5,390 research outputs found
Mechanical characterization of solution-derived nanoparticle silver ink thin films
Mechanical properties of sintered silver nanoparticles are investigated via substrate curvature and nanoindentation methods. Substrate curvature measurements reveal that permanent microstructural changes occur during initial heating while subsequent annealing results in nearly elastic behavior of the thinner films. Thicker films were found to crack upon thermal treatment. The coefficient of thermal expansion was determined from linear slopes of curvature curves to be 1.9±0.097 ppm/°C, with elastic modulus and hardness determined via nanoindentation. Accounting for substrate effects, nanoindentation hardness and modulus remained constant for different film thicknesses and did not appear to be a function of annealing conditions. Hardness of 0.91 GPa and modulus of 110 GPa are somewhat lower than expected for a continuous nanocrystalline silver film, most likely due to porosity
Reversible and irreversible trapping at room temperature in poly(thiophene) thin-film transistors
We measured the bias stress characteristics of poly(thiophene)
semi-crystalline thin-film transistors (TFTs) as a function stress times, gate
voltages and duty-cycles. At room temperature, the bias stress has two
components: a fast reversible component and a slow irreversible component. We
hypothesize that the irreversible component is due to charge trapping in the
disordered areas of the semiconductor film. At low duty-cycle (<2%), the fast
bias stress component is reversed during the off-part of the cycle therefore
the observed VT shift in only caused by irreversible trapping. Irreversible
trapping follows power-law kinetics with a time exponent approximately equal to
0.37. We use these findings to estimate the lifetime of TFTs used as switches
in display backplanes
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Intrinsic hole mobility and trapping in a regio-regular poly(thiophene)
The transport properties of high-performance thin-film transistors (TFT) made
with a regio-regular poly(thiophene) semiconductor (PQT-12) are reported. The
room-temperature field-effect mobility of the devices varied between 0.004
cm2/V s and 0.1 cm2/V s and was controlled through thermal processing of the
material, which modified the structural order. The transport properties of TFTs
were studied as a function of temperature. The field-effect mobility is
thermally activated in all films at T<200 K and the activation energy depends
on the charge density in the channel. The experimental data is compared to
theoretical models for transport, and we argue that a model based on the
existence of a mobility edge and an exponential distribution of traps provides
the best interpretation of the data. The differences in room-temperature
mobility are attributed to different widths of the shallow localized state
distribution at the edge of the valence band due to structural disorder in the
film. The free carrier mobility of the mobile states in the ordered regions of
the film is the same in all structural modifications and is estimated to be
between 1 and 4 cm2/V s.Comment: 20 pages, 8 figure
Hydrogen dynamics and light-induced structural changes in hydrogenated amorphous silicon
We use accurate first principles methods to study the network dynamics of
hydrogenated amorphous silicon, including the motion of hydrogen. In addition
to studies of atomic dynamics in the electronic ground state, we also adopt a
simple procedure to track the H dynamics in light-excited states. Consistent
with recent experiments and computer simulations, we find that dihydride
structures are formed for dynamics in the light-excited states, and we give
explicit examples of pathways to these states. Our simulations appear to be
consistent with aspects of the Staebler-Wronski effect, such as the
light-induced creation of well separated dangling bonds.Comment: 9 pages, 8 figures, submitted to PR
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