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In this study, we evaluated the read-out signal quality from narrow track patterns, utilizing linearly arranged slender track patterns, while changing the track width from 10 to 0.1 μm and the pattern density from 200 nm line-and-space (L/S) to 120 nm L/S. To acquire narrow track readout signals, we adjusted the aperture’s in-plane position to cross a linear track at shallow angles of less than 1°, and we could successfully transform directly acquired signals into those of an aperture crossing tracks at a right angles. The results of an experiment utilizing a 10-μm-wide track (which is thought to represent an infinitely wide track) clarified that the stationary field was spread to an approximately 1.2–1.6 times larger region than the typical aperture size of 330 nm. The results also clarified that the “field spread” depended on the pattern density, that is, the case in which polarization direction θ equals 0 or 45°, and that the field spread increased monotonically as the line or space width became smaller. When the polarization direction equals 90°, the field spread had its local maximum when the line or space width was approximately 150 nm. An approximate prediction of the read-out signal amplitude was based on the rule that the signal amplitude was proportional to the net field spread that passed across the track pattern, and this prediction corresponded well to the experimental results, except when the interaction between the stationary field and the track side walls was not taken into account.

In near-field optical recording, the combination of a triangular aperture and a polarized illuminating light is thought to be one of the most promising breakthroughs for improving both spatial resolution and signal-to-noise ratio. In light of this, we have already fabricated a triangular-aperture mounted optical head slider and demonstrated its superior performance while clarifying the influence of the polarization direction on the spatial resolution in the circumferential direction. When the polarization direction was perpendicular to the bottom side (which is parallel to the slider trailing edge) of the aperture, the highest spatial resolution and signal contrast were obtained, in spite of the usage of a fairly large aperture, indicating the presence of clear readout signal waveforms corresponding down to 100 nm line-and-space (L/S) patterns. In this study, we tried to experimentally clarify the influence of the polarization direction of the illuminating light on an aperture's field spread in the radial direction. In order to concretely evaluate the field spread, we prepared 1-mm-long linearly arranged (in the circumferential direction) L/S patterns on a metal-layered medium, and a piezo-electric actuator combined positioner. Intersecting the aperture at two portions of the tracks, directly acquired signal waveforms could be successfully transformed into the waveforms that would be obtained if the aperture had crossed the track at right angles. The field spreads in the radial direction were estimated to be approximately 250 nm when the polarization direction was perpendicular to the bottom side. In contrast, when the polarization direction was 45 degrees, the stationary field spread in the radial direction was estimated to be approximately 350 - 370 nm. It could be confirmed experimentally that both the highest spatial resolution in the circumferential direction and the smallest field spread in the radial direction were realized with the combination of the triangular aperture and the illuminating polarized light whose direction was perpendicular to the bottom side. Based on these results, the signal-to-noise ratio will be evaluated and discussed in the future with respect to the above-mentioned optimum aperture structure and conditions.

The continual advancement of the digital network society demands higher density and higher data transfer rates for all sorts of data storage. Optical memory based on the “near-field” principle is considered one of the most promising ones because it has no apparent physical density limit such as that due to the thermal instability encountered in magnetic recording. In light of this, we have previously demonstrated the superior readout performance of an optical head slider which is mounted on a non-circular aperture, specifically a triangular aperture having a bottom side size of 330 nm irradiated by polarized light, with this scheme indicating a clear signal response corresponding to a 70-nm-long single slit pattern. In order to fully realize the superior potential of the triangular aperture’s high spatial resolution and high signal output, it is essential to minimize aperture-to-medium spacing. In this paper, we introduce a protruded aperture mounted on a 1.5-mm-long miniaturized optical head slider whose aperture protrudes approximately 20 nm from an air-bearing surface level based on nano-step lithography technology. Utilizing a triangular aperture of 140 nm per side, a readout experiment was carefully performed at an aperture-to-medium spacing down to approximately 30 nm, corresponding to a circumferential velocity of 2.18 m/s. The influence of the incident light’s polarization direction (in relation to the bottom side of the triangular aperture) on the readout signals was evaluated by flying the aperture above a chromium patterned medium having single-space or line-and-space patterns whose line lengths ranged from 300 to 50 nm.

Optical memory based on the “near-field” principle is considered one of the most promising technological breakthroughs because it has no apparent physical density limit such as that due to the thermal instability encountered in magnetic recording. In light of this, we have demonstrated the superior readout performance of an optical head slider mounted on a triangular aperture with a typical side size of 140 nm irradiated by polarized light. With this scheme, we have indicated a clear signal response corresponding to a 150-nm line-and-space (L/S) pattern. In this paper, we introduce a protruded aperture mounted on a 1.5-mm-long miniaturized optical head slider whose aperture protrudes approximately 25 nm from an air-bearing surface. Utilizing a triangular aperture irradiating polarized violet laser light, we performed a readout experiment at an aperture-to-medium spacing down to approximately 29 nm. A clear readout signal was obtained corresponding to the pattern down to 100-nm line width, in spite of the usage of a fairly large side size of 330 nm. We also evaluated the influence of the incident light’s polarization direction on the readout signals while changing the line width of the L/S patterns from 300 to 100 nm. A polarization direction perpendicular to the bottom side of the aperture provided both higher spatial resolution and better signal contrast. We also observed a “spike phenomenon” when the aperture passed through the boundaries between the metal portion and the space (or line-and-space) portion. We believe this phenomenon is the cause of the enhancement or suppression of specific L/S pattern or period signals.

The near-field principle combined with thin-film gas-lubricated slider bearing technology is thought to be one of the most promising breakthroughs to overcome the difficult optical diffraction limit (or wavelength shortening limit), which governs traditional optical recording performance. In light of this, we have demonstrated high linear density (150 nm pattern length) and high speed 10 MHz readout signals using the combination of a tapered circular aperture and a planar lens mounted on a quartz slider, flying above a metal patterned medium. In order to further improve both the spatial resolution and signal-to-noise ratio of this device, it is essential to minimize the spacing and laser power throughput of an aperture. Also investigated was the effectiveness of a non-circular aperture, which has approximately triangular configuration in combination with polarized light in simultaneously improving spatial resolution and increasing signal output. In this paper, we confirmed the predicted effectiveness on more practical condition of both high speed and compactness of head construction using a sub-micrometer size non-circular aperture, which was mounted on a 1.5-mm-long miniaturized optical head slider, flying above a ROM medium having sub-100-nm-long chromium patterns. The influence of the electric-field direction of the incident light and aperture to medium spacing on the readout signal are carefully evaluated by flying the aperture at spacing down to less than 50 nm.

Recent rapid progress in a digital network society necessitates storage devices with higher-density and faster transfer rates. In optical storage, a novel recording principle is eagerly awaited that will drastically improve recording density without being restricted by a wavelength shortening limit or a numerical aperture (NA) limit of the optics utilized. Storage based on the “near-field” principle is thought to be one of the most promising breakthroughs for overcoming various limitations governing traditional optical recording. We have already proposed an integrated optical head slider assembly that relies on the novel near-field principle for its operation; it is mounted on a minute tapered aperture and has a planar focusing lens and a micro silicon mirror. Readout signals corresponding to a 200-nm-long bit have demonstrated a frequency band up to approximately 10 MHz, using a chromium patterned medium. In this study, we have investigated the accuracy of the tracking characteristics of an aperture-mounted head slider by using linearly arranged 1-mm-long line-and-space patterns. Based on the step or inverse step responses that occur when an aperture flies obliquely across the linearly arranged pattern region boundary, we present a simple method of predicting accurate tracking characteristics in detail, and also by using a 350-nm line-and-space pattern signal, we were able to predict both tracking characteristics and tracking sensitivities of arbitrary wide tracks to a track width of 100 nm.

We have developed a small near-field optical head for high-recording-density data storage applications, to overcome the disadvantage of conventional near-field optical heads, such as large light introduction, low optical throughput, and difficulty in controlling the aperture-medium distance. The optical head structure has miniaturized light introduction using an optical fiber placed horizontally. To decrease the optical loss, an integrated microlens focuses on the aperture tip that has a shortened cut-off region. The fabricated optical head (3.2×3.6×0.9 mm3) with a 200 nm aperture of the same height as the sliders shows a clear readout signal of a 200-nm-wide line and space pattern at a speed of 5.2 MHz. We show that the optical head has the ability to read 4 times the recording density by simulations of the finite difference time domain (FDTD).

A near-field optical head with a triangular aperture has been precisely analyzed on the basis of a three-dimensional finite-difference time-domain method in order to obtain both higher spatial resolution and signal output performance for a near-field optical data storage system. The numerical analysis revealed that in contrast to a conventional aperture, this triangular-shaped aperture can successfully enhance energy distribution intensity at only the side perpendicular to the incident polarization direction, generating an extremely small optical spot not limited by its entire aperture size. The read-out performance was also simulated for the aperture passing over a space-patterned metal medium, resulting in both superior spatial resolution and signal output.

Recently, near-field surface recording based on near-field optical principles has been vigorously studied for higher data storage density. In near-field optics which utilizes an aperture, in addition to the high spatial resolution property, there is another characteristic that the shape of the optical spot can be arbitrarily controlled by the aperture configuration, and its application to various technologies in the optical disk drive is possible. From this perspective, we propose a novel tracking method utilizing an asymmetric configured aperture head which could provide continuous signal of readout data and tracking error simultaneously, and analyze its data read-out and tracking detection performance through the three-dimensional finite-difference time-domain (3D-FDTD) method. Our simulations reveal that this novel tracking head has sufficient data readout performance and high tracking sensitivity, and has the potential to readout both a data signal and a tracking signal simultaneously.

The finite difference time domain method is combined with eigenmode analysis of the waveguide and the Helmholtz-Kirchhoff integral to study the field distribution and the throughput of the near-field optical probe. This includes a waveguide, a Si substrate with A1 coating, and a subwavelength aperture. It is found that the optics inside the probe and the optical properties of the probe depend strongly on the field distribution of the incident light.

Q-Chem 2.0 is a new release of an electronic structure programpackage, capable of performing first principles calculations on the ground andexcited states of molecules using both density functional theory and wavefunction-based methods. A review of the technical features contained withinQ-Chem 2.0 is presented. This article contains brief descriptive discussions of thekey physical features of all new algorithms and theoretical models, together withsample calculations that illustrate their performance. c 2000 John Wiley S electronic structure; density functional theory;computer program; computational chemistry Introduction A reader glancing casually at this article mightsuspect on the basis of its title that it is a thinlydisguised piece of marketing for a program pack-age. This is not the case. Rather, it is an attemptto document the key methodologies and algorithmsof our electronic structure program package, Q-Chem 2.0, in a complete and scientifically accurateway, with full references to the original literature.This is important for two principal reasons. First,while the use of electronic structure programs isburgeoning, many users of such programs do nothave much feel for the underlying algorithms thatmake large-scale calculations routine even on suchreadily available hardware as personal computers.Therefore, a link between the program package andthe original literature that is written at the level ofan introductory overview can be a useful bridge.Second, while citations of large-scale commercialprograms in published applications are tradition-ally part of the conditions of use of such codes, they

The excitation energies and excited states of trans-chalcone (trans-(s-cis)-1,3-diphenylpropenone), and several related molecules (trans-(s-cis)-3-phenylpropenal, s-cis-1-phenylpropenone, propenal, trans-(s-cis)-1-(4-hydroxyphenyl)-3-phenylpropenone, trans-(s-cis)3-(4-hydroxyphenyl)-1-phenylpropenone) have been calculated using single reference ab initio molecular orbital methods, and characterized by attachment–detachment density analysis. The results suggest assignments for the lowest three electronic transitions observed experimentally for trans-(s-cis)-chalcone in solution. The extent of localization of the electronic transitions is established by calculations on the excited states of trans-(s-cis)-3-phenylpropenal, s-cis-1-phenylpropenone and propenal, as well as analysis of the chalcone calculations. Contrary to some previous work, none of these excitations are strongly delocalized over the entire molecule. Calculated substituent shifts for the hydroxy chalcones are in qualitative agreement with experimental data, and support the localized interpretation of the main π→π* transition.

A family of quasidegenerate second-order perturbation theories that correct excitation energies from single-excitation configuration interaction (CIS) are introduced which generalize the earlier non-degenerate second-order method, CIS(D). The new methods are termed CIS(Dn), where n ranges from 0 to ∞, according to the number of terms retained in a doubles denominator expansion. Truncation at either n = 0 or n = 1 yields methods which involve the diagonalization of a dressed singles-only response matrix, where the dressing is state-independent. Hence CIS(D0) and CIS(D1) can be implemented efficiently using semidirect methods, which are discussed. Test calculations on formaldehyde, ethylene, chlorine nitrate, styrene, benzaldehyde, and chalcone are presented to assess the performance of these methods. CIS(D0) and CIS(D1) both show significant improvements relative to CIS(D) in cases of near-degeneracy.

A ‘theta diagnostic’ is introduced that measures the reliability of the single excitation configuration interaction (CIS) approach to excitation energies, and a second order perturbation correction, CIS(D). This diagnostic characterizes the extent of mixing between CIS excited states due to electron correlation effects through second order in a Moller-Plesset expansion. Its evaluation requires negligible additional computation in a CIS(D) calculation. Calculations on ethylene, formaldehyde, nitric acid, chlorine nitrate, styrene and benzaldehyde are presented to show its utility. Small diagnostic values indicate the CIS states are stable to near-degeneracy effects.

A perturbative correction, termed RCIS(D), to restricted open shell single excitation configuration interaction (ROCIS) is formulated and implemented for excited states of radicals. RCIS(D) gives spin-pure energies (but not wavefunctions), is size-consistent, and has computational complexity scaling with the fifth power of molecular size. All these properties are analogous to second order restricted Moller-Plesset theory for the ground state. Comparison of calculated vertical excitation energies against experiment for a diverse series of small radicals, BeH, BeF, CH, CH 3 , CN, CO + , NO and OH, suggests that RCIS(D) constitutes a useful improvement over ROCIS.

Near-field optical performance is greatly improved using our proposed near-field structure, in which a metal scatterer formed in an aperture enhances localized surface plasmon (LSP) excitation and functions as an alternative near-field light source. Based on the design through a finite-difference time-domain method, the scatterer-formed aperture is fabricated with an electron beam technique, and its near-field optical distribution is observed using a scanning near-field optical microscope. The scatterer-formed aperture enhances the near-field optical energy due to LSP excitation, thereby realizing a significant and simultaneous improvement in throughput and spatial resolution.

A perturbative correction to the method of configuration interaction with single substitutions (CIS) is presented. This CIS(D) correction approximately introduces the effect of double substitutions which are absent in CIS excited states. CIS(D) is a second-order perturbation expansion of the coupled-cluster excited state method, restricted to single and double substitutions, in a series in which CIS is zeroth order, and the first-order correction vanishes. CIS (D) excitation energies are size consistent and the calculational complexity scales with the fifth power of molecular size, akin to second-order Moller-Plesset theory for the ground state. Calculations on singlet excited states of ethylene, formaldehyde, acetaldehyde, butadiene and benzene show that CIS (D) is a uniform improvement over CIS. CIS(D) appears to be a promising method for examining excited states of large molecules, where more accurate methods are not feasible.

Near-field optics is one of super-resolution techniques for future data storage system. We have already proposed a near-field optical flying head with a circular aperture. Realizing higher performance aperture, we also have developed a triangular one which has been experimentally evaluated with scanning near-field optical microscope probe. In this paper, we demonstrate readout performance of this novel aperture mounted near-field head introducing polarization control. In order to scan over a media surface at small spacing condition, we fabricate a "contact" type head having contact pads and a polarization maintaining fiber, because this type of an aperture can only effectively function on condition both of extremely small spacing and applying polarized light. The contact pads and the tip are formed by photolithography with hydrofluoric acid (HF) solution. An aluminum film is formed on the tip. The aperture is formed by squeezing the shading film. Measurement of surface configuration by an interferometer shows that the aperture and the contact pads are almost on the same plane within 5 nm deviation. The media consists of a glass substrate, a titanium layer, a carbon protective layer, and a lubricant layer in sequence. Line-and-space (L&S) patterns whose width are 40~200nm are formed on the titanium layer. The contact head approaches the media surface, and then the media is scanned by a piezo stage. The near-field light generate from the triangular aperture is scattered by the L&S pattern and detected by a photomultiplier tube. Signal readout from the 40-nm-wide L&S pattern is demonstrated.

Recent rapid progress in a digital network society necessitates storage devices with higher-density and faster transfer rates. In optical storage, a novel recording principle is eagerly awaited that will drastically improve recording density without being restricted by a wavelength shortening limit or a numerical aperture (N.A.) limit of the optics utilized. Storage based on the "near-field" principle is thought to be one of the most promising breakthroughs for overcoming various tough limitations governing traditional optical recording. From this perspective, we have already proposed an integrated optical head slider assembly that relies on the novel near-field principle for its operation; it is mounted on a minute tapered aperture and has a planar focusing lens and a micro silicon mirror. Readout signals corresponding to a 200-nm-long bit have demonstrated a frequency band up to approximately 10 MHz, using a chromium patterned medium. In this study, we have investigated a tribological (glide height) property and flying stability of a miniaturized 1.5-mm-long optical head slider by using acoustic emission sensor signal and readout signal from the medium. We have also evaluated detecting performance separately using traditional 3.2-mm-long slider and a chromium patterned medium whose bit patterns are accurately scored with bit lengths less than 100 nm using electron beam lithography including reactive ion etching. We have confirmed stable flying performance of 1.5-mm-long slider assembly and furthermore, ability of detecting sub-100-nm long bit patterns.

Advances in a digital network society require both higher densities and higher transfer rates in all sorts of storage devices. In optical recording, the trend toward higher recording density and larger storage capacity requires novel surface recording technologies that would drastically improve recording density. To satisfy these severe requirements, we have already proposed a compact integrated optical head slider assembly for proximity optical recording based on the "near field principle". Using the optical head slider, we have successfully demonstrated readout signals from 200 to 150-nm-long bit patterns at frequency bands up to approximately 10 MHz. However, from the practical point of view, it is quite necessary to evaluate readout signals from patterns of smaller (sub-micron to sub-sub-micron) track width in order to prove high-density recording potential. In this paper, we have investigated tracking accuracy characteristics utilizing sub-micron sized alternate patterns of 1-mm length formed in a straight line in the circumferential direction of the medium. Arranging precisely the head's relative position to these recorded patterns, we have successfully obtained readout signals just crossing the sub-micron line-and-space pattern's boundaries. Assuming that an aperture runs along an accurate trajectory of the arc of a circle, readout signal amplitude variations when crossing the pattern edge at a right angle have precisely predicted. Also, the influences of track width on maximum readout signal intensity and tracking sensitivity are discussed in detail.

One of the most important parameters related to the near-field readout principle is aperture-to-media spacing (effective spacing). We proposed a near-field optical head with a protruding aperture that can reduce the effective spacing beyond the mechanical limit of the flying height and localize the near-field on the medium. Using nanostep lithography, we fabricated the protruding aperture, whose extension is 20 nm with 5 nm accuracy, so that the effective spacing is successfully reduced to 50 nm on a 3.2×3.6 mm flying head. We demonstrated signal readout with a 150 nm-long line-and-space pattern in chromium with the head. The flying height was estimated to be 75 nm, so that the effective spacing was 54 nm. The circumferential speed was 2.7 m/s and the signal frequency was 9.1 MHz. We also propose a promising structure for an optical head of higher density.

Recently, various researches on optical recording based on near-field optical principles have been conducted for higher data storage density. However, there is a problem of the trade-off between signal output and spatial resolution, especially when an aperture-type near-field optical head is utilized for high speed data-readout. In order to solve this problem, we propose a novel near-field optical head, the planar aperture-mounted head with a minute scatterer, and analyze its read-out performance through the three-dimensional finite-difference time-domain (3D-FDTD) method. Our simulations reveal that the Silver scatterer placed at the center of the planar aperture strongly enhances optical energy due to the local surface plasmon excitation, and that this head has the potential to realize high resolution and high signal output simultaneously.