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Interdigital structures are realized on silicon substrates with high sensitivity to acceleration. The process employs a combination of anisotropic back-side micromachining with front-side vertical deep reactive ion etching of silicon. The incorporation of silicon-based nano-structures on the vertical planes of fingers leads to a significant increase in the capacitance of the device from 0.45 for simple planes to 40pF for the nano-structured planes. Such structures show high sensitivity to inclination and accelerations, which could be due to field emission of electrons from nano-metric features. Around 8% change in the capacitance is observed upon a tilting sensor from 0? to 90? angle, which makes it proper for possible use as an earthquake sensor. A preliminary model for the capacitance and its dependence on the measurement voltage is presented. Incorporation of silicon-based nano-structures on the vertical planes of fingers.Significant increase in capacitance of nano structured nanostructured device.High sensitivity to inclination and accelerations.Around 8% change in the capacitance upon the tilting sensor from 0 to 90 degree 90? angle.Preliminary model for the capacitance and its dependence on the measurement voltage.

Carbon nanotubes have been used as cold cathode emitter in the fabrication of a sensitive field emission pressure sensor. Vertically aligned carbon nanotubes were grown using the plasma-enhanced chemical vapor deposition (PECVD) on a micro-machined silicon substrate. A silicon membrane was used as the flexible anode against the fabricated CNT-based cathode. A 2-μm thick SiO 2 layer has been applied as the anode–cathode spacer and the output results have been compared with a similar sensor with 120 μm spacer. Results show that the sensitivity and the output emission current of the fabricated sensor have been highly improved by decreasing the anode–cathode spacing. Measurements show an ultra-high sensitivity of about 100–970 μA/kPa which is higher than the similar pressure sensors. Low working voltage and high thermal stability of the fabricated sensor are among the other advantages of the presented sensor.

In this paper, investigation of field-emission devices on silicon substrates using vertically grown carbon nanotubes (CNTs) is reported. CNTs were grown in a plasma-enhanced chemical vapor deposition reactor from the Ni catalyst islands at a temperature of 650 °C. The grown CNTs are electrically isolated using a TiO 2 film. Chromium- or phosphor-doped silicon is deposited on the TiO2 film as the gate layer. The effects of the surrounding gate as well as the current-voltage behavior are discussed. By applying a proper negative gate voltage around 7 V, a dramatic drop in the emission current is observed. Moreover, the electrical behavior of such devices has been examined at different anode-cathode distances. Under proper conditions of the anode-cathode spacing, a saturation is observed in the anode current with respect to the anode-cathode voltage. In addition, a preliminary field-emission display has been fabricated.

Branched carbon nanostructures have been successfully grown on interdigital comb-like structures for a gas sensing application. Field emission scanning electron microscopy has been utilized to investigate the morphology and structure of the grown nanostructures at different stages of growth process. Tunneling current of the fabricated sensor has been measured when a monotonically increasing voltage is applied between the electrodes. The effect of exposure to three different gases on the measured current has been studied. A data processing on the measured current voltage characteristics results in the evolution of various peaks at distinct voltages which depends on the type of the gas.

We report the realization of a miniaturized H 2 S gas sensor using micromachining of silicon substrate assisted by a porous oxide formation for selective patterning of CuO-doped SnO 2 layers. The formation of sensing material (SnO 2 /CuO) is through a sol–gel spin coating process. The sol–gel adhesion to porous silicon dioxide is significantly better than regular plain SiO 2 surfaces. The formation of a nano-porous and highly textured oxide layer is feasible through a sequential reactive ion etching process which utilizes one short step of reactive etching followed by another step of passivation. By repeating these subsequences for many times, desired textures are created which in turn would lead to a highly selective deposition of the sol–gel layer on the porous silicon dioxide. The sensor response to various H 2 S concentrations has been investigated showing a high sensitivity. Since the device is realized on a silicon-based membrane, the effect of electric current passing through the heating element has also been studied. SEM and XRD analyses have been used to investigate the surface morphology and crystallinity of SnO 2 and porous SiO 2 films.

Si nanocrystals have been prepared by hydrogenation and subsequent annealing of as-deposited amorphous Si layers on glass and Si substrates. The hydrogenation process has been performed at 350 °C under radio frequency hydrogen plasma. The nanocrystallites were processed by sequential reactive ion etching to allow light emission. Photoluminescence (PL) measurements demonstrate that the nanocrystallites emit light in the range of 500–570 nm. The evolution of nanocrystals has been studied using scanning electron microscopy, while atomic force microscopy and transmission electron microscopy have been utilized to examine the structure of the Si nanocrystals. Multilayer luminescent Si nanocrystals have been fabricated using alternating layers of Si nanocrystals and Si oxy-nitride. Bilayer structures have higher efficiency than a single layer structure, while multilayers with three layers of luminescent nanocrystals and above did not show a higher PL intensity. Transparent light emitting diodes have been realized based on multilayer luminescent Si nanocrystals that displayed bright emission which was visible to the naked eye in a bright room.

We have investigated the entrapment of colon cancer cells with two different metastatic grades on arrays of multiwall carbon nanotubes. It has been observed that the fraction of entrapment of higher metastatic cancer cells is significantly more than lower metastatic grades. The observed effects are due to the more deformability and softness of higher metastatic malignant cells in comparison with the lower ones both for live and fixed cells. Also cell fixation results in a decrease of their entrapment due to an increase in cell rigidity by the fixation process. The present phenomenon describes a new application of vertically aligned carbon nanotubes to distinguish the healthy and cancerous cells by means of their different deformability properties during entrapment on such arrays.

Highly controllable silicon nano-grass formation is reported based on a hydrogen assisted reactive ion etching method in desirable shapes and locations. By controlling the etching parameters, one can achieve grass-free high aspect ratio vertical or three-dimensional structures on silicon substrates. On the other hand, one can program the etching procedure to arrive at grass-full surfaces and structures in pre-designed features and in desired places. The improved wetting properties of the grass-full surfaces have been investigated. In addition, the grass-full surface has been used to entrap kidney cells. Aspect ratios of the order of 40–50 and features of the size of 250 nm can be achieved.

We report a novel interdigital sensor and actuator device based on branched tree-like carbon nanotubes (CNT) on silicon-based membranes with a high capacitance value. The presence of tree-like CNTs leads to a high overlap between interdigital fingers owing to their three dimensional nanometric features, hence increasing the value of the capacitance from 0.2 to 15 pF. The electromechanical behavior of the device has been investigated with monitoring capacitive characteristics of the sensor. An almost linear rise in the capacitance value by applying the external voltage is observed which could be due to the modulated overlapping between neighboring electrodes. The response of the sensor/actuator device to various frequencies has been studied.

Novel, high capacitance interdigital structures based on branched carbon nanotubes (B-CNTs) are realized using plasma enhanced chemical vapor deposition. Extensive overlapping between parallel fingers due to the branched carbon nanostructures leads to high capacitance values in the fabricated interdigital structures. A significant rise in the capacitance up to 100 times is reported by means of branched carbon nanotubes. The high electron emission of such nanostructures over regular CNTs can be applied to realize high sensitivity sensors. To investigate the functionality of fabricated B-CNT-based actuator, both sensor and actuator configurations have been designed on a silicon-based membrane and the electro-mechanical response of the whole structure has been investigated. These structures show a superior actuation behavior owing to their high capacitance due to extensive overlapping fingers.

Surface plasma treatment in a reactive ion etching system is used to observe a considerable decrease in permeability of polyethylene terephthalate to gases. The effects of oxygen plasma on the surface properties and morphology of PET polymers are investigated by scanning electron microscopy (SEM), x-ray photo-electron spectroscopy (XPS) and atomic force microscopy (AFM). In addition, the optical transmission properties of the treated samples have been investigated corroborating the findings of SEM and AFM analyses. Moreover, the penetration of air through the treated substrates was investigated using a vacuum test. The treated PET substrates can be used to realize flexible plasma display panels.

Etching of poly-ethylene terephathalate (PET) is achieved using a chemical solution in di-methyl-formamide assisted by ultra-violet illumination. Deep vertical features suitable for plastic micro-machining, are obtained with features of the order of 2 μm and aspect ratios of the order of 10. By using tin (Sn) as the masking layer, the problem of crack formation on the PET surface during this photochemical etching technique is totally resolved. High etch-rates as 20 μm/h are obtained at a low etching temperature of 60 °C. To improve the thermal dissipation during the etching and to minimize the plastic shrinkage, a layer of silicone–rubber is applied on the backside of the PET. We have successfully fabricated and assembled an all-plastic one directional micro-valve. Preliminary plastic-based micro-structures are demonstrated.

The authors report the realization of highly featured three-dimensional structures on silicon substrates with a single masking layer using a hydrogen-assisted deep reactive ion etching process. Oxygen, hydrogen, and SF6 are used in a sequential passivation and etching process to achieve high aspect ratio features. By controlling the flows of these gases and the power and timing of each subsequence, it is possible to achieve desired deep vertical etching, controlled underetching, and recovery, yielding three-dimensional features directly on silicon substrates. Etch rates up to 0.75 μm/min have been achieved with a low plasma power density of 1 W/cm2. In addition, features with a controllable underetching and recovery with more than 8 μm in sidewall recession have been achieved. Furthermore, values of aspect ratio higher than 40 can be obtained. The formation of three-dimensional features with nanowall structures is reported.

A considerable decrease in permeability of polyethylene terephthalate (PET) films by means of surface plasma treatment in a reactive ion etching system is reported. The effects of oxygen and hydrogen radio frequency plasma on the surface properties of PET polymers are investigated by infrared spectroscopy, scanning electron microscopy (SEM), and X-ray photon spectroscopy (XPS). The surface morphology of the samples has been investigated using SEM and atomic force microscopy (AFM). The optical transmission spectroscopy has been studied further confirming the significant effect of O-plasma. Also the penetration of air through the treated substrates was investigated using a vacuum test. It is found that oxygen and hydrogen plasmas lead to about four-fold reduction in the penetration of air through the PET films, while the effect of hydrogen plasma has been more significant. In addition, oxygen plasma results in a rougher surface as observed both by AFM and SEM analyses. The formation of nanostructures on PET surfaces has been observed at plasma powers of 0.3 W/cm 2 .

We report the preparation and characterization of high quality silicon dioxide (SiO 2 ) layers from nano-structured silicon thin films on silicon substrates at a maximum processing temperature of 350 °C. Hydrogenation-assisted plasma processing was used to prepare nano-porous silicon from amorphous silicon films and a subsequent plasma enhanced oxidation step converted the nano-crystalline silicon into silicon dioxide. The nano-structured materials were characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. Metal–oxide-semiconductor (MOS) devices were prepared and the electrical properties of the oxide layer were investigated by current–voltage and capacitance–voltage measurements. The composition of the SiO x films was found to be near stoichiometry with a value of ‘ x ’ equal to 1.95 ± 0.18 and a dielectric constant of 3.8 ± 0.2. The leakage current in MOS capacitive devices was well below 1 nA.

In this paper a new asymmetric Schottky barrier MOSFET structure is presented which employs a thin interfacial insulator layer in the metal/silicon junction at the source. This asymmetric structure leads to a considerable improvement in the on/off ratio of the device by significantly lowering the off-current while leaving the on-current of the transistor unaffected. In addition the sub-threshold slope is reduced due to the dominance of the tunneling component of the drive current. The simulation has been performed on a 100 nm channel length device although the fabrication has been carried out on micrometer scale transistors. The results of conventional Schottky and asymmetric devices have been compared both experimentally and numerically, confirming the significant improvement in our proposed structure.

The effect of hydrogenation processing as a pregrowth treatment on carbon nanotubes (CNTs) has been investigated. The growth of CNTs on patterned structures strongly depends on the plasma power during the hydrogenation step. Etching of the patterned nickel occurred at higher hydrogen plasma power densities. By controlling the plasma power of hydrogen plasma applied on catalyst layer and using a refinement process, an array of isolated nanotubes was obtained without using a nanolithography method. Finally, the effects of hydrogen plasma during the growth are represented. This study shows that direction of grown nanotubes depends on condition of plasma during the growth.

Micromachining of (111) silicon wafers by means of a plasma hydrogenation and chemical etching sequence is achieved. Vertical etching is used to define the depth of the craters as well as the thickness of the final suspended silicon body. After protecting the 3-D structure by a thermally grown oxide, a hydrogenation step is used to remove the oxide layer from the bottom of the crater, allowing a lateral underetching. Final exposure of the processed silicon to a KOH solution, etches silicon in a lateral fashion and in the exposed places. A lateral aspect ratio of four to six has been achieved. The evolution of suspended structures on (111) wafers, suitable for sensor fabrication, is feasible without a need to a 3-D lithography. Using this technique suspended interdigital structures have been realized with a depth up to 70 mum. In addition, ultrathin fully suspended structures have been successfully fabricated. A preliminary capacitive accelerometer has been realized and tested on (111) substrate.

We report ultra low temperature lateral crystallization of amorphous silicon films on flexible plastic substrates suitable for the realization of thin-film transistors. A sequential hydrogenation and annealing is necessary to crystallize silicon films aided with an external mechanical stress at a temperature of 170 °C. Ni is used as the seed for the crystallization using a metal induced crystallization method. For the formation of polycrystalline-silicon thin-film transistors, a lateral crystallization is tried where the seed is placed on the source and drain regions and crystallization progresses from the seed regions towards the central parts of the channel of the thin-film transistor. Scanning electron and transmission electron microscopies were used to investigate the morphology and crystallinity of the layers. The fabricated lateral transistors show an on/off ratio of 2000 and an effective mobility of about 25 cm 2 /V s.

Effects of plasma power on the growth of the multi-wall carbon nanotubes (CNTs) are reported. CNTs were grown on the silicon wafers by plasma enhanced chemical vapor deposition (PECVD) method using a mixture of acetylene and hydrogen at the temperature of 650 °C. Plasma powers ranging from zero to 35 W were applied on the samples and the effects of different magnitudes of the plasma power on the growth direction of the CNTs were investigated. Regular vertically aligned nanotubes were obtained at plasma power of 25 W. In order to set on the plasma during the growth, electrical force was applied on the carbon ions. Nickel layer was used as a catalyst, and prior to the nanotubes growth step, it was treated by hydrogen plasma bombardment in order to obtain the Ni nano-islands. In this step, as the plasma power on the Ni layer was increased, the grain size of nickel nano-particles decreased, and hence, nanotubes of smaller diameter were obtained later on. At the last step some anomalous structures of agglomerated CNTs were obtained by controlling the plasma power. Samples were analyzed by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM).

Silicon nano-crystalline structures have been prepared from amorphous silicon films on silicon substrates using direct-current plasma hydrogenation and annealing at temperatures about 450 °C. Plasma power densities about 5.5 W/cm 2 were found to be suitable for the creation of nano-porous layers. The nano-porous structures produced visible luminescence at room temperature as confirmed by photoluminescence spectroscopy. The effects of plasma power and annealing temperature on the grain size and luminescence properties of these layers have been investigated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and photoluminescence. Lowering the temperature during the hydrogenation step led to an increase in the diameter of the grains. In addition, lowering the plasma power density caused the distribution of the porous surface structures to become less widely distributed and the formation of more packed structures resulted.

Vertically aligned carbon nanotubes (CNT) have been grown in a DC-PECVD apparatus on quartz membranes. 〈1 0 0〉-oriented Si wafer has been anisotropically etched in a KOH solution. A mixture of acetylene and hydrogen gases is used to grow CNT while Ni acts as the catalyst layer. As-grown structures have been coated by titanium dioxide using chemical vapor deposition at atmospheric pressure. By means of a polishing and ashing process steps followed by total removing of the quartz membrane both ends of CNTs are opened and nano holes are obtained. SEM analysis is used to study the evolution of such nanostructures.

The fabrication of nanocrystalline silicon light-emitting diodes is reported using a novel plasma-enhanced hydrogenation method. The fabrication process consisted of the deposition of amorphous silicon on a silicon substrate, a hydrogen plasma treatment, and subsequent annealing, and the deposition of TiO2, indium-tin oxide, and metal contact layers. The entire process was performed at temperatures below 400 degC and is compatible with standard silicon fabrication technologies. The current-voltage (I-V) characteristics of the device showed a rectifying diode behavior where electrons tunneled through the thin TiO2 layer and recombined with the holes injected from the P-type silicon substrate leading to photon generation. The structure of the nanocrystalline silicon films was investigated by scanning electron and transmission electron microscopies, and the spectral distribution of the emitted light was measured by a cathodoluminescence

Riveting process is one of the important ways to keep fastening the lap joints in aircraft structures. Failure of aircraft lap joints directly depends on the stress field in the joint. An important application of riveting process is in the construction of aircraft fuselage structures. In this paper, a 3D finite element method is carried out in order to optimize residual stress field in a riveted lap joint and also to estimate its fatigue life. In continue, a number of experiments are designed and analyzed using design of experiments (DOE). Then, Taguchi method is used to select an optimized case between different levels of each factor. Besides that, the factor which affects the most on residual stress field is investigated. Such optimized case provides the maximum residual stress field. Fatigue life of the optimized joint is estimated by Paris-Erdogan law. Stress intensity factors (SIFs) are calculated using both finite element analysis and experimental formula. In addition, the effect of residual stress field, geometry and secondary bending are considered in SIF calculation. A good agreement is found between results of such methods. Comparison between optimized fatigue life and fatigue life of other joints has shown an improvement in the joint's life., {"references":["S.H. Cheraghi, Effect of variations in the riveting process on the quality\nof riveted joints. Int J Adv Manuf Technol 2008: 39: 1144-1155.","R.P.G. Muller. An experimental and analytical investigation on the\nfatigue behavior of fuselage riveted lap joints. PhD thesis, Delft\nUniversity of Technology, Delft, The Netherlands: 1995.","N.E. Frost, K.J. Marsh, L.P. Pook, Metal fatigue. Oxford University\nPress, London, 1974.","A. Trego, D. Cope, Evaluation of damage tolerance analysis tools for lap\njoints. AIAA Journal 2001: 39(12): 2250-2254.","C. Ranse, P.V. Straznicky, Riveting process induced residual stresses\naround solid rivets in mechanical joints. Journal of Aicraft 2007: 44(1):\n323-329.","K. Iyer, C.A. Rubin, G.T. Hahn, Three-dimensional analysis of single\nrivet row lap joints-part I: Elastic-Plastic response. Recent Adv Solids\nStruct 1999: 398: 41-57.","Z. Kaifu, C. Hui, L. Yuan, Riveting process modeling and simulating for\ndeformation analysis for aircraft's thin-walled sheet-metal parts. Chinese\nJournal of Aeronautics 2011: 24: 369-377.","M.R. Urban, Analysis of the fatigue life of riveted sheet metal helicopter\nairframe joints. International Journal of Fatigue 2003: 25: 1013-1026.","C.P. Fung, Smart J., Riveted single lap joints. Part 1: Fatigue life\nprediction. Proceedings of the institution of mechanical engineers, part\nG (Journal of Aerospace Engineering) 1997: 211(1): 13-27.\n[10] C.P. Fung, Smart J., Riveted single lap joints. Part 2: A numerical\nparametric study. Proceedings of the institution of mechanical engineers,\npart G (Journal of Aerospace Engineering) 1997: 211(2): 123-128.\n[11] X. Deng, J.W. Hutchinson, The clamping stress in a cold driven rivet.\nInternational Journal of Mechanical Sciences 1998: 40(7): 683-694.\n[12] M.P. Szolwinski, T.N. Farris, Linking riveting process parameters to the\nfatigue performance of riveted aircraft structures. Journal of Aircraft\n2000: 37(1): 130-137.\n[13] P.M.G.P. Moreira, P.F.P. de Matos,S.T. Pinho, D. Pastrama, P.P.\nCamanho, P.M.S.T. de Castro, The residual stress intensity factors for\ncold-worked cracked holes: A technical note. Fatigue and Fracture of\nEngineering Materials and Structures 2004: 27(9): 879-886.\n[14] J.J.M Rijck, J.J. Homan, J. Schijve, R. Benedictus, The driven rivet head\ndimensions as an indication of the fatigue performance of aircraft lap\njoints. International Journal of Fatigue 2007: 29: 2208-2218.\n[15] H.K. Yoon, S.P. Lee, B.H. Min, S.W. Kim, Y. Katoh, A. Kohyama.\nFatigue life and fatigue crack propagation behavior of JLF-1 steel.\nFusion Engineering and Design 2002: 61: 677-682.\n[16] P.C. Paris, F. Erdogan, A critical analysis of crack propagation laws.\nTransactions ASME Journal of Basic Engineering 1963: 85: 528-534. [17] J.L Beuth, J.W. Hutchinson, Fracture analysis of multi-site cracking in\nfuselage lap joints, Computational Mechanics 1994:13: 315-331.\n[18] J.J.M. Rijck, S.A. Fawaz, Schijve J., Benedictus R., Homan J.J., Stress\nanalyses of mechanically fastened joints in aircraft fuselages, 24th ICAF\nSymposium, Naples, 2007."]}

The effects of RF-Plasma hydrogenation and applied mechanical strain on the crystallization of silicon layers deposited on plastic substrates have been investigated where the maximum temperature remained below 170 °C for the entire process. The structural properties of the samples have been studied by optical, scanning-electron and transmission-electron microscopy where the nano-crystallinity of the silicon layers has been confirmed. The maximum average diameter of the silicon grains was 4.5 nm and occurred for an applied tensile strain of 4%. In addition, a thin-film transistor on a plastic substrate has been fabricated and found to possess an electron mobility of 2.4 cm2/V s.

Anisotropic etching of silicon is achieved in the presence of ultra-violet exposure in a solution containing hydrofluoric/nitric/acetic acids (HNA). The HNA solution is typically used for polishing silicon and etching polysilicon due to its isotropic etching property. In the technique proposed in this paper which is called UV-HNA, the etching of silicon is enhanced in the direction determined by UV exposure. A mixture of HF/HNO 3 /CH 3 COOH with a relative composition of 1:15:5 seems suitable for revealing 〈111〉 planes with an etch rate of 10 μ m/h at 35 °C. The bottom of the etched craters is hillock-free and etch rates as high as 60 μ m/h can be achieved using higher concentration of HF acid in HNA solution. In the latter case the etching is more isotropic and mask undercut is observed. Also membranes with a depth of 400 μ m are fabricated on n -type Si 〈100〉 with a thickness of 500 μ m by means of standard 34 wt% solution of KOH at temperature of 60 °C. Problems encountered during the experiment, and their solutions are discussed and results of these experiments are reported.

PECVD-grown carbon nanotubes on (100)silicon substrates have been studied and exploited for electron emission applications. After the growth of vertical CNT's [Y. Abdi, J. Koohsorkhi, J. Derakhshan ...

The preparation of porous silicon films by DC-plasma hydrogenation and subsequent annealing of amorphous silicon films on silicon and glass substrates is reported for the first time. The effects of ...

DC plasma display panels are fabricated on flexible polyethylene terephtalate (PET) substrates. Each pixel consists of laterally placed anode and cathode electrodes. All electrical elements are formed on a single PET substrate, whereas a second substrate is needed to encapsulate the panel. Silver is used as the metal for each electrode and standard photolithography is used to form each cell. A 150-/spl mu/m-thick layer of a UV-curable polymeric adhesive was used to form barrier ribs to both electrically isolate neighboring cells and to encapsulate the plasma. Conversion of vacuum UV into visible light is possible by blast-embedding of proper phosphor grains into the top substrate. The current-voltage and turn-on voltage versus pressure characteristics are examined. Effect of curvature on turn-on voltage is addressed.

A novel lateral pixel structure where both anodes and cathodes are placed on a single plate is devised to realize monochrome dc plasma display panels. UV curable adhesives are used as the electrical insulating layers for the separation of anode and cathode addressing lines. 5/spl times/6-cm displays have been successfully fabricated on both glass and flexible substrates.

The low–high transition behavior of SnO2-based sensors and the effect of ceria as a major additive are studied. The response of the sensors is studied in the presence of synthetic automobile exhaust gases comprising air and CO and/or C2H6 reducing gases (fuel), with different weight ratios of the air and fuel, defined as air-to-fuel ratio. A sharp S-shape transition is observed in the resistance of the sensor, when the air-to-fuel ratio of the synthetic gas varies. The resistance reads low values if the air-to-fuel ratio is less than a critical value, while passing through the transition point, the sensor resistance shows a dramatic increase. Using a catalytic burning chamber (CBC) just before the sensor, results in a sharp S-shape transition at the stoichiometirc air-to-fuel ratio. For pure SnO2 sensors and without a CBC, this transition point occurs at values other than the expected stoichiometric ratio, whereas for ceria doped SnO2 samples this transition point approaches the stoichiometric value. Using a composition of 10 wt.% ceria in SnO2 leads to a sharp S-shape behavior right at the stoichiometric value. The electrical as well as physical characteristics of ceria–SnO2 layers have been investigated. The proposed structure can be used as a reference-less lambda-ratio sensor for automotive applications.

We report vertical growth of carbon nanotubes using a plasma enhanced CVD technique suitable for realization of field‐emission electronic devices on silicon substrates. Vertically grown carbon nanotubes are formed on silicon substrates at temperatures ranging from 500 to 650°C and at a pressure of 3.5 torr using a mixture of C2H2 and H2 and in the presence of a DC plasma with an applied voltage between 300 and 500 V. Vertical tubes with a height up to 10 µm have been realized. The growth conditions and the emission of electrons from nanotubes have been investigated. By varying the growth temperature during the deposition process, conical structures are formed. The sharp points of such structures make them suitable for realization of field‐emission devices and transistors.

Fabrication of Ge-based thermocouple on polyethylene-terephthalate (PET) plastic substrates is reported. The amorphous Ge film, deposited using electron beam evaporation, is post treated to form a polycrystalline film. The annealing process has been performed at temperatures ranging from 120/spl deg/C to 175/spl deg/C and study of physical characteristics of Ge films using XRD and SEM confirms its crystallinity. A value of 100 /spl mu/V//spl deg/C is extracted for the Ge-Al junctions. The thermocouple fabrication and its response to flow are reported. A novel approach is described to perform the micromachining of PET substrates for the formation of craters and membranes. Di-methyl-formamide (DMF) is used as the solvent of the PET substrate, masked with a Ge/Cu multilayer. An average chemical etch rate of 12 /spl mu/m/h is achieved in the presence of 6.5 mW/cm/sup 2/ of 360-nm UV at ambient temperature.

A self-contained, miniaturized, electrochemical-type solid-reference oxygen sensor is described which uses yttria-doped ceria (YDC) as an oxygen ion conducting solid electrolyte. Unlike conventional oxygen sensors, in which one side of the sensor needs to be directly exposed to the air reference, the oxygen sensor presented in this paper exploits a solid solution of 25 mol% zirconia in ceria as the reference. Designing a combination structure, the sensing capability of this sensor is compared with a YSZ electrolyte oxygen sensor under the same conditions. This novel oxygen sensor exhibits an anomalous behavior in transition from rich-to-lean regimes where the polarity of the created voltage changes from a positive value of +500 mV to a negative value of −150 mV at λ = 1.01.

An ultraviolet assisted chemical etching of plastic is reported in which the etching of PET substrates is anisotropic in the direction of light illumination. A strong solvent as di-methyl-formamide (DMF) is exploited to perform the chemical etching process and patterning of the desired structures is feasible using a Ge/Cu bi-layer as the masking film. Etch rate depends strongly on the intensity of the ultra-violet light and temperature of the solution during this etching process. An average etch rate of 15 m/h is achieved with little mask undercut in the presence of 6–8 mW/cm 2 of 365 nm UV at a temperature of 120 ◦ C. The highest achieved etch rate in this technique is 40 m/h using an intensity of 16 mW/cm 2 for the UV illumination. The effects of solution temperature during etching, the intensity of light, and the amount of the solvent above the sample have been studied. This technique has been applied to etch 80m of PET substrates and to make 40m thick square membranes with an area of 500m × 500m. Also 120m thick micro-gears have been realized with a diameter of 900m. The gears have been freed and installed on their corresponding axels with a diameter of 100m. © 2004 Elsevier B.V. All rights reserved.

Ultrahigh-sensitivity SnO/sub 2/-CuO sensors were fabricated on Si(100) substrates for detection of low concentrations of hydrogen sulfide. The sensing material was spin coated over platinum electrodes with a thickness of 300 nm applying a sol-gel process. The SnO/sub 2/-based sensors doped with copper oxide were prepared by adding various amounts of Cu(NO/sub 3/)/sub 2/.3H/sub 2/O to a sol suspension. Conductivity measurements of the sensors annealed at different temperatures have been carried out in dry air and in the presence of 100 ppb to 10-ppm H/sub 2/S. The nanocrystalline SnO/sub 2/-CuO thin films showed excellent sensing characteristics upon exposure to low concentrations of H/sub 2/S below 1 ppm. The 5% CuO-doped sensor having an average grain size of 20 nm exhibits a high sensitivity of 2.15/spl times/10/sup 6/ (R/sub a//R/sub g/) for 10-ppm H/sub 2/S at a temperature of 85/spl deg/C. By raising the operating temperature to 170/spl deg/C, a high sensitivity of /spl sim/10/sup 5/ is measured and response and recovery times drop to less than 2 min and 15 s, respectively. Selectivity of the sensing material was studied toward various concentrations of CO, CH/sub 4/, H/sub 2/, and ethanol. SEM, XRD, and TEM analyses were used to investigate surface morphology and crystallinity of SnO/sub 2/ films.

Depletion-mode poly-Ge thin-film transistors (TFTs) with an effective hole mobility of 110 cm2/Vs and an ON/OFF ratio of 104 have been fabricated on flexible polyethylene therephtalate (PET) substrates, taking advantage of a novel stress-assisted crystallization technique. Proper manipulation of an otherwise destructive mechanical stress leads to a drastic drop of crystallization temperature from 400°C to 130°C. External compressive stress is transferred to the Ge/PET interface by bending the flexible substrate inward, during the thermal post-treatment. Proper patterning of the a-Ge layer before thermomechanical post-treatment leads to a minimal crack density in the processed poly-Ge layer. Reduction in the crack density plays a crucial role in alleviating the stress-induced gate leakage current emanated from the crack traces propagating from the channel into the gate oxide.

Crystallization of a-Ge was performed on flexible plastic substrates at temperatures as low as 130 °C. Copper has been primarily used as the seed of crystallization, while an external stress was applied onto the flexible substrate to enhance the crystallization. The substrates used for this study were mainly 0.1 mm thick Polyethylene terephthalate (PET) films, which remain flexible during post treatment at low temperatures. Various samples were subject to tensile or compressive stress for the annealing step. It has been observed that only in the case of a compressive stress, crystallization becomes possible. A final electrical sheet resistance of less than 45 kΩ/□ is achieved after an annealing period of 3 h. XRD, SEM and Hall mobility measurement have been exploited to study the crystallization and explain the drastic drop of electrical resistance in samples subjected to external compressive stress. The 〈2 2 0〉 peak of Ge is discernible in the XRD spectra, confirming the crystallization. Also the study of surface morphology using SEM corroborates the crystalline nature of the annealed Ge film and the evolution of cracks. A carrier mobility of more than 110 cm 2 /V s is observed for holes using Hall measurement. The shrinkage of PET during annealing induces compressive stress both in the substrate and the over-layer, in addition to the externally applied stress. This causes the progressive evolution of cracks in the Ge layer and a weak interfacial buckling of the Ge film.

Germanium-induced crystallization of amorphous silicon is reported at temperatures below 500 °C. Thick silicon films of 0.1 μm are covered with 500 A of germanium as the seed of crystallization. Applying an electric current enhances the growth from both cathode and anode sides. Crystallinity of the samples, treated under different annealing conditions, has been examined using XRD, SEM and TEM analyses. All these techniques verify the polycrystalline nature of the annealed films. The value of the applied voltage plays a crucial role in the crystalline quality of Si layers. While samples treated without an external voltage are not polycrystalline, an electric voltage of 10 V applied for a 1 cm separation between anode and cathode, seems suitable for achieving good polycrystalline Si layers. By increasing the applied voltage to 100 V, severe degradation is observed in both electrical and physical characteristics of the films. The size of grains varies between 0.1 and 0.2 μm, as observed using SEM.

Polysilicon films are grown on ordinary glass substrates at temperatures as low as 380/spl deg/C using a novel ultra-violet assisted metal-induced-crystallization technique. The silicon films grown using this method are suitable for the fabrication of thin film transistors. Samples prepared, consist of 1500 /spl Aring/ of silicon film deposited on 1000 /spl Aring/ silicon nitride and 2000 /spl Aring/ of chromium layers, and Ni is used as the seed for crystallization. Annealing occurred in the presence of an ultra-violet exposure, leads to a high crystallinity of silicon film as examined using TEM, XRD and SEM. The lateral growth as the main feature of this technique is presented using optical microscopy analysis. The preliminary results of transistor fabrication on ordinary glass is reported. Transistors fabricated using this technique show a hole mobility of 50 cm/sup 2//Vs.

A UV-assisted metal-induced crystallization technique is reported to grow poly-Si films on glass at temperatures around 400 °C. Samples prepared consist of 150 nm of silicon film deposited on 100 nm silicon nitride and 200 nm of chromium layers, and Ni is used as the seed for crystallization. Annealing in the presence of an ultraviolet exposure leads to a high crystallinity of silicon film as confirmed with XRD, TEM and SEM analyses. Incorporation of the chromium layer in the sample structure has significantly enhanced the crystallization of the film as studied using XRD spectroscopy. Also the result of lateral crystallization with a rate of about 4 μm / h is reported.

UV-assisted deep vertical etching of polyethylene terephthalate (PET) is shown to be suitable for realizing high resolution and high-aspect-ratio features, and is applied to fabrication of microelectromechanical systems (MEMS) and photonics devices. The technique has the potential to be used for structures below micrometer regime

A simple analytical model for ion-solid interactions, suitable for low energy beam depositions, is reported. An approximation for the nuclear stopping power is used to obtain the analytic solution for the deposited energy in the solid. The ratio of the deposited energy in the bulk to the energy deposited in the surface yields a ceiling for the beam energy above which more defects are generated in the bulk resulting in defective films. The numerical evaluations agree with the existing results in the literature.

We report the growth of vertically aligned high-crystallinity silicon nanotube (SiNT) arrays on silicon substrate by means of a Ni–Au bilayer catalyst engineering technique. Nanotubes were synthesized through solid–liquid–solid method as well as vapor–liquid–solid. A precise evaluation utilizing atomic force microscopy and lateral force microscopy describes that the gold profile in Ni regions leads to the construction of multiwall SiNTs. The agreement of the structural geometry and stiffness of the obtained SiNTs with previous theoretical predictions suggest sp(3) hybridization as the mechanism of tube formation. Apart from scanning electron and transmission electron microscopy techniques, photoluminescence spectroscopy (PL) has been conducted to investigate the formation of nanostructures. PL spectroscopy confirms the evolution of ultrafine walls of the silicon nanotubes, responsible for the observed photoemission properties.

Vertically aligned carbon nanotube (VACNT) arrays have been demonstrated as probes for rapid quantifying of cancer cell deformability with high resolution. Through entrapment of various cancer cells on CNT arrays, the deflections of the nanotubes during cell deformation were used to derive the lateral cell shear force using a large deflection mode method. It is observed that VACNT beams act as sensitive and flexible agents, which transfer the shear force of cells trapped on them by an observable deflection. The metastatic cancer cells have significant deformable structures leading to a further cell traction force (CTF) than primary cancerous one on CNT arrays. The elasticity of different cells could be compared by their CTF measurement on CNT arrays. This study presents a nanotube-based methodology for quantifying the single cell mechanical behavior, which could be useful for understanding the metastatic behavior of cells.

There is an increasing demand for more practical while being easy to perform methods to study cell behavior. Here a developed Electric Cell-substrate Impedance Sensor (ECIS) biosensor has been utilized to study different grade of cancerous cells. ECIS biosensor consists of a number pair of gold electrodes in micrometer scale on glass substrate. The impedance is measured by NI DAQ. An equivalent electrical circuit has been developed to model the ECIS behavior in the cell culture. The size of the circuit elements has been calculated by curve fitting method in MATLAB. The impedance of two grades of human colon cancerous cell, HT29 and SW48 has been studied. Previous studies have shown that the expression of adhering molecule has been affected in the cancerous cell. Regarding this studies, cancer can change the cell properties. This changes can occurred in the membrane properties as well as expression of a series of molecule. Impedance spectrometry can detect the changes in cell size as well as adhering properties of cell caused by cancer. Developing this method, it can be used to detect the grade of cancer.