Two-dimensional Dot Research Articles

Organic Thin-Film Transistor Memory with Nanocrystal Carbon Dots

Organic thin-film transistor (OTFT) memory devices were fabricated with nanocrystal carbon (nc-C) dots incorporated into the pentacene/oxide interface in the active layer. The nc-C dots were arranged precisely in order on the OTFT channel region by a focused ion beam (FIB) technique using low-energy Ga + ions and phenanthrene as the carbon source. The structural information of nc-C dot arrays was obtained by scanning ion microscopy (SIM) and atomic force microscopy (AFM). These images indicate that the nc-C dot array was successfully formed on the oxide layer. The density of the two-dimensional nc-C dots was 1.3-1.5A—108 cm-2. The current-voltage (I-V ) characteristics showed that the OTFTs exhibit memory behavior upon the application of forward and reverse gate bias stresses. Depending on the polarity of gate bias, write and erase modes were induced, and a maximum threshold voltage shift I”Vth of 0.97 V was obtained. © The Surface Science Society of Japan.

Four beams surface plasmon interference nanoscale lithography for patterning of two-dimensional periodic features

The interference of multiple counterpropagating surface plasmon waves as a lithography technique to pattern periodic two-dimensional features is proposed and illustrated in this article. The surface plasmons are generated by prism coupling method, by employing a custom made prism layer configuration and with a single exposure. 175nm periodic two-dimensional dot array patterns, with feature size as small as 93nm, have been realized using an exposure radiation of 364nm wavelength.

Anomalous temperature dependence of electron tunneling between a two-dimensional electron gas and Si dots

We present our observation of an anomalous temperature and optical excitation intensity dependence of the electron tunneling between a two-dimensional electron gas (2DEG) and Si dots in the direct tunneling mode. We find that the gate voltages required for the electron injection from the 2DEG to Si-dots become smaller with increase in the temperature or in the optical excitation intensity. The experimental results are discussed in terms of the geometrical matching of the wave functions of a 2DEG and an electron in a Si-dot.

ImmPort FLOCK: Automated cell population identification in high dimensional flow cytometry data (42.17)

Abstract Historically, investigators have analyzed flow cytometry (FCM) data using manual gating strategies and two-dimensional dot plot visualization to identify and compare specific cell populations between samples. However, this approach is subjective and does not scale well as the number of parameters detectable with different fluorochrome reagents increases. We have developed a software system for automated population discovery in multidimensional FCM data - FLOw Clustering without K (FLOCK), which specifically takes into account the unique features of FCM data, including non-spherical parameter distributions and sparse cell populations. FLOCK includes the following steps: data cleansing, data shrinking, data normalization, informative dimension selection, dense hyper-region identification, histogram partitioning, centroid calculation, clustering, visualization, population statistics calculation, cell ontology mapping. As a result, FLOCK automatically and objectively determines the number of cell populations detectable in a sample and assigns population membership to each cell event, from the multi-parameter flow cytometry data, in the absence of manual gating. Our study of normal human peripheral blood has identified 17 unique B lymphocyte populations based on the expression of IgD, IgG, CD24, CD27, CD38 & B220. Supported by NIH N01AI40076.

Carbon Nanocrystal-Based Organic Thin-Film Transistors for Nonvolatile Memory Nanodevices

Organic semiconductor nonvolatile memory devices were successfully fabricated from organic thin-film transistors (OTFTs) embedded with nanocrystal carbon (nc-C) dots incorporating pentacene as an active layer. The nc-C dots were arranged in the channel region by a focused ion beam (FIB) technique using a precursor of low energy Ga+ ions and a carbon source. The formation and morphology of nc-C dot arrays were investigated using a scanning ion microscopy (SIM) and atomic force microscopy (AFM), respectively. The SIM and AFM images show that the nc-C dot array was successfully grown on the SiO 2 layer. The density of the two-dimensional nc-C dots was 5 x 10 9 cm-2. The current-voltage (I - V) characteristics at room temperature show that the fabricated OTFTs exhibit a memory effect upon the application of forward and reverse bias. Under the effect of gate bias, on and off states were induced and a threshold voltage shift (I”Vth = 0.23 V) was obtained. The charge carrier mobility (I¼) of the OTFTs is similar in both on and off states. The memory effect was attributed to the nc-C dots in the pentacene-dielectric interface. © 2009 The Surface Science Society of Japan.

Experimental validation for the determination of particle positions by the correlation coefficient method in digital particle holography

The feasibility and the accuracy of the correlation coefficient (CC) method for the determination of particle positions along the optical axis in digital particle holography were verified by validation experiments. A translation system capable of high precision was used to move the particle objects by exact known distances between several different positions. The particle positions along the optical axis were calculated by the CC method and compared with their exact values to obtain the errors of the focus plane determination. The tested particles were two-dimensional (2D) dots in a calibration target along with different-sized glass beads and droplets that reflected and caused a three-dimensional (3D) effect. The results show that the CC method can work well for both the 2D dots and the 3D particles. The effect of other particles on the focus plane determination was also investigated. The CC method can locate the focus plane of particles with high precision, regardless of the existence of other particles.

A diffusion pattern composed of two-dimensional diffusion dots for encrypting a digital image

Diffusion patterns composed of two-dimensional (2D) diffusion dots can show dynamic images by changing their illuminating or viewing conditions. In this study, a binary-exposure method is applied to the diffusion dots of a diffusion pattern to encode binary data into the diffusion pattern. Then the diffusion pattern not only can show a dynamic image but can also encrypt a covert digital image. The reconstructed covert image decoded from the diffusion pattern is exactly the same as the original covert image. Encoding a covert image into a diffusion pattern with 2D diffusion dots is very easy for a manufacturer, but decoding the covert image from the diffusion pattern is very difficult for counterfeiters. Therefore, the proposed encrypting scheme possesses both feasible and confidential features.

Fabrication of Line-Shaped Embossing Structure by Holographic Lithography and Its Application to Electronic Device

Holographic lithography has been an efficient and versatile method to fabricate nanosize patterned devices during past several years. This technique is based on the interference of UV-laser beams for patterning regular arrays of fine features without the use of mask as used in conventional lithography. Simple gratings and two-dimensional dot arrays has been fabricated by using the interference principle. Using this technique, we fabricated line-shaped embossing gold (Au) structure on silicon substrates. Towards the characterization of fabricated line-shaped Au nano-structure Field Effect Scanning Electron Microscopy (FE-SEM) is used and our results clearly show the fine structure of fabricated Au lines. Further characterization towards our patterned substrates we used Atomic Force Microscopy (AFM) for analysis of Au patterned lines. A bioelectronic device consisting of cysteine modified azurin was fabricated where the protein was covalently immobilized on the nano-patterned substrate and we investigated the electrochemical property of the device by Cyclic Voltammetry (CV) experiments comparing with that of a normal flat Au substrate. We think these nano-patterned Au substrates can be applied as potentially usable elements for the development of biosensor and other bioelectronic devices.

Coupled Quantum Dots as Two-Level Systems: A Variational Monte Carlo Approach

The electronic properties of two-dimensional double-quantum dots in the presence of external magnetic fields are investigated by a variational Monte Carlo method with s and s-p trial wavefunctions. We compute the exchange energy between two electrons as well as the two-electron total Coulomb energy for the singlet and triplet states in both strongly and weakly coupled quantum dots, and compare our data with the results of the numerically exact diagonalization of the Schrödinger Equation. In both systems, the singlet Coulomb energy decreases in magnetic fields as a consequence of magnetic localization, whereas the triplet Coulomb energy reaches a maximum value at intermediate magnetic fields before decreasing. Overall, good agreement between the two methods is obtained with s-p orbital trial wavefunction in strongly and weakly coupled quantum dots

Diffractive position sensing devices using two-dimensional grating dots

A new type of position sensing device (PSD) is proposed in this paper. The proposed PSDs are composed of two-dimensional grating dots. The grating dots of a new PSD can diffract an incident laser beam into many spots. By identifying the maximum and minimum values of the designed numbers of the diffracted spots, the one- or two-dimensional position of the center of the laser beam can be precisely determined. Because the operations are very easy and the mass-production costs are cheap for the proposed PSDs, the PSDs are useful.

Identification of two distinct populations of endothelial progenitor cells differing in size and antigen expression from human umbilical cord blood

Endothelial progenitor cells (EPCs) have been isolated from peripheral blood, bone marrow, and umbilical cord blood (CB) and determined to be in heterogeneous populations; however, specific variations in their characteristics remain to be clarified. In this study, we observed that mononuclear cells (MNCs) of CB change in morphology to differentiate into mature endothelial cells (EC) after 6 weeks of culture. In early days of culture along with the differentiation, two distinct populations of EPCs were detected, defined by two-dimensional dot plots (forward scatter vs side scatter) with flow cytometry, namely, relatively small cells (S-EPCs) and relatively large cells (L-EPCs). S-EPCs were found to express CD34 but not CD14, while the converse was the case for L-EPCs. When CD34(+)/CD14(-) cells and CD34(-)/CD14(+) cells were isolated from original MNCs of CB and cultured independently, S-EPCs and L-EPCs were derived from CD34(+)/CD14(-) and from CD34(-)/CD14(+) cells, respectively. Furthermore, when the two EPCs at day 7 were separated by cell sorter and recultured, there was no crossover in terms of CD34 and CD14 expression. While expression of VE-cadherin and vascular endothelial growth factor receptor-2 (VEGFR-2) on L-EPCs was significantly greater than on S-EPCs, levels of CD31 were lower. In addition, L-EPCs exhibited greater proliferative ability on stimulation with VEGF. Although these two EPCs expressed different phenotypes, including growth factor receptors, and had different proliferative ability, they both eventually differentiated into mature ECs after more than 3 weeks of culture.

Pattern composed of two-dimensional diffusion dots for showing dynamic images

A new type of diffusion pattern is proposed. The proposed patterns are composed of 2D diffusion dots. The diffusion dots are created on a photoresist plate by recording the image of a local area of a piece of ground glass dot by dot. An imaging lens covered by a mask with a slit aperture is used to form the image. By changing the orientation of the slit aperture on the mask plane, the diffusion dots can have different microintensity distributions for the same incident light beam. Therefore the diffusion dots created by the same slit aperture orientation show the same brightness, and the diffusion dots created by different slit orientations show different brightness for the same illuminating and viewing conditions. Thus a proposed diffusion pattern can show dynamic images by changing its illuminating or viewing directions. By applying the double-exposure technique to the diffusion dots of a pattern, the pattern not only can show dynamic effects but also can possess several hidden features for identifying the pattern. Therefore the proposed patterns are dynamic and anticounterfeiting.

Random-dot pattern design of a light guide in an edge-lit backlight: integration of optical design and dot generation scheme by the molecular-dynamics method

We present the methodology of an integration of a dot generation scheme by a molecular-dynamics (MD) method and the subsequent software optical design phase by software. The MD dot generation scheme proposed has great advantages when integrated into the optical design phase. These advantages include the variable r-cut and reflective boundary condition techniques, both of which could achieve a high-density variation of dot distribution. In addition, we use a cell technique where the domain is divided into a number of smaller cells, allowing for flexibility in adjusting the dot density within each cell, as well as for using the add-on or remove-from technique of the dots in one cell to achieve an equal-luminance condition. In addition, a simple proportional rule of luminance to dot density is also proposed to perform dot optimization. Finally, an illustration is shown for the optimal dot distribution of a LED backlight. The result that a two-dimensional dot density distribution near the light source changes gradually to a one-dimensional dot density distribution with increasing distance from the light source shows the validity of the present integration of the MD dot generation scheme into the optical design phase.

Quasi-exact solutions for two interacting electrons in two-dimensional anisotropic dots

We present an analysis of the two-dimensional Schrödinger equation for two electrons interacting via Coulombic force and confined in an anisotropic harmonic potential. The separable case of ωy:ωx = 2 is studied particularly carefully. The closed-form expressions for bound-state energies and the corresponding eigenfunctions are found at some particular values of ωx. For highly accurate determination of energy levels at other values of ωx, we apply an efficient scheme based on the Fröbenius expansion.

Demonstrations of Spatiotemporal Integration and what they Tell us about the Visual System

Five sets of displays are presented on the journal website to be viewed in conjunction with the text. We concentrate on the factors that give rise to the integration and disruption of the direction of apparent motion in two-dimensional and three-dimensional space. In the first set of displays we examine what factors contribute to the integration and disruption of apparent motion in the Ramachandran/Anstis clustered bistable quartets. In the second set we examine what factors give rise to the perception of the direction of motion in rotating two-dimensional wheels and dots. In the third and fourth sets we examine how the depth cues of shading and disparity contribute to the perception of apparent motion of opaque displays, and to the perception of rotating unoccluded displays, respectively. In the fifth set we examine how the depth cue of motion parallax influences the perception of apparent motion. Throughout, we make inferences about the roles which various parallel pathways and cortical areas play in the perceptions produced by the displays shown.

Using random features of dot-matrix holograms for anticounterfeiting

The images on a dot-matrix hologram contain many two-dimensional (2D) dots with different grating orientations and different grating pitches. Because the zeroth-order light nondiffracted by different grating structures has the same progress direction, the nondiffracted light can be diffracted to a 2D spot spectrum by the 2D dot structure. The 2D spot spectrum depends on grating depths and dot sizes. Although ordinary noises are troublesome for 2D spots, noises caused by special dot arrangement defects or special grating moiré fringes are useful in checking holograms. Since the features of grating depths, dot sizes, dot arrangement defects, and grating moiré fringes can be randomly changed on a case by case basis, 2D spot spectra in different cases are different. The aforementioned random features are used to identify dot-matrix holograms.

Self-assembled Fe nanodots on Ge(001)

The initial nucleation of Fe onto the (2×1) reconstructed Ge(001) surface is studied. Uniformly sized two-dimensional Fe dots are shown to nucleate. They have an apparent corrugation height ∼1.1Å and lateral dimensions ∼12×8Å2. Further to their uniform size, due to their registry with respect to the substrate, they are shown to nucleate on a single equivalent surface site. It is suggested that their stability is due to either a “magic” number effect or adsorbate-substrate interactions. Tunneling I(V) spectra show the dot/Ge(001) contact to exhibit marked current rectifying behavior, which is extremely well confined to the contact area.

Ground State of a Two-Electron Quantum Dot with a GaussianConfining Potential

We investigate the ground-state properties of a two-dimensional two-electronquantum dot with a Gaussian confining potential under the influence ofperpendicular homogeneous magnetic field. Calculations are carried out by using themethod of numerical diagonalization of Hamiltonian matrix within theeffective-mass approximation. A ground-state behaviour(singlet⟶triplet state transitions) as a function of the strength ofa magnetic field has been found. It is found that the dot radius R of theGaussian potential is important for the ground-state transition and thefeature of ground-state for the Gaussian potential quantum dot (QD), and the parabolicpotential QDs are similar when R is larger. The larger the quantum dotradius, the smaller the magnetic field for the singlet-triplet transition ofthe ground-state of two interacting electrons in the Gaussian quantum dot.

Expression of Major Cold Shock Proteins and Genes by Yersinia enterocolitica in Synthetic Medium and Foods

Yersinia enterocolitica is a psychrotrophic foodborne pathogen that has been implicated in outbreaks of foodborne illness involving cold-stored foods, especially milk and pork. A major mechanism bacteria use to adapt to cold is expression of cold shock proteins. The objective of this research was to study the expression of major cold shock proteins of Y. enterocolitica in Luria-Bertani (LB) broth, milk, and pork following a temperature downshift from 30 to 4°C. Y. enterocolitica was inoculated into 10 ml of LB broth, sterile skim milk, or pork, and the samples were stored at 4°C (cold shock) or 30°C (control) for 0, 4, 8, 12, and 24 h. At each sampling time, total protein and total RNA were extracted from Y. enterocolitica harvested from LB broth, milk, and pork and subjected to two-dimensional gel electrophoresis and dot blot analysis. Two major cold shock proteins (CspA1 and CspA2) of ∼7 kDa and their genes were expressed by Y. enterocolitica following cold shock. However, the CspA1 and CspA2 proteins were not expressed by Y. enterocolitica at 30°C. Y. enterocolitica CspA1 and CspA2 were observed as early as 2 h of cold shock in cultures from LB broth and milk and at 8 h of cold shock in cultures from pork.

Fano regime of one-dot Aharonov-Bohm interferometers

We use the Landauer-B\"uttiker formalism to study the mesoscopic Fano effect in Aharonov-Bohm rings with an embedded two-dimensional noninteracting dot. The magnetic field dependence of the dot levels leads to a global shift of the Fano lines which becomes important for small ring/dot area ratios. As the magnetic field is varied the Fano dips move periodically from one side of the peak to the other, as reported by Kobayashi et al. [Phys. Rev. Lett. 88, 256806 (2002)]. We show that this effect appears due to a specific magnetic control of the difference between the phase of the single nonresonant path via the free arm of the ring and the global phase of all trajectories involving resonant tunnelings through the dot.