Novel light-sensitive nanocrystal skins

Ankara : Materials Science and Nanotechnology and the Graduate School of Engineering and Science of Bilkent Univ., 2013.Thesis (Master's) -- Bilkent University, 2013.Includes bibliographical references leaves 89-100.Light sensing devices traditionally made from crystalline or amorphous silicon, operating at the visible and near-infrared wavelengths, have led to a multibillion-dollar annual market. However, silicon faces various limitations including weak detection at long wavelengths (insufficient beyond 1.1 µm) with a cut-off at short wavelengths (in the ultraviolet) and small-area applications. On the other hand, solution-processed semiconductor nanocrystals (NCs), also known as colloidal quantum dots, offer large-area light sensing platforms with strong absorption cross-section. In this thesis we propose and demonstrate a new class of large-area, semi-transparent, light-sensitive nanocrystal skin (LS-NS) devices intended for large-surface applications including smart transparent windows and light-sensitive glass facades of smart buildings. These LS-NS platforms, which are fabricated over areas up to many tens of cm2 using spraycoating and several cm-squares using dip-coating, are operated on the basis of photogenerated potential buildup, as opposed to conventional charge collection. The close interaction of the monolayer NCs of the LS-NS with the top interfacing metal contact results in highly sensitive photodetection in the absence of external bias, while the bottom side is isolated using a high dielectric spacing layer. In operation, electron-hole pairs created in the NCs of the LS-NS are disassociated and separated at the NC monolayer - metal interface due to the difference in the workfunctions. As a result, the proposed LS-NS platforms perform as highly sensitive photosensors, despite using a single NC monolayer, which makes the device semi-transparent and reduces the noise generation Furthermore, because of the band gap tunability, it is possible to construct cascaded NC layers with a designed band gap gradient where the NC diameters monotonically change. Here we present the first account of exciton funneling in an active device, which leads to significant performance improvement in the device. We show highly photosensitive NC skins employing the exciton funneling across the multiple layers of NC film. To further enhance the device photosensitivity performance, we demonstrate embedding plasmonic nanoparticles into the light-sensitive skins of the NCs. In addition, we exhibit the LS-NS device sensitivity enhancement utilizing the device architecture of semi-transparent tandem skins, the addition of TiO2 layer for increased charge carrier dissociation, and the phenomenon of multiexciton generation in infrared NCs. With fully sealed NC monolayers, LS-NS is found to be highly stable under ambient conditions, promising for low-cost large-area UV/visible sensing in windows and facades of smart buildings. We believe the findings presented in this thesis have significant implications for the future design of photosensing platforms and for moving toward next generation large-surface light-sensing platforms.Akhavan, ShahabM.S

Fabrication and microfluidic analysis of graphene-based molecular communication receiver for Internet of Nano Things (IoNT).

Bio-inspired molecular communications (MC), where molecules are used to transfer information, is the most promising technique to realise the Internet of Nano Things (IoNT), thanks to its inherent biocompatibility, energy-efficiency, and reliability in physiologically-relevant environments. Despite a substantial body of theoretical work concerning MC, the lack of practical micro/nanoscale MC devices and MC testbeds has led researchers to make overly simplifying assumptions about the implications of the channel conditions and the physical architectures of the practical transceivers in developing theoretical models and devising communication methods for MC. On the other hand, MC imposes unique challenges resulting from the highly complex, nonlinear, time-varying channel properties that cannot be always tackled by conventional information and communication tools and technologies (ICT). As a result, the reliability of the existing MC methods, which are mostly adopted from electromagnetic communications and not validated with practical testbeds, is highly questionable. As the first step to remove this discrepancy, in this study, we report on the fabrication of a nanoscale MC receiver based on graphene field-effect transistor biosensors. We perform its ICT characterisation in a custom-designed microfluidic MC system with the information encoded into the concentration of single-stranded DNA molecules. This experimental platform is the first practical implementation of a micro/nanoscale MC system with nanoscale MC receivers, and can serve as a testbed for developing realistic MC methods and IoNT applications.Tis work was supported in part by the ERC (Project MINERVA, ERC-2013-CoG #616922) and by the AXA Research Fund (AXA Chair for Internet of Everything at Koc University)

Hybrid Devices Based On Graphene And Related Materials For Wearable (Opto)Electronics

It was as far back as 30,000 years ago that human beings began to wear clothing made from woven fibers. Yet, in the last decades an acceleration in textile technology has seen unprecedented levels of innovation in power loom and spinning frame techniques. With the current competitive global ingenuity in nanoscience and nanotechnology and its implication in textile industry, wearable electronics seems to be the next promising trend in this giant market (25.19 billion US dollars by 2020). Part of this revolution includes the integration of electronics and textiles, which has dramatically cross fertilized the technology and design worlds. However, the use of rigid technologies hindered the viability of the wearable. This dissertation focuses on exploiting graphene and related materials in order to develop novel hybrid device concepts with various functionality and amenability. Here, I propose an on-demand, scalable and cost-effective fully inkjet lithography technique to make sensitive (~337 A/W), broadband (visible till 2.7 µm) and fast response time (~50 ms) hybrid photodetectors (PDs) at 1 V, which is the highest reported performance for PDs among liquid phases exfoliated based PDs. Furthermore, I successfully exploit this technique to fabricate flexible and washable PDs on fabrics operating at only 1 V. Additionally, I present the design and fabrication of conductive fibers via controlled rolling of single layer graphene around individual fibers to construct state-of-the-art all-fiber gate-tunable PDs. Fiber-based PDs exhibit broad spectral photodetection from visible to near infrared (870 nm), fast temporal response time (~5 ms) and high external responsivity (~22,000 A/W) at only 1 V. The devices endure against rigorous standard mechanical and washing tests. I then utilize the same platform to fabricate wearable fiber-based gas sensors for detection of toxic gas molecules. Finally, I demonstrate the novel mesoscopic fabrication method, suitable for graphene and flexible-based solar cells via transferring pre-sintered mesoscopic TiO2 structure. I believe that these findings are not only scientifically intriguing, but also technologically important, the implications of which could see large scale implementation in the next generation of wearable electronics

Nanocrystal skins with exciton funneling for photosensing

Highly photosensitive nanocrystal (NC) skins based on exciton funneling are proposed and demonstrated using a graded bandgap profile across which no external bias is applied in operation for light-sensing. Four types of gradient NC skin devices (GNS) made of NC monolayers of distinct sizes with photovoltage readout are fabricated and comparatively studied. In all structures, polyelectrolyte polymers separating CdTe NC monolayers set the interparticle distances between the monolayers of ligand-free NCs to <1 nm. In this photosensitive GNS platform, excitons funnel along the gradually decreasing bandgap gradient of cascaded NC monolayers, and are finally captured by the NC monolayer with the smallest bandgap interfacing the metal electrode. Time-resolved measurements of the cascaded NC skins are conducted at the donor and acceptor wavelengths, and the exciton transfer process is confirmed in these active structures. These findings are expected to enable large-area GNS-based photosensing with highly efficient full-spectrum conversion

Photosensitivity Enhancement with TiO₂ in Semitransparent Light-Sensitive Skins of Nanocrystal Monolayers

We propose and demonstrate light-sensitive nanocrystal skins that exhibit broadband sensitivity enhancement based on electron transfer to a thin TiO₂ film grown by atomic layer deposition. In these photosensors, which operate with no external bias, photogenerated electrons remain trapped inside the nanocrystals. These electrons generally recombine with the photogenerated holes that accumulate at the top interfacing contact, which leads to lower photovoltage buildup. Because favorable conduction band offset aids in transferring photoelectrons from CdTe nanocrystals to the TiO₂ layer, which decreases the exciton recombination probability, TiO₂ has been utilized as the electron-accepting material in these light-sensitive nanocrystal skins. A controlled interface thickness between the TiO₂ layer and the monolayer of CdTe nanocrystals enables a photovoltage buildup enhancement in the proposed nanostructure platform. With TiO₂ serving as the electron acceptor, we observed broadband sensitivity improvement across 350–475 nm, with an approximately 22% enhancement. Furthermore, time-resolved fluorescence measurements verified the electron transfer from the CdTe nanocrystals to the TiO₂ layer in light-sensitive skins. These results could pave the way for engineering nanocrystal-based light-sensing platforms, such as smart transparent windows, light-sensitive walls, and large-area optical detection systems

Prevalence of renal complications of levetiracetam in neonates with seizures in Qom from 2015 to 2020

&nbsp;&nbsp;Introduction: Spasms or seizures during the first month of life are the most common clinical manifestations of central nervous system failure in infants and occur due to overactivity of a group of nerve cells in the brain and excessive electrical stimulation of neurons. The purpose of the present study was to evaluate the prevalence of renal complications of Levetiracetam in neonates with seizures. Methods: This descriptive-analytical and retrospective study was performed on creatinine level, blood urea and duration of levetiracetam use for all neonates studied and only renal ultrasound was performed for cases where their creatinine was elevated. Finally, the obtained information was used for statistical analysis. Results: According to the results, there was no statistically significant differences in neonatal subgroups,&nbsp;&nbsp; especially in infants on levetiracetam, except transient increased creatinine and urea. During 6 months follow-up, only three cases with increased creatinine above 1.4 was observed. This 3 cases had normal genitourinary ultrasound. &nbsp;Also, in neonates diagnosed with choroid cyst on ultrasound, in one case the creatinine level was more than 1.4 and in the other cases the serum creatinine level was less than 1.4. Conclusion: According to the results of the present study, no serious renal complication was observed with Levetiracetam and its use can be recommended for patients

Plasmon-Enhanced Energy Transfer in Photosensitive Nanocrystal Device

Förster resonance energy transfer (FRET) interacted with localized surface plasmon (LSP) gives us the ability to overcome inadequate transfer of energy between donor and acceptor nanocrystals (NCs). In this paper, we show LSP-enhanced FRET in colloidal photosensors of NCs in operation, resulting in substantially enhanced photosensitivity. The proposed photosensitive device is a layered self-assembled colloidal platform consisting of separated monolayers of the donor and the acceptor colloidal NCs with an intermediate metal nanoparticle (MNP) layer made of gold interspaced by polyelectrolyte layers. Using LBL assembly, we fabricated and comparatively studied seven types of such NC-monolayer devices (containing only donor, only acceptor, Au MNP–donor, Au MNP–acceptor, donor–acceptor bilayer, donor–Au MNP–acceptor trilayer, and acceptor–Au MNP–donor reverse trilayer). In these structures, we revealed the effect of LSP-enhanced FRET and exciton interactions from the donor NCs layer to the acceptor NCs layer. Compared to a single acceptor NC device, we observed a significant extension in operating wavelength range and a substantial photosensitivity enhancement (2.91-fold) around the LSP resonance peak of Au MNPs in the LSP-enhanced FRET trilayer structure. Moreover, we present a theoretical model for the intercoupled donor–Au MNP–acceptor structure subject to the plasmon-mediated nonradiative energy transfer. The obtained numerical results are in excellent agreement with the systematic experimental studies done in our work. The potential to modify the energy transfer through mastering the exciton–plasmon interactions and its implication in devices make them attractive for applications in nanophotonic devices and sensors

Epidemiological Investigation of Pediatric Tuberculosis in Tehran Province, 2006-2015

Background: On tuberculosis control standpoint, the treatment of children with TB is not considered a priority as they rarely transmit the disease and contribute little to the maintenance of the tuberculosis epidemic. Therefor this study conducted to describe pediatric TB cases, and to identify pattern of risk factors in non-endemic communities Materials and Methods: The present cross- sectional study conducted on 139 children under-five years of old with TB in Tehran province from March 2006 to March 2015. Data were extracted from TB registry system. Data were analyzed using Stata software version, 12. Results: Overall, records on 139 children with TB had been evaluated. Most of under-five TB cases were boys (58%) and urban dwellers (88%), roughly half of the sample (54%) was diagnosed as extra- pulmonary TB, while most of them (66%) had been reported through public health networks. Treatment success rate were nearly 85%, and 11% of them had been deceased. There was a significant relationship between household contacts and type of TB (