8 research outputs found
Nondestructive Measurement of the Evolution of Layer-Specific Mechanical Properties in Sub-10 nm Bilayer Films
We
use short wavelength extreme ultraviolet light to independently measure
the mechanical properties of disparate layers within a bilayer film
for the first time, with single-monolayer sensitivity. We show that
in Ni/Ta nanostructured systems, while their density ratio is not
meaningfully changed from that expected in bulk, their elastic properties
are significantly modified, where nickel softens while tantalum stiffens,
relative to their bulk counterparts. In particular, the presence or
absence of the Ta capping layer influences the mechanical properties
of the Ni film. This nondestructive nanomechanical measurement technique
represents the first approach to date able to distinguish the properties
of composite materials well below 100 nm in thickness. This capability
is critical for understanding and optimizing the strength, flexibility
and reliability of materials in a host of nanostructured electronic,
photovoltaic, and thermoelectric devices
Supplement 1: Tabletop nanometer extreme ultraviolet imaging in an extended reflection mode using coherent Fresnel ptychography
Originally published in Optica on 22 July 2014 (optica-1-1-39
Tabletop Femtosecond VUV Photoionization and PEPICO Detection of Microreactor Pyrolysis Products
We
report the combination of tabletop vacuum ultraviolet photoionization
with photoion–photoelectron coincidence spectroscopy for sensitive,
isomer-specific detection of nascent products from a pyrolysis microreactor.
Results on several molecules demonstrate two essential capabilities
that are very straightforward to implement: the ability to differentiate
isomers and the ability to distinguish thermal products from dissociative
ionization. Here, vacuum ultraviolet light is derived from a commercial
tabletop femtosecond laser system, allowing data to be collected at
10 kHz; this high repetition rate is critical for coincidence techniques.
The photoion–photoelectron coincidence spectrometer uses the
momentum of the ion to identify dissociative ionization events and
coincidence techniques to provide a photoelectron spectrum specific
to each mass, which is used to distinguish different isomers. We have
used this spectrometer to detect the pyrolysis products that result
from the thermal cracking of acetaldehyde, cyclohexene, and 2-butanol.
The photoion–photoelectron spectrometer can detect and identify
organic radicals and reactive intermediates that result from pyrolysis.
Direct comparison of laboratory and synchrotron data illustrates the
advantages and potential of this approach
Solvents Effects on Charge Transfer from Quantum Dots
To predict and understand the performance
of nanodevices in different environments, the influence of the solvent
must be explicitly understood. In this Communication, this important
but largely unexplored question is addressed through a comparison
of quantum dot charge transfer processes occurring in both liquid
phase and in vacuum. By comparing solution phase transient absorption
spectroscopy and gas-phase photoelectron spectroscopy, we show that
hexane, a common nonpolar solvent for quantum dots, has negligible
influence on charge transfer dynamics. Our experimental results, supported
by insights from theory, indicate that the reorganization energy of
nonpolar solvents plays a minimal role in the energy landscape of
charge transfer in quantum dot devices. Thus, this study demonstrates
that measurements conducted in nonpolar solvents can indeed provide
insight into nanodevice performance in a wide variety of environments
Quantitative Chemically Specific Coherent Diffractive Imaging of Reactions at Buried Interfaces with Few Nanometer Precision
We
demonstrate quantitative, chemically specific imaging of buried nanostructures,
including oxidation and diffusion reactions at buried interfaces,
using nondestructive tabletop extreme ultraviolet (EUV) coherent diffractive
imaging (CDI). Copper nanostructures inlaid in SiO<sub>2</sub> are
coated with 100 nm of aluminum, which is opaque to visible light and
thick enough that neither visible microscopy nor atomic force microscopy
can image the buried interface. Short wavelength high harmonic beams
can penetrate the aluminum layer, yielding high-contrast images of
the buried structures. Quantitative analysis shows that the reflected
EUV light is extremely sensitive to the formation of multiple oxide
layers, as well as interdiffusion of materials occurring at the metal–metal
and metal–insulator boundaries deep within the nanostructure
with few nanometers precision
Full Characterization of the Mechanical Properties of 11–50 nm Ultrathin Films: Influence of Network Connectivity on the Poisson’s Ratio
Precise characterization
of the mechanical properties of ultrathin
films is of paramount importance for both a fundamental understanding
of nanoscale materials and for continued scaling and improvement of
nanotechnology. In this work, we use coherent extreme ultraviolet
beams to characterize the full elastic tensor of isotropic ultrathin
films down to 11 nm in thickness. We simultaneously extract the Young’s
modulus and Poisson’s ratio of low-<i>k</i> a-SiC:H
films with varying degrees of hardness and average network connectivity
in a single measurement. Contrary to past assumptions, we find that
the Poisson’s ratio of such films is not constant but rather
can significantly increase from 0.25 to >0.4 for a network connectivity
below a critical value of ∼2.5. Physically, the strong hydrogenation
required to decrease the dielectric constant <i>k</i> results
in bond breaking, lowering the network connectivity, and Young’s
modulus of the material but also decreases the compressibility of
the film. This new understanding of ultrathin films demonstrates that
coherent EUV beams present a new nanometrology capability that can
probe a wide range of novel complex materials not accessible using
traditional approaches
Materials Properties and Solvated Electron Dynamics of Isolated Nanoparticles and Nanodroplets Probed with Ultrafast Extreme Ultraviolet Beams
We
present ultrafast photoemission measurements of isolated nanoparticles
in vacuum using extreme ultraviolet (EUV) light produced through high
harmonic generation. Surface-selective static EUV photoemission measurements
were performed on nanoparticles with a wide array of compositions,
ranging from ionic crystals to nanodroplets of organic material. We
find that the total photoelectron yield varies greatly with nanoparticle
composition and provides insight into material properties such as
the electron mean free path and effective mass. Additionally, we conduct
time-resolved photoelectron yield measurements of isolated oleylamine
nanodroplets, observing that EUV photons can create solvated electrons
in liquid nanodroplets. Using photoemission from a time-delayed 790
nm pulse, we observe that a solvated electron is produced in an excited
state and subsequently relaxes to its ground state with a lifetime
of 151 ± 31 fs. This work demonstrates that femotosecond EUV
photoemission is a versatile surface-sensitive probe of the properties
and ultrafast dynamics of isolated nanoparticles
Mapping Nanoscale Absorption of Femtosecond Laser Pulses Using Plasma Explosion Imaging
We make direct observations of localized light absorption in a single nanostructure irradiated by a strong femtosecond laser field, by developing and applying a technique that we refer to as plasma explosion imaging. By imaging the photoion momentum distribution resulting from plasma formation in a laser-irradiated nanostructure, we map the spatial location of the highly localized plasma and thereby image the nanoscale light absorption. Our method probes individual, isolated nanoparticles in vacuum, which allows us to observe how small variations in the composition, shape, and orientation of the nanostructures lead to vastly different light absorption. Here, we study four different nanoparticle samples with overall dimensions of ∼100 nm and find that each sample exhibits distinct light absorption mechanisms despite their similar size. Specifically, we observe subwavelength focusing in single NaCl crystals, symmetric absorption in TiO<sub>2</sub> aggregates, surface enhancement in dielectric particles containing a single gold nanoparticle, and interparticle hot spots in dielectric particles containing multiple smaller gold nanoparticles. These observations demonstrate how plasma explosion imaging directly reveals the diverse ways in which nanoparticles respond to strong laser fields, a process that is notoriously challenging to model because of the rapid evolution of materials properties that takes place on the femtosecond time scale as a solid nanostructure is transformed into a dense plasma