Nano biosensors for neurochemical monitoring

Meyyappan M. 나노기술연구협의회 2015 Nano Convergence Vol.2 No.18

Neurochemicals such as dopamine (DA) and serotonin (S-HT) are linked to disorders such as Parkinson’s disease, epilepsy, addiction and many others. Detection of and monitoring these neurochemicals in vivo and in vitro has become important in treating various disorders. The electroactive nature of DA and S-HT has enabled employing electrochemical techniques to detect them at low concentrations, and a variety of electrodes and approaches have been reported. The use of nanomaterials such as carbon nanotubes, graphene and nanowires has been advocated in recent years for the sensitive detection of neurochemicals. This article reviews the advances in nano biosensors for this application and discusses the future outlook and challenges.

The effect of Ga content on In_2xGa_2−2xO₃ nanowire transistor characteristics

Suh, Misook,Meyyappan, M,Ju, Sanghyun IOP Pub 2012 Nanotechnology Vol.23 No.30

<P>We have investigated the change in structural and electrical properties of In<SUB>2x</SUB>Ga<SUB>2−2x</SUB>O<SUB>3</SUB> nanowires (x = 1, 0.69 and 0.32) grown with varied indium (In) and gallium (Ga) contents. The as-grown In<SUB>2x</SUB>Ga<SUB>2−2x</SUB>O<SUB>3</SUB> nanowires kept the cubic crystal structure of In<SUB>2</SUB>O<SUB>3</SUB> intact even when the atomic percentages of Ga were increased to 31% (x = 0.69) and 68% (x = 0.32) in comparison to the total amount of In and Ga. However, as Ga added to In<SUB>2</SUB>O<SUB>3</SUB> structure was substituted with In, the lattice constant decreased and, consequently, the main peaks observed in x-ray diffraction in the direction of (222), (400) and (440) shifted by around ∼0.08°. The average threshold voltage values for the In<SUB>2x</SUB>Ga<SUB>2−2x</SUB>O<SUB>3</SUB> nanowire transistors were −9.9 V (x = 1), −6.6 V (x = 0.67) and −5.6 V (x = 0.32), exhibiting a more positive shift and the sub-threshold slope increased to 0.53 V /dec (x = 1), 0.33 V /dec (x = 0.67) and 0.27 V /dec (x = 0.32), showing an improved switching characteristic with increasing Ga. </P>

LaF₃ electrolyte-insulator-semiconductor sensor for detecting fluoride ions

Cho, Hyeonsu,Kim, Kihyun,Meyyappan, M.,Baek, Chang-Ki Elsevier Sequoia 2019 Sensors and actuators. B Chemical Vol.279 No.-

<P><B>Abstract</B></P> <P>Electrolyte-insulator-semiconductor (EIS) sensor is commonly considered for chemical and biosensing applications due to its small size and simple fabrication method. Here, we demonstrate a fluoride-sensitive EIS sensor using thermally-deposited polycrystalline lanthanum fluoride (poly LaF<SUB>3</SUB>) film as sensing membrane, which is cheaper than single-crystal LaF<SUB>3</SUB>. The sensing characteristics are analyzed for poly LaF<SUB>3</SUB> layers deposited at different temperatures, and the EIS sensors with the sensing membrane formed at 500 °C exhibit excellent sensing response to fluoride ions with a high sensitivity of 52.3 mV/pF and low limit of detection of 1.9 ppb. This limit of detection is lower than previously reported values in the literatures. In addition, the poly LaF<SUB>3</SUB> film deposited at 500 °C has good stability with a low hysteresis voltage of 5.1 mV and a small drift rate of 0.67 mV/h. These superior metrics come from a rather well crystallized LaF<SUB>3</SUB> structure including denser surface grains, enhanced preferential crystalline (002) plane, and improved stoichiometric composition. Furthermore, the sensors show a good selectivity over other ions such as NO<SUB>3</SUB> <SUP>−</SUP> and SO<SUB>4</SUB> <SUP>2−</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We fabricated fluoride-sensitive EIS sensor using thermally deposited poly LaF<SUB>3</SUB> membrane. </LI> <LI> The effect of deposition temperature on the structural and sensing properties of poly LaF<SUB>3</SUB> was investigated. </LI> <LI> Poly LaF<SUB>3</SUB> sensor formed at 500 °C exhibits high sensitivity, low limit of detection, small hysteresis voltage and small drift rate. </LI> <LI> The improved sensing characteristics come from excellent membrane quality. </LI> </UL> </P>

Control of Semiconducting and Metallic Indium Oxide Nanowires

Lim, Taekyung,Lee, Sumi,Meyyappan, M.,Ju, Sanghyun American Chemical Society 2011 ACS NANO Vol.5 No.5

<P>Oxide semiconductors are candidates for chemical sensors, transparent electrodes, and electronic devices. Here, we have investigated metal-to-semiconductor transitions during In<SUB>2</SUB>O<SUB>3</SUB> nanowire growth with variations in the O<SUB>2</SUB> gas rate. Photoluminescence and current–voltage characteristics of In<SUB>2</SUB>O<SUB>3</SUB> nanowire transistors have been used to understand the transition behavior. The proportion of metallic nanowires to semiconducting nanowires significantly changes from 80:20 to 25:75 when the O<SUB>2</SUB> fraction in argon increases from 0.005% to 0.2%. We believe that excessive oxygen vacancies at low O<SUB>2</SUB> gas rates increase the conductivity and thereby the number of nanowires with metallic characteristics. With an increase in oxygen flow, the oxygen vacancies in the nanowires are substituted with oxygen and the subsequent reduction in oxygen vacancies increases the number of semiconducting nanowires. The threshold voltage of transistors fabricated with semiconducting nanowires shifts in a positive direction by about +3.3 eV between nanowires grown with 0.005% and 0.2% oxygen. The results here indicate that electrical and optical characteristics of oxide nanowires can be controlled by the amount of oxygen during growth instead of relying on conventional postgrowth high-temperature annealing or other postprocessing techniques.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-5/nn200390d/production/images/medium/nn-2011-00390d_0004.gif'></P>

<i>In situ</i> observation of morphological change in CdTe nano- and submicron wires

Davami, Keivan,Ghassemi, Hessam M,Sun, Xuhui,Yassar, Reza S,Lee, Jeong-Soo,Meyyappan, M IOP Pub 2011 Nanotechnology Vol.22 No.43

<P>We report growth and characterization of CdTe wires 30–400 nm in diameter by the vapor–liquid–solid technique. Individual nanowires were placed on a movable piezotube, which allowed three-dimensional motion toward a scanning tunneling microscope (STM). A bias was applied to the STM tip in contact with the nanowire, and the morphological changes due to Joule heating were observed <I>in situ</I> using a transmission electron microscope (TEM) in real time. For thick CdTe wires (<I>d</I> > ∼ 150 nm), the process results in the growth of superfine nanowires (SFNWs) of 2–4 nm diameter on the surface of the wire. Smaller diameter nanowires, in contrast, disintegrate under the applied bias before the complete evolution of SFNWs on the surface. </P>

Photostable Zn₂SnO₄ Nanowire Transistors for Transparent Displays

Lim, Taekyung,Kim, Hwansoo,Meyyappan, M.,Ju, Sanghyun American Chemical Society 2012 ACS NANO Vol.6 No.6

<P>Although oxide nanowires offer advantages for next-generation transparent display applications, they are also one of the most challenging materials for this purpose. Exposure of semiconducting channel areas of oxide nanowire transistors produces an undesirable increase in the photocurrent, which may result in unstable device operation. In this study, we have developed a Zn<SUB>2</SUB>SnO<SUB>4</SUB> nanowire transistor that operates stably regardless of changes in the external illumination. In particular, after exposure to a light source of 2100 lx, the threshold voltage (<I>V</I><SUB>th</SUB>) showed a negative shift of less than 0.4 V, and the subthreshold slope (SS) changed by ∼0.1 V/dec. ZnO or SnO<SUB>2</SUB> nanowire transistors, in contrast, showed 1.5–2.0 V negative shift in <I>V</I><SUB>th</SUB> and an SS change of ∼0.3 V/dec under the same conditions. Furthermore, the Zn<SUB>2</SUB>SnO<SUB>4</SUB> nanowire transistors returned to their initial state immediately after the light source was turned off, unlike those using the other two nanowires. Thus, Zn<SUB>2</SUB>SnO<SUB>4</SUB> nanowires achieve photostability without the application of a black material or additional processing, minimizing the photocurrent effect for display devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-6/nn300401w/production/images/medium/nn-2012-00401w_0008.gif'></P>

Coal as a carbon source for carbon nanotube synthesis

Moothi, K.,Iyuke, S.E.,Meyyappan, M.,Falcon, R. Pergamon Press ; Elsevier Science Ltd 2012 Carbon Vol.50 No.8

This article reviews the recent advances on the various processes used in the synthesis of carbon nanotubes (CNTs) from different types of coal (anthracite, bituminous, etc.) and on the role played by coal as carbon source in the production of CNTs. The molecular solid coal is inexpensive and widely available in comparison to the most widely used solid carbon precursor, graphite (a lattice solid) and high purity hydrocarbon gas sources. An account is given on the different processes involved in the synthesis of various CNTs (single and multi-walled, bamboo-shaped, branched, etc.) from different types of coal (anthracite, bituminous, etc.). Both arc-discharge and thermal plasma jet produce high quality CNTs but fundamental disadvantages limit their use as large-scale synthesis routes. Chemical vapour deposition appears to be promising but further experimental work is necessary in order to develop an understanding of the complex factors governing the formation of different carbon nanomaterials from coal. Successful utilization of CNTs in various applications is strongly dependent on the development of simple, efficient and inexpensive technology for mass production and coal as a carbon source has the potential to meet the needs.

Nanoscale memory devices

Chung, Andy,Deen, Jamal,Lee, Jeong-Soo,Meyyappan, M IOP Pub 2010 Nanotechnology Vol.21 No.41

<P>This article reviews the current status and future prospects for the use of nanomaterials and devices in memory technology. First, the status and continuing scaling trends of the flash memory are discussed. Then, a detailed discussion on technologies trying to replace flash in the near-term is provided. This includes phase change random access memory, Fe random access memory and magnetic random access memory. The long-term nanotechnology prospects for memory devices include carbon-nanotube-based memory, molecular electronics and memristors based on resistive materials such as TiO<SUB>2</SUB>. </P>

Bandgap Engineering and Strain Effects of Core–Shell Tunneling Field-Effect Transistors

Yoon, Jun-Sik,Kim, Kihyun,Meyyappan, M.,Baek, Chang-Ki IEEE 2018 IEEE transactions on electron devices Vol.65 No.1

<P>DC characteristics of n-type SiGe heterojunction nanowire tunneling field-effect transistors (TFETs) adopting a core–shell structure are investigated using 3-D numerical simulation. Different mole fractions between the core and the shell regions induce strain effects along the nanowire, which modulate the energy bandgap and thus the dc performance of the devices. The SiGe core–shell TFETs with greater mole fractions in the core regions increase the drive currents greatly by both Ge content and strain effects which decrease the tunneling length and increase the band-to-band (BTB) generation rate according to Kane’s nonlocal tunneling model. In addition, tensile (compressive) strains for the shell (core) regions as well as shear strains reduce the energy bandgap according to the deformation potential theory, decreasing the subthreshold swing as well as increasing the BTB generation rate. Compared to all other Si/Ge heterojunction TFETs, the proposed SiGe core–shell TFETs are superior with high drive currents and on/off-current ratios.</P>

A computational and experimental investigation of the mechanical properties of single ZnTe nanowires

Davami, Keivan,Mortazavi, Bohayra,Ghassemi, Hessam M.,Yassar, Reza S.,Lee, Jeong-Soo,Ré,mond, Yves,Meyyappan, M. The Royal Society of Chemistry 2012 Nanoscale Vol.4 No.3

<P>One-dimensional nanostructures such as ZnTe, CdTe, Bi(2)Te(3) and others have attracted much attention in recent years for their potential in thermoelectric devices among other applications. A better understanding of their mechanical properties is important for the design of devices. A combined experimental and computational approach has been used here to investigate the size effects on the Young's modulus of ZnTe nanowires (NWs). The mechanical properties of individual ZnTe nanowires in a wide diameter range (50-230 nm) were experimentally measured inside a high resolution transmission electron microscope using an atomic force microscope probe with the ability to record in situ continuous force-displacement curves. The in situ observations showed that ZnTe NWs are flexible nanostructures with the ability to withstand relatively high buckling forces without becoming fractured. The Young's modulus is found to be independent of nanowire diameter in the investigated range, in contrast to reported results for ZnO NWs and carbon nanotubes where the modulus increases with a decrease in diameter. Molecular dynamics simulations performed for nanowires with diameters less than 20 nm show limited size dependence for diameters smaller than 5 nm. The surface atoms present lower Young's modulus according to the simulations and the limited size dependency of the cylindrical ZnTe NWs is attributed to the short range covalent interactions.</P>