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Solar cells built with arrays of semiconductor wires have been studied for several years. They present some potential advantages over their bulk counterparts, such as (much) less use of semiconduct...

This work reports experiments on the oriented growth by electric field of free-standing carbon nanotubes(CNTs) by chemical vapor deposition (CVD) for field emission (FE) applications. The growths were observed in a scanning electron microscope (SEM) and in an environmental transmission electron microscope (ETEM) with the ETEM growths observed in real time. The effects of various applied voltage during growth will be presented. For high voltages, videos show that the maximum length of CNTs are limited either by the mechanical breakdown or FE induced thermal evaporation. Finally, the I(V) curves and current densities obtained will be presented with a focus on the different destruction mechanisms.

This work reports the non-covalent functionalization of SWNTs with Fe-porphyrin, Co-porphyrin and Co-phthalocyanine molecules. The functionalized SWNTs were first characterized using Raman and X-ray photoelectron spectroscopies. Observations down to nanoscale resolution were also performed by atomic force microscopy, as well as scanning and transmission electron microscopies. The spectroscopic methods evidenced an electronic interaction between the metal-centered molecules and the SWNTs, ensuring the robustness of the functionalization. High resolution microscopy characterizations reveal that the porphyrin and phthalocyanine molecules are adsorbed on the surface of SWNTs. The electrical characterizations show a weak charge transfer between those grafted molecules and the SWNTs, confirming the electronic interaction between the molecules and the SWNTs. Density functional theory (DFT) supports experimental data and helps understanding the experimental results of selective interaction of metal complexes with one type of semiconducting SWNTs.

We present a detailed study on graphene-coated aluminum thin films for Li-ion battery anode applications. The best electrode ageing behavior is obtained for Al films encapsulated with four porous graphene layers. Graphene encapsulation prevents “crushed” Al nanoparticles from detaching from the anode, thus allowing prolonged charge–discharge cycling. Graphene also provides surface conduction paths for electrons as well as diffusion paths for Li atoms. For the first time, we report the electrochemical room temperature formation of phases such as Li3Al2 and even Li9Al4, with a higher Li content than β-LiAl. More interestingly, we observe a progressive change of the composite thin film electrode, switching from a pure galvanic to a pseudocapacitive behavior as the size of the Al grains decreases from ∼100 to 5–10 nm due to repeated Li alloying-dealloying. The capacity values of ∼900 and 780 mAh/g are obtained after, respectively, 500 and 1000 charge–discharge cycles at 0.1C. Our results may refocus the inter...

Fast charging rate and large energy storage are becoming key elements for the development of next-generation batteries, targeting high-performance electric vehicles. Developing electrodes with high volumetric and gravimetric capacity that could be operated at a high rate is the most challenging part of this process. Using silicon as the anode material, which exhibits the highest theoretical capacity as a lithium-ion battery anode, we report a binder-free electrode that interconnects carbon-sheathed porous silicon nanowires into a coral-like network and shows fast charging performance coupled to high energy and power densities when integrated into a full cell with a high areal capacity loading. The combination of interconnected nanowires, porous structure, and a highly conformal carbon coating in a single system strongly promotes the reaction kinetics of the electrode. This leads to fast-charging capability while maintaining the integrity of the electrode without structural collapse and, thus, stable cycling performance without using binder and conductive additives. Specifically, this anode shows high specific capacities (over 1200 mAh g-1) at an ultrahigh charging rate of 7 C over 500 charge-discharge cycles. When coupled with a commercial LiCoO2 or LiFePO4 cathode in a full cell, it delivers a volumetric energy density of 1621 Wh L-1 with a LiCoO2 cathode and a power density of 7762 W L-1 with a LiFePO4 cathode.

The dynamic spray-gun deposition method was developed in 2006 to fabricate field effect transistors based on random arrays of carbon nanotubes (CNTs) field effect transistors for gas sensing applications. Thanks to this deposition method, we were able to fabricate hundreds of operational devices in a reproducible way that were integrated in electronic chips. Following this first implementation, we decided to widen the application of the deposition technique to the field of Energy and specifically to the fabrication of supercapacitors. In this context, we demonstrated in 2012 the fabrication of nanostructured electrodes for supercapacitors, using mixtures of graphene/graphite and CNTs increasing the device capacitance and the power delivered of a factor 2.5 compared to CNT based electrochemical-double-layer-capacitors. Indeed, with high quality graphene we could reach a value of around 100 W Kg−1. This value is extremely promising also considering that it has been obtained with an industrially suitable technique. This dynamic spray-gun deposition has been also exploited for the fabrication of resistance based random access memories, making use of thin layers of graphene oxide and of oxidized carbon nanofibers. In the first case, 5000 cycles of ‘write’ and ‘read’ phases were demonstrated. These results pave the way for the fabrication of very low cost memories that can be embedded in smart-cards, patches for health monitoring (e.g. diabetes), ID cards, RFID tags and more generally smart packaging. Finally we are also working on the utilization of this technique for the fabrication of layers for electro-magnetic interference shielding application. Thanks to a new machine with four nozzles, developed within the frame of the Graphene Flagship project, we are able to deposit four different nanomaterials at the same time or alternatively on a large surface (30 cm × 30 cm) creating specific nano-structuration and therefore ad hoc architectures allowing the smart absorption of specific frequencies (e.g. X-band). All these applications demonstrate the extreme versatility of this technique that constitutes a real breakthrough for exploiting the nanomaterials characteristics in real devices, using an industrial suitable fabrication method that can be implemented using roll-to-roll technique.

In order to reduce substrate costs and increase light absorption, solar cells based on semiconductor wire arrays are currently being actively studied. Whether built with Si, InP or other semiconductor materials, wire-based cells invariably use a transparent conductive coating for one of the electrodes, which complicates the processing and does not contribute to the reduction of the overall cost of the cell. Here, we propose a totally novel connection process, where the transparent conductive electrode is replaced with an array of in situ grown metallic nanowires. During their growth, these metallic nanowires randomly connect to core–shell p-i-n Si wires previously synthesized by chemical vapor deposition. We demonstrate the feasibility of this new random connection concept by using a coplanar solar cell design with interdigitated base and emitter contacts. We obtain a high fill factor of ~74% and efficiencies of 4.5% with only 33% of the surface covered by p-i-n Si wires.

The successful mechanical exfoliation and chemical synthesis of graphene has attracted considerable attention for the synthesis of other two-dimensional materials on graphene template. Chalcogenide materials such as Sb2Te3 are of interest due to the rhombohedral lattice structure with two-dimensional hexagonally closed-packed atomic layers along the c-axis. Here we synthesized c-axis-oriented Sb2Te3 nanoplates (NPs) on graphene substrates by the microwave-assisted solvothermal method. The microwave irradiation resulted in a higher temperature of graphene, compared with the synthesis solution, which was revealed by the single-mode microwave experiments and an analytical model based on energy balance and convective heat transfer. Besides, the lattice mismatch between c-axis-oriented Sb2Te3 and bridge sites of graphene was only 4%, which is also favorable for the graphene-templated Sb2Te3 synthesis. c-Axis-oriented single-crystalline Sb2Te3 NPs as large as 7 μm could be successfully synthesized on graphene w...

In this work, we present a practical approach for controlling single walled carbon nanotubes (SWCNTs) diameter distribution through thin film Ru catalyst, coupled with hydrogen pre-treatment. Uniform and stable Ru nanoclusters were obtained after dewetting the Ru thin films under atomic hydrogen pre-treatment. SWCNTs were synthetized by double hot filament chemical vapor deposition (d-HFCVD) on SiO2/Si substrates at different temperatures. We found that the temperature is an important synthesis parameter that in fluences the diameter distribution of the final SWCNTs. Statistical analysis of the Raman radial breathing modes evidences the growth of highly enriched semi-conducting SWCNTs (about 90%) with narrow diameter distribution that correlates directly with the catalyst particle size distribution. Electrical measurement results on as-grown SWCNTs show good thin-film transistor characteristics.

Targeting the integration of embedded non-volatile memories on thin-silicon body technology, high temperature oxide (HTO) is evaluated on a 40nm automotive eFlash process as replacement of furnace grown thick gate oxide for high voltage transistors. Different thermal treatments are evaluated to enhance HTO quality, including growth of interfacial layer, reoxidation and high temperature annealings. Transistor performance and reliability are thoroughly studied, showing that the main challenge for HTO integration is time-dependent dielectric breakdown. Because of higher charge trapping, HTO is found to be less reliable than grown oxide. However, optimized dedicated treatments successfully improve HTO quality and reliability.

This paper deals with the tests of carbon nanotube field effect transistors (CNTFETs) for gas sensing applications, exploiting an original sensing technique to dramatically improve selectivity. Such devices exploit the extremely gas-sensitive change of the Schottky barrier heights between carbon nanotubes (CNTs) and drain/source metal electrodes. This effect is at the origin of the change of the CNTFET transfer characteristics. Indeed the main effect is related to the gas adsorption creating an interfacial dipole that modifies the Fermi levels alignment and so the bending and the height of the Schottky barrier at the contacts with the CNTs. This change is strictly dependent on the metal/CNTs junction and on the gas involved. We have fabricated on the same chip an array of four CNTFETs composed of four different metals (Pd, Pt, Au, Ti) as electrodes and we have demonstrated that each CNTFET interacts in a very specific way, identifying a sort of electronics fingerprinting. This array has been tested after exposure to NO2, NH3 and di-methyl-methyl-phosphonate (DMMP, a sarin gas simulant) with gas concentrations varying from 10 ppb to 10 ppm using air as gas carrier.

We present a robust and versatile approach for the reproducible and controllable growth of single-walled carbon nanotubes (SWNTs) through a self-assembled monolayer (SAM) technique coupled with an atomic hydrogen (Hat) pretreatment to control the catalytic metallic nanoparticles size and density. The nanoparticles are obtained from a self-assembled monolayer of metal complexes or salts on a SiO2 substrate using a two-step strategy. The oxide is first functionalized by silanization with a coordinating ligand leading to the formation of an anchoring SAM on the substrate. Then, metallic complexes such as ruthenium porphyrin (RuTPP) or metallic salts (FeCl3, RuCl3) are assembled by coordination bonds on the preformed organic SAM. Pyrolysis under radical hydrogen atmosphere of the as-prepared SAM yields metallic nanoparticles whose size and density are controlled and tuned. Using the as-formed nanoparticles as catalysts, SWNTs are grown by double hot-filament-assisted chemical vapor deposition (d-HFCVD). They ...

Enhanced carrier–carrier interactions in hybrid nanostructures exhibit exceptional electronic and optoelectronic properties. Carbon nanotubes demonstrate excellent switching behavior with high on/off ratio and high mobility but do not show photoresponse in the visible range, whereas quantum dots (QDs) shows excellent optical response in various optical ranges which can be tuned with diameter. Here, a simple and effective way to develop hybrid phototransistors with extraordinary optoelectronic properties is presented by decorating semiconducting QDs on the surface of a single-walled carbon nanotube (SWCNT). This hybrid structure demonstrates clear negative photoresponse and optical switching behavior, which could be further tuned by applying external gate bias in the future. A clear type conversion of SWCNT transistor from p-type to n-type caused by a charge transfer from attached QDs to CNT is demonstrated. Moreover, this hybrid structure also demonstrates an enhancement in ‘optical Stark effect’ without applying any external electric field. Charged SWCNT surface plays a key role behind the enhancement of optical Stark effect in QDs. The carrier dynamics of the QD and CNT heterostructures system highlights the potential application opportunity of the quantum dot systems, which can be adaptable to the current technologies.

67 This contribution deals with the fabrication of electrodes and supercapacitor cells using a new dynamic air-brush deposition technique. This method yields highly uniform mats with finely tuned thickness and weight in a completely reproducible way. Using this deposition technique, we analyze the effect of mixtures of CNTs and graphite on the electrode and cell properties (energy, power and capacitance) and observe that with a mixture of 75% of graphite and 25% of CNTs, we increase the power by a factor 2.5 compared to bare CNT-based electrodes. We also analyze the effect of the electrodes’ weight first on the capacitance and specific energy and second on the specific power. We report a specific power of 200 kW/Kg and a specific energy of 9.1 Wh/Kg with electrodes having a surface of 2 cm 2 and a weight of 0.25 mg composed by 50% of CNTs and graphite (using a common aqueous electrolyte). Our deposition technique delivers supercapacitors with ad-hoc characteristics, by simply modulating the weight and the concentration of the CNT/graphite mixture in a completely reproducible way and with an industrially suitable and low-cost method. 8 9 10 11 12 13 14 15 16

The isolation of a single layer of graphite, known today as graphene, not only demonstrated amazing new properties but also paved the way for a new class of materials often referred to as two-dimensional (2D) materials. Beyond graphene, other 2D materials include h-BN, transition metal dichalcogenides (TMDs), silicene, and germanene, to name a few. All tend to have exciting physical and chemical properties which appear due to dimensionality effects and modulation of their band structure. A more recent member of the 2D family is graphene-like zinc oxide (g-ZnO) which also holds great promise as a future functional material. This review examines current progress in the synthesis and characterization of g-ZnO. In addition, an overview of works dealing with the properties of g-ZnO both in its pristine form and modified forms (e.g., nano-ribbon, doped material, etc.) is presented. Finally, discussions/studies on the potential applications of g-ZnO are reviewed and discussed.

Metal oxide nanoparticles decorating graphene have attracted abundant interest in the scientific community owing to their significant application in various areas such as batteries, gas sensors, and photocatalysis. In addition, metal and metal oxide nanoparticles are of great interest for the etching of graphene, for example, to form nanoribbons, through gasification reactions. Hence it is important to have a good understanding of how nanoparticles interact with graphene. In this work we examine, in situ, the behavior of CuO and ZnO nanoparticles on graphene at room temperature while irradiated by electrons in a transmission electron microscope. ZnO is shown to etch graphene through gasification. In the gasification reaction C from graphene is released as CO or CO2. We show that the reaction can occur at room temperature. Moreover, CuO and ZnO particles trapped within a graphene fold are shown to effuse out of a fold through small ruptures. The mass transport in the effusion process between the CuO and ZnO particles is fundamentally different. Mass transport for CuO occurs in an amorphous phase, while for ZnO mass transport occurs through the short-lived gliding of vacancies and dislocations. The work highlights the potential and wealth of electron beam driven chemical reactions of nanomaterials, even at room temperature.

Silicon nanowire field-effect transistors (SiNW FETs) have emerged as good candidates for ultra-sensitive electrical detection of biological species, presenting a label-free alternative to colorimetry and fluorescence techniques. Here, a top-down approach has been used to fabricate the SiNW FETs using silicon-on-insulator (SOI) substrates. As in previous work, a change of the transistor conductance according to the pH of the solution is observed on a large pH interval [3–10.5], even for small variations of 0.1 pH units. The influence of several physico-chemical parameters such as gate voltage and buffer salinity, usually not adequately taken into account in previous papers, is discussed to achieve a better understanding of the detection phenomena.

Carbon nanotubes are actively studied for thin-film transistor and electronics applications. Although these nanomaterials were first considered as potential candidates for the replacement of Si MOS type transistors in VLSI circuits, their main field of application is shifting towards large area electronics on flexible, plastic-type substrates, a domain which is at present, less demanding in terms of device dimensions and integration density. In particular, random networks of carbon nanotubes, which can be obtained by solution-processing or grown at low temperature, represent an attractive and viable option for the fabrication of electronic circuitry on non-refractory substrates. This paper briefly reviews some recent advances in the field, highlighting realisations beyond the fabrication of simple transistors.

We propose a novel growth technique, in which graphene is synthesized on capped Cu thin films deposited on c-plane sapphire. The cap is another sapphire plate which is just laid upon the Cu thin film, in direct contact with it. Thanks to this 'contact cap', Cu evaporation can be suppressed at high temperature and the 400 nm-thick Cu films can be annealed above 1000 °C, resulting in (1 1 1)-oriented grains of millimeter size. Following this high temperature annealing, graphene is grown by chemical vapor deposition during the same pump-down operation, without removing the contact cap. The orientation and doping type of the as-grown graphene were first studied, using low energy electron diffraction, as well as high resolution angle-resolved photoemission spectroscopy. In particular, the orientation relationships between the graphene and copper thin film with respect to the sapphire substrate were precisely determined. We find that the graphene sheets exhibit a minimal rotational disorder, with ~90% of the grains aligned along the copper high symmetry direction. Detailed transport measurements were also performed using field-effect transistor structures. Carrier mobility values as high as 8460 cm2 V−1 s−1 have been measured on top gate transistors fabricated directly on the sapphire substrate, by etching the Cu film from underneath the graphene sheets. This is by far the best carrier mobility value obtained to date for graphene sheets synthesized on a thin film-type metal substrate.

This paper deals with the fabrication of CNTFET obtained using carbon nanotube networks and with the utilization of these last as gas sensors. The method for depositing uniform and highly controlled density CNT mats is spray-gun technique. Using this technique we have demonstrated that we can achieve CNTFET with Ion/IOff reproducible ratios of around 5/6 orders. These transistors have been subsequently exposed to Acetic Anhydride which is a heroin precursor, showing a very short response time and a recovery time, without heating, of around 30 minutes. In this paper are also shown preliminary results after exposure of CNTFET to subppm concentrations of DMMP and NH3 using two different metals as electrodes. In this case devices were obtained using drop-casting technique.

We present some of our first experiments on the controlled growth of silicon nanowires and carbon nanotubes in lateral porous alumina templates synthesized by anodic oxidation of Al thin films. Under adapted chemical vapor deposition growth conditions, and using the vapor-solid-liquid mechanism, the pores of the lateral membranes can be partially filled with silicon nanowires or carbon nanotubes, yielding a composite thin film of parallel-organized nano-objects. Such composite thin films can be further tailored and shaped by classical microelectronic-type tools and processes, in order to fabricate electronic devices.

[*] Dr. J.-Y. Choi, H.-J. Shin, S.-M. Yoon Display Device and Processing Laboratory Samsung Advanced Institute of Technology PO Box 111, Suwon 440-600 (Republic of Korea) E-mail: jaeyoung88.choi@samsung.com Prof. Y. H. Lee, S. J. Chae, F. Gunes, Dr. K. K. Kim, E. S. Kim, G. H. Han, S. M. Kim, H.-J. Shin BK21 Physics Division Sungkyunkwan Advanced Institute of Nanotechnology Center for Nanotubes and Nanostructured Composites Sungkyunkwan University Suwon 440-746 (Republic of Korea) E-mail: leeyoung@skku.edu M. H. Park, Prof. C. W. Yang Department of Advanced Materials Engineering Sungkyunkwan University Suwon 440-746 (Republic of Korea)

In this paper we present recent studies concerning gas sensors based on carbon nanotube field effect transistors (CNTFETs). Although these devices have allowed one to realize sensors with an impressive sensitivity compared to existing technologies, the physical interpretation of the interaction between the gas molecules and the CNTFETs has not been clarified yet. In this contribution, we try to find some consistency between the physical interpretations advanced by the different scientific teams working on the subject and to answer some unsolved questions. Moreover, considering that the selectivity is the main issue, we analyze the different routes that have been proposed to overcome this problem: functionalization using polymers, diversification of the source/drain metal electrodes, metal decoration of SWCNT mats, exploitation of the desorption time of the different gases. For each technique we try to evaluate the advantages and the drawbacks.

A fabrication method for silicon beams and membranes defined in lateral and vertical dimensions, as well as superposed silicon membranes, all realized in bulk silicon using only one lithographic step is proposed. This proposal is based on observations made on structures obtained by High Temperature Annealing (HTA) in hydrogen atmosphere process. The combination of design configuration and materials technology (hard mask) with the process shows the possibility of new 3D devices and cavities beyond previously reported capabilities of with this technique. The specific design and hard mask engineering presented can lead to structures used in a bulk silicon platform for 3D devices with optical and electronic functions for the fabrication of bulk silicon waveguides and transistors on stressed membranes with enhanced mobility.

This paper deals with the fabrication of carbon nanotube field effect transistors (CNTFETs) for gas sensing applications. Such devices exploit the extremely sensitive change of the Schottky barrier heights between carbon nanotubes (CNTs) and drain/source metal electrodes: the gas adsorption creates an interfacial dipole that modifies the metal work function and so the band bending and the height of the Schottky barrier at the contacts. Our aim is to achieve the fingerprinting of a specific gas using a CNTFET based sensor array. This fingerprinting concept is based on the fact that the change of the metal electrode work function strictly depends on the metal/gas interaction. Consequently the CNTFET transfer characteristics will change specifically as a function of this interaction. To demonstrate this new concept, we have fabricated arrays of CNTFETs with different metal contacts: Au, Pd, Ti and Pt. Using these transistors, we have shown that a particular gas, in our case DiMethyl-Methyl-Phosphonate (DMMP,...

The effects of an atomic hydrogen ( H at ) pretreatment of the catalyst layer on the low temperature growth of single-walled carbon nanotubes (SWCNTs) have been investigated using a modified catalytic chemical vapor deposition system. Well-defined and isolated individual Fe nanoparticles as a catalyst are successfully formed on the defects with high trapping energy which are created on the Al 2 O 3 surface by H at pretreatment, yielding highly dense SWCNTs. The pretreatment mechanism of H at , compared to H 2 , is also discussed. It was also found that the quality of SWCNTs can be enhanced when H at is flowed with CH 4 during nanotubes growth at low temperature. In this case, the undesired carbon products and defects on catalyst seeds and nanotube walls can be selectively removed by H at . Therefore it is essential to use H at in the pretreatment stage for increasing catalytic activity and to keep the size of nanoparticles in the nm range. H at can also be employed in growth stage for enhancing SWCNTs quality and density at low temperature.

We present some comparisons concerning field emission as well as processing parameters from two types of nanostructures, namely multiwall carbon nanotubes grown by plasma enhanced chemical vapour deposition and metal nanowires grown by electrochemical deposition in porous membranes. Various treatments are presented, either during deposition or after, in order to improve the uniformity of the emitted current. We also review and propose simple processes to manufacture large arrays, having in mind LCD backlighting applications.

We report on the growth mechanism and density control of vertically aligned carbon nanotubes using a triode plasma enhanced chemical vapor deposition system. The deposition reactor was designed in order to allow the intermediate mesh electrode to be biased independently from the ground and power electrodes. The CNTs grown with a mesh bias of + 300 V show a density of ∼ 1.5 μm− 2 and a height of ∼ 5 μm. However, CNTs do not grow when the mesh electrode is biased to − 300 V. The growth of CNTs can be controlled by the mesh electrode bias which in turn controls the plasma density and ion flux on the sample.

International audience; Multi-walled carbon nanotubes have been grown on 7 nm Ni-coated substrates consisting of 300 lm thick highly n-doped (1 0 0) sil- icon covered with a diffusion barrier layer (10 nm thick) of SiO2 or TiN, by combining hot-wire chemical vapor deposition and direct current plasma-enhanced chemical vapor deposition at low temperature (around 620 °C). Acetylene gas was used as carbon source and ammonia and hydrogen were used either for dilution or etching. Growth of dense aligned nanotubes could be observed only if the ammonia content was minimized (rv5%). In order to improve the electron field emission properties of the films, different geometrical factors have been taken into account: average length, length/radius ratio and spacing between nanotubes. The nanotube growth rate was controlled by the substrate temperature and the pressure in the reactor, and the nanotube height by the growth time. The nanotube diam- eter was controlled by the catalyst dot volume, and the nanotube spacing was adjusted during the patterning process of the catalyst dots. Using optical lithography, 1 lm Ni dots were obtained and several multi-walled nanotubes with diameter and length in the range 60- 120 nm and rv2.3 lm were grown on each dot. Thus, based on a two-dimensional square lattice with a lattice translation vector of 4 lm, I-V characteristics yielded an onset electric field of 16 V/lm and a maximum emission current density of 40 mA/cm2, due to the large screening effect. Using electron-beam lithography, 100 nm Ni dots were obtained and individual multi-walled nanotubes were grown on each dot. Based on a square lattice with 10 lm translation vector, I-V characteristics gave an onset field of 8 V/lm and a max- imum emission current density of 0.4 A/cm2.

Either at pixel or driver levels, low-temperature polysilicon (LTPS) is becoming a standard technology for the fabrication of thin-film transistors (TFTs) used in active matrix liquid crystal displays and in active matrix organic light emissive displays. Given the complexity of addressing or pixel circuits, simulation is becoming more and more necessary. In order to reach the required level of simulation efficiency, an accurate model has been developed. This model takes into account all the operating regimes, capacitors contributions, and frequency dispersion effects. In order to be able to simulate large number of matrix pixels and/or integrated drivers, this model is simple enough to allow simulator convergence. Based on 38 parameters, it presents an easy electrical parameters characterization methodology. Moreover, physical parameters use allows an easy modification of the model performances depending on polycrystalline silicon TFT technology properties and evolution.

Plasma enhanced chemical vapour deposition (PECVD) is a controlled technique for the production of vertically aligned multiwall carbon nanotubes for field emission applications. In this paper, we investigate the electrical properties of individual carbon nanotubes which is important for designing field emission devices. PECVD nanotubes exhibit a room temperature resistance of 1–10 kΩ/μm length (resistivity 10 −6 to 10 −5 Ω m) and have a maximum current carrying capability of 0.2–2 mA (current density 10 7 –10 8 A/cm 2 ). The field emission characteristics show that the field enhancement of the structures is strongly related to the geometry (height/radius) of the structures and maximum emission currents of ∼10 μA were obtained. The failure of nanotubes under field emission is also discussed.

The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.

After more than 20 years of steady progress, lithium-ion batteries seem to have reached their asymptotic storage capacity values with the present combination of graphite at the anode and insertion oxide or phosphate materials at the cathode. New applications, particularly for all-electric vehicles are pushing the development of electrode materials with higher Li storage capacities, for both electrodes. Concerning anodes, many materials with potentially higher capacities have been investigated in view of replacing graphite, but their lifetime is usually short, due to large volume changes between the lithiated and unlithiated states. This chapter presents recent developments in the field of anodes, essentially based on the use of nanostructures. Silicon appears as the most promising material and several companies are already proposing nanostructured anodes, eventually incorporating other nanomaterials such as graphene.

The overall aim of this work is to produce arrays of field emitting microguns, based on carbon nanotubes, which can be utilised in the manufacture of large area field emitting displays, parallel e-beam lithography systems and electron sources for high frequency amplifiers. This paper will describe the work carried out to produce patterned arrays of aligned multiwall carbon nanotubes (MWCNTs) using a dc plasma technique and a Ni catalyst. We will discuss how the density of the carbon nanotube/fibres can be varied by reducing the deposition yield through nickel interaction with a diffusion layer or by direct lithographic patterning of the Ni catalyst to precisely define the position of each nanotube/fibre. Details of the field emission behaviour of the different arrays of MWCNTS will also be presented.

A broadband antireflective nanostructure with Ag nanoparticles on SiO2 nanocolumns has been presented. Ag nanoparticles are located at the top of SiO2 nanocolumns which are deposited on Si substrates. SiO2 nanocolumns are fabricated by oblique angle deposition through electron beam evaporation, and Ag nanoparticles are fabricated by thermal evaporation. Experimental results show that the average reflection can reach 3.84% in the range of 400–700 nm and 5.75% in the range of 400–1100 nm, much lower than that of Ag islands on SiO2 thin films. The simulation shows that the broadband low reflection can be attributed to the localized surface plasmon resonance of Ag nanoparticles whose resonance wavelengths depends on the size of Ag nanoparticles. The different diameters of SiO2 nanocolumns determine the size distribution of Ag nanoparticles which resonate in a wide wavelength range and lead to a broadband low reflection. This provides a possible way to fabricate a broadband antireflection structure.

International audience; The low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalystparticles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are "replaced" by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering themechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality.

We have studied the influence of the surface roughness of copper foils on the sheet resistance of graphene sheets grown by chemical vapor deposition. The surface roughness of the copper foils was reproducibly controlled by electropolishing. We have found that the graphene sheet resistance monotonically decreases as the surface roughness of the copper foils decreases. We show that a pre-annealing treatment combined with an optimized electropolishing process of the Cu foils and a fast CVD growth prevents the evolution of the Cu surface roughness during graphene synthesis. This combination of fabrication conditions produces small grain polycrystalline graphene films with a sheet resistance of 210 Ω □(-1) and carrier mobility values as high as 5450 cm(2) V(-1) s(-1) after transfer onto SiO2/Si.

This paper presents a 14nm technology designed for high speed and energy efficient applications using strain-engineered FDSOI transistors. Compared to the 28nm FDSOI technology, this 14nm FDSOI technology provides 0.55× area scaling and delivers a 30% speed boost at the same power, or a 55% power reduction at the same speed, due to an increase in drive current and low gate-to-drain capacitance. Using forward back bias (FBB) we experimentally demonstrate that the power efficiency of this technology provides an additional 40% dynamic power reduction for ring oscillators working at the same speed. Finally, a full single-port SRAM offering is reported, including an 0.081°m 2 high-density bitcell and two 0.090°m 2 bitcell flavors used to address high performance and low leakage-low Vmin requirements.

We report on the fabrication of field emission microcathodes which use carbon nanotubes as the field emission source. The devices incorporated an integrated gate electrode in order to achieve truly low-voltage field emission. A single-mask, self-aligned technique was used to pattern the gate, insulator and catalyst for nanotube growth. Vertically-aligned carbon nanotubes were then grown inside the gated structure by plasma-enhanced chemical vapour deposition. Our self-aligned fabrication process ensured that the nanotubes were always centred with respect to the gate apertures (2 µm diameter) over the entire device. In order to obtain reproducible emission characteristics and to avoid degradation of the device, it was necessary to operate the gate in a pulsed voltage mode with a low duty cycle. The field emission device exhibited an initial turn-on voltage of 9 V. After the first measurements, the turn-on voltage shifted to 15 V, and a peak current density of 0.6 mA cm-2 at 40 V was achieved, using a duty cycle of 0.5%.

Organic semiconductors have now proven their ability to be incorporated as the active layer in a light emitting diode. We report here on the status of emerging materials (both evaporated molecules and polymers), then we consider colour patterning and addressing issues. Finally, we describe the first commercial OLED displays and we review the different demonstrators which have been disclosed so far.

In this work, the excimer-laser-induced crystallization of a-Si films on SiO2 was investigated using a long-pulse-duration (200 ns) XeCl source. The microstructural analysis of the laser-irradiated area, for incident energy densities comprised between the thresholds corresponding to the surface and full melting, respectively, of the Si layer, was performed by scanning electron microscopy and Raman spectroscopy. A super-lateral-growth regime was evidenced quite comparable to that which occurs when classical excimer laser pulses of short duration (≈20 ns) are used. A numerical simulation of the surface melt dynamics was also performed and compared to the experimental observations.

The control of the structural properties of polysilicon obtained by excimer laser crystallization has become of great importance to further develop the polysilicon thin-film transistors technology. The most attractive crystallization regime is the so-called super lateral growth (SLG), characterized, however, by a very narrow energy density window and a strongly non-uniform grain size distribution. In this work we have investigated several approaches to achieve a control of the lateral growth mechanism through lateral thermal gradients, established by the opportune spatial modulation of the heating. To this purpose, three different patterned capping layers have been used: anti-reflective (SiO2), heat-sink (silicon nitride) and reflective (metal) overlayers. For all three types of overlayers, when the conditions to trigger the lateral growth mechanism are achieved, a band of oriented grains (1–2 μm wide) appears at the boundary between capped and uncapped region and extending in the more heated region. Among the different approach the use of reflective overlayers appears promising and further engineering of this process is in progress.

In this work, the excimer laser induced crystallization of a-Si films on SiO2 was investigated, using a long pulse duration (200 ns) XeCl source. The microstructural analysis of the laser irradiated area, for incident energy densities comprised between the surface and full melting thresholds of the a-Si layer, respectively, was performed by scanning electron microscopy. A numerical simulation of the surface melt dynamics was also presented and compared to the experimental observations.

Polysilicon thin-film transistors (TFTs) are of great interest for their circuit application in the large area microelectronics. A successful circuit design requires an accurate prediction of the circuit performances, which in turn needs a proper modeling of the electrical device characteristics. In this present work the specific aspects of the anomalous current increase in the output characteristics, often called the “kink” effect, are analysed. A new procedure to determine the excess current is presented and we analysed the excess current for different gate voltages, temperatures and device geometries. We show that, from the parameters that can be extracted by analysing a reduced set of experimental data, the excess current can be easily predicted for any bias and temperature condition and also for devices with different geometries. These results can be used to further up-grade the modeling of the electrical characteristics of polysilicon TFTs in circuit simulators.

Polycrystalline silicon thin-film transistors (TFTs) have been fabricated by using a combined fast solid-phase crystallization (SPC) process followed by excimer laser annealing (ELA). The electrical characteristics of the devices, after post-hydrogenation, show average field effect mobilities > 100 cm2/Vs and better noise performance, if compared to conventional SPC-polysilicon TFTs. A main advantage of the presented technique is the reduced sensitivity of the device performances to the energy density used during ELA.

This contribution deals with the fabrication of electrode and supercapacitor cell using a new dynamic air-brush deposition technique. This method allows to achieve extremely (ou highly) uniform mats with finely tuned thickness and weight in a completely reproducible way. Using this deposition technique, we have analyzed the effect of mixture of CNTs and graphene/graphite on the electrode and cell properties (energy, power and capacitance). using a mixture of 75% of graphene/graphite and 25% of CNTs we increased the power by a factor 2.5 compared to bare CNTs based electrodes. We also analyzed the effect of the weight firstly on the capacitance and specific energy and then on the specific power. We were able to reach a specific power of 200kW/Kg and a specific energy of 9.1Wh/Kg with an electrode having a surface of 2cm 2 and a weight of 0.25mg composed by 50% of CNTs and graphene/graphite (using a common aqueous electrolyte). using our deposition technique we are able to achieve supercapacitors with ad-hoc characteristics simply modulating the weight and the concentration of the mixture in a completely reproducible way.

We present a systematic study of grain size and carrier mobility behaviour in polycrystalline graphene films grown on copper substrates with various surface roughness values. We first observe that as the surface roughness of the substrate decreases, the graphene grain size increases significantly, thus decreasing the density of grain boundaries. Then, using field-effect transistor structures, we confirm that as the substrate roughness decreases, carrier mobility values in graphene increase, whatever the channel length of the transistor. For a substrate rms roughness around 5 nm (measured on a 10 × 10 µm2 field) and using a fast growth process (~40 min), we obtain mobility values as high as ~6900 cm2 Vs−1 for electrons and ~6000 cm2 Vs−1 for holes in polycrystalline graphene with a small grain size of ~12–14 µm.

We present electronically controlled field emission characteristics of arrays of individually ballasted carbon nanotubes synthesized by plasma-enhanced chemical vapor deposition on silicon-on-insulator substrates. By adjusting the source-drain potential we have demonstrated the ability to controllable limit the emission current density by more than 1 order of magnitude. Dynamic control over both the turn-on electric field and field enhancement factor have been noted. A hot electron model is presented. The ballasted nanotubes are populated with hot electrons due to the highly crystalline Si channel and the high local electric field at the nanotube base. This positively shifts the Fermi level and results in a broad energy distribution about this mean, compared to the narrow spread, lower energy thermalized electron population in standard metallic emitters. The proposed vertically aligned carbon nanotube field-emitting electron source offers a viable platform for X-ray emitters and displays applications that require accurate and highly stable control over the emission characteristics.