Barrier height imaging of Si(1 1 1)3 × 1-Ag reconstructed surfaces

We investigated the bias voltage polarity dependence of atomically resolved barrier height (BH) images on Si(1 1 1)3 × 1-Ag surfaces. The BH images were very similar to scanning tunneling microscopy (STM) images in both the empty and filled states. This similarity strongly supports the interpretation that the BH image reflects the vertical decay rate of the surface local density of states (LDOS). Differences in contrast and protrusion shapes between BH and STM images were observed. We attributed these differences to the geometric contribution to the STM image and to the improved spatial resolution of the BH image due to the lock-in technique.     

Study of high- lying states in 147Eu

The high-spin states of ¹⁴⁷Eu have been studied in the reaction ¹³⁹La(¹³C, 5n)¹⁴⁷Eu at a beam energy of 98 MeV. Based onthe in-beam measurements ofγ-γ-t coincidences and γ-ray angular distributions, the level scheme of ¹⁴⁷Eu has been extended from 4174 keVup to 8137 keV in excitation energies. A zeroth-order approximation of weak coupling model was applied to explain the observed level structure of ¹⁴⁷Eu.     

Multi-quasiparticle excitations in145Tb

High-spin states in¹⁴⁵Tb have been populated using the¹¹⁸Sn (³²S, 1p4n) reaction at beam energy of 165 MeV. The level scheme of¹⁴⁵Tb has been established up toEx≈7.4 MeV. The level scheme shows characteristics of a spherical or slightly oblate nucleus. Based on the systematic trends of the level structure in the neighboringN=80 isotones, the level structure in¹⁴⁵Tb below 2 MeV excitation is well eplained by coupling anh _11/2 valence proton to the even-even¹⁴⁴Gd core. Above 2 MeV excitation, most of the yrast levels are interpreted with multi-quasiparticle shell-model configurations.     

Fourier transform microwave spectroscopy of 1,1-dimethylsilacyclobutane. Interplay of two types of large-amplitude motions: two-top internal rotation and ring puckering

1,1-Dimethylsilacyclobutane, abbreviated as DMSCB, was investigated by Fourier transform microwave spectroscopy, by paying special attention to two types of large-amplitude motions in the molecule: two-top internal rotation and four-membered ring puckering and also to the coupling between the two. In order to clarify the unique feature of the internal dynamics in DMSCB in detail, two independent approaches were employed, one being a combination of a standard two-top theory of internal rotation and an established theory of ring puckering and the other a theory of large-amplitude motions developed by Hougen and his collaborators. In accordance with predictions by the two approaches based on symmetry consideration, the observed rotational spectra were found split into eight (or six when AE/EA lines were not resolved) components, which were assigned to the two-top states of AA, AE, EA, and EE symmetry, each being further split by puckering into two: the symmetric and antisymmetric states. The analyses by two approaches gave spectroscopic results, which were in good agreement with each other. The spectroscopic data on the normal species, combined with those on Si and C isotopic species, yielded molecular structure parameters including the puckering angle (the dihedral angle between the CSiC and CCC planes) of 28.64° or 30.26° (two possible sets). The splitting between the two lowest puckering states was determined to be 11.90(22) MHz, which led, with the equilibrium puckering angle, to the potential barrier to puckering of 395.3 or 347.0 cm⁻¹ for the two sets, respectively, which was slightly lower than the value 440 cm⁻¹ in a “parent” molecule: silacylcobutane. The first-order terms of the coupling between CH₃ internal rotation and overall rotation were converted to the barrier to internal rotation of 567.8 and 505.1 cm⁻¹ in the AE (two methyl groups rotating in the same direction, as viewed from Si) and EA (two methyl groups rotating in the opposite direction) states, respectively, which corresponded to the torsional frequencies of 154 and 144 cm⁻¹, at variance with the Raman data of 177 and 172 cm⁻¹, previously reported in literature.     

H2 dissociative adsorption at the armchair edges of graphite

We investigate and discuss how hydrogen behaves at the edges of a graphite sheet, in particular the armchair edge. Our density functional theory-based calculations results show that, in contrast to the zigzag edge [W.A. Diño, H. Nakanishi, H. Kasai, T. Sugimoto, T. Kondoe, e-J. Surf. Sci. Nanotech. 2 (2004) 77. [25]], regardless of orientation, there is an activation barrier hindering H₂ dissociation at the armchair edges. And once they do get dissociatively adsorbed at the armchair edges, we find that it would be extremely hard to desorb the H from their adsorption sites at the armchair edges. Furthermore, we also found that, consistent with our earlier conclusions [W.A. Diño, Y. Miura, H. Nakanishi, H. Kasai, T. Sugimoto, J. Phys. Soc. Jpn. 72 (2003) 1867. [24]], it is unlikely that we would find a whole H₂ in between plain graphite sheets.     

First-principles calculation of defect formation energy in chalcopyrite-type CuInSe2, CuGaSe2 and CuAlSe2

In order to quantitatively evaluate the formation energies of Cu, In/Ga/Al and Se vacancies in chalcopyrite-type CuInSe₂ (CIS), CuGaSe₂ (CGS) and CuAlSe₂ (CAS), first-principles pseudopotential calculations using plane-wave basis functions were performed. All calculations were performed using a supercell with 64 atoms, which was eight times greater than the number of atoms in a primitive cell with eight atoms. The formation energies of point defects were calculated as a function of the atomic chemical potentials of constituent elements. Atomic arrangements around the vacancy were optimized allowing relaxation of the first- and second-nearest-neighbor atoms of the vacancy. The obtained results were as follows: (1) the formation energy of Cu vacancy was smaller than those of the other vacancies in CIS, CGS and CAS. Under the Cu-poor condition, the formation energy of Cu vacancy in CIS was lowest among those in them; (2) the formation energy of Se vacancy in CIS was relatively lower than those in CGS and CAS; (3) the formation energy of (2V_Cu+In_Cu) pair in CIS was greatly dependent on the chemical potential of the constituent elements, i.e. Cu, In and Se. On the other hand, the formation energies of (2V_Cu+Ga_Cu) in CGS and (2V_Cu+Al_Cu) in CAS were not largely dependent on the chemical potential of the constituent elements. Under the Cu-poor condition, the formation energy of (2V_Cu+In_Cu) pair in CIS was much lower than those of (2V_Cu+Ga_Cu) in CGS and (2V_Cu+Al_Cu) in CAS.     

Nuclear Spin Maser Oscillation of 129Xe by Means of Optical-Detection Feedback

We have developed the nuclear spin maser oscillating at a low frequency of 34 Hz with highly polarized nuclear spins of the noble gas element ¹²⁹Xe. The system is advantageous for detecting a small frequency shift of the nuclear spin precession. We are thus planning to apply this system to the search for an atomic electric dipole moment of ¹²⁹Xe. We here report the development of the system and its performance.