R-3 Repository :: Browsing by Author "Ajayan, Pulickel M. "

Browsing by Author "Ajayan, Pulickel M."

Now showing 1 - 20 of 150

2D material integrated macroporous electrodes for Li-ion batteries
(Royal Society of Chemistry, 2017) Gullapalli, Hemtej; Kalaga, Kaushik; Vinod, Soumya; Rodrigues, Marco-Tulio F.; George, Antony; Ajayan, Pulickel M.
Three-dimensionally structured architectures are known to improve the performance of electrodes used in Li ion battery systems. In addition, integration of select 2D materials into 3D structures, for enhancing both electrical conductivity and electrochemical activity, will prove advantageous. Here a scalable one-step chemical vapor deposition technique is demonstrated for the controlled etching and simultaneous graphene growth on stainless steel substrates resulting in a 3D micro-mesh architecture that is ideal for high rate/high capacity electrodes; the graphene coated 3D stainless steel current collector is used with an MoS2 electrode material for demonstrating high stability and rate capacity in Li-ion batteries.
2D Materials in Lego Style: Synthesis, Characterizations and Applications
(2015-12-04) Gong, Yongji; Ajayan, Pulickel M.; Jun, Lou; Marti, Angel
Recently, the emergence and development of 2D materials with various optical and electrical properties has opened up new routes for electronic and optoelectronic device fabrication based on atomically thin layers. For example, graphene behaves as a semi-metal with extremely high mobility, hexagonal boron nitride (h-BN) is a good insulator and monolayer TMDs such as MoS2, MoSe2 and WSe2 are semiconductors with direct band gap. This diversity offers the opportunity to construct atomically thin electronics based entirely on 2D materials. One of the most promising applications is to get 2D integrated circuits to replace the traditional silicon based ones, which will be much thinner and faster. 2D materials can be considered to be analogous to Lego blocks. The Lego game is to use different Lego blocks to get a complicated Lego building. Similarly, we can use different 2D materials to get the corresponding integrated circuits or devices for energy related applications. Based on this purpose, we need different 2D blocks, which are the most fundamental parts in the 2D world, 2D materials with tunable properties, and different strategies to combine the 2D materials together. Chapter 1 focuses on synthesis, characterization and applications of pristine 2D materials, which are the fundamental blocks for the 2D world. In this part, we synthesized different 2D materials such as insulator (h-BN), metal (graphene) and semiconductors (MX2, M = metal and X = chalcogen) for different applications. There are two directions in this part: one is to explore new 2D materials and the other one is to improve the growth of 2D materials to push them closer to their real applications. Moreover, semiconductors with different band gap (from 1.1 eV to 2.8 eV) and different type (p type and n type) have been developed. Furthermore, we improved the growth of different 2D materials to get their millimeter-scale single crystals or even continuous film. In the coming Chapter 2, we focused on the 2D alloys. The purpose of alloying 2D materials is to engineer the phase and band gap by changing the composition in the alloys. By this, we can tune the optical and electrical properties in 2D materials very easily. The first project in this part is about h-BNC system, which can open a band gap in graphene system, resulting in both high mobilities and high ON-OFF ratio in their transistors. Then we developed the MoS2-xSex (x, 0-2) alloys, in which the band gap can be continuously tuned from 1.50 eV to 1.84 eV. At last, RexMo1-xS2 (x, 0-1) system is developed to study the phase transition with different x. In Chapter 3, heterostructures based on different 2D materials are developed by different strategies. For example, we can get h-BN/h-BNC/graphene lateral heterostructure by combing a conversion method and lithography. We also developed the heterostructures based on MoS2/WS2 and MoSe2/WSe2 by a one-step growth method and two-step growth method, respectively. In both of them, we can get the in-plane and vertical heterostructures. The interface of the in-plane interface is atomically seamless and sharp and the bilayer heterostructures have fixed stacking orientations, which are more advantageous than other methods. At last, we developed more complicated heterostructures, which can be composed by 3 or 4 different 2D materials. In Chapter 4, we further developed several different 3D structures constructed by 2D materials for energy storage and conversion. Basically, this part is inspired by graphene aerogel with porous 3D structure. The porous structure enables the access of electrolyte very easily and the graphene network has very good electrical conductivity, advantageous to work as electrochemical applications. In this part, we developed several different structures for different applications, including MoS2/GO as the anode for lithium ion battery, VO2/GO as the cathode for lithium ion battery and h-BNC as ORR catalyst. For the lithium ion battery, the structures developed here have better performance than the commercial ones with higher capacity, better stability and much higher charge and discharge rate. H-BNC aerogel can even beat the performance of commercial Pt/C as the ORR catalyst. In summary, the research based on 2D materials is like the Lego game, including exploring the Lego blocks (pristine 2D materials and their alloys) and combining them together to form the functional devices (2D heterostructures and 3D porous structure from 2D materials).
3D Macroporous Solids from Chemically Cross-linked Carbon Nanotubes
(Wiley, 2014) Ozden, Sehmus; Narayanan, Tharangattu N.; Tiwary, Chandra S.; Dong, Pei; Hart, Amelia H.C.; Vajtai, Robert; Ajayan, Pulickel M.
Suzuki reaction for covalently interconnected 3D carbon nanotube (CNT) architectures is reported. The synthesis of 3D macroscopic solids made of CNTs covalently connected via Suzuki cross-coupling, a well-known carbon-carbon covalent bond forming reaction in organic chemistry, is scalable. The resulting solid has a highly porous, interconnected structure of chemically cross-linked CNTs. Its use for the removal of oil from contaminated water is demonstrated.
A common tattoo chemical for energy storage: henna plant-derived naphthoquinone dimer as a green and sustainable cathode material for Li-ion batteries
(The Royal Society of Chemistry, 2018) Miroshnikov, Mikhail; Kato, Keiko; Babu, Ganguli; Divya, Kizhmuri P.; Arava, Leela Mohana Reddy; Ajayan, Pulickel M.; John, George
The burgeoning energy demands of an increasingly eco-conscious population have spurred the need for sustainable energy storage devices, and have called into question the viability of the popular lithium ion battery. A series of natural polyaromatic compounds have previously displayed the capability to bind lithium via polar oxygen-containing functional groups that act as redox centers in potential electrodes. Lawsone, a widely renowned dye molecule extracted from the henna leaf, can be dimerized to bislawsone to yield up to six carbonyl/hydroxyl groups for potential lithium coordination. The facile one-step dimerization and subsequent chemical lithiation of bislawsone minimizes synthetic steps and toxic reagents compared to existing systems. We therefore report lithiated bislawsone as a candidate to advance non-toxic and recyclable green battery materials. Bislawsone based electrodes displayed a specific capacity of up to 130 mA h g−1 at 20 mA g−1 currents, and voltage plateaus at 2.1–2.5 V, which are comparable to modern Li-ion battery cathodes.
Advanced Synthesis Techniques and Characterization of Functional Semiconductor Nanomaterials
(2014-01-15) Gullapalli, Sravani; Wong, Michael S.; Verduzco, Rafael; Ajayan, Pulickel M.
Semiconductor materials are used in several modern day applications ranging from photovoltaic devices to environmental remediation. The electronic, optical, catalytic and physical properties of semiconductor nanomaterials can be precisely tuned by altering their size, shape and composition. It is thus imperative to develop simplified cost-effective techniques to synthesize functional semiconductor nanomaterials with structural and morphological control. The overall goal of this thesis is to design new synthetic schemes for well-characterized semiconductor nanomaterials and subsequently demonstrate their potential in photovoltaic and photocatalytic applications. Shape control of semiconductor nanomaterials is crucial for photovoltaic applications. Longer armed cadmium selenide (CdSe) tetrapods have demonstrated enhanced performance in hybrid solar cells. Conventional long arm tetrapod syntheses necessitate multiple injections of flammable phosphorous based chemicals. A new non-phosphorous route to long CdSe tetrapods with arm lengths > 70 nm is demonstrated by manipulating the “greener” selenium precursor temperature in the presence of a quaternary ammonium salt as the shape directing agent. Another interesting shape is the hollow morphology that provides the advantage of higher surface-to-volume ratio. However this shape for CdSe is much less investigated in photovoltaic applications. A novel molten-droplet synthesis strategy is developed to synthesize quantum confined CdSe HNPs based on the slow heating of a low melting point cadmium salt, elemental Se, alkylammonium surfactant in octadecene solvent with no external ligand. This generic technique is shown to be applicable for a variety of metal chalcogenide compositions. Further, photovoltaic device characterization of HNPs in a hybrid solar cell indicate that HNPs have improved electron transport characteristics compared to standard CdSe quantum dots. Hybrid photovoltaic device fabrication is based on low cost colloidal solution-based techniques. A new insight to understanding nanoparticle solvent interactions is provided using coarse-grained computational models and experimental characterization of oleate-capped NPs in various solvents. Solvent polarity was shown to strongly affect NP hydrodynamic diameter, colloidal stability and aggregation behavior. Photocatalytic removal of organic contaminants using semiconductor nanomaterials provides a low-cost, environmentally clean alternative for the utilization of renewable energy sources. Most photocatalytic environmental remediation techniques are oxidative and result in either partial or complete mineralization of the contaminant. A less explored reductive photocatalytic approach to organohalide removal has been demonstrated without necessitating an external co-feed of hydrogen (H2). Hydrodechlorination (HDC) of trichloroethene (TCE) as the test reaction. Bifunctional palladium-based titanium dioxide (TiO2) reduction catalysts were synthesized for the photocatalytic TCE HDC reaction with simultaneous in-situ H2 generation by photocatalytic water splitting. Extension of this reductive photocatalytic approach to other groundwater contaminants could simplify future remediation efforts.
Advances in electric two-wheeler technologies
(Elsevier, 2023) Nayak, Anish K.; Ganguli, Babu; Ajayan, Pulickel M.
Cost effective modes of transport keeping in conjunction with sustainable outlooks for the future have ensured new technologies and initiatives being taken across the globe. Lighter electric vehicles including two-wheelers or scooters have risen in popularity, with both government and private backed industries investing heavily in green energy. Various state of the art energy systems has been discussed, along with unique approaches to ensure optimum efficiency and lifetime, such as preventing thermal runway reactions, and minimal degradation of electrodes. Supercapacitors, and hybrid fuel cells show potential to be adapted on large scale. New materials and approaches to synthesising the former have also been addressed, with emphasis on the powering of the next generation vehicles. Hybrid motor and engine setups developed over the last several years show great improvement and consume minimal quantity of energy. Clever braking technologies further showcase regenerative techniques and improve mileage. Fuel cost comparisons and recycling methodologies are seen to be researched extensively, while multiple challenges have been addressed. Major problems such as reducing carbon footprints and minimising several particulate pollutions present in the atmosphere are demonstrated to be overcome by implementation of electric two wheelers with regions like Europe and Asia showing the most promise in current times. This review will aim to integrate the individual functions and piece the whole system together. Analysis of future opportunities will allow for a comprehensive overview as well.
Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes
(Nature Publishing Group, 2015) Kabbani, Mohamad A.; Tiwary, Chandra Sekhar; Autreto, Pedro A.S.; Brunetto, Gustavo; Som, Anirban; Krishnadas, K.R.; Ozden, Sehmus; Hackenberg, Ken P.; Gong, Yongi; Galvao, Douglas S.; Vajtai, Robert; Kabbani, Ahmad T.; Pradeep, Thalappil; Ajayan, Pulickel M.
Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.
Atomic cobalt on nitrogen-doped graphene for hydrogen generation
(Nature Publishing Group, 2015) Fei, Huilong; Dong, Juncai; Arellano-Jiménez, M. Josefina; Ye, Gonglan; Kim, Nam Dong; Samuel, Errol L.G.; Peng, Zhiwei; Zhu, Zhuan; Qin, Fan; Bao, Jiming; Yacaman, Miguel Jose; Ajayan, Pulickel M.; Chen, Dongliang; Tour, James M.
Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.
Atomically thin gallium layers from solid-melt exfoliation
(AAAS, 2018) Kochat, Vidya; Samanta, Atanu; Zhang, Yuan; Bhowmick, Sanjit; Manimunda, Praveena; Asif, Syed Asif S.; Stender, Anthony S.; Vajtai, Robert; Singh, Abhishek K.; Tiwary, Chandra S.; Ajayan, Pulickel M.
Among the large number of promising two-dimensional (2D) atomic layer crystals, true metallic layers are rare. Using combined theoretical and experimental approaches, we report on the stability and successful exfoliation of atomically thin “gallenene” sheets on a silicon substrate, which has two distinct atomic arrangements along crystallographic twin directions of the parent α-gallium. With a weak interface between solid and molten phases of gallium, a solid-melt interface exfoliation technique is developed to extract these layers. Phonon dispersion calculations show that gallenene can be stabilized with bulk gallium lattice parameters. The electronic band structure of gallenene shows a combination of partially filled Dirac cone and the nonlinear dispersive band near the Fermi level, suggesting that gallenene should behave as a metallic layer. Furthermore, it is observed that the strong interaction of gallenene with other 2D semiconductors induces semiconducting to metallic phase transitions in the latter, paving the way for using gallenene as promising metallic contacts in 2D devices.
Atomistic measurement and modeling of intrinsic fracture toughness of two-dimensional materials
(PNAS, 2022) Zhang, Xu; Nguyen, Hoang; Zhang, Xiang; Ajayan, Pulickel M.; Wen, Jianguo; Espinosa, Horacio D.
Quantifying the intrinsic mechanical properties of two-dimensional (2D) materials is essential to predict the long-term reliability of materials and systems in emerging applications ranging from energy to health to next-generation sensors and electronics. Currently, measurements of fracture toughness and identification of associated atomistic mechanisms remain challenging. Herein, we report an integrated experimental–computational framework in which in-situ high-resolution transmission electron microscopy (HRTEM) measurements of the intrinsic fracture energy of monolayer MoS 2 and MoSe 2 are in good agreement with atomistic model predictions based on an accurately parameterized interatomic potential. Changes in crystalline structures at the crack tip and crack edges, as observed in in-situ HRTEM crack extension tests, are properly predicted. Such a good agreement is the result of including large deformation pathways and phase transitions in the parameterization of the inter-atomic potential. The established framework emerges as a robust approach to determine the predictive capabilities of molecular dynamics models employed in the screening of 2D materials, in the spirit of the materials genome initiative. Moreover, it enables device-level predictions with superior accuracy (e.g., fatigue lifetime predictions of electro- and opto-electronic nanodevices).
Bacteria as Bio-Template for 3D Carbon Nanotube Architectures
(Springer Nature, 2017) Ozden, Sehmus; Macwan, Isaac G.; Owuor, Peter S.; Kosolwattana, Suppanat; Autreto, Pedro A.S.; Silwal, Sushila; Vajtai, Robert; Tiwary, Chandra S.; Mohite, Aditya D.; Patra, Prabir K.; Ajayan, Pulickel M.
It is one of the most important needs to develop renewable, scalable and multifunctional methods for the fabrication of 3D carbon architectures. Even though a lot of methods have been developed to create porous and mechanically stable 3D scaffolds, the fabrication and control over the synthesis of such architectures still remain a challenge. Here, we used Magnetospirillum magneticum (AMB-1) bacteria as a bio-template to fabricate light-weight 3D solid structure of carbon nanotubes (CNTs) with interconnected porosity. The resulting porous scaffold showed good mechanical stability and large surface area because of the excellent pore interconnection and high porosity. Steered molecular dynamics simulations were used to quantify the interactions between nanotubes and AMB-1 via the cell surface protein MSP-1 and flagellin. The 3D CNTs-AMB1 nanocomposite scaffold is further demonstrated as a potential substrate for electrodes in supercapacitor applications.
Bifunctional Luminomagnetic Rare-Earth Nanorods for High-Contrast Bioimaging Nanoprobes
(Springer Nature, 2016) Gupta, Bipin Kumar; Singh, Satbir; Kumar, Pawan; Lee, Yean; Kedawat, Garima; Narayanan, Tharangattu N.; Vithayathil, Sajna Antony; Ge, Liehui; Zhan, Xiaobo; Gupta, Sarika; Martí, Angel A.; Vajtai, Robert; Ajayan, Pulickel M.; Kaipparettu, Benny Abraham
Nanoparticles exhibiting both magnetic and luminescent properties are need of the hour for many biological applications. A single compound exhibiting this combination of properties is uncommon. Herein, we report a strategy to synthesize a bifunctional luminomagnetic Gd2−xEuxO3 (x = 0.05 to 0.5) nanorod, with a diameter of ~20 nm and length in ~0.6 μm, using hydrothermal method. Gd2O3:Eu3+ nanorods have been characterized by studying its structural, optical and magnetic properties. The advantage offered by photoluminescent imaging with Gd2O3:Eu3+ nanorods is that this ultrafine nanorod material exhibits hypersensitive intense red emission (610 nm) with good brightness (quantum yield more than 90%), which is an essential parameter for high-contrast bioimaging, especially for overcoming auto fluorescent background. The utility of luminomagnetic nanorods for biological applications in high-contrast cell imaging capability and cell toxicity to image two human breast cancer cell lines T47D and MDA-MB-231 are also evaluated. Additionally, to understand the significance of shape of the nanostructure, the photoluminescence and paramagnetic characteristic of Gd2O3:Eu3+ nanorods were compared with the spherical nanoparticles of Gd2O3:Eu3+.
Blueshift of the A-exciton peak in folded monolayer 1H-MoS2
(American Physical Society, 2013) Crowne, Frank J.; Amani, Matin; Birdwell, A. Glen; Chin, Matthew L.; O'Regan, Terrance P.; Najmaei, Sina; Liu, Zheng; Ajayan, Pulickel M.; Lou, Jun; Dubey, Madan
Carbon nanotube based hybrid nanostructures: Synthesis and applications
(2010) Ou, Fung Suong; Ajayan, Pulickel M.
Hybrid nanostructures are fascinating materials for their promising applications in future nanoelectronics, electrical interconnects and energy storage devices. Practical ways of connecting individual carbon nanotubes to metal contacts for their use as interconnects and in electronic devices have been challenging. In this thesis, carbon nanotube based hybrids that combine the best properties of carbon nanotubes and metal nanowires have been fabricated. The electrical properties and Raman spectra of the hybrid nanowires are also studied. This thesis will focus on our recent results in the development of carbon nanotube hybrids for various applications. Various hybrid structures of multiwalled carbon nanotubes and metal nanowires can be fabricated using a combination of electrodeposition and chemical vapor deposition techniques. Controlled fabrication of multi-segmented structures will be studied. Several novel applications of these structures, for example, as electrodes in ultra-high power supercapacitors, multi-functional smart materials are also studied. The thesis will also highlight the development of carbon nanotube hybrids based smart materials. Hybrid nanowires with hydrophobic carbon nanotube tails and hydrophilic metal nanowire heads, allows for the assembly of spheres in solution. The design and manipulation of these carbon nanotube hybrids based smart structures for various novel applications will be discussed. Such new class of carbon nanotube hybrids surfactants are likely to lead as new tools in various fields such as microfluidics or water purification. In addition, we will also look at other variations of hybrid nanostructures fabricated from our method.
Carbon Nanotube Doping Procedures for Three-Dimensional Macro-Structures and Gallium-Nitride Functionalization
(2014-05-05) Hashim, Daniel Paul; Ajayan, Pulickel M.; Lou, Jun; Rau, Carl
Carbon nanotubes (CNTs) in all of their forms are considered “gamechanger” materials that will revolutionize the modern world through many diverse applications. Over 20 years of research has gone into CNT materials, yet we still see their limited use in feasible real-world applications. Part of the reason is because it still remains a challenge for materials scientists to engineer these extraordinary nano-scale building blocks into covalently interconnected three-dimensional (3-D) structures, and to realize macro-scaled sizes via a bulk synthesis process. Another challenge is being able to create CNT-semiconductor hybrid materials by covalently joining other useful semiconductor compounds with CNTs in order to harness their value for electronics applications. The experimental research compiled in the first part of this thesis pioneers an innovative approach to synthesize 3-D macro-structured forms of CNTs by utilizing a heteroatom doping strategy via chemical vapor deposition (CVD). The importance of substitutional doping effects of boron on CNT structural morphology is characterized experimentally and theoretically for the first time so as to create a robust, solid, 3-D networked, CNT “sponge” form. The CNT “sponge” was characterized to exhibit an exotic combination of multifunctional properties including high porosity, high surface area, low density, superhydorphicity, oleophilicity, ferromagnetism, and good elastic mechanical performance. It was also demonstrated that 3-D porous CNT “sponges” could be used for environmental needs as reusable oil spill sorbent materials in seawater. In an effort to combine group III–V semiconductors with CNTs, the second part of this thesis involve a simple solution-based technique for gallium functionalization of nitrogen-doped multi-wall carbon nanotubes. With an aqueous solution of a gallium salt (GaI3), it was possible to form covalent bonds between the Ga3C ion and the nitrogen atoms of the doped carbon nanotubes to form a gallium nitride–carbon nanotube hybrid at room temperature. This functionalization was evaluated by x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy.
Cement-based direct ink for 3D printing of complex architected structures
(2021-02-09) Rahman, Muhammad M.; Sajadi, Seyed Mohammad; Kumar, Ashok; Boul, Peter J.; Thaemlitz, Carl; Ajayan, Pulickel M.; Rice University; Saudi Arabian Oil Company, Dhahran (SA); United States Patent and Trademark Office
Provide is a cement ink for a cement ink for 3D printing (which also includes additive manufacturing) of 3D cement structures and materials. The cement ink includes an American Petroleum Institute (API) Class G cement, a nano-clay, a superplasticizer, a hydroxyethyl cellulose, and a defoamer. The nano-clay may be hydrophilic bentonite. The superplasticizer may be a polycarboxylate ether. The defoamer may be 2-ethyl-1-hexanol. Processes for forming the cement ink and printing 3D cement structures using the cement ink are also provided.
Characterizations of two-photon absorption process induced by defects in aluminum nitride using Z-scan method
(IOP Publishing, 2024) Zhou, Jingan; Li, Tao; Zhao, Xuan; Zhang, Xiang; Doumani, Jacques; Xu, Mingfei; He, Ziyi; Luo, Shisong; Mei, Zhaobo; Chang, Cheng; Robinson, Jacob T.; Ajayan, Pulickel M.; Kono, Junichiro; Zhao, Yuji; Smalley-Curl Institute
In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in Aluminum nitride single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.
Charge coupled device based on atomically layered van der waals solid state film for opto-electronic memory and image capture
(2016-08-30) Lei, Sidong; Ge, Liehui; George, Antony; Li, Bo; Vajtai, Robert; Ajayan, Pulickel M.; Rice University; United States Patent and Trademark Office
An opto-electronic sensor may provide one or more layers of atomically layered photo-sensitive materials. The sensor may include a gate electrode layer, a dielectric layer in contact with the gate electrode layer, and a working media layer that is photo-sensitive deposited on the dielectric layer. The working media layer may provide one or more layers of one or more materials where each of the one or more layers is an atomic layer. The sensor may also include side electrodes in contact with the working media layer.
Charge-transfer-based Gas Sensing Using Atomic-layer MoS2
(Nature Publishing Group, 2015) Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M.; Kim, Dong-Ho
Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2ﾠsynthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2was developed.ﾠIn situﾠphotoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2ﾠand NH3ﾠmolecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2ﾠand NH3ﾠmolecules are likely to adsorb onto the surface of the MoS2. Theﾠin situﾠPL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2ﾠand the gas molecules.
Chemical and Physical Graphene Modifications
(2013-07-11) Pembroke, Elvira; Tour, James M.; Ajayan, Pulickel M.; McDevitt, John T.
This dissertation is inspired by recent progress in the chemistry, physics, and nanotechnology of graphene, a single layer of carbon atoms. Studying and controllably modifying the electrical properties of graphene while minimizing damage to the lattice continues to be a challenge to the scientific community. Chapter 1 focuses on the covalent attachment of molecules with different functional groups to graphene and how functionalization modifies the electrical transport properties of graphene field effect transistors (FET) devices. Functionalization is shown to predominantly induce p-type doping, undiminished mobility, and increased conductivity at the neutrality point. Physisorbed molecules desorb easily and do not have a significant effect. Statistical analysis enables us to extract trends even though identically fabricated graphene devices can exhibit a wide range of electrical behaviors, emphasizing that conclusions should not be drawn based on singular extremes. In Chapter 2 we present the fabrication and characterization of graphene antidot lattices produced by placing graphene on pre-patterned substrates. While the graphene remains intact atop a periodic well pattern we observe a surface potential differential inside vs. outside the wells. Chapter 3 investigates graphene FETs with multiple neutrality points. We used Raman mapping to determine if multiple local gating fields can be spatially resolved. While we were able to show doping inhomogeneity in graphene devices, there was no obvious difference between devices with one vs. multiple neutrality points. In Chapter 4 we demonstrate a method to grow graphene from solid carbon sources. I confirmed the single layer nature of the produced graphene using atomic force microscopy (AFM) and fabricated and characterized intrinsic FETs based on solid-derived graphene. In Chapter 5 we propose that graphene layers nucleate along and underneath the edges of existing graphene layers with a continuous layer remaining on top. My AFM characterization of hexagonal graphene onions provided evidence for our proposed nucleation mechanism. Chapter 6 is a report on graphene resistor devices that were contributed to an experiment aboard the International Space Station which seeks to investigate the effects of radiation exposure. Overall, the work accomplished in this dissertation constitutes a step forward toward controllable device behavior in graphene based electronics.

Browsing by Author "Ajayan, Pulickel M."

Results Per Page

Sort Options