2,486 research outputs found
Development of a direct metalisation method for micro-engineering
This research concentrates on the establishment of a metalisation and micro-patterning
technique that eliminates metal evaporation and/or photoresist molding procedures.
The process design is chosen from the analysis of the broad field of direct metalisation
techniques where novel photocatalysts or photoreducing agents are increasingly
employed to create new processes.
The new photolithographic process in this study introduces two novel photoreducing
agents for additive metal thin film fabrication: methoxy poly(ethylene glycol) and
photosystem I. This work proves the concept of using light energy to directly reduce
metal ions incorporated within an ion-exchanged polyimide substrate to produce metal
thin films. The patterning step can be operated at atmospheric pressure, in a dry
environment, using a coating of the photoreducing agent. This process offers a
significant improvement to prior related work that relied on a water layer to enable the
metalisation. Of particular importance for this process is the influence of light energy
dose and heat treatment, which promote silver nanoparticles growth at the cost of
degradation of the substrate polymer. The investigation was carried out thoroughly by
laser writing experiments for a selected range of laser power and scan speed. To
complement the phenomenon observed in the laser experiments, prolonged UV light
exposure time and heat treatment experiments were carried out to confirm the
hypothesis postulated in this thesis.
The morphology of the silver nanoparticles produced, the changes of the substrate
surface and the adhesion of electroless plating were characterised. Results indicate that
UV irradiation with the energy density required for reasonable production speed causes
inevitable molecular damage to the polymer substrate. Photosystem I was found to be
able to catalyse the production of visually similar silver thin film by light sources in the
blue region. Using a similar light intensity, the exposure time was reduced by an order
of magnitude whilst the degradation phenomenon observed during the UV process
appears to be eradicated. With the fundamentals of the process established in this
thesis, future optimization is suggested for the transition from a proof of concept to
industrial implementation
A low cost direct writing process for flexible circuit and interconnect fabrication
This
thesis
investigates
the
development
of
a
low
cost
fabrication
process
for
flexible
electronics
and
interconnects.
By
using
a
‘direct
writing’
process,
the
use
of
vacuum-‐based
metal
evaporation
and
photoresist
steps
is
not
necessary
and
so
less
complex
equipment
is
needed.
The
process
forms
silver
embedded
on
top
of
a
polyimide
substrate
and
was
first
tested
using
a
UV
laser
to
perform
writing
before
switching
to
a
blue
laser
due
to
excessive
substrate
degradation
observed
from
UV
exposures.
The
blue
light
was
combined
with
a
biologically
friendly
photo
reducing
agent,
which
was
found
to
be
much
more
efficient
at
the
creation
of
silver.
The
methods
of
silver
formation
by
various
means
are
the
main
focus
of
investigation
in
this
thesis
but
process
expansion
and
improvement
were
the
main
goals.
To
this
end,
a
chemical,
rather
than
light-‐based,
process
for
silver
creation
was
found
to
produce
more
consistent
silver
coatings,
however
the
patterning
by
this
method
was
found
to
be
more
challenging.
The
process
was
also
extended
to
a
different
substrate
in
polyetherimide
Ultrafast Laser Direct Writing of Conductive Patterns on Polyimide Substrate
Laser direct writing (LDW) is a fast and cost-effective method for printing conductive patterns in flexible polymer substrates. The electrical, chemical, and mechanical properties of polyimide (PI) make it an attractive material choice for laser writing of conductive circuits in such polymer. Electrically insulating PI has shown great potential for flexible printed electronics as LDW enables selective carbonization in the bulk of such material leading to the formation of conductive lines. However, existing studies in this area reveal a few key limitations of this approach including limited conductivity of written structures and fragility of carbonized PI. Therefore, more research is required to overcome those limitations and reap the benefits of the LDW approach in writing flexible electronic circuits in PI. The proposed study investigates potential approaches to enhance the electrical conductivity of femtosecond laser written bulk carbon structures in PI films. Deposition of laser energy was varied by changing key process parameters such as pulse energy, pulse picker divider, and hatch distance of laser scan to maximize the conductively of the carbon structure. The experimental findings show a strong dependency of laser energy deposition on the conductivity carbon structures in PI films. To further enhance the electrical conductivity of laser written structures, the feasibility of adding copper microparticles to the PI solution and subsequent laser carbonization was studied. The proposed LDW of conductive lines has potential in flexible electronic circuits and sensing applications
Experimental studies and simulation of laser ablation of high-density polyethylene films
This thesis lays the groundwork for a simulation model for the laser ablation of polymer materials. A thorough review of the laser ablation of various polymer materials has been provided. The current trends and challenges in utilizing laser ablation for micro/nano manufacturing and information essential to the choice of an appropriate laser source for a polymer material have been provided. Experimental studies on laser ablation-based drilling of micro-holes on high-density polyethylene films have been performed. The influence of an increasing number of pulses and laser power on the depth and area of the micro-holes has been analyzed. The experimental results were utilized to validate a quantitative area-depth approximation model that was formulated based on the gain factors and the laser intensity profile. Additionally, a finite element method-based model has been developed for predicting the surface temperature and depth profile evolution with time during laser ablation of polymer materials
Laser structuring of materials for biomedical applications
Laser processing methods have become very appealing for the fabrication of micro/nano structures. To fabricate 3D structures with high resolution andarbitrary complexity, several material deposition processes are in use. By using appropriate moulding techniques, these structures can be fabricated out of a variety of materials such as polymers, ceramics and composites. In this work different lasers have been investigated regarding their suitability for additive and subtractive patterning of small features for biomedical applications. The main focus is on a technique based on two-photon polymerisation of photosensitive materials; this is a nonlinear optical stereo lithography which allows direct-writing of high-resolution three dimensional structures. During the two-photon absorption process, temporal and spatial overlap of photons leads to nonlinear absorption in a highly localized volume. Absorbed photons induce chemical reactions which cause a polymer to form. Due to the quadratic intensity dependence of the process, resolutions of less than 100nm in polymerized structures can potentially be achieved because of the well-defined polymerization threshold. Here, we have emphasised another regime whereby deep structures (~300µm) can be generated in a single pass. This allows rapid fabrication of structures suitable for cell scaffolds where the length scales are small (~10µm) and are required over long ranges (~cm). A Ti: sapphire femtosecond laser at 800nm wavelength with 150fs pulse duration and 1kHz repetition rate was used to determine the two-photon absorption cross section of photoinitiators. This approach was used to initiate two-photon polymerization of resin allowing the fabrication of cell scaffolds suitable for biomedical applications. Diffraction calculations for the imaging optics employed, show that spherical aberration plays a significant role in determining the feature sizes achieved.For subtractive patterning of materials, a femtosecond laser system and an ArF excimer laser have been used. Using ablative techniques keratin films were processed to investigate physical realisation of the commonly used theoretical bricks-and-mortar description of skin. This structure was successfully fabricated and is being used for skin cream research. Also the threshold fluence for ablation of Polyimide Kapton (HN) foils has been measured at oblique angles as an analogue for corneal sculpturing based on beam scanning
Laser-assisted processing of multilayer films for inexpensive and flexible biomedical microsystems
Flexible/stretchable electronics offer ideal properties for emerging health monitoring devices that can seamlessly integrate with the soft, curvilinear, and dynamic surfaces of the human body. The resulting capabilities have allowed novel devices for monitoring physiological parameters, improving surgical procedures, and human-machine interfaces. While the attractiveness of these devices are indubitable, their fabrication by conventional cleanroom techniques makes them expensive and incompatible with rapid large-scale (e.g., roll-to-roll) production. The purpose of this research is to develop inexpensive fabrication technologies using low-cost commercial films such as polyimide, paper, and metalized paper that can be utilized for developing various flexible/stretchable physical and chemical sensors for wearable and lab-on-chip applications. The demonstrated techniques focus on an array of laser assisted surfaces modification and micromachining strategies with the two commonly used CO2 and Nd: YAG laser systems. The first section of this dissertation demonstrates the use of localized pulsed CO2 laser irradiation to selectively convert thermoset polymer films (e.g., polyimide) into electrically conductive highly porous carbon micro/nanostructures.Thisprocessprovidesauniqueandfacileapproachfordirect writing of carbonized conductive patterns on flexible polyimide sheets in ambient conditions, eliminating complexities of current methods such as expensive CVD processes and complicated formulation/preparation of conductive carbon based inks used in ink jet printing. The highly porous laser carbonized layer can be transferred to stretchable elastomer or further functionalized with various chemical substances such as ionic solutions, nanoparticles, and chemically conductive polymers to create different mechanical and chemical sensors. The second section of this dissertation describes the use of laser ablation for selective removal of material from multilayer films such as ITO-coated PET, parchment paper, and metalized paper to create disposable diagnostic platforms and in-vitro models for lab-on-chip based studies. The ablated areas were analyzed using electrical, mechanical, and surface analysis tools to understand change in physical structure and chemical properties of the laser ablated films. As proof-of-concept demonstrations of these technologies, four different devices are presented here: mechanical, electrochemical, and environmental sensors along with an in-vitro cell culture platform. All four devices are designed, fabricated, and characterized to highlight the capability of commercial laser processing systems in the production of the next generation, low-cost and flexible biomedical devices
X-Ray microcalorimeter detectors - Technology developments for high energy astrophysics space missions
Improvements in the design, fabrication, and performance of astronomical detectors has ushered in the so-called era of multi messenger astrophysics, in which several different signals (electromagnetic waves, gravitational waves, neutrinos, cosmic rays) are processed to obtain detailed descriptions of their sources.
Soft x-ray instrumentation has been developed in the last decades and used on board numerous space missions. This has allowed a deep understanding of several physical phenomena taking place in astrophysical sources of different scales from normal stars to galaxy clusters and huge black holes. On the other hand, imaging and spectral capabilities in the the hard x-rays are still lagging behind with high potentials of discovery area.
Modern cryogenic microcalorimeters have two orders of magnitude or more better energy resolution with respect to CCD detectors at the same energy in the whole X-ray band. This significant improvement will permit important progress in high energy astrophysics thanks to the data that will be provided by future missions adopting this detector technology such as the ESA L2 mission Athena, the JAXA/NASA mission XRISM, both under development, or the NASA LYNX mission presently under investigation. The JAXA/NASA mission Hitomi, launched in 2016 and failed before starting normal operation, has already given a hint of the high potential of such detectors.
Due to their very high sensitivity, X-ray cryogenic microcalorimeters need to be shielded from out of band radiation by the use of efficient thin filters.
These microcalorimeters work by measuring the temperature increase caused by a photon that hits an X-ray absorber. In neutron transmutation doped germanium (NTD Ge) devices the temperature increase in the absorber is measured by a semiconductor thermometer made of germanium doped by the neutron transmutation doping technique. They are characterized by relatively low specific heat and low sensitivity to external magnetic fields. These characteristics make them promising detectors for hard X-ray detectors for space and laboratory applications.
Research groups of the the X-ray Astronomy Calibration and Testing (XACT) Laboratory of the Osservatorio Astronomico di Palermo – Istituto Nazionale di Astrofisica (INAF-OAPA), and of the Dipartimento di Fisica e Chimica “Emilio Segrè” (DiFC) of the Università di Palermo have already developed experience related to the design, fabrication and testing of NTD Ge microcalorimeters. Furthermore, the research group has participated for many years in the design and development of filters for x-ray detectors in different space missions.
This thesis concerns the development of materials and technologies for high energy microcalorimeters. In particular its aim is to design and fabricate thick bismuth absorbers for NTD germanium microcalorimeter arrays to extend their detection band toward hard X-ray energies. Filters for shielding microcalorimeters from different background radiation arriving on the detectors were also studied.
The design and fabrication of thick bismuth absorbers for hard x-rays detection (20 keV ≤ E ≤ 100 keV) is part of an ongoing effort to develop arrays of NTD Ge microcalorimeters by planar technologies for astrophysical applications. One potential application of such detectors is in the high spectral resolution (∆E ~ 50 eV) investigation of the hard X-ray emission from the solar corona, which is the goal of a stratospheric balloon borne experiment concept named MIcrocalorimeters STratospheric ExpeRiment for solar hard X rays (MISTERX) presently under study at INAF-OAPA.
The characterization activity of filters for microcalorimeters in also related to the implementation of the European Space Agency high energy mission named Athena (Advanced Telescopes for High Energy Astrophysics).
This thesis describes the design, fabrication, and characterization of the bismuth absorbers, as well as the characterization of filters for Athena.
Chapter one summarizes the working principles of NTD Ge microcalorimeters and their applications. Chapter 2 describes the design of the bismuth absorber array on suitable substrates. Chapter 3 focuses on the electroplating process for the bismuth layer deposition, with details about the design and fabrication of the microlithographic mask for the array patterning, and about the development of the microlithographic process for the array fabrication on the chosen substrates. The fabrication of 4 x 4 absorber arrays is also described. Chapter 4 reports on the characterization activity of deposited bismuth layers by different techniques; their morphology was investigated by scanning electron microscopy. The electrochemical impedance spectroscopy technique was used to increase grown layer quality. Fabricated arrays were also characterized. Chapter 5 describes the characterization activity for different filter prototype samples developed for Athena. Mechanical robustness, radio frequency attenuation and radiation damage caused by protons were evaluated. Radiation damage effects at different doses were in particular investigated on silicon nitride filters by scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-Vis-IR spectroscopy and x-ray attenuation measurements.
Details on both technical detector requirements and different sensor types are given in the Appendix
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