Cd1-xMgxS CQD thin films for high performance and highly selective NIR photodetection.

Development of high-performance and highly selective NIR photodetectors (PDs) using wide band gap semiconductors is a significant field of research in the present scenario. Herein, cost effective and easy fabrication of NIR PDs is demonstrated by employing the thin films of Cd1-xMgxS (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) colloidal quantum dots (CQDs). The influence of doping on the transport behaviour of Cd1-xMgxS CQD films was investigated by device performance under laser light illumination at various wavelengths ranging from 405 nm to 782 nm. An improvement in the photoresponsivity of the material (CdS) beyond its intrinsic absorption spectral range due to the incorporation of the dopant is noticed. In spite of the cost effective and easy fabrication process without the requirement of any rigorous synthesis procedure, the devices presented here demonstrate competitive figures of merit to those that are designed with complex structures and tedious procedures. The performance parameters viz response time, responsivity, photosensitivity, quantum efficiency, and specific detectivity were improved as a consequence of Mg doping and attained a maximum value of 110 ms, ∼26.9 A W-1, ∼4.7 × 104%, ∼41.23% and ∼3.45 × 1013 Jones, respectively. Besides, the sensing range of the PDs can be tuned from visible (650 nm) to NIR (782 nm) with a huge improvement in selectivity by incorporation of Mg.

Amine-Functionalized MoO3@RGO Nanohybrid-Based Biosensor for Breast Cancer Detection.

We report results of studies relating to development of an ultrasensitive, rapid, and label-free biosensor based on molybdenum trioxide (MoO3) anchored onto the reduced graphene oxide (RGO) for breast cancer detection. The human epidermal growth factor receptor-2 (HER-2) secreted in the serum of breast cancer patients was used as an analyte for the detection. The in situ growth of 1D MoO3 onto reduced graphene oxide (RGO), a 2D carbon substrate, was carried out via one-pot low-temperature hydrothermal synthesis. Subsequently, the surface conjugation of the monoclonal antibodies (anti-HER-2) onto the APTES/MoO3@RGO/ITO electrode was conducted via EDC-NHS covalent chemistry. The structural and morphological properties of the MoO3@RGO nanohybrid were investigated using electron microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopic techniques. The surface area of the MoO3@RGO nanohybrid determined via Brauner-Emmett-Teller analysis was found to be 14 times greater than that of the pristine MoO3. The binding kinetics and the electrochemical activity of the developed platform were determined by cyclic voltammetry, differential pulse voltammetry, and impedance spectroscopic techniques. This nanohybrid based immunosensor exhibited improved sensitivity (13 uA mLng-1cm-2) in a broad concentration range (0.001-500 ng mL-1) with a correlation coefficient of 0.98. The limit of detection of this MoO3@RGO nanohybrid based immunosensor was found to be 0.001 ng mL-1. The results obtained via the developed immunosensor for the quantification of serum HER-2 were validated using ELISA.

CdS nanodroplets over silica microballs for efficient room-temperature LPG detection.

An efficient room-temperature sensor for liquified petroleum gas (LPG) is demonstrated by employing CdS:SiO2 nanocomposite thin films (CdS:SiO2 NCTFs) for the first time. CdS:SiO2 NCTFs exhibiting the morphology of CdS nanodroplets on micron-sized spherical balls of SiO2 were deposited using the pulsed laser deposition (PLD) method, followed by thermal annealing. The targets of chemically synthesized CdS nanoparticles and commercially procured SiO2 were used to deposit CdS:SiO2 NCTFs by swapping them at a frequency ratio of 2 : 8 laser pulses per second, which was selected to ensure nearly the same ratio of CdS to SiO2 in NCTFs and was confirmed by X-ray photoelectron spectroscopy. Sensor fabrication was carried out on bare CdS thin films and as-grown and annealed CdS:SiO2 NCTFs using an Ag paste over Pt interdigitated electrodes to measure the resistance of the films in air and in the presence of reducing gases, viz., LPG, H2, H2S, NO2 and CO2. The present sensor showed the highest response for LPG and the observed value was ∼71% for 1000 ppm at RT with the response time and recovery time of 91 s and 140 s, respectively. The response of the sensor was sustainable up to 75 °C and then decreased, which suggested its promising usage for low-temperature regions as well. A low detection limit of 20 ppm at RT for LPG was determined; however, a significant response was observed only at 50 ppm. The sensor retained ∼96% of its initial response even after 8 weeks and that too at 100 °C. The present LPG sensor is highly promising due to its high sensitivity, low detection limit, low response and recovery times, good reproducibility, RT operation and simple fabrication technique.

Silicon-on-insulator chip-to-chip coupling via out-of-plane or vertical grating couplers.

In this work, we study the possibility of chip-to-chip interconnections via out-of-plane grating couplers or vertical grating couplers (VGCs) fabricated on silicon-on-insulator (SOI) technology. Mathematical and experimental results for the efficiency of coupling light between two such grating couplers have been presented. The VGCs are placed vertically against each other in order to study the effect of spatial misalignments on the light coupling efficiency. Waveguides and VGCs are designed according to standard SOI fabrication processes. A two-dimensional finite-difference time-domain method is used for the simulations. Measurements are performed on different combinations of 4 samples on the chip. Light coupling efficiency of -8 dB is achieved and tolerances to misalignments in 3 spatial dimensions are provided.

Nanotwinning and structural phase transition in CdS quantum dots.

Nanotwin structures are observed in high-resolution transmission electron microscopy studies of cubic phase CdS quantum dots in powder form by chemical co-precipitation method. The deposition of thin films of nanocrystalline CdS is carried out on silicon, glass, and TEM grids keeping the substrates at room temperature (RT) and 200°C by pulsed laser ablation. These films are then subjected to thermal annealing at different temperatures. Glancing angle X-ray diffraction results confirm structural phase transitions after thermal annealing of films deposited at RT and 200°C. The variation of average particle size and ratio of intensities in Raman peaks I2LO/I1LO with annealing temperature are studied. It is found that electron-phonon interaction is a function of temperature and particle size and is independent of the structure. Besides Raman modes LO, 2LO and 3LO of CdS at approximately 302, 603, and 903 cm-1 respectively, two extra Raman modes at approximately 390 and 690 cm-1 are studied for the first time. The green and orange emissions observed in photoluminescence are correlated with phase transition.

Opto-structural studies of well-dispersed silicon nano-crystals grown by atom beam sputtering.

Synthesis and characterization of nano-crystalline silicon grown by atom beam sputtering technique are reported. Rapid thermal annealing of the deposited films is carried out in Ar + 5% H2 atmosphere for 5 min at different temperatures for precipitation of silicon nano-crystals. The samples are characterized for their optical and structural properties using various techniques. Structural studies are carried out by micro-Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy, and selected area electron diffraction. The optical properties are studied by photoluminescence and UV-vis absorption spectroscopy, and bandgaps are evaluated. The bandgaps are found to decrease after rapid thermal treatment. The micro-Raman studies show the formation of nano-crystalline silicon in as-deposited as well as annealed films. The shifting and broadening in Raman peak suggest formation of nano-phase in the samples. Results of micro-Raman, photoluminescence, and TEM studies suggest the presence of a bimodal crystallite size distribution for the films annealed at higher temperatures. The results show that atom beam sputtering is a suitable technique to synthesize nearly mono-dispersed silicon nano-crystals. The size of the nano-crystals may be controlled by varying annealing parameters.

Ultrafast and bias-free all-optical wavelength conversion using III-V-on-silicon technology.

Using a 7.5 µm diameter disk fabricated with III-V-on-silicon fabrication technology, we demonstrate bias-free all-optical wavelength conversion for non-return-to-zero on-off keyed pseudorandom bit sequence (PRBS) data at the speed of 10 Gbits/s with an extinction ratio of more than 12 dB. The working principle of such a wavelength converter is based on free-carrier-induced refractive index modulation in a pump-probe configuration. We believe it to be the first bias-free on-chip demonstration of all-optical wavelength conversion using PRBS data. All-optical gating measurements in the pump-probe configuration with the same device have revealed that it is possible to achieve wavelength conversion beyond 20 Gbits/s.

Histological analysis of lesions of the pineal region: a retrospective study of 12 years.

Various types of tumors and non-tumor lesions arise in the pineal region. This study summarizes the experience the authors have gained with 54 lesions of the pineal region over the last 12 years. Histology was analyzed in all cases. Out of these 54 cases, four were non-tumor lesions. Of the 50 tumors, pineal parenchymal tumors (PPTs) were most common (42% (21/54)), followed by gliomas (40% (20/54)). The PPTs were pineoblastomas (10/21), PPT of intermediate differentiation (7/21), and pineocytomas (4/21). The other tumors included germ cell tumors (4/54), meningiomas (2/54), craniopharyngiomas (2/54), and choroid plexus papilloma (1/54). The non-tumor lesions were epidermoid cysts (2/54), tuberculous abscess (1/54), and cysticercosis (1/54). Immunohistochemically, all the PPTs showed cytoplasmic positivity for synaptophysin. Glial fibrillary acidic protein (GFAP) stained only the reactive astrocytes in these tumors except two cases of pineoblastoma, which showed GFAP positivity in some tumor cells, indicating glial differentiation. There are very few studies of pineal lesions, and there is no study from India in the indexed literature.

Atypical cells in bronchoalveolar lavage specimens from bone marrow transplant recipients. A potential pitfall.

Numerous nonneoplastic conditions of the lungs may result in atypical cells in bronchoalveolar lavage (BAL) specimens mimicking malignant neoplasms. Bone marrow transplant (BMT) recipients have many predisposing factors that would lead to atypical cells in BAL specimens, presenting diagnostic challenges. We reviewed BAL specimens from BMT recipients and correlated our findings with clinical information. During a 5.5-year period, 21 BMT recipients had atypical cells in 27 BAL specimens at Fairview-University Medical Center, Minneapolis, MN. The atypical cells had the cytologic features of squamous or glandular cells. The nuclear/cytoplasmic ratio, atypical cells per case, and background varied from case to case. Most of the patients had 1 or more of the clinical findings that would lead to atypia in BAL specimens: 13 had recent cytoreductive treatment, 9 had positive cultures, and 7 had graft-vs-host disease. There was substantial overlap between the reactive atypia and carcinoma. Clinical correlation was the most important factor in making accurate diagnosis.