17 research outputs found
Strategies for Potential Age Dating of Fingerprints through the Diffusion of Sebum Molecules on a Nonporous Surface Analyzed Using Time-of-Flight Secondary Ion Mass Spectrometry
Age dating of fingerprints
could have a significant impact in forensic
science, as it has the potential to facilitate the judicial process
by assessing the relevance of a fingerprint found at a crime scene.
However, no method currently exists that can reliably predict the
age of a latent fingerprint. In this manuscript, time-of-flight secondary
ion imaging mass spectrometry (TOF-SIMS) was used to measure the diffusivity
of saturated fatty acid molecules from a fingerprint on a silicon
wafer. It was found that their diffusion from relatively fresh fingerprints
(<i>t</i> ≤ 96 h) could be modeled using an error
function, with diffusivities (mm<sup>2</sup>/h) that followed a power
function when plotted against molecular weight. The equation <i>x</i> = 0.02<i>t</i><sup>0.5</sup> was obtained for
palmitic acid that could be used to find its position in millimeters
(where the concentration is 50% of its initial value or <i>c</i><sub>0</sub>/2) as a function of time in hours. The results show
that on a clean silicon substrate, the age of a fingerprint (<i>t</i> ≤ 96 h) could reliably be obtained through the
extent of diffusion of palmitic acid
Exploring the Surface Sensitivity of TOF-Secondary Ion Mass Spectrometry by Measuring the Implantation and Sampling Depths of Bi<sub>n</sub> and C<sub>60</sub> Ions in Organic Films
The surface sensitivity of Bi<sub>n</sub><sup>q+</sup> (<i>n</i> = 1, 3, 5, <i>q</i> = 1, 2) and C<sub>60</sub><sup>q+</sup> (<i>q</i> = 1, 2) primary ions in static time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments were investigated for molecular trehalose and polymeric tetraglyme organic films. Parameters related to surface sensitivity (impact crater depth, implantation depth, and molecular escape depths) were measured. Under static TOF-SIMS conditions (primary ion doses of 1 × 10<sup>12</sup> ions/cm<sup>2</sup>), the 25 keV Bi<sub>1</sub><sup>+</sup> primary ions were the most surface sensitive with a molecular escape depth of 1.8 nm for protein films with tetraglyme overlayers, but they had the deepest implantation depth (∼18 and 26 nm in trehalose and tetraglyme films, respectively). The 20 keV C<sub>60</sub><sup>+2</sup> primary ions were the second most surface sensitive with a slightly larger molecular escape depth of 2.3 nm. The most important factor that determined the surface sensitivity of the primary ion was its impact crater depth or the amount of surface erosion. The most surface sensitive primary ions, Bi<sub>1</sub><sup>+</sup> and C<sub>60</sub><sup>+2</sup>, created impact craters with depths of 0.3 and 1.0 nm, respectively, in tetraglyme films. In contrast, Bi<sub>5</sub><sup>+2</sup> primary ions created impact craters with a depth of 1.8 nm in tetraglyme films and were the least surface sensitive with a molecular escape depth of 4.7 nm
Vapor–Liquid–Solid Etch of Semiconductor Surface Channels by Running Gold Nanodroplets
We
show that Au nanoparticles spontaneously move across the (001)
surface of InP, InAs, and GaP when heated in the presence of water
vapor. As they move, the particles etch crystallographically aligned
grooves into the surface. We show that this process is a negative
analogue of the vapor–liquid–solid (VLS) growth of semiconductor
nanowires: the semiconductor dissolves into the catalyst and reacts
with water vapor at the catalyst surface to create volatile oxides,
depleting the dissolved cations and anions and thus sustaining the
dissolution process. This VLS etching process provides a new tool
for directed assembly of structures with sublithographic dimensions,
as small as a few nanometers in diameter. Au particles above 100 nm
in size do not exhibit this process but remain stationary, with oxide
accumulating around the particles
Ultraviolet/Ozone as a Tool To Control Grafting Density in Surface-Initiated Controlled-Radical Polymerizations via Ablation of Bromine
We used an ultraviolet-ozone (UVO)
cleaner to create substrates
for atom-transfer radical polymerization (ATRP) with varying surface
initiator coverage. We collected complementary time-of-flight secondary
ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy
(XPS) measurements to investigate the precise chemical origin of the
variation in grafting density. At short exposure times, the atomic
composition underwent minor changes except for the relative amount
of bromine. At longer UVO exposure times, there is clear evidence
of exposure-dependent surface initiator oxidation. We interpret these
data as evidence of a bromine ablation process within the UVO cleaner,
with additional oxidative modification of the rest of the surface.
We then used these substrates to create a series of polyÂ(methyl methacrylate)
(PMMA) brushes varying in grafting density, demonstrating the utility
of this tool for the control of polymer brush density. The measured
brush grafting densities were correlated with the bromine concentration
measured by both ToF-SIMS and XPS. XPS and brush thicknesses correlated
strongly, following an exponential decay with a half-life of 18 ±
1 s
Increased Carrier Mobility and Lifetime in CdSe Quantum Dot Thin Films through Surface Trap Passivation and Doping
Passivating
surface defects and controlling the carrier concentration
and mobility in quantum dot (QD) thin films is prerequisite to designing
electronic and optoelectronic devices. We investigate the effect of
introducing indium in CdSe QD thin films on the dark mobility and
the photogenerated carrier mobility and lifetime using field-effect
transistor (FET) and time-resolved microwave conductivity (TRMC) measurements.
We evaporate indium films ranging from 1 to 11 nm in thickness on
top of approximately 40 nm thick thiocyanate-capped CdSe QD thin films
and anneal the QD films at 300 °C to densify and drive diffusion
of indium through the films. As the amount of indium increases, the
FET and TRMC mobilities and the TRMC lifetime increase. The increase
in mobility and lifetime is consistent with increased indium passivating
midgap and band-tail trap states and doping the films, shifting the
Fermi energy closer to and into the conduction band
TOF-SIMS 3D Imaging of Native and Non-Native Species within HeLa Cells
In
this study, a non-native chemical species, bromodeoxyuridine
(BrdU), was imaged within single HeLa cells using time-of-flight secondary
ion mass spectrometry (TOF-SIMS). z-corrected 3D images were reconstructed
that accurately portray the distribution of intracellular BrdU as
well as other intracellular structures. The BrdU was localized to
the nucleus of cells, whereas structures composed of C<sub><i>x</i></sub>H<sub><i>y</i></sub>O<sub><i>z</i></sub><sup>–</sup> species were located in bundles on the
periphery of cells. The C<sub><i>x</i></sub>H<sub><i>y</i></sub>O<sub><i>z</i></sub><sup>–</sup> subcellular features had a spatial resolution at or slightly below
a micrometer (900 nm), as defined by the distance between the 16%
and 84% intensities in a line scan across the edge of the features.
Additionally, important parameters influencing the quality of the
HeLa cell 3D images were investigated. Atomic force microscopy measurements
revealed that the HeLa cells were sputtered at a rate of approximately
4 nm per 10<sup>13</sup> C<sub>60</sub><sup>+</sup> ions/cm<sup>2</sup> at 10 keV and a 45° incident angle. Optimal 3D images were
acquired using a Bi<sub>3</sub><sup>+</sup> liquid metal ion gun operating
in the simultaneous high mass and spatial resolution mode
Increased Carrier Mobility and Lifetime in CdSe Quantum Dot Thin Films through Surface Trap Passivation and Doping
Passivating
surface defects and controlling the carrier concentration
and mobility in quantum dot (QD) thin films is prerequisite to designing
electronic and optoelectronic devices. We investigate the effect of
introducing indium in CdSe QD thin films on the dark mobility and
the photogenerated carrier mobility and lifetime using field-effect
transistor (FET) and time-resolved microwave conductivity (TRMC) measurements.
We evaporate indium films ranging from 1 to 11 nm in thickness on
top of approximately 40 nm thick thiocyanate-capped CdSe QD thin films
and anneal the QD films at 300 °C to densify and drive diffusion
of indium through the films. As the amount of indium increases, the
FET and TRMC mobilities and the TRMC lifetime increase. The increase
in mobility and lifetime is consistent with increased indium passivating
midgap and band-tail trap states and doping the films, shifting the
Fermi energy closer to and into the conduction band
XPS spectra.
<p>Representative high resolution XPS spectra showing the (a) C 1s and (b) Zn 2p3/2 core lines for the freshly prepared bare zinc and PEGylated zinc nanoparticles stored 1 day at 278 K (5 <sup>o</sup>C), with the spectra offset to facilitate viewing. The Zn 2p spectra are shown in log-scale. The solid curves indicate the experimentally obtained spectra, with the dotted curves underneath indicating their best-fit chemical components. For the C 1s spectra, from lower to higher binding energy, the components are C-C, C-O, and C = O. For the Zn 2p spectra, the components are Zn and ZnO. For the (a) C 1s plots, the solid vertical line represents the position of the C-C peaks, to which all spectra were calibrated to, with the dotted lines showing the spectral shift of the C-O peaks, which were 286 eV, 286.4 eV, and 286.2 eV for the Zn, ZnPEG400, and ZnPEG1000 systems, respectively. For (b) Zn 2p plots, the solid line represents the position of the Zn peak for the bare Zn system, while the dotted lines show the spectral shift of the ZnO peaks, which were 1024.6 eV, 1025.6 eV, and 1026.0 eV for the Zn, ZnPEG400, and ZnPEG1000 systems, respectively. Each spectrum represents an average of six spectral runs.</p
Designing High-Performance PbS and PbSe Nanocrystal Electronic Devices through Stepwise, Post-Synthesis, Colloidal Atomic Layer Deposition
We
report a simple, solution-based, postsynthetic colloidal, atomic
layer deposition (PS-cALD) process to engineer stepwise the surface
stoichiometry and therefore the electronic properties of lead chalcogenide
nanocrystal (NC) thin films integrated in devices. We found that unlike
chalcogen-enriched NC surfaces that are structurally, optically, and
electronically unstable, lead chloride treatment creates a well-passivated
shell that stabilizes the NCs. Using PS-cALD of lead chalcogenide
NC thin films we demonstrate high electron field-effect mobilities
of ∼4.5 cm<sup>2</sup>/(V s)
Properties of PEG on the surface of zinc nanoparticles.
<p>Properties of PEG on the surface of zinc nanoparticles.</p