Search

Strong-field photoemission produces attosecond (10−18 s) electron pulses that are synchronized to the waveform of the incident light. This nonlinear photoemission lies at the heart of current attosecond technologies. Here we report a new nonlinear photoemission behaviour—the nonlinearity in strong-field regime sharply increases (approaching 40th power-law scaling), making use of sub-nanometric carbon nanotubes and 800 nm pulses. As a result, the carrier-envelope phase sensitive photoemission current shows a greatly improved modulation depth of up to 100% (with a total modulation current up to 2 nA). The calculations reveal that the behaviour is an interplay of valence band optical-field emission with charge interaction, and the nonlinear dynamics can be tunable by changing the bandgap of carbon nanotubes. The extreme nonlinear photoemission offers a new means of producing extreme temporal-spatial resolved electron pulses, and provides a new design philosophy for attosecond electronics and photonics. Strong-field photoemission is the emission of electrons driven by a strong electric field of light. Here the authors demonstrate a highly non-linear strong-field photoemission, approaching the 40th power-law scaling, from carbon nanotubes, yielding a photoemission current with up to 100% carrier-envelope phase modulation depth. [ABSTRACT FROM AUTHOR]

The nanocone-shaped carbon nanotubes field-emitter array (NCNA) is a near-ideal field-emitter array that combines the advantages of geometry and material. In contrast to previous methods of field-emitter array, laser ablation is a low-cost and clean method that does not require any photolithography or wet chemistry. However, nanocone shapes are hard to achieve through laser ablation due to the micrometer-scale focusing spot. Here, we develop an ultraviolet (UV) laser beam patterning technique that is capable of reliably realizing NCNA with a cone-tip radius of ≈300 nm, utilizing optimized beam focusing and unique carbon nanotube–light interaction properties. The patterned array provided smaller turn-on fields (reduced from 2.6 to 1.6 V/μm) in emitters and supported a higher (increased from 10 to 140 mA/cm2) and more stable emission than their unpatterned counterparts. The present technique may be widely applied in the fabrication of high-performance CNTs field-emitter arrays. [ABSTRACT FROM AUTHOR]

A hybrid liquid crystal and carbon nanotube‐based device which shows the capacity to perform as a switchable diffraction grating is demonstrated. A liquid crystal layer was sandwiched between two electrodes (patterned into gratings). The bottom electrode consists of a two dimensional square array of carbon nanotubes, while the top electrode comprises an ITO‐based in‐plane switching electrode on glass. The carbon nanotubes, due to their high aspect ratios, produce defects within the liquid crystal layer, producing a two dimensional grating. The device displays distinct voltage‐dependent diffraction patterns due to the two different electrodes. The diffraction patterns are studied both computationally and experimentally, with good agreement between the results obtained. Both the diffraction pattern and efficiency from the device could be switched by varying the applied voltage across the liquid crystal layer. [ABSTRACT FROM AUTHOR]

Abstract: We report a novel utilization of periodic arrays of carbon nanotubes in the realization of diffractive photonic crystal lenses. Carbon nanotube arrays with nanoscale dimensions (lattice constant 400nm and tube radius 50nm) displayed a negative refractive index in the optical regime where the wavelength is of the order of array spacing. A detailed computational analysis of band gaps and optical transmission through the nanotubes based planar, convex and concave shaped lenses was performed. Due to the negative-index these lenses behaved in an opposite fashion compared to their conventional counter parts. A plano-concave lens was established and numerically tested, displaying ultra-small focal length of 1.5μm (∼2.3λ) and a near diffraction-limited spot size of 400nm (∼0.61λ). [Copyright &y& Elsevier]

In this manuscript, we demonstrate metamaterials based on two-dimensional high density arrays of metallic multiwalled carbon nanotubes. They demonstrate a cutoff response toward electromagnetic waves and can be utilized for filtering applications. The plasma frequency, where the metamaterial displayed a sharp change in the reflection and transmission, depends on the geometry of their two-dimensional cubic lattice. A plasma frequency in the near infrared region of 1.5 μm was calculated numerically, for an array consisting of multiwalled nanotubes, having radius of 50 nm and lattice constant of 400 nm. Reflection experiments conducted on the nanoscale structures were in excellent agreement with numerical calculations. [ABSTRACT FROM AUTHOR]

We present a switchable liquid crystal cylindrical lens array fabricated with a combination of a sparse electrode array of multiwall carbon nanotubes (MWCNTs) grown upon a silicon substrate, and a second glass substrate featuring an in-plane switching (IPS) electrode structure. A cylindrical shape of an electric field profile was produced between the MWCNT substrate and the IPS substrate. This cylindrical shape was controlled by the application of an external electric field. The average focal lengths at different voltages were calculated. This adaptive lenticular lens array can be used in autostereoscopic displays. [ABSTRACT FROM AUTHOR]

A photodiode consistingof nanopillars of thin-film silicon p-i-non an array of vertically aligned carbon nanotubes (CNTs) with a noncontinuouscathode electrode is demonstrated. The structure exploits the intrinsicenhancement of the CNTs’ electric field, which leads to reductionin the photodiode’s operating voltage and response time andenhancement of optical coupling due to better light trapping, as comparedwith the conventional planar photodiode. These improvements translateto higher resolution and higher frame rate flat-panel imaging systemsfor a broad range of applications, including computed tomography andparticle detection. [ABSTRACT FROM AUTHOR]

Electron emission from well-aligned, few-walled carbon nanotube arrays was triggered by a low power (<110 mW), continuous-wave, 650 nm light. Significant electron emission was obtained at low bias voltage. Photo-thermionic emission was found to be the mechanism of emission since the local temperature was measured to be higher than 2000 K, and the emission was consistent with the Richardson Law. A high thermionic emission current of ∼300 μA was obtained under a low electric field of 0.45 V/μm. The space-charge-limited emission was observed during the current–voltage testing, which obeyed the Child Law. Under high bias voltage, thermal-assisted field emission was also observed. The emission exhibited high stability (<5%), fast response (<1.8 ms), and low emittance (∼2°). [ABSTRACT FROM AUTHOR]

Field emission (FE) electron sources based on carbon nanotubes (CNTs) have the potential to serve as cold cathodes for various vacuum microelectronic and nanoelectronic devices. Emission currents are extremely sensitive to variation in emitter geometry and local surface states, both of which are difficult to synthesize uniformly when fabricating a CNT field emission array (FEA). Such non-uniformities cause unstable emission, limiting the current output. Here, we propose a method for simulating and fabricating a high performance CNT-FEA with emission units that are individually connected to a single crystalline silicon pillar (SP), which acts as an non-linear ballast resistor. Results showed that the driving field for this CNT-FEA was greatly reduced relative to CNT-FEAs on a flat silicon substrate. This improvement was due to the high aspect ratio of the CNT clusters combined with SPs. The FE behavior demonstrated that the emission current was limited by the non-linear resistors (NLRs). Emitted currents density over 1.65 A/cm 2 at a low extraction field of 5.8 V/μm were produced by a 1 mm 2 emmiting area. The proposed technology may be used to fabricate cathodes capable of reliable, uniform, and high current emission. [ABSTRACT FROM AUTHOR]