Infrared Quantum Dots Research Articles

A monolithically integrated plasmonic infrared quantum dot camera

In the past few years, there has been increasing interest in surface plasmon-polaritons, as a result of the strong near-field enhancement of the electric fields at a metal-dielectric interface. Here we show the first demonstration of a monolithically integrated plasmonic focal plane array (FPA) in the mid-infrared region, using a metal with a two-dimensional hole array on top of an intersubband quantum-dots-in-a-well (DWELL) heterostructure FPA coupled to a read-out integrated circuit. Excellent infrared imagery was obtained with over a 160% increase in the ratio of the signal voltage (V(s)) to the noise voltage (V(n)) of the DWELL camera at the resonant wavelength of λ=6.1 μm. This demonstration paves the way for the development of a new generation of pixel-level spectropolarimetric imagers, which will enable bio-inspired (for example, colour vision) infrared sensors with enhanced detectivity (D) or higher operating temperatures.

THE EFFECT OF ELECTRODE MATERIALS ON THE OPTICAL CHARACTERISTICS OF INFRARED QUANTUM DOT-LIGHT EMITTING DEVICES

We present an optical model based on Green's function to investigate the efiect of using Single Wall Carbon Nanotube (SWCNT) as anode for infrared quantum dot light emitting devices (IR QD- LEDs). To the best of our knowledge there is no report in using SWCNT as anode in IR QD-LEDs. We have studied the emitted power distribution among the difierent optical modes (air, substrate, anode/organics, and surface plasmon modes (SP)), angular intensity distribution, and the emission spectral characteristics. We have found that the light outcoupling e-ciency of IR QD-LEDs based on SWCNT as anode was increased nearly by a factor of 4 relative to that one based on indium-tin oxide (ITO). We also investigated the efiect of using difierent cathode materials on the optical characteristics of IR QD-LEDs.

High performances III-Nitride Quantum Dot infrared photodetector operating at room temperature

In this paper we present a novel long wave length infrared quantum dot photodetector. A cubic shaped 6nm GaN quantum dot (QD) within a large 18 nm Al(0.2)Ga(0.8)N QD (capping layer) embedded in Al(0.8)Ga(0.2)N has been considered as the unit cell of the active layer of the device. Single band effective mass approximation has been applied in order to calculate the QD electronic structure. The temperature dependent behavior of the responsivity and dark current were presented and discussed for different applied electric fields. The capping layer has been proposed to improve upon the dark current of the detector. The proposed device has demonstrated exceptionally low dark current, therefore low noise, and high detectivity. Excellent specific detectivity (D*) up to approximately 3 x 10(8)CmHz(1/ 2)/W is achieved at room temperature.

Targeted near-IR QDs-loaded micelles for cancer therapy and imaging

The use of water-soluble, functionalized quantum dots (QDs) that are highly stable against oxidation for biological and biomedical applications is currently one of the fastest growing fields of nanotechnology. Polymer-based nanoparticles are now widely used for drug delivery and targeted therapy. We modified the surface of near Infrared QDs by the solid dispersion method using PEG–PCDA and PCDA–Herceptin conjugates to demonstrate water-solubility and target-specific properties. Upon UV irradiation, QD cores located within nanoprobes were further stabilized by intramicellar cross-linking between neighboring PCDA–Herceptin moieties. These cross-linked nanoprobes showed higher stability and less toxicity. Near-IR QDs-loaded micelles were spherical with diameters of around 130–150 nm. The anti-tumor effect of near-IR QDs-loaded micelles against MDA-MB-231 tumors was remarkably better than that of control. Mice treated with the near-IR QDs-loaded micelles had a tumor volume of about 285 mm 3, indicating shrinkage in initial tumor volume and inhibition of tumor growth by 77.3% compared to that of control group (saline injection). In addition, near-IR QDs-loaded micelles were injected intravenously into tumor-bearing nude mice for simultaneous tumor therapy and imaging. We observed that the targeted near-IR QDs-loaded micelles distributed rapidly throughout the animal body including the tumor in real time. These multi-functional nanoprobes could therefore be used for both active and passive targeting, imaging and treatment of cancers in the early stage.

Anode material based on SWCNT for infrared quantum dot light-emitting devices

We present an optical model based on Green’s function to investigate the effect of using single-wall carbon nanotube (SWCNT) as anode for infrared quantum dot light-emitting devices (IR QD-LEDs). To the best of our knowledge, there is no report in using SWCNT as anode in IR QD-LEDs. We have studied the emitted power distribution among the different optical modes (external propagating mode (photon outcoupling efficiency), substrate, anode/organics, and surface plasmon modes (SP)), angular intensity distribution, viewing angle effect on the optical characteristics, and the emission spectral characteristics. We have found that the light outcoupling efficiency of IR QD-LEDs based on SWCNT as anode was increased nearly by a factor of 4 relative to that one based on indium-tin oxide (ITO). We also investigated the effect of using different cathode materials on the optical characteristics of IR QD-LEDs.

Imaging morphogenesis, in Xenopus with Quantum Dot nanocrystals

Mesoderm migration is a well studied morphogenetic movement that takes place during Xenopus gastrulation. The study of mesoderm migration and other morphogenetic movements has been primarily based on in vitro assays due to the inability to image deep tissue movements in the opaque embryo. We are the first to report the use of Near Infra Red Quantum Dots (NIR QD’s) to image mesoderm migration in vivo with single cell resolution and provide quantitative in vivo data regarding migration rates. In addition we use QD’s to address the function of the focal adhesion kinase (FAK) in this movement. Inhibition of FAK blocks mesoderm spreading and migration both in vitro and in vivo without affecting convergent extension highlighting the molecular differences between the two movements. These results provide new insights about the role of FAK and of focal adhesions during gastrulation and provide a new tool for the study of morphogenesis in vivo.

Development of Silicon-Integrated Infrared Quantum Dot Light Emitting Diodes

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Preparation and Characterization of Highly Fluorescent, Glutathione-coated Near Infrared Quantum Dots for in Vivo Fluorescence Imaging

Fluorescent probes that emit in the near-infrared (NIR, 700–1,300 nm) region are suitable as optical contrast agents for in vivo fluorescence imaging because of low scattering and absorption of the NIR light in tissues. Recently, NIR quantum dots (QDs) have become a new class of fluorescent materials that can be used for in vivo imaging. Compared with traditional organic fluorescent dyes, QDs have several unique advantages such as size- and composition-tunable emission, high brightness, narrow emission bands, large Stokes shifts, and high resistance to photobleaching. In this paper, we report a facile method for the preparation of highly fluorescent, water-soluble glutathione (GSH)-coated NIR QDs for in vivo imaging. GSH-coated NIR QDs (GSH-QDs) were prepared by surface modification of hydrophobic CdSeTe/CdS (core/shell) QDs. The hydrophobic surface of the CdSeTe/CdS QDs was exchanged with GSH in tetrahydrofuran-water. The resulting GSH-QDs were monodisperse particles and stable in PBS (phosphate buffered saline, pH = 7.4). The GSH-QDs (800 nm emission) were highly fluorescent in aqueous solutions (quantum yield = 22% in PBS buffer), and their hydrodynamic diameter was less than 10 nm, which is comparable to the size of proteins. The cellular uptake and viability for the GSH-QDs were examined using HeLa and HEK 293 cells. When the cells were incubated with aqueous solutions of the GSH-QDs (10 nM), the QDs were taken into the cells and distributed in the perinuclear region of both cells. After 12 hrs incubation of 4 nM of GSH-QDs, the viabilities of HeLa and HEK 293 cells were ca. 80 and 50%, respectively. As a biomedical utility of the GSH-QDs, in vivo NIR-fluorescence imaging of a lymph node in a mouse is presented.

Proposal for ultra-high performance infrared Quantum Dot

In this paper, effect of an introduced defect on electrical and optical properties of quantum box and spherical quantum dot is studied. 3D-self-consistent solution of the Schrödinger-Poisson equations for evaluation of the proposed complex quantum box and analytical solution for spherical quantum dot are used. It is shown that with increasing the defect size and height a considerable enhancement in matrix element, optical nonlinearities (second order, quadratic electro-optic effect and the resonant third order nonlinear susceptibilities), optical linear absorption coefficient ( 4.5 -10 nm, 10(-4) approximately 10(-2) m.V(-1), 10(-12) approximately 10(-9) m(2) / V (2) , 10(-11) approximately 10(-9) m(2) / V(2) and 4.7 x 10(2) approximately 3.8 x 10(4) cm(-1) respectively) and electroabsorption properties associated with intersublevel transition of centered defect quantum dot are examined. Also, it is shown that enhancement of optical nonlinearity is approximately independent of defect position that is so excellent from practical implementation point of view. A THZ-IR photodetector based on resonant tunneling spherical centered defect quantum dot (RT-SCDQD) operating at room temperature is also investigated. Inserting the centered defect in quantum dot increases the dipole transition matrix element and so increases the absorption coefficient considerably (1.05 x 10(6) approximately 7.33 x 10(6)at 83 microm ). Therefore the quantum efficiency in SCDQD structure enhances which leads to increasing the responsivity of the proposed system. The double barrier reduces the dark current. These improvements concludes to ultra high detectivity 5 x 10(16) 2.25 x 10(9) cm Hz (1/2)/W at 83 and 300 degrees K at 83 microm respectively.

A modulation-doped longwave infrared quantum dot photodetector with high photoresponsivity

An InAs–InGaAs quantum dot (QD) longwave infrared (LWIR) photodetector (QDIP) with a peak wavelength of 8.2 µm is presented. The QDIP has modulation-doped QD active layers. At 77 K, the QDIP showed high photoresponsivities of 5.4 A W−1 and 3.6 A W−1 at biases of −0.8 V and 0.6 V, respectively. A peak photodetectivity of 7.8 × 109 cm Hz1/2 W−1 was obtained at 77 K in an IR detector compatible package.

Simultaneous two-color spectral fluorescence lymphangiography with near infrared quantum dots to map two lymphatic flows from the breast and the upper extremity

Due to their small size and poor access, the lymphatic function has been difficult to study in vivo. Especially difficult is the mapping of lymphatic drainage from two basins into the same node. Quantum dots can be used to perform multicolor images with high fluorescent intensity and are of a nano-size size suitable for lymphatic imaging via direct interstitial injection. Here we show simultaneous two-color in vivo wavelength-resolved spectral fluorescence lymphangiography using two near infrared quantum dots with different emission spectra, which allow non-invasive and simultaneous visualization of two separate lymphatic flows draining the breast and the upper extremity and variations in the drainage patterns and the water sheds within the axillary node. Two-color spectral fluorescence lymphangiography can provide insight into mechanisms of drainage from different lymphatic basins that may lead to sentinel lymph nodes detection of the breast cancer as well as prevention of complications such as lymphedema of the arm.

Near-infrared peptide-coated quantum dots for small animal imaging.

We have synthesized high quality type-II CdTe/CdSe near infrared quantum dots using successive ion layer adsorption and reaction chemistry. Transmission electron microscopy reveals that CdTe/CdSe can be synthesized layer by layer yielding quantum dots of narrow size distribution. Excitation and photoluminescence spectra reveal discrete type-II transitions, which correspond to energy lower that type-I bandgap. We have used a peptide coating technique on type-II and commercial near infrared quantum dots for delivery in live animals and cultured cells.

High detectivity InGaAs/InGaP quantum-dot infrared photodetectors grown by low pressure metalorganic chemical vapor deposition

We report a high detectivity middle-wavelength infrared quantum dot infrared photodetector (QDIP). The InGaAs quantum dots were grown by self-assembly on an InGaP matrix via low pressure metalorganic chemical vapor deposition. Photoresponse was observed at temperatures above 200 K with a peak wavelength of 4.7 μm and cutoff wavelength of 5.2 μm. The background limited performance temperature was 140 K, and this was attributed to the super low dark current observed in this QDIP. A detectivity of 3.6×1010 cm Hz1/2/W, which is comparable to the state-of-the-art quantum well infrared photodetectors in a similar wavelength range, was obtained for this InGaAs/InGaP QDIP at both T=77 K and T=95 K at biases of −1.6 and −1.4 V, respectively.

Novel Infrared Quantum Dot Lasers: Theory and Reality

Semiconductor heterostructures with size quantization of carriers in all three directions, or quantum dots (QDs), open a new era in device engineering. An important breakthrough occurred when the self-organised growth approach had been refined to such an extent, that defect-free QDs made with these technique exhibited properties predicted for zero-dimensional structures. Their practical application in devices, first of all lasers, became possible. When used for active layers in injection lasers differential gain is strongly increased potentially providing improved dynamic properties. The cut-off frequencies larger than 10 GHz are presently demonstrated. The saturation material gain is as high as 15 x 10 4 cm -1 as compared to QW values of about 3 x 10 3 cm -1 , The wavelength dependence of gain is best described by Master equations of microstates. High internal (>96%) and differential (70%) efficiencies at 300 K and output power up to 4 W are realized now for QD lasers emitting in the 0.94-1.15 μm range. Transparency current density of 18 A/cm 2 has been recently demonstrated at 1.15 μm. GaAs-based QD lasers emit near 1.3 μm with J th = 70 A/cm 2 (L = 1.9 mm, 300 K) and CW output power of ∼3 W. In narrow (7 μm) stripes almost chirp-free operation and relaxation oscillations at 2.4 GHz (L = 400 μm) are manifested. Differential efficiency is 55% and internal losses are 1.5 cm -1 . 1.3 μm GaAs-based QD VCSELs (300 K, I th = 1.8 mA, η diff > 40%) are realized.