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Leema Rose Viannie

Bio: Leema Rose Viannie is an academic researcher from VIT University. The author has contributed to research in topics: Cantilever & Materials science. The author has an hindex of 3, co-authored 9 publications receiving 37 citations. Previous affiliations of Leema Rose Viannie include KLE Technological University & Indian Institute of Science.

Papers
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Journal ArticleDOI
01 Jun 2018
TL;DR: In this article, a chemical oxidative synthesis of HCl doped polyaniline (PANI)/polyvinyl alcohol (PVA) nanocomposite using ammonium persulphate as oxidizing agent was presented.
Abstract: Studies on organic conducting polymers have gained attention in the past decade due to their simple, low cost fabrication processes, low temperature operation and ability to conform to various device shapes and geometries. This paper presents chemical oxidative synthesis of HCl doped polyaniline (PANI)/polyvinyl alcohol (PVA) nanocomposite using ammonium persulphate as oxidizing agent. PANI/PVA blends were prepared by adding 0.05mM, 0.1mM and 0.15mM concentrations of PVA into synthesized PANI in aqueous solvent. UV-Visible spectroscopy and FTIR spectroscopy were used to investigate the analytical and functional groups present in the synthesized nanocomposites. The results indicated the formation of highly conducting PANI/PVA blends. Humidity sensors were prepared by casting thin films of as-prepared nanocomposites with varying concentrations of PVA onto interdigitated electrodes over PCB. On exposure to humidity, it was observed that the electrical resistance of the fabricated sensors reduced by 60-75% for 90% humidity. It may be concluded that the addition of appropriate amount of PVA to PANI enhanced the humidity sensitivity.

23 citations

Journal ArticleDOI
TL;DR: In this paper, a polycrystalline vanadium dioxide (VO2) coated silicon microcantilever was applied to the silicon surface at 520°C using metal organic chemical vapor deposition and the formation of the M1 monoclinic phase was confirmed by X-ray diffraction studies and further verified by temperature variable Raman spectroscopy.
Abstract: Structural phase transition assisted micromechanical actuation of a vanadium dioxide (VO2) coated silicon microcantilever is presented. A 300 nm polycrystalline VO2 film was deposited over the silicon surface at 520 °C using metal organic chemical vapor deposition. The formation of the M1 monoclinic phase of the as-deposited VO2 film was confirmed by X-ray diffraction studies and further verified by temperature variable Raman spectroscopy. The heated VO2 film exhibits semiconductor-to-metal transition at 74 °C, which produces a change in the electrical resistance almost of three orders in magnitude. Consequently, the VO2 film undergoes structural phase transition from the monoclinic phase (011)M1 to a tetragonal phase (110)R. This generates a compressive stress within the VO2 film resulting in large, reversible cantilever deflection. This deflection was measured with a non-contact 3D optical profilometer, which does not require any vacuum conditions. Upon heating, the VO2 coated silicon cantilever produced a large reversible tip deflection of 14 μm at 50 °C. Several heating and cooling cycles indicate steep changes in the cantilever tip deflection with negligible hysteresis. In addition, the effect of thermal stress induced cantilever deflection was estimated to be as small as 6.4%, and hence can be ignored. These results were found to be repeatable within controlled experimental conditions.

13 citations

Journal ArticleDOI
TL;DR: In this article, the authors report the design, nonlinear thermomechanical analysis, fabrication, and thermal actuation of SU8 actuators using surface micromachining techniques and the electrical interconnects are made to them using flip chip bonding.
Abstract: SU8-based micromechanical structures are widely used as thermal actuators in the development of compliant micromanipulation tools. This paper reports the design, nonlinear thermomechanical analysis, fabrication, and thermal actuation of SU8 actuators. The thermomechanical analysis of the actuator incorporates nonlinear temperature-dependent properties of SU8 polymer to accurately model its thermal response during actuation. The designed SU8 thermal actuators are fabricated using surface micromachining techniques and the electrical interconnects are made to them using flip-chip bonding. The issues due to thermal stress during fabrication are discussed and a novel strategy is proposed to release the thermal stress in the fabricated actuators. Subsequent characterization of the actuator using an optical profilometer reveals excellent thermal response, good repeatability, and low hysteresis. The average deflection is $\sim 8.5~\mu \text{m}$ for an actuation current of $\sim 5$ mA. The experimentally obtained deflection profile and the tip deflection at different currents are both shown to be in good agreement with the predictions of the nonlinear thermomechanical model. This underscores the need to consider nonlinearities when modeling the response of SU8 thermal actuators. [2015-0087]

12 citations

Journal ArticleDOI
TL;DR: In this paper, a vanadium oxide sheet was used for resistive switching in lateral devices with room-temperature and humidity varying from 11% to 95% and clear hysteresis in the switching cycles was shown.
Abstract: Resistive switching in lateral devices using vanadium oxide sheets is reported. The devices undergo an electric field induced insulator-to-metal transition (E-IMT). A sudden jump in the current level up to two orders in magnitude at a defined bias voltage and linearly increasing with a further increase in the bias voltage is observed. Further, the devices also show up multi-step sequential breakdown. The relative change in the resistance from high resistance state (HRS) to low resistance states (LRS) during the resistive switching is up to 700. The breakdown voltage and the switching characteristics of the devices strongly depend on the relative humidity. By varying relative humidity controllably from 11% to 95%, the robustness of the switching device is studied. Clear hysteresis in the switching cycles is shown (current–voltage characteristics) at various humidity levels at room temperature. The threshold voltage reduces exponentially with humidity. This dependence of switching voltage with humidity is attributed to the dissociation of water molecules on the VO2 surface. The water molecule donates charge carriers to the VO2 by dissociating on the surface resulting in two hydroxyl ions on the surface in combination with oxygen defect available on the VO2 surface.

11 citations

Journal ArticleDOI
TL;DR: In this article, the authors developed highly flexible polymer nanocomposite sheets using multi-walled carbon nanotube (MWCNT) in a poly(dimethylsiloxane) (PDMS) matrix.
Abstract: In this study, the development of highly flexible polymer nanocomposite sheets using multi-walled carbon nanotube (MWCNT) in a poly (dimethylsiloxane) (PDMS) matrix has been presented. Solution processing technique was employed, and MWCNTs were dispersed in n-hexane, and PDMS is resulting in a homogenous dispersion (between 2 wt% and 10 wt%). Scanning electron micrograph (SEM) images show the distribution of MWCNTs within PDMS matrix, which form continuous conductive networks resulting in percolation threshold even at 2 wt% filler concentrations. The electrical conductivity of the fabricated nanocomposite sheets was found to be about 1.3–158.2 S/m. Samples with 2 wt% and 4 wt% filler concentrations exhibit excellent temporal stability both in ambient and vacuum conditions, with near-zero temperature coefficient of resistance. The nanocomposite sheets used for mechanical studies were made as per ASTM D-412-C standards. For an optimal filler concentration of 5.58 wt% can be observed with stiffness of 0.486 MPa, the tensile strength of 0.422 MPa, the electrical conductivity of about 39.5 S/m, and elongation up to 120%. Therefore, this filler concentration is most suited for fabricating flexible strain sensors with good conductivity and temporal stability.

7 citations


Cited by
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Journal Article
TL;DR: Nilsson et al. as discussed by the authors described the basic design of the ambient pressure XPS setup that combines differential pumping with an electrostatic focusing, and presented examples of the application of XPS to studies of water adsorption on the surface of metals and oxides including Cu(110), Cu(111), TiO 2 (110) under environmental conditions of water vapor pressure.
Abstract: In-situ X-ray photoelectron spectroscopy studies of water metals and oxides at ambient conditions Ev Vi si ua t w tio ww n Ed .a ct itio iv n eP of DF ac .c tiv om eP DF fo rm So or ftw e d e ar ta e. ils on S Yamamoto 1 , H Bluhm 2 , K Andersson 1,3,6 , G Ketteler 4,7 , H Ogasawara 1 , M Salmeron 4,5 and A Nilsson 1,3 Stanford Synchrotron Radiation Laboratory, P.O.B. 20450, Stanford, CA 94309, USA. Lawrence Berkeley National Laboratory, Chemical Sciences Division, Berkeley, CA 94720, USA. FYSIKUM, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden. Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA 94720, USA. Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA. E-mail: nilsson@slac.stanford.edu Running head: In-Situ XPS studies of water on metals and oxides at ambient conditions Present address: Center for Individual Nanoparticle Functionality (CINF), Department of Physics, Technical University of Denmark, Fysikvej 312, DK-2800 Kgs. Lyngby, Denmark. Present address: Department of Applied Physics, Chalmers University of Technology, SE-412 96 Goteborg, Sweden. Abstract . X-ray photoelectron spectroscopy (XPS) is a powerful tool for surface and interface analysis, providing the elemental composition of surfaces and the local chemical environment of adsorbed species. Conventional XPS experiments have been limited to ultrahigh vacuum (UHV) conditions due to a short mean free path of electrons in a gas phase. The recent advances in instrumentation coupled with third-generation synchrotron radiation sources enables in-situ XPS measurements at pressures above 5 Torr. In this review, we describe the basic design of the ambient pressure XPS setup that combines differential pumping with an electrostatic focusing. We present examples of the application of in-situ XPS to studies of water adsorption on the surface of metals and oxides including Cu(110), Cu(111), TiO 2 (110) under environmental conditions of water vapor pressure. On all these surfaces we observe a al general trend where hydroxyl groups form first, followed by molecular water adsorption. The importance of surface OH groups and their hydrogen bonding to water molecules in water adsorption on surfaces is discussed in detail.

217 citations

Journal ArticleDOI
06 Nov 2019-Sensors
TL;DR: It is concluded that although many chipless RFID sensors provide adequate performance characteristics, more work is needed to ensure that this technology is capable/robust enough to operate in many of the applications it has been earmarked for.
Abstract: Chipless Radio Frequency Identification (RFID) has been used in a variety of remote sensing applications and is currently a hot research topic. To date, there have been a large number of chipless RFID tags developed in both academia and in industry that boast a large variation in design characteristics. This review paper sets out to discuss the various design aspects needed in a chipless RFID sensor. Such aspects include: (1) Addressing strategies to allow for unique identification of the tag, (2) Sensing mechanisms used to allow for impedance-based response signal modulation and (3) Sensing materials to introduce the desired impedance change when under the influence of the target stimulus. From the tabular comparison of the various sensing and addressing techniques, it is concluded that although many sensors provide adequate performance characteristics, more work is needed to ensure that this technology is capable/robust enough to operate in many of the applications it has been earmarked for.

40 citations

Journal ArticleDOI
TL;DR: In this article, the structural and optical properties of nanocomposites have been studied and the experimental results of optical properties showed that the absorbance, absorption coefficient of (CMC-PVP) blend increase while the transmittance and energy band gap decrease with increase in CoFe2O4 nanoparticles concentrations.
Abstract: In this paper, preparation of [carboxyl methyl cellulose (CMC)–polyvinyl pyrrolidone (PVP)–cobalt iron oxides nanoparticles (CoFe2O4)] nanocomposites for humidity sensors at different temperatures have been investigated. The synthesized humidity sensors have low cost, lightweight, flexible, high corrosion resistance, high sensitivity compare with other sensors. The structural and optical properties of nanocomposites have been studied. The experimental results of optical properties showed that the absorbance, absorption coefficient of (CMC–PVP) blend increase while the transmittance and energy band gap decrease with increase in CoFe2O4 nanoparticles concentrations. The results of humidity sensors showed that the electrical resistance of (CMC–PVP–CoFe2O4) nanocomposites decreases with an increase in CoFe2O4 nanoparticles concentrations and temperature. The (CMC–PVP–CoFe2O4) nanocomposites have high sensitivity for humidity for different temperatures.

38 citations

01 Jan 1996
TL;DR: In this paper, a new process was developed to fabricate arrays of cantilevers with integrated tips for atomic force microscope (AFM) imaging and a piezoelectric layer for vertical actuation and detection.
Abstract: We have developed a new process to fabricate arrays of cantilevers with integrated tips for atomic force microscope (AFM) imaging and a piezoelectric layer for vertical actuation and detection. A good homogeneity of the tip shape is obtained thanks to a self-sharpening effect. The cantilevers have been characterized mechanically and electrically.

36 citations

Journal ArticleDOI
Jiran Liang1, Qun Lou1, Wenhao Wu1, Kangqiang Wang1, Chang Xuan1 
TL;DR: In this article, a VO2(B) ultrathin vertical nanosheet array was prepared by the hydrothermal method and the influence of the concentration of oxalic acid on the crystal structure and room-temperature NO2 sensing performance was studied.
Abstract: A VO2(B) ultrathin vertical nanosheet array was prepared by the hydrothermal method. The influence of the concentration of oxalic acid on the crystal structure and room-temperature NO2 sensing performance was studied. The morphology and crystal structure of the nanosheets were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Room-temperature gas sensing measurements of this structure to NO2 with a concentration span from 0.5 to 5 ppm were carried out. The experimental results showed that the thickness of the vertical VO2(B) nanosheet was lower than 20 nm and close to the 2 times Debye length of VO2(B). The response of the sensor based on this structure to 5 ppm NO2 was up to 2.03, and the detection limit was 20 ppb. Its high response performance was due to the fact that the target gas could completely control the entire conductive path by forming depletion layers on the surface of VO2(B) nanosheets. Density functional theory was used to analyze the adsorption of NO2 on the VO2(B) surface. It is found that the band gap of VO2(B) becomes narrower and the Fermi level moves to the valence band after NO2 adsorption, and the density of states near the Fermi level increases significantly. This ultrathin vertical nanosheet array structure can make VO2(B) detect NO2 with high sensitivity at room temperature and therefore has potential applications in the field of low-power-consumption gas sensors.

25 citations