Mechanical Engineering Publications

Permanent URI for this collection

https://hdl.handle.net/1911/64878

Browse

Now showing 1 - 15 of 15

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
Dynamic Self-Stiffening in Liquid Crystal Elastomers
(Nature Publishing Group, 2013) Agrawal, Aditya; Chipara, Alin C.; Shamoo, Yousif; Patra, Prabir K.; Carey, Brent J.; Ajayan, Pulickel M.; Chapman, Walter G.; Verduzco, Rafael
Biological tissues have the remarkable ability to remodel and repair in response to disease, injury and mechanical stresses. Synthetic materials lack the complexity of biological tissues, and man-made materials that respond to external stresses through a permanent increase in stiffness are uncommon. Here we report that polydomain nematic liquid crystal elastomers increase in stiffness by up to 90% when subjected to a low-amplitude (5%), repetitive (dynamic) compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through rheological and X-ray diffraction measurements, stiffening can be attributed to a mobile nematic director, which rotates in response to dynamic compression. Stiffening under dynamic compression has not been previously observed in liquid crystal elastomers and may be useful for the development of self-healing materials or for the development of biocompatible, adaptive materials for tissue replacement.
Electrical performance of monolayer MoS2 field-effect transistors prepared by chemical vapor deposition
(American Institute of Physics, 2013) Amani, Matin; Chin, Matthew L.; Birdwell, A. Glen; O'Regan, Terrance P.; Najmaei, Sina; Liu, Zheng; Ajayan, Pulickel M.; Lou, Jun; Dubey, Madan
Molybdenum disulfide (MoS2) field effect transistors (FET) were fabricated on atomically smooth large-area single layers grown by chemical vapor deposition. The layer qualities and physical properties were characterized using high-resolution Raman and photoluminescence spectroscopy, scanning electron microscopy, and atomic force microscopy. Electronic performance of the FET devices was measured using field effect mobility measurements as a function of temperature. The back-gated devices had mobilities of 6.0 cm2/V s at 300K without a high-j dielectric overcoat and increased to 16.1 cm2/V s with a high-j dielectric overcoat. In addition the devices show on/off ratios ranging from 105 to 109.
Fluorinated Graphene Oxide: a New Multimodal Material for Biological Applications
(Wiley, 2013) Romero-Aburto, Rebeca; Narayanan, Tharangattu N.; Nagaoka, Yutaka; Hasumura, Takashi; Mitcham, Trevor M.; Fukuda, Takahiro; Cox, Paris J.; Bouchard, Richard R.; Maekawa, Toru; Kumar, Sakthi; Torti, Suzy V.; Mani, Sendurai A.; Ajayan, Pulickel M.
Fluorinated graphene oxide (FGO) is reported for the first time as a magnetically responsive drug carrier that can serve as a MRI and photoacoustic contrast agent, under pre-clinical settings, as well as a photothermal therapy Its hydrophilic nature facilitates biocompatibility. FGO as a broad wavelength absorber, with high charge transfer and strong nonlinear scattering is optimal for NIR laser-induced hyperthermia.
Hybrid 2D Nanomaterials as Dual-mode Contrast Agents in Cellular Imaging
(Wiley-VCH Verlag, 2012) Narayanan, Tharangattu N.; Gupta, Bipin K.; Vithayathil, Sajna A.; Aburto, Rebeca R.; Mani, Sendurai A.; Taha-Tijerina, Jaime; Xie, Bin; Kaipparettu, Benny A.; Torti, Suzy V.; Ajayan, Pulickel M.
Liquid metal nanodroplet dynamics inside nanocontainers
(Nature Publishing Group, 2013) Jung, Hyun Young; Chun, Hyunkyung; Park, Sora; Kang, Seoung-Hun; Ahn, Chi Won; Kwon, Young-Kyun; Upmanyu, Moneesh; Ajayan, Pulickel M.; Jung, Yung Joon
Here we report direct observations of spatial movements of nanodroplets of Pb metal trapped inside sealed carbon nanocontainers. We find drastic changes in the mobility of the liquid droplets as the particle size increases from a few to a few ten nanometers. In open containers the droplet becomes immobile and readily evaporates to the vacuum environment. The particle mobility strongly depends on confinement, particle size, and wetting on the enclosed surface. The collisions between droplets increase mobility but the tendency is reversed if collisions lead to droplet coalescence. The dynamics of confined nanodroplets could provide new insights into the activity of nanostructures in spatially constrained geometries.
Lithium storage mechanisms in purpurin based organic lithium ion battery electrodes
(Nature Publishing Group, 2012) Reddy, Arava Leela Mohana; Nagarajan, Subbiah; Chumyim, Porramate; Gowda, Sanketh R.; Pradhan, Padmanava; Jadhav, Swapnil R.; Dubey, Madan; John, George; Ajayan, Pulickel M.
Current lithium batteries operate on inorganic insertion compounds to power a diverse range of applications, but recently there is a surging demand to develop environmentally friendly green electrode materials. To develop sustainable and eco-friendly lithium ion batteries, we report reversible lithium ion storage properties of a naturally occurring and abundant organic compound purpurin, which is non-toxic and derived from the plant madder. The carbonyl/hydroxyl groups present in purpurin molecules act as redox centers and reacts electrochemically with Li-ions during the charge/discharge process. The mechanism of lithiation of purpurin is fully elucidated using NMR, UV and FTIR spectral studies. The formation of the most favored six membered binding core of lithium ion with carbonyl groups of purpurin and hydroxyl groups at C-1 and C-4 positions respectively facilitated lithiation process, whereas hydroxyl group at C-2 position remains unaltered.
Metallic 1T phase source/drain electrodes for field effect transistors from chemical vapor deposited MoS2
(AIP, 2014) Kappera, Rajesh; Voiry, Damien; Yalcin, Sibel Ebru; Jen, Wesley; Acerce, Muharrem; Torrel, Sol; Branch, Brittany; Lei, Sidong; Chen, Weibing; Najmaei, Sina; Lou, Jun; Ajayan, Pulickel M.; Gupta, Gautam; Mohite, Aditya D.; Chhowalla, Manish
Two dimensional transitionmetal dichalcogenides (2D TMDs) offer promise as optoelectronic materials due to their direct band gap and reasonably good mobility values. However, most metals form high resistance contacts on semiconducting TMDs such as MoS2. The large contact resistance limits the performance of devices. Unlike bulk materials, low contact resistance cannot be stably achieved in 2D materials by doping. Here we build on our previous work in which we demonstrated that it is possible to achieve low contact resistance electrodes by phase transformation. We show that similar to the previously demonstrated mechanically exfoliated samples, it is possible to decrease the contact resistance and enhance the FET performance by locally inducing and patterning the metallic 1T phase of MoS2 on chemically vapor deposited material. The device properties are substantially improved with 1T phase source/drain electrodes.
Paintable Battery
(Springer, 2012) Singh, Neelam; Galande, Charudatta; Miranda, Andrea; Mathkar, Akshay; Gao, Wei; Reddy, Arava Leela Mohana; Vlad, Alexandru; Ajayan, Pulickel M.
If the components of a battery, including electrodes, separator, electrolyte and the current collectors can be designed as paints and applied sequentially to build a complete battery, on any arbitrary surface, it would have significant impact on the design, implementation and integration of energy storage devices. Here, we establish a paradigm change in battery assembly by fabricating rechargeable Li-ion batteries solely by multi-step spray painting of its components on a variety of materials such as metals, glass, glazed ceramics and flexible polymer substrates. We also demonstrate the possibility of interconnected modular spray painted battery units to be coupled to energy conversion devices such as solar cells, with possibilities of building standalone energy capture-storage hybrid devices in different configurations.
Recent Advances in Optical Limiting Properties of Fluorinated Graphene Oxides
(SPIE, 2013) Chantharasupawong, Panit; Philip, Reji; Narayanan, Narayanan T.; Sudeep, Parambath M.; Mathkar, Akshay; Ajayan, Pulickel M.; Thomas, Jayan
There is a substantial interest in finding materials with high nonlinear optical (NLO) properties of materials because of its attractive applications in optical limiting for safety protections. In an effort to develop highly performing optical limiting materials, recently we have found that fluorination of graphene oxides leads to improvement in their NLO properties.
Roll up nanowire battery from silicon chips
(National Academy of Sciences, 2012) Vlad, Alexandru; Reddy, Arava Leela Mohana; Ajayan, Anakha; Singh, Neelam; Gohy, Jean-François; Melinte, Sorin; Ajayan, Pulickel M.
Here we report an approach to roll out Li-ion battery components from silicon chips by a continuous and repeatable etch-infiltratepeel cycle. Vertically aligned silicon nanowires etched from recycled silicon wafers are captured in a polymer matrix that operates as Liþ gel-electrolyte and electrode separator and peeled off to make multiple battery devices out of a single wafer. Porous, electrically interconnected copper nanoshells are conformally deposited around the silicon nanowires to stabilize the electrodes over extended cycles and provide efficient current collection. Using the above developed process we demonstrate an operational full cell 3.4 V lithium-polymer silicon nanowire (LIPOSIL) battery which is mechanically flexible and scalable to large dimensions.
Second harmonic microscopy of monolayer MoS2
(American Physical Society, 2013) Kumar, Nardeep; Najmaei, Sina; Cui, Qiannan; Ceballos, Frank; Ajayan, Pulickel M.; Lou, Jun; Zhao, Hui
We show that the lack of inversion symmetry in monolayer MoS2 allows strong optical second harmonic generation. The second harmonic of an 810-nm pulse is generated in a mechanically exfoliated monolayer, with a nonlinear susceptibility on the order of 10−7 m/V. The susceptibility reduces by a factor of seven in trilayers, and by about two orders ofmagnitude in even layers. A proof-of-principle second harmonicmicroscopymeasurement is performed on samples grown by chemical vapor deposition, which illustrates potential applications of this effect in the fast and noninvasive detection of crystalline orientation, thickness uniformity, layer stacking, and single-crystal domain size of atomically thin films of MoS2 and similar materials.
Super-stretchable, Transparent Carbon Nanotube-Based Capacitive Strain Sensors for Human Motion Detection
(Nature Publishing Group, 2013) Cai, Le; Song, Li; Luan, Pingshan; Zhang, Qiang; Zhang, Nan; Gao, Qingqing; Zhao, Duan; Zhang, Xiao; Tu, Min; Yang, Feng; Zhou, Wenbin; Fan, Qingxia; Luo, Jun; Zhou, Weiya; Ajayan, Pulickel M.; Xie, Sishen
Realization of advanced bio-interactive electronic devices requires mechanically compliant sensors with the ability to detect extremely large strain. Here, we design a new multifunctional carbon nanotube (CNT) based capacitive strain sensors which can detect strains up to 300% with excellent durability even after thousands of cycles. The CNT-based strain gauge devices exhibit deterministic and linear capacitive response throughout the whole strain range with a gauge factor very close to the predicted value (strictly 1), representing the highest sensitivity value. The strain tests reveal the presented strain gauge with excellent dynamic sensing ability without overshoot or relaxation, and ultrafast response at sub-second scale. Coupling these superior sensing capabilities to the high transparency, physical robustness and flexibility, we believe the designed stretchable multifunctional CNT-based strain gauge may have various potential applications in human friendly and wearable smart electronics, subsequently demonstrated by our prototypical data glove and respiration monitor.
Supercapacitor Operating At 200 Degrees Celsius
(Nature Publishing Group, 2013) Borges, Raquel S.; Reddy, Arava Leela Mohana; Rodrigues, Marco-Tulio F.; Gullapalli, Hemtej; Balakrishnan, Kaushik; Silva, Glaura G.; Ajayan, Pulickel M.
The operating temperatures of current electrochemical energy storage devices are limited due to electrolyte degradation and separator instability at higher temperatures. Here we demonstrate that a tailored mixture of materials can facilitate operation of supercapacitors at record temperatures, as high as 2006C. Composite electrolyte/separator structures made from naturally occurring clay and room temperature ionic liquids, with graphitic carbon electrodes, show stable supercapacitor performance at 2006C with good cyclic stability. Free standing films of such high temperature composite electrolyte systems can become versatile functional membranes in several high temperature energy conversion and storage applications.
Using the Plasmon Linewidth To Calculate the Time and Efficiency of Electron Transfer between Gold Nanorods and Graphene
(American Chemical Society, 2013) Hoggard, Anneli; Wang, Lin-Yung; Ma, Lulu; Fang, Ying; You, Ge; Olson, Jana; Liu, Zheng; Chang, Wei-Shun; Ajayan, Pulickel M.; Link, Stephan; Laboratory for Nanophotonics
We present a quantitative analysis of the electron transfer between single gold nanorods and monolayer graphene under no electrical bias. Using single-particle dark-field scattering and photoluminescence spectroscopy to access the homogeneous linewidth, we observe broadening of the surface plasmon resonance for gold nanorods on graphene compared to nanorods on a quartz substrate. Because of the absence of spectral plasmon shifts, dielectric interactions between the gold nanorods and graphene are not important and we instead assign the plasmon damping to charge transfer between plasmon-generated hot electrons and the graphene that acts as an efficient acceptor. Analysis of the plasmon linewidth yields an average electron transfer time of 160 ± 30 fs, which is otherwise difficult to measure directly in the time domain with single-particle sensitivity. In comparison to intrinsic hot electron decay and radiative relaxation, we furthermore calculate from the plasmon linewidth that charge transfer between the gold nanorods and the graphene support occurs with an efficiency of ∼10%. Our results are important for future applications of light harvesting with metal nanoparticle plasmons and efficient hot electron acceptors as well as for understanding hot electron transfer in plasmon-assisted chemical reactions.

Browse

Browsing Mechanical Engineering Publications by Author "Ajayan, Pulickel M."

Results Per Page

Sort Options