Author Archives: Flexible Electronics Group @ POSTECH

An autonomously electrically self-healing liquid metal–elastomer composite for robust soft-matter robotics and electronics

Author: Eric J. Markvicka, and Carmel Majidi

Journal: Nature materials

Publication date: 21 May 2018

Summarized by Hyuk Park

 

– Material architecture and framework
v. Creating circuit interconnects that are capable of autonomous, electrical self-healing
v. Liquid metal(LM) alloy – EGaIn + silicone elastomer
v. Insulating property even high LM fraction (> 50%)
v. Extreme local pressure(damaged) → locally conductive pathways (conductivity of 1.37 x 10^3 Sm^-1)

– 2-phenyl7-alkylated-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-Cn; n≥ 5)
v. High layered crystallinity
v. Bilayer type layered herringbone structure
v. Strong intermolecular interaction
v. Flake-like crystals composed of multiply-stacked molecular bilayer (no single layer)

1.png

Fig. 1

– Geometrical frustration – different alkyl chain lengths
v. Blade coating
v. Ph-BTBT-Cn and Ph-BTBT-Cn` (n` > n)
v. φlong: volume fraction of longer chain molecules
v. Longer alkyl chain is more effective for fabricating SMBs than that of shorter ones

2.png

Fig. 2

3.png

Fig. 3

v. single component film → flat outer surface → multilayer crystallization

4.png

Fig. 4

 

– SMB measurement
v. AFM – SMB thickness = 4.4 nm
v. High resolution AFM alkyl chain difference = 170 pm
v. In-plane XRD: no out-of-plane diffraction → single layer
v. X-ray reflectivity: calculation = experiment

5.png

Fig. 5

 

– Semiconducting properties – bottom gate TFTs
v. Saturation mobility of 2.6 cm2/Vs
v. Hysteresis due to scattering of carriers with the formation of traps at semiconductor/air interface

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Fig. 6

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Highly efficient luminescent solar concentrators based on earth-abundant indirect-bandgap silicon quantum dots

Author: Francesco Meinardi, and Sergio Brovelli

Journal: Nature photonics

Publication date: 20 Feb 2017

Summarized by Hyuk Park

 

– Background
v. Low-cost and earth-abundant of silicon: silicon based photovoltaic (Si-PV)
v. ‘Nearly zero energy building’ by the EU:
building operation power = collecting power of Si-PV
v. Luminescent solar concentrators (LSCs) – semi-transparent PV windows
Sunlight → matrix → absorbed by fluorophores → re-emitted at a longer wave length → total internal reflection → waveguide edge → electricity

1.png

Fig. 1

v. LSC area > waveguide edge → photo-current increase
v. Unmatched design freedom of LSC
v. Lack of suitable emitters of LSC: limited spectral coverage, large overlap between the absorption and emission spectra → quantum dots

 

– Si quantum dots
v. Indirect bandgap of Si: light emission from Xconduction → Γvalence transition requires assistance of phonons = small transition probability, and negligible luminescence
v. Stokes shift: emitted photon energy < absorbed photon due to vibration relaxation

2.png

Fig. 2

Fig. 3

 

v. Below exciton Bohr diameter (8.6 nm), Si nano-structure → strong confinement → broadens the k-space → band-edge electronic transition (indirect → semi direct bandgap)

4.png

Fig. 4

v. Optical absorption and photoluminescence spectra tuned by particle size: visible to NIR

5.png

Fig. 5

 

– P(LMA-co-EGDM) nanocomposite waveguide 12 cm x 12 cm x 0.26 cm comprising 0.09% wt% quantum dots

Fig. 6

23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability

Author: Michael D. McGehee

Journal: Nature energy

Publication date: 17 Feb 2017

Summarized by Hyuk Park

 

– Perovskite solar cells: CaTiO3 structure
v. Bandgap of 1.5 to 2.3 eV
v. Cation and halide select for bandgap, stability and transport properties tuning
v. ITO as top transparent electrode by sputtering
v. Sputtering damage to perovskite layer: window layer is required.
v. Window layer requirements:

-High optical transmission (no parasitic absorption)
-No reaction with the halides in perovskite
-Diffusion barrier of organic cation and moisture penetration
-Efficient electron transfer

Fig. 1

v. Conventional window layer: MoOx long term stability issue (reaction with halide)
– Bilayer of 4 nm SnO2 and 2 nm ZTO as window layer
v. Minimal parasitic absorption
v. Efficient electron transfer
v. Sufficient buffer properties to prevent the sputter damage.

– p-i-n structure (Fig. 2)
v. p-n junction depletion region restricted by carrier life time
v. p-i-n structure: intrinsic layer extends E-field area  efficiency increase for materials   having superior absorption but inferior transport (multi-interfaces is useful.)
3.png

Fig. 2

– Tandem structure
v. Different wavelength absorption: energy spatial efficiency increase compared to   single-junction solar cell
v. Expensive process unit price

4

Fig. 3

5

Fig. 4

v. a-Si/c-Si heterojunction solar cell:
– Simple structure without complicated fabrication
– Surface passivation by reducing surface dangling bond
– Carrier life time: c-Si surface cleaning < a-Si:H passivation
– Low temperature  surface damage decrease
– Inserted insulating layer suppresses surface recombination

v. Random pyramid back surface:
scattering of weakly absorbed near-bandgap light EQE↑

v. SiNP(silicon nanoparticle)/silver stack as reflector

6.png

Fig. 5

v. Single-junction and Tandem EQE

Fig. 6

v. Long-term stability of single-junction

9.png

Fig. 7

Electrophoretic drug delivery for seizure control

Journal: Science Advances

Authors: C. M. Proctor and G. G. Malliaras et al.

Affiliation: The University of Cambridge (UK)

Publication date: 2018.08.29

Summarized by Inyeol Yun

 

– Topics
v. Neural probes incorporation an ion pump for on-demand drug delivery and   electrodes for recording local neural activity. (Fig. 1)
v. Seizure-like events (SLE) were induced by local injection of 4-aminopryridine (4AP)
v. γ-aminobutryic acid (GABA) inhibit neural activity.

1.png

<Fig. 1>

–Fabrication
v. Gold electrode: ion pump source electrode, PEDOT:PSS electrode : recording   electrophysiological activity (Fig. 2)

2.png

<Fig. 2>

– Results
v. Ion transfer efficiency: ~10-3 nmol of GABA transported in few seconds (Fig. 3)

3

<Fig. 3>

  v. Seizure control (Fig. 4)

4.png

<Fig. 4>

Low-Power, Electrochemically Tunable Graphene Synapses for Neuromorphic Computing

Journal: Advanced Materials

Authors: M. T. Sharbati and F. Xiong et al.

Affiliation: The University of Pittsburgh (USA)

Publication date: 2018.07.23

Summarized by Inyeol Yun

 

– Background
v. The neural network in a human brain has ≈1011 neurons. Each neuron is typically   connected to ≈5,000 to 10,000 other neurons through synapse.
v. Synapse plasticity is the ability of synapses to strengthen or weaken over time, in   response to increases or decreases in their activity (Wikipedia). It related to memory   function.
v. Typical artificial synapses cannot mimic the analog behaviors of biological synapses.
v. In this paper, authors demonstrate the synapse plasticity using “nano-battery”   technology. (Fig. 1)

1.png

<Fig. 1>

– Structure & Fabrication
v. Graphene layers – Solid electrolyte (LiClO4 in poly(ethylene oxide) (PEO) – Lithium   iron phosphate (LFP) (Fig. 2)

2.png

<Fig. 2>

 v. Metal contacts (80 nm of Cu) were defined by e-beam lithography and deposited   through e-beam evaporation.
v. Real image (Fig. 3)

3.png

<Fig. 3>

– Results
v. Raman spectroscopy shows weakening of bond between graphene layers as   increasing Li-ion. (Fig. 4)

4.png

<Fig. 4>

 v. Resistance change (Figure. 5)

5.png

<Fig. 5>

Flexible wireless powered drug delivery system for targeted administration on cerebral cortex

Journal: Nano Energy

Authors: S. Sung and K. Lee et al.

Affiliation: KAIST (Republic of Korea)

Publication date: 2018.06.07

Summarized by Inyeol Yun

 

– Flexible wireless powered drug delivery system (Fig. 1)

1.png

<Fig. 1>

– Device fabrication
v. Structure (Fig. 2)

2.png

<Fig. 2>

 v. Steps (Fig. 3)

3.jpg

<Fig. 3>

– Technical points
v. Heat transfer simulation (LLO damage x) (Fig.4)

4.png

<Fig. 4>

 v. Gold membrane dissolution process (Fig. 5)

5a

5

<Fig. 5>

  v. Wireless power efficiency (Fig. 6)

6.png

<Fig. 6>

Functional, RF-Trilayer Sensors for Tooth-Mounted, WirelessMonitoring of the Oral Cavity and Food Consumption

Journal: Advanced Materials

Authors: P. Tseng and F. G. Omenetto et al.

Affiliation: Tufts University (U.S.A.)

Publication date: 2018.03.23

Summarized by Inyeol Yun

 

– Structure
v. Au-Ti-(interlayer)-Ti-Au
v. 2 mm x 2 mm size

fig1.png

Fig. 1

fig2.png

Fig. 2

 

– Result
v. S11 change of various solvents and solutions (Fig. 3)
v. Resonant frequency vs. glucose concentration (Fig. 4)
v. Resonant frequency vs. temperature and pH (Fig. 5)

fig3.png

Fig. 3

fig4.png

Fig. 4

fig5

Fig. 5

 

– Measurement
v. In-vitro : HP 8753E impedance analyzer
v. In-vivo : miniVNA (Fig. 6)

fig6.png

Fig. 6