20 research outputs found
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Evaluation of a Density-Based Rapid Diagnostic Test for Sickle Cell Disease in a Clinical Setting in Zambia
Although simple and low-cost interventions for sickle cell disease (SCD) exist in many developing countries, child mortality associated with SCD remains high, in part, because of the lack of access to diagnostic tests for SCD. A density-based test using aqueous multiphase systems (SCD-AMPS) is a candidate for a low-cost, point-of-care diagnostic for SCD. In this paper, the field evaluation of SCD-AMPS in a large (n = 505) case-control study in Zambia is described. Of the two variations of the SCD-AMPS used, the best system (SCD-AMPS-2) demonstrated a sensitivity of 86% (82ā90%) and a specificity of 60% (53ā67%). Subsequent analysis identified potential sources of false positives that include clotting, variation between batches of SCD-AMPS, and shipping conditions. Importantly, SCD-AMPS-2 was 84% (62ā94%) sensitive in detecting SCD in children between 6 months and 1 year old. In addition to an evaluation of performance, an assessment of end-user operability was done with health workers in rural clinics in Zambia. These health workers rated the SCD-AMPS tests to be as simple to use as lateral flow tests for malaria and HIV
Fractionating Polymer Microspheres as Highly Accurate Density Standards
This paper describes a method of
isolating small, highly accurate
density-standard beads and characterizing their densities using accurate
and experimentally traceable techniques. Density standards have a
variety of applications, including the characterization of density
gradients, which are used to separate objects in a variety of fields.
Glass density-standard beads can be very accurate (Ā±0.0001 g
cm<sup>ā3</sup>) but are too large (3ā7 mm in diameter)
for many applications. When smaller density standards are needed,
commercial polymer microspheres are often used. These microspheres
have standard deviations in density ranging from 0.006 to 0.021 g
cm<sup>ā3</sup>; these distributions in density make these
microspheres impractical for applications demanding small steps in
density. In this paper, commercial microspheres are fractionated using
aqueous multiphase systems (AMPS), aqueous mixture of polymers and
salts that spontaneously separate into phases having molecularly sharp
steps in density, to isolate microspheres having much narrower distributions
in density (standard deviations from 0.0003 to 0.0008 g cm<sup>ā3</sup>) than the original microspheres. By reducing the heterogeneity in
densities, this method reduces the uncertainty in the density of any
specific bead and, therefore, improves the accuracy within the limits
of the calibration standards used to characterize the distributions
in density
Exploratory Combustion Synthesis: Amorphous Indium Yttrium Oxide for Thin-Film Transistors
We report the implementation of amorphous indium yttrium
oxide
(a-IYO) as a thin-film transistor (TFT) semiconductor. Amorphous and
polycrystalline IYO films were grown via a low-temperature solution
process utilizing exothermic ācombustionā precursors.
Precursor transformation and the IYO films were analyzed by differential
thermal analysis, thermogravimetric analysis, X-ray diffraction, atomic
force microscopy, X-ray photoelectron spectroscopy, and optical transmission,
which reveal efficient conversion to the metal oxide lattice and smooth,
transparent films. a-IYO TFTs fabricated with a hybrid nanodielectric
exhibit electron mobilities of 7.3 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup> (<i>T</i><sub>anneal</sub> = 300
Ā°C) and 5.0 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup> (<i>T</i><sub>anneal</sub> = 250 Ā°C) for 2 V operation
In-Situ Probe of Gate Dielectric-Semiconductor Interfacial Order in Organic Transistors: Origin and Control of Large Performance Sensitivities
Organic thin film transistor (OTFT) performance is highly
materials
interface-dependent, and dramatic performance enhancements can be
achieved by properly modifying the semiconductor/gate dielectric interface.
However, the origin of these effects is not well understood, as this
is a classic āburied interfaceā problem that has traditionally
been difficult to address. Here we address the question of how <i>n</i>-octadecylsilane (OTS)āderived self-assembled monolayers
(SAMs) on Si/SiO<sub>2</sub> gate dielectrics affect the OTFT performance
of the archetypical small-molecule p-type semiconductors P-BTDT (phenylbenzoĀ[<i>d</i>,<i>d</i>]ĀthienoĀ[3,2-<i>b</i>;4,5-<i>b</i>]Ādithiophene) and pentacene using combined in situ sum
frequency generation spectroscopy, atomic force microscopy, and grazing
incidence and reflectance X-ray scattering. The molecular order and
orientation of the OTFT components at the dielectric/semiconductor
interface is probed as a function of SAM growth mode in order to understand
how this impacts the overlying semiconductor growth mode, packing,
crystallinity, and carrier mobility, and hence, transistor performance.
This understanding, using a new, humidity-specific growth procedure,
leads to a reproducible, scalable process for highly ordered OTS SAMs,
which in turn nucleates highly ordered p-type semiconductor film growth,
and optimizes OTFT performance. Surprisingly, the combined data reveal
that while SAM molecular order dramatically impacts semiconductor
crystalline domain size and carrier mobility, <i>it does not
significantly influence the local orientation of the overlying organic
semiconductor molecules</i>
Oxygen āGetterā Effects on Microstructure and Carrier Transport in Low Temperature Combustion-Processed aāInXZnO (X = Ga, Sc, Y, La) Transistors
In
oxide semiconductors, such as those based on indium zinc oxide
(IXZO), a strong oxygen binding metal ion (āoxygen getterā),
X, functions to control O vacancies and enhance lattice formation,
hence tune carrier concentration and transport properties. Here we
systematically study, in the IXZO series, the role of X = Ga<sup>3+</sup> versus the progression X = Sc<sup>3+</sup> ā Y<sup>3+</sup> ā La<sup>3+</sup>, having similar chemical characteristics
but increasing ionic radii. IXZO films are prepared from solution
over broad composition ranges for the first time via low-temperature
combustion synthesis. The films are characterized via thermal analysis
of the precursor solutions, grazing incidence angle X-ray diffraction
(GIAXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy
(XPS), and scanning transmission electron microscopy (STEM) with high
angle annular dark field (HAADF) imaging. Excellent thin-film transistor
(TFT) performance is achieved for all X, with optimal compositions
after 300 Ā°C processing exhibiting electron mobilities of 5.4,
2.6, 2.4, and 1.8 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup> for Ga<sup>3+</sup>, Sc<sup>3+</sup>, Y<sup>3+</sup>, and La<sup>3+</sup>, respectively, and with <i>I</i><sub>on</sub>/<i>I</i><sub>off</sub> = 10<sup>7</sup>ā10<sup>8</sup>.
Analysis of the IXZO TFT positive bias stress response shows X = Ga<sup>3+</sup> to be superior with mobilities (Ī¼) retaining >95%
of the prestress values and threshold voltage shifts (Ī<i>V</i><sub>T</sub>) of <1.6 V, versus <85% Ī¼ retention
and Ī<i>V</i><sub>T</sub> ā 20 V for the other
trivalent ions. Detailed microstructural analysis indicates that Ga<sup>3+</sup> most effectively promotes oxide lattice formation. We conclude
that the metal oxide lattice formation enthalpy (Ī<i>H</i><sub>L</sub>) and metal ionic radius are the best predictors of IXZO
oxygen getter efficacy
Printed Indium Gallium Zinc Oxide Transistors. Self-Assembled Nanodielectric Effects on Low-Temperature Combustion Growth and Carrier Mobility
Solution-processed amorphous oxide
semiconductors (AOSs) are emerging as important electronic materials
for displays and transparent electronics. We report here on the fabrication,
microstructure, and performance characteristics of inkjet-printed,
low-temperature combustion-processed, amorphous indium gallium zinc
oxide (a-IGZO) thin-film transistors (TFTs) grown on solution-processed
hafnia self-assembled nanodielectrics (Hf-SANDs). TFT performance
for devices processed below 300 Ā°C includes >4Ć enhancement
in electron mobility (Ī¼<sub>FE</sub>) on Hf-SAND versus SiO<sub>2</sub> or ALD-HfO<sub>2</sub> gate dielectrics, while other metrics
such as subthreshold swing (SS), current on:off ratio (<i>I</i><sub>ON</sub>:<i>I</i><sub>OFF</sub>), threshold voltage
(<i>V</i><sub>th</sub>), and gate leakage current (<i>I</i><sub>g</sub>) are unchanged or enhanced. Thus, low voltage
IGZO/SAND TFT operation (<2 V) is possible with <i>I</i><sub>ON</sub>:<i>I</i><sub>OFF</sub> = 10<sup>7</sup>,
SS = 125 mV/dec, near-zero <i>V</i><sub>th</sub>, and large
electron mobility, Ī¼<sub>FE</sub>(avg) = 20.6 Ā± 4.3 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>, Ī¼<sub>FE</sub>(max) = 50 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>. Furthermore, X-ray diffraction analysis indicates that the 300
Ā°C IGZO combustion processing leaves the underlying Hf-SAND microstructure
and capacitance intact. This work establishes the compatibility and
advantages of all-solution, low-temperature fabrication of inkjet-printed,
combustion-derived high-mobility IGZO TFTs integrated with self-assembled
hybrid organicāinorganic nanodielectrics
Dialkoxybithiazole: A New Building Block for Head-to-Head Polymer Semiconductors
Polymer semiconductors have received great attention
for organic
electronics due to the low fabrication cost offered by solution-based
printing techniques. To enable the desired solubility/processability
and carrier mobility, polymers are functionalized with hydrocarbon
chains by strategically manipulating the alkylation patterns. Note
that head-to-head (HH) linkages have traditionally been avoided because
the induced backbone torsion leads to poor ĻāĻ
overlap and amorphous film microstructures, and hence to low carrier
mobilities. We report here the synthesis of a new building block for
HH linkages, 4,4ā²-dialkoxy-5,5ā²-bithiazole (<b>BTzOR</b>), and its incorporation into polymers for high performance organic
thin-film transistors. The small oxygen van der Waals radius and intramolecular
SĀ(thiazolyl)Ā·Ā·Ā·OĀ(alkoxy) attraction promote HH macromolecular
architectures with extensive Ļ-conjugation, low bandgaps (1.40ā1.63
eV), and high crystallinity. In comparison to previously reported
3,3ā²-dialkoxy-2,2ā²-bithiophene (<b>BTOR</b>), <b>BTzOR</b> is a promising building block in view of thiazole geometric
and electronic properties: (a) replacing (thiophene)ĀCāH with
(thiazole)N reduces steric encumbrance in <b>āBTzORāArā</b> dyads by eliminating repulsive CāHĀ·Ā·Ā·HāC
interactions with neighboring arene units, thereby enhancing ĻāĻ
overlap and film crystallinity; and (b) thiazole electron-deficiency
compensates alkoxy electron-donating characteristics, thereby lowering
the <b>BTzOR</b> polymer HOMO versus that of the <b>BTOR</b> analogues. Thus, the new <b>BTzOR</b> polymers show substantial
hole mobilities (0.06ā0.25 cm<sup>2</sup>/(V s)) in organic
thin-film transistors, as well as enhanced <i>I</i><sub>on</sub>:<i>I</i><sub>off</sub> ratios and greater ambient
stability than the <b>BTOR</b> analogues. These geometric and
electronic properties make <b>BTzOR</b> a promising building
block for new classes of polymer semiconductors, and the synthetic
route to <b>BTzOR</b> reported here should be adaptable to many
other bithiazole-based building blocks
Basic Characteristics of the Study Population.
<p>Basic Characteristics of the Study Population.</p
Tabulation of Results of SCD-AMPS Tests Compared to Reference Test Results by Hemoglobin Electrophoresis.
<p>*Samples found to have>50% Hb S but non-zero levels of Hb A, potentially a result of Hb S with Ī²-thalassemia or a transfused Hb SS subject.</p><p>Tabulation of Results of SCD-AMPS Tests Compared to Reference Test Results by Hemoglobin Electrophoresis.</p