Electron spin resonance of nitrogen-vacancy centers in optically trapped nanodiamonds

Using an optical tweezers apparatus, we demonstrate three-dimensional control of nanodiamonds in solution with simultaneous readout of ground-state electron-spin resonance (ESR) transitions in an ensemble of diamond nitrogen-vacancy (NV) color centers. Despite the motion and random orientation of NV centers suspended in the optical trap, we observe distinct peaks in the measured ESR spectra qualitatively similar to the same measurement in bulk. Accounting for the random dynamics, we model the ESR spectra observed in an externally applied magnetic field to enable d.c. magnetometry in solution. We estimate the d.c. magnetic field sensitivity based on variations in ESR line shapes to be ~50 microTesla/Hz^1/2. This technique may provide a pathway for spin-based magnetic, electric, and thermal sensing in fluidic environments and biophysical systems inaccessible to existing scanning probe techniques.Comment: 29 pages, 13 figures for manuscript and supporting informatio

Comparative Study of Soluble Naphthalene Diimide Derivatives Bearing Long Alkyl Chains as n-type Organic Thin-Film Transistor Materials

ArticleORGANIC ELECTRONICS. 14(2):516-522 (2013)journal articl

DESIGN OF GRAPHENE-BASED SENSORS FOR NUCLEIC ACIDS DETECTION AND ANALYSIS

DNA (Deoxyribonucleic Acid) is the blueprint of life as it encodes all genetic information. In genetic disorder such as gene fusion, Copy Number Variation (CNV), and single nucleotide polymorphism, Nucleic acids such as DNA bases detection and analysis is used as the gold standard for successful diagnosis. Researchers have been conducting rigorous studies to achieve genome sequences at low cost while maintaining high accuracy and high throughput. A quick, accurate, and low-cost DNA detection approach would revolutionize medicine. Genome sequence helps to enhance people’s perception of inheritance, disease, and individuality. This research aims to improve DNA bases detection accuracy, and efficiency, and reduce the production cost, thus novel based sensors were developed to detect and identify the DNA bases. This work aims at first to develop specialized field effect transistors which will acquire real-time detection for different concentrations of DNA. The sensor was developed with a channel of graphite oxide between gold electrodes on a substrate of a silicon wafer using Quantumwise Atomistix Toolkit (ATK) and its graphical user interfaces Virtual Nanolab (VNL). The channel was decorated with trimetallic nanoclusters that include gold, silver, and platinum which have high affinity to DNA. The developed sensor was investigated by both simulation and experiment. The second aim of this research was to analyze the tissue transcriptome through DNA bases detection, thus novel graphene-based sensors with a nanopore were designed and developed to detect the different DNA nucleobases (Adenine (A), Cytosine (C), Guanine (G), Thymine (T)). This research focuses on the simulation of charge transport properties for the developed sensors. This work includes experimental fabrication and software simulation studies of the electronic properties and structural characteristics of the developed sensors. Novel sensors were modeled using Quantumwise Atomistix Toolkit (ATK) and its graphical user Interface Virtual Nanolab (VNL) where several electronic properties were studied including transmission spectrum and electrical current of DNA bases inside the sensor’s nanopore. The simulation study resulted in a unique current for each of the DNA bases within the nanopore. This work suggests that the developed sensors could achieve DNA sequencing with high accuracy. The practical implementation of this work represents the ability to predict and cure diseases from the genetic makeup perspective

Morphological Design of Conjugated Polymer Thin Films for Charge Transport and Energy Conversion.

Conjugated polymers hold great promise as a versatile class of materials for a wide range of optoelectronic applications, but unlocking their full potential requires deeper understanding of relationships between their complex structure and physical properties at multiple length scales. For polymer/fullerene blends used for thin film photovoltaics, controlling the “bulk heterojunction” morphology is of paramount importance to solar cell performance. By incorporating a small amount of an interfacially-active copolymer, the nano-scale phase separation was enhanced, generating more favorable pathways for transport and collection of photo-generated charges. The copolymer also enriched the region near the electrode, shifting the interfacial work function and suppressing surface recombination. Together these effects yielded up to a 20% increase in power conversion efficiencies. Even as pure components, conjugated polymers exhibit very diverse morphologies. By aligning the polymer chains, it is possible to borrow their molecular anisotropy and exploit it at the macroscopic level. Highly-aligned films were fabricated consisting of fibers with uniaxial orientation over centimeter-scale regions, and it was experimentally demonstrated that chain alignment could enable photo-excited charges to migrate distances over 400 µm. The measured anisotropy of optical properties, photocurrent migration, and carrier mobilities are all correlated to the morphology of the aligned films. As a contrasting yet complementary study, the effect of structural disorder on different transport mechanisms/regimes was investigated. To this end, a novel vacuum deposition technique was used to fabricate conjugated polymer films with unique globular morphologies. Despite being more disordered, vacuum-deposited thin film transistors (0.0083 cm^2/V*s) exhibited comparable in-plane mobilities to spin-cast analogues (0.0055 cm^2/V*s). Their out-of-plane mobilities, on the other hand, were nearly an order of magnitude lower. The seemingly contradictory results were rationalized in terms of the morphologies and carrier densities at interfaces versus within the bulk. Through different approaches to exploring various aspects of structure-property relationships in conjugated polymers, the work presented in this dissertation yields important insights for the future design and application of these materials.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120716/1/awli_1.pd

Combined Molecular Design, Morphology Control, and Device Engineering Towards Superior Organic Semiconductors

Department of Energy Engineering (Energy Engineering)Owing to the valuable features of organic polymers, such as inexpensive materials, ease of mass production, light-flexible properties, in recent days, the organic semiconductors have attracted significant research interests of challenging scientists in conducting and semiconducting organic polymers. The main concept of the conjugation of conducting organic polymers has occurred from the continuously connected pz-orbitals of sp2(or sp)-hybridized carbon atoms from the alternating sequence of single and multi-bonds (double and triple bonds) in the polymeric backbone. Based on the concept of conjugation structure, until now, many ??-conjugated organic polymers and small molecules have been designed with great expectation for various advents of the electronic application, like as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field-effect transistors (OFETs). Over the past decades, many pioneering research groups have paid attention to the design and development of novel organic semiconductors for next generated optoelectronic devices due to the aforementioned advantages of organic semiconductors. Moreover, many research interests have been concentrated on not only the invention of completely brand-new molecular structures but also fine-tuning of the existing molecular structures with marginal trade-off their outstanding own properties. In particular, the fine-tuning approaches are quite effective methods because the parent molecules had exhibited remarkable performances in optoelectronic devices. Therefore, the modified molecules usually have shown comparable or much better performances compared to parent molecules. In terms of modification of backbone, I present the article describes the synthesis and characterization as well as OFET characteristics of a collection of TBIG-based polymers with varied compositions between TBIG and IIG accepting segments and bithiophene counterpart donor. Secondly, based on the designed and synthesized with 2-ethylhexyl and 5-ethylnonyl side chains on the CPDT core, I demonstrated its effectiveness of side-chain engineering for the CPDT-based polymers and CPDT-based small molecules on the OFET performance and semi-transparent OPV performance, respectively. Finally, to fine-tuning of molecular properties, the substituents have been used without the sacrificial of the mainstream of organic semiconductors. The most universal substituent, fluorine with single proton, I investigated the constitutional isomeric effects on the photovoltaic performances via atomic level insight from the computational simulation and nano-second transient absorption spectroscopy.clos

Solid state physicochemical properties and applications of organic and metallo-organic fullerene derivatives

We review the fundamental properties and main applications of organic derivatives and complexes of fullerenes in the solid-state form. We address in particular the structural properties, in terms of crystal structure, polymorphism, orientational transitions and morphology, and the electronic structure and derived properties, such as chemical activity, electrical conduction mechanisms, optical properties, heat conduction and magnetism. The last two sections of the review focus on the solid-state optoelectronic and electrochemical applications of fullerene derivatives, which range from photovoltaic cells to field-effect transistors and photodetectors on one hand, to electron-beam resists, electrolytes and energy storage on the other.Peer ReviewedPreprin

Optimal 2-D cell layout with integrated transistor folding

ABSTRACT Folding, a key requirement in high-performance cell layout, implies breaking a large transistor into smaller, equal-sized transistors (legs) that are connected in parallel and placed contiguously with diffusion sharing. We present a novel technique FCLIP that integrates folding into the generation of optimal layouts of CMOS cells in the twodimensional (2-D) style. FCLIP is based on integer linear programming (ILP) and precisely formulates cell width minimization as a 0-1 optimization problem. Folding is incorporated into the 0-1 ILP model by variables that represent the degrees of freedom that folding introduces into cell layout. FCLIP yields optimal results for three reasons: (1) it implicitly explores all possible transistor placements; (2) it considers all diffusion sharing possibilities among folded transistors; and (3) when paired P and N transistors have unequal numbers of legs, it considers all their relative positions. FCLIP is shown to be practical for relatively large circuits with up to 30 transistors. We then extend FCLIP to accommodate and-stack clustering, a requirement in most practical designs due to its benefits on circuit performance. This reduces run times dramatically, making FCLIP viable for much larger circuits. It also demonstrates the versatility of FCLIP's ILP-based approach in easily accommodating additional design constraints. INTRODUCTION Cell layout synthesis falls in the category of constrained optimization whose goal is to find a solution that optimizes some cost function under a set of constraints. The cost function can be the cell area, its delay, or a combination of these. The constraints include bounds on width or height, aspect ratio, number of diffusion rows, or the maximum size of transistors. Since cell layout optimization is NP-hard [3], any exact algorithm can, in the worst case, have an exponential run time. Therefore, most prior techniques for cell synthesis have avoided optimal algorithms in favor of faster, but less exact heuristic methods. Maziasz and Hayes FCLIP minimizes cell area in the following stages: First, transistors are folded based on user-specified limits on the maximum size of the P and N transistors. The input circuit is preprocessed to generate P/N pairs and identify and-stacks, that is, transistors that are connected in series. And-stack clustering is not only necessary in practical designs, but also reduces the complexity of the problem and, in turn, FCLIP's run times. Then an ILP model is formulated and solved to determine a 2-D layout of minimum width W min ; this model maximizes diffusion sharing among folded transistors and minimizes vertical inter-row connections. A second ILP model is then constructed to generate a layout that has width W min and minimum height, measured by the number of horizontal routing tracks. This paper only discusses 2-D cell width minimization with folding; however, FCLIP can be extended to minimize cell height also. FCLIP yields optimal results with folding for two reasons: (1) It implicitly explores all diffusion sharing possibilities among folded transistors; and (2) when paired P/N transistors have unequal numbers of legs, it considers all their relative positions. Not only does FCLIP support 2-D layout, it is superior to prior folding techniques proposed for 1-D layou