Random lasing from dye doped polymer within biological source scatters: The pomponia imperatorial cicada wing random nanostructures

Photonic structures found in biological organisms are often startling in their complexity and surprising in their optical function. In this paper we explore whether biologically derived nanostructures can be utilized to form the resonator structures of organic dye doped polymer lasers. Surprisingly, we find that the random nanostructures on the wing of the pomponia imperatoria cicada can support coherent random lasing when covered with a layer of dye doped polymer film. Due to the scattering role of cicada wing nanostructures, the device emits a resonant multimode peak centered at a wavelength of 605 nm with a mode linewidth of <0.55 nm and exhibits a threshold excitation intensity as low as 70.4 mW/cm². Our results indicate that abundant, naturally occurring biological nanostructures can provide effective platforms for the study of random lasing, and that the laser properties may provide insight into the degree of disorder exhibited by these natural structures.     

Fabrication of antireflection nanostructures by hybrid nano-patterning lithography

Antireflection (AR) nanostructures are fabricated on a glass substrate using hybrid nano-patterning lithography (H-NPL) consisting of nanosphere lithography (NSL) and UV-nanoimprint lithography (UV-NIL). The shape and diameter of the AR nanostructures were controlled by fabricating Si masters with different RIE conditions. The shapes of the AR nanostructures were a pillar-type and a corn-type. The diameters of the AR nanostructures were about 350 and 250 nm, respectively. AR nanostructures were successfully nanoimprinted on glass in accordance with Si master prepared by NSL. The pillar-type AR nanostructure with diameter of 350 nm exhibited the transmittance of over 98% in the wavelength range from 1100 to 2200 nm. From the results, the fabricated AR nanostructures demonstrate the possibility to improve the efficiency of optoelectronic devices such as a photo-detector and an IR-LED.     

自组装法制备团簇Ag纳米结构衬底及其SERS

采用自组装方法,在3-Aminopropyltrimethoxy silane(APS)分子修饰后的玻璃衬底表面,获得了二维Ag纳 米结构衬底。在波长为532nm激光激发下,研究了沉积在衬底表面的 Rhodamine 6G(Rh6G)分子的拉曼光谱特性。结 果表明,制备的二维Ag纳米结构衬底具有强的拉曼增强特性,增强因子可以达到 10⁷ 倍。这说明,在外光场作用下,制备的Ag纳米结构衬底表面能够形成的强局部电磁场分布, 可以有效提升探针分子的光谱辐射效率,从而获得高增强拉曼散射。     

Metallic nanogaps with access windows for liquid based systems

A new method has been established for the reproducible fabrication of high quality, metallic nanogaps on silicon chips suitable for liquid based nanometer scale devices. Realization of μm structures connected to nanogaps with gap sizes down to 30 nm has been achieved by a combination of an optical and an electron-beam (e-beam) lithography step using an optimised adhesion layer/metallic layer combination (Ti/Pt/Au—three layer combination) and an adopted two layer e-beam resist. The quality of the interconnects between optically and e-beam lithographically defined structures and the surface roughness of the gold nanogaps have been improved by a controlled temperature treatment. With this method the production of a variety of different gap shapes could be demonstrated. Specifically the lithographic structures have been successfully covered by a protection layer, except of a 200 nm×400 nm size access window located on top of the nanogaps, making it suitable for applications in liquid environment such as molecular and/or electrochemical metal deposition.     

Bimorph nano actuators synthesized by focused ion beam chemical vapor deposition

Bimorph nano actuators synthesized by a two-layer focused ion beam (FIB) chemical vapor deposition (CVD) process have been demonstrated. The core bimorph segment of the actuator is a column structure made of two 200-nm thick tungsten-based-conductor (TBC) and diamond-like-carbon (DLC) layers. Several segments can be connected together of different angles to construct actuators with various moving capabilities when joule heating is applied via silicon MEMS (Microelectromechanical System) heater as the actuation source. Experimentally, a prototype five-segment actuator has shown projection displacement of 600 ± 60 nm under an input power of 1.02 W (160 mA and 6.41 V). The actuator has been repeatedly operated for over 100 times without any indication of degradation. As such, this work represents a new class of nano actuators based on versatile and flexible FIB-CVD bimorph nanostructures.     

Metal direct nanoimprinting for photonics

In this paper metal direct nanoimprinting (embossing) for the production of metallic microparts is discussed, with a main focus on its suitability for the fabrication of metal-containing optical devices such as photonic crystals, plasmon waveguides or chiral structures. Silver and gold were chosen, since they have the lowest light absorption in the near infrared and visible range. They are also easily formable due to their good ductility, which can be further enhanced by processing at elevated temperature. The mold material, which may form part of the optical device, usually consisted of silicon, but other dielectric materials such as silicon oxide and silicon nitride were also successfully tested.Cylindrical and line-shaped holes with lateral dimensions down to 250 nm and aspect ratios of up to 5 were etched in silicon wafers. All the structures were successfully filled with silver and gold, and the filling of smaller dimensions is also deemed possible. This technique is therefore suitable for producing metal-containing optical devices working in the infrared, at least down to the standard telecom wavelength of 1.5 μm, which requires metallic dimensions of 200-300 nm.     

Gas sensing of colloidal polyaniline in a chemoresistor consisting of nanometer electrodes

The high conductivity of colloid-conducting polymers is explained by the networking structures and the hopping mechanisms of the metallic particles [1], [2] and [4]. To observe how the metallic region and the networking structures differ in sensing NH₃ gas, E-beam lithography and electromigration were used to make chemoresistors with nanometer-gap electrodes. Colloid Pani was coated on a nanometer gap as a reaction matrix for the gas. The I-V curves were measured in a vacuum and the NH₃ gas was nonlinear. In sensors with a gap of less than 10 nm, there was a two- or threefold increase in the conductivity, and the work function decreased from 600 meV in a vacuum to 250 meV in NH₃ gas. In contrast, the conductivity of sensors with gaps of 200 and 500 nm decreased to 1/1000 in the NH₃ gas environment. The decrease of the conductivity can be explained by electron-hole annihilation, which appears to occur on the surface of the secondary particles. With comb-type electrodes, the operating voltage can be decreased by three orders of magnitude. In electrodes with 200 and 500 nm gaps, the I-V has a step-type response to NH₃ gas.     

Electrical properties of Pt interconnects for passive crossbar memory arrays

We report on the fabrication and the electrical characterization of platinum interconnects for novel non-volatile memory technologies. These nanowires present an important and essential contribution to the deep nanometer scaling of alternative architectures beyond CMOS, e.g. nanocrossbar arrays with resistance switching junctions. The nanowires, which have a thickness of 25 nm and a width ranging from 200 nm down to 40 nm, were patterned using electron beam direct writing. They were deposited by UHV electron beam evaporation in combination with a lift-off process.The electrical characteristic is increasingly affected by the contribution of surface effects like scattering at grain boundaries and scattering at the surfaces as the wire dimensions become smaller. With decreasing width of the platinum wire an increasing resistivity was observed, which is consistent with the theories of Fuchs-Sondheimer and Mayadas-Shatzkes. Our studies have shown that the investigated structures possess a high stability concerning the operational current densities up to 4 × 10⁷ A/cm², and an additional annealing step results in an improvement of the electrical wire properties, which is explained by a higher quality of the grain boundaries and side walls.     

纳米结构分子吸附引起的表面增强拉曼散射研究

利用模板印刷技术,制备了具有不同局域表面等离子体共振(LSPR)峰的Au纳米空心半球壳结构,并以4-巯基苯胺(4-ATP)为探针分子研究了纳米结构表面吸附分子对表面增强拉曼散射(SERS)强度的影响。结果表明,当纳米结构的LSPR峰位处于激发光波长的短波长或"马鞍型"位置时,SERS强度随吸附分子数的增加而增大;当处于长波长位置时,SERS强度呈现先增大后减小的趋势。利用分子吸附理论和纳米结构表面局域场强度变化,对此现象进行了解释。     

Design and optimisation of a high-temperature silicon micro-hotplate for nanoporous palladium pellistors

The conventional design of the heater in a silicon micro-hotplate employ a simple meandering resistive track to form a square element. We show that this heater structure produces an uneven thermal profile characterised by a central hot spot with a significant variation in temperature of some 50 °C across the plate at an average temperature of 500 °C. Four novel micro-heater designs are reported here and fabricated on hotplates with an active area that ranges from (200×200) μm² to (570×570) μm² in order to vary systematically the ratio of membrane to heater length from a value of 5.0-2.7, respectively. All the designs have been simulated using a 3D electro-thermo-mechanical finite element model and results agree well with thermal profiles taken using an infrared microscope. One of the designs, referred to here as ‘drive-wheel’ structure, performs best and reduces the lateral variation in temperature to only ±10 °C. The different resistive micro-heaters have been calibrated with the lowest power consumption being 50 mW at 500 °C, which is well below the power consumption of any commercial pellistor; the maximum temperature before rupture being 870 °C. The micro-hotplates were electrochemically coated with a 20 nm thick mesoporous palladium catalyst and the pellistors' response tested to 2.5% methane in air. The micro-heaters were observed to be stable for a period of 1000 h and should provide a good platform for exploitation in commercial catalytic pellistors.     

Large area silicon epitaxy using pulsed DC magnetron sputtering deposition

Pulsed DC magnetron sputtering is used for the deposition of large area crystalline (200 mm) silicon 100 nm thin films. p doped Si substrates are flashed (T_s = 900 °C) under high vacuum (5 × 10⁻⁶ Pa) for removing native oxide and restoring surface crystallinity. Subsequent boron-doped Si homoepitaxy is obtained at substrate temperature below 500 °C for pulse frequency of 150 kHz.     

Anomalous thermal oxidation of gadolinium thin films deposited on silicon by high pressure sputtering

Thin gadolinium metallic layers were deposited by high-pressure sputtering in pure Ar atmosphere. Subsequently, in situ thermal oxidation was performed at temperatures ranging from 150 to 750 °C. At an oxidation temperature of 500 °C the films show a transition from monoclinic structure to a mixture of monoclinic and cubic. Regrowth of interfacial SiO_x is observed as temperature is increased, up to 1.6 nm for 750 °C. This temperature yields the lowest interface trap density, 4 × 10¹⁰ eV⁻¹ cm⁻², but the effective permittivity of the resulting dielectric is only 7.4. The reason of this low value is found on the oxidation mechanism, which yields a surface with located bumps. These bumps increase the average thickness, thus reducing the capacitance and therefore the calculated permittivity.     

A CMOS fast transient response low-dropout regulator with a compact NMOS output driver

We present a CMOS low-dropout voltage regulator with a high-speed NMOS compact driver suitable for supplying on-chip voltages for the digital core of a SoC. The LDO is part of a power management controller hardblock integrated within a microcontroller. The die area of the circuit implemented in a 90 nm CMOS process is only 0.054 mm². Experimental results show that the developed LDO can supply up to 15 mA and it presents a very fast transient response, with a settling time of approximately 30 ns and a voltage drop of 200 mV when the load current changes from 100 nA to 9 mA.     

Large‐Area Fabrication of Periodic Arrays of Nanoholes in Metal Films and Their Application in Biosensing and Plasmonic‐Enhanced Photovoltaics

Plasmonics is a fast developing research area with a great potential for practical applications. However, the implementation of plasmonic devices requires low cost methodologies for the fabrication of organized metallic nanostructures that covers a relative large area (～1 cm²). Here the patterning of periodic arrays of nanoholes (PANHs) in gold films by using a combination of interference lithography, metal deposition, and lift off is reported. The setup allows the fabrication of periodic nanostructures with hole diameters ranging from 110 to 1000 nm, for 450 and 1800 nm of periodicity, respectively. The large areas plasmonic substrates consist of 2 cm × 2 cm gold films homogeneously covered by nanoholes and gold films patterned with a regular microarray of 200 μm diameter circular patches of PANHs. The microarray format is used for surface plasmon resonance (SPR) imaging and its potential for applications in multiplex biosensing is demonstrated. The gold films homogeneously covered by nanoholes are useful as electrodes in a thin layer organic photovoltaic. This is first example of a large area plasmonic solar cell with organized nanostructures. The fabrication approach reported here is a good candidate for the industrial‐scale production of metallic substrates for plasmonic applications in photovoltaics and biosensing.     

Downscaling of n-channel organic field-effect transistors with inkjet-printed electrodes

In this contribution we demonstrate for the first time a downscaled n-channel organic field-effect transistors based on N,N′-dialkylsubstituted-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) with inkjet printed electrodes. First we demonstrate that the use of a high boiling point solvent is critical to achieve extended crystalline domains in spin-coated thin films and thus high electron mobility >0.1 cm² V⁻¹ s⁻¹ in top-gate devices. Then inkjet-printing is employed to realize sub-micrometer scale channels by dewetting of silver nanoparticles off a first patterned gold contact. By employing a 50 nm crosslinked fluoropolymer gate dielectric, ∼200 nm long channel transistors can achieve good current saturation when operated <5 V with good bias stress stability.     

Structural and electrical characteristics of RF-sputtered HfO2 high-k based MOS capacitors

The HfO₂ high-k thin films have been deposited on p-type (1 0 0) silicon wafer using RF magnetron sputtering technique. The XRD, AFM and Ellipsometric characterizations have been performed for crystal structure, surface morphology and thickness measurements respectively. The monoclinic structured, smooth surface HfO₂ thin films with 9.45 nm thickness have been used for Al/HfO₂/p-Si metal-oxide-semiconductor (MOS) structures fabrication. The fabricated Al/HfO2/Si structure have been used for extracting electrical properties viz dielectric constant, EOT, barrier height, doping concentration and interface trap density through capacitance voltage and current-voltage measurements. The dielectric constant, EOT, barrier height, effective charge carriers, interface trap density and leakage current density are determined are 22.47, 1.64 nm, 1.28 eV, 0.93 × 10¹⁰, 9.25 × 10¹¹ cm⁻² eV⁻¹ and 9.12 × 10⁻⁶ A/cm² respectively for annealed HfO₂ thin films.     

Fabrication of submicron photon sieve using E-beam lithography and X-ray lithography

In this paper, a new hybrid method to fabricate submicron photon sieve is proposed, where the E-beam lithography and the X-ray lithography are used. It is found that 2.8 μm thickness of the polyimide film, 400 nm thickness of the ZEP-520 and 280 μC/cm² exposure dose are good for E-beam lithography, while 500 nm thickness of the PMMA and 30 s developing time are good for X-ray lithography. We have successfully fabricated the photon sieve with these parameters (the diameter of photon sieve: 250 μm, the focal length: 150 μm, the diameter of the outmost pinhole: 420 nm). Some key techniques of this method are analyzed respectively, and the error analysis are done at the end of this paper. It provides a direction of nanoscale optical element fabrication with higher resolution and lower cost.     

Visible photoluminescence from Ge nanoclusters implanted in nanoporous aluminum oxide films

Nanoporous aluminum oxide (Al₂O₃) films with uniform porous size of 45 nm prepared by the electrochemical process in inorganic acid medium were implanted at room temperature (RT) with 120 keV Ge⁺ ions with a fluence of 1.2×10¹⁶ cm⁻². The nucleation and growths of Ge nanoparticles, were obtained by thermal annealing of the implanted samples at the temperature range of 200-600 °C. The size and distribution of the nanoparticles were characterized by photoluminescence (PL) measurements. The photoluminescence measurements as a function of the annealing temperature shows that at low annealing temperature (200 °C), the sample presents a low intensity and broad emission band centered at 5456 Å consistent with emission band characteristics of nanocluster of Ge with diameter in the range of 4-8 nm, as the annealing temperature increases to 400 °C the PL intensity increases by a factor of almost 20 and the emission band suffers a small red shift. The intensity increases can be related to the increase of the number of Ge nanocluster. At the annealing temperature of 600 °C, the emission band is considerably red shifted by almost 172 Å and the emission intensity decreases significantly, strongly suggesting that nanocrystalline Ge having a character of direct optical transitions exhibits the visible photoluminescence.     

Effects of post-annealing on thermoelectric properties of bismuth-tellurium thin films deposited by co-sputtering

This paper reports the microstructure evolution of Bi-Te thermoelectric films upon post-annealing and its effects on the thermoelectric properties. Bi-Te films with the composition of around 61 at.% Te and the thickness of 300 nm were deposited onto SiO₂-coated Si substrates by using bismuth and tellurium targets in a radio frequency (RF) magnetron sputtering system. We annealed the films at different temperatures (100, 150 and 200 °C) under N₂ ambient for 8 h, and characterized the crystallinity and morphology of the Bi-Te films. Microstructure characterization using X-ray diffraction and scanning electron microscopy disclosed that the post-annealing treatment entailed a drastic microstructural evolution by inducing the development of a strong texture of grains with their c-axis oriented normal to the substrate. In addition, we measured the electrical transport and thermoelectric properties of the films to reveal their close link with the microstructure changes. The electron mobility and Seebeck coefficient increase significantly, leading to a remarkable improvement in the power factor from 3.3 μW/K² cm for the as-deposited sample to 24.1 μW/K² cm for the 200 °C-annealed sample.     

Pentacene thin-film transistors with sol-gel derived amorphous Ba0.6Sr0.4TiO3 gate dielectric

An amorphous Ba_0.6Sr_0.4TiO₃ (BST) film with the thickness of 200 nm was deposited on indium-tin-oxide (ITO)-coated glass substrate through sol-gel route and post-annealing at 500 °C. The dielectric constant of the BST film was determined to be 20.6 at 100 kHz by measuring the Ag/BST/ITO parallel plate capacitor, and no dielectric tunability was observed with the bias voltage varying from −5 to 5 V. The BST film shows a dense and uniform microstructure as well as a smooth surface with the root-mean-square (RMS) roughness of about 1.4 nm. The leakage current density was found to be 3.5 × 10⁻⁸ A/cm² at an applied voltage of −5 V. The transmittance of the BST/ITO/glass structure is more than 70% in the visible region. Pentacene based transistor using the as-prepared BST film as gate insulator exhibits a low threshold voltage of −1.3 V, the saturation field-effect mobility of 0.68 cm²/Vs, and the current on/off ratio of 3.6 × 10⁵. The results indicate that the sol-gel derived BST film is a promising high-k gate dielectric for large-area transparent organic transistor arrays on glass substrate.