We demonstrate a novel displacement etch technique for epitaxial GaAsSb quantum dot formation with density tunability spanning three orders of magnitude and telecommunications wavelength emission at 1550 nm.

Fracture of second-phase particles is a prominent mechanism for void nucleation linked to ductile rupture in structural metals and metal matrix composites. Following the fracture event, such a void becomes shielded by the two halves of the broken inclusion, drastically influencing its growth behavior. However, the plasticity mechanisms that enable axial and transverse growth of these voids remain elusive. This work provides insights into these processes by leveraging experimental characterization of void morphologies in aluminum alloy 2219-T851 and molecular dynamics simulations of void growth tracking dislocation evolution. Notably, following inclusion fracture and elastic recovery, void growth is driven by dislocation absorption at the free surfaces and the nearby matrix-inclusion interface, rather than by dislocation emission. Axial growth is accommodated without the need for prismatic loops by the absorption of dislocations from different slip systems, which allow for the necessary atomic displacements while minimizing disruptions to the interface structure. Cross-slip facilitates dislocation activity in these regions, further promoting void growth. As stress triaxiality increases, transverse growth is driven by the absorption of prismatic loops with dislocation segments that glide independently, followed by extension of the void along the matrix-inclusion interface. These findings demonstrate voids nucleated via inclusion fracture follow very distinct micromechanics from those of unconstrained voids, and provide a more complete picture of the void growth process with potential to inform the development of better models of damage evolution and mitigation strategies.

During operation, power electronics generate large heat fluxes, and therefore, controlling temperature is key to improving performance and preventing failure. To lower operation temperature in power electronics, substantial attention has focused on placing the semiconductor material, such as gallium nitride (GaN), in close proximity to a high thermal conductivity solid heat sink. Here, diamond is the intuitive selection, having an exceptionally high thermal conductivity (>2000 W/m K); however, poor GaN-diamond thermal boundary conductance (TBC) can ultimately limit performance. Here, we provide comprehensive characterization of a vertically-integrated GaN-diamond architecture, consisting of a 260 nm gold bond, using hyperspectral frequency domain thermoreflectance imaging. Thermal model parameter uncertainty is propagated through fitting using a Monte Carlo method, which results in a highly asymmetric distribution for the subsurface GaN-diamond TBC. A three parameter fit that includes non-uniformity in GaN's thermal conductivity substantiated by hyperspectral confocal Raman stress mapping, results in a GaN-diamond TBC greater than 144 MW/m(2)K. Taken together, this work provides a rigorously determined value for the GaN-diamond TBC in a vertical power device as well as a comprehensive methodology to approach subsurface TBC analysis.

GeSn is a group-IV alloy with immense potential to advance microelectronics technology due to its intrinsic compatibility with existing Si CMOS processes. With a sufficiently high Sn composition, GeSn is classified as a direct bandgap semiconductor. Polycrystalline GeSn holds several additional advantages, including its significantly lower synthesis cost compared to its epitaxial counterpart, as well as the versatility to grow these films on a variety of substrates. Here, we present a polycrystalline thin-film GeSn phototransistor on a fused silica substrate with a Sn composition of ∼10%, showing a photoresponse in the short-wave infrared wavelength range, critical for emerging sensing applications. This device shows a gate-tunable response, with responsivities approaching up to 1.7 mA/W with only a 30 nm-thick GeSn layer. Furthermore, phototransistors offer additional adaptability through gating, which allows for the reduction of dark current. This not only enhances the signal-to-noise ratio but also offers more flexible integration with various image sensor readout implementations using different substrates. The specific detectivity of this phototransistor is within an order of magnitude of those of previously reported GeSn photodetectors grown by molecular beam epitaxy and chemical vapor deposition, even though the absorber is 3 to 20× thinner while the electrode spacing for photocarrier transport is approximately 15× longer than the carrier diffusion length in this work, showing great potential benefits of extending similar device structures to epitaxial GeSn layers. As these GeSn phototransistors utilize a noncrystalline substrate, our work establishes a fundamentally more versatile path toward monolithically integrated GeSn-based photodetectors for next-generation multimodal sensors.

Photoinitiated polymerization enables spatiotemporal control of reaction conditions and can thereby generate materials with high complexity while consuming minimal energy. Where ring opening metathesis polymerization (ROMP) is concerned, photo-activated processes are typically enabled by chemical inhibition of ruthenium carbenes via the careful design of complexed ligands such that photoactivation can proceed through an isomerization or ligand dissociation event. In this contribution, we have explored a new approach to photoinitiation of ROMP based on physical inhibition through microencapsulation and controlled release of metathesis catalysts. Micron-sized particles of poly(phthalaldehyde) (PPA), catalyst, and photoacid generator were fabricated by spray drying. The particles were dispersed in dicyclopentadiene monomer, after which polymerization was initiated through temperature or UV exposure, both inducing depolymerization of the PPA particles and in situ catalyst release. The monomer/particle dispersions were found to be stable and reproducibly polymerizable with 3 weeks of storage at room temperature. Furthermore, the dispersions can be used for both photo- and thermal-initiated frontal ROMP, yielding a polymerized thermoset of equivalent properties to conventional bulk- and frontally-polymerized analogues. This work will ultimately enable new manufacturing techniques for ROMP-based materials, due to the modular, easily tunable nature of the underlying initiating system and its unparalleled stability.

Bonding diamond to the back side of gallium nitride (GaN) electronics has been shown to improve thermal management in lateral devices; however, engineering challenges remain with the bonding process and characterizing the bond quality for vertical device architectures. Here, integration of these two materials is achieved by room-temperature compression bonding centimeter-scale GaN and a diamond die via an intermetallic bonding layer of Ti/Au. Recent attempts at GaN/diamond bonding have utilized a modified surface activation bonding (SAB) method, which requires Ar fast atom bombardment immediately followed by bonding within the same tool under ultrahigh vacuum (UHV) conditions. The method presented here does not require a dedicated SAB tool yet still achieves bonding via a room-temperature metal-metal compression process. Imaging of the buried interface and the total bonding area is achieved via transmission electron microscopy (TEM) and confocal acoustic scanning microscopy (C-SAM), respectively. The thermal transport quality of the bond is extracted from spatially resolved frequency-domain thermoreflectance (FDTR) with the bonded areas boasting a thermal boundary conductance of >100 MW/m2·K. Additionally, Raman maps of GaN near the GaN-diamond interface reveal a low level of compressive stress, <80 MPa, in well-bonded regions. FDTR and Raman were coutilized to map these buried interfaces and revealed some poor thermally bonded areas bordered by high-stress regions, highlighting the importance of spatial sampling for a complete picture of bond quality. Overall, this work demonstrates a novel method for thermal management in vertical GaN devices that maintains low intrinsic stresses while boasting high thermal boundary conductances.

Complex oxide thin films cover a range of physical properties and multifunctionalities that are critical for logic, memory, and optical devices. Typically, the high-quality epitaxial growth of these complex oxide thin films requires single crystalline oxide substrates such as SrTiO3 (STO), MgO, LaAlO3, a-Al2O3, and many others. Recent successes in transferring these complex oxides as free-standing films not only offer great opportunities in integrating complex oxides on other devices, but also present enormous opportunities in recycling the deposited substrates after transfer for cost-effective and sustainable processing of complex oxide thin films. In this work, the surface modification effects introduced on the recycled STO are investigated, and their impacts on the microstructure and properties of subsequently grown epitaxial oxide thin films are assessed and compared with those grown on the pristine substrates. Detailed analyses using high-resolution scanning transmission electron microscopy and geometric phase analysis demonstrate distinct strain states on the surfaces of the recycled STO versus the pristine substrates, suggesting a pre-strain state in the recycled STO substrates due to the previous deposition layer. These findings offer opportunities in growing highly mismatched oxide films on the recycled STO substrates with enhanced physical properties. Specifically, yttrium iron garnet (Y3Fe5O12) films grown on recycled STO present different ferromagnetic responses compared to that on the pristine substrates, underscoring the effects of surface modification. The study demonstrates the feasibility of reuse and redeposition using recycled substrates. Via careful handling and preparation, high-quality epitaxial thin films can be grown on recycled substrates with comparable or even better structural and physical properties toward sustainable process of complex oxide devices.

Heat-treated FeCo-based magnetic alloys were characterized using a suite of electron microscopy techniques to gain insight into their structural properties. Electron channeling contrast imaging (ECCI) in the scanning electron microscope (SEM) found unique grains towards the outer edge of a FeCo sample with nonuniform background contrast. High-magnification ECCI imaging of these nonuniform grains revealed a weblike network of defects that were not observed in standard uniform background contrast grains. High-resolution electron backscattered diffraction (HR-EBSD) confirmed these defect structures to be dislocation networks and additionally found subgrain boundaries within the nonuniform contrast grains. The defect content within these grains suggests that they are unrecrystallized grains, and ECCI can be used as a rapid method to quantify unrecrystallized grains. To demonstrate the insight that can be garnered via ECCI on these unique grains, the sample was imaged before and after micro indentation. This experiment showed that slip bands propagate throughout the material until interacting with the dislocation networks, suggesting that these specific defects provide a barrier to plastic deformation. Taken together, these results show how ECCI can be used to better understand failure mechanisms in alloys and provides further evidence that dislocation networks play a critical role in the brittle failure of FeCo alloys.

Journal Article 3D Chemical Mapping via P-FIB Tomography and Machine Learning Get access Paul G Kotula, Paul G Kotula Sandia National Laboratories, Albuquerque, NM, USA Corresponding author: paul.kotula@sandia.gov Search for other works by this author on: Oxford Academic Google Scholar Andrew T Polonsky, Andrew T Polonsky Sandia National Laboratories, Albuquerque, NM, USA Search for other works by this author on: Oxford Academic Google Scholar Daniel Perry, Daniel Perry Sandia National Laboratories, Albuquerque, NM, USA Search for other works by this author on: Oxford Academic Google Scholar Damion Cummings, Damion Cummings Sandia National Laboratories, Albuquerque, NM, USA Search for other works by this author on: Oxford Academic Google Scholar Julia I Deitz, Julia I Deitz Sandia National Laboratories, Albuquerque, NM, USA Search for other works by this author on: Oxford Academic Google Scholar Joseph R Boro, Joseph R Boro Sandia National Laboratories, Albuquerque, NM, USA Search for other works by this author on: Oxford Academic Google Scholar Dustin Ellis Dustin Ellis Sandia National Laboratories, Albuquerque, NM, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 539–540, https://doi.org/10.1093/micmic/ozad067.254 Published: 22 July 2023

As scaling for CMOS transistors asymptotically approaches the end of Moore's Law, the need to push into 3D integration schemes to innovate capabilities is gaining significant traction. Further, rapid development of new semiconductor solutions, such as heterogeneous integration, has turned the semiconductor industry's consistent march towards next generation products into new arenas. In 2018, the Department of Energy Office of Science (DOE SC) released their "Basic Research Needs for Microelectronics," communicating a strong push towards "parallel but intimately networked efforts to create radically new capabilities,"1 which they have coined as "co-design."

We report an unusual artifact induced by Ga+ or Xe+ focused ion beam (FIB) preparation in transmission electron microscopy (TEM) samples with epitaxial layers on a GaSb substrate. The Ga+ FIB-ed TEM samples with a quantum structure made of Al/AlSb/GaSb/InAs/Al0.33Ga0.67Sb multilayers on a GaSb substrate are found to undergo phase modifications under certain conditions related to the beam energy. Dependent on the voltage used during thinning, the Al islands initially on top of the multilayer stack are gradually replaced by Ga, leading to the epitaxial formation of AlxGa1-xSb (AlGaSb) quantum dots (QDs) whose shapes are conformed to the initial Al islands. A similar effect is observed when the top Al islands are capped by an amorphous As layer. The artifacts can be avoided by extensive thinning at 5 kV followed by 2 kV polishing. Further experiments using Xe+ plasma FIB (PFIB) also produce similar artifacts, and those effects are eliminated by Xe+ PFIB under cryogenic conditions regardless of the beam conditions. The mechanism for forming the epitaxial AlGaSb QDs is investigated, and potential use of this phenomenon for QD fabrication is discussed.

Nanostructured plasmonic-magnetic metamaterialshave gainedgreat research interest due to their enhanced magneto-optical couplingeffects. Here, we report a complex three-phase nanocomposite designcombining ferromagnetic CoFe2 with plasmonic TiN and Auas a multifunctional hybrid metamaterial using either a cogrowth ora templated method. Via the first method of cogrowing three phases,three different morphologies of Au-CoFe2 core-shellnanopillars were formed in the TiN matrix. Via the second method ofsequential deposition of a TiN-Au seed layer and a TiN-CoFe2 layer, highly ordered and uniform single-type core-shellnanopillars (i.e., the CoFe2 shell with a Au core) formin the TiN matrix. Both cogrowth and templated growth TiN-CoFe2-Au hybrid systems exhibit excellent epitaxial quality,hyperbolic dispersion, magnetic anisotropy, and a magneto-opticalcoupling effect. This study provides an effective approach for achievinghighly uniform multiphase vertically aligned nanocomposite structureswith well-integrated optical, magnetic, and coupling properties.

Metamaterials have gained great research interest in recent years owing to their potential for property tunability, multifunctionality, and property coupling. As a new group of self‐assembled thin films, vertically aligned nanocomposite (VAN)‐based hybrid metamaterials have been demonstrated with significant anisotropic physical properties and a broad range of property tailorability, such as optical anisotropy, magnetic anisotropy, hyperbolic dispersion, and enhanced second harmonic generation properties. Herein, self‐assembled ZrO 2 ‐Co nanocomposite films, with high epitaxial quality and ultra‐fine vertically aligned Co nanopillars (with an average diameter of ≈2 nm) embedded in a ZrO 2 matrix, are fabricated using a pulsed laser deposition (PLD) method. The Co pillar density can be effectively tuned by varying the Co concentration in the target, which results in tunable optical properties and magnetic properties. Specifically, a high saturation magnetization of 100 emu cm −3 , strong out‐of‐plane magnetic anisotropy and tailorable magnetization properties are achieved via tuning the Co nanopillar density. Coupled with hyperbolic dispersion of dielectric constant from 950 to 1500 nm in wavelength, plasmonic Co metal nanopillars, and the unique dielectric ZrO 2 matrix, this new nanoscale hybrid metamaterial shows great potential for future integrated optical and magnetic device designs.

As scaling for CMOS transistors asymptotically approaches the end of Moore's Law, the need to push into 3D integration schemes to innovate capabilities is gaining significant traction. Further, rapid development of new semiconductor solutions, such as heterogeneous integration, has turned the semiconductor industry's consistent march towards next generation products into new arenas. In 2018, the Department of Energy Office of Science (DOE SC) released their "Basic Research Needs for Microelectronics," communicating a strong push towards "parallel but intimately networked efforts to create radically new capabilities,"1 which they have coined as "co-design." Advanced packaging and heterogeneous integration, particularly with mixed semiconductor materials (e.g., CMOS FPGAs & GaN RF amplifiers) is a realm ripe for applicability towards DOE SC's co-design call to action. In theory, development occurring at all scales across the semiconductor ecosystem, particularly across disciplines that are not traditionally adjacent, should significantly accelerate innovation. In reality, co-design requires a paradigm shift in approach, requiring not only interconnected parallel development. Further, accurate ground truth data during learning cycles is critical in order to effectively and efficiently communicate across disparate disciplines and advise design iterations across the microelectronics ecosystem. This talk will outline three orthogonal facets towards co-design for HI: (1) on-going efforts towards development of materials characterization and failure analysis techniques to enable accurate evaluation of materials and heterogeneously integrated components, (2) development of artificial intelligence & machine learning algorithms for large scale, high throughput process development and characterization, and (3) development of capabilities for rapid communication and visualization of data across disparate disciplines.