Budhi Singh

Bio: Budhi Singh is an academic researcher from Sungkyunkwan University. The author has contributed to research in topics: Ferromagnetism & Graphene. The author has an hindex of 13, co-authored 34 publications receiving 557 citations. Previous affiliations of Budhi Singh include Jawaharlal Nehru University.

Dielectrophoretic assembly of Pt nanoparticle-reduced graphene oxide nanohybrid for highly-sensitive multiple gas sensor

Abstract: Reduced graphene oxide (rGO) gas sensors functionalized with platinum (Pt) nanoparticles were fabricated. An alternating current dielectrophoresis technique was used for the precise alignment of the Pt-GO nanohybrid between microgap electrodes, proceeded by the mid-temperature thermal annealing. The gas sensing response was determined for the assembled rGO nanostructure-based devices with and without Pt decoration at various ambient temperature and gas concentrations. The tested device exhibited sensitivities of 14% (7%), 8% (5%), and 10% (8%), for 1000 ppm hydrogen, ammonia, and nitric oxide gases, respectively with (without) Pt nanoparticles, at room temperature. The Pt-decorated samples show an improvement of 100%, 60% and 25% to hydrogen, ammonia, and nitric oxide gases, respectively, over without Pt decorated sensors. Besides, improving the sensitivity, the dielectrophoresis assembled rGO-Pt nanohybrid sensors have been demonstrated as a viable material for multiple gas sensors.

Origin of ferromagnetism in Cu-doped ZnO.

Abstract: It is widely reported during last decade on the observation of room temperature ferromagnetism (RTFM) in doped ZnO and other transition metal oxides. However, the origin of RTFM is not understood and highly debated. While investigating the origin of RTFM, magnetic ion doped oxides should be excluded because it is not yet settled whether RTFM is intrinsic or due to the magnetic ion cluster in ZnO. Hence, it is desirable to investigate the origin of RTFM in non-magnetic ion doped ZnO and Cu-doped ZnO will be most suitable for this purpose. The important features of ferromagnetism observed in doped ZnO are (i) observation of RTFM at a doping concentration much below than the percolation threshold of wurtzite ZnO, (ii) temperature independence of magnetization and (iii) almost anhysteretic magnetization curve. We show that all these features of ferromagnetism in ZnO are due to overlapping of bound magnetic polarons (BMPs) which are created by exchange interaction between the spin of Cu2+ ion and spin of the localized hole due to zinc vacancy [Formula: see text]. Both the experimental and theoretical investigation show that the exchange interaction between Cu2+-Cu2+ ions mediated by [Formula: see text] is responsible for RTFM in Cu-doped ZnO.

Capacitance-voltage characteristics of organic Schottky diode with and without deep traps

Abstract: Capacitance based spectroscopic techniques have been used to characterize defects in organic Schottky diode based on copper phthalocyanine. Deep traps in organic thin films introduced by varying growth conditions have been identified and characterized by voltage and temperature dependence of capacitance. These results are interpreted using a consistent modelling of capacitance of organic Schottky diode with and without deep traps.

Dielectrophoresis of graphene oxide nanostructures for hydrogen gas sensor at room temperature

Abstract: Hydrogen gas sensors based on graphene oxide (GO) nanostructures have been fabricated using ac dielectrophoresis (DEP) process. The GO nanostructures synthesized by an improved Hummer's method were first characterized by atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. GO nanostructures were assembled into gold electrodes using DEP process by varying parameters such as frequency, peak-to-peak voltage ( V pp ), and processing time ( t ). The devices were investigated by scanning electron microscopy, current-voltage measurement, and hydrogen sensing experiment at room temperature. It was found that the optimum DEP parameters that manipulates GO nanostructures in precise manner for hydrogen gas sensing were V pp = 10 V, frequency = 500 kHz, and t = 30 s. The optimized device was proved to be an effective and better hydrogen gas sensor over a typical drop-dried device with a good sensing response of 5%, fast response time (

Multifunctional van der Waals Broken-Gap Heterojunction

Abstract: The finite energy band-offset that appears between band structures of employed materials in a broken-gap heterojunction exhibits several interesting phenomena. Here, by employing a black phosphorus (BP)/rhenium disulfide (ReS2 ) heterojunction, the tunability of the BP work function (Φ BP ) with variation in flake thickness is exploited in order to demonstrate that a BP-based broken-gap heterojunction can manifest diverse current-transport characteristics such as gate tunable rectifying p-n junction diodes, Esaki diodes, backward-rectifying diodes, and nonrectifying devices as a consequence of diverse band-bending at the heterojunction. Diversity in band-bending near heterojunction is attributed to change in the Fermi level difference (Δ) between BP and ReS2 sides as a consequence of Φ BP modulation. No change in the current transport characteristics in several devices with fixed Δ also provides further evidence that current-transport is substantially impacted by band-bending at the heterojunction. Optoelectronic experiments on the Esaki diode and the p-n junction diode provide experimental evidence of band-bending diversity. Additionally, the p+ -n-p junction comprising BP (38 nm)/ReS2 /BP(5.8 nm) demonstrates multifunctionality of binary and ternary inverters as well as exhibiting the behavior of a bipolar junction transistor with common-emitter current gain up to 50.

Recent advances in graphene based gas sensors

Abstract: Graphene, a single, one-atom-thick sheet of carbon atoms arranged in a honeycomb lattice and the two-dimensional building block for carbon materials, has attracted great interest for a wide range of applications. Due to its superior properties such as thermo-electric conduction, surface area and mechanical strength, graphene materials have inspired huge interest in sensing of various chemical species. In this timely review, we discuss the recent advancement in the field of graphene based gas sensors with emphasis on the use of modified graphene materials. Further, insights of theoretical and experimental aspects associated with such systems are also discussed with significance on the sensitivity and selectivity of graphene towards various gas molecules. The first section introduces graphene, its synthesis methods and its physico-chemical properties. The second part focuses on the theoretical approaches that discuss the structural improvisations of graphene for its effective use as gas sensing materials. The third section discusses the applications of pristine and modified graphene materials in gas sensing applications. Various graphene modification methods are discussed including using dopants and defects, decoration with metal/metal oxide nanoparticles, and functionalization with polymers. Finally, a discussion on the future challenges and perspectives of this enticing field of graphene sensors for gas detection is provided.

Flexible Graphene-Based Wearable Gas and Chemical Sensors

Abstract: Wearable electronics is expected to be one of the most active research areas in the next decade; therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, lightweight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating ...

A Review on Graphene-Based Gas/Vapor Sensors with Unique Properties and Potential Applications

Abstract: Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects, etc. Herein, we summarize recent advantages in graphene preparation, sensor construction, and sensing properties of various graphene-based gas/vapor sensors, such as NH3, NO2, H2, CO, SO2, H2S, as well as vapor of volatile organic compounds. The detection mechanisms pertaining to various gases are also discussed. In conclusion part, some existing problems which may hinder the sensor applications are presented. Several possible methods to solve these problems are proposed, for example, conceived solutions, hybrid nanostructures, multiple sensor arrays, and new recognition algorithm.

Graphene oxide: strategies for synthesis, reduction and frontier applications

Abstract: Till now, several innovative methods have been developed for the synthesis of graphene materials including mechanical exfoliation, epitaxial growth by chemical vapor deposition, chemical reduction of graphite oxide, liquid-phase exfoliation, arc discharge of graphite, in situ electron beam irradiation, epitaxial growth on SiC, thermal fusion, laser reduction of polymers sheets and unzipping of carbon nanotubes etc. Generally large scale graphene nanosheets are reliably synthesized utilizing other forms of graphene-based novel materials, including graphene oxide (GO), exfoliated graphite oxide (by thermal and microwave), and reduced graphene oxide. The degree of GO reduction and number of graphene layers are minimized mainly by applying two approaches via chemical or thermal treatments. The promising and excellent properties together with the ease of processability and chemical functionalization makes graphene based materials especially GO, ideal candidates for incorporation into a variety of advanced functional materials. Chemical functionalization of graphene can be easily achieved, by the introduction of various functional groups. These functional groups help to control and manipulate the graphene surfaces and help to tune the properties of the resulting hybrid materials. Importantly, graphene and its derivatives GO, have been explored in a wide range of applications, such as energy generation/storage, optical devices, electronic and photonic devices, drug delivery, clean energy, and chemical/bio sensors. In this review article, we have incorporated a general introduction of GO, its synthesis, reduction and some selected frontier applications.

Zinc Vacancy induced magnetism in ZnO thin films and nanowires

Abstract: Extensive calculations based on density functional theory have been carried out to understand the origin of magnetism in undoped ZnO thin films as found in recent experiments. The observed magnetism is confirmed to be due to Zn, instead of O, vacancy. The main source of the magnetic moment, however, arises from the unpaired 2p electrons at O sites surrounding the Zn vacancy with each nearest-neighbor O atom carrying a magnetic moment ranging from 0.490 to 0.740 B. Moreover, the study of vacancy-vacancy interactions indicates that in the ground state, the magnetic moments induced by Zn vacancies prefer to ferromagnetically couple with the antiferromagnetic state lying 44 meV higher in energy. Since this is larger than the thermal energy at room temperature, the ferromagnetic state can be stable against thermal fluctuations. Calculations and discussions are also extended to ZnO nanowires that have larger surface to volume ratio. Here, the Zn vacancies are found to lead to the ferromagnetic state too. The present theoretical study not only demonstrates that ZnO samples can be magnetic even without transition-metal doping but also suggests that introducing Zn vacancy is a natural and an effective way to fabricate magnetic ZnO nanostructures. In addition, vacancy mediated magnetic ZnO nanostructures may have certain advantages over transition-metal doped systems in biomedical applications.