19 research outputs found
Detection mechanism for ferroelectric domain boundaries with lateral force microscopy
The contrast mechanism for the visualization of ferroelectric domain
boundaries with lateral force microscopy is generally assumed to be caused by
mechanical deformation of the sample due to the converse piezoelectric effect.
We show, however, that electrostatic interactions between the charged tip and
the electric fields arising from the surface polarization charges dominate the
contrast mechanism. This explanation is sustained by quantitative analysis of
the measured forces as well as by comparative measurements on different
materials
A stochastical model for periodic domain structuring in ferroelectric crystals
A stochastical description is applied in order to understand how
ferroelectric structures can be formed. The predictions are compared with
experimental data of the so-called electrical fixing: Domains are patterned in
photorefractive lithium niobate crystals by the combination of light-induced
space-charge fields with externally applied electrical fields. In terms of our
stochastical model the probability for domain nucleation is modulated according
to the sum of external and internal fields. The model describes the shape of
the domain pattern as well as the effective degree of modulation
Electrostatic topology of ferroelectric domains in YMnO
Trimerization-polarization domains in ferroelectric hexagonal YMnO were
resolved in all three spatial dimensions by piezoresponse force microscopy.
Their topology is dominated by electrostatic effects with a range of 100 unit
cells and reflects the unusual electrostatic origin of the spontaneous
polarization. The response of the domains to locally applied electric fields
explains difficulties in transferring YMnO into a single-domain state. Our
results demonstrate that the wealth of non-displacive mechanisms driving
ferroelectricity that emerged from the research on multiferroics are a rich
source of alternative types of domains and domain-switching phenomena
Lateral Signals in Piezoresponse Force Microscopy at Domain Boundaries of Ferroelectric Crystals
In piezoresponse force microscopy a lateral signal at the domain boundaries
is occasionally observed. In recent years, a couple of experiments have been
reported and varying explanations for the origin of this lateral signal have
been proposed. Additionally, elaborated theoretical modeling for this
particular issue has been carried out. Here we present experimental data
obtained on different crystallographic cuts of , ,
and single crystals. We could thereby rule out some of the
explanations proposed so far, introduce another possible mechanism, and
quantitatively compare our results to the existing modeling
Impact of elasticity on the piezoresponse of adjacent ferroelectric domains investigated by scanning force microscopy
As a consequence of elasticity, mechanical deformations of crystals occur on
a length scale comparable to their thickness. This is exemplified by applying a
homogeneous electric field to a multi-domain ferroelectric crystal: as one
domain is expanding the adjacent ones are contracting, leading to clamping at
the domain boundaries. The piezomechanically driven surface corrugation of
micron-sized domain patterns in thick crystals using large-area top electrodes
is thus drastically suppressed, barely accessible by means of piezoresponse
force microscopy
Contrast Mechanisms for the Detection of Ferroelectric Domains with Scanning Force Microscopy
We present a full analysis of the contrast mechanisms for the detection of
ferroelectric domains on all faces of bulk single crystals using scanning force
microscopy exemplified on hexagonally poled lithium niobate. The domain
contrast can be attributed to three different mechanisms: i) the thickness
change of the sample due to an out-of-plane piezoelectric response (standard
piezoresponse force microscopy), ii) the lateral displacement of the sample
surface due to an in-plane piezoresponse, and iii) the electrostatic tip-sample
interaction at the domain boundaries caused by surface charges on the
crystallographic y- and z-faces. A careful analysis of the movement of the
cantilever with respect to its orientation relative to the crystallographic
axes of the sample allows a clear attribution of the observed domain contrast
to the driving forces respectively.Comment: 8 pages, 8 figure
Depth resolution of Piezoresponse force microscopy
Given that a ferroelectric domain is generally a three dimensional entity, the determination of its area as well as its depth is mandatory for full characterization. Piezoresponse force microscopy (PFM) is known for its ability to map the lateral dimensions of ferroelectric domains with high accuracy. However, no depth profile information has been readily available so far. Here, we have used ferroelectric domains of known depth profile to determine the dependence of the PFM response on the depth of the domain, and thus effectively the depth resolution of PFM detection
DNA methylation profiling to predict recurrence risk in meningioma: development and validation of a nomogram to optimize clinical management
Abstract Background Variability in standard-of-care classifications precludes accurate predictions of early tumor recurrence for individual patients with meningioma, limiting the appropriate selection of patients who would benefit from adjuvant radiotherapy to delay recurrence. We aimed to develop an individualized prediction model of early recurrence risk combining clinical and molecular factors in meningioma. Methods DNA methylation profiles of clinically annotated tumor samples across multiple institutions were used to develop a methylome model of 5-year recurrence-free survival (RFS). Subsequently, a 5-year meningioma recurrence score was generated using a nomogram that integrated the methylome model with established prognostic clinical factors. Performance of both models was evaluated and compared with standard-of-care models using multiple independent cohorts. Results The methylome-based predictor of 5-year RFS performed favorably compared with a grade-based predictor when tested using the 3 validation cohorts (ÎAUC = 0.10, 95% CI: 0.03â0.018) and was independently associated with RFS after adjusting for histopathologic grade, extent of resection, and burden of copy number alterations (hazard ratio 3.6, 95% CI: 1.8â7.2, P < 0.001). A nomogram combining the methylome predictor with clinical factors demonstrated greater discrimination than a nomogram using clinical factors alone in 2 independent validation cohorts (ÎAUC = 0.25, 95% CI: 0.22â0.27) and resulted in 2 groups with distinct recurrence patterns (hazard ratio 7.7, 95% CI: 5.3â11.1, P < 0.001) with clinical implications. Conclusions The models developed and validated in this study provide important prognostic information not captured by previously established clinical and molecular factors which could be used to individualize decisions regarding postoperative therapeutic interventions, in particular whether to treat patients with adjuvant radiotherapy versus observation alone. </jats:sec
UV laser radiation inhibits domain inversion in lithium niobate
Continuous wave UV laser (λ=244 nm) irradiation of the +z face of lithium niobate single crystals inhibits ferroelectric domain inversion in the volume of the crystal which lies immediately below the UV exposed surface