Michael C. Hegg

Detection of malarial byproduct hemozoin utilizing its unique scattering properties

The scattering characteristics of the malaria byproduct hemozoin, including its scattering distribution and depolarization, are modeled using Discrete Dipole Approximation (DDA) and compared to those of healthy red blood cells. Scattering (or dark-field) spectroscopy and imaging are used to identify hemozoin in fresh rodent blood samples. A new detection method is proposed and demonstrated using dark-field in conjunction with cross-polarization imaging and spectroscopy. SNRs greater than 50:1 are achieved for hemozoin in fresh blood without the addition of stains or reagents. The potential of such a detection system is discussed.

Nanogap quantum dot photodetectors with high sensitivity and bandwidth

We report high-performance nanoscale photodetectors utilizing annealed nanocrystal quantum dots (QDs) within a nanoscale metal electrode gap. By optimizing the nanogap size and fabrication process, the device demonstrates a significantly better sensitivity (noise equivalent power=7.76×10−14 W/Hz1/2) and bandwidth (≥125 kHz) than previously reported nanoscale photodetectors. Furthermore, by utilizing a lateral photoconduction structure and a self-assembled layer of QDs, the detector fabrication is highly compatible with many substrates and device architectures.

Near-field photodetection with high spatial resolution by nanocrystal quantum dots.

We report a new demonstration of nanoscale solution-processed photodetectors by fabricating a nano-sized gap between two electrodes and drop-casting nanocrystal quantum dots (NCQDs) into the gap. We demonstrate a detection sensitivity of 62 pW with a max responsivity of 2.7 mA/W over a device with a nano-gap of 25 nm. Additionally, we characterize the dependence of signal-to-dark current ratio and responsivity on nano-gap size. Responsivity ranges from 1 - 90 mA/W for a nano-gap size range of 25 nm - 1.5 nm. Our results represent the first demonstration of how near-field optical detection for sub-diffraction nanophotonic integrated circuits can be achieved in principle using NCQDs.

Remote Monitoring of Resin Transfer Molding Processes by Distributed Dielectric Sensors

Feed-forward adaptive control of resin transfer molding (RTM) processes is crucial for producing a high yield of usable parts for industrial applications. The enabling technique for this process is non-invasive monitoring of the fill-front position and the degree of cure of the resin as it is injected into the mold. Successful implementation of a sensing system capable of meeting these criteria will result in a high yield of composite parts that can be used for the next generation of aircraft. This article articulates the possibility of a hybrid sensing system for multiparameter monitoring during RTM processes. It addresses the fundamental engineering trade-offs between penetration depth and signal strength, discussing how to account for fringing electric field (FEF) effects present in the system. FEF effects hinder the measurement accuracy of the sensor system. This article describes how these effects are addressed using a mapping algorithm that is developed using numerical simulations of the experimental setup. The experimental setup utilizes a rectangular RTM tool and a water-glycerin mixture which simulates mechanical properties of epoxy resins, prior to cure. Modeling of the FEF effects helps to achieve high measurement accuracy of the fill front location.

Influence of variable plate separation on fringing electric fields in parallel-plate capacitors

Measurement of bulk physical properties in dielectric materials is typically performed using a parallel-plate capacitor configuration, where a dielectric material is placed between two conducting plates and the complex permittivity is found by measuring capacitance and conductance between the electrodes. Fringing electric fields exist between any two parallel conducting plates of finite length and the additional capacitance these fields add is not easily accounted for. It is important to account for edge effects in many capacitive sensing applications in order to ensure accurate results. Unfortunately, these edge effects are not easily quantifiable and are subject to change with varying sensor geometries. A quantitative relationship between fringing field strength and sensor geometry will improve the accuracy of many capacitive sensing applications. This work presents finite element simulations showing the influence of variable plate separation on fringing field effects in a system designed to measure the dielectric properties of a fluid. A quantitative relationship is established that relates the sensor response to the plate distance and fluid position. This relationship can be applied to experimental data in order to compensate for any edge effects present in the system.

A nano-scale quantum dot photodetector by self-assembly

Modern CMOS transistors will not scale well in the next decade due to leakage currents, sources of variation, and platform requirements. To keep the cost per transistor decreasing, and to realize the feasibility of ultra-high density integrated circuits, low power techniques and efficiency optimization are being explored to counter these problems. Parallel to the development of electronic VLSI, using photons as a means of carrying information has been an appealing approach, due to the high speed and broad bandwidth of light, and the elimination of on-chip parasitic and electro-magnetic interference as its electronic counterpart. This paper focuses on photonic integrated circuits to solve the high-density problem, and presents a design for a nano-scale QD optical transducer (QDOT) that will function as a near-field photodetector and that can easily interface into a self- assembled QD integrated circuit (QDIC). The optical transducer consists of a QD between two metal electrodes. The tunneling current between the metal electrodes is mediated by the QD and can be gated by changing the optical signal intensity impinging on the QD. The device can be fabricated via self-assembly using QDs. In this method, a chemistry linker such as DNA or APTES is covalently bound to pre- defined zones on a substrate. The global location of these zones is defined via electron-beam lithography (EBL). Numerical simulations are discussed and ideal characteristics of the device are presented.

Nano-scale Nanocrystal Quantum Dot Photodetectors

We present the design, fabrication and testing results of a nano-scale quantum dot photodetector composed of quantum dots that are positioned between a nano-gap in electrodes and optically excited with CW light.

Quantum dot nanophotonics - from waveguiding to integration

Due to its unique optoelectronic properties, the quantum dot (QD) has become a promising material for realizing photonic components and devices with high quantum efficiencies. Quantum dots in colloidal form can have their surfaces modified with various molecules, which enables new fabrication process utilizing molecular self-assembly and can result in new QD photonic device structures in nano-scale. In this review paper, we describe our work on QD waveguides for sub-diffraction limit waveguiding that utilizies near-field optical coupling between QDs, nano-scale QD photodetectors with nanogaps for sensing with high spatial resolution and sensitivity, as well as integration of these two nanophotonic components. The QD waveguide achieved a transmission loss of 3 dB/4 Pm, which is lower than the experimental results from other sub-diffraction limit waveguides that have been reported. It also demonstrated a comparable waveguiding effect through a waveguide with a sharp bend. The QD photodetector showed a sensitivity of 60 pW over a device with a nano- gap of 25 nm for detection. The compatibility between the fabrication processes for these two components with colloidal QDs allows integration of them through self-assembly fabrications.

Nano-scale quantum dot optical transducers by self-assembly

We propose a nano-scale optical transducer for future all-optical quantum circuits. The device is comprised of an array of quantum dot islands between opposing electrodes, fabricated by self-assembly. The device operates under low bias and produces a measurable photocurrent in response to light. Modeling, fabrication, and preliminary experimental results are presented in this paper.

MOESM1 of Development of new malaria diagnostics: matching performance and need

Additional file 1: Annex S1. Example target product profiles for malaria diagnostic markets.