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1.
Artigo em Inglês | MEDLINE | ID: mdl-32096978

RESUMO

If thermoplasmonic applications such as heat-assisted magnetic recording are to be commercially viable, it is necessary to optimize both thermal stability and plasmonic performance of the devices involved. In this work, a variety of different adhesion layers were investigated for their ability to reduce dewetting of sputtered 50 nm Au films on SiO2 substrates. Traditional adhesion layer metals Ti and Cr were compared with alternative materials of Al, Ta, and W. Film dewetting was shown to increase when the adhesion material diffuses through the Au layer. An adhesion layer thickness of 0.5 nm resulted in superior thermomechanical stability for all adhesion metals, with an enhancement factor of up to 200× over 5 nm thick analogues. The metals were ranked by their effectiveness in inhibiting dewetting, starting with the most effective, in the order Ta > Ti > W > Cr > Al. Finally, the Au surface-plasmon polariton response was compared for each adhesion layer, and it was found that 0.5 nm adhesion layers produced the best response, with W being the optimal adhesion layer material for plasmonic performance.

2.
ACS Appl Mater Interfaces ; 11(7): 7607-7614, 2019 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-30682242

RESUMO

The use of a metallic adhesion layer is known to increase the thermo-mechanical stability of Au thin films against solid-state dewetting, but in turn results in damping of the plasmonic response, reducing their utility in applications such as heat-assisted magnetic recording (HAMR). In this work, 50 nm Au films with Ti adhesion layers ranging in thickness from 0 to 5 nm were fabricated, and their thermal stability, electrical resistivity, and plasmonic response were measured. Subnanometer adhesion layers are demonstrated to significantly increase the stability of the thin films against dewetting at elevated temperatures (>200 °C), compared to more commonly used adhesion layer thicknesses that are in the range of 2-5 nm. For adhesion layers thicker than 1 nm, the diffusion of excess Ti through Au grain boundaries and subsequent oxidation was determined to result in degradation of the film. This mechanism was confirmed using transmission electron microscopy and X-ray photoelectron spectroscopy on annealed 0.5 and 5 nm adhesion layer samples. The superiority of subnanometer adhesion layers was further demonstrated through measurements of the surface-plasmon polariton resonance; those with thinner adhesion layers possessed both a stronger and spectrally sharper resonance. These results have relevance beyond HAMR to all Ti/Au systems operating at elevated temperatures.

3.
Opt Express ; 26(15): 18842-18854, 2018 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-30114145

RESUMO

To achieve a feasible heat-assisted magnetic recording (HAMR) system, a near-field transducer (NFT) is necessary to strongly focus the optical field to a lateral region measuring tens of nanometres in size. An NFT must deliver sufficient power to the recording medium as well as maintain its structural integrity. The self-heating problem in the NFT causes materials failure that leads to the degradation of the hard disk drive performance. The literature reports NFT structures with physical sizes well below 1 micron which were found to be thermo-mechanically unstable at an elevated temperature. In this paper, we demonstrate an adiabatic NFT to address the central challenge of thermal engineering for a HAMR system. The NFT is formed by an isosceles triangular gold taper plasmonic waveguide with a length of 6 µm and a height of 50 nm. Our study shows that in the full optically and thermally optimized system, the NFT efficiently extracts the incident light from the waveguide core and can improve the shape of the heating source profile for data recording. The most important insight of the thermal performance is that the recording medium can be heated up to 866 K with an input power of 8.5 mW which is above the Curie temperature of the FePt film while maintaining the temperature in the NFT at 390 K without a heat spreader. A very good thermal efficiency of 5.91 is achieved also. The proposed structure is easily fabricated and can potentially reduce the NFT deformation at a high recording temperature making it suitable for practical HAMR application.

4.
Opt Lett ; 43(15): 3477-3480, 2018 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-30067689

RESUMO

A design process for creating integrated diffractive focusing elements for use in planar waveguides is presented. The elements consist of a linear array of holes etched into the core layer of a planar dielectric waveguide. A complete element is a few micrometers in size, while the individual holes are sub-micrometer. The focusing element was designed using analytical Mie theory. The performance of the complete 3D structure was then evaluated using 3D finite difference time domain (FDTD) method. A focal spot width of 227 nm (full width at half maximum) was predicted by 3D FDTD simulations with a peak intensity more than 10x the incident intensity and back-reflections lower than 1%. The focusing elements were fabricated using electron beam lithography and plasma etching. Fluorescence imaging was used to map the intensity in the waveguide core. The experimentally measured intensity maps were in good agreement with the simulations when the finite spatial resolution of the imaging system was taken into account.

5.
ACS Nano ; 12(5): 4727-4735, 2018 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-29726674

RESUMO

Optically transparent photodetectors are crucial in next-generation optoelectronic applications including smart windows and transparent image sensors. Designing photodetectors with high transparency, photoresponsivity, and robust mechanical flexibility remains a significant challenge, as is managing the inevitable trade-off between high transparency and strong photoresponse. Here we report a scalable method to produce flexible crystalline Si nanostructured wire (NW) networks fabricated from silicon-on-insulator (SOI) with seamless junctions and highly responsive porous Si segments that combine to deliver exceptional performance. These networks show high transparency (∼92% at 550 nm), broadband photodetection (350 to 950 nm) with excellent responsivity (25 A/W), optical response time (0.58 ms), and mechanical flexibility (1000 cycles). Temperature-dependent photocurrent measurements indicate the presence of localized electronic states in the porous Si segments, which play a crucial role in light harvesting and photocarrier generation. The scalable low-cost approach based on SOI has the potential to deliver new classes of flexible optoelectronic devices, including next-generation photodetectors and solar cells.

6.
Nanotechnology ; 29(32): 325204, 2018 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-29781804

RESUMO

The optical response of metallic nanohelices is mainly governed by a longitudinal localised surface plasmon resonance (LSPR) which arises due to the helical anisotropy of the system. Up to now, experimental studies have predominantly addressed the far-field response, despite the fact that the LSPR being of broad interest for converting incoming light into strongly enhanced (chiral) optical near-fields. Here, we demonstrate the control and spatial reproducibility of the plasmon-induced electromagnetic near-field around metallic nanohelices via surface-enhanced Raman scattering. We discuss how the near-field intensity of these nanostructures can be custom-tailored through both the nanoscaled helical structure and the electronic properties of the constituting metals. Our experiments, which employ graphene as an accurate probing material, are in quantitative agreement with corresponding numerical simulations. The findings demonstrate metallic nanohelices as reference nanostructured surfaces able to provide and fine-tune optical fields for fundamental studies as well as sensing or (chiro-optical) imaging applications.

7.
Opt Express ; 26(2): 1752-1765, 2018 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-29402045

RESUMO

We investigate a tapered, hybrid plasmonic waveguide which has previously been proposed as an optically efficient near-field transducer (NFT), or component thereof, in several devices which aim to exploit nanofocused light. We numerically analyze how light is transported through the waveguide and ultimately focused via effective-mode coupling and taper optimization. Crucial dimensional parameters in this optimization process are identified that are not only necessary to achieve maximum optical throughput, but also optimum thermal performance with specific application towards heat-assisted magnetic recording (HAMR). It is shown that existing devices constructed on similar waveguides may benefit from a heat spreader to avoid deformation of the plasmonic element which we achieve with no cost to the optical efficiency. For HAMR, our design is able to surpass many industry requirements in regard to both optical and thermal efficiency using pertinent figure of merits like 8.5% optical efficiency.

8.
Sci Rep ; 7: 45548, 2017 03 30.
Artigo em Inglês | MEDLINE | ID: mdl-28358022

RESUMO

Reproducible and enhanced optical detection of molecules in low concentrations demands simultaneously intense and homogeneous electric fields acting as robust signal amplifiers. To generate such sophisticated optical near-fields, different plasmonic nanostructures were investigated in recent years. These, however, exhibit either high enhancement factor (EF) or spatial homogeneity but not both. Small interparticle gaps or sharp nanostructures show enormous EFs but no near-field homogeneity. Meanwhile, approaches using rounded and separated monomers create uniform near-fields with moderate EFs. Here, guided by numerical simulations, we show how arrays of weakly-coupled Ag nanohelices achieve both homogeneous and strong near-field enhancements, reaching even the limit forreproducible detection of individual molecules. The unique near-field distribution of a single nanohelix consists of broad hot-spots, merging with those from neighbouring nanohelices in specific array configurations and generating a wide and uniform detection zone ("hot-volume"). We experimentally assessed these nanostructures via surface-enhanced Raman spectroscopy, obtaining a corresponding EF of ~107 and a relative standard deviation <10%. These values demonstrate arrays of nanohelices as state-of-the-art substrates for reproducible optical detection as well as compelling nanostructures for related fields such as near-field imaging.

9.
Nanoscale ; 8(7): 4311-23, 2016 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-26838813

RESUMO

Liquid phase exfoliation is a powerful and scalable technique to produce defect-free mono- and few-layer graphene. However, samples are typically polydisperse and control over size and thickness is challenging. Notably, high throughput techniques to measure size and thickness are lacking. In this work, we have measured the extinction, absorption, scattering and Raman spectra for liquid phase exfoliated graphene nanosheets of various lateral sizes (90 ≤ 〈L〉 ≤ 810 nm) and thicknesses (2.7 ≤ 〈N〉 ≤ 10.4). We found all spectra to show well-defined dependences on nanosheet dimensions. Measurements of extinction and absorption spectra of nanosheet dispersions showed both peak position and spectral shape to vary with nanosheet thickness in a manner consistent with theoretical calculations. This allows the development of empirical metrics to extract the mean thickness of liquid dispersed nanosheets from an extinction (or absorption) spectrum. While the scattering spectra depended on nanosheet length, poor signal to noise ratios made the resultant length metric unreliable. By analyzing Raman spectra measured on graphene nanosheet networks, we found both the D/G intensity ratio and the width of the G-band to scale with mean nanosheet length allowing us to establish quantitative relationships. In addition, we elucidate the variation of 2D/G band intensities and 2D-band shape with the mean nanosheet thickness, allowing us to establish quantitative metrics for mean nanosheet thickness from Raman spectra.

10.
Opt Express ; 23(20): 26326-35, 2015 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-26480146

RESUMO

We experimentally and numerically study near-field and far-field visible light scattering from lithographically defined micron scale dielectric particles. We demonstrate field confinement and elongated intensity features known as photonic nanojets in the Fresnel zone. An experimental setup is introduced which allows simultaneous mapping of the angular properties of the scattering in the Fresnel zone and far-field regions. Precise control over the shape, size and position of the scatterers, allows direction control of the near-field intensity distribution. Intensity features with 1/3 the divergence of free space Gaussian beams of similar waist are experimentally observed. Additionally the direction and polarization of the incident light can be used to switch on and off intensity hot spots in the near-field. Together these parameters allow a previously un-obtainable level of control over the intensity distribution in the near-field, compared to spherically and cylindrically symmetric scattering particles.

11.
ACS Nano ; 9(5): 5551-8, 2015 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-25938797

RESUMO

In this article, we present a comprehensive investigation of the photothermal properties of plasmonic nanowire networks. We measure the local steady-state temperature increase, heat source density, and absorption in Ag, Au, and Ni metallic nanowire networks under optical illumination. This allows direct experimental confirmation of increased heat generation at the junction between two metallic nanowires and stacking-dependent absorption of polarized light. Due to thermal collective effects, the local temperature distribution in a network is shown to be completely delocalized on a micrometer scale, despite the nanoscale features in the heat source density. Comparison of the experimental temperature profile with numerical simulation allows an upper limit for the effective thermal conductivity of a Ag nanowire network to be established at 43 Wm(-1) K(-1) (0.1 κbulk).

12.
Nat Commun ; 5: 4576, 2014 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-25099520

RESUMO

Two-dimensional nanomaterials such as MoS2 are of great interest both because of their novel physical properties and their applications potential. Liquid exfoliation, an important production method, is limited by our inability to quickly and easily measure nanosheet size, thickness or concentration. Here we demonstrate a method to simultaneously determine mean values of these properties from an optical extinction spectrum measured on a liquid dispersion of MoS2 nanosheets. The concentration measurement is based on the size-independence of the low-wavelength extinction coefficient, while the size and thickness measurements rely on the effect of edges and quantum confinement on the optical spectra. The resultant controllability of concentration, size and thickness facilitates the preparation of dispersions with pre-determined properties such as high monolayer-content, leading to first measurement of A-exciton MoS2 luminescence in liquid suspensions. These techniques are general and can be applied to a range of two-dimensional materials including WS2, MoSe2 and WSe2.

13.
ACS Nano ; 5(7): 5457-62, 2011 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-21657203

RESUMO

We study the ability of a plasmonic structure under illumination to release heat and induce fluid convection at the nanoscale. We first introduce the unified formalism associated with this multidisciplinary problem combining optics, thermodynamics, and hydrodynamics. On this basis, numerical simulations were performed to compute the temperature field and velocity field evolutions of the surrounding fluid for a gold disk on glass while illuminated at its plasmon resonance. We show that the velocity amplitude of the surrounding fluid has a linear dependence on the structure temperature and a quadratic dependence on the structure size (for a given temperature). The fluid velocity remains negligible for single nanometer-sized plasmonic structures (<1 nm/s) due to a very low Reynolds number. However thermal-induced fluid convection can play a significant role when considering either micrometer-size structures or an assembly of nanostructures.

15.
J Cardiothorac Vasc Anesth ; 23(3): 336-8, 2009 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-19201206

RESUMO

OBJECTIVE: To determine the level of carboxyhemoglobin found in banked blood in the Albany, NY region. DESIGN: A retrospective descriptive analysis of carboxyhemoglobin (COHb) levels in a series of packed red blood cell (PRBC) units. SETTING: The blood bank of a university tertiary care hospital in Albany, NY. PARTICIPANTS: All PRBC units considered for possible use in pediatric cardiac surgery were first analyzed for levels of COHb. INTERVENTIONS: Only those units with COHb levels of <1.5% were deemed acceptable for use during pediatric cardiac surgery. MEASUREMENTS AND RESULTS: A sample of blood drawn from the sample side arm of each PRBC unit was analyzed on a Chiron 855 Blood Gas Analyzer (Chiron Inc, Emeryville, CA, now Siemens/Bayer RapidLab 865) to determine the level of COHb. The average COHb level was 0.78% (standard deviation +/- 1.48%), and out of the 468 units tested, 48 (10.3%) had COHb levels of 1.5% or greater. The highest recorded COHb level was 12%. CONCLUSIONS: The transfusion of PRBC units may artificially elevate readings of COHb and cause confusion over possible causes. Certain high-risk populations (eg, cyanotic neonates undergoing cardiopulmonary bypass) may be especially at risk. Although levels of COHb in the US blood supply are dropping, institutions may want to consider analyzing COHb levels in their PRBC units before transfusion in these high-risk populations.


Assuntos
Bancos de Sangue/normas , Carboxihemoglobina/efeitos adversos , Carboxihemoglobina/análise , Transfusão de Eritrócitos , Gasometria/métodos , Transfusão de Eritrócitos/efeitos adversos , Transfusão de Eritrócitos/normas , Eritrócitos/química , Humanos , Pediatria/normas , Estudos Retrospectivos , Medição de Risco
16.
BMC Health Serv Res ; 6: 109, 2006 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-16945156

RESUMO

BACKGROUND: Despite the wide availability of prenatal screening and diagnosis, a number of studies have reported no decrease in the rate of babies born with Down syndrome. The objective of this study was to investigate the geodemographic characteristics of women who have prenatal diagnosis in Victoria, Australia, by applying a novel consumer behaviour modelling technique in the analysis of health data. METHODS: A descriptive analysis of data on all prenatal diagnostic tests, births (1998 and 2002) and births of babies with Down syndrome (1998 to 2002) was undertaken using a Geographic Information System and socioeconomic lifestyle segmentation classifications. RESULTS: Most metropolitan women in Victoria have average or above State average levels of uptake of prenatal diagnosis. Inner city women residing in high socioeconomic lifestyle segments who have high rates of prenatal diagnosis spend 20% more on specialist physician's fees when compared to those whose rates are average. Rates of prenatal diagnosis are generally low amongst women in rural Victoria, with the lowest rates observed in farming districts. Reasons for this are likely to be a combination of lack of access to services (remoteness) and individual opportunity (lack of transportation, low levels of support and income). However, there are additional reasons for low uptake rates in farming areas that could not be explained by the behaviour modelling. These may relate to women's attitudes and choices. CONCLUSION: A lack of statewide geodemographic consistency in uptake of prenatal diagnosis implies that there is a need to target health professionals and pregnant women in specific areas to ensure there is increased equity of access to services and that all pregnant women can make informed choices that are best for them. Equally as important is appropriate health service provision for families of children with Down syndrome. Our findings show that these potential interventions are particularly relevant in rural areas. Classifying data to lifestyle segments allowed for practical comparisons of the geodemographic characteristics of women having prenatal diagnosis in Australia at a population level. This methodology may in future be a feasible and cost-effective tool for service planners and policy developers.


Assuntos
Amniocentese/estatística & dados numéricos , Amostra da Vilosidade Coriônica/estatística & dados numéricos , Síndrome de Down/diagnóstico , Aceitação pelo Paciente de Cuidados de Saúde/estatística & dados numéricos , Adulto , Distribuição por Idade , Demografia , Síndrome de Down/epidemiologia , Síndrome de Down/genética , Feminino , Geografia , Humanos , Idade Materna , Pessoa de Meia-Idade , Aceitação pelo Paciente de Cuidados de Saúde/psicologia , Gravidez , Características de Residência , População Rural , População Urbana , Vitória/epidemiologia
17.
Anesth Analg ; 97(1): 289-90, table of contents, 2003 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-12818984

RESUMO

IMPLICATIONS: Increased levels of carboxyhemoglobin (COHb) are frequently found in units of packed red blood cells. We report a congenital heart surgery where increased levels of COHb were found in the patient after a blood transfusion and hypothesize that this phenomenon could be dangerous in a cyanotic newborn undergoing open heart surgery.


Assuntos
Bancos de Sangue , Preservação de Sangue , Carboxihemoglobina/análise , Adolescente , Dióxido de Carbono/sangue , Monóxido de Carbono/sangue , Ponte Cardiopulmonar , Eritrócitos/química , Feminino , Comunicação Interventricular/cirurgia , Humanos , Monitorização Intraoperatória , Oxigênio/sangue
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