Highly sensitive electronic whiskers based on patterned carbon nanotube and silver nanoparticle composite films.

Mammalian whiskers present an important class of tactile sensors that complement the functionalities of skin for detecting wind with high sensitivity and navigation around local obstacles. Here, we report electronic whiskers based on highly tunable composite films of carbon nanotubes and silver nanoparticles that are patterned on high-aspect-ratio elastic fibers. The nanotubes form a conductive network matrix with excellent bendability, and nanoparticle loading enhances the conductivity and endows the composite with high strain sensitivity. The resistivity of the composites is highly sensitive to strain with a pressure sensitivity of up to ∼8%/Pa for the whiskers, which is >10× higher than all previously reported capacitive or resistive pressure sensors. It is notable that the resistivity and sensitivity of the composite films can be readily modulated by a few orders of magnitude by changing the composition ratio of the components, thereby allowing for exploration of whisker sensors with excellent performance. Systems consisting of whisker arrays are fabricated, and as a proof of concept, real-time two- and three-dimensional gas-flow mapping is demonstrated. The ultrahigh sensitivity and ease of fabrication of the demonstrated whiskers may enable a wide range of applications in advanced robotics and human-machine interfacing.

Carbon nanotube electronics--moving forward.

Single-walled carbon nanotubes (SWNTs) possess fascinating electrical properties and offer new entries into a wide range of novel electronic applications that are unattainable with conventional Si-based devices. The field initially focused on the use of individual or parallel arrays of nanotubes as the channel material for ultra-scaled nanoelectronic devices. However, the challenge in the deterministic assembly has proven to be a major technological barrier. In recent years, solution deposition of semiconductor-enriched SWNT networks has been actively explored for high performance and uniform thin-film transistors (TFTs) on mechanically rigid and flexible substrates. This presents a unique niche for nanotube electronics by overcoming their limitations and taking full advantage of their superb chemical and physical properties. This review focuses on the large-area processing and electronic properties of SWNT TFTs. A wide range of applications in conformal integrated circuits, radio-frequency electronics, artificial skin sensors, and displays are discussed--with emphasis on large-area systems where nm-scale accuracy in the assembly of nanotubes is not required. The demonstrations show SWNTs' immense promise as a low-cost and scalable TFT technology for nonconventional electronic systems with excellent device performances.

Carbon nanotube active-matrix backplanes for mechanically flexible visible light and X-ray imagers.

We report visible light and X-ray imagers on lightweight and mechanically flexible plastic substrates. The process involves solution processing of organic photodetectors on top of an active-matrix backplane consisting of carbon nanotube thin-film transistors. The system takes advantage of the high mobility of nanotube transistors for low operating voltages and efficient light absorption of organic bulk-heterojunctions for high imaging sensitivity. With this highly scalable process scheme, 18 × 18 pixel-array flexible imagers (physical size of 2 cm × 1.5 cm) with high performance are successfully demonstrated. In addition, as the absorption peak of the adopted organic photodiodes covers the green band of the light spectrum, X-ray imaging is readily demonstrated by placing a scintillator film on top of the flexible imagers.

Fully printed, high performance carbon nanotube thin-film transistors on flexible substrates.

Fully printed transistors are a key component of ubiquitous flexible electronics. In this work, the advantages of an inverse gravure printing technique and the solution processing of semiconductor-enriched single-walled carbon nanotubes (SWNTs) are combined to fabricate fully printed thin-film transistors on mechanically flexible substrates. The fully printed transistors are configured in a top-gate device geometry and utilize silver metal electrodes and an inorganic/organic high-κ (~17) gate dielectric. The devices exhibit excellent performance for a fully printed process, with mobility and on/off current ratio of up to ~9 cm(2)/(V s) and 10(5), respectively. Extreme bendability is observed, without measurable change in the electrical performance down to a small radius of curvature of 1 mm. Given the high performance of the transistors, our high-throughput printing process serves as an enabling nanomanufacturing scheme for a wide range of large-area electronic applications based on carbon nanotube networks.

Extremely bendable, high-performance integrated circuits using semiconducting carbon nanotube networks for digital, analog, and radio-frequency applications.

Solution-processed thin-films of semiconducting carbon nanotubes as the channel material for flexible electronics simultaneously offers high performance, low cost, and ambient stability, which significantly outruns the organic semiconductor materials. In this work, we report the use of semiconductor-enriched carbon nanotubes for high-performance integrated circuits on mechanically flexible substrates for digital, analog and radio frequency applications. The as-obtained thin-film transistors (TFTs) exhibit highly uniform device performance with on-current and transconductance up to 15 µA/µm and 4 µS/µm. By performing capacitance-voltage measurements, the gate capacitance of the nanotube TFT is precisely extracted and the corresponding peak effective device mobility is evaluated to be around 50 cm(2)V(-1)s(-1). Using such devices, digital logic gates including inverters, NAND, and NOR gates with superior bending stability have been demonstrated. Moreover, radio frequency measurements show that cutoff frequency of 170 MHz can be achieved in devices with a relatively long channel length of 4 µm, which is sufficient for certain wireless communication applications. This proof-of-concept demonstration indicates that our platform can serve as a foundation for scalable, low-cost, high-performance flexible electronics.

High-performance single layered WSe2 p-FETs with chemically doped contacts.

We report high performance p-type field-effect transistors based on single layered (thickness, ∼0.7 nm) WSe(2) as the active channel with chemically doped source/drain contacts and high-κ gate dielectrics. The top-gated monolayer transistors exhibit a high effective hole mobility of ∼250 cm(2)/(V s), perfect subthreshold swing of ∼60 mV/dec, and I(ON)/I(OFF) of >10(6) at room temperature. Special attention is given to lowering the contact resistance for hole injection by using high work function Pd contacts along with degenerate surface doping of the contacts by patterned NO(2) chemisorption on WSe(2). The results here present a promising material system and device architecture for p-type monolayer transistors with excellent characteristics.

Multifunctional, flexible electronic systems based on engineered nanostructured materials.

The development of flexible electronic systems has been extensively researched in recent years, with the goal of expanding the potential scope and market of modern electronic devices in the areas of computation, communications, displays, sensing and energy. Uniquely, the use of soft polymeric substrates enables the incorporation of advanced features beyond mechanical bendability and stretchability. In this paper, we describe several functionalities which can be achieved using engineered nanostructured materials. In particular, reversible binding, self-cleaning, antireflective and shape-reconfigurable properties are introduced for the realization of multifunctional, flexible electronic devices. Examples of flexible systems capable of spatial mapping and/or responding to external stimuli are also presented as a new class of user-interactive devices.

Contact printing of compositionally graded CdS(x)Se(1-x) nanowire parallel arrays for tunable photodetectors.

Spatially composition-graded CdS(x)Se(1-x) (x = 0-1) nanowires are grown and transferred as parallel arrays onto Si/SiO(2) substrates by a one-step, directional contact printing process. Upon subsequent device fabrication, an array of tunable-wavelength photodetectors is demonstrated. From the spectral photoconductivity measurements, the cutoff wavelength for the device array, as determined by the bandgap, is shown to cover a significant portion of the visible spectrum. The ability to transfer a collection of crystalline semiconductor nanowires while preserving the spatially graded composition may enable a wide range of applications, such as tunable lasers and photodetectors, efficient photovoltaics, and multiplexed chemical sensors.

Carbon nanotube active-matrix backplanes for conformal electronics and sensors.

In this paper, we report a promising approach for fabricating large-scale flexible and stretchable electronics using a semiconductor-enriched carbon nanotube solution. Uniform semiconducting nanotube networks with superb electrical properties (mobility of ∼20 cm2 V(-1) s(-1) and ION/IOFF of ∼10(4)) are obtained on polyimide substrates. The substrate is made stretchable by laser cutting a honeycomb mesh structure, which combined with nanotube-network transistors enables highly robust conformal electronic devices with minimal device-to-device stochastic variations. The utility of this device concept is demonstrated by fabricating an active-matrix backplane (12×8 pixels, physical size of 6×4 cm2) for pressure mapping using a pressure sensitive rubber as the sensor element.

Nanowire active-matrix circuitry for low-voltage macroscale artificial skin.

Large-scale integration of high-performance electronic components on mechanically flexible substrates may enable new applications in electronics, sensing and energy. Over the past several years, tremendous progress in the printing and transfer of single-crystalline, inorganic micro- and nanostructures on plastic substrates has been achieved through various process schemes. For instance, contact printing of parallel arrays of semiconductor nanowires (NWs) has been explored as a versatile route to enable fabrication of high-performance, bendable transistors and sensors. However, truly macroscale integration of ordered NW circuitry has not yet been demonstrated, with the largest-scale active systems being of the order of 1 cm(2) (refs 11,15). This limitation is in part due to assembly- and processing-related obstacles, although larger-scale integration has been demonstrated for randomly oriented NWs (ref. 16). Driven by this challenge, here we demonstrate macroscale (7×7 cm(2)) integration of parallel NW arrays as the active-matrix backplane of a flexible pressure-sensor array (18×19 pixels). The integrated sensor array effectively functions as an artificial electronic skin, capable of monitoring applied pressure profiles with high spatial resolution. The active-matrix circuitry operates at a low operating voltage of less than 5 V and exhibits superb mechanical robustness and reliability, without performance degradation on bending to small radii of curvature (2.5 mm) for over 2,000 bending cycles. This work presents the largest integration of ordered NW-array active components, and demonstrates a model platform for future integration of nanomaterials for practical applications.

Three-dimensional nanopillar-array photovoltaics on low-cost and flexible substrates.

Solar energy represents one of the most abundant and yet least harvested sources of renewable energy. In recent years, tremendous progress has been made in developing photovoltaics that can be potentially mass deployed. Of particular interest to cost-effective solar cells is to use novel device structures and materials processing for enabling acceptable efficiencies. In this regard, here, we report the direct growth of highly regular, single-crystalline nanopillar arrays of optically active semiconductors on aluminium substrates that are then configured as solar-cell modules. As an example, we demonstrate a photovoltaic structure that incorporates three-dimensional, single-crystalline n-CdS nanopillars, embedded in polycrystalline thin films of p-CdTe, to enable high absorption of light and efficient collection of the carriers. Through experiments and modelling, we demonstrate the potency of this approach for enabling highly versatile solar modules on both rigid and flexible substrates with enhanced carrier collection efficiency arising from the geometric configuration of the nanopillars.

Monolayer resist for patterned contact printing of aligned nanowire arrays.

Large-area, patterned printing of nanowires by using fluorinated self-assembled monolayers as the resist layer is demonstrated. By projecting a light pattern on the surface of the monolayer resist in an oxygen-rich environment, sticky and nonsticky regions on the surface are directly defined in a single-step process which then enables the highly specific and patterned transfer of the nanowires by the contact printing process, without the need for a subsequent lift-off step. This work demonstrates a simple route toward scalable, patterned printing of nanowires on substrates by utilizing light-tunable, nanoscale chemical interactions and demonstrates the versatility of molecular monolayers for use as a resist layer.

[Multicenter comparative study of the recurrence-inhibitory effect of oral fluoropyrimidine drugs in patients with colorectal cancer following curative resection].

HCFU and UFT were reported effective in adjuvant chemotherapy for colorectal cancer. This investigation was planned as a randomized study to compare the usefulness of combination therapies with mitomycin C (MMC)+HCFU and MMC+UFT as postoperative adjuvant chemotherapy in patients with colorectal cancer following curative resection, in terms of survival rate, recurrence rate, and adverse drug reactions. A total of 501 patients consisting of 252 patients with stage III/IV colon cancer (Colorectal Cancer Handling Rules, 4th Ed.) for which macroscopic curative resection was possible and 249 patients with stage II/III/IV rectal cancer (ibid, 4th Ed.) were registered from 40 participating institutions. The patients were randomly allocated to two groups with colon cancer and rectal cancer employed as stratification factors. Beginning on Day 14 after surgery, HCFU at 300 mg/day was administered to one group and UFT at 300 mg/day or 400 mg/day to another group, both orally and daily for one year. MMC 6 mg/m2 was administered intravenously to both groups on the day of surgery and the day following. Among the 501 patients, 496 patients (99%) were eligible. The 5-year survival rates were 77.1% for the MMC+ HCFU group and 79.2% for the MMC+UFT group, with the 5-year recurrence-free survival rates were 76.1% and 72.9%, respectively, neither showing a significant difference between the groups. Adverse drug reactions appeared in 23% of patients in the MMC+HCFU group and in 19% in the MMC+UFT group, with no serious reactions. One year after surgery the administration completion rates were good, at 82% for the MMC+HCFU group and 83% for the MMC+UFT group. No clear difference in effectiveness was noted between MMC+HCFU therapy and MMC+UFT therapy as postoperative adjuvant chemotherapy for colorectal cancer. The administration completion rates were good, and no serious adverse drug reactions were observed for either therapy. It was thus considered that both therapies could be administered safely, and both were useful as postoperative adjuvant chemotherapies for colorectal cancer. It is considered necessary to compare them with standard therapies in Western countries in the future.

Nanoscale semiconductor "X" on substrate "Y"--processes, devices, and applications.

Recent advancements in the integration of nanoscale, single-crystalline semiconductor 'X' on substrate 'Y' (XoY) for use in transistor and sensor applications are presented. XoY is a generic materials framework for enabling the fabrication of various novel devices, without the constraints of the original growth substrates. Two specific XoY process schemes, along with their associated materials, device and applications are presented. In one example, the layer transfer of ultrathin III-V semiconductors with thicknesses of just a few nanometers on Si substrates is explored for use as energy-efficient electronics, with the fabricated devices exhibiting excellent electrical properties. In the second example, contact printing of nanowire-arrays on thin, bendable substrates for use as artificial electronic-skin is presented. Here, the devices are capable of conformably covering any surface, and providing a real-time, two-dimensional mapping of external stimuli for the realization of smart functional surfaces. This work is an example of the emerging field of "translational nanotechnology" as it bridges basic science of nanomaterials with practical applications.

Parallel array InAs nanowire transistors for mechanically bendable, ultrahigh frequency electronics.

The radio frequency response of InAs nanowire array transistors on mechanically flexible substrates is characterized. For the first time, GHz device operation of nanowire arrays is demonstrated, despite the relatively long channel lengths of ∼1.5 µm used in this work. Specifically, the transistors exhibit an impressive maximum frequency of oscillation, f(max) ∼ 1.8 GHz, and a cutoff frequency, f(t) ∼ 1 GHz. The high-frequency response of the devices is due to the high saturation velocity of electrons in high-mobility InAs nanowires. The work presents a new platform for flexible, ultrahigh frequency devices with potential applications in high-performance digital and analog circuitry.