6 research outputs found
THERMAL CHARACTERIZATION OF CARBON NANOTUBES BY PHOTOTHERMAL TECHNIQUES
No full textHeat transport at nanoscale is of importance for many nanotech- nology applications. The request to reduce the size of electronic devices and integrated micro/ nano-electro-mechanical systems provides the main driving force behind the scientific research and technological advancement in nanotechnology. It is now widely accepted that the thermal management in nanosize devices becomes fundamental as the size of the device reduces. Thermal conduction in nanostructures plays a critical role in controlling the performances and stability of nanodevices
THERMAL CHARACTERIZATION OF CARBON NANOTUBES BY PHOTOTHERMAL TECHNIQUES
No full textCarbon nanotubes (CNT) are multifunctional materials commonly used in a large number of applications in electronics, sensors, nanocomposites, thermal management, actuators, energy storage and conversion, and drug delivery.
Despite recent important advances in the development of CNT purity assessment tools and atomic resolution imaging of individual nanotubes by scanning tunnelling microscopy and high-resolution transmission electron microscopy, the macroscale assessment of the overall surface qualities of commercial CNT materials remains a great challenge. The lack of quantitative measurement technology to characterize and compare the surface qualities of bulk manufactured and engineered CNT materials has negative impacts on the reliable and consistent nanomanufacturing of CNT products
In this paper we show how photothermal and photoacoustic techniques represent useful non-destructive tools to study the thermal properties of carbon nanotubes films. The photoacoustic spectroscopy (PAS) is used for a direct measurement of the absorbance spectra of CNT showing many advantages with respect to the standard optical spectra measurements which are usually affected by relevant scattering phenomena. We applied PAS in the UV/VIS range from 250 to 650 nm by using 400 W Arc Xe lamp. On the other side photothermal radiometry (PTR) has been applied by using an Ar++ pump laser beam, modulated at a frequency in the range 1Hz -100 kHz, and a MCT infrared detector, in order to measure the effective thermal parameters, the IR emission properties from CNT thin films, and evaluate the average thermal boundary resistances at the film/bulk interface.
We investigated two set of CNT; in the first group the nanostructures are aligned (“forest”) and deposited onto a silicon substrate. The diameter of the nanotubes ranges from 20-50nm, and the total thickness of the CNT film ranges from 70m to 240m. In the second group the CNT are randomly oriented in plane, and the CNT film is deposited on different transparent substrate (PET and quartz).
Experimental results show how both PAS and PTR represent an excellent tool for quantitative measurement of the thermal properties of CNT thin films
PHOTOACUSTIC CHARACTERIZATION OF RANDOMLY ORIENTED SILVER NANOWIRES FILMS
No full textMetallic nanowires have cross-sectional diameters included between few to hundreds nanometers, while their lengths span from several to some hundreds microns. Metallic nanowires films show peculiar optical properties, such as high optical transmittance in the visible range, connected to the extremely reduced dimension of wires diameter, while still allowing for good electrical conduction, thus being suitable for those applications where transparent electrodes are required. As a consequence, metallic nanowires mesh, both randomly of systematically oriented, can be employed to tune the effective optical constants of the resulting film, and get peculiar spectral absorbance properties.
In this work we present the photoacustic characterization in the UV/VIS range of randomly oriented silver nanowires films deposited onto either quartz or polymeric substrate. This study was performed over a set of films differing in both metallic nanowires’ dimensions, as well as metal content.
Samples were prepared using suspensions of Ag-nanowires in isopropanol (IPA) (25 mg/ml), purchased from Seashell Technology, differing by both nanowires’ length and diameter. The starting IPA dispersion was added to de-ionized water, and then ultrasonicated for few minutes, filtrated and transferred onto the substrate by drop casting. The obtained films were characterized by scanning electron micrography (SEM images), thus the metal filling factor was retrieved with a matlab software based on visual method [1].
Following the morphological characterization, we employed photoacoustic spectroscopy (PAS) to investigate in details the absorbance spectra of silver nanowires films, in order to evidence their peculiar ab sorbance properties in the UV/VIS range. The us of PAS is particularly useful to investigate film that my display relevant scattering phenomena, as for silver nanowires films. We applied PAS in the UV/VIS range from 250 to 650 nm by using a low modulation frequency from 1Hz to 100Hz. The experimental results show that the choice of metal filling factor may affect the absorbance spectra of the resulting mesh.
Acknowledgments
This work has been performed in the framework of “FISEDA” program granted by Italian Ministry of Defence
Thermal Characterization of Carbon Nanotubes by Photothermal Techniques
No full textCarbon nanotubes (CNTs) are multifunctional materials commonly used in
a large number of applications in electronics, sensors, nanocomposites, thermal management,
actuators, energy storage and conversion, and drug delivery. Despite recent
important advances in the development of CNT purity assessment tools and atomic
resolution imaging of individual nanotubes by scanning tunnelling microscopy and
high-resolution transmission electron microscopy, the macroscale assessment of the
overall surface qualities of commercial CNT materials remains a great challenge. The
lack of quantitative measurement technology to characterize and compare the surface
qualities of bulk manufactured and engineered CNT materials has negative impacts
on the reliable and consistent nanomanufacturing of CNT products. In this paper it is
shown how photoacoustic spectroscopy and photothermal radiometry represent useful
non-destructive tools to study the optothermal properties of carbon nanotube thin
films
Photoacoustic Characterization of Randomly Oriented Silver Nanowire Films
No full textIn this work, the photoacoustic characterization in the UV/Vis range of
randomly oriented silver nanowire films deposited onto either a quartz or polymeric
substrate is presented. This study was performed for a set of films differing in both
metallic nanowire dimensions, as well as metal content. Samples were prepared starting
from suspensions of Ag nanowires in isopropanol (IPA) (25 mg·ml−1), differing in
both the length and diameter of the nanowires. The obtained films were characterized
by scanning electron micrography (SEM) images; thus, the metal filling factor was
retrieved with MATLAB software based on a visual method. Following the morphological
characterization, both spectrophotometry and the photoacoustic spectroscopy
(PAS) technique were employed to investigate in detail the absorbance spectra of silver
nanowire films, in order to evidence their peculiar properties in the UV/Vis spectral
range. Specifically, this photothermal technique is particularly useful to investigate a
film that may exhibit relevant scattering phenomena, as for metallic nanowire films.
The obtained experimental results show that the choice of the metal filling factor may
affect the absorbance spectra of the resulting mesh
Dispersive properties of finite, one-dimensional photonic band gap structures: Applications to nonlinear quadratic interactions
No full textWe discuss the linear dispersive properties of finite one-dimensional photonic band-gap structures. We introduce the concept of a complex effective index for structures of finite length, derived from a generalized dispersion equation that identically satisfies the Kramers-Kronig relations. We then address the conditions necessary for optimal, phase-matched, resonant second harmonic generation. The combination of enhanced density of modes, field localization, and exact phase matching near the band edge conspire to yield conversion efficiencies orders of magnitude higher than quasi-phase-matched structures of similar lengths. We also discuss an unusual and interesting effect: counterpropagating waves can simultaneously travel with different phase velocities, pointing to the existence of two dispersion relations for structures of finite length
