Noel Dawson

Bio: Noel Dawson is an academic researcher from University of New Mexico. The author has contributed to research in topics: Graphene & Quantum dot. The author has an hindex of 11, co-authored 27 publications receiving 396 citations. Previous affiliations of Noel Dawson include Santa Cruz Institute for Particle Physics & University of California, Santa Cruz.

Development of n-on-p silicon sensors for very high radiation environments

Abstract: We have developed a novel and highly radiation-tolerant n-in-p silicon microstrip sensor for very high radiation environments such as in the Super Large Hadron Collider. The sensors are designed for a fluence of 1×1015 neq/cm2 and are fabricated from p-type, FZ, 6 in. (150 mm) wafers onto which we lay out a single 9.75 cm×9.75 cm large-area sensor and several 1 cm×1 cm miniature sensors with various n-strip isolation structures. By evaluating the sensors both pre- and post-irradiation by protons and neutrons, we find that the full depletion voltage evolves to approximately 800 V and that the n-strip isolation depends on the p+ concentration. In addition, we characterize the interstrip resistance, interstrip capacitance and the punch-through-protection (PTP) voltage. The first fabrication batch allowed us to identify the weak spots in the PTP and the stereo strip layouts. By understanding the source of the weakness, the mask was modified accordingly. After modification, the follow-up fabrication batches and the latest fabrication of about 30 main sensors and associated miniature sensors have shown good performance, with no sign of microdischarge up to 1000 V.

Stable and Controllable Polymer/Fullerene Composite Nanofibers through Cooperative Noncovalent Interactions for Organic Photovoltaics

Abstract: A novel methodology of precisely constructing stable and controllable conjugated polymer (CP)/fullerene nanostructures is presented. By building in noncovalent interactions between CP nanofibers (NFs) and fullerene derivatives, supramolecular polymer/fullerene composite NFs are obtained in solution for the first time. Specifically, a conjugated block copolymer having poly(3-hexylthiophene) (P3HT) backbone selectively functionalized with polar isoorotic acid (IOA) moieties, P1, is used as the building block. Self-assembly of P1 in mixed solvents leads to well-defined NFs decorated with IOA groups on the periphery, onto which phenyl-C61-butyric acid methyl ester (PCBM) molecules are subsequently attached noncovalently. Formation of such complex structures are studied in detail and confirmed by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray scattering measurements. Application of these composite NFs in organic photovoltaic (OPV) devices not on...

Complementary Hydrogen Bonding and Block Copolymer Self-Assembly in Cooperation toward Stable Solar Cells with Tunable Morphologies

Abstract: We report the synthesis and characterization of a polythiophene diblock copolymer selectively functionalized with 1-n-hexylisoorotic acid moieties (P4) and a 2,6-diaminopyridine tethered fullerene derivative (PCBP). Self-assembly between P4 and PCBP through “three-point” complementary hydrogen bonding interactions is utilized to control and stabilize blend morphologies. These interactions have been studied both in solution and in solid state by 1H NMR and UV–vis spectroscopies as well as optical and atomic force microscopies (AFM). Solar cells employing P4 blended with different weight ratios of PCBP and phenyl-C61-butyric acid methyl ester (PCBM) were fabricated and tested. The best power conversion efficiencies (PCEs) were observed in devices made from P4/PCBP blends (10/8 by wt) and ternary blends of P4/PCBP/PCBM (10/4/4 by wt) as active layers. Thermal stabilities of these solar cells were studied in detail by aging tests, and corresponding morphological changes were closely monitored by absorption sp...

Testing of bulk radiation damage of n-in-p silicon sensors for very high radiation environments

Abstract: We are developing n+-in-p, p-bulk and n-readout, microstrip sensors, fabricated by Hamamatsu Photonics, as a non-inverting radiation hard silicon detector for the ATLAS tracker upgrade at the super-LHC (sLHC) proposed facility. The bulk radiation damage after neutron and proton irradiations is characterized with the leakage current, charge collection and full depletion voltage. The detectors should provide acceptable signal, signal-to-noise ratio exceeding 15, after the integrated luminosity of 6000 fb−1, which is twice the sLHC integrated luminosity goal.

Testing of surface properties pre-rad and post-rad of n-in-p silicon sensors for very high radiation environment

Abstract: We are developing n+-in-p, p-bulk and n-readout, microstrip sensors as a non-inverting radiation hard silicon detector for the ATLAS Tracker Upgrade at the super LHC experiment. The surface radiation damages of the sensors fabricated by Hamamatsu Photonics are characterized on the interstrip capacitance, interstrip resistance and punch-through protection evolution. The detector should provide acceptable strip isolation, exceeding the input impedance of the signal readout chip ∼1 kΩ, after the integrated luminosity of 6 ab−1, which is twice the luminosity goal.

Wearable Flexible Sensors: A Review

Abstract: This paper provides a review on some of the significant research work done on wearable flexible sensors (WFSs). Sensors fabricated with the flexible materials have been attached to a person along with the embedded system to monitor a parameter and transfer the significant data to the monitoring unit for the further analyses. The use of wearable sensors has played a quite important role to monitor the physiological parameters of a person to minimize any malfunctioning happening in the body. This paper categorizes the work according to the materials used for designing the system, the network protocols, and different types of activities that were being monitored. The challenges faced by the current sensing systems and future opportunities for the WFSs regarding its market values are also briefly explained in this paper.

Light Generation and Harvesting in a Van der Waals Heterostructure

Abstract: Two-dimensional (2D) materials are a new type of materials under intense study because of their interesting physical properties and wide range of potential applications from nanoelectronics to sensing and photonics. Monolayers of semiconducting transition metal dichalcogenides MoS2 or WSe2 have been proposed as promising channel materials for field-effect transistors. Their high mechanical flexibility, stability, and quality coupled with potentially inexpensive production methods offer potential advantages compared to organic and crystalline bulk semiconductors. Due to quantum mechanical confinement, the band gap in monolayer MoS2 is direct in nature, leading to a strong interaction with light that can be exploited for building phototransistors and ultrasensitive photodetectors. Here, we report on the realization of light-emitting diodes based on vertical heterojunctions composed of n-type monolayer MoS2 and p-type silicon. Careful interface engineering allows us to realize diodes showing rectification and light emission from the entire surface of the heterojunction. Electroluminescence spectra show clear signs of direct excitons related to the optical transitions between the conduction and valence bands. Our p–n diodes can also operate as solar cells, with typical external quantum efficiency exceeding 4%. Our work opens up the way to more sophisticated optoelectronic devices such as lasers and heterostructure solar cells based on hybrids of 2D semiconductors and silicon.

10.8% Efficiency Polymer Solar Cells Based on PTB7‐Th and PC71BM via Binary Solvent Additives Treatment

Abstract: In this work, polymer solar cells are fabricated based on the blend of PTB7-Th: PC71BM by using a mixed solvent additive of 1,8-diiodooctane and N-methyl pyrrolidone to optimize the morphology of the blend. A high power conversion efficiency (PCE) of 10.8% has been achieved with a simple conventional device. In order to deeply investigate the influence of the mixed solvent additives on the morphology and device performance, the variations of the molecular packing and bulk morphology of the blend film cast from ortho-dichlorobenzene with single or binary solvent additives are measured. Although all the blend films exhibit similar domain size and nanoscale phase separation, the blend film processed with mixed solvent additive shows the highest domain purity, resulting in the least bimolecular recombination, relatively high Jsc and FF, and hence enhanced PCE. Therefore, the best photovoltaic performance with the Voc of 0.82 V, Jsc of 19.1 mA cm−2, FF of 69.1%, and PCE of 10.8% are obtained for the device based on the blend with binary solvent additive treatment.

Detection of Nucleic Acids with Graphene Nanopores: Ab Initio Characterization of a Novel Sequencing Device

Abstract: We report an ab initio density functional theory study of the interaction of four nucleobases, cytosine, thymine, adenine, and guanine, with a novel graphene nanopore device for detecting the base sequence of a single-stranded nucleic acid (ssDNA or RNA). The nucleobases were inserted into a pore in a graphene nanoribbon, and the electrical current and conductance spectra were calculated as functions of voltage applied across the nanoribbon. The conductance spectra and charge densities were analyzed in the presence of each nucleobase in the graphene nanopore. The results indicate that due to significant differences in the conductance spectra the proposed device has adequate sensitivity to discriminate between different nucleotides. Moreover, we show that the nucleotide conductance spectrum is affected little by its orientation inside the graphene nanopore. The proposed technique may be extremely useful for real applications in developing ultrafast, low-cost DNA sequencing methods.