11 research outputs found
Polymeric tandem organic light-emitting diodes using a self-organized interfacial layer
The authors have demonstrated efficient polymeric tandem organic light-emitting diodes (OLEDs) with a self-organized interfacial layer, which was formed by differences in chemical surface energy. Hydrophilic poly(styrene sulfonate)-doped poly(3,4-ethylene dioxythiophene) (PEDOT:PSS) was spin coated onto the hydrophobic poly(9,9-dyoctilfluorene) (PFO) surface and a PEDOT:PSS bubble or dome was built as an interfacial layer. The barrier heights of PEDOT:PSS and PFO in the two-unit tandem OLED induced a charge accumulation at the interface in the heterojunction and thereby created exciton recombination at a much higher level than in the one-unit reference. This effect was confirmed in both the hole only and the electron only devices. (c) 2008 American Institute of Physicsopen8
Inert Gas Enhanced Laser-Assisted Purification of Platinum Electron-Beam-Induced Deposits
Electron-beam-induced deposition
patterns, with composition of PtC<sub>5</sub>, were purified using
a pulsed laser-induced purification reaction to erode the amorphous
carbon matrix and form pure platinum deposits. Enhanced mobility of
residual H<sub>2</sub>O molecules via a localized injection of inert
Ar–H<sub>2</sub> (4%) is attributed to be the reactive gas
species for purification of the deposits. Surface purification of
deposits was realized at laser exposure times as low as 0.1 s. The
ex situ purification reaction in the deposit interior was shown to
be rate-limited by reactive gas diffusion into the deposit, and deposit
contraction associated with the purification process caused some loss
of shape retention. To circumvent the intrinsic flaws of the ex situ
anneal process, in situ deposition and purification techniques were
explored that resemble a direct write atomic layer deposition (ALD)
process. First, we explored a laser-assisted electron-beam-induced
deposition (LAEBID) process augmented with reactive gas that resulted
in a 75% carbon reduction compared to standard EBID. A sequential
deposition plus purification process was also developed and resulted
in deposition of pure platinum deposits with high fidelity and shape
retention
Electron-Beam-Assisted Oxygen Purification at Low Temperatures for Electron-Beam-Induced Pt Deposits: Towards Pure and High-Fidelity Nanostructures
Nanoscale
metal deposits written directly by electron-beam-induced
deposition, or EBID, are typically contaminated because of the incomplete
removal of the original organometallic precursor. This has greatly
limited the applicability of EBID materials synthesis, constraining
the otherwise powerful direct-write synthesis paradigm. We demonstrate
a low-temperature purification method in which platinum–carbon
nanostructures deposited from MeCpPtIVMe<sub>3</sub> are purified
by the presence of oxygen gas during a post-electron exposure treatment.
Deposit thickness, oxygen pressure, and oxygen temperature studies
suggest that the dominant mechanism is the electron-stimulated reaction
of oxygen molecules adsorbed at the defective deposit surface. Notably,
pure platinum deposits with low resistivity and retain the original
deposit fidelity were accomplished at an oxygen temperature of only
50 °C
Room-Temperature Activation of InGaZnO Thin-Film Transistors via He<sup>+</sup> Irradiation
Amorphous indium gallium zinc oxide
(a-IGZO) is a transparent semiconductor which has demonstrated excellent
electrical performance as thin-film transistors (TFTs). However, a
high-temperature activation process is generally required which is
incompatible for next-generation flexible electronic applications.
In this work, He<sup>+</sup> irradiation is demonstrated as an athermal
activation process for a-IGZO TFTs. Controlling the He<sup>+</sup> dose enables the tuning of charge density, and a dose of 1 ×
10<sup>14</sup> He<sup>+</sup>/cm<sup>2</sup> induces a change in
charge density of 2.3 × 10<sup>12</sup> cm<sup>–2</sup>. Time-dependent transport measurements and time-of-flight secondary
ion mass spectroscopy (ToF-SIMS) indicate that the He<sup>+</sup>-induced
trapped charge is introduced because of preferential oxygen-vacancy
generation. Scanning microwave impedance microscopy confirms that
He<sup>+</sup> irradiation improves the conductivity of the a-IGZO.
For realization of a permanent activation, IGZO was exposed with a
He<sup>+</sup> dose of 5 × 10<sup>14</sup> He<sup>+</sup>/cm<sup>2</sup> and then aged 24 h to allow decay of the trapped oxide charge
originating for electron–hole pair generation. The resultant
shift in the charge density is primarily attributed to oxygen vacancies
generated by He<sup>+</sup> sputtering in the near-surface region
Purification of Nanoscale Electron-Beam-Induced Platinum Deposits via a Pulsed Laser-Induced Oxidation Reaction
Platinum–carbon
deposits made via electron-beam-induced
deposition were purified via a pulsed laser-induced oxidation reaction
and erosion of the amorphous carbon to form pure platinum. Purification
proceeds from the top down and is likely catalytically facilitated
via the evolving platinum layer. Thermal simulations suggest a temperature
threshold of ∼485 K, and the purification rate is a function
of the PtC<sub>5</sub> thickness (80–360 nm) and laser pulse
width (1–100 μs) in the ranges studied. The thickness
dependence is attributed to the ∼235 nm penetration depth of
the PtC<sub>5</sub> composite at the laser wavelength, and the pulse-width
dependence is attributed to the increased temperatures achieved at
longer pulse widths. Remarkably fast purification is realized at cumulative
laser exposure times of less than 1 s
Ion Migration Studies in Exfoliated 2D Molybdenum Oxide via Ionic Liquid Gating for Neuromorphic Device Applications
The formation of
an electric double layer in ionic liquid (IL) can electrostatically
induce charge carriers and/or intercalate ions in and out of the lattice
which can trigger a large change of the electronic, optical, and magnetic
properties of materials and even modify the crystal structure. We
present a systematic study of ionic liquid gating of exfoliated 2D
molybdenum trioxide (MoO<sub>3</sub>) devices and correlate the resultant
electrical properties to the electrochemical doping via ion migration
during the IL biasing process. A nearly 9 orders of magnitude modulation
of the MoO<sub>3</sub> conductivity is obtained for the two types
of ionic liquids that are investigated. In addition, notably rapid
on/off switching was realized through a lithium-containing ionic liquid
whereas much slower modulation was induced via oxygen extraction/intercalation.
Time of flight–secondary ion mass spectrometry confirms the
Li intercalation. Density functional theory (DFT) calculations have
been carried out to examine the underlying metallization mechanism.
Results of short-pulse tests show the potential of these MoO<sub>3</sub> devices as neuromorphic computing elements due to their synaptic
plasticity
Role of Electrical Double Layer Structure in Ionic Liquid Gated Devices
Ionic liquid gating
of transition metal oxides has enabled new
states (magnetic, electronic, metal–insulator), providing fundamental
insights into the physics of strongly correlated oxides. However,
despite much research activity, little is known about the correlation
of the structure of the liquids in contact with the transition metal
oxide surface, its evolution with the applied electric potential,
and its correlation with the measured electronic properties of the
oxide. Here, we investigate the structure of an ionic liquid at a
semiconducting oxide interface during the operation of a thin film
transistor where the electrical double layer gates the device using
experiment and theory. We show that the transition between the ON
and OFF states of the amorphous indium gallium zinc oxide transistor
is accompanied by a densification and preferential spatial orientation
of counterions at the oxide channel surface. This process occurs in
three distinct steps, corresponding to ion orientations, and consequently,
regimes of different electrical conductivity. The reason for this
can be found in the surface charge densities on the oxide surface
when different ion arrangements are present. Overall, the field-effect
gating process is elucidated in terms of the interfacial ionic liquid
structure, and this provides unprecedented insight into the working
of a liquid gated transistor linking the nanoscopic structure to the
functional properties. This knowledge will enable both new ionic liquid
design as well as advanced device concepts