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This work demonstrates APCVD synthesis of stable 2D CrOCl, a magnetic oxyhalide for spintronics and quantum devices. It reveals controllable gas-phase growth, with characterization confirming high-quality CrOCl free from Cr 2 O 3 and oxidation.
Synthesis of 2D metallic Janus SNbSe and SeNbS in 1T phase from 1H-phase NbS 2 and NbSe 2 , respectively, is achieved through using a room temperature plasma-assisted technique that induces a structural phase transition.
Electron paramagnetic resonance (EPR) is used to identify and characterize neutral zinc acceptors in Zn-doped β-Ga 2 O 3 crystals. Two EPR spectra are observed at low temperatures, one from Zn ions at tetrahedral Ga(1) sites (the $Zn$$^{0}_{Ga 1}$ acceptor) and one from Zn ions at octahedral Ga(2) sites (the $Zn$$^{0}_{Ga 2}$ acceptor). These Zn acceptors are small polarons, with the unpaired spin localized in each case on a threefold coordinated oxygen O(I) ion adjacent to the Zn ion. Resolved hyperfine interactions with neighboring 69 Ga and 71 Ga nuclei allow the EPR spectra from the two acceptors to be easily distinguished: $Zn$$^{0}_{Ga 1}$ acceptors interact equally with two Ga(2) ions and $Zn$$^{0}_{Ga 2}$ acceptors interact unequally with a Ga(1) ion and a Ga(2) ion. The as-grown crystals are compensated, with the Zn ions initially present as singly ionized acceptors ($Zn$$^{-}_{Ga 1}$ and $Zn$$^{-}_{Ga 2}$). Exposing a crystal to 325 nm laser light, while being held at 140 K, primarily produces neutral $Zn$$^{0}_{Ga 2}$ acceptors when photoinduced holes are trapped at $Zn$$^{-}_{Ga 2}$ acceptors. This suggests that there may be significantly more Zn ions at Ga(2) sites than at Ga(1) sites. Warming the crystal briefly to room temperature, after removing the light, destroys the EPR spectrum from the shallower $Zn$$^{0}_{Ga 2}$ acceptors and produces the EPR spectrum from the more stable $Zn$$^{0}_{Ga 1}$ acceptors. Furthermore, the $Zn$$^{0}_{Ga 2}$ acceptors decay in the 240–260 K region with a thermal activation energy near 0.65 eV, similar to $Mg$$^{0}_{Ga 2}$ acceptors, whereas the slightly deeper $Zn$$^{0}_{Ga 1}$ acceptors decay close to room temperature with an approximate thermal activation energy of 0.78 eV.
Electron emission spectroscopy was performed on metalorganic chemical vapor deposition grown p-n – -n + junctions with p-thicknesses ranging from 50 to 300 nm, doped with [Mg] = 3.5 × 10 19 cm –3 . By measuring the decreasing emitted electron intensity from a cesiated p-GaN surface with increasing p-thickness, we were able to extract the minority carrier diffusion length of electron in p-type GaN, L e = 26 ± 3 nm. The measured value is in good agreement with literature reported values. In conclusion, the extrapolated electron current at the n – region–p-GaN interface is in reasonable agreement with the simulated electron current at the interface.
Two-dimensional (2D) layered materials, whether in bulk form or reduced to just a single layer, have potential applications in spintronics and capacity for advanced quantum phenomena. A prerequisite for harnessing these opportunities lies in gaining a comprehensive understanding of the spin behavior in 2D materials. The low dimensionality motivates an understanding of the spin correlations over a wide length scale, from local to long-range order. In this context, we focus on the magnetism in bulk MnPSe 3 and MnPS 3 , 2D layered van der Waals antiferromagnetic semiconductors. These materials have similar honeycomb Mn layers and magnetic ordering temperatures, but distinct spin orientations and exchange interactions. Here, we utilize neutron scattering to gain deeper insights into the local magnetic structures and spin correlations in the paramagnetic and ordered phases by systematically investigating a MnPS 𝑥 Se 3−𝑥 (𝑥 = 0, 1, 1.5, 2, 3) series of powder samples using total neutron scattering measurements. By employing magnetic pair distribution function analysis, we unraveled the short-range magnetic correlations in these materials and explored how the nonmagnetic anion S/Se mixing impacts the magnetic correlations. The results reveal that the magnetism can be gradually tuned through alteration of the nonmagnetic S/Se content, which tunes the atomic structure. The change in magnetic structure is also accompanied by a control of the magnetic correlation length within the 2D honeycomb layers. Complimentary inelastic neutron scattering measurements allowed a quantification of the change in the magnetic exchange interactions for the series and further highlighted the gradual evolution of spin interactions in the series MnPS 𝑥 Se 3−𝑥 .
Three-dimensional characterization of materials at the nano- and meso-scale has become possible with transmission and scanning transmission electron microscopes (S/TEM). Its importance has extended to a wide class of nanomaterials such as hydrogen fuel cells, solar cells, industrial catalysts, new battery materials and semiconductor devices, as well as spanning high-tech industry, universities, and national labs. While capable instrumentation is abundant, this rapidly expanding demand for high-resolution tomography is bottlenecked by software that is instead tailored for lower-dose, biological applications and not optimized for higher-resolution materials applications. Existing tomography fails to utilize the chemical information provided by S/TEM spectrometers. To address this problem, this project delivered a scalable, fully functional, freely-distributable, open Source materials tomography package with a modern user interface that enables automated acquisition, alignment, and real-time reconstruction of raw tomography data, and provides advanced segmentation, three-dimensional chemical visualization and analysis optimized for materials applications. It has established an extendable framework capable of automation for high-throughput for the tomography of materials from data acquisition to visualization. Phase I and II delivered a full-featured, cross-platform, clean and integrated application for S/TEM materials tomography. It can read projection data from the microscope, with graphical tools for alignment of data, tomographic reconstruction, segmentation, and visualization of the reconstructed 3D volume. The entire pipeline can be saved to an XML state file, enabling fully reproducible data processing and analysis with a full Python environment for the development of custom algorithms, processing, and analysis requirements. Phase IIB extended the application to provide real-time tomographic reconstruction, "live updates" as data is processed, analysis of big data, and multi-channel tomography. Here, quantitative assessment of nanomaterials can occur as data is being recorded on a 3D visualization platform that accommodates additional information from multiple channels. We provide unmatched high-throughput tomography, where the complete tomographic pipeline from measurement to 3D visualization can occur rapidly. The project was extended to offer capabilities for micro-CT, X-ray, neutron, focused ion beam, atomic electron tomography and atom probe tomography. With over 600 transmission electron microscopes worldwide and approximately 50 coming online each year, the demand and impact of an open-source tomography tool is large. Significant opportunities exist in high-tech industry, universities, and national labs to enable or enhance three-dimensional imaging at the nanoscale and bring automated high-throughput approaches that will accelerate progress in materials characterization and metrology. The project supports a service based business model by enabling lab-specific acquisition and processing customization and integration-support and development that will be provided into Phase III and beyond.
We develop lattice-mismatched GaInAsP as an alternative alloy to pure As-based alloys currently used in III-V multijunction solar cells. Increasing the alloy phosphorous and indium content while maintaining an optimal bandgap may allow high efficiency multijunction devices with increased radiation hardness. Here, 1.0-eV GaInAsP is developed and implemented into single and multijunction solar cell devices. The lattice-mismatched GaInAsP must be grown strain free, and the subcell thickness must be maintained below the thickness where surface-driven phase separation occurs. As observed in transmission electron microscopy and cathodoluminescence imaging, phase separation strengthens in the GaInAsP layer and leads to interfacial defect formation when the cell thickness is too great. We show single junction 1.0-eV Ga 0.5 In 0.5 As 0.7 P 0.3 with excellent carrier collection and a bandgap-voltage offset of 0.40 V. This material quality approaches that of 1.0-eV Ga 0.7 In 0.3 As used in inverted metamorphic multijunction devices, but has increased phosphorus content and consequently is expected to have a higher radiation resistance. We incorporate the 1.0-eV GaInAsP subcell into a 3-junction inverted metamorphic solar cell to test the performance of the subcell in a multijunction. No additional loss is observed upon integration into a multijunction cell: both the carrier collection and voltage of the GaInAsP subcell are unchanged from single junction devices. While further materials development and radiation testing is still required, these preliminary results indicate that lattice-mismatched GaInAsP can be effectively used in multijunction solar cells to replace radiation-soft materials.
Recent advances in nanoscience have opened ways of recycling substrates for nanomaterial growth. Novel materials, such as atomically thin materials, are highly desirable for the recycling substrates. In this work, we report recycling of monolayer graphene as a growth template for synthesis of single crystalline ZnO nanowires. Selective nucleation of ZnO nanowires on graphene was elucidated by scanning electron microscopy and density functional theory calculation. Growth and subsequent separation of ZnO nanowires was repeated up to seven times on the same monolayer graphene film. Raman analyses were also performed to investigate the quality of graphene structure along the recycling processes. The chemical robustness of graphene enables the repetitive ZnO nanowire growth without noticeable degradation of the graphene quality. This work presents a route for graphene as a multifunctional growth template for diverse nanomaterials such as nanocrystals, aligned nanowires, other two-dimensional materials, and semiconductor thin films.
Direct growth of III–V semiconductors on Si promises to combine the superior optoelectronic properties of III–Vs with the existing large-scale fabrication capabilities for Si. Vapor-liquid-solid-based growth techniques have previously been used to grow optoelectronic-quality III–Vs in polycrystalline films and various photolithography-defined features. We show that templated vapor-liquid-solid growth can produce epitaxial material when performed on crystalline substrates. In templated vapor-liquid-solid growth, the metal group-III precursor is evaporated along with a capping SiO 2 layer on the crystalline substrate, then melted and converted with exposure to a vapor-phase group-V precursor. We demonstrate homoepitaxial growth of InP on InP wafers using two forms of the SiO x capping layer to confine the liquid metal: evaporated SiO 2 and solgel SiO x , the latter of which is necessary for growth on Si. We then demonstrate heteroepitaxial growth of InP islands on Si substrates from both evaporated and electroplated In metals. The templated vapor-liquid-solid process provides better material utilization and growth rates than common vapor-phase techniques, with similar control and convenience, providing a path toward the large-scale fabrication of integrated optoelectronic components.
Moiré materials are artificial crystals formed at van der Waals heterojunctions that have emerged as a highly tunable platform that is able to realize much of the rich quantum physics of electrons in atomic scale solids, and in several cases even new quantum phases of matter. Here we use finite-size exact diagonalization methods to explore the physics of single-band itinerant electron ferromagnetism in semiconductor moiré materials. As a result, we predict where ferromagnetism is likely to occur in triangular-lattice moiré systems, and where it is likely to yield the highest Curie temperatures.
Self-assembly, a process in which molecules, polymers, and particles are driven by local interactions to organize into patterns and functional structures, is being exploited in advancing silicon electronics and in emerging, unconventional electronics. Additionally, silicon electronics has relied on lithographic patterning of polymer resists at progressively smaller lengths to scale down device dimensions. Yet, this has become increasingly difficult and costly. Assembly of block copolymers and colloidal nanoparticles allows resolution enhancement and the definition of essential shapes to pattern circuits and memory devices. As we look to a future in which electronics are integrated at large numbers and in new forms for the Internet of Things and wearable and implantable technologies, we also explore a broader material set. Semiconductor nanoparticles and biomolecules are prized for their size-, shape-, and composition-dependent properties and for their solution-based assembly and integration into devices that are enabling unconventional manufacturing and new device functions.
This Perspective builds upon insights from the National Institute of Standards and Technology (NIST)-organized workshop, “Materials and Metrology Needs for Advanced Semiconductor Packaging Strategies,” held at the 35th annual Electronics Packaging Symposium in Binghamton, NY, on September 5, 2024. It outlines critical challenges and opportunities related to polymer-based “soft” materials in advanced semiconductor packaging, with emphasis on polymer science, measurement science (metrology), and the strategic development of Research-Grade Test Materials (RGTMs). These efforts, led by the NIST CHIPS team, aim to advance the fundamental understanding of structure-property-processing relationships, promote standardized guidelines and innovative methods for material characterization, and accelerate the development, qualification, and adoption of next-generation packaging materials. The Perspective also distills key insights from the panel discussion with industry experts, emphasizing the need for close collaboration among materials scientists, process engineers, and metrology experts to enable a holistic strategy, further highlighting the importance of cross-sector partnerships among industry, academia, and government to address pressing challenges in packaging materials and processes.
Notably, metasurfaces have attracted significant attention owing to their broad capability to achieve exotic electromagnetic responses, and their potential as optical devices for wavefront control. Wide ranging materials may be used to form metasurfaces including noble and non-noble metals, oxides, ceramics, phase change materials, and semiconductors, permitting versatile and reconfigurable properties ideal for applications. In particular, applications that affect the science and technology of light—i.e., photonics—are of interest and will continue to grow in importance as our society becomes more digitally connected, but yet environmentally conscious.
This work expands upon previous research related to transfer printed virtual substrates: a technique for generating low-cost engineered substrates that is not based on wafer reuse. Here, silicon and sapphire are evaluated as candidate low-cost handle materials, validated by metal organic chemical vapor deposition regrowth of GaAs single-junction solar cells. Resulting devices are studied via materials and electrical characterization techniques, including concentration measurements that indicate GaAs//sapphire TPVS open-circuit voltage at >10 suns comparable with identical devices grown on a prime GaAs substrate.
Thallium bromide (TlBr) is a promising material for semiconductor gamma-ray detectors due to its high atomic number (Tl = 81, Br = 35), high density (7.56 g/cm 3 ), and relatively low melting point (460 °C). These properties give TlBr several competitive features, including high detection efficiency, good energy resolution, and lower fabrication costs, making it suitable for applications requiring compact, highly sensitive gamma-ray detection systems. Recent developments of TlBr detectors have progressed toward thicker crystals, up to 10–20 mm, configured as pixelated or virtual Frisch-grid (VFG) devices with volumes >1 cm 3 . Despite these advances, challenges remain in practical implementation, including material and fabrication issues that affect energy resolution, device stability, performance, and longevity. These challenges are similar to those faced by HgI 2 and lead-halide perovskite detectors. Here, this study presents results from characterizing over 100 position-sensitive 5×5×12 mm 3 virtual Frisch-grid detectors fabricated by Radiation Monitoring Devices Inc. For a prototype Radioisotope Identification Device (RIID). The work identified factors limiting the performance and longevity of TlBr detectors, including stochastic response variations that limit the energy resolution to 2–3 % (at 662 keV) for most devices, performance degradation associated with defect decoration, and contact delamination. Addressing these issues advances the use of TlBr and similar materials for reliable, high-resolution gamma-ray spectroscopy.
Here, bulk GeAs 2 was synthesized utilizing a vapor transport reaction with iodine. Thermal stability tests under dynamic conditions show that GeAs 2 decomposes below 700 K, in contrast to the reported congruent melting at 1029 K measured at saturated As vapor pressure. GeAs 2 is a p-type narrow bandgap (~0.4 eV) semiconductor. From a thermoelectric standpoint, GeAs 2 outperforms previous computational predictions in thermopower and thermal conductivity. Yet, electrical resistivity is significantly higher than predicted values, resulting in the low overall thermoelectric figure of merit. Aliovalent doping strategies for GeAs 2 should be developed to achieve reasonable thermoelectric performance.
We report point defects and compensation in zinc telluride have been subjects of study for several decades due to the compound’s scientific/technological applications. Despite this, there remains some disagreement in the literature as to the fine details of its defect chemistry. Recently, it has also come under renewed interest due to the emerging Cd( 1–x )Zn x Te( 1–y )Se y material family, used in nuclear radiation detector applications. In this article, we use state-of-the-art computational tools to re-examine the native defect chemistry of ZnTe and explore how it changes upon addition of selenium using density functional theory with screened hybrid exchange–correlation functionals, thermochemical models of the equilibration environment, and statistical mechanics models of the point defect ensemble.
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