Jun'ichi Kanasaki

Site-sensitive yield of atomic emission induced by laser irradiation on Si(111)−7×7 surface

Abstract The atomic structure of the Si(111)−7×7 surface after irradiation of 2.48 eV laser pulses has been studied using scanning tunneling microscopy. In the range of fluence at which no indication of melting is observed, the examination of more than 300 unit cells on irradiated surface has revealed that the number of vacancies formed at the center-adatom site is much larger than that at the corner-adatom site, showing the strong site-dependent yield of laser-induced atomic emission.

Laser-induced bond breaking of the adatoms of the Si(111)-7 × 7 surface

Abstract Tunneling images of the Si(111)-7 × 7 surface before and after laser irradiation have been compared. Examination of more than 300 unit cells shows that the number of unit cells with missing center adatoms increases by 2.48 eV laser pulse irradiation at fluences slightly above the threshold laser fluence above which the emissions can be detected. No indication of melting is observed in the unit cells with missing adatoms. The results give clear evidence that laser-induced atomic emissions from semiconductor surfaces are electronic and site selective.

Proton energy loss spectroscopy for surface layer analysis in the monolayer regime

Abstract A new technique of surface analysis by means of proton energy loss spectroscopy (PELS) with a high energy resolution is described. It is demonstrated that the present PELS technique is able to detect the particles scattered from the first layer of a Si crystal and from a monolayer thick Au layer evaporated on a Si crystal.

Laser-Induced Electronic Emissions of Si Atoms from Si(100) Surfaces

We have carried out highly sensitive measurements of Si° atoms from the Si(100) surfaces emitted by irradiation with 2.48 eV laser pulses. The results indicate all characteristics of the defect-initiated emissions of electronic origin obtained for the emission of Ga° atoms from GaP and GaAs surfaces: we found that the yield is a superlinear function of the fluence and decreases first rapidly and then slowly as the irradiation with laser pulses is repeated. The emission yield after eliminating the rapidly decaying component is found to be enhanced by deposition of submonolayer Br atoms.

Laser-induced desorption from STM-selected semicondutor sites

Abstract We review recent scanning tunneling microscopy studies of laser-induced site-selective removal of atoms from Si surfaces. We discuss the possible mechanism of the process, which is entirely due to bond scission via electronic excitation. It is pointed out that any bond scission of electronic origin on Si surfaces needs a localized excited state. Experimental results of laser-induced desorption from the Si(111)7×7 surfaces, on which the localized excited state is considered to be formed preferentially at the adatom site, indicate that there is a selectivity for the removal of non-equivalent adatoms. The removal of the outermost layer of the Si(100)2×1 surface reveals an unreconstructed surface, which is more stable against laser irradiation than the outermost surface. Uses of site-selectiveness for surface modification are also described.

The DIET from semiconductor surfaces by excitation of valence electrons

Abstract We discuss the desorption induced by electronic transitions (DIET) of constituent atoms from several types of non-metallic solids, particularly the DIET from semiconductors by valence electron excitations. We first classify the non-metallic solids into type A, in which no self-trapping of excitons occurs, and type B, in which self-trapping occurs. We argue that in type B solids the localization of electron-hole pairs or excitons through the self-trapping on the surfaces induces the Menzel-Gomer-Redhead-type anti-bonding state resulting in DIET. For the DIET from type A non-metals, typically semiconductors, in which the self-trapping is not induced, we derive two important characteristics: (1) the emission is related to defects on the surfaces and (2) single electronic excitation cannot induce the emissions. The recent experimental observations of laser-induced emissions satisfying these characteristics for the DIET from semiconductors are surveyed. Furthermore we present experimental evidence demonstrating that the observed emissions are of the electronic origin: the emission occurs dominantly when the excitation is localized on the surface. Finally, surface phenomena, such as laser ablation and dry etching, related to the DIET from semiconductors, and the applications of the DIET from semiconductors are discussed.

Defect initiated particle emission from semiconductor surfaces by laser irradiation

Abstract We review current studies of high sensitivity measurements of laser-induced emission of Ga atoms from GaP and GaAs surfaces, emphasizing its application to characterization of defects on surfaces and to studies of the reactions of defects with adsorbates of small coverage.

Photon energy dependence of the laser-induced emission yield of Si atoms from the Si(100) surface

We have carried out measurements of the temperature dependence of the emission yield of Si atoms from the Si(100) surfaces induced by nanosecond laser pulses of several photon energies. The yield is plotted as a function of , where is the photon energy and is the band-gap energy at temperature T where the yield is measured. We find that the Si emission yield is within the noise level for E = 0.9 - 1.15 eV (region I), increases to a saturation level for E = 1.15 - 1.42 eV (region II) and increases further for E = 1.42 - 2.15 eV (region III). The results are compared with those for GaP, GaAs and InP.

Defect-initiated atomic emissions from semiconductor surfaces induced by laser irradiation: electronic cleaning of defects on surfaces

Abstract We compare the emission of Si atoms from Si (100) surfaces and of Ga atoms from GaAs (110) and GaP (110) surfaces induced by irradiation with low-fluence laser pulses, each of which emits atoms of about 10 -6 monolayers, and found a strong correlation between the laser fluence that can cause emission and the strength of the bond by which the emitted atoms are bound.

High-resolution analysis of protons scattered from solid surfaces

Abstract A survey is given for new information that can be obtained by high energy-resolution analysis of protons backscattered from solid surfaces: layer-by-layer analysis of composition, atomic and electronic structures of surfaces. Optimization of the scattering yield leads to the result that scattering geometries of both glancing angle (PELS-I) and 180° (PELS-II) are feasible. Results obtained by PELS-I are mainly described: Au atom location for Au/Si(111) and surface contraction of W(111). The impact parameter-dependent inelastic energy loss function is mentioned.