13,314 research outputs found
Nanoscale roughness and morphology affect the IsoElectric Point of titania surfaces
We report on the systematic investigation of the role of surface nanoscale
roughness and morphology on the charging behaviour of nanostructured titania
(TiO2) surfaces in aqueous solutions. IsoElectric Points (IEPs) of surfaces
have been characterized by direct measurement of the electrostatic double layer
interactions between titania surfaces and the micrometer-sized spherical silica
probe of an atomic force microscope in NaCl aqueous electrolyte. The use of a
colloidal probe provides well-defined interaction geometry and allows
effectively probing the overall effect of nanoscale morphology. By using
supersonic cluster beam deposition to fabricate nanostructured titania films,
we achieved a quantitative control over the surface morphological parameters.
We performed a systematical exploration of the electrical double layer
properties in different interaction regimes characterized by different ratios
of characteristic nanometric lengths of the system: the surface rms roughness
Rq, the correlation length {\xi} and the Debye length {\lambda}D. We observed a
remarkable reduction by several pH units of IEP on rough nanostructured
surfaces, with respect to flat crystalline rutile TiO2. In order to explain the
observed behavior of IEP, we consider the roughness-induced self-overlap of the
electrical double layers as a potential source of deviation from the trend
expected for flat surfaces.Comment: 63 pages, including 7 figures and Supporting Informatio
Impact of Electrostatic Forces in Contact Mode Scanning Force Microscopy
In this contribution we address the question to what extent surface
charges affect contact-mode scanning force microscopy measurements. % We
therefore designed samples where we could generate localized electric field
distributions near the surface as and when required. % We performed a series of
experiments where we varied the load of the tip, the stiffness of the
cantilever and the hardness of the sample surface. % It turned out that only
for soft cantilevers could an electrostatic interaction between tip and surface
charges be detected, irrespective of the surface properties, i.\,e. basically
regardless its hardness. % We explain these results through a model based on
the alteration of the tip-sample potential by the additional electric field
between charged tip and surface charges
Carbon fibre tips for scanning probe microscopy based on quartz tuning fork force sensors
We report the fabrication and the characterization of carbon fibre tips for
their use in combined scanning tunnelling and force microscopy based on
piezoelectric quartz tuning fork force sensors. We find that the use of carbon
fibre tips results in a minimum impact on the dynamics of quartz tuning fork
force sensors yielding a high quality factor and consequently a high force
gradient sensitivity. This high force sensitivity in combination with high
electrical conductivity and oxidation resistance of carbon fibre tips make them
very convenient for combined and simultaneous scanning tunnelling microscopy
and atomic force microscopy measurements. Interestingly, these tips are quite
robust against occasionally occurring tip crashes. An electrochemical
fabrication procedure to etch the tips is presented that produces a sub-100 nm
apex radius in a reproducible way which can yield high resolution images.Comment: 14 pages, 10 figure
Pembinaan dan penilaian program rekabentuk rasuk keluli (PRRK) sebagai alat kognitif dalam pembelajaran rekabentuk struktur di kalangan pelajar diploma kejuruteraan awam KUiTTHO
Kajian awal yang telah dijalankan mendapati pelajar Kejuruteraan Awam KUiTTHO menghadapi masalah kognitif dalam pembelajaran mata pelajaran Rekabentuk Struktur khasnya dalam pemahaman konsep dan prosedur reka bentuk. Langkah pengiraan yang terlalu banyak selalunya mengelirukan pelajar sehinggakan mereka hilang minat dan tumpuan. Bagi membantu mereka, satu program telah disediakan dengan menggunakan perisian Microsoft Excel bagi tujuan menganalisis dan mereka bentuk rasuk keluli bagi meningkatkan tahap kemahiran kognitif terhadap matapelajaran tersebut. Program Rekabentuk Rasuk Keluli (PRRK) ini disediakan berdasarkan kaedah reka bentuk yang diamalkan oleh British Standard Institution, Structural Use of Steel Work In Building. Seramai dua puluh satu orang pelajar semester akhir Diploma Kejuruteraan A warn yang mengambil mata pelajaran Rekabentuk Struktur telah diminta menilai program ini. Penilaian telah dijalankan terhadap isi, sifat mesra pengguna dan kebolehlaksanaan program menggunakan kaedah skor min. Selain itu perkaitan antara pengalaman pelajar menggunakan komputer sebagai sumber pembelajaran dengan penilaian PRRK juga telah dilihat. Keputusan skor min menunjukkan isi PRKK adalah baik, bersifat mesra pengguna dan mempunyai sifat kebolehlaksanaan. Ujian korelasi Spearman pula menunjukkan bahawa tidak terdapat sebarang perkaitan yang signifikan di antara pengalaman pelajar menggunakan komputer sebagai sumber pembelajaran dengan penilaian PRRK
Force-induced acoustic phonon transport across single-digit nanometre vacuum gaps
Heat transfer between bodies separated by nanoscale vacuum gap distances has
been extensively studied for potential applications in thermal management,
energy conversion and data storage. For vacuum gap distances down to 20 nm,
state-of-the-art experiments demonstrated that heat transport is mediated by
near-field thermal radiation, which can exceed Planck's blackbody limit due to
the tunneling of evanescent electromagnetic waves. However, at sub-10-nm vacuum
gap distances, current measurements are in disagreement on the mechanisms
driving thermal transport. While it has been hypothesized that acoustic phonon
transport across single-digit nanometre vacuum gaps (or acoustic phonon
tunneling) can dominate heat transfer, the underlying physics of this
phenomenon and its experimental demonstration are still unexplored. Here, we
use a custom-built high-vacuum shear force microscope (HV-SFM) to measure heat
transfer between a silicon (Si) tip and a feedback-controlled platinum (Pt)
nanoheater in the near-contact, asperity-contact, and bulk-contact regimes. We
demonstrate that in the near-contact regime (i.e., single-digit nanometre or
smaller vacuum gaps before making asperity contact), heat transfer between Si
and Pt surfaces is dominated by force-induced acoustic phonon transport that
exceeds near-field thermal radiation predictions by up to three orders of
magnitude. The measured thermal conductance shows a gap dependence of
in the near-contact regime, which is consistent with acoustic
phonon transport modelling based on the atomistic Green's function (AGF)
framework. Our work suggests the possibility of engineering heat transfer
across single-digit nanometre vacuum gaps with external force stimuli, which
can make transformative impacts to the development of emerging thermal
management technologies.Comment: 9 pages with 4 figures (Main text), 13 pages with 7 figures
(Methods), and 13 pages with 6 figures and 1 table (Supplementary
Information
Casimir probe based upon metallized high Q SiN nanomembrane resonator
We present the instrumentation and measurement scheme of a new Casimir force
probe that bridges Casimir force measurements at microscale and macroscale. A
metallized high Q silicon nitride nanomembrane resonator is employed as a
sensitive force probe. The high tensile stress present in the nanomembrane not
only enhances the quality factor but also maintains high flatness over large
area serving as the bottom electrode in a sphere-plane configuration. A fiber
interferometer is used to readout the oscillation of the nanomembrane and a
phase-locked loop scheme is applied to track the change of the resonance
frequency. Because of the high quality factor of the nanomembrane and the high
stability of the setup, a frequency resolution down to and a
corresponding force gradient resolution of 3 N/m is achieved. Besides
sensitive measurement of Casimir force, our measurement technique
simultaneously offers Kelvin probe measurement capability that allows in situ
imaging of the surface potentials
Fast Ultrahigh-Density Writing of Low Conductivity Patterns on Semiconducting Polymers
The exceptional interest in improving the limitations of data storage,
molecular electronics, and optoelectronics has promoted the development of an
ever increasing number of techniques used to pattern polymers at micro and
nanoscale. Most of them rely on Atomic Force Microscopy to thermally or
electrostatically induce mass transport, thereby creating topographic features.
Here we show that the mechanical interaction of the tip of the Atomic Force
Microscope with the surface of a class of conjugate polymers produces a local
increase of molecular disorder, inducing a localized lowering of the
semiconductor conductivity, not associated to detectable modifications in the
surface topography. This phenomenon allows for the swift production of low
conductivity patterns on the polymer surface at an unprecedented speed
exceeding 20 ; paths have a resolution in the order of the tip
size (20 nm) and are detected by a Conducting-Atomic Force Microscopy tip in
the conductivity maps.Comment: 22 pages, 6 figures, published in Nature Communications as Article (8
pages
- …