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 (±0.0001 g cm^–3) but are too large (3–7 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^–3; 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^–3) 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

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 “buried interface” problem that has traditionally been difficult to address. Here we address the question of how <i>n</i>-octadecylsilane (OTS)–derived self-assembled monolayers (SAMs) on Si/SiO₂ gate dielectrics affect the OTFT performance of the archetypical small-molecule p-type semiconductors P-BTDT (phenylbenzo­[<i>d</i>,<i>d</i>]­thieno­[3,2-<i>b</i>;4,5-<i>b</i>]­dithiophene) 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>

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 °C includes >4× enhancement in electron mobility (μ_FE) on Hf-SAND versus SiO₂ or ALD-HfO₂ gate dielectrics, while other metrics such as subthreshold swing (SS), current on:off ratio (<i>I</i>_ON:<i>I</i>_OFF), threshold voltage (<i>V</i>_th), and gate leakage current (<i>I</i>_g) are unchanged or enhanced. Thus, low voltage IGZO/SAND TFT operation (<2 V) is possible with <i>I</i>_ON:<i>I</i>_OFF = 10⁷, SS = 125 mV/dec, near-zero <i>V</i>_th, and large electron mobility, μ_FE(avg) = 20.6 ± 4.3 cm² V^–1 s^–1, μ_FE(max) = 50 cm² V^–1 s^–1. Furthermore, X-ray diffraction analysis indicates that the 300 °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 organic–inorganic 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 π–π overlap and amorphous film microstructures, and hence to low carrier mobilities. We report here the synthesis of a new building block for HH linkages, 4,4′-dialkoxy-5,5′-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 S­(thiazolyl)···O­(alkoxy) attraction promote HH macromolecular architectures with extensive π-conjugation, low bandgaps (1.40–1.63 eV), and high crystallinity. In comparison to previously reported 3,3′-dialkoxy-2,2′-bithiophene (<b>BTOR</b>), <b>BTzOR</b> is a promising building block in view of thiazole geometric and electronic properties: (a) replacing (thiophene)­C–H with (thiazole)N reduces steric encumbrance in <b>–BTzOR–Ar–</b> dyads by eliminating repulsive C–H···H–C interactions with neighboring arene units, thereby enhancing π–π 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 (0.06–0.25 cm²/(V s)) in organic thin-film transistors, as well as enhanced <i>I</i>_on:<i>I</i>_off 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

Schematic of the density-based tests to identify SCD.

<p>Both versions of the SCD-AMPS are designed to separate dense red blood cells present in SCD from whole blood. Blood passes through the phases—top (T) and bottom (B) for SCD-AMPS-2 and top (T), middle (M), and bottom (B) for SCD-AMPS-3—upon centrifugation. If sickled cells are present, they collect at the interface between the bottom phase and the seal (<i>B/S</i>), and provide a visual readout for the presence of SCD. In SCD-AMPS-3, the additional phase allows the discrimination of Hb SS from Hb SC by evaluating the distribution of red cells at the upper interfaces (between the top and middle phases (<i>T/M</i>) and the middle and bottom phases (<i>M/B</i>).</p

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 β-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

Equipment for the SCD-AMPS rapid test.

<p>All the equipment necessary to run the rapid test in a rural clinic fits inside a backpack and were evaluated at rural health centers in Zambia.</p

Inclusion and Exclusion Criteria for Study.

<p>Inclusion and Exclusion Criteria for Study.</p

The sensitivity and specificity of SCD-AMPS as a function of the amount of time between collecting samples and running tests.

<p>The specificity shows a decline over each 24 hour increment, with a significant decline over 48 hours (p-value <0.0005). The sensitivity increased between the first and second time interval, but then decreased between the second and third interval (p-values <0.01). The sample size used for each time interval is provided below each bar.</p