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 (mm²/h) that followed a power function when plotted against molecular weight. The equation <i>x</i> = 0.02<i>t</i>^0.5 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>₀/2) 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_n and C₆₀ Ions in Organic Films

The surface sensitivity of Bi_n^q+ (<i>n</i> = 1, 3, 5, <i>q</i> = 1, 2) and C₆₀^q+ (<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 × 10¹² ions/cm²), the 25 keV Bi₁⁺ 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 C₆₀⁺² 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, Bi₁⁺ and C₆₀⁺², created impact craters with depths of 0.3 and 1.0 nm, respectively, in tetraglyme films. In contrast, Bi₅⁺² 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 poly­(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_<i>x</i>H_<i>y</i>O_<i>z</i>^– species were located in bundles on the periphery of cells. The C_<i>x</i>H_<i>y</i>O_<i>z</i>^– 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 10¹³ C₆₀⁺ ions/cm² at 10 keV and a 45° incident angle. Optimal 3D images were acquired using a Bi₃⁺ 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 ^oC), 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 cm²/(V s)

Properties of PEG on the surface of zinc nanoparticles.

<p>Properties of PEG on the surface of zinc nanoparticles.</p