Priyanka Dwivedi

Wafer-Scale Synthesized MoS2/Porous Silicon Nanostructures for Efficient and Selective Ethanol Sensing at Room Temperature

This paper presents the performance of a highly selective ethanol sensor based on MoS2-functionalized porous silicon (PSi). The uniqueness of the sensor includes its method of fabrication, wafer scalability, affinity for ethanol, and high sensitivity. MoS2 nanoflakes (NFs) were synthesized by sulfurization of oxidized radio-frequency (RF)-sputtered Mo thin films. The MoS2 NFs synthesis technique is superior in comparison to other methods, because it is chip-scalable and low in cost. Interdigitated electrodes (IDEs) were used to record resistive measurements from MoS2/PSi sensors in the presence of volatile organic compound (VOC) and moisture at room temperature. With the effect of MoS2 on PSi, an enhancement in sensitivity and a selective response for ethanol were observed, with a minimum detection limit of 1 ppm. The ethanol sensitivity was found to increase by a factor of 5, in comparison to the single-layer counterpart levels. This impressive response is explained on the basis of an analytical resistive model, the band gap of MoS2/PSi/Si, the interface formed between MoS2 and PSi, and the chemical interaction of the vapor molecules and the surface. This two-dimensional (2D) composite material with PSi paves the way for efficient, highly responsive, and stable sensors.

Synthesis of .ALPHA.-MoO3 nano-flakes by dry oxidation of RF sputtered Mo thin films and their application in gas sensing

Synthesis of orthorhombic (α) MoO3 nano-flakes by dry oxidation of RF sputtered Mo thin film is presented. The influence of Mo thickness variation, oxidation temperature and time on the crystallographic structure, surface morphology and roughness of MoO3 thin films was studied using SEM, AFM, XRD and Raman spectroscopy. A structural study shows that MoO3 is polycrystalline in nature with an α phase. It was noticed that oxidation temperature plays an important role in the formation of nano-flakes. The synthesis technique proposed is simple and suitable for large scale productions. The synthesis parameters were optimized for the fabrication of sensors. Chrome gold-based IDE (interdigitated electrodes) structures were patterned for the electrical detection of organic vapors. Sensors were exposed to wide range 5–100 ppm of organic vapors like ethanol, acetone, IPA (isopropanol alcohol) and water vapors. α-MoO3 nano-flakes have demonstrated selective sensing to acetone in the range of 10–100 ppm at 150 °C. The morphology of such nanostructures has potential in applications such as sensor devices due to their high surface area and thermal stability.

Selective acetone electrical detection using functionalized nano-porous silicon

This paper reports selective acetone sensing portrayed by functionalized nano-porous silicon (PS). Functionalization of nanostructure was performed using hexamethyldisilazane (HMDS). Nano-PS fabrication and morphology analysis were done using electrochemical etching and SEM respectively. Optical properties of PS were analyzed using Raman and Photoluminescence (PL) spectroscopy. Parallel aluminium electrodes were formed on nano-PS surface using thermal evaporation technique. These electrodes were used for recording electrical measurements from porous surface in presence of volatile organic compounds (VOCs) and moisture. Resistance variations due to interaction of sensing surface with different concentrations of ethanol, acetone, moisture and isopropyl alcohol vapors were monitored at room temperature. Various sensor parameters were calculated like sensitivity, response- and recovery-time. Sensor based on functionalized nano-PS was found to be most responsive for acetone in comparison to other VOCs or moisture. Since, acetone is one of the important metabolite components in the circulated blood of the human body therefore, its concentration determination is necessary. The approach for selective sensing presented in this work is simple and low cost.

High performance broadband photodetector based on MoS2/porous silicon heterojunction

A high speed efficient broadband photodetector based on a vertical n-MoS2/p-porous silicon heterostructure has been demonstrated. Large area MoS2 on electrochemical etched porous silicon was grown by sulphurization of a sputtered MoO3 thin film. A maximum responsivity of 9 A/W (550–850 nm) with a very high detectivity of ∼1014 Jones is observed. Transient measurements show a fast response time of ∼9 μs and is competent to work at high frequencies (∼50 kHz). The enhanced photodetection performance of the heterojunction made on porous silicon over that made on planar silicon is explained in terms of higher interfacial barrier height, superior light trapping property, and larger junction area in the MoS2/porous silicon junction.

MoO3/nano–Si heterostructure based highly sensitive and acetone selective sensor prototype: a key to non-invasive detection of diabetes

This paper presents the development of an extremely sensitive and selective acetone sensor prototype which can be used as a platform for non-invasive diabetes detection through exhaled human breath. The miniaturized sensors were produced in high yield with the use of standard microfabrication processes. The sensors were based on a heterostructure composed of MoO3 and nano-porous silicon (NPS). Features like acetone selective, enhanced sensor response and 0.5 ppm detection limit were observed upon introduction of MoO3 on the NPS. The sensors were found to be repeatable and stable for almost 1 year, as tested under humid conditions at room temperature. It was inferred that the interface resistance of MoO3 and NPS played a key role in the sensing mechanism. With the use of breath analysis and lab-on-chip, medical diagnosis procedures can be simplified and provide solutions for point-of-care testing.

Design, fabrication, characterization and packaging of bottom gate and nano-porous TiO 2 based FET

Bottom gate field effect transistors (FETs) with nano-porous TiO2 as channel has been designed, fabricated, characterized and packaged. The fabrication process is simple, scalable and reproducible. Reactive RF sputtering and lift off process was used for depositing and patterning TiO2 respectively. TiO2 was annealed to tune its crystallinity from amorphous to anatase. Microscopy study of TiO2 film reveals nano-porous morphology which improves the surface properties and makes it useful for sensing applications. The transistor characteristics of FET show p-channel behavior and the device has been packaged onto headers for testing it in presence of analytes.