ALBERT

Notes: Ultrafine nickel particles have intriguing physical and chemical properties, which are interesting both in fundamental and applied research. The size of the particle was controlled by gas pressure. X-ray diffraction studies showed that fine Ni particles have fcc crystal structure and are coated with thin Ni oxide on the surface. Electron micrographs showed a spherical particle shape, forming a long chain. Size dependence of magnetic properties were studied. The specific magnetic moment drastically decreases when reducing the diameter d of particles 〈15 nm. The coercivity Hc also approaches zero when d is about 15 nm. Therefore, we can suppose that the critical size for superparamagnetism at room temperature is about 15 nm. According to the superparamagnetic formula KV=25 kT, the value of the magnetic anisotropy constant can be determined, K = −5.8 × 105 (erg/cc). It is found to be larger than bulk Ni [K=−3.4–5.1 × 104 (erg/cc)], the same as Fe particles. The maximum of coercivity at room temperature is about 250 Oe, that is less than the theory value for the coherent rotation model, Hc = 4 K/3Ms=1600 Oe. The mechanism of reversal magnetization can be understood by the sphere chain model. The critical diameter of the single domain is about 65 nm. Curie temperature Tc obviously decreases for 9-nm average diameter particles rather than bulk. It may be in connection with the lattice contraction.

Notes: The fundamental complex susceptibilities χ=χ'−jχ‘ are calculated from the symmetric critical-state hysteresis loops M(H) for an infinitely long hard superconductor with a rectangular cross section 2a×2b (a≤b). For the critical-state model, the Bean, the Kim, the exponential law, and the triangular-pulse local-internal-field-dependent critical-current densities Jc(Hi) are chosen. The results of χ' and χ‘ are given as functions of the field amplitude Hm normalized to the full-penetration field Hp, the sample dimensional ratio a/b, and the p parameter that characterizes the Hi nonuniformity in the sample at H = Hp on the initial M(H) curve. χ‘(−χ') curves are also given for the different functional Jc(Hi) and other conditions. These theoretical critical-state susceptibilities are particularly useful in the study of sintered high-Tc superconductors. For these materials, the procedures to determine the effective grain volume fraction f*g and the averaged and the local intergranular critical-current densities 〈Jc〉acs and Jc(Hi) by means of ac susceptibility measurements using such theoretical critical-state-susceptibility functions are described. Related problems met in the high-Tc superconductor study such as sample performance nonuniformity, frequency dependence, grain clusters, and susceptibilities for the grains are discussed.

Notes: We report on the first study of N+-implanted silicon on insulator by energy-filtered imaging using an Opton electron microscope CEM 902 equipped Castaing–Henry electron optical system as a spectrometer. The inelastic images, energy window set at ΔE=16 eV and ΔE=25 eV according to plasmon energy loss of crystal Si and of silicon nitride respectively, give much structure information. The interface between the top silicon layer and the upper silicon nitride layer can be separated into two sublayers.

Notes: The solvation dynamics of acetonitrile were characterized by a time resolved fluorescence shift measurement determined via the fluorescence upconversion technique. The solvation response is clearly two part in character. The fast initial relaxation accounts for ∼80% of the amplitude and is well fit by a Gaussian of 120 fs FWHM, giving a decay time of 70 fs. The slower tail is exponential with a decay time of ∼200 fs. Comparison of the results to molecular dynamics simulations performed by Maroncelli [J. Chem. Phys. 94, 2085 (1991)] reveal the fast initial part of the solvent response arises from small amplitude inertial rotational motion of molecules in the first solvation shell. The implications of a large amplitude, rapid inertial Gaussian component in the solvent response for theoretical descriptions of chemical reaction dynamics in solution are discussed.

Notes: We introduce a novel spectroscopic technique which utilizes a two-pulse sequence of femtosecond duration phase-locked optical laser pulses to resonantly excite vibronic transitions of a molecule. In contrast with other ultrafast pump–probe methods, in this experiment a definite optical phase angle between the pulses is maintained while varying the interpulse delay with interferometric precision. For the cases of in-phase, in-quadrature, and out-of-phase pulse pairs, respectively, the optical delay is controlled to positions that are integer, integer plus one quarter, and integer plus one half multiples of the wavelength of a selected Fourier component. In analogy with a double slit optical interference experiment, the two the two pulse experiments reported herein involve the preparation and quantum interference of two nuclear wave packet amplitudes state of a molecule.These experiments are designed to be sensitive to the total phase evolution of the wave packet prepared by the initial pulse. The direct determination of wave packet phase evolution is possible because phase locking effectively transforms the interferogram to a frame which is referenced to the optical carrier frequency, thereby eliminating the high (optical) frequency modulations. This has the effect of isolating the rovibrational molecular dynamics. The phase locking scheme is demonstrated for molecular iodine. The excited state population following the passage of both pulses is detected as the resultant two-beam dependent fluorescence emission from the B state. The observed signals have periodically recurring features that result from the vibrational dynamics of the molecule on the electronically excited potential energy surface. In addition, coherent interference effects cause the magnitude and sign of the periodic features to be strongly modulated. The two-pulse phase-locked interferograms are interpreted herein by use of a simple analytic model, by first order perturbation theory and by quantum mechanical wave packet calculations. We find the form of the interferogram to be determined by the ground state level from which the amplitude originates, the deviation from impulsive preparation of the wave packet due to nonzero pulse duration, the frequency and anharmonicity of the target vibrational levels in the B state, and the detuning of the phase-locked frequency from resonance. The dependence of the interferogram on the phase-locked frequency and phase angle is investigated in detail.