Pc) nanomolecules adsorbed on various electrodes, namely, (1) MgO(001) thin films grown on Ag(001), (2) noble metals of Cu(111) and Ag(001), and (3) 3d magnetic metals of Fe(001) and Mn(001), adupting scanning tunneling spectroscopy techniques with an ultrahigh-vacuum scanning tunneling microscopy setup at room temperature. Since MgO thin films cut the electronic coupling from the substrate Ag(001), we could observe H2Pc molecular states at -1.5 and +1.0 eV. H2Pc molecules on the noble metal substrates form a pattern with a square unit cell of about 1.5×1.5 nm2 and have similar LDOS peaks near the Fermi energy. Strong hybridizations between the substrate 3d spin-polarized states and the molecular π orbitals produce new molecular states of H2Pc molecules adsorbed on Fe(001) and Mn(001) near the energy positions of the Fe(001) minority spin state and the Mn(001) majority spin state, respectively.

Organic nanomolecules have become one of the most attractive materials for new nanoelectronics devices. Understanding of the electronic density of states around the Fermi energy of low-dimensional molecules is crucial in designing the electronic properties of molecular devices. The low dimensionality of nanomolecules results in new electronic properties owing to their unique symmetry. Scanning tunneling spectroscopy is one of the most effective techniques for studying the electronic states of nanomolecules, particularly near the Fermi energy (±1.5 eV), whereas these molecular electronic states are frequently buried by the tunneling probability background in tunneling spectroscopy, resulting in incorrect determination of the molecular electronic states. Here, we demonstrate how to recover nanomolecular electronic states from dI/dV curves obtained by tunneling spectroscopy. Precise local density of states (LDOS) peaks for low-dimensional nanostructures (monolayer ultrathin films, one-dimensional chains, and single molecules) of phthalocyanine (H2Pc) molecules grown on noble fcc-Cu(111) were obtained.

Magnetoelectric coupling at metal surfaces opens up a new possibility for metallic nonvolatile magnetic data-storage devices, in which the magnetic bits are controlled by an electric field. We studied the atomic and magnetic order in bilayer Fe nano-islands grown on a Cu(111) substrate with a scanning tunneling microscopy setup in ultra high vacuum at 4.5 K. Electric field pulses (108–109 V/m) were found to be able to cause a displacement of the Fe atoms, switching simultaneously the crystalline and the magnetic order, which is the prove of magnetoelectric coupling at the metallic Fe surface. We also succeeded in controlling the direction of the switching by the polarity of the electric field.

The atomic and electronic structures at the apex of W tips were studied by means of field ion microscopy and field emission microscopy, before and after the thermal deposition of a 5 nm Fe film. Two geometries of W tip, a conventional hemi-spherical type and a chisel (flat needle) type, were prepared. The hemispherical and the chisel W tips had a 110 direction parallel and perpendicular to the tip axis, respectively. The coated Fe films were found to be most likely in a non-crystalline phase, and to have a lower work function leading to a drastic change in electron emission from the apexes. The spin-polarization vectors of field-emitted electrons from these Fe/W tips were investigated with a Mott detector with a rotatable mechanism of tips. A similar absolute value of the spin-polarization vector was obtained for each Fe/W, while the direction of the spin-polarization vector was dependent on the shape of the apex. The angle from the tip axis was θ=45° for the hemispherical apex and θ=66° for the chisel apex. A spin-polarized scanning tunneling microscopy setup with a rotation mechanism of such Fe/W tips made it possible to detect both the in-plane and the out-of-plane spin component of a sample magnetization.