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Covalent bonding interactions determine the energy-momentum (E-k) dispersion (band structure) of solid-state materials. Here, we show that noncovalent interactions can modulate the E-k dispersion near the Fermi level of a low-dimensional nanoscale conductor. We demonstrate that low energy band gaps may be opened in metallic carbon nanotubes through polymer wrapping of the nanotube surface at fixed helical periodicity. Electronic spectral, chiro-optic, potentiometric, electronic device, and work function data corroborate that the magnitude of band gap opening depends on the nature of the polymer electronic structure. Polymer dewrapping reverses the conducting-to-semiconducting phase transition, restoring the native metallic carbon nanotube electronic structure. These results address a long-standing challenge to develop carbon nanotube electronic structures that are not realized through disruption of π conjugation, and establish a roadmap for designing and tuning specialized semiconductors that feature band gaps on the order of a few hundred meV.
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Three-dimensional (3D) graphene microstructures have the potential to boost performance in high-capacity batteries and ultrasensitive sensors. Numerous techniques have been developed to create such structures; however, the methods typically rely on structural supports, and/or lengthy post-print processing, increasing cost and complexity. Additive manufacturing techniques, such as printing, show promise in overcoming these challenges. This study employs aerosol jet printing for creating 3D graphene microstructures using water as the only solvent and without any post-print processing required. The graphene pillars exhibit conductivity immediately after printing, requiring no high-temperature annealing. Furthermore, these pillars are successfully printed in freestanding configurations at angles below 45° relative to the substrate, showcasing their adaptability for tailored applications. When graphene pillars are added to humidity sensors, the additional surface area does not yield a corresponding increase in sensor performance. However, graphene trusses, which add a parallel conduction path to the sensing surface, are found to improve sensitivity nearly 2×, highlighting the advantages of a topologically suspended circuit construction when adding 3D microstructures to sensing electrodes. Overall, incorporating 3D graphene microstructures to sensor electrodes can provide added sensitivity, and aerosol jet printing is a viable path to realizing these conductive microstructures without any post-print processing.
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Printing thin-film transistors (TFTs) using nanomaterials is a promising approach for future electronics. Yet, most inks rely on environmentally harmful solvents for solubilizing and postprint processing the nanomaterials. In this work, we demonstrate water-only TFTs printed from all-carbon inks of semiconducting carbon nanotubes (CNTs), conducting graphene, and insulating crystalline nanocellulose (CNC). While suspending these nanomaterials into aqueous inks is readily achieved, printing the inks into thin films of sufficient surface coverage and in multilayer stacks to form TFTs has proven elusive without high temperatures, hazardous chemicals, and/or lengthy postprocessing. Using aerosol jet printing, our approach involves a maximum temperature of 70 °C and no hazardous chemicalsâall inks are aqueous and only water is used for processing. An intermittent rinsing technique was utilized to address the surface adhesion challenges that limit film density of printed aqueous CNTs. These findings provide promising steps toward an environmentally friendly realization of thin-film electronics.
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To ensure stability for low-cost electronics used in direct contact with ionic solutions (such as electronic biosensors), electrodes are frequently passivated to protect against current leakage, which leads to corrosion. The epoxy-based polymer SU-8 yields favorable properties for passivation against ionic solutions. However, it is nearly universally patterned via cleanroom techniques, which increases device cost and fabrication complexity. Printing electronic components has been shown to be a viable approach for decreasing fabrication cost. Previous reports on SU-8 printing focus on the resultant printed structure, with little emphasis on its subsequent use as a passivation layer. Here, we demonstrate the printing of SU-8 with an aerosol jet printer using ultrasonic aerosolization. We show that SU-8 can be printed without reformulation, and that printed SU-8 is a viable passivation layer over conductive silver lines, when tested in ionic solutions. Extending the printed SU-8 film beyond the underlying conductive electrodes by 100 µm produced a six order of magnitude decrease in leakage current and resulted high stability over 20 voltage sweeps. Finally, we optimized post-printing cure time to 15 minutes at 160°C, which further minimized leakage current. While the development of low-cost, electronic biosensing devices has increasingly moved towards printing methods, the lack of a printed passivation strategy has hindered this transition. The advancements made in this study towards an aerosol jet printable SU-8 passivation layer provide useful progress towards a fully printed, stable electronic biosensing device.
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Ion gel-based dielectrics have long been considered for enabling low-voltage operation in printed thin-film transistors (TFTs), but their compatibility with in-place printing (a streamlined, direct-write printing approach where devices never leave the printer mid- or post-process) remains unexplored. Here, we demonstrate a simple and rapid 4-step in-place printing procedure for producing low-voltage electrolyte-gated carbon nanotube (CNT) thin-film transistors at low temperature (80 °C). This process consists of the use of polymer-wrapped CNT inks for printed channels, silver nanowire inks for printed electrodes, and imidazolium-based ion gel inks for printed gate dielectrics. We find that the efficacy of rinsing CNT films and printing an ion gel in-place is optimized using an elevated platen temperature (as opposed to external rinsing or post-process annealing), where resultant devices exhibited on/off-current ratios exceeding 103, mobilities exceeding 10 cm2V-1s-1, and gate hysteresis of only 0.1 V. Additionally, devices were tested under mechanical strain and long-term bias, showing exceptional flexibility and electrochemical stability over the course of 14-hour bias tests. The findings presented here widen the potential scope of print-in-place (PIP) devices and reveal new avenues of investigation for the improvement of bias stress stability in electrolyte-gated transistors.
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Thousands of reports have demonstrated the exceptional performance of sensors based on carbon nanotube (CNT) transistors, with promises of transformative impact. Yet, the effect of long-term bias stress on individual CNTs, critical for most sensing applications, has remained uncertain. Here, we report bias ranges under which CNT transistors can operate continuously for months or more without degradation. Using a custom characterization system, the impacts of defect formation and charge traps on the stability of CNT-based sensors under extended bias are determined. In addition to breakdown, which is well-known, we identify three additional operational modes: full stability, slow decay, and fast decay. We identify a current drift behavior that reduces dynamic range by over four orders of magnitude but is avoidable with appropriate sensing modalities. Identification of these stable operation modes and limits for nanotube-based sensors addresses concerns surrounding their development for a myriad of sensing applications.
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Atomically thin two-dimensional (2D) materials are promising candidates for sub-10 nm transistor channels due to their ultrathin body thickness, which results in strong electrostatic gate control. Properly scaling a transistor technology requires reducing both the channel length (distance from source to drain) and the contact length (distance that source and drain interface with semiconducting channel). Contact length scaling remains an unresolved epidemic for transistor scaling, affecting devices from all semiconductors-silicon to 2D materials. Here, we show that clean edge contacts to 2D MoS2 can provide immunity to the contact-scaling problem, with performance that is independent of contact length down to the 20 nm regime. Using a directional ion beam, in situ edge contacts of various metal-MoS2 interfaces are studied. Characterization of the intricate edge interface using cross-sectional electron microscopy reveals distinct morphological effects on the MoS2 depending on its thickness-from monolayer to few-layer films. The in situ edge contacts also exhibit an order of magnitude higher performance compared to the best-reported ex situ metal edge contacts. Our work provides experimental evidence for a solution to contact scaling in transistors, using 2D materials with clean edge contact interfaces, opening a new way of designing devices with 2D materials.
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Nurse leaders must utilize diverse operational skills in today's healthcare delivery system. Thus, the purposes of this article are to describe 1 institution's experience in expanding the role of a nonclinical house administrator to a nurse-led Hospital Operations Administrator team. The skills reflective of the American Organization of Nurse Executives competencies needed to successfully implement the newly configured role are discussed. The expansion of this role has been beneficial in showcasing the unique contributions of nurse leaders.
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Competência Clínica/normas , Administração Hospitalar , Liderança , Enfermeiros Administradores/organização & administração , Competência Profissional/normas , Humanos , Papel do Profissional de Enfermagem , Pesquisa Operacional , Estados UnidosRESUMO
The mechanisms of carrier transport in the cross-plane crystal orientation of transition metal dichalcogenides are examined. The study of in-plane electronic properties of these van der Waals compounds has been the main research focus in recent years. However, the distinctive physical anisotropies, short-channel physics, and tunability of cross layer interactions can make the study of their electronic properties along the out-of-plane crystal orientation valuable. Here, the out-of-plane carrier transport mechanisms in niobium diselenide and hafnium disulfide are explored as two broadly different representative materials. Temperature-dependent current-voltage measurements are preformed to examine the mechanisms involved. First principles simulations and a tunneling model are used to understand these results and quantify the barrier height and hopping distance properties. Using Raman spectroscopy, the thermal response of the chemical bonds is directly explored and the insight into the van der Waals gap properties is acquired. These results indicate that the distinct cross-plane carrier transport characteristics of the two materials are a result of material thermal properties and thermally mediated transport of carriers through the van der Waals gaps. Exploring the cross-plane electron transport, the exciting physics involved is unraveled and potential new avenues for the electronic applications of van der Waals layers are inspired.
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It has been shown that a ferroelectric material integrated into the gate stack of a transistor can create an effective negative capacitance (NC) that allows the device to overcome "Boltzmann tyranny". While this switching below the thermal limit has been observed with Si-based NC field-effect transistors (NC-FETs), the adaptation to 2D materials would enable a device that is scalable in operating voltage as well as size. In this work, we demonstrate sustained sub-60 mV/dec switching, with a minimum subthreshold swing (SS) of 6.07 mV/dec (average of 8.03 mV/dec over 4 orders of magnitude in drain current), by incorporating hafnium zirconium oxide (HfZrO2 or HZO) ferroelectric into the gate stack of a MoS2 2D-FET. By first fabricating and characterizing metal-ferroelectric-metal capacitors, the MoS2 is able to be transferred directly on top and characterized with both a standard and a negative capacitance gate stack. The 2D NC-FET exhibited marked enhancement in low-voltage switching behavior compared to the 2D-FET on the same MoS2 channel, reducing the SS by 2 orders of magnitude. A maximum internal voltage gain of â¼28× was realized with â¼12 nm thick HZO. Several unique dependencies were observed, including threshold voltage (Vth) shifts in the 2D NC-FET (compared to the 2D-FET) that correlate with source/drain overlap capacitance and changes in HZO (ferroelectric) and HfO2 (dielectric) thicknesses. Remarkable sub-60 mV/dec switching was obtained from 2D NC-FETs of various sizes and gate stack thicknesses, demonstrating great potential for enabling size- and voltage-scalable transistors.
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Aligned single-walled carbon nanotubes (SWNTs) synthesized by the chemical vapor deposition (CVD) method have exceptional potential for next-generation nanoelectronics. However, the coexistence of semiconducting (s-) and metallic (m-) SWNTs remains a considerable challenge since the latter causes significant degradation in device performance. Here we demonstrate a facile and effective approach to selectively break all m-SWNTs by stacking two layers of horizontally aligned SWNTs to form crossbars and applying a voltage to the crossed SWNT arrays. The introduction of SWNT junctions amplifies the disparity in resistance between s- and m-pathways, leading to a complete deactivation of m-SWNTs while minimizing the degradation of the semiconducting counterparts. Unlike previous approaches that required an electrostatic gate to achieve selectivity in electrical breakdown, this junction process is gate-free and opens the way for straightforward integration of thin-film s-SWNT devices. Comparison to electrical breakdown in junction-less SWNT devices without gating shows that this junction-based breakdown method yields more than twice the average on-state current retention in the resultant s-SWNT arrays. Systematic studies show that the on/off ratio can reach as high as 1.4 × 10(6) with a correspondingly high retention of on-state current compared to the initial current value before breakdown. Overall, this method provides important insight into transport at SWNT junctions and a simple route for obtaining pure s-SWNT thin film devices for broad applications.
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Among the challenges hindering the integration of carbon nanotube (CNT) transistors in digital technology are the lack of a scalable self-aligned gate and complementary n- and p-type devices. We report CNT transistors with self-aligned gates scaled down to 20 nm in the ideal gate-all-around geometry. Uniformity of the gate wrapping the nanotube channels is confirmed, and the process is shown not to damage the CNTs. Further, both n- and p-type transistors were realized by using the appropriate gate dielectric-HfO2 yielded n-type and Al2O3 yielded p-type-with quantum simulations used to explore the impact of important device parameters on performance. These discoveries not only provide a promising platform for further research into gate-all-around CNT devices but also demonstrate that scalable digital switches with realistic technological potential can be achieved with carbon nanotubes.
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The addition of surface acoustic wave (SAW) technologies to microfluidics has greatly advanced lab-on-a-chip applications due to their unique and powerful attributes, including high-precision manipulation, versatility, integrability, biocompatibility, contactless nature, and rapid actuation. However, the development of SAW microfluidic devices is limited by complex and time-consuming micro/nanofabrication techniques and access to cleanroom facilities for multistep photolithography and vacuum-based processing. To simplify the fabrication of SAW microfluidic devices with customizable dimensions and functions, we utilized the additive manufacturing technique of aerosol jet printing. We successfully fabricated customized SAW microfluidic devices of varying materials, including silver nanowires, graphene, and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). To characterize and compare the acoustic actuation performance of these aerosol jet printed SAW microfluidic devices with their cleanroom-fabricated counterparts, the wave displacements and resonant frequencies of the different fabricated devices were directly measured through scanning laser Doppler vibrometry. Finally, to exhibit the capability of the aerosol jet printed devices for lab-on-a-chip applications, we successfully conducted acoustic streaming and particle concentration experiments. Overall, we demonstrated a novel solution-based, direct-write, single-step, cleanroom-free additive manufacturing technique to rapidly develop SAW microfluidic devices that shows viability for applications in the fields of biology, chemistry, engineering, and medicine.
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Electrical biosensors, including transistor-based devices (i.e., BioFETs), have the potential to offer versatile biomarker detection in a simple, low-cost, scalable, and point-of-care manner. Semiconducting carbon nanotubes (CNTs) are among the most explored nanomaterial candidates for BioFETs due to their high electrical sensitivity and compatibility with diverse fabrication approaches. However, when operating in solutions at biologically relevant ionic strengths, CNT-based BioFETs suffer from debilitating levels of signal drift and charge screening, which are often unaccounted for or sidestepped (but not addressed) by testing in diluted solutions. In this work, we present an ultrasensitive CNT-based BioFET called the D4-TFT, an immunoassay with an electrical readout, which overcomes charge screening and drift-related limitations of BioFETs. In high ionic strength solution (1X PBS), the D4-TFT repeatedly and stably detects subfemtomolar biomarker concentrations in a point-of-care form factor by increasing the sensing distance in solution (Debye length) and mitigating signal drift effects. Debye length screening and biofouling effects are overcome using a poly(ethylene glycol)-like polymer brush interface (POEGMA) above the device into which antibodies are printed. Simultaneous testing of a control device having no antibodies printed over the CNT channel confirms successful detection of the target biomarker via an on-current shift caused by antibody sandwich formation. Drift in the target signal is mitigated by a combination of: (1) maximizing sensitivity by appropriate passivation alongside the polymer brush coating; (2) using a stable electrical testing configuration; and (3) enforcing a rigorous testing methodology that relies on infrequent DC sweeps rather than static or AC measurements. These improvements are realized in a relatively simple device using printed CNTs and antibodies for a low-cost, versatile platform for the ongoing pursuit of point-of-care BioFETs.
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Mycobacterial glycolipids are important cell envelope structures that drive host-pathogen interactions. Arguably, the most important are lipoarabinomannan (LAM) and its precursor, lipomannan (LM), which are trafficked from the bacterium to the host via unknown mechanisms. Arabinomannan is thought to be a capsular derivative of these molecules, lacking a lipid anchor. However, the mechanism by which this material is generated has yet to be elucidated. Here, we describe the identification of a glycoside hydrolase family 76 enzyme that we term LamH (Rv0365c in Mycobacterium tuberculosis) which specifically cleaves α-1,6-mannoside linkages within LM and LAM, driving its export to the capsule releasing its phosphatidyl-myo-inositol mannoside lipid anchor. Unexpectedly, we found that the catalytic activity of this enzyme is important for efficient exit from stationary phase cultures, potentially implicating arabinomannan as a signal for growth phase transition. Finally, we demonstrate that LamH is important for M. tuberculosis survival in macrophages.
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Proteínas de Bactérias , Glicosídeo Hidrolases , Lipopolissacarídeos , Macrófagos , Mananas , Mycobacterium tuberculosis , Mycobacterium tuberculosis/metabolismo , Mycobacterium tuberculosis/crescimento & desenvolvimento , Lipopolissacarídeos/metabolismo , Mananas/metabolismo , Macrófagos/metabolismo , Macrófagos/microbiologia , Glicosídeo Hidrolases/metabolismo , Proteínas de Bactérias/metabolismo , Animais , Camundongos , Humanos , Fosfatidilinositóis/metabolismo , Cápsulas Bacterianas/metabolismoRESUMO
Although carbon nanotube (CNT) transistors have been promoted for years as a replacement for silicon technology, there is limited theoretical work and no experimental reports on how nanotubes will perform at sub-10 nm channel lengths. In this manuscript, we demonstrate the first sub-10 nm CNT transistor, which is shown to outperform the best competing silicon devices with more than four times the diameter-normalized current density (2.41 mA/µm) at a low operating voltage of 0.5 V. The nanotube transistor exhibits an impressively small inverse subthreshold slope of 94 mV/decade-nearly half of the value expected from a previous theoretical study. Numerical simulations show the critical role of the metal-CNT contacts in determining the performance of sub-10 nm channel length transistors, signifying the need for more accurate theoretical modeling of transport between the metal and nanotube. The superior low-voltage performance of the sub-10 nm CNT transistor proves the viability of nanotubes for consideration in future aggressively scaled transistor technologies.
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Nanotubos de Carbono/química , Transistores Eletrônicos , Tamanho da Partícula , Propriedades de SuperfícieRESUMO
Printing technologies offer an attractive means for producing low-cost surface-enhanced Raman spectroscopy (SERS) substrates with high-throughput methods. The development of these substrates is especially important for field-deployable detection of environmental contaminants. Toward this end, we demonstrate SERS-based substrates fabricated through aerosol jet printing of silver nanoparticles and graphene inks on Kapton films. Our printed arrays exhibited measurable intensities for fluorescein and rhodamine dyes down to concentrations of 10-7 M, with the highest SERS intensities obtained for four print passes of Ag nanoparticles. The substrates also exhibited an excellent shelf life, with little reduction in fluorescein intensities after 9 months of shelf storage. We also demonstrated the capability of our substrates to sense perfluoroalkyl substances (PFAS), the so-called forever chemicals that resist degradation due to their strong C-F bonds and persist in the environment. Interestingly, the addition of graphene to the Ag nanoparticles greatly enhanced the SERS intensity of the perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) molecules under basic conditions (pH â¼ 9) compared to that of fluorescein and rhodamine. We were able to successfully detect SERS spectra from nano- and picomolar (â¼0.4 ppt) concentrations of PFOA and PFOS, respectively, demonstrating the viability of deploying our SERS sensors in the environment for the ultrasensitive detection of contaminants.
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2D semiconducting materials have immense potential for future electronics due to their atomically thin nature, which enables better scalability. While the channel scalability of 2D materials has been extensively studied, the current understanding of contact scaling in 2D devices is inconsistent and oversimplified. Here physically scaled contacts and asymmetrical contact measurements (ACMs) are combined to investigate the contact scaling behavior in 2D field-effect transistors. The ACMs directly compare electron injection at different contact lengths while using the exact same MoS2 channel, eliminating channel-to-channel variations. The results show that scaled source contacts can limit the drain current, whereas scaled drain contacts do not. Compared to devices with long contact lengths, devices with short contact lengths (scaled contacts) exhibit larger variations, 15% lower drain currents at high drain-source voltages, and a higher chance of early saturation and negative differential resistance. Quantum transport simulations reveal that the transfer length of Ni-MoS2 contacts can be as short as 5 nm. Furthermore, it is clearly identified that the actual transfer length depends on the quality of the metal-2D interface. The ACMs demonstrated here will enable further understanding of contact scaling behavior at various interfaces.
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Mycobacterial glycolipids are important cell envelope structures that drive host-pathogen interactions. Arguably, the most important amongst these are lipoarabinomannan (LAM) and its precursor, lipomannan (LM), which are both trafficked out of the bacterium to the host via unknown mechanisms. An important class of exported LM/LAM is the capsular derivative of these molecules which is devoid of its lipid anchor. Here, we describe the identification of a glycoside hydrolase family 76 enzyme that we term LamH which specifically cleaves α-1,6-mannoside linkages within LM and LAM, driving its export to the capsule releasing its phosphatidyl-myo-inositol mannoside lipid anchor. Unexpectedly, we found that the catalytic activity of this enzyme is important for efficient exit from stationary phase cultures where arabinomannan acts as a signal for growth phase transition. Finally, we demonstrate that LamH is important for Mycobacterium tuberculosis survival in macrophages. These data provide a new framework for understanding the biological role of LAM in mycobacteria.