Plasmons in assembled metal nanostructures: radiative and nonradiative properties, near-field coupling and its universal scaling behavior

Noble metal nanostructures possess unique properties including large near-field enhancement and strong light scattering and absorption due to their plasmon resonance - the collective coherent oscillation of the metal free electrons in resonance with the electromagnetic field of light. The effect of nanostructure size, shape, composition, and environment on the plasmon resonance frequency and plasmonic enhancement is well known. In this thesis, we describe the effect of inter-particle coupling in assembled plasmonic nanostructures on their radiative and non-radiative properties. When metal nanoparticles assemble, plasmon oscillations of neighboring particles couple, resulting in a shift in the plasmon resonance frequency. Our investigation of plasmon coupling in gold nanorods shows that the coupling between the plasmons is "bonding" in nature when the plasmon oscillations are polarized along the inter-particle axis, whereas an "anti-bonding" interaction results when the polarization is perpendicular. We studied the distance-dependence of plasmon coupling using electrodynamic simulations and experimental plasmon resonances of lithographically fabricated gold nanoparticle pairs with systematically varying inter-particle separations. The strength of plasmon bonding, reflected by the fractional plasmon shift, decays near-exponentially with the inter-particle separation (in units of particle size) according to a universal trend independent of the nanoparticle size, shape, metal type, or medium. From the universal scaling model, we obtain a "plasmon ruler equation" which calculates (in good agreement with the experiments of Alivisatos and Liphardt) the inter-particle separation in a gold nanosphere pair from its plasmon resonance shift, making it applicable to the determination of inter-site distances in biological systems. Universal size-scaling is valid also in the metal nanoshell structure, a nanosphere trimer, and pairs of elongated nanoparticles, thus making it a generalized fundamental model, which is useful in optimizing plasmon coupling for achieving tunable plasmon resonances, enhanced plasmonic sensitivities, and large SERS cross-sections. Ultrafast laser pump-probe studies of non-radiative electronic relaxation in coupled metal nanospheres in aggregates and in gold nanospheres conjugated to thiol SAMs are also reported. We also show that the relative contribution of scattering (radiative) to absorption (non-radiative) part of the plasmon relaxation, respectively useful in optical and photothermal applications, can be increased by increasing the nanostructure size.Ph.D.Committee Chair: El-Sayed, Mostafa A.; Committee Member: Lyon, L. Andrew; Committee Member: Sherrill, C. David; Committee Member: Wang, Zhong Lin; Committee Member: Whetten, Robert L

Phase transition of copper (I) sulfide and its implication for purported superconductivity of LK-99

Lee, Kim, and coworkers have recently claimed ambient temperature and pressure superconductivity in a modified lead apatite material named LK-99. However, the polycrystalline material synthesized has a significant fraction of copper (I) sulfide. Copper (I) sulfide has a known phase transition at 104 degrees C from an ordered low-temperature phase to a high-temperature superionic phase. As a result of this phase transition, copper (I) sulfide exhibits sharp transitions in electrical resistivity and heat capacity, which are expected to coincide with the temperature-induced transitions reported for LK-99. This implies that LK-99 must be synthesized without any copper (I) sulfide to allow unambiguous validation of the superconducting properties of LK-99.Comment: 5 pages, 2 figure

In situ formation of catalytically active graphene in ethylene photo-epoxidation.

Ethylene epoxidation is used to produce 2 × 107 ton per year of ethylene oxide, a major feedstock for commodity chemicals and plastics. While high pressures and temperatures are required for the reaction, plasmonic photoexcitation of the Ag catalyst enables epoxidation at near-ambient conditions. Here, we use surface-enhanced Raman scattering to monitor the plasmon excitation-assisted reaction on individual sites of a Ag nanoparticle catalyst. We uncover an unconventional mechanism, wherein the primary step is the photosynthesis of graphene on the Ag surface. Epoxidation of ethylene is then promoted by this photogenerated graphene. Density functional theory simulations point to edge defects on the graphene as the sites for epoxidation. Guided by this insight, we synthesize a composite graphene/Ag/α-Al2O3 catalyst, which accomplishes ethylene photo-epoxidation under ambient conditions at which the conventional Ag/α-Al2O3 catalyst shows negligible activity. Our finding of in situ photogeneration of catalytically active graphene may apply to other photocatalytic hydrocarbon transformations

Energy Efficient Clustering Protocols in Cognitive Network for Better CR Performances

Volume 7 Issue 11 (November 201

Comparative study to assess the functional outcome in management of inter-trochanteric fractures by proximal femoral nail versus proximal femoral nail anti-rotation

Background: Proximal femoral fractures are one of the most common fractures occurring in elderly due to osteoporosis and increase in life expectancy. The management of these fractures poses a serious challenge in terms of obtaining a stable fixation and a good post-operative outcome. In this study, we compare two intramedullary devices: Proximal femoral nail (PFN) and proximal femoral nail anti-rotation (PFN-A), used commonly for the fixation of proximal femoral fractures.Methods: Patients presenting with inter-trochanteric fractures were included and randomly allocated to two groups for treatment with either PFN or PFN-A. Pre-operative radiographs of normal side were used to grade osteoporosis by Singh’s index. Post-operative radiographs were used to assess the tip-apex distance and quality of reduction. Functional outcome was compared on the basis of Harris hip score at final follow-up. Patients were followed up at an interval of 1, 3 and 6 months respectively.Results: The study included 30 patients with 15 patients in each group. The duration of surgery and blood loss was significantly less in PFN-A group as compared to PFN. Functional outcome as assessed by Harris hip score was similar in both the groups. Implant related complications, though less in PFN-A group, had statistically insignificant difference.Conclusions: It can be safely concluded that, in spite of no differences in functional outcome between the two groups, a shorter duration of surgery and less blood loss would still make PFN-A a better choice in such patients, especially the elderly and co-morbid/compromised patients

Comparative study between delto-pectoral and deltoid splitting approach in surgical treatment of proximal humerus fractures using philos plating

Background: The present study was done to compare the two approaches of proximal humerus PHILOS plating on the basis of functional outcome of patients and other perioperative parameters.Methods: 40 patients with type 2 and type 3 proximal humerus were assigned to group A and B pre-operatively using random alternate allocation. Patients in group-A were operated with deltoid splitting approach while patients in group-B were operated with delto-pectoral approach. Functional outcome was assessed at 6 weeks, 3-months and 6-months. Perioperative parameters like duration of surgery, associated complications, and hospital stay were also noted and compared.Results: In each group, there were 12 two-part fractures and 8 three-part fractures. For 2-part fractures the mean duration of surgery was 51.33 min for group A and 63.37 min for group B. While for 3-part fractures it was 67.5 min and 80 min respectively. Irrespective of fracture type, there was statistically significant difference between the constant scores in both groups at 3 months (2-part: group A: 67.67; group B: 44.7; p value=0.001. 3-part: group A: 66; group B: 48; p value=0.001). However, the difference between two groups at 6 months was not statistically significant.Conclusions: Both approaches show satisfactory outcomes over a long period. However, the significantly less operative time and minimal soft tissue dissection in deltoid splitting approach can be used as an advantage in particular cases. Moreover, there was an early return to day-to-day activities for the deltoid splitting group which should be considered when treating an active individual

Closed reduction and internal fixation with titanium elastic nailing system in pediatric both-bone forearm fractures

Background: The present study is designed to analyse the postoperative clinical and functional outcome of closed reduction and internal fixation of pediatric both-bone forearm fractures with titanium elastic nailing system (TENS).Methods: A total of 32 patients in the age group of 5 to 15 years with fracture both-bone forearm underwent closed reduction and internal fixation with TENS at our hospital. Patients with displaced fractures having angulation more than 10° and rotation of more than 45° or fractures with unacceptable reduction post conservative management were included in this study. For functional outcome, upper extremity rating scale (UERS) was used to evaluate the range of motion and grip strength.Results: Patients were followed up for a period of 6 months. In all cases fracture united in the range of 6-14 weeks without any malunion. All 32 cases had excellent outcomes according to UERS score. Two patients had deficient forearm pronation of 10° and 15° respectively. Skin irritation and implant impingement was seen in two patients each at final follow-up.Conclusions: Closed reduction and internal fixation with TENS seems to be a good treatment option for fixation of pediatric both bone forearm fractures. It gives excellent functional outcome in terms of range of motion and grip strength without any major complications

Aromatic nucleophilic substitution reactions of O-aryl oximes with piperidine and hexylamine in cyclohexane

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