Integrative Atom Probe Tomography Using Scanning Transmission Electron Microscopy-Centric Atom Placement as a Step Toward Atomic-Scale Tomography.

Current reconstruction methodologies for atom probe tomography (APT) contain serious geometric artifacts that are difficult to address due to their reliance on empirical factors to generate a reconstructed volume. To overcome this limitation, a reconstruction technique is demonstrated where the analyzed volume is instead defined by the specimen geometry and crystal structure as determined by transmission electron microscopy (TEM) and diffraction acquired before and after APT analysis. APT data are reconstructed using a bottom-up approach, where the post-APT TEM image is used to define the substrate upon which APT detection events are placed.

Extreme Ultraviolet Radiation Pulsed Atom Probe Tomography of III-Nitride Semiconductor Materials.

Laser-pulsed atom probe tomography (LAPT) is a materials characterization technique that has been widely applied in the study and characterization of III-nitride semiconductors. To date, most of these studies have used light sources ranging from the visible to the near-ultraviolet region of the spectrum. In this manuscript, we demonstrate that a recently developed extreme ultraviolet (EUV) radiation pulsed atom probe tomograph can trigger controlled field ion evaporation from III-nitride samples.

Synthesis of Tunable SnS-TaS Nanoscale Superlattices.

Nanoscale superlattices represent a compelling platform for designed materials as the specific identity and spatial arrangement of constituent layers can lead to tunable properties. A number of kinetically stabilized, nonepitaxial superlattices with almost limitless structural tunability have been reported in telluride and selenide chemistries but have not yet been extended to sulfides. Here, we present SnS-TaS nanoscale superlattices with tunable layer architecture.

Field Ion Emission in an Atom Probe Microscope Triggered by Femtosecond-Pulsed Coherent Extreme Ultraviolet Light.

This paper describes initial experimental results from an extreme ultraviolet (EUV) radiation-pulsed atom probe microscope. Femtosecond-pulsed coherent EUV radiation of 29.6 nm wavelength (41.

Orientation mapping with Kikuchi patterns generated from a focused STEM probe and indexing with commercially available EDAX software.

Relating a crystal's microscopic structure-such as orientation and size-to a material's macroscopic properties is of great importance in materials science. Although most crystal orientation microscopy is performed in the scanning electron microscope (SEM), transmission electron microscopy (TEM)-based methods have a number of benefits, including higher spatial resolution. Current TEM orientation methods have either specific hardware requirements or use software that has limited scope, utility, or availability.

High-Throughput Experimental Study of Wurtzite Mn Zn O Alloys for Water Splitting Applications.

We used high-throughput experimental screening methods to unveil the physical and chemical properties of Mn Zn O wurtzite alloys and identify their appropriate composition for effective water splitting application. The Mn Zn O thin films were synthesized using combinatorial pulsed laser deposition, permitting for characterization of a wide range of compositions with varying from 0 to 1. The solubility limit of ZnO in MnO was determined using the disappearing phase method from X-ray diffraction and X-ray fluorescence data and found to increase with decreasing substrate temperature due to kinetic limitations of the thin-film growth at relatively low temperature.

A Three-Dimensional Atom Probe Microscope Incorporating a Wavelength-Tuneable Femtosecond-Pulsed Coherent Extreme Ultraviolet Light Source.

Pulsed coherent extreme ultraviolet (EUV) radiation is a potential alternative to pulsed near-ultraviolet (NUV) wavelengths for atom probe tomography. EUV radiation has the benefit of high absorption within the first few nm of the sample surface for elements across the entire periodic table. In addition, EUV radiation may also offer athermal field ion emission pathways through direct photoionization or core-hole Auger decay processes, which are not possible with the (much lower) photon energies used in conventional NUV laser-pulsed atom probe.

Self-consistent atom probe tomography reconstructions utilizing electron microscopy.

Atom probe tomography reconstructions provide valuable information on nanometer-scale compositional variations within materials. As such, the spatial accuracy of the reconstructions is of primary importance for the resulting conclusions to be valid. Here, the use of transmission electron microscopy images before and after atom probe analysis to provide additional information and constraints is examined for a number of different materials.

Understanding crystallization pathways leading to manganese oxide polymorph formation.

Hydrothermal synthesis is challenging in metal oxide systems with diverse polymorphism, as reaction products are often sensitive to subtle variations in synthesis parameters. This sensitivity is rooted in the non-equilibrium nature of low-temperature crystallization, where competition between different metastable phases can lead to complex multistage crystallization pathways. Here, we propose an ab initio framework to predict how particle size and solution composition influence polymorph stability during nucleation and growth.

Electron diffraction and imaging for atom probe tomography.

Previous work has shown that pre- and post-experiment quantification of atom probe tomography (APT) specimen geometry using electron microscopy can constrain otherwise unknown parameters, leading to an improvement in data fidelity. To that end, an electron microscopy and diffraction system has been developed for in situ compatibility with modern APT hardware. The system is capable of secondary and backscattered scanning electron imaging, bright field and dark field scanning transmission electron imaging, and scanning transmission electron diffraction.

Theory-Guided Synthesis of a Metastable Lead-Free Piezoelectric Polymorph.

Many technologically critical materials are metastable under ambient conditions, yet the understanding of how to rationally design and guide the synthesis of these materials is limited. This work presents an integrated approach that targets a metastable lead-free piezoelectric polymorph of SrHfO . First-principles calculations predict that the previous experimentally unrealized, metastable P4mm phase of SrHfO should exhibit a direct piezoelectric response (d ) of 36.

p-type doping efficiency in CdTe: Influence of second phase formation.

Cadmium telluride (CdTe) high purity, bulk, crystal ingots doped with phosphorus were grown by the vertical Bridgman melt growth technique to understand and improve dopant solubility and activation. Large net carrier densities have been reproducibly obtained from as-grown ingots, indicating successful incorporation of dopants into the lattice. However, net carrier density values are orders of magnitude lower than the solubility of P in CdTe as reported in literature, 10/cm to 10/cm [J.

Correlative Raman spectroscopy and focused ion beam for targeted phase boundary analysis of titania polymorphs.

Site-specific preparation of specimens using focused ion beam instruments for transmission electron microscopy is at the forefront of targeting regions of interest for nanoscale characterization. Typical methods of pinpointing desired features include electron backscatter diffraction for differentiating crystal structures and energy-dispersive X-Ray spectroscopy for probing compositional variations. Yet there are situations, notably in the titanium dioxide system, where these techniques can fail.

High-fraction brookite films from amorphous precursors.

Structure-specific synthesis processes are of key importance to the growth of polymorphic functional compounds such as TiO, where material properties strongly depend on structure as well as chemistry. The robust growth of the brookite polymorph of TiO, a promising photocatalyst, has been difficult in both powder and thin-film forms due to the disparity of reported synthesis techniques, their highly specific nature, and lack of mechanistic understanding. In this work, we report the growth of high-fraction (~95%) brookite thin films prepared by annealing amorphous titania precursor films deposited by pulsed laser deposition.

Junction Quality of SnO-Based Perovskite Solar Cells Investigated by Nanometer-Scale Electrical Potential Profiling.

Electron-selective layers (ESLs) and hole-selective layers (HSLs) are critical in high-efficiency organic-inorganic lead halide perovskite (PS) solar cells for charge-carrier transport, separation, and collection. We developed a procedure to assess the quality of the ESL/PS junction by measuring potential distribution on the cross section of SnO-based PS solar cells using Kelvin probe force microscopy. Using the potential profiling, we compared three types of cells made of different ESLs but otherwise having an identical device structure: (1) cells with PS deposited directly on bare fluorine-doped SnO (FTO)-coated glass; (2) cells with an intrinsic SnO thin layer on the top of FTO as an effective ESL; and (3) cells with the SnO ESL and adding a self-assembled monolayer (SAM) of fullerene.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys.

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys.

Electron Beam-Induced Deposition for Atom Probe Tomography Specimen Capping Layers.

Six precursors were evaluated for use as in situ electron beam-induced deposition capping layers in the preparation of atom probe tomography specimens with a focus on near-surface features where some of the deposition is retained at the specimen apex. Specimens were prepared by deposition of each precursor onto silicon posts and shaped into sub-70-nm radii needles using a focused ion beam. The utility of the depositions was assessed using several criteria including composition and uniformity, evaporation behavior and evaporation fields, and depth of Ga+ ion penetration.

Probing Grain-Boundary Chemistry and Electronic Structure in Proton-Conducting Oxides by Atom Probe Tomography.

A laser-assisted atom-probe-tomographic (LAAPT) method has been developed and applied to measure and characterize the three-dimensional atomic and electronic nanostructure at an yttrium-doped barium zirconate (BaZrYO, BZY10) grain boundary. Proton-conducting perovskites, such as BZY10, are attracting intense interest for a variety of energy conversion applications. However, their implementation has been hindered, in part, because of high grain-boundary (GB) resistance that is attributed to a positive GB space-charge layer (SCL).

Effect of Diels-Alder Reaction in C-Tetracene Photovoltaic Devices.

Developing organic photovoltaic materials systems requires a detailed understanding of the heterojunction interface, as it is the foundation for photovoltaic device performance. The bilayer fullerene/acene system is one of the most studied models for testing our understanding of this interface. We demonstrate that the fullerene and acene molecules chemically react at the heterojunction interface, creating a partial monolayer of a Diels-Alder cycloadduct species.

Bandgap Tuning of Silicon Quantum Dots by Surface Functionalization with Conjugated Organic Groups.

The quantum confinement and enhanced optical properties of silicon quantum dots (SiQDs) make them attractive as an inexpensive and nontoxic material for a variety of applications such as light emitting technologies (lighting, displays, sensors) and photovoltaics. However, experimental demonstration of these properties and practical application into optoelectronic devices have been limited as SiQDs are generally passivated with covalently bound insulating alkyl chains that limit charge transport. In this work, we show that strategically designed triphenylamine-based surface ligands covalently bonded to the SiQD surface using conjugated vinyl connectivity results in a 70 nm red-shifted photoluminescence relative to their decyl-capped control counterparts.

Exploring the limits of N-type ultra-shallow junction formation.

Low resistivity, near-surface doping in silicon represents a formidable challenge for both the microelectronics industry and future quantum electronic devices. Here we employ an ultra-high vacuum strategy to create highly abrupt doping profiles in silicon, which we characterize in situ using a four point probe scanning tunnelling microscope. Using a small molecule gaseous dopant source (PH3) which densely packs on a reconstructed silicon surface, followed by encapsulation in epitaxial silicon, we form highly conductive dopant sheets with subnanometer control of the depth profiles.

Atom probe analysis of III-V and Si-based semiconductor photovoltaic structures.

The applicability of atom probe to the characterization of photovoltaic devices is presented with special emphasis on high efficiency III-V and low cost ITO/a-Si:H heterojunction cells. Laser pulsed atom probe is shown to enable subnanometer chemical and structural depth profiling of interfaces in III-V heterojunction cells. Hydrogen, oxygen, and phosphorus chemical profiling in 5-nm-thick a-Si heterojunction cells is also illustrated, along with compositional analysis of the ITO/a-Si interface.