Tunable device properties of free-standing inorganic/organic flexible hybrid structures obtained by exfoliation

We report the fabrication of free-standing flexible inorganic/organic hybrid structures by exfoliating ZnO nanostructured films from the flat indium tin oxide (ITO)/silicon/sapphire substrates using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). Strong interaction between ZnO and PEDOT: PSS and the thermomechanical response of PEDOT: PSS are the key issues for the exfoliation to prevail. The performance of the free-standing hybrid structures as rectifiers and photodetectors is better as compared to ITO supported hybrid structures. It is also shown that device properties of hybrid structures can be tuned by using different electrode materials. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4729550]

Dielectric tunability in (1-x)[Pb(Mg 1/3Nb 2/3)O 3]-xPbTiO 3 ceramics for tunable devices application

The dielectric properties of the 0.65[Pb(Mg 1/3Nb 2/3)O 3]-0.35PbTiO 3 ferroelectric ceramic composition were investigated viewing the capability to be used for tunable microwave applications. The dielectric response has been studied for three selected temperatures (300 K, 370 K and 400 K), below the paraelectric- ferroelectric phase transition temperature, as a function of the applied 'bias' electric field. The obtained dielectric tunability was found to be around 60 %, under an electric field of 19 kV/cm, which makes the studied ceramic composition an excellent candidate for application in the electro-electronic industry, as tunable devices. © 2010 IEEE.

Efficient Gate-tunable light-emitting device made of defective boron nitride nanotubes: from ultraviolet to the visible

Boron nitride is a promising material for nanotechnology applications due to its two-dimensional graphene-like, insulating, and highly-resistant structure. Recently it has received a lot of attention as a substrate to grow and isolate graphene as well as for its intrinsic UV lasing response. Similar to carbon, one-dimensional boron nitride nanotubes (BNNTs) have been theoretically predicted and later synthesised. Here we use first principles simulations to unambiguously demonstrate that i) BN nanotubes inherit the highly efficient UV luminescence of hexagonal BN; ii) the application of an external perpendicular field closes the electronic gap keeping the UV lasing with lower yield; iii) defects in BNNTS are responsible for tunable light emission from the UV to the visible controlled by a transverse electric field (TEF). Our present findings pave the road towards optoelectronic applications of BN-nanotube-based devices that are simple to implement because they do not require any special doping or complex growth

2D tunable graded index prism beam steering device based on nematic liquid crystals

Liquid crystal devices are being used in many non-display applications in order to construct small devices controlled by low voltage electronics without mechanical components. In this work, we present a novel liquid crystal device for laser beam steering. In this device the orientation of the liquid crystal molecules can be controlled. A change in the liquid crystal orientation results in a change of the refractive index. When a laser beam passes through the device, the beam will be deviated (Fig.1) and the device works a prism. The main difference between this device and a prism is that in the device the orientation profile of the liquid crystal molecules can be modified so that the laser beam can be deviated a required angle: the device is tuneable.

Wedged analog tunable beam steering device based on cholesteric liquid crystals

In this work we propose a novel cholesteric liquid crystal beam steering device based on the Kerr effect. The first version of the device consists of two ITO coated glass plates, with intentionally prepared electrodes, assembled together with a thickness gradient between both sides of the device. One side of the cell has two substrates at direct contact; the other side has separated substrates to form the wedge. The cell was filled with a cholesteric liquid crystal. The liquid crystal material is an innovative mixture called 1892E with extremely low viscosity doped with a ZLI chiral nematogen. The proposed beam steering device based on cholesteric liquid crystals has great potential for many photonic applications. Results describing the performance of the device and the properties of the selected liquid crystals are presented.

Tunable “Nano-Shearing” : A physical mechanism to displace nonspecific cell adhesion during rare cell detection

We report a tunable alternating current electrohydrodynamic (ac-EHD) force which drives lateran fluid motion within a few nanometers of an electrode surface. Because the magnitude of this fluid shear force can be tuned externally (e.g., via the application of an ac electric field), it provides a new capability to physically displace weakly (nonspecifically) bound cellular analytes. To demonstrate the utility of the tunable nanoshearing phenomenon, we present data on purpose-built microfluidic devices that employ ac-EHD force to remove nonspecific adsorption of molecular and cellular species. Here, we show that an ac-EHD device containing asymmetric planar and microtip electrode pairs resulted in a 4-fold reduction in nonspecific adsorption of blood cells and also captured breast cancer cells in blood, with high efficiency (approximately 87%) and specificity. We therefore feel that this new capability of externally tuning and manipulating fluid flow could have wide applications as an innovative approach to enhance the specific capture of rare cells such as cancer cells in blood.

Band gap tunable N-type molecules for organic field effect transistors

A series of four novel n-type molecules has been synthesized. Unlike previous approaches, the end group of these molecules was fixed and the molecular core was varied. The resulting materials were thoroughly analyzed. Electronic properties were derived from photoemission spectroscopy, optical properties were derived with the help of optical spectroscopy, and the structure of thin films on Au(111) was derived by scanning tunneling microscopy (STM). In addition, prototypical organic field-effect transistors (OFETs) (forming n-channels in OFETs) have been fabricated and tested. The correlation between the device performance of the respective OFETs (i.e., electron mobility) and their electronic as well as structural properties was investigated. It turned out that a combination of beneficial electronic and structural properties provides the best results. These findings are important for the design of new materials for future device applications.

Thermoelectric properties of electrostatically tunable antidot lattices

We report on the fabrication and characterization of a device which allows the formation of an antidot lattice (ADL) using only electrostatic gating. The antidot potential and Fermi energy of the system can be tuned independently. Well defined commensurability features in magnetoresistance as well as magnetothermopower are observed. We show that the thermopower can be used to efficiently map out the potential landscape of the ADL. (C) 2010 American Institute of Physics. doi: 10.1063/1.3493268]

Multilayer Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 thin films for tunable microwave applications

Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5-2nm and grain size of 100-150 nm. Total film thickness has been measure to be 375 nm. The BZN thin films at 300 K, on Pt(1 1 1)/SiO2/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1 MHz. Thin films annealed at 700 degrees C shows the dielectric tunability of 18% with biasing field 500 kV/cm at 0.1 MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications. (C) 2010 Elsevier B.V. All rights reserved.

Mechanically tunable conjugated polymer distributed feedback lasers

Herein we report a low-threshold organic laser device based on semiconducting poly(9, 9′ -dioctylfluoren-2,7-diyl-alt-benzothiadiazole) (F8BT) encapsulated in a mechanically stretchable polydimethylsiloxane (PDMS) matrix. We take advantage of the natural flexibility of PDMS to alter the periodicity of the distributed feedback grating which in turn tunes the gain wavelength at which the resonant feedback is obtained. This way, we demonstrate that low-threshold lasing [6.1 μJ cm-2 (5.3 nJ)] is maintained over a large stretching range of 0%-7% which translates into a tuning range of about 20 nm. © 2010 American Institute of Physics.

Generation of 1.5-12 ns width-tunable 532 nm pulses by adopting laser-induced plasma shutter technique

The pulse-shaping technique has found widespread applications in nonlinear optics and material processing. Experimental research on laser-induced plasma shutter to control the 532 nm pulse width is conducted. The impacts of the total pulse output energy on pulse compression are investigated, and a useful conclusion can be drawn that there exists an optimal value of pulse energy at which the shortest output pulse of 3.23 ns can be obtained without a device for delay-time. Once the device for delay-time is employed to change the optical differences between two laser paths, the pulse width can be further shortened to 1.51 ns. In short, the 1.5-12 ns width-tunable 532 nm laser pulses have been obtained by adopting the laser-induced plasma shutter technique. (C) 2007 Elsevier GmbH. All rights reserved.

Tunable electronic transport characteristics of surface-architecture-controlled ZnO nanowire field effect transistors.

Surface-architecture-controlled ZnO nanowires were grown using a vapor transport method on various ZnO buffer film coated c-plane sapphire substrates with or without Au catalysts. The ZnO nanowires that were grown showed two different types of geometric properties: corrugated ZnO nanowires having a relatively smaller diameter and a strong deep-level emission photoluminescence (PL) peak and smooth ZnO nanowires having a relatively larger diameter and a weak deep-level emission PL peak. The surface morphology and size-dependent tunable electronic transport properties of the ZnO nanowires were characterized using a nanowire field effect transistor (FET) device structure. The FETs made from smooth ZnO nanowires with a larger diameter exhibited negative threshold voltages, indicating n-channel depletion-mode behavior, whereas those made from corrugated ZnO nanowires with a smaller diameter had positive threshold voltages, indicating n-channel enhancement-mode behavior.

Voltage programmable dual-band bandpass/bandstop filter response in a single micro-electro-mechanical device

This paper reports on a switchable multi-band filter response achieved within a single micro-electro-mechanical device. A prototype device fabricated in a SOI process demonstrates a voltage programmable and tunable, dual-band, band-pass/band-stop response. Both analytical and finite element models are introduced in this paper to elucidate the operating principle of the filter and to guide filter design. Voltage programmability of the filter characteristic is demonstrated with the ability to independently tune the centre frequency and bandwidth for each band. A representative measurement shows that the minimum 3 dB-bandwidth (BW) is 155 Hz, 140Hz, and 20 dB-BW is 216 Hz, 203Hz for the upper-band and lower-band center frequencies located at 131.5 kHz and 130.7 kHz, respectively. © 2011 IEEE.

Variable repetition rate monolithically integrated mode-locked-laser- modulator-MOPA device

A monolithically integrated MLLD-modulator-MOPA is presented generating 12.5 ps pulses. The Mach-Zehnder modulator allows tunable repetition rates from 14 GHz to 109 MHz, and the MOPA boosts the peak power by 3.2 dB. © 2012 IEEE.