Search

We propose a system for rectification of acoustic waves. The system consists of an array of triangular holes drilled in an elastically isotropic material. Assuming the propagation of transverse acoustic waves with polarization parallel to the holes, we confirm numerically that the rectification of acoustic waves occurs even in the frequency region with corresponding wavelength comparable to the dimensions of the scatterers. The rectification effects appear above a threshold frequency due to the Bragg diffraction owing to the periodic structures. The threshold frequency depends on the structural parameters, which enables the realization of a tunable rectifier.

The role of SiO2/Si3N4 interfacial transition (IFT) layer in the oxide–nitride–oxide (ONO) tri-layer is quantitatively analyzed for the first time by simulating the temperature and stress-accelerated retention characteristics of p-channel silicon–oxide–nitride–oxide–silicon (SONOS) devices. The ONO tri-layer is modeled as an alloy-dielectric by changing the atomic concentration of silicon, oxygen and nitrogen. It is revealed that simulated results including the IFT layer are more consistent with the experimental data than those neglecting the IFT layer. In addition, the results show that the trapped charge density in IFT layer is two times larger than in the bulk Si3N4 film, due to the oxygen atoms penetrated from SiO2 cause the extrinsic defects in the IFT layer. The energy levels of the trapped charge are continuously distributed, and the peak value is ~1.6 eV below the conduction band of the ONO tri-layer with a full width at half maximum of 0.45 eV.

A comprehensive numerical study of threshold voltage fluctuation (ΔV T) in scaled NAND flash memory caused by random telegraph noise (RTN) and discrete dopant fluctuation (RDF) in both the channel and the cell-to-cell space [source/drain (S/D)] region was carried out. Following a three-dimensional (3D) Monte Carlo (MC) procedure, the statistical distribution of ΔV T is estimated, considering the effects of both the random placement of discrete doping atoms and a discrete single trap at the tunnel oxide/substrate interface. The result demonstrates the significant influence of the doping in the S/D regions. For the cells with and without an S/D junction, the electron concentration in the S/D region is determined by the pass voltage of the unselected cell (V pass) and the neighboring cell V T (V T(n)), owing to the fringing fields of neighboring floating gates (FGs). As a result, ΔV T increases in the S/D region as V pass - V T(n) decreases. The fluctuation amplitude strongly depends on the [single-trap RTN] position along the cell length (L) and width (W) directions. For the cell shape with rounding of the active area (AA) at the shallow trench isolation (STI) edge, the results indicate that the high ΔV T area moves from the AA edge towards the center area along the W-direction.

In this study, we precisely investigate the charge distribution in SiN layer by dynamic programming of channel hot hole induced hot electron injection (CHHIHE) in p-channel silicon–oxide–nitride–oxide–silicon (SONOS) memory device. In the dynamic programming scheme, gate voltage is increased as a staircase with fixed step amplitude, which can prohibits the injection of holes in SiN layer. Three-dimensional device simulation is calibrated and is compared with the measured programming characteristics. It is found, for the first time, that the hot electron injection point quickly traverses from drain to source side synchronizing to the expansion of charged area in SiN layer. As a result, the injected charges quickly spread over on the almost whole channel area uniformly during a short programming period, which will afford large tolerance against lateral trapped charge diffusion by baking.

Local charge distribution around the titanium atom of amorphous and α-crystalline TiOPc films was investigated using Ti 2 p X-ray absorption and emission spectroscopy. The X-ray emission spectra show two characteristic features that correspond to charge transfer states that result from in-plane Ti–N and apical Ti–O hybridizations. In the amorphous phase, the Ti–O charge transfer state has both localized and delocalized properties, whereas in the α-crystalline phase it has only the delocalized property. These different properties evidence the role of the oxygen atom in forming a network with a neighboring molecule and in balancing the total dipole moment in the α-crystalline phase.

Novel laser etching was demonstrated by one-shot femtosecond laser ablation of a transparent organic amorphous film. The etch depth increased stepwise with increasing laser fluence and each step is constant and independent of the fluence, while the number of steps and etching area increase with the fluence. The successive depths were 270, 480, 690 and 820 nm, for which the thresholds were 180, 180, 210 and 290 mJ/cm2, respectively. A fifth step was not observed in the present fluence range. Both the etched surfaces and slopes between the steps are very smooth with a roughness of less than 10 nm. The mechanism is proposed and discussed in view of the optical interference effect and a possible application is mentioned.

The 4.7 GB digital versatile disc-recordable (DVD-R) disc format has been developed to introduce very useful recordable feature in the digital versatile disc (DVD) family. We developed disc media and the write pulse control method. In our examination, recorded signal qualities of the DVD-R disc are equivalent to those of the DVD-Read-Only disc (ROM). We realized a jitter value of less than 6% using write pulse strategy with the adaptive edge shift control technology. The physical characteristics of the recorded signals satisfy all the requirements of single-layered DVD-ROM disc.

NiO/CoFeB/Cu/CoFeB spin valves with B content of 0 to 10 at.% were prepared to investigate the dependence of the giant magnetoresistance(GMR) effect on the thickness of free magnetic layers. In the spin valves, GMR effects were observed even when the free magnetic layers were very thin, 1 or even 0.5 nm. For lower B content, the magnetoresistance (MR) ratio rapidly increased with the increase of free magnetic layer thickness, while for higher B content, the MR ratio was maximum at the thickness roughly equal to the mean free path of electrons in the magnetic layers. By using the Camley-Barnas model, the value of the MR ratio and the resistivity can be consistently explained if the specular reflection of electrons is considered at the interface between magnetic and nonmagnetic layers.

We have studied the photochemically induced phase transition from SmC A * to SmC* by Ar+ laser light irradiation (wavelength 514 nm) in an antiferroelectric liquid crystal doped with photochromic azo-dye molecules. Using this phase transition, we have demonstrated the optical switching under a bias voltage of 6.2 V. A response time of 1.5 s was achieved by 55 mW/cm2 irradiation at 30°C.

Second-harmonic generation (SHG) interferometry has been applied to determine the phase of SHG from an SHG-active side-chain polyimide (PI) alignment layer with SHG-active liquid crystal molecules evaporated onto it. The phase difference between SH waves from the PI layer and from the PI layer with evaporated LC molecules monotonically increases with increasing evaporation time, while the SHG intensity increases after an inital decrease. These two facts indicate that LC molecules are adsorbed with an antiparallel polar orientation with respect to the polar side-chain orientation. The applicability of this method in studying the orientational relationship between an alignment layer and a LC monolayer is pointed out.

We have determined the orientational distribution function (ODF) of a liquid crystal (LC) monolayer on rubbed polyimide films by optical second-harmonic generation (SHG) using the maximum entropy method without assuming the independence of the polar and azimuthal angular distributions. The LC samples used were a homologous series of 4'-n-alkyl-4-cyanobiphenyl (n CB; n=5–8). The rubbing strength dependence of the pretilt angle was also measured and was found to be classified into two types according to even or odd number of carbon atoms in the alkyl chain. However, we could not observe a distinct difference in ODFs of 7CB and 8CB monolayers to explain the two kinds of rubbing strength dependence of the pretilt angle.

The effect of morphology on the photovoltaic properties of titanyl phthalocyanine (TiOPc) has been studied. pn-Heterojunction devices consisting of TiOPc with different morphologies and N,N'-dimethyl-3,4:9,10-perylenebis(dicarboximide) (MPCI) sandwiched between indium tin oxide (ITO) and Au electrodes were fabricated. Cells fabricated using crystalline α-TiOPc film as the p-type semiconductor exhibit much higher conversion efficiency upon irradiation with light which is mainly absorbed by TiOPc than devices fabricated using amorphous TiOPc film.

We propose a modified crystal rotation method which enables us to measure high pretilt angles in liquid crystal cells. This method is based on the use of two prisms made of the same material as the liquid crystal cell substrates. We demonstrate the ability for measuring a pretilt angle of over 21°.

We have determined the orientational distribution function (ODF) of the side chains of polyimide films for liquid crystal alignment. To determine ODF, optical second-harmonic generation was measured as a function of sample rotation angle. Using nonlinear susceptibility components obtained by a fitting procedure, ODF was obtained by means of information entropy. The symmetry of the polymer side chains changes from C∞v to C s by rubbing treatment. Asymmetry of the polar angle along the rubbing direction is induced, though the change is very small.

A new model for the substrate hole current that occurs during Fowler-Nordheim (FN) stress of thin oxides is proposed. The model is based on the assumption that hot hole injection occurs at the anode. The probability that a hole is emitted in the oxide and contributes to the hole current is described by an empirical relation that is a function of the effective barrier height and the average energy of the electrons arriving at the anode. To compute the average electron energy in the oxide, an energy dependent energy relaxation distance is used. The results obtained with the model are in very good agreement with the measurements for oxides within a thickness range of 5.5 to 12.5 nm.

The influence of the compression process on the formation of H-aggregates has been studied by means of the absorption spectra of the hemicyanine monolayer on the water surface. It was found that the conventional compression by moving the barrier does not bring about the formation of the H-aggregates but that the compression by spreading the dye solution does cause the formation. Absorption spectra in several geometries reveal that most of the aggregated molecules deposited on a substrate (LB film) are aligned along the surface normal and that the molecules on water (L film) tilt from the water-surface normal.

The molecular orientational structure and the optical nonlinearity in mixed monolayers of hemicyanine and arachidic acid were investigated as a function of temperature by means of second-harmonic generation, linear optical absorption and X-ray diffraction. The average molecular tilt angle with respect to the surface normal has an inflection point in the temperature dependence for the films with low dye concentration. This phenomenon is explainable by the melting of arachidic acid. The molecular hyperpolarizability, β, shows a maximum at about 60°C in the films with a high dye fraction. This originates from the competition between the increase of β due to the dissociation of H-aggregates and the decrease of β due to protonation effect, the isomerization and decomposition.