Thickness Of Dots Research Articles

77‐2: Quantum‐Dot Color Conversion Achieved by A Novel Structure of Hollow Cylindrical Blue MicroLED

This study proposes a novel design for achieving color conversion in micro light‐emitting diodes (Micro‐LEDs) using a hollow cylindrical structure. Instead of printing quantum dots (QDs) on the upper surface of the Micro‐LEDs, QDs are printed in a hollow place created by designing hollows of varying sizes and applying a layer of highly reflective metal to the top and outer walls. The design of this structure confines the emission light to the hollows, reduces photon leakage, and increases the path length of the excitation light in the quantum dot area. The color conversion capabilities of 60, 70, 80, and 90 μm hollows were investigated, and a 3×3 array was demonstrated. Using this approach, the thickness of the quantum dots on the upper surface of the LED can be reduced, without the need for a thick black matrix for reducing the problem of light crosstalk. This hollow cylindrical design presents a promising new approach for achieving color conversion in Micro‐LEDs, with potential applications in displays and lighting technologies.

P‐10.9: Quantum Dot Color Conversion Achieved by A Novel Structure of Hollow Cylindrical Blue Micro‐LED

This paper proposes a novel approach to achieve color conversion in micro light-emitting diodes (Micro-LEDs) using a hollow cylindrical design, which allows the printing of quantum dots (QDs) in a hollow place. By varying the sizes of the hollows and applying a highly reflective metal layer to the top and outer walls, the emission light can be confined to the hollows, reducing the leakage of photons and increasing the path length of the excitation light in the quantum dot area. We investigated the color conversion capabilities of 60, 70, 80, and 90 um hollows, and demonstrated a 3x3 array. This approach reduces the thickness of the quantum dots on the LED surface and eliminates the need for a thick black matrix, thereby reducing the problem of light crosstalk. This hollow cylindrical design has potential applications in displays and lighting technologies.

Fast, eco-friendly synthesis of blue luminescent nitrogen-doped graphene quantum dots in glycerol

Nitrogen-functionalized graphene quantum dots (N-GQDs) were synthesized by hydrothermal transformation of glycine precursors in glycerol. Functionalization of GQDs with nitrogen was confirmed with FTIR spectroscopy. Atomic force microscopy (AFM) analysis revealed that the thickness of the quantum dots is around ~ 1 nm while the lateral dimensions are in the range from 20 to 80 nm. N-GQDs exhibit strong fluorescence in the blue (420 nm) region and they are suitable for bioimaging applications.

Predicting retinal pigment epithelium remodelling and its functional impact.

To identify predictive factors for RPE tear remodelling and its correlation with functional and morphological outcomes. Retrospective longitudinal study of patients with retinal pigment epithelium (RPE) tears secondary to age-related macular degeneration (AMD). Imaging was performed using spectral-domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF). RPE layer integrity in the RPE-denuded area was examined with SD-OCT, and variation in the RPE-denuded homogeneous hypofluorescent area was examined with FAF over time for each case (eye). Patients were divided in two groups, according to the presence (Rem) or absence (No Rem) of evidence of RPE tear remodelling. Data were collected at three different time points: at baseline (at diagnosis of exudative AMD), at RPE tear diagnosis, and at the last available follow-up. Using SD-OCT, the following parameters were evaluated: type of CNV, type of PED and its dimensions, presence of subretinal (SRF) or intraretinal (IRF) fluid, central retinal thickness (CRT), presence and location of hyperreflective dots, and dimension and location of RPE tear. This study included 32 eyes from 31 patients (19 female and 12 male), with RPE tears secondary to AMD. RPE remodelling after tear development was evident in 17 (53.1%) eyes after 7 [1-59] months. Anatomical recovery was associated with a younger age at RPE tear diagnosis (73 ± 7 vs. 81 ± 7 years old, p=0.01), smaller and narrower retinal pigment epithelial detachment (PED) at tear diagnosis (height 369 vs. 602 μm, p=0.02; width 2379 vs. 3378 μm, p=0.04), and the presence of SRF at tear diagnosis (94% vs. 53%, p=0.02). After adjusting for other covariates, a younger age at RPE tear diagnosis maintained significant association with RPE tear remodelling. RPE tear remodelling did not correlate with a better visual outcome at last follow-up (43 ± 22.8 vs. 34 ± 23.8 ETDRS letters, p=0.30). Final VA was directly proportional to VA at tear diagnosis (r= 0.654; p<0.001) and correlated negatively with PED width at tear diagnosis (r = -0.388; p=0.03). RPE remodelling was evident in half of our sample and was associated with a younger age, smaller and narrower PED at RPE tear diagnosis, and presence of SRF also at tear diagnosis. Nevertheless, this structural recovery did not result in a better functional outcome.

不同核心尺寸及壳层厚度CdTe/CdS量子点非线性光学及超快动力学特性

CdTe core-shell semiconductor quantum dots are being widely explored due to their special nonlinear optics and ultrafast dynamics characteristics that include solar cells, optoelectronic devices, biological labeling, and optics fiber sensing fields. In this work, the six kinds of CdTe/CdS core-shell quantum dots were researched in the different core sizes and shell thicknesses for the nonlinear optics and ultrafast dynamics characteristics. The nonlinear absorption and refraction coefficients of the samples were measured by using Z-scan technology under the action of 400 nm wavelength and 130 fs laser pulse width. The experimental results show that the shell thickness of CdTe/CdS core-shell quantum dots affects the nonlinear absorption and refraction characteristics, in which the nonlinear absorption and refraction coefficients increase with the shell thickness. And the core size mainly affects the nonlinear absorption characteristics, while the nonlinear absorption coefficient decreases with the increase of the core size. At the same time, femtosecond time-resolved transient absorption spectroscopy technology was used to measure the ultrafast dynamics characteristics of the samples under the conditions of 400 nm wavelength, 130 fs pulse width, 1 kHz frequency, and 400 nJ single-pulse energy. The transient absorption spectra and ultrafast dynamics curves were obtained. The results suggest that the rising time of bleaching signal increases with the shell thickness. The decay time of the fast process increases with the shell thickness and core size. The decay time of the slow process increases with the shell thickness. The research reveals the influence of the core size and shell thickness of CdTe core-shell quantum dots on the nonlinear optics and ultrafast dynamics, providing a theoretical basis for the preparation of core-shell quantum dots and the research of the photophysical properties.

Whispering gallery and surface mode of electrons in lateral and corrugated quantum dots

Quantum dots (QDs) are fundamental elements in the applications related to light–matter interaction, such as solar cells, lasers and sensors. Moreover, some modes of electrons including whispering galley modes (WGMs) and surface modes can be incorporated in many electronic systems, in high Q-resonators, and quantized reflection/transmission. Therefore, controlling and manipulating their energy spectra is vital. Here, we investigate energy spectra as well as WGM and surface mode of electrons in lateral and corrugated QDs. Although, lateral QDs are usually modelled by a 2D harmonic oscillator (with zero thickness), we show that even very small thickness of dots can change their energy spectra, also they can contain surface mode of electrons. Moreover, we investigate WGM in deformed QDs, and the dots which contain corners in their outermost region, and show that some degenerated points would be created. Meanwhile, in the corrugated QDs, the wavefunction would be distributed in the specific teeth based on its energy level.

The two-dimensional boron nitride hierarchical nanostructures: Controllable synthesis and superhydrophobicity

Layered boron nitride materials are used as superb protective coatings and reinforcing materials due to their high mechanical strength and chemical inertness. Herein, we report on the synthesis of two dimensional boron nitride (2D-BN) hierarchical nanostructures by a facile and efficient approach using boric acid (H3BO3) and hexamethylenetetramine (C6H12N4) as a reaction precursors. Our findings indicate that 2D hierarchical nanostructure was an assembling of BN quantum dots and exhibit varied wetting properties. The shape, size, and thickness of the BN quantum dots were well controlled by properly adjusting the growth parameters. With changing the temperature and other reaction conditions as well as ratios of reactants, the average size of BN quantum dots varies from 35 nm to 5 nm. Strong superhydrophobic properties with the contact angle of 155° are obtained for 2D-BN. These 2D-BN nanostructure possesses the properties conflicting to carbon nanomaterials such as high temperature stability, high chemical inertness and intrinsically semiconducting and may find application in nanoelectronics, catalyst support, as a composite materials and self-cleaning coatings etc., especially those working in harsh environment and at high temperature.

Wavelength-tunable InAsP quantum dots in InP nanowires

There is considerable interest in quantum dots incorporated in nanowires for nanolasers and quantum emitters. In this letter, we demonstrate single InAsP quantum dots embedded in InP nanowires grown by metalorganic vapor-phase epitaxy. Despite the abrupt change of growth conditions at the interface, InAsP quantum dots can be grown in pure wurtzite InP nanowires. We develop a model and analyze the effects of the thickness of InAsP quantum dots and the composition of As on the formation of dislocations. Furthermore, the InAsP/InP quantum dot nanowires show bright photoluminescence up to room temperature without any surface passivation. The emission from the quantum dots could be well tuned by adjusting the dot size either vertically or laterally. The study demonstrates the potential of this material system for optoelectronic applications.

Influence of Ga(Al)As substrates on surface morphology and critical thickness of InGaAs quantum dots

Influence of Ga(Al)As substrates on surface morphology of InGaAs quantum dots and critical thickness of In0.5Ga0.5As film grown by molecular beam epitaxy is investigated. The In0.5Ga0.5As quantum dots are grown on (001) surfaces of GaAs and Al0.25Ga0.75 A at 450 °C, scanning tunneling microscope images show that the size of quantum dots varied slightly for 10 ML of In0.5Ga0.5As grown on GaAs and Al0.25Ga0.75As surfaces. Reflection high energy electron diffraction (RHEED) is used to monitor the growth of 4 monolayers (ML) In0.5Ga0.5As on Al0.25Ga0.75As and GaAs surfaces during deposition. The critical thickness is theoretically calculated by adding energy caused by surface roughness and heat from substrate. The calculations show that the critical thickness of In0.5Ga0.5As grown on GaAs and Al0.25Ga0.75As are 3.2 ML and 3.8 ML, respectively. The theoretical calculation agrees with the experimental results.

Study on nonlinear optical thin films of CdZnSe quantum dots

By one pot method prepared high quality Cd0.5Zn0.5Se uniform quantum dots, and the Cd0.5Zn0.5Se quantum dot film with uniform thickness was prepared by rotating coating method on the surface of FTO glass. The thickness and surface morphology of the quantum dots were measured and characterized by using a bench and scanning electron microscope. Third order nonlinear optical properties of quantum dots film was investigated by Z-scan method. The results show that at a wavelength of 532 nm laser induced, Cd0.5Zn0.5Se quantum dots film perform out of the excellent reverse saturable absorption effect, the third order nonlinear refractive index n2 is 8.2 × 10−12esu, third-order nonlinear absorption beta coefficient of 2.3 × 10−5m/W.

Down-conversion monochromatic light-emitting diodes with the color determined by the active layer thickness and concentration of carbon dots

Monochrome LEDs and color graphical patterns were fabricated by changing the thickness and doping concentration of carbon dot layers.

Fabrication of CdSe/ZnS quantum dots thin film by electrohydrodynamics atomization technique for solution based flexible hybrid OLED application

Abstract The synthesis and novel fabrication of quantum dot layers has been performed by using electrohydrodynamics atomization technique. The surface, optical and electrical properties of the fabricated films have been characterized by FE-SEM, TEM, spectroscopes and semiconductor device analyzer. The CdSe/ZnS core/shell quantum dots have been synthesized and dispersed in toluene and DMSO as cosolvents. The sprayed CdSe/ZnS quantum dots have been employed as emissive layer. The conjugate polymers of PEDOT:PSS and MEH-PPV are used as the hole and electron transport layers. The thickness of emissive layer for hybrid device has been optimized by changing the standoff distance of electrohydrodynamics atomization system. The flexible hybrid device with optimized thickness of quantum dots showed red light at 634 nm wavelength in visible range with 165 mA/cm2 current density and 2.2 lux of luminance at 15 V.

Optical investigation of InAs/InP(1 0 0) quantum dots grown by gas source molecular beam epitaxy

We report on the optical characteristics of InAs quantum dots based on the InP(100) substrate grown by gas source molecular beam epitaxy without assisting any other methods. The photoluminescence was carefully investigated by adjusting the thickness of InAs layers and the growth temperature. A wide range of emitting peaks is obtained with the increase in the thickness of InAs layers. In addition, we find that the morphology and shape of quantum dots also greatly depend on InAs layers. The images of atomic force microscopy show that the quantum dots like forming into quantum dashes elongated along the [01−1] direction when the thickness of InAs layers increased. A critical thickness of formation quantum dots or quantum dash is obtained. At the same time, we observe that the growth temperature also has a great impact on the emission wavelength peaks. High qualities of InAs/InP(100) quantum dots providing their emission wavelength in 1.55μm are obtained, and good performances of quantum dots lasers are fabricated.

Chirality control via double vortices in asymmetric Co dots

Reproducible control of the magnetic vortex state in nanomagnets is of critical importance. We report on chirality control by manipulating the size and/or thickness of asymmetric Co dots. Below a critical diameter and/or thickness, chirality control is achieved by the nucleation of a single vortex. Interestingly, above these critical dimensions, chirality control is realized by the nucleation and subsequent coalescence of two vortices, resulting in a single vortex with the opposite chirality as found in smaller dots. Micromagnetic simulations and magnetic force microscopy highlight the role of edge-bound half vortices in facilitating the coalescence process.

Nano-arrays of SAM by dip-pen nanowriting (DPN) technique for futuristic bio-electronic and bio-sensor applications

Nano-arrays of bio-molecules have potential applications in many areas namely, bio-sensors, bio/molecular electronics and virus detection. Spot array, micro-contact printing and photolithography are used for micron size array fabrications while Dip-Pen Nanowriting (DPN) is employed for submicron/nano size arrays. We have fabricated nano-dots of 16-MHA (16-mercaptohexadecanoic acid) self-assembled monolayer (SAM) on gold substrate by DPN technique with different dwell time under varying relative humidity. These patterns were imaged in the same system in LFM (Lateral Force Microscopy) mode with fast scanning speed (5 Hz). The effect of humidity on size variation of nano-dots has been studied. During experiments, relative humidity (RH) was varied from 20% to 60%, while the temperature was kept constant ~ 25 °C. The minimum measured diameter of the dot is ~ 294 nm at RH = 20% for a dwell time of 2 s. The thickness of the 16-MHA dots, estimated in NanoRule image analysis software is ~ 2 nm, which agrees well with the length of single MHA molecule (2.2 nm). The line profile has been used to estimate the size and thickness of dots. The obtained results will be useful in further development of nano-array based bio-sensors and bio-electronic devices.

Magnetic Properties of Various Thick Co-Fe Circular Dot Arrays

We have studied the magnetic properties of Co-Fe circular dot arrays with various thicknesses and diameters in order to determine the optimum thickness and diameter of these dot arrays with a single-domain state for the transmission of spin information. For the thickness of 10 nm, the magnetic state changes from a multi-domain state to a closure-domain state and further to a single-domain state with decreasing diameter. On the other hand, for the thickness of 30 nm and 50 nm, all magnetic states are in a vortex state, regardless of the diameter. From these results, it is found that the optimum thickness and diameter of Co-Fe circular dots with a single-domain state are, respectively, 10 nm and less than 100 nm.

Enhanced Photoelectrochemical Response of Zn-Dotted Hematite

Photoelectrochemical response of thin films ofα-Fe2O3, Zn dopedα-Fe2O3, and Zn dots deposited on dopedα-Fe2O3prepared by spray pyrolysis has been studied. Samples of Zn dots were prepared using thermal evaporation method by evaporating Zn through a mesh having pore diameter of 0.7 mm. The presence of Zn-dotted islands on dopedα-Fe2O3surface exhibited significantly large photocurrent density as compared to other samples. An optimum thickness of Zn dots∼230 Å is found to give enhanced photoresponse. The observed results are analyzed with the help of estimated values of resistivity, band gap, flatband potential, and donor density.

Periodicity and alignment of large-scale carbon nanotubes arrays

Intensive studies have been carried out on controlling the periodicity and alignment of large-scale periodic arrays of carbon nanotubes (CNTs) using plasma-enhanced chemical vapor deposition. Catalytic dots are first prepared by self-assembly of polystyrene spheres on chromium-coated silicon substrates. Preparation parameters for CNTs growth including temperature, thickness of catalytic dots, plasma current intensity, and pregrowth plasma etching time are fine tuned and analyzed to achieve optimal combinations. High-quality aligned CNTs arrays with long-range periodicity and controlled diameters have been achieved. The good periodicity and alignment are critical for their applications such as photonic crystals, negative index of refraction, etc.

A simple theoretical analysis of the thermo-electric power in quantum dots of nonparabolic semiconductors in the presence of a parallel magnetic field

Abstract In this paper an attempt is made to study the thermoelectric power in quantum dots of non-parabolic semiconductors in the presence of a parallel magnetic field on the basis of a new electron dispersion law. It is found, taking Hg1 − xCdxTe and In 1 − xGaxAsyP1 − y lattice matched to InP as examples, that the thermoelectric power exhibits strong oscillatory dependencies with increasing magnetic field, alloy composition and thickness of the quantum dots, respectively. The thermopower increases with decreasing electron concentration and the numerical values of the same power in quaternary materials are greater in comparison with ternary compounds.

Laser chemical vapor deposition of TiN dots: A comparison of theoretical and experimental results

A mathematical model for the concentration profile of TiCl4 at the top surface of an Incoloy 800H substrate placed inside a laser chemical vapor deposition (LCVD) reactor is developed by using the three-dimensional transient mass diffusion equation. The model is used for studying the spatial variation of the thickness of TiN dots deposited by LCVD, using a CO2 laser and a reactive atmosphere consisting of TiCl4, N2, and H2. By assuming that the chemical reaction is first-order with respect to TiCl4, and that the sticking coefficient of TiN at the substrate surface is temperature dependent, the deposited TiN film is found to have a volcanic profile under certain conditions, which is in good agreement with experimental results.