Preparation and application of fluorescence dendritic macromolecular nanoparticles

Abstract

In recent years, carbon dots have shown great potential in biological imaging, drug delivery, and other fields. In this study, red fluorescent carbon dots with carboxyl functional groups on the surface were designed and prepared, and the fluorescence properties were studied. At the same time, the carbon dot was combined with dendritic macromolecules, and the aggregate particle size was about 25nm. This combination has good dispersion and stability in both water and methanol, and the DOX-loaded is about 6.72%. The small particle size makes it easy to enter the cells, so as to achieve the function of tumor treatment and cell imaging.     

Quantum Dots-in-a-Well Focal Plane Arrays

In this paper, the basics and some of the recent developments in quantum dots-in-a-well (DWELL) focal plane arrays (FPAs) are reviewed. Fundamentally, these detectors represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP), in which the active region consists of quantum dots (QDs) embedded in a quantum well (QW). This hybridization grants DWELLs many of the advantages of its components. These advantages include normally incident photon sensitivity without gratings or optocoupers, like QDIPs, and reproducible control over operating wavelength through ldquodial-in recipesrdquo as seen in QWIPs. Recently reported high-temperature operation results for DWELL FPAs now back up the conclusions drawn by the long carrier lifetimes observed in DWELL heterostructures using femtosecond spectroscopy. This paper will conclude with a preview of some upcoming advances in the field of DWELL FPAs.     

Effect of quantum dots on InAs/GaAs p-i-p quantum dots infrared photodetectors

ABSTRACT

In this paper, the InAs/GaAs p-i-p quantum dots infrared photodetectors (QDIPs) were successfully demonstrated by Apsys software. It consists of Al_0.3Ga_0.7As/GaAs structure to reduce dark current and InAs quantum dots (QDs) embedded in In_0.15Ga_0.85As as an active layer. The effect of structure parameters of InAs QDs on the dark current, photocurrent of the device and SNR (signal to noise) is discussed respectively, including different QDs density, the number of QD layer, GaAs thickness between QDs layers and Al_0.3Ga_0.7As, and GaAs thickness between two the QD layers.     

Optical and Electrical Properties of Colloidal Quantum Dots in Electrolytic Environments: Using Biomolecular Links in Chemically-Directed Assembly of Quantum Dot Networks

The threshold of the absorption spectra of colloidal cadmium sulfide (CdS) quantum dots in electrolytic solutions is shown to shift as the concentration of the electrolyte is varied. The shift in the absorption threshold as a function of the electrolytic concentration is given by electrolytic screening of the field caused by the intrinsic spontaneous polarization of these würtzite quantum dots. These electrolyte-dependent absorption properties are compared with Fermi-level tuning in carbon nanotubes in electrolytic environments.Moreover, concepts for integrating such colloidal quantum dots in high density networks with biomolecular links are discussed. Such biomolecular links are used to facilitate the chemically-directed assembly of quantum dots networks with densities approximating 10¹⁷ cm⁻³.     

Fabrication of infrared photodetectors

Abstract

This paper presents the fabrication of an integrated optoelectronic circuit consisting of a waveguide and photodetector. Fabrication of the waveguides took place in a RIBE system with 1·5 sccm CH₄/H₂ (60:40) and 0·5 sccm Ar. Wet etching defines the photodetector regions. The detection of surface damage is minimal, using a novel differential optical reflectance technique.     

Effects of substrate orientation on opto-electronic properties in self-assembled InAs/GaAs quantum dots

Electronic structure and optical transition characteristics in (100), (110), and (111) oriented InAs/GaAs quantum dots (containing \({\sim }2\) million atoms) were studied using a combination of valence force-field molecular mechanics and 20-band \(sp^{3}d^{5}s^{*}\) atomistic tight-binding framework. These quantum dots are promising candidates for non-traditional applications such as spintronics, quantum cryptography and quantum computation, but suffer from the deleterious effects of various internal fields. Here, the dependence of strain and polarization fields on the substrate orientation is reported and discussed. It is found that, compared to the (100) and (110) oriented counterparts, quantum dots grown on the (111) oriented substrate exhibit a smaller splitting (non-degeneracy) in the excited \(P\) states and enhanced isotropy in the interband optical emission characteristics.     

Quantum dot blinking: relevance to physical limits for nanoscale optoelectronic device

In designing nanoscale optoelectronic devices based on a small number of active quantum dots, it is of interest to consider that semiconductor nanocrystals (quantum dots) are observed to blink “on” and “off”. The time probability distributions scale as an inverse power law for colloidal quantum dots and exponentially for self-assembled dots. Possible mechanisms that cause the inverse power law and exponential blinking statistics are discussed in the paper and the relevance to quantum-dot based system architectures is discussed.     

Synthesis and luminescence of ceria decorated graphene quantum dots (GQDs): Evolution of band gap

ABSTRACT

Graphene quantum dots (GQDs) and CeO₂-GQDs were synthesized by using a facile hydrothermal method at 140°C. All the synthesized materials were characterized by TEM, UV-Vis Spectroscopy, FT-IR, Raman Spectroscopy and PL. Ceria decorated GQDs show different emission peaks with different excitation of wavelengths. The discrete change in dominant luminescence features of the GQDs and their composites indicate that the variation in PL occurs because of alteration in its shape, size and bandgap. Based on the experimental results of PL peak wavelength, the emission is attributed to quasi-molecular PL from the fragments composed of a few aromatic rings with oxygen containing functional groups.     

光栅型成像光谱仪杂散光校正技术研究

成像光谱仪中杂散光的存在会导致光谱测量误差,对杂散光的校正可以得到精确的测量结果。采用He-Ne激光器测出成像光谱仪的点扩展函数,假设成像光谱仪是线性波长不变系统的前提下,构建光谱函数矩阵,确定影响波长权重,再通过带宽校正矩阵对其进行带宽校正,从而对仪器测量中的杂散光误差进行校正。最后,通过实验表明此杂散光的修正方法基本上消除了杂散光对测量信号的影响。     

Anisotropic Quantum Dots

This paper presents a detailed calculation of the electronic structure of quantum dots with various geometries. In particular, non-circular quantum dots are examined and their characteristic properties analysed. A general matrix method was developed that allows us to treat a wide range of quantum dots with arbitrarily complex confinement potentials. The Hartree-Fock self-consistent method is applied to study quantum dots with many-electrons.     

Standing-wave Fourier transform spectrometer based on integratedMEMS mirror and thin-film photodetector

We report a novel, miniature Fourier transform spectrometer with a linear architecture that works by sampling a standing wave. The spectrometer consists of an electrostatically actuated microelectromechanical mirror with on-resonance displacement of up to 65 μm, a thin-film photodetector, and an electrical back plane for actuating the mirror. The integrated device offers mirror stability and fixed relative alignment of the three components. The spectrometer has better than 32-nm resolution at 633 nm     

An integrated target field framework for point-of-care halbach array low-field MRI system design

Objective

Low-cost low-field point-of-care MRI systems are used in many different applications. System design has correspondingly different requirements in terms of imaging field-of-view, spatial resolution and magnetic field strength. In this work an iterative framework has been created to design a cylindrical Halbach-based magnet along with integrated gradient and RF coils that most efficiently fulfil a set of user-specified imaging requirements.

Methods

For efficient integration, target field methods are used for each of the main hardware components. These have not been used previously in magnet design, and a new mathematical model was derived accordingly. These methods result in a framework which can design an entire low-field MRI system within minutes using standard computing hardware.

Results

Two distinct point-of-care systems are designed using the described framework, one for neuroimaging and the other for extremity imaging. Input parameters are taken from literature and the resulting systems are discussed in detail.

Discussion

The framework allows the designer to optimize the different hardware components with respect to the desired imaging parameters taking into account the interdependencies between these components and thus give insight into the influence of the design choices.

     

氧化物薄膜抑制量子点的光衰性能

量子点应用于LED中,可获得高饱和性、宽色域光源,在液晶显示背光源领域前景广阔。但是,影响量子点寿命的因素很多,如温度、水氧等,严重阻碍了其推广应用。目前,水氧对量子点光衰性能影响的研究较少,本文旨在研究无机氧化物薄膜阻隔层对量子点光衰性能的影响。量子点成膜后表面溅射Al2O3、SiO2水氧隔离薄膜,蓝光LED激发绿光量子点,研究其光衰性能。结果表明,与无隔离膜的样品相比,单层SiO2薄膜的样品光衰性能有所改善;双层的SiO2薄膜及SiO2/Al2O3复合薄膜,可以有效地减小薄膜孔洞大小和孔洞密度,阻隔水氧的进入,抑制量子点的光衰减,提高量子点寿命。     

Blinking mechanism of colloidal semiconductor quantum dots: Blinking mechanisms

Nanoscale semiconductor quantum dots in colloidal suspensions are observed to blink with off times, τ_off, that scale as 1/τ < eqid2 > ^3/2. In this paper, it is shown by relating the fluctuations of the surface charge density on the quantum dot to fluctuations in the double layer potential, that the related fluctuations in the barrier potential have exactly the functional form needed to result in an inverse-power-law distribution for off times.     

A vision of 14 T MR for fundamental and clinical science

Objective

We outline our vision for a 14 Tesla MR system. This comprises a novel whole-body magnet design utilizing high temperature superconductor; a console and associated electronic equipment; an optimized radiofrequency coil setup for proton measurement in the brain, which also has a local shim capability; and a high-performance gradient set.

Research fields

The 14 Tesla system can be considered a ‘mesocope’: a device capable of measuring on biologically relevant scales. In neuroscience the increased spatial resolution will anatomically resolve all layers of the cortex, cerebellum, subcortical structures, and inner nuclei. Spectroscopic imaging will simultaneously measure excitatory and inhibitory activity, characterizing the excitation/inhibition balance of neural circuits. In medical research (including brain disorders) we will visualize fine-grained patterns of structural abnormalities and relate these changes to functional and molecular changes. The significantly increased spectral resolution will make it possible to detect (dynamic changes in) individual metabolites associated with pathological pathways including molecular interactions and dynamic disease processes.

Conclusions

The 14 Tesla system will offer new perspectives in neuroscience and fundamental research. We anticipate that this initiative will usher in a new era of ultra-high-field MR.

     

Numerical modeling of a CMOS UV/blue photodetector based on MOSFET and lateral photosensitive diode

A complementary metal‐oxide semiconductor photodetector with ring‐shaped structure is presented in this paper, which consists of a p‐channel metal‐oxide‐semiconductor field‐effect transistor and lateral photodiodes and can be applied for ultraviolet (UV)/blue detection. The p‐channel metal‐oxide‐semiconductor is enclosed by ring‐shaped lateral photodiodes and lateral ring‐shaped photodiodes for enlarging near‐surface depletion region of the photodetector. Photoelectric conversion process of the photodetector has been modeled, and some performance parameters of photodetector have been derived and evaluated. The simulation results show that the photodetector can exhibit a high current responsivity of 1 × 10⁻³ Å even for ultra‐weak light such as 0.01 μW. The composite photodetector is fabricated in a standard 0.18 µm complementary metal‐oxide semiconductor technology. The test results reveal that the presented photodetector, which just like predicted by the model, is an effective way to solve the low response of silicon‐based UV detector. In a word, the presented photodetector has a big potential application value in weak light and UV/blue light detection. Copyright © 2015 John Wiley & Sons, Ltd.     

High-resolution MR imaging of the rat spinal cord in vivo in a wide-bore magnet at 17.6 Tesla

The objective was to demonstrate the feasibility and to evaluate the performance of high-resolution in vivo magnetic resonance (MR) imaging of the rat spinal cord in a 17.6-T vertical wide-bore magnet. A probehead consisting of a surface coil that offers enlarged sample volume suitable for rats up to a weight of 220 g was designed. ECG triggered and respiratory-gated gradient echo experiments were performed on a Bruker Avance 750 wide-bore spectrometer for high-resolution imaging. With T^*₂ values between 5 and 20 ms, good image contrast could be obtained using short echo times, which also minimizes motion artifacts. Anatomy of healthy spinal cords and pathomorphological changes in traumatically injured rat spinal cord in vivo could be visualized with microscopic detail. It was demonstrated that imaging of the rat spinal cord in vivo using a vertical wide-bore high-magnetic-field system is feasible. The potential to obtain high-resolution images in short scan times renders high-field imaging a powerful diagnostic tool.Volker C. Behr and Thomas Weber contributed equally to this work.     

Microscopic modeling of gain and luminescence in semiconductors

The capabilities of a fully microscopic approach for the calculation of optical material properties of semiconductor lasers are reviewed. Several comparisons between the results of these calculations and measured data are used to demonstrate that the approach yields excellent quantitative agreement with the experiment. It is outlined how this approach allows one to predict the optical properties of devices under high-power operating conditions based only on low-intensity photo luminescence (PL) spectra. Examples for the gain-, absorption-, PL- and linewidth enhancement factor-spectra in single and multiple quantum-well structures, superlattices, Type II quantum wells and quantum dots, and for various material systems are discussed.     

The bulk photovoltaic effect in ferroelectric Pb(Zr,Ti)O3 thin films

Abstract

The bulk photovoltaic effect (BPE) has been investigated in lead zirconate titanate (PZT) thin films. Measurements of the kinetics, spectral distribution and photocurrent hysteresis loops have been made. In the extrinsic spectral region, the steady-state photocurrent is primarily due to the BPE, where the photovoltaic tensor component has been determined to be G₃₁ = 10_?9 cm/V. However, in the intrinsic region, the BPE has not been determined due to the strong contribution from photoinjection currents. Finally, it is shown that the BPE may be the driving force for photoinduced hysteresis changes in PZT thin films, particularly in the extrinsic spectral region.     

Semiconductor quantum-dot nanostructures: Their application in anew class of infrared photodetectors

Semiconductor quantum-dot nanostructures are interesting objects for fundamental as well as practical reasons. Fundamentally, they can form the basis of systems in which to study the quantum mechanics of electrons confined in zero-dimensional (0-D) space. In practice, the dots can be embedded in the active regions of a new class of electronic and optoelectronic devices with novel functionalities. This paper reviews the state-of-the-art in the use of these objects in infrared detectors. It describes the progress, challenges, and projections for continued development of normal-incidence intersublevel detectors operating in the spectral region between 6 and 20 μm