Studies on Space Grade Nano-Iconic Radiation Sensors Using Additive Manufacturing Technology
Authors: Ullah Shah Mohammad Rahmot 
Published: September 2020

Though Additive manufacturing technology has been developing for 30 years, in recent
years, it gets researchers' and industries' attention for new expansion in fabricated
electronics devices, especially on a flexible substrate. This technology allows fabricating
complex design of electronics devices with multi-functionality. Its application has been
significantly expanded to different fields such as sensors and other device prototypes for
nuclear facilities, aerospace manufacturing, bio-medical, solar energy, etc. due to its
low-cost efficiency and sustainable manufacturing. It has a huge advantage over traditional
methods such as lower materials waste during production, avoiding complex etching system and
harmful chemicals, simplified assembly system eliminating lithography, etching, and packaging process.

This work is focused on developing a fabrication process of GexSe100-x (x=20,
30, 40) based Chalcogenide glass (ChG) printed space-grade radiation sensing device for NASA space
exploration application using additive manufacturing technology. By following this fabrication
process, astronauts can fabricate a radiation sensor in the international space station to reduce
high transport cost and payload. The function of this radiation sensing device depends on
triggered by irradiation Ag+ ions migration into a Ge-Se based ChG printed films,
as a result of which conductivity increases several orders of magnitude. These studied devices
were printed on different substrates, including lightweight flexible substrates at room temperature.

The research work presented in this thesis is divided into four major parts; these are:
(i) Ge-Se based ChG ink formation, (ii) printing of the ChG ink on the substrate and sintering
process, (iii) printed films analysis, and (iv) device fabrication & testing. Although two types
of inks were produced, such as dissolution based ChG inks and nanoparticles based ChG inks, this
work mainly focuses on the dissolution based ChG inks fabricated devices, because of the complexity
of ink formation and the important correlated effects of the interaction of the ChG and solvents.

The inks were characterized by different methods such as tensiometer measurement of the contact
angle of ink with the substrate, the dynamic light scattering (DLS) to check the particles' size,
and viscometer to measure the viscosity of inks. The inks can be modified for use in different types
of printers by varying their viscosity, particle size, and solvents. Different kinds of printing
methods were used for printing on the substrates with ChG inks, such as screen printing and inkjet
printing. The printer's parameters were optimized for obtaining a good printing pattern. The sintering
process also was optimized to evaporate solvents and create a solid film. The effects of different
UV light radiation doses and Xe+ irradiation on the ChG printed film devices were studied
and analyzed in order to give proof of concept of the printed radiation sensor operation. Different
kinds of materials and structural characterization methods such as energy dispersive x-ray spectroscopy
(EDS), scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffraction spectroscopy
(XRD) and Raman spectroscopy have been used to study and analyze the printed ChG compositions, and verify
the occurrence of oxidation, topography, surface roughness and structural changes at different radiation
doses. These studies help to understand the origin of printed materials characteristics, which is a vital
part of establishing a bridge between materials' parameters and device performance. The last part of
this work is fabrication of the radiation sensing devices and their testing under different irradiation
doses. The ChG printed radiation sensing devices based on all studied compositions and applied solvents
were tested using a semiconductor parameter analyzer and probe station. The conductivity change results
were presented as a function of radiation doses. The radiation-induced Ag diffusion process was studied
to identify the perfect working device. The Ag diffusion was investigated by EDS and XRD spectroscopy
to determine the Ag diffusion by-products forming, their crystal sizes, and compositional changes of
the hosting ChG after Ag diffusion. Reversible dissolution based screen printed devices were also
fabricated and tested using the same conditions. Along with that, these devices have also been tested
under different energy of Xe+ ions irradiation. All the results of dissolution based inks
and devices, including ink characterizations, printed film analysis, and device performance were compared
with the nanoparticles based inks and devices. The performance of devices strongly depends on the
composition of ChG.