Search

Solution-processed two-dimensional materials offer a scalable route toward next-generation printed devices. In this report, we demonstrate fully inkjet-printed photodetectors using molybdenum disulfide (MoS2) nanosheets as the active material and graphene as the electrodes. Percolating films of semiconducting MoS2 with high electrical conductivity are achieved with an ethyl cellulose-based ink formulation. Two classes of photodetectors are fabricated, including thermally annealed devices on glass with fast photoresponse of 150 μs and photonically annealed devices on flexible polyimide with high photoresponsivity exceeding 50 mA/W. The photonically annealed photodetector also reduces the curing time to milliseconds and maintains functionality over 500 bending cycles.

We report on the dynamics of spatial temperature distributions in aligned semiconducting carbon nanotube array devices with submicrometer channel lengths. By using high-resolution optical microscopy in combination with electrical transport measurements, we observe under steady state bias conditions the emergence of time-variable, local temperature maxima with dimensions below 300 nm, and temperatures above 400 K. On the basis of time domain cross-correlation analysis, we investigate how the intensity fluctuations of the thermal radiation patterns are correlated with the overall device current. The analysis reveals the interdependence of electrical current fluctuations and time-variable hot spot formation that limits the overall device performance and, ultimately, may cause device degradation. The findings have implications for the future development of carbon nanotube-based technologies.

Arc discharge single-walled carbon nanotubes (SWCNTs) possess superlative optical and electronic properties that are of high interest for technologically important applications including fiber optic communications, biomedical imaging, and field-effect transistors. However, as-grown arc discharge SWCNTs possess a mixture of metallic and semiconducting species in addition to a wide diameter distribution (1.2 to 1.7 nm) that limit their performance in devices. While previous postsynthetic sorting efforts have achieved separation by electronic type and diameter refinement for metallic arc discharge SWCNTs, tight diameter distributions of semiconducting arc discharge SWCNTs have not yet been realized. Herein, we present two advances in density gradient ultracentrifugation that enable the isolation of high purity (>99%) semiconducting arc discharge SWCNTs with narrow diameter distributions centered at ∼1.6 and ∼1.4 nm. The resulting diameter-refined populations of semiconducting arc discharge SWCNTs possess mon...

A central challenge for printed electronics is to achieve high operating frequencies (short transistor switching times) at low supply biases compatible with thin film batteries. In this report, we demonstrate partially printed five-stage ring oscillators with20 kHz operating frequencies and stage delays5 μs at supply voltages below 3 V. The fastest ring oscillator achieved 1.2 μs delay time at 2 V supply. The inverter stages in these ring oscillators were based on ambipolar thin film transistors (TFTs) employing semiconducting, single-walled carbon nanotube (CNT) networks and a high capacitance (∼1 μF/cm(2)) ion gel electrolyte as the gate dielectric. All materials except the source and drain electrodes were aerosol jet printed. The TFTs exhibited high electron and hole mobilities (∼20 cm(2)/(V s)) and ON/OFF current ratios (up to 10(5)). Inverter switching times t were systematically characterized as a function of transistor channel length and ionic conductivity of the gel dielectric, demonstrating that both the semiconductor and the ion gel play a role in switching speed. Quantitative scaling analysis suggests that with suitable optimization low voltage, printed ion gel gated CNT inverters could operate at frequencies on the order of 1 MHz.

The method by which surfactants selectively interact with particular electronic types of single-walled carbon nanotubes (SWCNTs) and thereby enable the isolation of metallic and semiconducting species is not well understood. While density gradient ultracentrifugation (DGU) has demonstrated its potential as a powerful nanomaterial separation technique, this study utilizes DGU as an analytic tool to probe the interactions between amphiphilic block copolymers, surfactants capable of electronic type extraction, and the SWCNT surface. By modulating the pH during DGU, we find that the linear shaped Pluronic copolymers can extract either metallic or semiconducting SWCNTs at purities in excess of 99%. Furthermore, the first electronic type sorting mechanism is given by which oxygen absorption and subsequent protonation of the SWCNT surface acts to template copolymer adhesion. Detailed characterization reveals the underlying mechanism for pH-shifted DGU and is thus likely to enable future development of more effic...

Methods of using a surface active block copolymer to disperse graphene in aqueous medium, such dispersions which can be subsequently separated and processed for a range of end-use applications, including biomedical applications.

In this paper we present a systematic comparison of the performance of different computational approaches to study the propagation and termination reactions of olefins with a prototype homogeneous group 4 ansa-metallocene catalyst. Chain propagation, beta-H transfer to the monomer, and beta-H elimination to the metal have been investigated for the H2Si-(CP)(2)ZrR+ (R = ethyl, n-butyl) + C2H4 system using ab initio and density functional theory (DFT) techniques. For all the species investigated, all the computational approaches we considered result in substantially similar geometries. A comparison of the DFT and Moller-Plesset theory (MP2) propagation and termination barriers with extrapolated coupled-cluster calculations with inclusion of single, double, and perturbatively connected triple excitation (CCSD(T)) values indicates that all the pure functionals considered underestimate the difference between termination and propagation by roughly 3-4 kcal/mol. In contrast, hybrid functionals are within 1 kcal/mol from extrapolated CCSD(T) values. For a comparison with experimental results inclusion of zero-point energy contributions and the use of an alkyl group longer than ethyl to simulate the growing chain in both termination reactions are mandatory.