A method to pattern Pd over-layers on GdMg films and its application to increase the transmittance of metal hydride optical switches

A process to pattern Pd over-layers on reactive metal films was developed using ion milling through a tungsten trioxide mask patterned by photolithography and wet etching. The WO₃ mask exhibited a low Ar⁺ sputter yield and, unlike conventional mask materials (SiO₂, Si₃N₄), was easily etched in a mild alkaline solution. This procedure was applied to convert a 20-nm Pd cap over a 160-nm GdMg film to a Pd grid with ≈9-μm-diameter openings covering ≈40% of the surface. The Pd grid proved sufficient to catalyze the (de)hydriding reactions required to reversibly switch the GdMg film from reflecting to transparent. The maximum transmittance of the patterned Pd/GdMg hydride bi-layer was twice that of an otherwise identical sample with a continuous Pd cap, with similar hydriding kinetics. Received: 2 May 2000 / Accepted: 9 May 2000 / Published online: 13 September 2000     

Direct measurement of bonded film thickness of A20H lubricant

Currently the bonded lubricant thickness is measured either by Fourier transform infrared spectroscopy (FTIR) or electron spectroscopy for chemical analysis (ESCA) on the remaining lubricant after using fluorocarbon solvent like Vertrel to rinse off the mobile lubricant from magnetic disk surfaces. As the thickness of the lubricant applied on a disk approaches to its molecular dimension (～10 Å), the current measurement methods face tremendous challenges in achieving the desired levels of accuracy and sensitivity. We propose a new method that makes use of a time-of-flight mass spectrometry (TOF-SIMS) to directly measure the bonded film thickness of A20H lubricant by quantifying the ratio of either the hydroxyl end-group or the phenoxy portion of the cyclotriphosphazene end-group with respect to their respective neighboring backbone fragments. The quantified ratios include C₂F₃/CF₂CH₂OH and C₆F₃O/CF₃C₆H₄ measured in the positive polarity and C₂F₃O/OCF₂CH₂OH, and C₇F₅/CF₃C₆H₄O₂H₂ measured in the negative polarity. The transfer function from the quantified ratios to the bonded lubricant thickness (t) is given in the form of t=α×ln?(100×R _T )?β, where α,β are constants for a selected ratio and R _T represents the quantity of the specific ratio. The results correlate very well with the FTIR method currently used in the measurement of the magnetic media during production (R ²>90). The new method can complete the measurement of the bonded lubricant thickness in a one-step process and it has a much higher spatial resolution at sub-micrometers than that of the FTIR or ESCA with order of a few tens of micrometers in resolution. The quantified ratio obtained from this TOF-SIMS technique makes the imaging of the localized bonded lubricant possible, which can be applied in the magnetic media failure analysis.     

Laser-induced local dehydroxylation on surface-oxidized silicon substrates: mechanistic aspects and prospects in nanofabrication

Processing of silicon oxide surfaces with a focused laser beam at a wavelength of 514 nm has been investigated. Laser processing of native silicon samples (d _ox=1–2 nm) allows the fabrication of reactive templates with laterally varying hydroxyl group density. Very similar results were also obtained on thermally oxidized silicon samples (d _ox≈100 nm), whereas respective experiments on quartz plates have failed. These results support a photothermal mechanism where laser irradiation causes a local temperature rise and initiates dehydroxylation. In agreement with a photothermally induced dehydroxylation reaction, a thermokinetic analysis of the experimental data points to a highly activated process. In conjunction with site-selective functionalization routines this opens up an avenue towards functional surface structures with lateral dimensions significantly below the optical diffraction limit.     

Excitation wavelength dependent pump–probe signatures of molecular crystals

The photodynamics of single crystals of 4-(diisopropylamino)benzonitrile (DIABN) have been studied by femtosecond UV/Vis and mid-IR absorption spectroscopy. The observed spectroscopic response, especially in the UV/Vis, strongly depends on the optical excitation conditions. For the excitation light in resonance with the absorption of DIABN, broad and structureless transient spectra are observed, which decay non-exponentially within pico- to nanoseconds. For off-resonance excitation in the very red wing of the absorption band a stimulated emission signal is detected, which decays in ∼10 ps matching the known behavior of the non-interacting chromophore in solution. The 10 ps decay is due to an intramolecular charge transfer process which is supported by femtosecond IR spectroscopy. The observed dependence on the excitation wavelength is assigned to a change in the density of excited chromophores and therefore bears relevance for time resolved X-ray diffraction experiments.     

A density-functional study of aluminium,iron, zirconium and cerium microclusters

The geometries and electronic structural properties of AB and ABC (A, B, C = Al, Fe, Zr, Ce) microclusters have been systematically investigated by using a hybrid density-functional method (B3LYP) approach. The spectroscopic constants of ground-state AB and ABC (A, B, C = Al, Fe, Zr, Ce) are obtained, and are found to be in agreement with other available experimental and theoretical results. The calculated gaps between highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) are clearly changed when X is doped into the AB dimers (X = Al, Fe, Zr, Ce). The calculated results indicate that a triangular form with D_3h, C_2v or C_s symmetry is the most stable for the corresponding ABC trimers, and, in addition, the possible isomers (linear structure) with D_∞h or C_∞v symmetry of three-atom clusters were found to be of higher energies. We conclude that AlFe and Al₂Fe have the highest chemical stability of all the AB dimers and ABC trimers, respectively, due to the high HOMO-LUMO gap. We also find that the binding energy of Ce₃ is the largest in magnitude among all ABC (A, B, C = Al, Fe, Zr, Ce) trimers, as is the case with Ce₂ among all AB (A, B, C = Al, Fe, Zr, Ce) dimers. The most stable geometry, charge transfer and possible dissociation channels are also discussed.     

Low voltage electro-optic polymer light modulator using attenuated total internal reflection

An improved electro-optic (EO) polymer light modulator based on attenuated-total-internal-reflection (ATR) is demonstrated. The modulator consists of a prism–metal–EO-polymer–metal multilayer structure. An applied electric field across the EO polymer layer electrically modulates the energy coupling efficiency of incoming light into guided wave resonance at fixed angles. Compared with conventional ATR modulators based on surface plasmon resonance, the driving voltage for this modulator has been greatly reduced because of the newly chosen working interior angle. It also offers advantages in terms of insertion loss and aperture size over other techniques for the amplitude modulation of a collimated light beam.     

相伴于平方根算子的Hp空间

本文利用椭圆算子的平方根所生成的热核给出了Hp空间的极大函数刻画.     

Isotopic effects on the control of molecular handedness of H 2 POSH by ultrashort laser pulses

The selective preparation of an enantiomer starting from a pure state of H₂POSH representing a 50%:50% mixture of two enantiomers with opposite chiralities is extended to its deuterated counterpart, H₂POSD. A one-dimensional model involving the torsional angle of S-H/D around a pre-oriented P-S axis is used. The design of an appropriate sequence of ultrashort infrared laser pulses to achieve molecular handedness for H₂POSH/D is based on the characteristic level splitting and tunneling times of both molecules. A simple scheme of two linearly polarized laser pulses involving a three level system serves to convert the different isotopomers to opposite enantiomers, for any given mixture of H₂POSH and H₂POSD molecules. Received 31 August 2000 and Received in final form 23 November 2000     

Effects of an avoided crossing on linewidths of resonances in the H2 i3Π g state

We have investigated the influence of nonadiabatic effects on the linewidths of quasi-bound rovibrational levels in the i³ _g state of molecular hydrogen. This state has a potential barrier due to the interaction of then=3³ _g Rydberg series and the Q1³ _g valence state. The radial coupling with the higher lying³ _g states has been modelled into a diabatic problem. The widths of thev=4 and 5 levels, a measure for their lifetimes, have been determined both in the adiabatic i³ _g potential, and in the two-state system. The results show small shifts of the i³ _g (v=4,5;N=1) levels of a few wavenumbers, and a significant increase of 49% in the lifetimes of these levels. Both effects are large enough to be important in spectroscopic experiments. The magnitude of the effect is in accordance with observed linewidths obtained in recent experiments. Model calculations for differently shaped potential barriers have been carried out to study the generality of the above conclusions.     

Large-area metallic photonic crystal fabrication with interference lithography and dry etching

Large-area one-dimensional periodic metallic structures were fabricated on a waveguide layer with interference lithography and dry etching. As narrow as 115-nm gold nanowires were obtained with a period of 395 nm, covering a homogeneous area as large as 5 × 5 mm². Extinction measurements demonstrate the strong coupling between waveguide mode and gold-particle plasmon resonance. We demonstrate good agreement with a scattering-matrix theory. The dispersion of the metallic photonic crystals was obtained by angle-resolved measurements. This method represents a simple and low-cost way to fabricate large-area metallic photonic crystals.