Mineharu Suzuki

Effects of humidity and tip radius on the adhesive force measured with atomic force microscopy

Abstract We have developed an ultrahigh vacuum (UHV) atomic force microscope with fibre-optic interferometer. The cleaved (100) surface of the LiF crystal was imaged with atomic resolution in UHV. Force vs. distance measurements were taken in air and in UHV, and the influence of the humidity and of the tip radius of several hundred angstroms on the adhesive force was studied. We observed a tendency for the adhesive force to increase with increase in humidity. We also observed that the adhesive force at constant humidity increased monotonically with increase in the radius of curvature. These adhesive forces were four orders of magnitude smaller than those for a glass sphere of radius several millimetres.

Observation of Atomic Defects on LiF(100) Surface with Ultrahigh Vacuum Atomic Force Microscope (UHV AFM)

We have constructed an atomic force microscope (AFM) operating under an ultrahigh vacuum (UHV). We have imaged the cleaved (100) surface of LiF ionic crystal to clarify the AFMs performance. As a result, for the first time, we have obtained atomically resolved AFM images of atomic defects penetrating the surface. This result seems to suggest that the cleaved LiF (100) surface was imaged under the condition of monoatomic or small cluster tip-sample interaction.

Atomic resolution imaging of InP(110) surface observed with ultrahigh vacuum atomic force microscope in noncontact mode

True atomic resolution imaging of the cleaved semi‐insulating InP(110) surface was demonstrated using an ultrahigh vacuum atomic force microscope (AFM) in noncontact mode. The force gradient acting on the tip was detected by the frequency modulation method. The rectangular lattice could be clearly observed. The image contrast suddenly changed during the scan, which suggests that the noncontact AFM imaging is performed under the condition of nearly monoatomic tip–sample force interaction. Atomic defects have been clearly and reproducibly observed. These results suggest that noncontact AFM has the potential for true atomic‐scale lateral resolution and is quite effective for atomic surface structure analysis in real space.

Development of ultrahigh vacuum-atomic force microscopy with frequency modulation detection and its application to electrostatic force measurement

We succeeded in high resolution force measurements by using a noncontact ultrahigh vacuum-atomic force microscope (UHV-AFM) with frequency modulation (FM) detection. We clearly observed adatoms and corner holes on the Si(111)7×7 reconstructed surface. Then we applied the noncontact UHV-AFM with FM detection to the high resolution measurement of the electrostatic force. We prevented deterioration of the spatial resolution of the topography by isolating the electrostatic interaction from van der Waals interaction. By simultaneous measurements of the topography and electrostatic force on a silicon oxide, a spatial resolution ∼15u2009A of the electrostatic force was achieved.

True atomic resolution imaging with noncontact atomic force microscopy

Abstract With an atomic force microscope (AFM) operating in the noncontact mode in an ultrahigh vacuum (UHV), the InP(110)1 × 1 surface and the Si(111)7 × 7 reconstructed surface were observed. The force gradient acting on the tip was detected by frequency modulation method. Rectangle lattice on the InP(110)1 × 1 surface, the adatoms and the corner holes on the Si(111)7 × 7 surface have been clearly and reproducibly resolved, including the atomic-scale point defects. The motion of the defects was observed on the InP(110) surface at room temperature, but not on the Si(111)7 × 7 surface. These results clearly show that the noncontact UHV AFM has true atomic-scale lateral resolution and is quite effective for atomic surface structure analysis in real space.

Roughness Evaluation of Thermally Oxidized Si(111) Surfaces by Scanning Force Microscopy

We used scanning force microscopy to evaluate the surface roughness of thermally oxidized Si(111). The initial surface, before oxidation, consisted of atomically flat terraces containing monoatomic steps and stepbands. The morphology of 10-nm-thick oxide surfaces formed at 800 to 1200°C was roughly similar to that of the initial surface. It is also revealed that a monoatomic step was retained on a 100-nm-thick oxide layer formed at 1100°C. The surface roughness tended to decrease as the oxidation temperature increased.

Atomically resolved image of cleaved surfaces of compound semiconductors observed with an ultrahigh vacuum atomic force microscope

An atomically resolved image of a cleaved InP(110) surface with an ultrahigh vacuum atomic force microscope (UHV AFM) was obtained under the contact mode for the first time. The rectangular lattice could be clearly observed. The distances and corrugation amplitudes between the protrusions along the [001] and [110] directions are estimated to be 5.8±0.6 and 4.1±0.4 A, and 1.3±0.2 and 0.7±0.2 A, respectively. These results suggest that the UHV AFM has potential for investigating III–V compound semiconductor surfaces on an atomic scale.

Step band structures on vicinal Si(111) surfaces created by DC resistive heating

Abstract DC-heating-induced step bunching is studied using vicinal Si(111) surfaces with different misorientation angles ranging from 1 to 10° toward [ 1 1 2 ¯ ] in an ultrahigh vacuum scanning electron microscope. Although the growth rate depends on the misorientation angle, the bunching structure basically grows in the same manner on the substrates misoriented from 1 to 8°; faceting of the surface into (111) terrace regions and step band regions, and then expansion of terrace regions. The size of the initial facet structure correlates with the misorientation angle; the period of the structure is proportional to the misorientation angle. During heating, step band regions link up with each other forming very straight structures. Thus the surface with parallel step bands is the final form of the DC-heating-induced step bunching. The growth rate of the bunching on 1 and 2° surfaces is much higher than on higher-misorientation-angle surfaces. On a 10° misoriented surface no DC-heating-induced bunching was observed.

Observation of GaAs(110) Surface by an Ultrahigh-Vacuum Atomic Force Microscope

Atomic-resolution imaging of a GaAs(110) surface with an ultrahigh-vacuum atomic force microscope (UHV-AFM) was performed for the very first time. We also observed that the rectangular lattice of the surface is atomically destroyed by sequential scanning. This atomic destruction might be due to the vertical loading force of the probing tip. Furthermore, we observed that the rows of atomic protrusions along the [10] direction were slightly in zigzag, and might be interpreted as quasi-one-dimensional zigzag chains consisting of alternating Ga and As atoms on the GaAs(110). These results suggest that the UHV-AFM has the potential for investigating semiconductor surfaces with dangling bonds on an atomic scale.

Step bunching structure on vicinal Si(111) surfaces studied by scanning force microscopy

We use scanning force microscopy (SFM) to observe the fine structure of the step-bunching region on vicinal Si(111) surfaces in air. A step-band structure is formed by direct-current heating at 1200°C, and then the samples are cooled down to near the (1 × 1)-(7 × 7) transition temperature (Tc). A sub-step-band forms from the side of each step-band to the central region by the step-bunching effect, which depends on the temperature. The surface profile of the step-band changes from flat and slanting to curved. This process can be explained by the fact the Tc is lower for a surface with a larger misorientation angle.