A new penternary semiconductor Cu2CoSn(SSe)4 nanocrystal: a study on structural,dielectric and optical properties

Journal of Materials Science: Materials in Electronics - In recent years, the penternary nanocrystals synthesized as an alternative to Pt in dye-sensitized solar cells have attracted the attention...     

Track membranes with embedded semiconductor nanocrystals: structural and optical examinations

We studied the optical properties of poly(ethylene terephthalate) ion track membranes of 1.5, 0.5 and 0.05?μm?pores impregnated with luminescent semiconductor CdSe/ZnS nanocrystals of different diameters (2.5 and 5?nm). The nanocrystals were embedded from their colloidal solutions in toluene by the immersion of a membrane in a colloidal solution. Localization of quasi-isolated weakly interacting CdSe/ZnS nanocrystals in a loosened layer on the track pore wall surface along with the existence of empty pores was demonstrated. We observed also the spatial separation of nanocrystals of 2.5 and 5?nm in size along the 50?nm pores.     

Integrated semiconductor optical sensors for cellular and neural imaging

We review integrated optical sensors for functional brain imaging, localized index-of-refraction sensing as part of a lab-on-a-chip, and in vivo continuous monitoring of tumor and cancer stem cells. We present semiconductor-based sensors and imaging systems for these applications. Measured intrinsic optical signals and tissue optics simulations indicate the need for high dynamic range and low dark-current neural sensors. Simulated and measured reflectance spectra from our guided resonance filter demonstrate the capability for index-of-refraction sensing on cellular scales, compatible with integrated biosensors. Finally, we characterized a thermally evaporated emission filter that can be used to improve sensitivity for in vivo fluorescence sensing.     

Fabrication of nanostructure and formation of nanocrystal for non-volatile memory

In this work, we have demonstrated that the nanocrystal created by combining the self-assembled block copolymer thin film with regular semiconductor processing can be applicable to non-volatile memory device with increased charge storage capacity over planar structures. Self-assembled block copolymer thin film for nanostructures with critical dimensions below photolithographic resolution limits has been used during all experiments. Nanoporous thin film from PS-b-PMMA diblock copolymer thin film with selective removal of PMMA domains was used to fabricate nanostructure and nanocrystal. We have also reported about surface morphologies and electrical properties of the nano-needle structure formed by RIE technique. The details of nanoscale pattern of the very uniform arrays using RIE are presented. We fabricated different surface structure of nanoscale using block copolymer. We also deposited Si-rich SiNx layer using ICP-CVD on the silicon surface of nanostructure. The deposited films were studied after annealing. PL studies demonstrated nanocrystal in Si-rich SiNx film on nanostructure of silicon.     

Structural, magnetic and optical behavior of pristine and Yb doped CoWO4 nanostructure

Nanocrystalline pure and Yb doped CoWO₄ nanostructures were synthesized successfully by single step chemical precipitation technique. The prepared sample was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal analysis (TGA). XRD pattern reveals the pure and doped CoWO₄ nanoparticles belongs to the monoclinic structure with the space group of P_2/c. Electron microscopy studies clearly evidence the formation of round edged nanocubes with an average particle size of 60–80 nm, emerges in the polycrystalline nature. UV–Visible absorption spectra of Yb³⁺ doped CoWO₄ nanocrystals shows a strong absorption peak at 278 nm due to CoWO₄ metal to ligand charge transfer within the [WO₆]^6? complex. Photoluminescence spectra of pure and doped CoWO₄ nanostructures substantiate the effect of Yb on the wolframite structure and its response for optical behavior. These results suggest that the addition of Yb into the Co-site on CoWO₄ has no significant contribution for luminescent enhancement when compared to pure one up to 5 % Yb concentration. Typical magnetization curve shows the mixed ferromagnetic and diamagnetic transition of CoWO₄ with respect to the Yb doping concentration.     

Electronic structure and self-assembly of cross-linked semiconductor nanocrystal arrays

We studied the electronic level structure of assemblies of InAs quantum dots and CdSe nanorods cross-linked by 1,4-phenylenediamine molecules using scanning tunneling spectroscopy. We found that the bandgap in these arrays is reduced with respect to the corresponding ligand-capped nanocrystal arrays. In addition, a pronounced sub-gap spectral structure commonly appeared which can be attributed to unpassivated nanocrystal surface states or associated with linker-molecule-related levels. The exchange of the ligands by the linker molecules also affected the structural array properties. Most significantly, clusters of close-packed standing CdSe nanorods were formed.     

External field-assisted laser ablation in liquid: An efficient strategy for nanocrystal synthesis and nanostructure assembly

Laser ablation in liquid (LAL) has received considerable attention over the last decade, and is gradually becoming an irreplaceable technique to synthesize nanocrystals and fabricate functional nanostructures because it can offer effective solutions to some challenges in the field of nanotechnology. The goal of this review is to offer a comprehensive summary of recent developments of LAL in nanocrystal synthesis and nanostructure fabrication. First, we will introduce the fundamental processes of microsecond, nanosecond, and femtosecond LAL, and how the active species act differently in plasma, cavitation bubbles, and droplets in the different LAL processes. Second, a variety of LAL-based techniques for nanomaterials synthesis and processing are presented, such as electric-, magnetic-, and temperature-field LAL, as well as electrochemically assisted LAL, pulsed laser deposition in liquid, and laser writing of nanopatterns in liquid. Third, new progress in LAL-generated nanomaterials is described. Fourth, we emphasize five applications of LAL-generated nanomaterials that have emerged recently in the fields of optics, magnetism, environment, energy, and biomedicine. Finally, we consider the core advantages of LAL, the limitations of LAL and corresponding solutions, and the future directions in this promising research area.     

Hydrothermal derived nanostructure rare earth (Er,Yb)-doped ZnO: structural,optical and electrical properties

The structural, optical and electrical properties of undoped and rare-earth (Er, Yb) doped zinc oxide (ZnO) nanopowder samples synthesized by hydrothermal method were investigated. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy. The optical properties of undoped and rare-earth (Er, Yb) doped ZnO were carried out with UV–visible diffuse reflectance spectroscopy techniques. XRD results reveal that Yb and Er doped ZnO nanopowders have single phase hexagonal (Wurtzite) structure without any impurities. SEM analysis indicate that dopants with different radii affected the surface morphology of ZnO nanostructures. The optical band gap of all samples were calculated from UV–Vis diffuse reflectance spectroscopy data. We have obtained band gap values of undoped, Er and Yb doped ZnO as 3.24, 3.23, 3.22 eV, respectively. Electrical characterization of the samples were made in the 280–350 K temperature range using Van der Pauw method based on Hall effect measurement. The carrier concentrations decreased for both Er and Yb doping while the Hall mobility and electrical resistivity increased with Yb, Er doping compared to undoped ZnO nanopowder at room temperature. The temperature dependent resistivity measurements of Er doped ZnO showed a metal–semiconductor transition at about 295 K, while Yb doped ZnO showed characteristic semiconductor behavior.     

Ultrafast laser-induced microstructure/nanostructure replication and optical properties

This paper demonstrates replication of ultrafast laser-induced micro/nano surface textures on poly(dimethylsiloxane) (PDMS). The surface texture replication process reduces the processing steps for microtexturing while improving light trapping. Two methods are demonstrated to replicate surface microtexture, a simple mold method and an embossing method. The laser microtextured silicon and titanium surfaces with micro to nanoscale features have been successfully replicated. Optical characterization of the replicated microtextured PDMS surfaces is performed and the results agree with model predictions. The replicated microtextured PDMS film is applied on a silicon surface and optical characterization shows that surface reflectance can be suppressed over 55% compared to the control value.     

Polychromatic axial behavior of aberrated optical systems: Wigner distribution function approach

We propose a new method for the computation of the tristimuli values that correspond to the impulse response along the optical axis provided by an imaging optical system working under polychromatic illumination. We show that all the monochromatic irradiance distributions needed for this calculation can be obtained from the Wigner distribution function associated with a certain version of the pupil function of the system. The use of this single phase-space representation allows us to obtain the above merit function for aberrated systems with longitudinal chromatic aberration and primary spherical aberration. Some numerical examples are given to verify the accuracy of our proposal.     

Suppression of self-pulsing behavior in erbium-doped fiber lasers with a semiconductor optical amplifier

We experimentally demonstrate that the stability of cw and mode-locked erbium-doped fiber ring lasers can be improved significantly with a semiconductor optical amplifier (SOA) inside the cavity. The fast saturable gain of the SOA suppresses significantly the self-pulsing that is due to ion pairs in the erbium-doped fiber, which acts as a saturable absorber. A linear stabilization analysis of the laser system agrees with our experimental results.     

Semiconductor nanocrystal quantum dots on single crystal semiconductor substrates: high resolution transmission electron microscopy

We report on high-resolution transmission electron microscope structural studies of InAs colloidal semiconductor nanocrystal quantum dots (NCQDs) on ultrathin GaAs (001) semiconductor single-crystal substrates. We employ a benign method for preparing electron transparent specimens that is suitable for the study of such fragile samples. The image contrast comprises contributions from electron scattering from both the NCs and the GaAs substrate. Long-term electron exposure studies reveal different damage mechanisms operative in the nanocrystals and the substrate.     

(Cd,Mn) Se semimagnetic semiconductor thin films: growth from solution,structural analysis and optical properties

The preparation details and a few aspects pertaining to the crystallographic and spectral characteristics of the Cd_1−xMn_xSe (0≤x≤0.5) semimagnetic semiconductor thin films are presented in this letter. A series of samples were obtained from an alkaline medium (pH≅10±0.2) composed of Cd²⁺, Mn²⁺ and Se²⁻ ions and were co-deposited from their salt solutions to produce thin solid films. The technique offers a free access for growth of these films first by an ion-by-ion condensation and later by adsorption of colloidal particles and is simple, non-expensive and permits for large area depositions. The deposition conditions and process parameters were so manipulated that good quality deposits were obtained. Few of the key parameters are the following: deposition temperature (50 °C), deposition time (120 min), pH (10±0.2) and speed of mechanical churning (70±2 rpm). The CdMnSe deposits were crystalline with preferred orientation along (100) direction and showed homogeneous phase formation up to a value of x equal to 0.1. Beyond this value, both CdSe and MnSe tend to separate out and formed an admixture. The lattice parameters and the intensities of reflections changed continuously with Mn content in CdSe. The optical spectra revealed high absorption coefficient with a band to band direct type of transitions. The estimated energy gap showed decrease, typically from 1.8 to 1.34 eV, on addition of Mn in CdSe and follows non-linear variation. Scanning electron microscopy also suggests the crystalline nature of the deposits.     

A large-area hybrid metallic nanostructure array and its optical properties

A process for fabricating a large-area hybrid metallic nanostructure array is presented. The structures consist of an array of metal capped dielectric nanopillars and an array of metallic holes, each possessing its individual optical properties. The plasmon response of such structures can be viewed as the collection of plasmons from two geometries to form an interacting system. Experimental results show two peak values in the extinction spectrum for p-polarized incident light. The two peaks in the extinction spectrum were shifted to longer wavelength and shorter wavelength respectively with the addition of absolute ethanol on the structure surface. The narrowest extinction peak appears at normal incidence.     

Electrical and optical properties of semiconductor nanocrystals

Application of semiconductor nanocrystals in optoelectronic devices requires an understanding not only of their emission and absorption properties, but also of the processes of charge injection and transport in nanocrystalline films. Here, we present measurements of the electrical properties of nanocrystalline films and of blends of nanocrystals with conjugated polymers. We also describe the attachment of nanocrystals to semiconductor surfaces, and we investigate the emission of nanocrystalline films in microcavity structures and at high excitation intensities.     

Integrated MD simulation of scratching and shearing of 3D nanostructure

An integrated MD simulation of scratching and shearing with one specimen is conducted to analyze the nanomachining mechanism and mechanics properties of nanostructures. Simulation results indicate that during scratching the onset and propagation of dislocations depend on the scratch depths; during shearing, the yielding stress of a small-size nanostructure is more sensitive to nanomachining imperfection and residual defects. Dislocations nucleate first near the burr in a scratched specimen. In an ideal nanostructure or a nanostructure with shallow scratched groove, the distribution of stress is generally lower and flatter. As the depth of groove increases, high stresses transit from the corner to either end of groove, especially near the burr or around the location of tool withdraw. During the deformation of nanostructures, shear stress plays a leading role in the elastic stage, and both normal stress gradients and shear stress determine the onset and evolvement of defects in the plastic stage. When the ratio of the depth of groove to the height of specimen is up to one third, the scratched groove determines the breakpoint of a nanostructure. The fluctuation of shear stress during the plastic deformation of specimen is caused by the competition between atoms which form new atomic planes and slip on different slip planes.     

Integrated optoelectronics for optical interconnections and optical processing

Integrated optoelectronics using III–V compound semiconductor technology has so far shown exciting advances for application in optical telecommunication systems. New applications of this technology are in optical interconnections and signal processing systems. The technology is expected to be very effective in solving the wiring limit in data transmission within electronic systems, using the advantages of optical techniques such as high data transmission rate and high parallelism, and thus improve the performance of overall systems. Optical interconnection devices currently being developed aim both at multiplexing vast amounts of data and exhibiting flexible interconnection functions using the advantageous characteristics of light. Future research is expected to explore new techniques such as that for multiplexing and processing data in the wavelength division as well as for integrating functional devices in two-dimensions. Synergetic collaboration among materials and processing, design and fabrication, and packaging areas is extremely important and this will lead to practical optical interconnections and signal processing systems.