Nanodot Research Articles

Effect with high density nano dot type storage layer structure on 20 nm planar NAND flash memory characteristics

The merits, concerns and design principle for the future nano dot (ND) type NAND flash memory cell are clarified, by considering the effect of storage layer structure on NAND flash memory characteristics. The characteristics of the ND cell for a NAND flash memory in comparison with the floating gate type (FG) is comprehensively studied through the read, erase, program operation, and the cell to cell interference with device simulation. Although the degradation of the read throughput (0.7% reduction of the cell current) and slower program time (26% smaller programmed threshold voltage shift) with high density (10 × 1012 cm−2) ND NAND are still concerned, the suppress of the cell to cell interference with high density (10 × 1012 cm−2) plays the most important part for scaling and multi-level cell (MLC) operation in comparison with the FG NAND. From these results, the design knowledge is shown to require the control of the number of nano dots rather than the higher nano dot density, from the viewpoint of increasing its memory capacity by MLC operation and suppressing threshold voltage variability caused by the number of dots in the storage layer. Moreover, in order to increase its memory capacity, it is shown the tunnel oxide thickness with ND should be designed thicker (>3 nm) than conventional designed ND cell for programming/erasing with direct tunneling mechanism.

Energy Spectra of CdS/Cd1-xZnx S Nano Dot Under The Influence of Magnetic Field

We present a theoretical study on shallow donor binding energies of CdS/ CdZnS nano dot as a strength of applied magnetic field along Z direction for various Zn concentration. Calculations are carried out by using the technique of variational ansatz within the frame work of effective mass approximation. Our results show that the binding energies are drastically affected by the dot radius, the strength of magnetic field and concentrations.

Nanosecond pulsed laser induced self-organized nano-dots patterns on GaSb surface

Abstract We report a technique for formation of two-dimensional (2D) nanodot (ND) patterns on gaillium antimoide (GaSb) using a nanosecond pulsed laser irradiation with 532 nm wavelength. The patterns have formed because of the interference and the self-organization under energy deposition of the laser irradiation, which induced the growth of NDs on the local area. The NDs are grown and shrunken in the pattern by energy depositions. In the laser irradiation with average laser energy density of 35 mJ cm−2, large and small NDs are formed on GaSb surface. The large NDs have grown average diameter from 160 to 200 nm with increase of laser pulses, and the small NDs have shrunken average diameter from 75 to 30 nm. The critical dot size is required about 107 nm for growth of the NDs in the patterns. Nanosecond pulsed laser irradiation can control the self-organized ND size on GaSb in air as a function of the laser pulses.

ChemInform Abstract: Sensitive and Selective Gold Nanomaterials Based Optical Probes

AbstractReview: 111 refs.

Luminescence properties of Si-capped β-FeSi2 nanodots epitaxially grown on Si(001) and (111) substrates

We studied the luminescence properties of Si-capped β-FeSi2 nanodots (NDs) epitaxially grown on Si substrates by using photoluminescence (PL) and electroluminescence (EL) spectroscopies. Codepositing Fe and Si on ultrathin SiO2 films induced the self-assembly of epitaxial β-FeSi2 NDs. The PL spectra of the Si/β-FeSi2 NDs/Si structure depended on the crystal orientation of the Si substrate. These structures exhibited a broad PL peak near 0.8 eV on both Si(001) and (111) substrates. The PL intensity depended on the shape of the β-FeSi2 NDs. For the flat NDs, which exhibited higher PL intensity, we also recorded EL spectra. We explained the luminescence properties of these structures by the presence of nanostructured Si offering radiative electronic states in the Si cap layers, generated by nano-stressors for upper Si layer: the strain-relaxed β-FeSi2 NDs.

22am2-A7 テンプレーテッド熱デウェッティングのためのプラスチックモールドを用いた金薄膜層への直接ナノインプリント法

A new fabrication process of a metal nano-dot array by the templated thermal dewetting process is developed in this paper. This process comprises 3 steps; the thin Au film deposition on a quartz glass substrate, the nano imprint by using the plastic mold on the Au film, and self-organization of a nano dot array by the thermal dewetting process. In this propose, self-organization of nano dot array on a groove patterned substrate is investigated. Effect of groove patterned on the dot morphology and arrangement are studied experimentally. The results show that the polymer film mold transfer grooves pattern on the surface of workpieces and it is show that grooves by this process is effective to control nano dot array generation in its thermal annealing process. It is confirmed that a nano dot array of good arrangement can be fabricated by the templated thermal dewetting method.

J1640202 プラスチック基板上に規則配列した金属ナノドットアレイの効率的製造法 : 超微細切削加工による石英ガラス基板へ微細溝加工法の検討([J164-02]マイクロ・ナノ理工学:nmからmmまでの表面制御とその応用(2))

The authors are developing a manufacturing process of a metal nano dot array on a plastic substrate. In this paper, machining technology of a quartz glass substrate with fine groove array used for the process is studied. It is shown that a fine groove narrower than 300 run can be machined on a quartz glass plate by using a specially designed machining tester. It is also demonstrated that a fine groove array of a large area (1cm × 1cm) can be fabricated.

Effect of Composition on Energy Spectra of CdS/Cd<I><SUB>1</SUB></I><SUB>–</SUB><I><SUB>X</SUB></I>Zn<I><SUB>X</SUB></I>S Nano Dots

Effect of Composition on Energy Spectra of CdS/Cd<I><SUB>1</SUB></I><SUB>–</SUB><I><SUB>X</SUB></I>Zn<I><SUB>X</SUB></I>S Nano Dots

Sensitive and Selective Gold Nanomaterials Based Optical Probes

AbstractGold nanomaterials (Au NMs) based optical probes have recently attracted considerable attention in the analysis of environmental and biological samples due to their simplicity, sensitivity, and selectivity. Au nanoparticles (NPs) having unique size‐ and shape‐dependent optical properties, high extinction coefficients, and super‐quenching capability, have been employed for development of sensitive absorption, fluorescence quenching, and light scattering approaches. On the other hand, small sizes of fluorescent Au nanodots (NDs) have been used for the photoluminescent detection of analytes. Preparation and optical properties of Au NMs are briefly discussed. Au NMs based colorimetric, fluorescent, and light scattering approaches for the detection of metal ion, DNA, and proteins are highlighted with respects to their simplicity in preparation, stability, selectivity, and sensitivity. The advantages and disadvantages of different detection methods for sensing of interesting analytes using functional Au NMs are discussed. DNA‐Au NMs are particularly emphasized to show their advantages for the detection of toxic heavy metal ions, specific sequence DNA, platelet‐derived growth factor (PDGF), and thrombin.

(Invited) Study on Charge Storage and Optical Response of Hybrid Nanodots Floating Gate MOS Devices for Their Optoelectronic Application

We have designed and fabricated hybrid nanodots structures, in which Si quantum dots (QDs) and either Ni-silicide or Pt-silicide nanodots (NDs) are stacked with ultrathin SiO2 interlayer, as a novel functional floating gate (FG) to satisfy both multiple valued capability and large capacity on charge storage. Multiple-step charge injection to sililcide NDs through discrete energy states in Si-QDs and stable storage of many charges in deep potential wells in silicide NDs have been confirmed from electrical characteristics of MOS capacitors and transistors measured at room temperature. A unique optical response of the hybrid NDs FG to near-infrared light irradiation, which is caused by the transfer of photo-excited electrons from silicide NDs to Si-QDs, has also been demonstrated.

Characterization of Ge Films on Si(001) Substrates Grown by Nanocontact Epitaxy

We quantitatively characterized Ge films epitaxially grown on Si(001) substrates by nanocontact epitaxy. The naocontact epitaxy was composed of three stages: elastically-strain-relaxed nanodot (ND) formation, second layer growth for surface flattening, and final layer growth for high crystallinity. X-ray diffraction results showed that the lattice mismatch strain was almost-fully relaxed on the order of ∼0.05% in Ge films as thin as 100 nm, and was independent of the growth condition of films (second and final layers) above NDs. This supports the idea of a mechanism in which strain relaxation is caused by elastically-strain-relaxed ND formation. It was also verified by simple elastic theory calculation and plan-view transmission electron microscopy. Photoluminescence was observed from the thin film at ∼0.8 eV, suggesting high quality with less point defects.

Nano Slit And Dot Array Pattern Of Au On SiO2 substrates Using Laser Beam Lithography

Highly monochromatic coherent light intensity of lasers provides the possibility of fabricating periodic nano-patterns which are needed in many applications. Here, we report 2D grating structure and periodic nano hole and dot arrays fabricated using two laser beam interference lithography. Using this method periodic grating as well as dot patterns have been fabricated with structure size of 50 -100 nm and pitch of 200-300 nm on SiO2 substrate. The nano-patterns are formed by inverting an array of photoresist posts by a lift-off process and subsequent reactive-ion etching using chromium as an etch mask. The depth of patterns can be tuned simple by laser dose to obtain high aspect ratio gratings. Transmission spectra measured in Au slits shows strong resonance features at 520 and 640 nm. Finite difference time domain simulations are used to estimate the near-field enhancement at the center of the slit pattern. Copyright © 2013 VBRI press.

Restrictions of Si-based Ge nanodots from porous alumina membranes

This paper reports growth of ordered Ge nanodots (NDs) with uniform sizes on silicon substrates using porous alumina membranes (PAMs) as templates. The relationships between substrate temperatures (400–600°C) and site distribution of Ge NDs are studied. Ordered arrangements of Ge NDs are realized at 400°C and 500°C, respectively. Due to joint effect of substrate temperature and restrictions from PAM, an uncommon size change trend is found. At 400°C, triangular pyramid-like and short cylindrical Ge NDs are obtained with different nanopore aspect ratios of PAMs. A geometrical optic method is used to analyze the mechanism of Ge NDs with such shapes. Raman characterization is utilized to study the strain in Ge NDs. As a result, almost pure Ge content and 1.5% tensile strain are revealed, which are attributed respectively to the low substrate temperature and thermal mismatch among Si substrate, Ge ND and PAM.

Organic Memory Transistors Using Monolayer of Semiconductor Colloidal Nano-Dots as a Floating Gate

We fabricated pentacene-based memory field-effect transistors (FETs) in which a monolayer of semiconductor colloidal nano-dots (NDs) is embedded as a floating gate. After a sufficiently large writing voltage was applied on the control gate, the fabricated FETs showed a large positive threshold voltage (Vth) shift that was attributed to electrons trapped in embedded NDs. The Vth shift was measured as a function of the writing voltage, and it was shown that the minimum writing voltage for memory FETs with small NDs is significantly larger than that for FETs with large ones. This result supports the proposed model of the memory effect in which electrons that tunneled from nearby pentacene molecules are trapped in embedded NDs because the electron energy level in small NDs is higher than that in large ones.

Epitaxial Growth of Iron-Silicide Nanodots on Si Substrates Using Ultrathin SiO2 Film Technique and Their Physical Properties

We developed a formation technique for iron silicide nanodots (NDs) on Si substrates using ultrathin SiO2 film technique. In this technique, the NDs were epitaxially grown on Si substrates with ultrahigh density (>1012 cm-2). Furthermore, the crystal structures in formed NDs are controllable even though iron silicide has complicated phase diagram. The optical properties of semiconductor β-FeSi2 NDs were measured on nanometer scale, which clarified their optical absorption band edges. Magnetic properties of formed Fe3Si NDs were investigated, which indicated the magnetic dipole interactions in ultrahigh density ND system. This strongly depended on ND morphology demonstrating magnetic properties could be controlled by manipulating ND formation.

Formation and Characterization of Hybrid Nanodots Floating Gate for Optoelectronic Application

ABSTRACTWe have fabricated a hybrid nanodots floating gate (FG) in which Si quantum dots (QDs) and silicide nanodots (NDs) are stacked with a very thin SiO2 interlayer in order to satisfy both multiple valued capability and charge storage capacity for a sufficient memory window and to open up novel functionality for optoelectronic application. In electron charging and discharging characteristics measured with application of pulsed gate biases to MOS capacitors with a hybrid NDs FG, stepwise changes in the rates for electron injection and emission were revealed with increasing pulse width at room temperature. Also, nMOSFETs with a hybrid NDs FG show unique hysteresis with stepwise changes in the drain current - gate voltage characteristics. The observed characteristics can be interpreted in terms that the electron injection and storage into silicide-NDs proceed through the discrete charged states of Si-QDs. For MOS capacitors with a triple-stacked hybrid NDs FG fabricated by adding another Si-QDs, by subgap light irradiation from the back side of the Si substrate, a distinct infrared optical response in C-V characteristics was detected at room temperature. The result is attributable to the shift of charge centroid in the hybrid NDs FG as a result of transfer of photoexcited electrons from silicide NDs to Si-QDs.

Improvement in Crystal Quality and Optical Properties of <I>n</I>-Type GaN Employing Nano-Scale SiO<SUB>2</SUB> Patterned <I>n</I>-Type GaN Substrate

n-type GaN epitaxial layers were regrown on the patterned n-type GaN substrate (PNS) with different size of silicon dioxide (SiO2) nano dots to improve the crystal quality and optical properties. PNS with SiO2 nano dots promotes epitaxial lateral overgrowth (ELOG) for defect reduction and also acts as a light scattering point. Transmission electron microscopy (TEM) analysis suggested that PNS with SiO2 nano dots have superior crystalline properties. Hall measurements indicated that incrementing values in electron mobility were clear indication of reduction in threading dislocation and it was confirmed by TEM analysis. Photoluminescence (PL) intensity was enhanced by 2.0 times and 3.1 times for 1-step and 2-step PNS, respectively.

A Study of Nano Materials and Their Reactions in Liquid Using in situ Wet Cell TEM Technology

AbstractSeveral nano material and reaction systems were in situ monitored with an electrochemical TEM wet cell set up. In a 1 g/L sliver particle aqueous solution, the particles were observed to be ca. 10 nm sized, in both discrete particle and nano cluster forms. The silver particles were attached to the 50 nm‐thick Si3N4 windows of the wet cell and could not move freely in the liquid. With a SiCl4 liquid loaded in the wet cell, silicon nano materials were controllably grown on the wet cell windows by means of a liquid phase electron beam induced deposition (EBID) method. The deposited nano dots were nicely round‐shaped, and demonstrated a power law growth dependency on beam exposure time in a log‐log plot. In a NiCl2 solution/Ni system, both electrochemical deposition and dissolution of the nickel nano films were observed while applying electric biases on to the nickel electrodes in the wet cell. Instead of extensional growth on existing crystals, interestingly, it is more commonly observed that new nickel nano particles grow out in front of the existing film first and then merged into the film. The wet cell set up is demonstrated to be a versatile tool for nano liquid system research.

In vivo Metabolic Imaging of Insulin with Multiphoton Fluorescence of Human Insulin–Au Nanodots

Functional human insulin-Au nanodots (NDs) are synthesized for the in vivo imaging of insulin metabolism. Benefiting from its efficient red to near infrared fluorescence, deep tissue subcellular uptake of insulin-Au NDs can be clearly resolved through a least-invasive harmonic generation and two-photon fluorescence (TPF) microscope. In vivo investigations on mice ear and ex vivo assays on human fat tissues conclude that cells with rich insulin receptors have higher uptake of administrated insulin. Interestingly, the insulin-Au NDs can even permeate into lipid droplets (LDs) of adipocytes. Using this newly discovered metabolic phenomenon of insulin, it is found that enlarged adipocytes in type II diabetes mice have higher adjacent/LD concentration contrast with small-sized ones in wild type mice. For human clinical samples, the epicardial adipocytes of patients with diabetes and coronary artery disease (CAD) also show elevated adjacent/LD concentration contrast. As a result, human insulin-Au nanodots provide a new approach to explore subcellular insulin metabolism in model animals or patients with metabolic or cardiovascular diseases.

InP nanocrystals on silicon for optoelectronic applications

One of the solutions enabling performance progress, which can overcome the downsizing limit in silicon technology, is the integration of different functional optoelectronic devices within a single chip. Silicon with its indirect band gap has poor optical properties, which is its main drawback. Therefore, a different material has to be used for the on-chip optical interconnections, e.g. a direct band gap III–V compound semiconductor material. In the paper we present the synthesis of single crystalline InP nanodots (NDs) on silicon using combined ion implantation and millisecond flash lamp annealing techniques. The optical and microstructural investigations reveal the growth of high-quality (100)-oriented InP nanocrystals. The current–voltage measurements confirm the formation of an n–p heterojunction between the InP NDs and silicon. The main advantage of our method is its integration with large-scale silicon technology, which allows applying it for Si-based optoelectronic devices.