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Sustainability plays an important role by utilising hazardous waste into green technology. This study includes various Class F Fly Ash (CFFA) and Brick Industrial Rice Husk Ash (BIRHA) proportions with alkalis to make matrix of geopolymer mortar under the curing temperature of 40 °C ± 2 °C till the testing ages. The effect of BIRHA upto 50% with NaOH concentration of 10 M was assessed with sodium based alkali ratio of 2.5. Morphology and mineralogy was determined using FESEM, XRD and Wet chemical analysis for the base binders. Fresh mortar properties like flowability and unit weight was determined and hardened properties like compressive strength was determined for both ambient curing upto 56 days and higher temperature effect at 56 days for all mix proportions. Research leads to the findings that the specimens made of 10 M NaOH and 30% BIRHA exhibits higher compressive strength at 56 days in ambient temperature beyond which it decreases. The mix made with 90% CFFA and 10% BIRHA is found to be optimum for fire load applications. Hence from the present investigation it can be revealed that the BIRHA is a promising solid waste material for geopolymer application.

In India the generation of agro waste rice husk ash is abundant. The utilization of rice husk ash in development of geopolymer binders can be suitable to alleviate the environmental problems associated with disposal of rice husk ash. Further, the utilization of rice husk ash generated from the stacks of brick kilns has not been addressed in past, particularly in development of geopolymer binders. This study proposes development of geopolymer paver (GEOPAV) blocks utilizing brick kiln rice husk ash (BKRHA). It presents fresh, mechanical and durability properties of GEOPAV blocks blended with fly ash, BKRHA, natural aggregates, NaOH and Na2SiO3 solution, and cured in both sundry and room temperature conditions. Microstructural analysis using scanning electron microscope (SEM) and X-ray diffraction (XRD) was adopted to study the influence of BKRHA on hardened properties of GEOPAV blocks. The results show that addition of BKRHA reduce the workability of GEOPAV mixes due to micro porous surface with honeycombed structure of BKRHA particles. The addition of BKRHA showed negligible improvement in compressive strength of GEOPAV blocks. However, the major advantage was observed with improved split tensile strength and flexural strength for GEOPAV blocks with BKRHA. Further, the durability properties in terms of resistance to acid and frost attack was significantly improved with the addition of BKRHA in GEOPAV blocks. Such improvements can be attributed to high amounts of amorphous silica in BKRHA which contribute towards dissolution and formation of polymeric gel, and thereby serve as a binder to enhance the geopolymer matrix making it dense. Finally, all the developed GEOPAV blocks satisfy the IS 15658–2021 specification requirements and perform much better when compared to commercially available paver blocks.

Brick kilns uses assorted amount of rice husk as fuel to fire the stacks of soil bricks. In India, the rice husk ash (RHA) created during the burning process of bricks has yet to be properly exploited. The main focus of this study is to enhance the structural properties of geopolymer composites using brick kiln incinerated rice husk ash waste. The Physico-chemical analysis of brick kiln rice husk ash indicates the presence of high silica (88%) content with the evidence of XRD and FTIR analysis, SEM images shows high porous structure and PSD analysis gives a bonding nature of particle size as binding ingredient. The geopolymer mixes were made manually with different percentage of RHA 0%, 10%, 20% and 30% replaced partially in Siliceous Flyash. To identify suitability of the mixture for geopolymer concrete production, properties like workability and fresh density of the mixture was investigated using manually casted cubes having a size of 100 ​mm and keeping for oven drying at 40° ±2 ​°C upto 24 ​h. Compressive strength as destructive structural test method was investigated at the respective duration of curing. The findings led to the conclusion that increasing the percentages of RHA in the combination improves the mixture for geopolymer concrete composites with the increase of curing time. At 10% RHA addition, the optimal compressive strength of 42.19 ​N/mm2 was achieved. The compressive strength of the RHA was found to decrease by 0.8% at 10% addition, which is negligible when compared to the control geopolymer mix (i.e., mix with 0% RHA), implying that the RHA from brick kilns can be employed to improve the structural qualities of geopolymer concrete composites.

Hierarchical hybrid microarchitectured 3D/1D titanium oxide (TiO2) films were developed by one-step surfactant-free hydrothermal method over TiO2 seeded FTO substrates. The TiO2 films synthesized from hydrothermal method at growth temperature 180 °C were dried at room temperature and then heat treatment at 70 °C, 150 °C, 250 °C, 350 °C and 450 °C formed hierarchical hybrid microarchitectural structures. X-ray diffraction and Raman spectral results of the prepared TiO2 hierarchical hybrid microarchitectured films confirmed the formation of single phase rutile tetragonal TiO2 system. Scanning electron microscopy results revealed that the heat treatment at various temperatures effectively modified the surface morphology of hydrothermally grown 3D/1D TiO2 hierarchical hybrid microstructures. The UV–vis and photoluminescence spectral results of the heat treated TiO2 films revealed modification in the bandgap energy and the electron-hole pairs recombination rate respectively when compared with that of the pristine film. The photoelectric measurements revealed that the heat treated film at 450 °C exhibited the relatively higher photocurrent density of 2.68 mA/cm2 and applied bias potential efficiency of 2.91% as compared with all other heat treated and pristine films.

Geopolymer concrete is a sustainable composite where concrete is supplanted totally by pozzolanic cementitious materials like coal fuel ash, granulated blast furnace slag, rice husk ash, metakioline etc. with binding alkaline solutions in the matrix. Since the geopolymer doesn’t have specific code determination, a study has been made to create mix design to achieve the required workability and fresh density as per the considerable limits. Mix design procedure is proposed for flyash rice husk ash composition considering the quantity and fineness of binder, grading of aggregates. Water glass solution with Na2O = 18.79 %, SiO2 = 34.21 % and H2O = 47 % and solution of sodium hydroxide having 10M and 12M concentration were maintained constant throughout the Design. Fluid to binder ratio of 0.56, sodium silicate-to-sodium hydroxide ratio of 2.5 by mass was fixed on the basis of flowability. Measurement of Workability of geopolymer concrete was done using slump cone apparatus as per IS 1199. The cubes of 100 mm size were casted and cured under sundried condition maintaining a temperature about 40°C. From the observation it is concluded that the brick industrial rice husk ash can be utilized upto 10% in class f flyash to satisfy the Mix design criteria.

In this paper, we study, analyze, and validate some important zero-dimensional physics-based models for vanadium redox batch cell (VRBC) systems and formulate an adequate physics-based model that can predict the battery performance accurately. In the model formulation process, a systems approach to multiple parameters estimation has been conducted using VRBC systems at low C-rates (∼C/30). In this batch cell system, the effect of ions' crossover through the membrane is dominant, and therefore, the capacity loss phenomena can be explicitly observed. Paradoxically, this means that using the batch system might be a better approach for identifying a more suitable model describing the effect of ions transport. Next, we propose an efficient systems approach, which enables to help understand the battery performance quickly by estimating all parameters of the battery system. Finally, open source codes, executable files, and experimental data are provided to enable people's access to robust and accurate models and optimizers. In battery simulations, different models and optimizers describing the same systems produce different values of the estimated parameters. Providing an open access platform can accelerate the process to arrive at robust models and optimizers by continuous modification from the users' side.

Understanding systematic trends in degradation of Li-ion batteries through a broad range of operating conditions is critical to improving their performance. Over the course of the last few years, researchers at Sandia National Labs have been conducting a systematic study of battery cycling behavior. In this study, dozens of commercial NCA (LiNixCoyAl1-x-yO2) and NMC (LiNixMnyCo1-x-yO2) cells were cycled to 80% capacity across a range of temperatures, discharge rates, and depth of discharge windows. Analysis of both in situ electrochemical data and postmortem materials degradation was done and correlated to determine root causes of rapid capacity fade. During cycling, Electrochemical Impedance Spectroscopy (EIS) and Incremental Capacity Analysis (ICA) experiments were conducted periodically. The data from these experiments were used to understand the state of health (SoH) of cycling cells, including SEI formation and Li plating, as well as general mass transport and kinetic properties. X-ray Computed Tomography (XCT) scans completed before cell disassembly showed large scale deformation in the cells’ jelly rolls. For the postmortem analysis, cells in pristine condition and 80% capacity were disassembled, and their electrodes were analyzed with X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Differential Scanning Calorimetry (DSC). These techniques analyzed different aspects of the electrodes’ physical and chemical properties, including Li plating, micro-cracking, SEI layer formation, and phase changes in cathode materials. DSC measurements also provided insight into changes in the degree to which aged electrodes undergo thermal runaway events. Correlation of the postmortem materials analysis with the in situ electrochemical analysis showed that cells with the most rapid rate of capacity fade had multiple degradation mechanisms active during cycling. The scale of this electrochemical and materials evaluation fills in gaps in the literature about commercial Li-ion battery performance. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Rechargeable alkaline Zn–MnO2 (RAM) batteries are a promising candidate for grid-scale energy storage owing to their high theoretical energy density rivaling lithium-ion systems (∼400 Wh/L), relatively safe aqueous electrolyte, established supply chain, and projected costs below $100/kWh at scale. In practice, however, many fundamental chemical and physical processes at both electrodes make it difficult to achieve commercially competitive energy density and cycle life. This review presents a detailed and timely analysis of the constituent materials, current commercial status, electrode processes, and performance-limiting factors of RAM batteries. We also examine recently reported strategies in RAM and related systems to address these issues through additives and modifications to the electrode materials and electrolyte, special ion-selective separators and/or coatings, and unconventional cycling protocols. We conclude with a critical summary of these developments and discussion of how future studies should be focused toward the goal of energy-dense, scalable, and cost-effective RAM systems.

In this paper, we developed a low-cost, highly sensitive magnetization characterization instrument using a sound card and compared its sensitivity with commercially available measurement techniques. Firstly, we use an RLC circuit to measure the frequency-dependent response of the sound card and compare it with a lock-in amplifier. Then, we construct a simple but versatile measuring instrument, vibrating sample magnetometer (VSM) based on audio components, where data acquisition is performed by the sound card and the commercial lock-in amplifier. We test our magnetometry by measuring the magnetic hysteresis of three distinct samples: Nickel bulk piece, perm-alloy thin film with an easy-plane anisotropy, and Co/Pt multilayer with perpendicular magnetic anisotropy. We also analyze the magnetizations of three samples for different vibration frequencies and compare the sensitivities of two data acquisition methods. Although the sound card performs slightly worse than the lock-in amplifier at the vibration frequencies lower than 20 Hz due to the frequency cut-off, the sound card provides approximately seven times better sensitivity than the lock-in amplifier does at higher frequencies up to 60 Hz. We found that the sound card based VSM can have a sensitivity as high as 2 micro-emu at 34.7 Hz vibration frequency, which can be suitable for various laboratory and industrial applications.

High voltage and energy density have increased the use of lithium-ion batteries (LiBs) in many applications, including consumer electronics, electric vehicles, and grid-tied energy storage systems (ESS). However, with increasing energy density and installation size come heightened concerns about safety, including the risk of thermal runaway and serious fires. To understand the risks and outcomes of LiB failure, numerous studies have examined the response of fresh cells to mechanical, electrical, and thermal abuse. However, given the expected lifetime of LiBs, it is critical to consider the abuse response of aged cells. In this presentation, we review previous results on the abuse of aged cells to facilitate understanding of how aging conditions (such as temperature and cycle rate) and abuse methodology (including calorimetry, short circuit, and overcharge) impact key metrics of safety relative to fresh cells. In general, the conditions used to produce aged cells in these studies have involved extreme temperatures. Thus, we also share more recent calorimetry of cells aged to 80% capacity by relatively mild protocols to understand the abuse response of cells from more typical device operating conditions. These results facilitate a more data-informed risk assessment of aged energy storage systems and the development and adoption of appropriate failure mitigation strategies. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Photovoltaic solar modules, which are mostly made of silicon based solar cells, are still expensive to the common people of Nepal. The high cost is, mainly, due to the processing difficulties to get pure crystalline silicon. Here, we present results on devising efficient and low-cost dye sensitized solar cells (DSSCs). The solar cells were fabricated from transparent thin film of zinc oxide (ZnO), as a semiconductor, on top of which a thin layer of synthetic organic dye was deposited for efficient light harvesting. In order to achieve the films with optimum conditions for solar cell fabrication, we prepared transparent thin films of ZnO of various thicknesses and characterized by measuring their light transmittance by UV-Visible spectrophotometry. The results clearly show variation in transmittance curves with variation in film’s thickness. Also for finding appropriate sensitizer for ZnO nanoparticles, we extensively investigated the light absorbance of synthetic organic dyes. Among the dye species investigated, Green-VS, Patent-Blue, and Black-ADLI show strong absorbance over the wide range in the visible spectrum, demonstrating prospect of utilizing for DSSCs. Then prototype solar cells from ZnO film with various thicknesses were constructed and were sensitized with the mixture of Green-VS and Black-ADLI dyes (with 1:1 ratio). The measured photo-voltage and photo-current from solar cell, from our modest ZnO film, after irradiation with 200 W commercial bulb (calibrated with Pyranometer) as a light source, were about 20 mV and 1 μA, respectively. Also, with increment of the power of radiation both the measured photo-current and photo-voltage increase. Performance of the cell in real sun condition has also been made. With the solar radiation power of 930 W, the observed photo-voltage and photo-current were ca. 230 mV and 50 μA, respectively. DOI: http://dx.doi.org/10.3126/bibechana.v11i0.10380 BIBECHANA 11(1) (2014) 53-59

Silicone elastomers exhibit a broad range of beneficial properties that are exploited in biomaterials. In some cases, however, problems can arise at silicone elastomer interfaces. With breast implants, for example, the fibrous capsule that forms at the silicone interface can undergo contracture, which can lead to the need for revision surgery. The relationship between surface topography and wound healing--which could impact on the degree of contracture--has not been examined in detail. To address this, we prepared silicone elastomer samples with rms surface roughnesses varying from 88 to 650 nm and examined the growth of 3T3 fibroblasts on these surfaces. The PicoGreen assay demonstrated that fibroblast growth decreased with increases in surface roughness. Relatively smooth (approximately 88 nm) PDMS samples had ca. twice as much fibroblast DNA per unit area than the 'bumpy' (approximately 378 nm) and very rough (approximately 604 and approximately 650 nm) PDMS samples. While the PDMS sample with roughness of approximately 650 nm had significantly fewer fibroblasts at 24h than the TCP control, fibroblasts on the smooth silicone surprisingly reached confluence much more rapidly than on TCP, the gold standard for cell culture. Thus, increasing the surface roughness at the sub-micron scale could be a strategy worthy of consideration to help mitigate fibroblast growth and control fibrous capsule formation on silicone elastomer implants.

An important issue in field emission vacuum microelectronics is the stability of the field emitters with the residual ambient gas. Particularly important is that the field emitter tips made of refractory metals like molybdenum, niobium and tungsten are susceptible to oxidation. The corresponding metal oxides are insulating and adversely affect the emission current characteristic by increasing the width of the effective tunneling barrier. With this perspective, we studied iridium oxide field emitters to evaluate the characteristics of conductive oxide tips. We studied the field emission characteristics of iridium and thermally prepared iridium oxide field emitters using field emission microscopy and current–voltage measurements. We found that, upon oxidation, the voltage required to achieve the desired emission current desire dropped significantly. In addition, oxidation led to a decrease of emission current fluctuations. The development of stable conductive oxide field emitters should improve the performa...

Distillation is a process in which a liquid fusion is separated into its component parts by vaporization technique. It is broadly used method for separating mixtures. To separate a mixture which has different boiling points enforced into gas phase and then the gas is condensed into liquid form and collected. Distillation column is widely used in pharmaceutical industries solvents. Acetone with water has been used in this process. Based on the boiling point of the solvent they are been placed at the top end bottom end of the extraction column. Before the extraction process could be done the two solvents has to be analyzed whether it is suitable for the distillation process. This analysis is done by PHA and PSSR test. It is done so that losses such as corrosion, error, leakage etc can be avoided. The output obtained is purified solvent which depends upon the input. The entire system is been controlled by PLC and SCADA. By continuous distillation column temperature, pressure, flow and level are been measured and controlled automatically. So the advantage here is time consumption, safe environment and smoothly handled.

A simple method for the evaluation of materials suitable for the fabrication of field emission displays is presented. The technique is based on the sensitivity of a large field emitter array to the outgassing or desorption of gas species from thin films under electron beam excitation. We demonstrate the usefulness of the technique for the evaluation of thin film materials suitable for use with Mo field emitter arrays.

Recent technical and market advances have created a resurgence of interest in miniature vacuum devices based on field-emission vacuum microelectronics. For several operational conditions, these new devices have inherent advantages over their solid-state counterparts. Vacuum microelectronic devices are less sensitive to temperature variations, provide high-speed switching capabilities, and are less susceptible to radiation damage. In addition, electron beams can be steered with external electric and magnetic fields, and electron devices are capable of operation with high current densities. In this article, we describe the development of this new generation of vacuum microelectronic devices and showcase some exciting applications arising from this technology, ranging from flat-panel displays to electron beam devices.

We report field emission microscopy images from single walled carbon nanotubes showing resolvable fine structure with five- and six-fold symmetry. We present evidence indicating that these images have atomic resolution and that they depict the electronic structure of individual nanotube caps under high-field conditions. Fine structure is observed only after removal of surface adsorbates. Prior to adsorbate removal, these images show symmetrical lobed patterns and several other behaviors characteristic of chemisorbed resonant tunneling states.

Multilayer indium-tin-oxide (ITO)–Ag–ITO stacks were evaluated as transparent conductors for flexible organic light-emitting diode (OLED) displays. The ITO–metal–ITO (IMI) samples exhibited significantly reduced sheet resistance over ITO and greater than 80% optical transmission. The IMI films deposited on plastic substrates showed dramatically improved mechanical properties when subjected to bending both as a function of radius of curvature as well as number of cycles to a fixed radius. OLEDs were fabricated on both ITO and IMI anodes, and the devices with IMI anodes showed improved performance at current densities greater than 1mA∕cm2 due to the improved conductivity of the anode.

Semiconductor luminescent Quantum Dots (QDs) constitute a growing area of research for biological imaging and other biomedical applications. One of the main challenges is to provide QDs with a biocompatible and easy to functionalize surface while retaining the core optical properties. Gelatine is an excellent candidate for that purpose as it is a very common natural polymer, highly biocompatible and bearing various functional groups. Here we present a simple, one-pot method for manufacturing gelatinated QDs with chosen optical properties.

Extracting large field-emission currents from individual single-walled carbon nanotubes degrades their current–voltage behavior and changes the nanotube structure. Field-emission microscopy observations and field-emission current–voltage measurements revealed behavior characteristic of local heating, followed by thermally assisted field evaporation of the atoms on the end of the nanotube, and subsequent restructuring of the cap. Field evaporation of carbon was found to result in reduction of the length of the tube without catastrophic arcing events. This process defines the upper limit for the field-emission current that can be obtained from an individual single-walled nanotube.

We report on the development of solid-state hydrogen sources utilizing thin-film metal hydrides. We demonstrate that integration of these metal hydride thin films facilitate a practical method to introduce controlled amounts of hydrogen into sealed field emission display assemblies. To prove the concept, we operated Mo field emitter arrays without emission current loss for 400 h of continuous operation with titanium-hydride-coated stainless steel anode plates. Comparable arrays operated in the absence of hydride films, but in ultrahigh vacuum, had emission current degradation of over 50% in less than 100 h of operation.

Residual gas analysis of a number of field emission displays showed that argon desorbed from molybdenum metal lines was the dominant gas in sealed vacuum packages. We present experimental results on the emission characteristics of molybdenum field emitter arrays in argon ambient. In argon, the emission current dropped rapidly similar to that in oxygenic gas ambients. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest a model based on shallow implantation of argon into the field emitter tips that increases the effective width of the tunneling barrier. Experimental support for this model comes from the following observations: emission current degraded only when the device was turned on; after gas exposure, significant current recovery which followed diffusion type behavior was noted; degradation and recovery rates were functions of partial pressure; and no detectable effects associated with sputtering were observed. This mechanism is also consistent with ion pumping known to occur in field emission displays.

Iridium field emitter arrays were fabricated using Spindt tip process. Ir field emitter cones show an aspect ratio of 0.95, slightly less than Mo field emitter arrays fabricated using the same microfabrication process. When compared to the Mo field emitter arrays, the current–voltage characteristics of the Ir arrays were found to scale with the work function difference between Ir and Mo. Under ultrahigh vacuum conditions, the emission current stability of the Ir arrays measured over 180 h was found to be similar or slightly better than the emission stability of Mo arrays. However, when operated in the presence of O2, Ir field emitter arrays proved to be more robust and showed improved emission current stability versus their Mo counterparts.

Recent studies have shown a current limiting effect in the field emission behavior of carbon nanotubes. In this letter, we demonstrate that an individual nanotube exhibits current saturation above 100 nA of emission current, and we show that this current saturation is a direct result of an adsorbate-enhanced field emission mechanism. Current saturation results from the displacement of adsorbates from configurations of tunneling enhancement as electric field and current are increased. Saturation is concurrent with rapid fluctuations in emission current and distinctive changes in the field emission patterns. At high fields, the adsorbate states are completely removed from the nanotube. A single, clean single-walled nanotube shows no evidence of current saturation for emission currents reaching 2 μA.

We demonstrate long-term field emission stability from single-walled carbon nanotubes. Unballasted nanotubes operate without degradation for over 350 h at 10−9 Torr. Nanotubes are shown to be significantly less sensitive to operating environments than metallic emitters. In 10−7 Torr of H2O, we demonstrate 100 h of continuous bias field emission with no current degradation. Protrusion growth and current runaway, typical problems for unballasted metal emitters, are not observed with nanotubes. Single-walled nanotubes do show susceptibility to damage by oxidation. We suggest that the exceptional environmental stability of carbon nanotubes is due to a combination of geometry, strong carbon bonding, and the lack of protrusion growth.

We present an improved liquid crystal microthermography technique for the detection of defects in large area field emission cathode arrays. Defects can cause electrical leakage paths, leading to localized heating at the defect location. The thermal gradients at these hot spots can be detected by liquid crystal microthermography, but, the direct placement of the liquid crystal is a two step process. First the liquid crystal is deposited by spin coating the device and the liquid crystal has to be removed from the device after the test. This process, apart from being time consuming, can lead to contamination of the test device. In this article, we present an improved liquid crystal microthermography technique for the detection of hot spots in field emitter arrays. The improvement is obtained by hermetically sealing the liquid crystal material inside a packaged assembly made from a glass support and a thin plastic membrane. We have used the new method for the detection of hot spots in large area field emissio...

The effect of thermal growth conditions on the morphology and surface work function of iridium oxide thin films grown by annealing Ir thin films in an O2 ambient is presented. The samples were analyzed using x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and photoelectric work function measurements. It is found that, with increasing temperature, IrO2 changes from (110) oriented to a mixture of (110) and (200) during the oxide growth. This is manifested as a sharpening of the photoelectric energy distributions at 800 °C. The surface work function was determined to be 4.23 eV using ultraviolet photoelectron spectroscopy. X-ray photoelectron spectroscopy analysis shows that IrO2 starts to form at 600 °C accompanied by surface roughening. Annealing the Ir film at 900 °C in O2 ambient leads to almost complete desorption of the film.

The use of brittle materials in flexible displays requires the understanding of the mechanical limitations of the materials and the various display architectures. We discuss various approaches to mechanical bend tests for components of flexible displays and describe a new test method based on a three-axis motion. We discuss the mechanical limitations of indium tin oxide (ITO) as a transparent conductor, and present results for a more mechanically robust multilayer transparent conductor made of an ITO-metal-ITO (IMI) stack. The IMI structures showed dramatically improved mechanical properties when subjected to bending both as a function of radius of curvature as well as number of cycles to a fixed radius. Organic light emitting devices fabricated on IMI anodes showed improved performance compared with those made on ITO anodes at current densities greater than 1 mA/cm2 due to the improved conductivity of the anode. We discuss the difficulties in analysis of the mechanical failure of transparent thin film permeation barriers. We present a novel approach for etching barrier-coated polymer substrates such that film cracking is readily visible. We report on the bend test results for sputter- deposited SiOxNy films.

Due to their unique electronic and structural properties, carbon nanotubes have attracted substantial attention as field emitters in vacuum microelectronics. Field emission from carbon nanotubes with high current densities at low applied electric fields has been demonstrated by several groups. The mechanism behind the field emission remains unclear. Not only are most samples mixtures of single-walled and multi-walled nanotubes with widely varying electrical properties, but the emission behavior reported for nanotubes varies widely. To get a better perspective on these basic issues, we studied the thermal field emission characteristics of single walled carbon nanotubes (SWNT) using a atomic resolution field emission microscope (FEM).

The continued shift towards the integration of diverse functions into single chips and chip assemblies requires a new vision in microelectronic systems integration. Over the last decade or so, there has been a tremendous push towards systems on chip (SoC) approach for increased functionality. While systems on a chip has received much deserved credit for the size and cost reduction of many products, a true system on a chip solution has not been practical for a number of applications. In some cases, this is simply an issue of chip size, in others material compatibility (Si and GaAs), in yet others electrical compatibility (high voltage, RF, analog, with digital) and in some others the overall cost of integration on silicon, even if technically feasible. The need to combine diverse materials and technologies to achieve increased functionality with decreased size and weight, along with the ever present pressure for lower cost, has created the opportunity for new system level integration opportunities. Among the new concepts, system in a package (SiP) and system on a substrate (SoS) have received the most attention. System in a package is a natural extension of system on a chip concept. Currently, there are aggressive programs to develop SiP capabilities to allow rapid, cost effective design and fabrication of subsystem level packages. System on a substrate is an emerging concept based on the integration of technologies in a wide area of electronics. SoS will take the next step to the full system level (e.g. a monolithic radio). However, there is another important concept that seeks the same objective of system-level integration, but with a different set of drivers. In situations where the product is required to be a certain size (e.g. a display or a smart card), further size reductions of the components is no longer productive. This creates the opportunity for alternative technologies such as thin film transistors and plastic substrates. Integration of these technologies offers the potential for significant cost savings because of lower manufacturing costs, and light weight, wearable, flexible products by elimination of today's rigid substrates. Such technologies not only offer new capabilities, but also change the basic premise of the electronics industry. We could move from the microelectronics to the macroelectronics era. In this paper, we will present an overview of this diverse and emerging technology.

Field emission displays can be seriously limited by the rapid current degradation of Mo field emitter arrays primarily due to poor vacuum conditions inside their thin vacuum packages. There have been a number of studies to understand the interaction mechanisms. However, we find that models that have been proposed so far are not consistent with observed device behavior in a variety of gas ambients including inert gases and hydrogen. In this paper, we present a summary of our results on residual gases inside a large number of field emission displays, and the effects of these gases on emission behavior. We describe how these issues and the inter-electrode spacing leading to local pressure buildup impact device life. We present an alternate model based on shallow ion implant to explain the observed device behavior.

Oxidation of emitter surfaces can be a serious problem for Mo field emitter arrays. We studied the oxidation and related changes in the electronic properties of Mo thin films as a function of annealing temperature. Experiments were done on Mo thin films prepared on Si and sodalime glass substrates. These films were thermally oxidized and characterized using a variety of techniques including x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and thermal desorption spectroscopy (TPD) methods. For films oxidized below 400°C, partial oxidation was observed, with MoO3(110) being the principal oxide phase. However, at a temperature of 500°C and above, oxidation of the film was complete. Electrical characteristics of the films undergo a rapid transition from semiconductive to highly insulating at temperatures between 475 to 500°C. Temperature programmed desorption spectra showed that the oxides are stable at elevated temperature with only a principal O2 desorption peak at approximately 786°C.

We report the spontaneous formation of uniformly distributed arrays of “tips” (tall conical hillocks) upon oxidation of palladium (Pd) thin films. The formation of the palladium oxide tips depended on the thickness and granularity of the Pd film and on annealing and oxidation conditions. As the Pd film thickness increased from 40 to 200 nanometers, the average height of the tips increased from 0.5 to 1.2 micrometers, their height distribution became broader, and their density decreased from 55 × 10 6 to 12 × 10 6 per square centimeter. Enhanced photoelectron emission from locations corresponding to the tips suggests their possible use in field emission applications.

Field emission current-voltage characteristics and simultaneous field emission electron energy distributions have been measured using single tip gate diodes. An energy distribution is generated at each step of a current-voltage characteristic using a compact low-cost simulated hemispherical energy analyzer. A PC programmed with graphics-based data acquisition software is used for data acquisition and control. The PC is connected to a CAMAC crate and a picoammeter through a GPIB interface. The picoammeter measures the current leaving the tip and the field emission electrons are energy analyzed, detected and processed in the CAMAC crate. The CAMAC crate also sends control voltages. to the gate anode and the energy analyzer. This apparatus was used to measure tip work functions and Fowler-Nordheim tip shape parameters for Mo and IrO2 field emission tips. Work function measurements from field emission tips are compared to photoelectric work function measurements from flat surfaces.

Field emission displays are currently undergoing rapid transition from laboratory prototypes into commercial display components. Display lifetime and reliability are critical issues that will determine success of these displays in the marketplace. In this paper, we will summarize issues affecting field emission display lifetime and a roadmap for creating long life field emission display devices.

A versatile analytical system based on thermal desorption spectroscopy of thin films is presented. We have found the apparatus to be a useful tool for measuring the desorption characteristics of trapped gases in physical vapor deposited thin films and in determining the thermal stability of multi-component thin film compounds and multilayer structures. The system was also found to be a convenient tool for determining outgassing properties of thin film and thick film materials for vacuum microelectronic device applications.

Field emission displays can be seriously limited by current degradation of Mo field emitter arrays, primarily due to inadequate vacuum conditions inside their thin vacuum packages. Most lifetime studies describe the deleterious effects of short exposures to oxygenic gases on device performance. Here, we review experimental results on the emission characteristics of molybdenum field emitter arrays in a variety of gas ambients for extended periods. We find that even in inert gas, the emission current degrades rapidly, comparable to that observed in oxygenic gas ambients. Surprisingly, after exposure when the device is again operated under high vacuum conditions, various levels of current recovery can be observed. No evidence for ion sputter damage is observed. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest that these results point toward a model common for all gaseous ambients based on shallow implantation of ions into the field emitter tips. This creates a near surface layer that modifies the tunneling barrier, and thus subsequently the emission current. Support for this mechanism comes from several experimental observations. The implant degradation model is also consistent with devices that incorporate a field emitter ion pump process as a means to reduce pressure in the sealed vacuum package.

Carbon atoms forming the cap of a carbon nanotube are selectively removed through a technique that causes field evaporation during field emission. The resulting changes in the spatially resolved electronic structure are imaged in real time using field emission microscopy. We demonstrate that through repetitive field evaporation cycles, a variety of cap states can be produced on the same nanotube. We measure differences in the electrical properties due to the presence of different cap states.

A thin film hydrogen ion source integrating field emission cathode arrays with metal hydride thin film technology is demonstrated. A prototype broad area hydrogen ion source was fabricated using Mo field emitter arrays to induce electron stimulated desorption and ionization of hydrogen from titanium hydride thin films on the gate electrodes. The hydrogen ion generation characteristics of the device were measured. In addition, these ion sources provide for the easy operation in pulsed mode by the direct modulation of gate voltage.

Field emission displays can be seriously limited by the rapid current degradation of Mo field emitter arrays primarily due to poor vacuum conditions inside their thin vacuum packages. There have been a number of studies to understand the degradation mechanisms. However, we find that degradation models that have been proposed so far are not consistent with observed device behavior in a variety of gas ambients. In this paper, we present a summary of our results on residual gases inside field emission displays and the effects of these gases on emission behavior. We describe how these issues and the inter-electrode spacing leading to local pressure buildup impact device life. We present an alternate model based on shallow ion implant to explain the device behavior.

We demonstrate that having hydrogen inside the operational ambient of field emission displays results in significantly improved display life. However, improving device performance by incorporation of gas phase hydrogen into thin glass packages is a difficult task. In this paper, we report on the development of solid state hydrogen sources utilizing thin film metal hydrides, which can be easily integrated into field emission displays. We show that these metal hydride thin films provide a practical means to incorporate solid state hydrogen sources into field emission displays. Using stainless steel anodes coated with TiH2 thin films, we demonstrate the successful operation of molybdenum field emitter arrays without emission current loss for 400 hours of continuous operation. Comparable arrays operated in the absence of hydrogen, but in an ultrahigh vacuum had emission current degradation of over 50% in less than 100 hours of operation.

We report on a process for the fabrication of Mo2C and HfC refractory metal carbide field emitter arrays using a modified Spindt tip fabrication process. Measurements of the aspect ratios of emitter cones showed that Mo2C tip structures have an aspect ratio similar to Mo field emitter tips. Where as with HfC, tip structures with a higher aspect ratio than either Mo or Mo2C were obtained. The measured aspect ratios for Mo, Mo2C, and HfC tips were 1.09, 1.10, and 1.20, respectively. While the target materials to fabricate the arrays were the appropriate carbides, x-ray photoelectron spectroscopy of the carbide films showed evidence for the presence of significant amount of oxygen throughout the films, mostly in the form of oxycarbides. The primary purpose of this report is to describe materials and processes suitable for large area field emission display applications. However, we also provide preliminary electrical results which demonstrate the feasibility of fabrication of metal carbide field emitters and ...