Hitoshi Ueyama

Defect Motion on an InP(110) Surface Observed with Noncontact Atomic Force Microscopy

With an atomic force microscope operating in the noncontact mode in an ultrahigh vacuum, atomic-resolution imaging of the cleaved semi-insulating InP(110) surface has been achieved. By this method, atomic scale point defects and their motion were observed at room temperature, without the field-induced effects associated with scanning tunneling microscopy.

Atomically Resolved InP(110) Surface Observed with Noncontact Ultrahigh Vacuum Atomic Force Microscope

Atomic resolution imaging of the cleaved InP(110) surface was demonstrated using an ultrahigh vacuum atomic force microscope (UHV-AFM) in a noncontact mode, for the first time. The force gradient acting on the tip was detected by the frequency modulation (FM) detection method. A rectangular lattice could be clearly resolved. Atomic defects were also clearly and reproducibly observed. These results suggest that the noncontact UHV-AFM has potential for imaging III-V compound semiconductor surfaces with true atomic-scale lateral resolution.

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.

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.

Detection mechanism of an optical evanescent field using a noncontact mode atomic force microscope with a frequency modulation detection method

By using the noncontact atomic force microscope with a frequency modulation detection method, the force gradient induced by the optical evanescent field was detected in a high vacuum. We succeeded in measuring the exponential distance dependence of the force gradient induced by the optical evanescent field. Furthermore, we investigated the incident beam intensity and bias voltage dependence of the force gradient induced by the optical evanescent field. We confirmed that the detection mechanism is not photothermal effect but the surface photovoltage effect.

Contact and non-contact mode imaging by atomic force microscopy

Abstract An atomic force microscope (AFM) with an optical interferometer method works as an atomic-scale corrugation microscope, while an atomic force/lateral force microscope (AFM/LFM) with an optical lever deflection method works as a two-dimensional frictional force microscope (2D-FFM) with an atomic resolution. Using an ultrahigh-vacuum AFM with an optical interferometer method, we demonstrated true atomic resolution imaging of the cleaved InP(110) surface in non-contact mode. Then, using a 2D-FFM in air, we studied the two-dimensional nature of friction by measuring the atomic-scale friction of a Si3N4 tip in contact with cleaved sample surfaces such as MoS2, graphite and NaF(100). As a result, we confirmed the existence of the two-dimensionally discrete friction with a lattice periodicity. Besides, using a two-dimensional stick-slip model, we managed to explain the tip trajectory quantitatively induced by the two-dimensionally discrete friction with a lattice periodicity.

Atomic-Resolution Imaging of ZnSSe(110) Surface with Ultrahigh-Vacuum Atomic Force Microscope(UHV-AFM).

The first demonstration of atomic-resolution imaging of a GaAs(HO) surface with an ultrahigh vacuum atomic force microscope (UHV-AFM) was performed. We also observed that the rows of the protrusions along [110] direction were slightly in zigzag, which might be interpreted as quasi-one-dimensional zigzag chains consisting of alternating Ga and As atoms on the GaAs(llO). This result suggests that the UHV-AFM has potential capability for observing the semiconductor surfaces having dangling bonds on an atomic scale. We further observed that the rectangular lattice of the surface was atomically destroyed by the sequential scanning. This destruction might be induced by the overload due to the vertical force of the probing tip.

Contrast of Atomic-Resolution Images from a Noncontact Ultrahigh-Vacuum Atomic Force Microscope

Contrast variations of atomic-resolution images were investigated on an InP(110) surface using an ultrahigh-vacuum atomic force microscope (UHV-AFM) in the noncontact mode. The contrast of the atomic-scale AFM image suddenly changed during scanning, which seems to be due to the positional change of the atoms on the tip apex. We observed atomic-scale point defects. These phenomena seem to occur only in monoatomic tip-sample interaction. We also observed an atomic-scale dark area which seems to be due to the convolution of the atomically flat tip and point defects.

True Atomic Resolution Imaging on Semiconductor Surfaces with Noncontact Atomic Force Microscopy

The constant vibration mode and the constant excitation mode in noncontact atomic force microscopy were compared to investigate the force interaction between tip and surface. As a result, we found that the constant excitation mode is much more gentle than the constant vibration mode. We also succeeded in atomic resolution imaging on InP(110) surface not only in the noncontact region but in the contact region for the first time. Furthermore, we found the discontinuity of the force gradient curve on reactive Si(111)7×7 reconstructed surface. We proposed a model to explain the discontinuity with the crossover between the physical and chemical bonding interaction.

Measurement of the evanescent field using noncontact mode atomic force microscope

Using the noncontact mode atomic force microscope (AFM) with frequency modulation detection method, force gradient acting on the AFM tip induced by the evanescent field was measured in a high vacuum. Exponential distance dependence of the force gradient by the evanescent field was successfully measured for the first time. Decay lengths of the force gradient were estimated to be 40±3 nm and 43±3 nm for Ar and He-Ne lasers, respectively, and independent of wavelength within the experimental error. The minimum detectable force was estimated to be about 0.1 pN. There was a tendency for the measured decay length to become shorter at a distance less than z=10 nm in many cases. The force gradient induced by the evanescent field inp-polarization was larger than that ins-polarization.