research focuses on hybrid hard/soft materials and systems, which can
create lots of interesting pehnomena and novel applications.
Specifically, we study hybrid hard/soft materials and systems in three
- We develop devices and systems that utilize the
advantages of both hard and soft materials, which cannot be achieved
through conventional means.
- We develop materials with unique
properties that can only be realized through the combination of
distinct properties of hard and soft materials.
- We study
fundamental mechanics of hybrid hard/soft systems that can advance our
understanding of such systems and guide the design and optimization of
devices and materials.
Stretchable Electronics: Devices, Materials, and Mechanics
combines the electronic performance of conventional wafer-based
devices and mechanical properties of a rubber band, and thus can have
broad applications that are impossible for hard, planar integrated
that exist today. Examples range from surgical and diagnostic
integrate with the human body to provide advanced therapeutic
structural health monitors and inspection systems for civil
engineering. In this research thrust, we develop materials and devices
for stretchable electronics, we also study fundamental mechanics to
further our understanding of the underlying physics and to guide the
design and opimization.
Bio-inspired Bug Eye Cameras (Artificial Compound Eye)
arthropods, evolution has created a remarkably sophisticated class of
imaging systems, with a wide-angle field of view, low aberrations, high
acuity to motion and an infinite depth of field. A challenge in
building digital cameras with the hemispherical, compound apposition
layouts of arthropod eyes is that essential design requirements cannot
be met with existing planar sensor technologies or conventional optics.
In this study, we combined elastomeric compound optical elements with
deformable arrays of thin silicon photodetectors into integrated sheets
that can be elastically transformed from the planar geometries in which
they are fabricated to hemispherical shapes for integration into
M. Song+, Y. Xie+, V. Malyarchuk+, J. Xiao+, I. Jung, K.-J. Choi, Z.
Liu, H. Park, C. Lu, R.-H. Kim, R. Li, K. B. Crozier, Y. Huang, and J.
A. Rogers, Digital Cameras With Designs Inspired By the Arthropod Eye,
Nature 497, 95–99 (2013)
Highlighted on the cover.
Tunable Eyeball Cameras With Zoom
our previously developed bio-inspired eyeball
cameras, photodetectors are distributed on curvilinear
surfaces to match the strongly nonplanar image surfaces (i.e.,
Petzval surfaces) that form with simple lenses. Although these systems
provide advantages compared to those with conventional, planar designs,
their fixed detector curvature renders them incompatible with changes
in the Petzval surface that accompany variable zoom achieved with
simple lenses.Here, we put stretchable photodetector arrays on thin
elastomeric membranes, capable of reversible deformation into
hemispherical shapes with radii of curvature that can be adjusted
dynamically, via hydraulics. Combining this type of detector with a
similarly tunable, fluidic planoconvex lens yields a hemispherical
camera with variable zoom and excellent imaging characteristics.|
Jung, J. Xiao, V. Malyarchuk, C. Lu, M. Li, Z. Liu, J. Yoon, Y. Huang,
and J. A. Rogers, Dynamically tunable hemispherical electronic eye
camera system with adjustable zoom capability, Proc. Natl. Acad. Sci.
USA 108, 1788-1793 (2011) (cover feature article)
C. Lü, M. Li, J. Xiao*, I. Jung, J.
Wu, Y. Huang, K.-C. Hwang, and J.A. Rogers, Mechanics of tunable
hemispherical electronic eye camera systems that combine rigid device
elements with soft elastomers, Journal of Applied
Mechanics-Transactions of the ASME (accepted)
Wang, J. Xiao, J. Song, H. C. Ko, K.-C. Hwang, Y. Huang, and J. A.
Rogers, Mechanics of curvilinear electronics, Soft Matter 6, 5757–5763
D.-H. Kim, J. Xiao, J. Song, Y. Huang and J. A. Rogers,
Stretchable, Curvilinear Electronics Based On Inorganic Materials,
Advanced Materials 22, 2108–2124 (2010)
S. Wang, J. Xiao, I. Jung,
J. Song, H. C. Ko, M. P. Stoykovich, Y. Huang, K.-C. Hwang and J. A.
Rogers, Mechanics of Hemispherical Electronics, Appl. Phys. Lett. 95,
J. Song, Y. Huang, J. Xiao, S. Wang, K.C. Hwang, H.C.
Ko, D.H. Kim, M.P. Stoykovich, and J.A. Rogers, Mechanics of
noncoplanar mesh design for stretchable electronic circuits, Journal of
Applied Physics 105, 123516 (2009).
H. C. Ko, M. P. Stoykovich, J.
Song, V. Malyarchuk, W. M. Choi, C.-J. Yu, J. B. Geddes, J. Xiao, S.
Wang, Y. Huang, and J. A. Rogers, A Hemispherical Electronic Eye Camera
Based on Compressible Silicon Optoelectronics. Nature 454, 748-753
(2008). (cover feature article)
Flexible, Ultrathin Sensors for Biomedical Applications
biomedical practices, many electronic devices are used to perform
diagnosis, treament and other functions. However, electronics are
usually very hard, and cannot comply with the complex geometries and
extreme deformabilities of biological tissues. This incompatibility
greatly limits the application of electronics in biomedical areas (one
extreme example is brain computer interface
developed electronics that are capable of intimate, non-invasive
integration with the soft, curvilinear surfaces of biological tissues,
which offer important opportunities for diagnosing and treating disease
and for improving interfaces between electronics and biological
tissues. As shown on the left are neural sensors on cat's brains (top
left and right) and cardiac sensor on pig's heart, for
Viventi et al., Flexible, Foldable, Actively Multiplexed, High-Density Electrode
Array for Mapping Brain Activity in vivo, Nature Neuroscience 14,
Kim et al., Dissolvable Films of Silk Fibroin for
Ultrathin Conformal Bio-Integrated Electronics, Nature Materials 9,
511-517 (2010) (cover feature article)
Viventi et al., A Conformal, Bio-interfaced Class of Silicon
Electronics for Mapping Cardiac Electrophysiology, Science
Translational Medicine 2, 24ra22 (2010). (cover feature article)
Stretchable Inorganic LEDs
light-emitting diodes and photodetectors represent important,
established technologies for solid-state lighting, digital imaging and
many other applications. Eliminating mechanical and geometrical design
constraints imposed by the supporting semiconductor wafers can enable
alternative uses in areas such as biomedicine and robotics. We
developed systems that consist of arrays of interconnected, ultrathin
inorganic light-emitting diodes and photodetectors configured in
mechanically optimized layouts on unusual substrates. As shown on the
left are LEDs poked by a pencil tip (top left), twisted to different
angles (top right), LEDs on a thread sutured underneath the skin
(bottom left) and LEDs and photodetectors (PDs) integrated on a glove
for detecting distance (bottom right).
Kim, D.-H. Kim, J. Xiao, B. H. Kim, S.-I. Park, B. Panilaitis, R.
Ghaffari, J. Yao, M. Li, Z. Liu, V. Malyarchuk, D. G. Kim, A.-P. Le, R.
G. Nuzzo, D. L. Kaplan, F. G. Omenetto, Y. Huang, Z. Kang, and J. A.
Rogers, Waterproof AlInGaP optoelectronics on stretchable substrates
with applications in biomedicine and robotics, Nature Materials 9,
Flexible Solar Cells
high natural abundance of silicon, together with its excellent
reliability and good efficiency in solar cells, suggest its continued
use in production of solar energy, on massive scales, for the
foreseeable future. Although organics, nanocrystals, nanowires and
other new materials hold significant promise, many opportunities
continue to exist for research into unconventional means of exploiting
silicon in advanced photovoltaic systems.Here,we developed modules that
use large-scale arrays of silicon solar microcells created from bulk
wafers and integrated in diverse spatial layouts on foreign substrates
by transfer printing. The resulting devices can offer useful features,
including high degrees of mechanical flexibility, user-definable
transparency and ultrathin-form-factor microconcentrator designs.
et al., Compact monocrystalline silicon solar modules with high
voltage outputs and mechanically flexible designs, Energy &
Environmental Science 3, 208-211 (2010) (cover feature article)
et al., Ultrathin silicon solar microcells for semitransparent,
mechanically flexible and microconcentrator module designs. Nat.
Mater. 7, 907-915 (2008). (cover feature article)
Stretchable and Compressible Conductors
developed stretchable Au thin films on elastomeric substrates of
polydimethylsiloxane that are designed with sinusoidal, “wavy”
features of surface relief. This approach eliminates the compressive
strains introduced into the thin films through commonly adopted
buckling approach, and therefore can provide both high stretchability
and compressibility. Such systems can be useful as stretchable
conductors in electronic or sensory devices.|
et al., Stretchable and Compressible Thin Films of Stiff Materials on
Compliant Wavy Substrates. Appl. Phys. Lett. 93, 013109 (2008)
et al., Analytical and Experimental Studies of the Mechanics of
Deformation in a Solid with a Wavy Surface Profile. Journal of Applied
Mechanics-Transactions of the ASME 77, 011003 (2010).
Wrinkling of Thin Films on Soft SubstratesBy
engineering the strain mismatch between adhered stiff thin films and
soft substrates, nonlinear wrinkling (buckling) of thin films can
create well-controlled wavy surface features. This capability can lead
to lots of interesting applications, such as stretchable electronics,
precision metrology, smart adhesion and friction, controllable wetting,
optical gratings, and sensing and actuating devices. We are interested
in novel surface engineering by utilizing nonlinear wrinkling
mechanics. We also explore novel materials for such phenomena, such as
carbon nanotubes and silicon nanowires. Underlying mechanics and
physics are also studied through analytical or numerical means.
Nonlinear Buckling of Silicon Ribbons on Elastomers
previous studies of thin film wrinkling on soft substrates, the
mechanics models usually assume plane-strain deformation, which was
found to disagree with experimental observations for narrow thin
films. Systematic experimental and analytical studies are conducted for
buckling of finite-width stiff thin films on compliant substrates. Both
experiments and analytical solution show that the buckling amplitude
and wavelength increase with the film width.The effect of film spacing
is also studied via the analytical solutions for two thin films and for
periodic thin films. |
Jiang, D.-Y. Khang, H. Fei, H. Kim, Y. Huang, J. Xiao, and J. A.
Rogers, Finite Width Effect of Thin-Films Buckling on Compliant
Substrate: Experimental and Theoretical Studies. J. Mech. Phys. Solids
56, 2585-2598 (2008).
Molecular Scale Buckling Mechanics of Carbon Nanotubes on Elastomers
have studied for the first time the scaling of controlled nonlinear
buckling processes in materials with dimensions in the molecular range
(i.e., ~1 nm) through experimental and theoretical studies of buckling
in individual single-wall carbon nanotubes on substrates of
poly(dimethylsiloxane). The results show not only the ability to create
and manipulate patterns of buckling at these molecular scales, but
also, that analytical continuum mechanics theory can explain,
quantitatively, all measurable aspects of this system. Inverse
calculation applied to measurements of diameter dependent buckling
wavelengths yields accurate values of the Young’s moduli of individual
SWNTs. As an example of the value of this system beyond its use in this
type of molecular scale metrology, we implement parallel arrays of
buckled SWNTs as a class of mechanically stretchable conductor. |
Khang, J. Xiao, C. Kocabas, S. Maclaren, T. Banks, H. Jiang, Y. Y.
Huang, and J. A. Rogers, Molecular Scale Buckling Mechanics in
Individual Aligned Single-Wall Carbon Nanotubes on Elastomeric
Substrates. Nano Lett. 8, 124-130 (2008).
J. Xiao, H. Jiang, D.-Y.
Khang, J. Wu, Y. Huang, and J.A. Rogers, Mechanics of buckled carbon
nanotubes on elastomeric substrates. J. Appl. Phys. 104, 033543 (2008).
In-plane Buckling of Silicon Nanowires on Elastomers
combined experimental and theoretical means to study the buckling
mechanics in silicon nanowires (SiNWs) on elastomeric substrates. The
system involves randomly oriented SiNWs grown using established
procedures on silicon wafers, and then transferred and organized into
aligned arrays on prestrained slabs of poly(dimethylsiloxane) (PDMS).
Releasing the prestrain leads to nonlinear mechanical buckling
processes that transform the initially linear SiNWs into sinusoidal
(i.e., “wavy”) shapes. We observed for the first time that the
displacements associated with these waves lie in the plane of the
substrate, unlike previously observed behavior in analogous systems of
silicon nanoribbons and carbon nanotubes where motion occurs
out-of-plane. Theoretical analysis indicates that the energy associated
with this in-plane buckling is slightly lower than the out-of-plane
case for the geometries and mechanical properties that characterize the
SiNWs. An accurate measurement of the Young’s modulus of individual
SiNWs, between ∼170 and ∼110 GPa for the range of wires examined
here. A simple strain gauge built using SiNWs in these wavy geometries
demonstrates one area of potential application. |
Ryu, J. Xiao, W.I. Park, K.S. Son, Y.Y. Huang, U. Paik, and J.A.
Rogers, Lateral Buckling Mechanics in Silicon Nanowires on Elastomeric
Substrates, Nano Letters 9, 3214-3219 (2009).
J. Xiao, S.Y. Ryu,
Y. Huang, K.-C. Hwang, U. Paik and J.A. Rogers, Mechanics of
nanowire/nanotube in-surface buckling on elastomeric substrates,
Nanotechnology 21, 085708 (2010).
Mechanics of NanomaterialsDue
to their attractive mechanical, electrical and optical properties,
nanomaterials have attracted a lot of research interest. We are
especially interested in the mechanics of nanomaterials, including
nanotubes, nanowires, and graphenes. The non-specific van der Waals
interaction, which is considered very weak forces in macroscale, can
play dominating roles in the mechanical behavior of nanomaterials. We
study the mechanical deformation of nanomaterials caused by this van
der Waals interaction, which could have important implications on the
application of nanomaterials in materials, electronics and
Self Folding of Graphene
like a sheet of paper, folds under mechanical forces. The folded
graphene edges can affect the electrical properties of graphenes.
The stability of folded graphene, however, depends on the folding
direction and the resulted graphene stacking. Suspended graphene in
liquids folds freely under random ultrasonic stimulations. We
determined the structure of ~100 folded graphene edges by electron
nanodiffraction. About 1/3 are armchair and 1/3 are zigzag. The results
are explained by the energetics of graphene folding and atomic
simulation. The zigzag edge has AB stacking, while in the armchair
edge, AB stacking is achieved in some areas by a small twist. An
analytical model based on finite deformation mechanics was also
developed to accurately describe the shapes of folded edges. |
Zhang, J. Xiao, X. Meng, C. Monroe, Y. Huang, and J.-M. Zuo, Free
Folding of Suspended Graphene Sheets by Random Mechanical Stimulation,
Physical Review Letters 104, 166805 (2010)
X. Meng, M. Li*, Z. Kang,
X. Zhang, J. Xiao*, Mechanics of Self-Folding of Single-layer Graphene,
J. Phys. D: Appl. Phys. 46, 055308 (2013)
Mechanics of Graphene Blisters
|Graphene membranes are adhered to substrates with patterned microcavities of prescribed volumes.
By controlling the gas pressure within the microcavity, the membrane
can be made to bulge and delaminate
in a stable manner from the substrate. We study the analytical
mechanics of this system, which is combined with experimental
measurement to determine the elasticity of graphene and
the adhesion energy between a substrate and a graphene (or other
two-dimensional solid) membrane.
A different microcavity configuration with a post in the center was
also used, to study the pull-in behavior of graphene, which allows
the determination of interfacial forces between two-dimensional
nanomaterials and substrates. |
X. Liu, N.G. Boddeti, M.R. Szpunar, L. Wang, M.A.
Rodriguez, R. Long, J. Xiao, M.L.
Dunn, and J.S. Bunch, Observation of Pull-in Instability in Graphene Membranes
under Interfacial Forces, Nano Letters
G. Boddeti, S. P. Koenig, R. Long, J. Xiao, J. S. Bunch, and M. L.
Dunn, Mechanics of Pressurized Graphene Blisters, Journal of Applied
Mechanics-Transactions of the ASME (accepted)
Alignment Controlled Growth of Carbon Nanotubes on Quartz
walled carbon nanotubes (SWNTs) possess extraordinary electrical
properties, with many possible applications in electronics.
Dense, horizonally aligned arrays of linearly configured SWNTs
represent perhaps the most attractive and scalable way to implement
this class of nanomaterial in practical systems. Recent work
shows that templated growth of tubes on certain crystalline substrates
yields arrays with the necessary levels of perfection, as demonstrated
by the formation of devices and full systems on quartz. Here, we
examine advanced implementations of this process on crystalline quartz
substrates with different orientations, to yield strategies for forming
diverse, but well-defined horizontal configurations of SWNTs.
Combined experimental and theoretical studies indicate that angle
dependent van der Waals interactions can account for nearly all aspects
of alignment on quartz with X, Y, Z and ST cuts, as well as quartz with
disordered surface layers. These findings provide important
insights into methods for guided growth of SWNTs, and possibly other
classes of nanomaterials, for applications in electronics, sensing,
photodetection, light emission and other areas.|
Xiao, S. Dunham, P. Liu, Y. Zhang, C. Kocabas, L. Moh, Y. Huang, K.-C.
Hwang, C. Lu, W. Huang and J. A. Rogers, Alignment controlled growth of
single-walled carbon nanotubes on quartz substrates, Nano Letters 9,
Collapse and Stability of Carbon Nanotubes
nanotubes (CNTs) usually possess circular cross sections. As the size
increases, van der Waals interaction could cause CNTs to collapse to a
dumbbell shape. The collapse and stability of carbon nanotubes (CNTs)
have important implications for their synthesis and applications. While
nanotube collapse has been observed experimentally, the conditions for
the collapse, especially its dependence on tube structures, are not
clear. We have studied the energetics of the collapse of single- and
multi-wall CNTs via atomistic simulations. The collapse is governed by
the number of walls and the radius of the inner-most wall. The
collapsed structure is energetically favored about a certain diameter,
which is 4.12, 4.96 and 5.76 nm for single-, double- and triple-wall
CNTs, respectively. The CNT chirality also has a strong influence on
the collapsed structure, leading to flat, warped and twisted CNTs,
depending on the chiral angle. |
Xiao, B. Liu, Y. Huang, J. Zuo, K.-C. Hwang, and M.-F. Yu, Collapse and
Stability of Single- and Multi-wall Carbon Nanotubes. Nanotechnology
18, 395703 (2007).