College of Sciencehttp://hdl.handle.net/10197/179720140421T14:59:17Z20140421T14:59:17ZThe approximation order of polysplinesKounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/551920140404T11:41:40Z20040701T00:00:00ZThe approximation order of polysplines
Kounchev, Ognyan; Render, Hermann
We show that the scaling spaces de ned by the polysplines of order
p provide approximation order 2p: For that purpose we re ne the re
sults on one dimensional approximation order by Lsplines obtained
in [2].
20040701T00:00:00ZVector piezoresponse force microscopyKalinin, S. V.Rodriguez, Brian J.Jesse, S.et al.http://hdl.handle.net/10197/551420140404T10:44:39Z20060601T00:00:00ZVector piezoresponse force microscopy
Kalinin, S. V.; Rodriguez, Brian J.; Jesse, S.; et al.
A novel approach for nanoscale imaging and characterization of the orientation dependence of electromechanical propertiesvector piezoresponse force microscopy (Vector PFM)is described. The relationship between local electromechanical response, polarization, piezoelectric constants, and crystallographic orientation is analyzed in detail. The image formation mechanism in vector PFM is discussed. Conditions for complete threedimensional (313) reconstruction of the electromechanical response vector and evaluation of the piezoelectric constants from PFM data are set forth. The developed approach can be applied to crystallographic orientation imaging in piezoelectric materials with a spatial resolution below 10 nm. Several approaches for data representation in 2DPFM and 3DPFM are presented. The potential of vector PFM for molecular orientation imaging in macroscopically disordered piezoelectric polymers and biological systems is discussed.
20060601T00:00:00ZPolyharmonicity and algebraic support of measuresKounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/551120140401T08:34:23Z20070201T00:00:00ZPolyharmonicity and algebraic support of measures
Kounchev, Ognyan; Render, Hermann
Our main result states that two signed measures μ and ν with bounded
support contained in the zero set of a polynomial P(χ) are equal if they coincide on the
subspace of all polynomials of polyharmonic degree NP where the natural number NP is
explicitly computed by the properties of the polynomial P(χ). The method of proof
depends on a definition of a multivariate Markov transform which is another major
objective of the present paper. The classical notion of orthogonal polynomial of second
kind is generalized to the multivariate setting: it is a polyharmonic function which has
similar features to those in the onedimensional case.
20070201T00:00:00ZConvergence of polyharmonic splines on semiregular grids Z x aZ^n for a to 0Kounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/551020140401T08:31:20Z20070701T00:00:00ZConvergence of polyharmonic splines on semiregular grids Z x aZ^n for a to 0
Kounchev, Ognyan; Render, Hermann
Let
p,n
∈
N
with 2
p
≥
n
+ 2
,
and let
I
a
be a polyharmonic spline of
order
p
on the grid
Z
×
a
Z
n
which satisfies the interpolating conditions
I
a
(
j,am
) =
d
j
(
am
) for
j
∈
Z
,m
∈
Z
n
where the functions
d
j
:
R
n
→
R
and the parameter
a>
0 are given. Let
B
s
(
R
n
) be the set of all integrable
functions
f
:
R
n
→
C
such that the integral
k
f
k
s
:=
Z
R
n
b
f
(
ξ
)
(1 +

ξ

s
)
dξ
is finite. The main result states that for given
σ
≥
0 there exists a
constant
c>
0 such that whenever
d
j
∈
B
2
p
(
R
n
)
∩
C
(
R
n
)
,j
∈
Z
,
satisfy
k
d
j
k
2
p
≤
D
·
(1 +

j

σ
) for all
j
∈
Z
there exists a polyspline
S
:
R
n
+1
→
C
of order
p
on strips such that

S
(
t,y
)
−
I
a
(
t,y
)
≤
a
2
p
−
1
c
·
D
·
(1 +

t

σ
)
for all
y
∈
R
n
,t
∈
R
and all 0
<a
≤
1.
20070701T00:00:00ZOn realanalytic recurrence relations for cardinal exponential BsplinesAldaz, J. M.Kounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/550820140401T08:23:56Z20071001T00:00:00ZOn realanalytic recurrence relations for cardinal exponential Bsplines
Aldaz, J. M.; Kounchev, Ognyan; Render, Hermann
Let LN+1 be a linear differential operator of order N + 1 with constant coefficients
and real eigenvalues λ 1, ..., λ N+1, let E( N+1) be the space of all C∞solutions of
LN+1 on the real line.We show that for N 2 and n = 2, ...,N, there is a recurrence
relation from suitable subspaces εn to εn+1 involving realanalytic functions, and
with εN+1 = E(Λ N+1) if and only if contiguous eigenvalues are equally spaced.
20071001T00:00:00ZPadé approximation for a multivariate Markov transformKounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/550320140331T09:18:05Z20081001T00:00:00ZPadé approximation for a multivariate Markov transform
Kounchev, Ognyan; Render, Hermann
Methods of Padè approximation are used to analyse a multivariate
Markov transform which has been recently introduced by the authors.
The first main result is a characterization of the rationality of the
Markov transform via Hankel determinants. The second main result
is a cubature formula for a special class of measure.
20081001T00:00:00ZOn the mixed Cauchy problem with data on singular conicsEbenfelt, PeterRender, Hermannhttp://hdl.handle.net/10197/550120140328T09:37:53Z20080801T00:00:00ZOn the mixed Cauchy problem with data on singular conics
Ebenfelt, Peter; Render, Hermann
We consider a problem of mixed Cauchy type for certain holomorphic partial differential
operators with the principal part Q2p(D) essentially being the (complex) Laplace operator to
a power, Δp. We provide inital data on a singular conic divisor given by P = 0, where P is a
homogeneous polynomial of degree 2p. We show that this problem is uniquely solvable if the
polynomial P is elliptic, in a certain sense, with respect to the principal part Q2p(D).
20080801T00:00:00ZThe Goursat problem for a generalized Helmholtz operator in the planeEbenfelt, PeterRender, Hermannhttp://hdl.handle.net/10197/550020140328T09:34:45Z20080901T00:00:00ZThe Goursat problem for a generalized Helmholtz operator in the plane
Ebenfelt, Peter; Render, Hermann
We consider the Goursat problem in the plane for partial differential operators whose principal part is the pth power of the standard Laplace operator. The data is posed on a union of 2p distinct lines through the origin. We show that the solvability of this Goursat problem depends on Diophantine properties of the geometry of lines on which the data is posed.
20080901T00:00:00ZReproducing kernels for polyharmonic polynomialsRender, Hermannhttp://hdl.handle.net/10197/549920140328T09:31:08Z20081001T00:00:00ZReproducing kernels for polyharmonic polynomials
Render, Hermann
The reproducing kernel of the space of all homogeneous polynomi
als of degree
k
and polyharmonic order
m
is computed explicitly, solving a
question of A. Fryant and M.K. Vemuri.
20081001T00:00:00ZBernstein operators for exponential polynomialsAldaz, J. M.Kounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/549820140328T09:30:16Z20090401T00:00:00ZBernstein operators for exponential polynomials
Aldaz, J. M.; Kounchev, Ognyan; Render, Hermann
Let
L
be a linear differential operator with constant coefficients of order
n
and complex eigenvalues
λ
0
,...,λ
n
. Assume that the set
U
n
of all solutions of the
equation
Lf
= 0 is closed under complex conjugation. If the length of the interval [
a,b
]
is smaller than
π/M
n
, where
M
n
:= max
{
Im
λ
j

:
j
= 0
,...,n
}
, then there exists a basis
p
n,k
,
k
= 0
,...n
, of the space
U
n
with the property that each
p
n,k
has a zero of order
k
at
a
and a zero of order
n
−
k
at
b,
and each
p
n,k
is positive on the open interval (
a,b
)
.
Under the additional assumption that
λ
0
and
λ
1
are real and distinct, our first main
result states that there exist points
a
=
t
0
<t
1
<...<t
n
=
b
and positive numbers
α
0
,..,α
n
, such that the operator
B
n
f
:=
n
X
k
=0
α
k
f
(
t
k
)
p
n,k
(
x
)
satisfies
B
n
e
λ
j
x
=
e
λ
j
x
, for
j
= 0
,
1
.
The second main result gives a sufficient condition
guaranteeing the uniform convergence of
B
n
f
to
f
for each
f
∈
C
[
a,b
].
20090401T00:00:00ZOn the Bernstein operator of S. Morigi and M. NeamtuKounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/549620140328T09:07:13Z20091001T00:00:00ZOn the Bernstein operator of S. Morigi and M. Neamtu
Kounchev, Ognyan; Render, Hermann
We discuss a Bernstein type operator introduced by S. Morigi and
M. Neamtu for
D
polynomials in the more general framework of exponential
polynomials
20091001T00:00:00ZShape preserving properties of generalized Bernstein operators on extended Chebyshev spacesAldaz, J. M.Kounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/549520140328T09:05:29Z20091201T00:00:00ZShape preserving properties of generalized Bernstein operators on extended Chebyshev spaces
Aldaz, J. M.; Kounchev, Ognyan; Render, Hermann
We study the existence and shape preserving properties of a generalized
Bernstein operator
B
n
fixing a strictly positive function
f
0
, and a second function
f
1
such
that
f
1
/f
0
is strictly increasing, within the framework of extended Chebyshev spaces
U
n
.
The first main result gives an inductive criterion for existence: suppose there exists a
Bernstein operator
B
n
:
C
[
a,b
]
→
U
n
with strictly increasing nodes, fixing
f
0
,f
1
∈
U
n
.
If
U
n
⊂
U
n
+1
and
U
n
+1
has a nonnegative Bernstein basis, then there exists a Bernstein
operator
B
n
+1
:
C
[
a,b
]
→
U
n
+1
with strictly increasing nodes, fixing
f
0
and
f
1
.
In
particular, if
f
0
,f
1
,...,f
n
is a basis of
U
n
such that the linear span of
f
0
,..,f
k
is an
extended Chebyshev space over [
a,b
] for each
k
= 0
,...,n
, then there exists a Bernstein
operator
B
n
with increasing nodes fixing
f
0
and
f
1
.
The second main result says that
under the above assumptions the following inequalities hold
B
n
f
≥
B
n
+1
f
≥
f
for all (
f
0
,f
1
)convex functions
f
∈
C
[
a,b
]
.
Furthermore,
B
n
f
is (
f
0
,f
1
)convex for all
(
f
0
,f
1
)convex functions
f
∈
C
[
a,b
]
.
20091201T00:00:00ZCauchy, Goursat and Dirichlet problems for holomorphic partial differential equationsRender, Hermannhttp://hdl.handle.net/10197/549220140327T15:57:12Z20110101T00:00:00ZCauchy, Goursat and Dirichlet problems for holomorphic partial differential equations
Render, Hermann
n this paper we survey recent results about Fischer decomposi
tions of polynomials or entire functions and their applications to holomorphic
partial di erential equations. We discuss Cauchy and Goursat problems for the
polyharmonic operator. Special emphasis is given to the KhavinsonShapiro
conjecture concerning polynomial solvability of the Dirichlet problem.
20110101T00:00:00ZThe KhavinsonShapiro conjecture and polynomial decompositionsLundberg, ErikRender, Hermannhttp://hdl.handle.net/10197/549020140327T15:51:19Z20110415T00:00:00ZThe KhavinsonShapiro conjecture and polynomial decompositions
Lundberg, Erik; Render, Hermann
The main result of the paper states the following: Let ψ be a polynomial
in n variables of degree t: Suppose that there exists a constant C > 0 such
that any polynomial f has a polynomial decomposition f = ψ qf + hf with
khf = 0 and deg qf deg f + C: Then deg ψ 2k. Here ∆k is the kth
iterate of the Laplace operator ∆ : As an application, new classes of domains
in Rn are identi ed for which the KhavinsonShapiro conjecture holds.
20110415T00:00:00ZPolyharmonic Hardy spaces on the complexified annulus and error estimates of cubature formulasKounchev, OgnyanRender, Hermannhttp://hdl.handle.net/10197/548920140327T15:50:00Z20121201T00:00:00ZPolyharmonic Hardy spaces on the complexified annulus and error estimates of cubature formulas
Kounchev, Ognyan; Render, Hermann
The present paper has a twofold contribution: first, we intro
duce a new concept of Hardy spaces on a multidimensional complexified
annular domain which is closely related to the annulus of the KleinDi
rac
quadric important in Conformal Quantum Field Theory. Secondly, for
functions in these Hardy spaces, we provide error estimate for the p
oly
harmonic GaußJacobi cubature formulas, which have been introduced
in previous papers.
20121201T00:00:00ZHarmonic divisors and rationality of zeros of Jacobi polynomialsRender, Hermannhttp://hdl.handle.net/10197/548820140327T15:47:30Z20130801T00:00:00ZHarmonic divisors and rationality of zeros of Jacobi polynomials
Render, Hermann
Let
Pn
(α,β
)
(
x
)
be the Jacobi polynomial of degree
n
with parameters
αβ
The main result of the paper states the following: If
b≠
1
;
3
and
c
are nonzero rel
atively prime natural numbers then
P
(
k
+(
d
3)
=
2
;k
+(
d
3)
=
2)
n
p
b=c
6
≠ 0
for all natural
numbers
d;n
and
k
2
N
0
:
Moreover, under the above assumption, the polynomial
Q
(
x
) =
b
c
x
2
1
+
:::
+
x
2
d
1
+
b
c
1
x
2
d
is not a harmonic divisor, and the Dirichlet problem for
the cone
f
Q
(
x
)
<
0
g
has polynomial harmonic solutions for polynomial data functions.
20130801T00:00:00ZRegularity of generalized Daubechies wavelets reproducing exponential polynomials with realvalued parametersDyn, NiraKounchev, OgnyanLevin, DavidRender, Hermannhttp://hdl.handle.net/10197/548420140327T15:27:02Z20140102T00:00:00ZRegularity of generalized Daubechies wavelets reproducing exponential polynomials with realvalued parameters
Dyn, Nira; Kounchev, Ognyan; Levin, David; Render, Hermann
We investigate nonstationary orthogonal wavelets based on a nonstationary
interpolatory subdivision scheme reproducing a given set of exponentials with realvalued
parameters. The construction is analogous to the construction of Daubechies wavelets
using the subdivision scheme of DeslauriersDubuc. The main result is the existence and
smoothness of these Daubechies type wavelets.
20140102T00:00:00ZConvergence of rational Bernstein operatorsRender, Hermannhttp://hdl.handle.net/10197/547820140327T14:32:26Z20140401T00:00:00ZConvergence of rational Bernstein operators
Render, Hermann
In this paper we discuss convergence properties and error estimates of rational
Bernstein operators introduced by P. Pit¸ul and P. Sablonni`ere. It is shown that the
rational Bernstein operators converge to the identity operator if and only if the maximal
difference between two consecutive nodes is converging to zero. Further a Voronovskaja
theorem is given based on the explicit computation of higher order moments for the
rational Bernstein operator
20140401T00:00:00ZQuantitative determination of tip parameters in piezoresponse force microscopyKalinin, S. V.Jesse, S.Rodriguez, Brian J.et al.http://hdl.handle.net/10197/547520140320T16:00:25Z20070524T00:00:00ZQuantitative determination of tip parameters in piezoresponse force microscopy
Kalinin, S. V.; Jesse, S.; Rodriguez, Brian J.; et al.
One of the key limiting factors in the quantitative interpretation of piezoresponse force microscopy (PFM) is the lack of knowledge on the effective tip geometry. Here the authors derive analytical expressions for a 180 degrees domain wall profile in PFM for the point charge, sphere plane, and disk electrode models of the tip. An approach for the determination of the effective tip parameters from the wall profile is suggested and illustrated for several ferroelectric materials. The calculated tip parameters can be used selfconsistently for the interpretation of PFM resolution and spectroscopy data, i.e., linear imaging processes.
20070524T00:00:00ZReal Bargmann spaces, Fischer decompositions and Sets of uniqueness for polyharmonic functionsRender, Hermannhttp://hdl.handle.net/10197/547420140320T15:48:50Z20080401T00:00:00ZReal Bargmann spaces, Fischer decompositions and Sets of uniqueness for polyharmonic functions
Render, Hermann
In this paper a positive answer is given to the following question of W.K.
Hayman: if a polyharmonic entire function of order k vanishes on k distinct ellipsoids
in the euclidean space Rn then it vanishes everywhere. Moreover a characterization of
ellipsoids is given in terms of an extension property of solutions of entire data functions
for the Dirichlet problem answering a question of D. Khavinson and H.S. Shapiro. These
results are consequences from a more general result in the context of direct sum decompositions
(Fischer decompositions) of polynomials or functions in the algebra A(BR)
of all realanalytic functions defined on the ball BR of radius R and center 0 whose
Taylor series of homogeneous polynomials converges compactly in BR. The main result
states that for a given elliptic polynomial P of degree 2k and sufficiently large radius
R > 0 the following decomposition holds: for each function f 2 A(BR) there exist
unique q, r 2 A(BR) such that f = Pq + r and kr = 0. Another application of this
result is the existence of polynomial solutions of the polyharmonic equation ku = 0 for
polynomial data on certain classes of algebraic hypersurfaces.
2000 Mathematical Subject Classification. Primary: 31B30. Secondary: 35A20,
14P99, 12Y05
20080401T00:00:00ZCoseismic velocity variations caused by static stress changes associated with the 2001 Mw=4.3 Agios Ionis earthquake in the Gulf of Corinth, GreeceCociani, L.Bean, Christopher J.LyonCaen, Heleneet al.http://hdl.handle.net/10197/544320140228T10:01:56Z20100701T00:00:00ZCoseismic velocity variations caused by static stress changes associated with the 2001 Mw=4.3 Agios Ionis earthquake in the Gulf of Corinth, Greece
Cociani, L.; Bean, Christopher J.; LyonCaen, Helene; et al.
The analysis of temporal variations in the seismic velocity across faults can be used to
estimate in situ stress changes. Seismic velocity of propagation depends on the fault
stiffness, which is a function of stress. The coda wave interferometry technique is applied
to seven families of repeating earthquakes (multiplets) recorded on the southern shore of
the Gulf of Corinth, Greece, to estimate high precision velocity changes in the Earth
’
s
crust associated with the
M
w
= 4.3 Agios Ioanis earthquake. Results show that the Agios
Ioanis event causes a perturbation in elastic properties at seismogenic depth, resulting in a
reduction of 0.2% in the seismic velocity. The results are not consistent with either damage
induced by dynamic stresses nor a fluid transient origin. In contrast, both the spatial
distribution and magnitude of the velocity perturbation correlate well with modeled static
stress variations. This suggests that the measured changes in the mechanical properties of
the seismogenic crust can be attributed to a change in static stress field associated with the
M
w
= 4.3 Agios Ioanis earthquake. The velocity changes indicate an unclamping of the
Pyrgaki fault at depth, which has local hazard implications
20100701T00:00:00ZStatistical selection of the 'best' seismic source mechanisms from inversions of synthetic volcanic longperiod eventsO'Brien, G. S.Lokmer, IvanBean, Christopher J.http://hdl.handle.net/10197/544120140228T09:51:23Z20100901T00:00:00ZStatistical selection of the 'best' seismic source mechanisms from inversions of synthetic volcanic longperiod events
O'Brien, G. S.; Lokmer, Ivan; Bean, Christopher J.
Inversions for the source mechanism of long‐period (LP) seismicity recorded on
volcanoes have become increasingly common and are used to interpret fluid‐driven
processes. The source mechanism considered for LP inversions usually consists of a
symmetric moment tensor with and without single forces. Also, constrained inversions have
been performed where one presumes a specific source geometry that reduces the degrees of
freedom in the inversion. To select the correct solution from the different possible
mechanisms, the Akaike information criterion (AIC) has been used. However, since
AIC performs well only if the inverted model is close to the true model, we tested its
ability to select the correct model in LP inversions. Using synthetic data sets generated on
Mt. Etna, Italy, with a tomography velocity model and the Green’s functions calculated for
a simplified, homogeneous velocity model, we have investigated (1) if any of the inversion
source models can recover the true mechanism and (2) the ability of the Akaike and
Bayesian information criteria (BIC) to select the correct model. Results show that in some
cases it is possible to recover the mechanism but never the source magnitude and that the
BIC is a better measure than the AIC in selecting the true source model, although in
numerous cases both criteria fail to select the correct solution. Therefore, the BIC should
be used as opposed to the AIC if it is necessary to select an appropriate source. Caution
should be used when using the statistical measure in any seismic inversion application.
20100901T00:00:00ZSource mechanism of long period events recorded by a high density seismic network during the 2008 eruption on Mount EtnaDe Barros, LouisLokmer, IvanBean, Christopher J.O'Brien, G. S.Zuccarello, Lucianoet al.http://hdl.handle.net/10197/544020140228T09:46:25Z20110101T00:00:00ZSource mechanism of long period events recorded by a high density seismic network during the 2008 eruption on Mount Etna
De Barros, Louis; Lokmer, Ivan; Bean, Christopher J.; O'Brien, G. S.; Zuccarello, Luciano; et al.
129 Long Period (LP) events, divided into two families of similar
events, were recorded by the 50 stations deployed on Mount Etna in the
second half of June 2008. During this period lava was flowing from a
lateral fracture after a summit strombolian eruption. In order to
understand the mechanisms of these events, we perform moment tensor
inversions. Inversions are initially kept unconstrained to estimate the
most likely mechanism. Numerical tests show that unconstrained inversion
leads to reliable moment tensor solutions because of the close
proximity of numerous stations to the source positions. However, single
forces cannot be accurately determined as they are very sensitive to
uncertainties in the velocity model. Constrained inversions for a crack,
a pipe or an explosion then allow us to accurately determine the
structural orientations of the source mechanisms. Both numerical tests
and LP event inversions emphasise the importance of using stations
located as close as possible to the source. Inversions for both
families show mechanisms with a strong volumetric component. These
events are most likely generated by cracks striking SWNE for both
families and dipping 70 degrees SE (Family 1) and 50 degrees NW
(Family 2). For Family 1 events, the crack geometry is nearly orthogonal
to the dikelike structure along which events are located, while for
Family 2 the location gave two pipelike bodies which belong to the same
plane as the crack mechanism. The orientations of the cracks are
consistent with local tectonics, which shows a SWNE weakness direction.
The LP events appear to be a response to the lava fountain occurring on
the 10th of May, 2008 as opposed to the flank lava flow.
20110101T00:00:00ZTime reverse location of seismic longperiod events recorded on Mt EtnaO'Brien, G. S.Lokmer, IvanDe Barro, LouisBean, Christopher J.Saccorotti, GilbertoMétaxian, J. P.Patané, Domenicohttp://hdl.handle.net/10197/543920140228T09:43:39Z20110101T00:00:00ZTime reverse location of seismic longperiod events recorded on Mt Etna
O'Brien, G. S.; Lokmer, Ivan; De Barro, Louis; Bean, Christopher J.; Saccorotti, Gilberto; Métaxian, J. P.; Patané, Domenico
We
present the first application of a time reverse location method in a
volcanic setting, for a family of longperiod events recorded on Mt
Etna. Results are compared with locations determined using a full
moment tensor grid search inversion and crosscorrelation method.
From June 18th to July 3rd, 2008, 50 broadband
seismic stations were deployed on Mt Etna, Italy, in close proximity
to the summit. Two families of longperiod events were detected with
dominant spectral peaks around 0.9 Hz. The large number of stations
close to the summit allowed us to locate all events in both families
using a time reversal location method. The method involves taking the
seismic signal, reversing it in time, and using it as a seismic
source in a numerical seismic wave simulator where the reversed
signals propagate through the numerical model, interfere
constructively and destructively, and focus on the original source
location. The source location is the computational cell with the
largest displacement magnitude at the time of maximum energy current
density inside the grid. Before we located the two longperiod
families we first applied the method to two synthetic datasets and
found a good fit between the time reverse location and true synthetic
location for a known velocity model. The time reverse location
results of the two families show a shallow seismic region close to
the summit in agreement with the locations using a moment tensor full
waveform inversion method and a crosscorrelation location method.
20110101T00:00:00ZModelling fluid induced seismicity on a nearby active faultMurphy, ShaneO'Brien, G. S.McCloskey, J.Bean, Christopher J.Nalbant, S.http://hdl.handle.net/10197/543020140228T09:17:16Z20130901T00:00:00ZModelling fluid induced seismicity on a nearby active fault
Murphy, Shane; O'Brien, G. S.; McCloskey, J.; Bean, Christopher J.; Nalbant, S.
We present a numerical investigation of the effect that static stress perturbations due to fluid
injection have on a nearby active fault where the fluid does not come in physical contact
with the fault. Our modelling employs a lattice Boltzmann pore diffusion model coupled
with a quasidynamic earthquake rupture model. As diffusivities and frictional parameters can
be defined independently at individual nodes/cells this allows us to replicate complex 3D
geological media in our simulations. We demonstrate the effect an injection can have on an
active nearby fault. Compared with our control catalogue (identical to the original simulation
but without the injection), the injection not only altered the timing of the next earthquake
sequence, it also changed its size, producing a Mw 6.7 event, the largest observed earthquake
on the fault. This large event pushes the fault into a subcritical state from which it took roughly
200 yr of continuous tectonic loading for the fault to return to a critical state.
20130901T00:00:00ZThe coupling between very long period seismic events, volcanic tremor, and degassing rates at Mount Etna volcanoZuccarello, LucianoBurton, Michael R.Saccorotti, GilbertoBean, Christopher J.Patané, Domenicohttp://hdl.handle.net/10197/542820140320T04:00:14Z20130901T00:00:00ZThe coupling between very long period seismic events, volcanic tremor, and degassing rates at Mount Etna volcano
Zuccarello, Luciano; Burton, Michael R.; Saccorotti, Gilberto; Bean, Christopher J.; Patané, Domenico
From December 2005 to January 2006, an anomalous degassing episode was observed
at Mount Etna, wellcorrelated with an increase in volcanic tremor, and in the almost
complete absence of eruptive activity. In the same period, more than 10,000 very long
period (VLP) events were detected. Through moment tensor inversion analyses of the VLP
pulses, we obtained quantitative estimates of the volumetric variations associated with these
events. This allowed a quantitative investigation of the relationship between VLP seismic
activity, volcanic tremor, and gas emission rate at Mount Etna. We found a statistically
significant positive correlation between SO2 gas flux and volcanic tremor, suggesting that
tremor amplitude can be used as a firstorder proxy for the background degassing activity of
the volcano. VLP volumetric changes and SO2 gas flux are correlated only for the last part of
our observations, following a slight change in the VLP source depth. We calculate that the
gas associated with VLP signal genesis contributed less than 5% of the total gas emission.
The existence of a linear correlation between VLP and degassing activities indicates a
general relationship between these two processes. The effectiveness of such coupling
appears to depend upon the particular location of the VLP source, suggesting that conduit
geometry might play a significant role in the VLPgenerating process. These results are the
first report on Mount Etna of a quantitative relationship between the amounts of gas
emissions directly estimated through instrumental flux measurements and the quantities of
gas mass inferred in the VLP source inversion.
20130901T00:00:00ZCovalent immobilization of alcohol dehydrogenase (ADH2) from Haloferax volcanii: how to maximize activity and optimize performance of halophilic enzymesAlsafadi, DiyaParadisi, Francescahttp://hdl.handle.net/10197/542320140228T08:37:47Z20140301T00:00:00ZCovalent immobilization of alcohol dehydrogenase (ADH2) from Haloferax volcanii: how to maximize activity and optimize performance of halophilic enzymes
Alsafadi, Diya; Paradisi, Francesca
Alcohol dehydrogenase from halophilic archaeon Haloferax volcanii (HvADH2) was successfully covalently immobilized on metalderivatized epoxy Sepabeads. The immobilization conditions were optimized by investigating several parameters that affect the halophilic enzymesupport interaction. The highest immobilization efficiency (100%) and retention activity (60%) were achieved after 48 h of incubation of the enzyme with Niepoxy Sepaeads support in 100 mM TrisHCl buffer, pH 8, containing 3 M KCl at 5 ◦C. No significant stabilization was observed after blocking the unreacted epoxy groups with commonly used hydrophilic agents. A significant increase in the stability of the immobilized enzyme was achieved by blocking the unreacted epoxy groups with ethylamine. The immobilization process increased the enzyme stability, thermal activity and organic solvents tolerance when compared to its soluble counterpart, indicating that the immobilization enhances the structural and conformational stability. One step purification–immobilization of this enzyme has been carried out on metal chelateepoxy Sepabeads, as an efficient method to obtain immobilized biocatalyst directly from bacterial extracts.
20140301T00:00:00ZHeterologous overexpression, purification and characterisation of an alcohol dehydrogenase (ADH2) from Halobacterium sp. NRC1Liliensiek, AnnKathrinCassidy, JenniferGucciardo, GabrieleWhitely, CliadhnaParadisi, Francescahttp://hdl.handle.net/10197/542220140224T09:42:07Z20131001T00:00:00ZHeterologous overexpression, purification and characterisation of an alcohol dehydrogenase (ADH2) from Halobacterium sp. NRC1
Liliensiek, AnnKathrin; Cassidy, Jennifer; Gucciardo, Gabriele; Whitely, Cliadhna; Paradisi, Francesca
Replacement of chemical steps with biocatalytic ones is becoming increasingly more interesting due to the remarkable catalytic properties of enzymes, such as their wide range of substrate specificities and variety of chemo, stereo and regioselective reactions.
This study presents characterization of an alcohol dehydrogenase (ADH) from the halophilic archaeum Halobacterium sp. NRC1 (HsADH2). A hexahistidinetagged recombinant version of HsADH2 (HisHsADH2) was heterologously overexpressed in Haloferax volcanii. The enzyme was purified in one step by immobilised Niaffinity chromatography (IMAC). HisHsADH2 was halophilic and mildly thermophilic with optimal activity for ethanol oxidation at 4 M KCl around 60 °C and pH 10.0. The enzyme was extremely stable, retaining 80 % activity after 30 days. HisHsADH2 showed preference for NADP(H) but interestingly retained 60 % activity towards NADH. The enzyme displayed broad substrate specificity, with maximum activity obtained for 1propanol. The enzyme also accepted secondary alcohols such as 2butanol and even 1phenylethanol. In the reductive reaction, working conditions for HisHsADH2 were optimised for acetaldehyde and found to be 4 M KCl and pH 6.0. HisHsADH2 displayed intrinsic organic solvent tolerance, which is highly relevant for biotechnological applications.
20131001T00:00:00ZLongperiod seismicity in the shallow volcanic edifice formed from slowrupture earthquakesBean, Christopher J.De Barros, LouisLokmer, Ivanet al.http://hdl.handle.net/10197/539820140220T14:29:24Z20131215T00:00:00ZLongperiod seismicity in the shallow volcanic edifice formed from slowrupture earthquakes
Bean, Christopher J.; De Barros, Louis; Lokmer, Ivan; et al.
Despite recent technological advances in volcano monitoring, eruption forecasting is
still inadequate. Improved forecasting requires a deeper understanding of when
unrest will lead to an actual eruption. Shallow Long Period (low spectral frequency)
seismic events are routinely employed as a primary tool in forecasting strategies as
they often precede eruptions. They are universally explained as resonating fluidfilled
cracks or conduits, indicating the presence of mechanically active nearsurface fluids.
We undertake very high resolution seismic field experiments at Mt Etna, Italy;
Turrialba, Costa Rica and Ubinas, Peru, in which we find that seismogram resonance
is propagation path related whilst the seismic sources comprise short pulses. Data
analysis and numerical modelling show that slowrupture failure in unconsolidated
volcanic materials reproduces all key aspects of these new observations. Contrary to
current interpretations, here we show that our observed Long Period events are not
direct indicators of fluid presence/migration, but rather are markers for upper edifice
deformation. This finding encapsulates this seismicity within growing observations of
a spectrum of deformation rates in other nonvolcanic environments, from slowslip
earthquakes through fast dynamic rupture. It calls for a reassessment of how lowfrequency
seismic signals are interpreted in their key role in eruption forecasting.
20131215T00:00:00ZPiezoresponse force microscopy for polarity imaging of GaNRodriguez, Brian J.Gruverman, A.Kingon, A. I.et al.http://hdl.handle.net/10197/537720140206T11:57:09Z20020601T00:00:00ZPiezoresponse force microscopy for polarity imaging of GaN
Rodriguez, Brian J.; Gruverman, A.; Kingon, A. I.; et al.
The polarity distribution of GaN based lateral polarity heterostructures is investigated by piezoresponse force microscopy (PFM). Simultaneous imaging of surface morphology, as well as the phase and magnitude of the piezoelectric response, is performed by PFM on a GaN film with patterned polarities on a cAl2O3 substrate. We demonstrate that the polarity distribution of GaN based lateral polarity heterostructures can be deduced from the phase image of the piezoresponse with nanometer scale spatial resolution.
20020601T00:00:00ZWavelengthdependent Raman scattering of hydrogenated amorphous silicon carbon with red, green, and blue light excitationPark, M.Sakhrani, V.Maria, JP.Rodriguez, Brian J.et al.http://hdl.handle.net/10197/537420140206T11:45:22Z20030401T00:00:00ZWavelengthdependent Raman scattering of hydrogenated amorphous silicon carbon with red, green, and blue light excitation
Park, M.; Sakhrani, V.; Maria, JP.; Rodriguez, Brian J.; et al.
This study presents results of wavelengthdependent Raman scattering from amorphous silicon carbon (aSi:C:H). The aSi:C:H films were produced by radiofrequency plasmaenhanced chemical vapor deposition. Prior results with amorphous carbon indicate that laser excitation selectively probes clusters with differing sizes. Our measurements with aSi:C:H indicate that when using red (632.8 nm), green (514.5 nm), and blue (488.0 nm) excitation, the Raman D and G peaks shift to higher wave numbers as the excitation energy increases. The higher frequency is associated with smaller clusters that are preferentially excited with higher photon energy. It appears that photoluminescence occurs due to radiative recombination from intracluster transitions in Sialloyed sp(2)bonded carbon clusters.
20030401T00:00:00ZSpatial inhomogeneity of imprint and switching behavior in ferroelectric capacitorsGruverman, A.Rodriguez, Brian J.Kingon, A. I.et al.http://hdl.handle.net/10197/537320140206T11:43:23Z20030501T00:00:00ZSpatial inhomogeneity of imprint and switching behavior in ferroelectric capacitors
Gruverman, A.; Rodriguez, Brian J.; Kingon, A. I.; et al.
Piezoresponse force microscopy has been used to perform nanoscale characterization of the spatial variations in the imprint and switching behavior of (111)oriented Pb(Zr,Ti)O3based capacitors on Pt electrodes. Mapping of polarization distribution in the poled capacitors as well as local d(33)V loop measurements revealed a significant difference in imprint and switching behavior between the peripheral and inner parts of the capacitors. It has been found that the inner regions of the capacitors are negatively imprinted (with the preferential direction of the normal component of polarization upward) and tend to switch back after application of the positive poling voltage. On the other hand, switchable regions at the edge of the integrated capacitors generally exhibit more symmetric hysteresis behavior. Application of an ac switching voltage, contrary to what was expected, resulted in an increase of the negatively imprinted regions. The observed effect has been explained by incomplete or asymmetric switching due to the mechanical stress conditions existing in the central parts of the capacitors. (C) 2003 American Institute of Physics.
20030501T00:00:00ZMicroRaman study of electronic properties of inversion domains in GaNbased lateral polarity heterostructuresPark, M.Cuomo, J. J.Rodriguez, Brian J.et al.http://hdl.handle.net/10197/537220140206T11:42:10Z20030601T00:00:00ZMicroRaman study of electronic properties of inversion domains in GaNbased lateral polarity heterostructures
Park, M.; Cuomo, J. J.; Rodriguez, Brian J.; et al.
The electronic properties of inversion domains in a GaNbased lateral polarity heterostructure were investigated using microRaman spectroscopy. The piezoelectric polarization of each domain was calculated from strain determined via Raman scattering. The free carrier concentration and electron mobility were deduced from the longitudinal optical phononplasmon coupled mode. The electron concentration in the Nface domain was slightly higher than that in the Gaface domain. It appears that during growth, a larger number of donor impurities may have been incorporated into the Nface domain than into the Gaface domain.
20030601T00:00:00ZMechanical stress effect on imprint behavior of integrated ferroelectric capacitorsGruverman, A.Rodriguez, Brian J.Kingon, A. I.et al.http://hdl.handle.net/10197/537120140206T11:40:20Z20030701T00:00:00ZMechanical stress effect on imprint behavior of integrated ferroelectric capacitors
Gruverman, A.; Rodriguez, Brian J.; Kingon, A. I.; et al.
Stressinduced changes in the imprint and switching behavior of (111)oriented Pb(Zr,Ti)O3 (PZT)based capacitors have been studied using piezoresponse force microscopy. Visualization of polarization distribution and d(33)loop measurements in individual 1x1.5mum(2) capacitors before and after stress application, generated by substrate bending, provided direct experimental evidence of stressinduced switching. Mechanical stress caused elastic switching in capacitors with the direction of the resulting polarization determined by the sign of the applied stress. In addition, stress application turned capacitors into a heavily imprinted state characterized by strongly shifted hysteresis loops and almost complete backswitching after application of the poling voltage. It is suggested that substrate bending generated a strain gradient in the PZT layer, which produced asymmetric lattice distortion with preferential polarization direction and triggered polarization switching due to the flexoelectric effect.
20030701T00:00:00ZPhotoelectron emission microscopy observation of inversion domain boundaries of GaNbased lateral polarity heterostructuresYang, W. C.Rodriguez, Brian J.Park, M.et al.http://hdl.handle.net/10197/536920140206T11:22:10Z20031101T00:00:00ZPhotoelectron emission microscopy observation of inversion domain boundaries of GaNbased lateral polarity heterostructures
Yang, W. C.; Rodriguez, Brian J.; Park, M.; et al.
An intentionally grown GaN film with laterally patterned Ga and Nface polarities is studied using in situ UVphotoelectron emission microscopy (PEEM). Before chemical vapor cleaning of the surface, the emission contrast between the Ga and Nface polarities regions was not significant. However, after cleaning the emission contrast between the different polarity regions was enhanced such that the Nface regions exhibited increased emission over the Gaface regions. The results indicate that the emission threshold of the Nface region is lower than that of the Ga face. Moreover, bright emission was detected from regions around the inversion domain boundaries of the lateral polarity heterostructure. The PEEM polarity contrast and intense emission from the inversion domain boundary regions are discussed in terms of the builtin lateral field and the surface band bending induced by the polarization bound surface charges.
20031101T00:00:00ZDirect measurement of periodic electric forces in liquidsRodriguez, Brian J.Jesse, S.Seal, K.et al.http://hdl.handle.net/10197/536320140206T10:06:12Z20080107T00:00:00ZDirect measurement of periodic electric forces in liquids
Rodriguez, Brian J.; Jesse, S.; Seal, K.; et al.
The electric forces acting on an atomic force microscope tip in solution have been measured using a microelectrochemical cell formed by two periodically biased electrodes. The forces were measured as a function of lift height and bias amplitude and frequency, providing insight into electrostatic interactions in liquids. Realspace mapping of the vertical and lateral components of electrostatic forces acting on the tip from the deflection and torsion of the cantilever is demonstrated. This method enables direct probing of electrostatic and convective forces involved in electrophoretic and dielectroforetic selfassembly and electrical tweezer operation in liquid environments.
20080107T00:00:00ZStructural, magnetic, and electric properties of La0.7Sr0.3MnO3/PbZrxTi1xO3 heterostructuresZiese, M.Setzer, A.Vrejoiu, I.Rodriguez, Brian J.et al.http://hdl.handle.net/10197/536220140206T10:04:21Z20080923T00:00:00ZStructural, magnetic, and electric properties of La0.7Sr0.3MnO3/PbZrxTi1xO3 heterostructures
Ziese, M.; Setzer, A.; Vrejoiu, I.; Rodriguez, Brian J.; et al.
Epitaxial La0.7Sr0.3MnO3/PbZrxTi1xO3 multilayers were fabricated by pulsedlaser deposition and studied by structural, magnetic, and electric characterization techniques. Transmission electron microscopy and xray diffractometry proved the excellent structural quality of the samples. A high ferroelectric polarization and stable piezoelectric switching were found for the lead zirconate titanate layers, whereas the manganite layers showed bulklike resistivity and magnetoresistance, both attesting to the high quality of the layers. In a detailed study of the magnetic response of the multilayers multiple magnetization switching was observed that was related to the complex strain state.
20080923T00:00:00ZThreedimensional highresolution reconstruction of polarization in ferroelectric capacitors by piezoresponse force microscopyRodriguez, Brian J.Gruverman, A.Kingon, A. I.et al.http://hdl.handle.net/10197/535720140204T11:41:21Z20040201T00:00:00ZThreedimensional highresolution reconstruction of polarization in ferroelectric capacitors by piezoresponse force microscopy
Rodriguez, Brian J.; Gruverman, A.; Kingon, A. I.; et al.
A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM, respectively) has been used to map the outofplane and inplane polarization distribution, respectively, of (111)oriented Pb(Zr,Ti)O3based (PZT) ferroelectric patterned and reactivelyionetched capacitors. While VPFM and LPFM have previously been used to determine the orientation of the polarization vector in ferroelectric crystals and thin films, this is the first time the technique has been applied to determine the threedimensional polarization distribution in thinfilm capacitors and, as such, is of importance to the implementation of nonvolatile ferroelectric random access memory. Sequential VPFM and LPFM imaging have been performed in poled 1x1.5 mum(2) PZT capacitors. Subsequent quantitative analysis of the obtained piezoresponse images allowed the threedimensional reconstruction of the domain arrangement in the PZT layers of the capacitors. It has been found that the poled capacitors, which appear as uniformly polarized in VPFM, are in fact in a polydomain state as is detected by LPFM and contain 90degrees domain walls. Despite the polycrystallinity of the PZT layer, regions larger than the average PZT grain size are found to have the same polarization orientation. This technique has potential for clarifying the switching behavior and imprint mechanism in micro and nanoscale ferroelectric capacitors.
20040201T00:00:00ZIn situ cleaning and characterization of oxygen and zincterminated, ntype, ZnO{0001} surfacesCoppa, B. J.Fulton, C. C.Hartlieb, P. J.Rodriguez, Brian J.et al.http://hdl.handle.net/10197/535520140204T11:32:45Z20040501T00:00:00ZIn situ cleaning and characterization of oxygen and zincterminated, ntype, ZnO{0001} surfaces
Coppa, B. J.; Fulton, C. C.; Hartlieb, P. J.; Rodriguez, Brian J.; et al.
A layer containing an average of 1.0 monolayer (ML) of adventitious carbon and averages of 1.5 ML and 1.9 ML of hydroxide was determined to be present on the respective Oterminated (000 (1) over bar) and Znterminated (0001) surfaces of ZnO. A diffuse lowenergy electron diffraction pattern was obtained from both surfaces. In situ cleaning procedures were developed and their efficacy evaluated in terms of the concentrations of residual hydrocarbons and hydroxide and the crystallography, microstructure, and electronic structure of these surfaces. Annealing ZnO(000 (1) over bar) in pure oxygen at 600650 degreesC+/20 degreesC reduced but did not eliminate all of the detectable hydrocarbon contamination. Annealing for 15 min in pure O2 at 700 degreesC and 0.100+/0.001 Torr caused desorption of both the hydrocarbons and the hydroxide constituents to concentrations below the detection limits (similar to0.03 ML=similar to0.3 at. \%) of our xray photoelectron spectroscopy instrument. However, thermal decomposition degraded the surface microstructure. Exposure of the ZnO(000 (1) over bar) surface to a remote plasma having an optimized 20\% O2/80\% He mixture for the optimized time, temperature, and pressure of 30 min, 525 degreesC, and 0.050 Torr, respectively, resulted in the desorption of all detectable hydrocarbon species. Approximately 0.4 ML of hydroxide remained. The plasmacleaned surface possessed an ordered crystallography and a stepandterrace microstructure and was stoichiometric with nearly flat electronic bands. A 0.5 eV change in band bending was attributed to the significant reduction in the thickness of an accumulation layer associated with the hydroxide. The hydroxide was more tightly bound to the ZnO(0001) surface; this effect increased the optimal temperature and time of the plasma cleaning process for this surface to 550 degreesC and 60 min, respectively, at 0.050 Torr. Similar changes were achieved in the structural, chemical, and electronic properties of this surface; however, the microstructure only increased slightly in roughness and was without distinctive features.
20040501T00:00:00ZPolarizationdependent electron affinity of LiNbO3 surfacesYang, W. C.Rodriguez, Brian J.Gruverman, A.Nemanich, R. J.http://hdl.handle.net/10197/535420140204T11:23:04Z20040901T00:00:00ZPolarizationdependent electron affinity of LiNbO3 surfaces
Yang, W. C.; Rodriguez, Brian J.; Gruverman, A.; Nemanich, R. J.
Polar surfaces of a ferroelectric LiNbO3 crystal with periodically poled domains are explored using UVphotoelectron emission microscopy (PEEM). Compared with the positive domains (domains with positive surface polarization charges), a higher photoelectric yield is found from the negative domains (domains with negative surface polarization charges), indicating a lower photothreshold and a corresponding lower electron affinity. The photonenergydependent contrast in the PEEM images of the surfaces indicates that the photothreshold of the negative domains is similar to4.6 eV while that of the positive domains is greater than similar to6.2 eV. We propose that the threshold difference between the opposite domains can be attributed to a variation of the electron affinity due to opposite surface dipoles induced by surface adsorbates.
20040901T00:00:00ZDomain growth kinetics in lithium niobate single crystals studied by piezoresponse force microscopyRodriguez, Brian J.Nemanich, R. J.Kingon, A. I.et al.http://hdl.handle.net/10197/535020140204T10:16:51Z20050101T00:00:00ZDomain growth kinetics in lithium niobate single crystals studied by piezoresponse force microscopy
Rodriguez, Brian J.; Nemanich, R. J.; Kingon, A. I.; et al.
The kinetics of sidewise domain growth in an inhomogeneous electric field has been investigated in stoichiometric LiNbO3 single crystals by measuring the lateral domain size as a function of the voltage pulse magnitude and duration using piezoresponse force microscopy. The domain size increases linearly with the voltage magnitude suggesting that the domain size is kinetically limited in a wide range of pulse magnitudes and durations. In spite of that, the written domains exhibit strong retention behavior. It is suggested that the switching behavior can be described by the universal scaling curve. Domain kinetics can be described as an activation process by calculating the field distribution using the charged sphere model under the assumption of an exponential field dependence of the wall velocity. The activation energy is found to be a function of the external field.
20050101T00:00:00ZPreparation and characterization of atomically clean, stoichlometric surfaces of AIN(0001)Mecouch, W. J.Wagner, B. P.Reitmeier, Z. J.Rodriguez, Brian J.et al.http://hdl.handle.net/10197/534920140204T10:12:30Z20050101T00:00:00ZPreparation and characterization of atomically clean, stoichlometric surfaces of AIN(0001)
Mecouch, W. J.; Wagner, B. P.; Reitmeier, Z. J.; Rodriguez, Brian J.; et al.
In situ exposure of the. (0001) surface of AlN thin films to flowing ammonia at 1120 degreesC and 10(4) Torr removes oxygen/hydroxide and hydrocarbon species below the detectable limits of xray photoelectron spectroscopy and decreases the Al/N ratio from 1.3 to 1.0. The positions of the Al 2p and the N 1s core level peaks acquired from the cleaned surfaces were 75.0 +/ 0.1 eV and 398.2 +/ 0.1 eV, respectively, which were similar to the values determined for the asloaded samples. The cleaning process left unchanged the (1 X 1) low energy electron diffraction pattern, the stepandterrace microstructure, and the root mean square roughness values observed for the surfaces of the asloaded samples; i.e., the surface structure and microstructure were not changed by the hightemperature exposure to ammonia at low pressures. Vacuum annealing under 10(7) Torr at 1175 degreesC for 15 min removed all detectable hydrocarbons; however, it did not remove the oxygen/hydroxide species. (C) 2005 American Vacuum Society.
20050101T00:00:00ZAtomic force microscopybased experimental setup for studying domain switching dynamics in ferroelectric capacitorsDehoff, C.Rodriguez, Brian J.Kingon, A. I.et al.http://hdl.handle.net/10197/534820140204T10:10:03Z20050201T00:00:00ZAtomic force microscopybased experimental setup for studying domain switching dynamics in ferroelectric capacitors
Dehoff, C.; Rodriguez, Brian J.; Kingon, A. I.; et al.
This article describes an experimental setup for combined measurements of domain switching dynamics and switching currents in micrometer scale ferroelectric capacitors. The setup is based on a commercial atomic force microscope (AFM) that is equipped with a piezoresponse mode for domain imaging and with a wide bandwidth current amplifier for switching current recording. The setup allows combined domain/current measurements in capacitors as small as 1 mum(2) with switching times resolved down to 10 ns. The incorporation of switching current measurement capability into piezoresponse AFM makes detailed analysis of switching behavior in ferroelectric memory devices possible.
20050201T00:00:00ZScanning probe investigation of surface charge and surface potential of GaNbased heterostructuresRodriguez, Brian J.Yang, W. C.Nemanich, R. J.Gruverman, A.http://hdl.handle.net/10197/534720140204T09:58:02Z20050301T00:00:00ZScanning probe investigation of surface charge and surface potential of GaNbased heterostructures
Rodriguez, Brian J.; Yang, W. C.; Nemanich, R. J.; Gruverman, A.
Scanning Kelvin probe microscopy (SKPM) and electrostatic force microscopy (EFM) have been employed to measure the surface potentials and the surface charge densities of the Ga and the Nface of a GaN lateral polarity heterostructure (LPH). The surface was subjected to an HCl surface treatment to address the role of adsorbed charge on polarization screening. It has been found that while the Gaface surface appears to be unaffected by the surface treatment, the Nface surface exhibited an increase in adsorbed screening charge density (1.6 +/ 0.5x10(10) cm(2)), and a reduction of 0.3 +/ 0.1 V in the surface potential difference between the N and Gaface surfaces.
20050301T00:00:00ZScanning frequency mixing microscopy of highfrequency transport behavior at electroactive interfacesRodriguez, Brian J.Jesse, S.Meunier, VincentKalinin, S. V.http://hdl.handle.net/10197/533920140131T10:06:54Z20060401T00:00:00ZScanning frequency mixing microscopy of highfrequency transport behavior at electroactive interfaces
Rodriguez, Brian J.; Jesse, S.; Meunier, Vincent; Kalinin, S. V.
An approach for highfrequency transport imaging, referred to as scanning frequency mixing microscopy (SFMM), is developed. Application of two highfrequency bias signals across an electroactive interface results in a lowfrequency component due to interface nonlinearity. The frequency of a mixed signal is chosen within the bandwidth of the optical detector and can be tuned to the cantilever resonances. The SFMM signal is comprised of an intrinsic device contribution and a capacitive mixing contribution, and an approach to distinguish the two is suggested. This technique is illustrated on a model metalsemiconductor interface. The imaging mechanism and surfacetip contrast transfer are discussed. SFMM allows scanning probe microscopy based transport measurements to be extended to higher, ultimately gigahertz, frequency regimes, providing information on voltage derivatives of interface resistance and capacitance, from which device characteristics such as Schottky barrier height, etc., can be estimated. (c) 2006 American Institute of Physics.
20060401T00:00:00ZHigh Resolution Electromechanical Imaging of Ferroelectric Materials in a Liquid Environment by Piezoresponse Force MicroscopyRodriguez, Brian J.Jesse, S.Baddorf, A. P.Kalinin, S. V.http://hdl.handle.net/10197/533820140131T09:55:04Z20060601T00:00:00ZHigh Resolution Electromechanical Imaging of Ferroelectric Materials in a Liquid Environment by Piezoresponse Force Microscopy
Rodriguez, Brian J.; Jesse, S.; Baddorf, A. P.; Kalinin, S. V.
Highresolution imaging of ferroelectric materials using piezoresponse force microscopy (PFM) is demonstrated in an aqueous environment. The elimination of both longrange electrostatic forces and capillary interactions results in a localization of the ac field to the tipsurface junction and allows the tipsurface contact area to be controlled. This approach results in spatial resolutions approaching the limit of the intrinsic domainwall width. Imaging at frequencies corresponding to highorder cantilever resonances minimizes the viscous damping and added mass effects on cantilever dynamics and allows sensitivities comparable to ambient conditions. PFM in liquids will provide novel opportunities for highresolution studies of ferroelectric materials, imaging of soft polymer materials, and imaging of biological systems in physiological environments on, ultimately, the molecular level.
20060601T00:00:00ZNanoelectromechanics of polarization switching in piezoresponse force microscopyKalinin, S. V.Gruverman, A.Rodriguez, Brian J.et al.http://hdl.handle.net/10197/533520140131T09:00:36Z20050401T00:00:00ZNanoelectromechanics of polarization switching in piezoresponse force microscopy
Kalinin, S. V.; Gruverman, A.; Rodriguez, Brian J.; et al.
Nanoscale polarization switching in ferroelectric materials by piezoresponse force microscopy in weak and strong indentation limits is analyzed using exact solutions for coupled electroelastic fields under the tip. Tipinduced domain switching is mapped on the Landau theory of phase transitions, with domain size as an order parameter. For a point charge interacting with a ferroelectric surface, switching by both first and the second order processes is possible, depending on the chargesurface separation. For a realistic tip, the domain nucleation process is first order in charge magnitude and polarization switching occurs only above a certain critical tip bias. In pure ferroelectric or ferroelastic switching, the late stages of the switching process can be described using a point charge model and arbitrarily large domains can be created. However, description of domain nucleation and the early stages of growth process when the domain size is comparable with the tip curvature radius (weak indentation) or the contact radius (strong indentation) requires the exact field structure. For higher order ferroic switching (e.g., ferroelectroelastic), the domain size is limited by the tipsample contact area, thus allowing precise control of domain size. (C) 2005 American Institute of Physics.
20050401T00:00:00ZElectromechanical imaging of biological systems with sub10 nm resolutionKalinin, S. V.Rodriguez, Brian J.Jesse, S.et al.http://hdl.handle.net/10197/533420140131T08:51:58Z20050801T00:00:00ZElectromechanical imaging of biological systems with sub10 nm resolution
Kalinin, S. V.; Rodriguez, Brian J.; Jesse, S.; et al.
Electromechanical imaging of tooth dentin and enamel has been performed with sub10 nm resolution using piezoresponse force microscopy. Characteristic piezoelectric domain size and local protein fiber ordering in dentin have been determined. The shape of a single protein fibril in enamel is visualized in real space and local hysteresis loops are measured. Because of the ubiquitous presence of piezoelectricity in biological systems, this approach is expected to find broad application in highresolution studies of a wide range of biomaterials. (c) 2005 American Institute of Physics.
20050801T00:00:00ZDirect studies of domain switching dynamics in thin film ferroelectric capacitorsGruverman, A.Rodriguez, Brian J.Dehoff, C.et al.http://hdl.handle.net/10197/533320140131T08:47:53Z20050801T00:00:00ZDirect studies of domain switching dynamics in thin film ferroelectric capacitors
Gruverman, A.; Rodriguez, Brian J.; Dehoff, C.; et al.
An experimental approach for direct studies of the polarization reversal mechanism in thin film ferroelectric capacitors based on piezoresponse force microscopy (PFM) in conjunction with pulse switching capabilities is presented. Instant domain configurations developing in a 3x3 mu m(2) capacitor at different stages of the polarization reversal process have been registered using stepbystep switching and subsequent PFM imaging. The developed approach allows direct comparison of experimentally measured microscopic switching behavior with parameters used by phenomenological switching models. It has been found that in the low field regime (just above the threshold value) used in the present study, the mechanism of polarization reversal changes during the switching cycle from the initial nucleationdominated process to the lateral domain expansion at the later stages. The classical nucleation model of KolmogorovAvramiIshibashi (KAI) provides reasonable approximation for the nucleationdominated stage of switching but is inapplicable to the slow switching stage. It has been suggested that the switching dynamics can be approximated by averaging the KAI model over a broad distribution of switching times. (c) 2005 American Institute of Physics.
20050801T00:00:00ZSimultaneous elastic and electromechanical imaging by scanning probe microscopy: Theory and applications to ferroelectric and biological materialsShin, J.Rodriguez, Brian J.Baddorf, A. P.et al.http://hdl.handle.net/10197/533220140130T16:14:37Z20050901T00:00:00ZSimultaneous elastic and electromechanical imaging by scanning probe microscopy: Theory and applications to ferroelectric and biological materials
Shin, J.; Rodriguez, Brian J.; Baddorf, A. P.; et al.
An approach for combined imaging of elastic and electromechanical properties of materials, referred to as piezoacoustic scanning probe microscopy (PASPM), is presented. Applicability of this technique for elastic and electromechanical imaging with nanoscale resolution in such dissimilar materials as ferroelectrics and biological tissues is demonstrated. The PASPM signal formation is analyzed based on the theory of nanoelectromechanics of piezoelectric indentation and signal sensitivity to materials properties and imaging conditions. It is shown that simultaneous measurements of local indentation stiffness and indentation piezocoefficient provide the most complete description of the local electroelastic properties for transversally isotropic materials, thus making piezoacoustic SPM a comprehensive imaging and analysis tool. The contrast formation mechanism in the low frequency regime is described in terms of tipsurface contact mechanics. Signal generation volumes for electromechanical and elastic signals are determined and relative sensitivity of piezoresponse force microscopy (PFM) and atomic force acoustic microscopy (AFAM) for topographic crosstalk is established. (c) 2005 American Vacuum Society.
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