63 research outputs found
Nonlinear viscoelastic dynamics of nano-confined water
The viscoelastic dynamics of nano-confined water is studied by means of
atomic force microscopy (AFM). We observe a nonlinear viscoelastic behavior
remarkably similar to that widely observed in metastable complex fluids. We
show that the origin of the measured nonlinear viscoelasticity in nano-confined
water is a strain rate dependent relaxation time and slow dynamics. By
measuring the viscoelastic modulus at different frequencies and strains, we
find that the intrinsic relaxation time of nano-confined water is in the range
0.1-0.0001 s, orders of magnitude longer than that of bulk water, and
comparable to the dielectric relaxation time measured in supercooled water at
170-210 K.Comment: 4 Figure
-Indentation for non-destructive elastic moduli measurements of supported ultra-hard ultra-thin films and nanostructures
During conventional nanoindentation measurements, the indentation depths are
usually larger than 1-10 nm, which hinders the ability to study ultra-thin
films ( 10 nm) and supported atomically thin two-dimensional (2D) materials.
Here, we discuss the development of modulated \r{A}-indentation to achieve
sub-\r{A} indentation depths during force-indentation measurements while also
imaging materials with nanoscale resolution. Modulated nanoindentation (MoNI)
was originally invented to measure the radial elasticity of multi-walled
nanotubes. Now, by using extremely small amplitude oscillations ( 1 \r{A})
at high frequency, and stiff cantilevers, we show how modulated
nano/\r{A}-indentation (MoNI/\r{A}I) enables non-destructive measurements of
the contact stiffness and indentation modulus of ultra-thin ultra-stiff films,
including CVD diamond films (modulus 1000 GPa), as well as the
transverse modulus of 2D materials. Our analysis demonstrates that in presence
of a standard laboratory noise floor, the signal to noise ratio of MoNI/\r{A}I
implemented with a commercial atomic force microscope (AFM) is such that a
dynamic range of 80 dB achievable with commercial Lock-in amplifiers is
sufficient to observe superior indentation curves, having indentation depths as
small as 0.3 \r{A}, resolution in indentation 0.05 \r{A}, and in normal
load 0.5 nN. Being implemented on a standard AFM, this method has the
potential for a broad applicability.Comment: 37 pages, 12 figure
Nanopatterning spin-textures: A route to reconfigurable magnonics
Magnonics is envisioned to enable highly efficient data transport and processing, by exploiting propagating perturbations in the spin-texture of magnetic materials. Despite the demonstrations of a plethora of proof-of-principle devices, the efficient excitation, transport and manipulation of spin-waves at the nanoscale is still an open challenge. Recently, we demonstrated that the spin-wave excitation and propagation can be controlled by nanopatterning reconfigurable spin-textures in a continuous exchange biased ferromagnetic film. Here, we show that by patterning 90° stripe-shaped magnetic domains, we spatially modulate the spin-wave excitation in a continuous film, and that by applying an external magnetic field we can reversibly â\u80\u9cswitch-offâ\u80\u9d the spin-wave excitation. This opens the way to the use of nanopatterned spin-textures, such as domains and domain walls, for exciting and manipulating magnons in reconfigurable nanocircuits
Layer dependence of graphene-diamene phase transition in epitaxial and exfoliated few-layer graphene using machine learning
The study of the nanomechanics of graphene and other 2D materials has
led to the discovery of exciting new properties in 2D crystals, such as their
remarkable in-plane stiffness and out of plane flexibility, as well as their
unique frictional and wear properties at the nanoscale. Recently, nanomechanics
of graphene has generated renovated interest for new findings on the
pressure-induced chemical transformation of a few-layer thick epitaxial
graphene into a new ultra-hard carbon phase, named diamene. In this work, by
means of a machine learning technique, we provide a fast and efficient tool for
identification of graphene domains (areas with a defined number of layers) in
epitaxial and exfoliated films, by combining data from Atomic Force Microscopy
(AFM) topography and friction force microscopy (FFM). Through the analysis of
the number of graphene layers and detailed \r{A}-indentation experiments, we
demonstrate that the formation of ultra-stiff diamene is exclusively found in
1-layer plus buffer layer epitaxial graphene on silicon carbide (SiC) and that
an ultra-stiff phase is not observed in neither thicker epitaxial graphene
(2-layer or more) nor exfoliated graphene films of any thickness on silicon
oxide (SiO).Comment: 30 pages, 7 figure
Imaging thermal conductivity with nanoscale resolution using a scanning spin probe
The ability to probe nanoscale heat flow in a material is often limited by lack of spatial resolution. Here, we use a diamond-nanocrystal-hosted nitrogen-vacancy centre attached to the apex of a silicon thermal tip as a local temperature sensor. We apply an electrical current to heat up the tip and rely on the nitrogen vacancy to monitor the thermal changes the tip experiences as it is brought into contact with surfaces of varying thermal conductivity. By combining atomic force and confocal microscopy, we image phantom microstructures with nanoscale resolution, and attain excellent agreement between the thermal conductivity and topographic maps. The small mass and high thermal conductivity of the diamond host make the time response of our technique short, which we demonstrate by monitoring the tip temperature upon application of a heat pulse. Our approach promises multiple applications, from the investigation of phonon dynamics in nanostructures to the characterization of heterogeneous phase transitions and chemical reactions in various solid-state systems
Imaging thermal conductivity with nanoscale resolution using a scanning spin probe
The ability to probe nanoscale heat flow in a material is often limited by lack of spatial resolution. Here, we use a diamond-nanocrystal-hosted nitrogen-vacancy centre attached to the apex of a silicon thermal tip as a local temperature sensor. We apply an electrical current to heat up the tip and rely on the nitrogen vacancy to monitor the thermal changes the tip experiences as it is brought into contact with surfaces of varying thermal conductivity. By combining atomic force and confocal microscopy, we image phantom microstructures with nanoscale resolution, and attain excellent agreement between the thermal conductivity and topographic maps. The small mass and high thermal conductivity of the diamond host make the time response of our technique short, which we demonstrate by monitoring the tip temperature upon application of a heat pulse. Our approach promises multiple applications, from the investigation of phonon dynamics in nanostructures to the characterization of heterogeneous phase transitions and chemical reactions in various solid-state systems
Thermal scanning probe lithography
Thermal scanning probe lithography (tSPL) is a nanofabrication method for the chemical and physical nanopatterning of a large variety of materials and polymer resists with a lateral resolution of 10 nm and a depth resolution of 1 nm. In this Primer, we describe the working principles of tSPL and highlight the characteristics that make it a powerful tool to locally and directly modify material properties in ambient conditions. We introduce the main features of tSPL, which can pattern surfaces by locally delivering heat using nanosized thermal probes. We define the most critical patterning parameters in tSPL and describe post-patterning analysis of the obtained results. The main sources of reproducibility issues related to the probe and the sample as well as the limitations of the tSPL technique are discussed together with mitigation strategies. The applications of tSPL covered in this Primer include those in biomedicine, nanomagnetism and nanoelectronics; specifically, we cover the fabrication of chemical gradients, tissue-mimetic surfaces, spin wave devices and field-effect transistors based on two-dimensional materials. Finally, we provide an outlook on new strategies that can improve tSPL for future research and the fabrication of next-generation devices
Room Temperature Metastability of Multilayer Graphene Oxide Films
International audienceGraphene oxide has multiple potential applications. The chemistry of graphene oxide and its response to external stimuli such as temperature and light are not well understood and only approximately controlled. This under- standing is crucial to enable future applications of this material. Here, a com- bined experimental and density functional theory study shows that multilayer graphene oxide produced by oxidizing epitaxial graphene via the Hummers method is a metastable material whose structure and chemistry evolve at room temperature with a characteristic relaxation time of about one month. At the quasi-equilibrium, graphene oxide reaches a nearly-stable reduced O/C ratio, and exhibits a structure intensively deprived of epoxide groups and enriched of hydroxyl groups. Our calculations show that the structural and chemical changes are driven by the availability of hydrogen in the oxidized graphitic sheets, which favors the reduction of epoxide groups and the formation of water molecules
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