Bulk Substrate Research Articles

Specific Features of Matching of a Lower Electrode and an RF Bias Generator for Reactive Ion Etching of Bulk Substrates

Specific Features of Matching of a Lower Electrode and an RF Bias Generator for Reactive Ion Etching of Bulk Substrates

Extended bound states in the continuum in a one-dimensional grating implemented on a distributed Bragg reflector

Abstract Bound states in the continuum (BICs) are observed in optical cavities composed of a high refractive index periodic structure embedded in significantly lower refractive index surroundings, enabling vertical confinement of the grating modes. Here, we propose a vertically nonsymmetric configuration, implemented on a high refractive index bulk substrate with a one-dimensional grating positioned on a distributed Bragg reflector (DBR). In this configuration, the grating modes are leaky, which could prohibit the creation of a BIC if the grating was implemented on uniform substrate. However, the judiciously designed DBR on which the grating is implemented reflects nonzero diffraction orders induced by the grating. We found that the laterally antisymmetric optical modes located at the center of the Brillouin zone of this structure create BICs that are robust against changes in the grating parameters, as long as the DBR reflects the diffraction orders. The configuration enables a high degree of design freedom, facilitating the realization of very high quality factor cavities in conventional all-semiconductor technology.

Analysis of electrical properties in Ni/GaN schottky contacts on nonpolar/semipolar GaN free-standing substrates

This work focuses on the electrical properties of Ni/n-GaN Schottky barrier diodes (SBDs) fabricated on GaN bulk substrates with different crystal orientations. For the SBDs on a-plane, m-plane, and s5-plane GaN, the Schottky barrier heights (SBHs) exhibited magnitudes of 0.65 eV, 0.69 eV, and 0.75 eV, respectively. The relatively small SBH of a-plane devices results in a relatively larger reverse leakage current than that of m-plane and s5-plane. In addition, the carrier concentrations extracted by C–V characteristics are comparable for the GaN substrates with different crystal orientations. The temperature-dependent I–V characteristics indicate how the barrier inhomogeneity of the Ni/GaN Schottky contacts on the a-plane GaN is smaller than the others. Based on the XPS spectra results, the discrepancy in Schottky contact characteristics stems from the different polarization charges and/or surface oxides of the different crystal planes. The low GaOx density on a-plane GaN surface contributes to the minimum barrier inhomogeneity of the corresponding SBD devices.

Using multi-polar scattering and near-field plasmonic resonances to achieve optimal emission enhancement from quantum emitters embedded in dielectric pillars

Recently, high refractive index micro-pillars have been widely used for enhancing the fluorescence of quantum emitters (vacancy/defect centers) embedded within the pillar. However, the maximum observed enhancement from these pillars has been limited to about a factor of 10. Within the dielectric pillars, the Purcell enhancement is restricted to around unity, and the fluorescence enhancement is mainly due to the enhancement of the collection efficiency of the dipole emission from inside the pillar if compared to a bulk substrate. Using multi-polar electromagnetic scattering resonances and near-field plasmonic field enhancement/confinement, here we report a simple metal–dielectric pillar resonator scheme to achieve a close to three orders of magnitude fluorescence enhancement from embedded solid state vacancy centers. The scheme comprises a silver (Ag) cylinder fabricated on top of a silicon-carbide (SiC) dielectric pillar, with both the SiC and Ag cylinders having the same diameter. A selective dipole orientation relative to the metal–dielectric interface for emitters close to the SiC pillar’s top surface leads to a large Purcell enhancement of the dipole’s emission. The Ag cylinder was found to function as an efficient resonator as well as an antenna, enhancing as well as directing a significant fraction of the dipole’s emission into far-field free space.

Lapping and polishing of additively manufactured 316L substrates and their effects on the microstructural evolution and adhesion of PVD CrAlN coatings

Laser powder bed fusion (LPBF) enables the manufacturing of three-dimensional parts from metallic powder with a high degree of design-freedom. Due to the low hardness in order to protect tribologically stressed surfaces against severe wear, the surface of LPBF parts made of 316L stainless steel needs to be modified by coating processes such as physical vapor deposition (PVD) using hard coatings. Although 316L is among the most investigated material for LPBF, the deposition of PVD hard coatings such as ternary nitride coatings on additively manufactured 316L substrates has not been studied yet.This study aims at evaluating the effects of lapping and polishing of 316L stainless steel substrates processed by LPBF on the resulting surface integrity and its influence on the microstructural evolution and adhesion of PVD CrAlN coatings. A 316L substrate bulk material served as reference throughout the investigations. The 316L substrate CrAlN coating composites were examined with respect to the microstructural characteristics and residual stresses using nanoindentation and two-dimensional X-ray diffraction. To assess the adhesion of the CrAlN coating on the differently pre-treated 316L substrates, scratch and Rockwell C adhesion tests were conducted. The resulting scratch tracks and Rockwell C indents were metallographically examined in order to determine the failure modes. The results demonstrate that the deposited PVD CrAlN coatings differ in their texture and mechanical properties, such as hardness and residual stresses, depending on the 316L substrate surface conditions. The CrAlN coatings generally exhibit good adhesion to both the 316L LPBF substrate and 316L bulk material. However, the findings indicate improved adhesion of CrAlN coatings on lapped 316L substrates. The residual stress gradient at coating-substrate interface and imperfections at the surface of the 316L LPBF substrate are found to primarily influence the performance and failure mode of the CrAlN coating.

Agrin-Matrix Metalloproteinase-12 axis confers a mechanically competent microenvironment in skin wound healing

An orchestrated wound healing program drives skin repair via collective epidermal cell proliferation and migration. However, the molecular determinants of the tissue microenvironment supporting wound healing remain poorly understood. Herein we discover that proteoglycan Agrin is enriched within the early wound-microenvironment and is indispensable for efficient healing. Agrin enhances the mechanoperception of keratinocytes by augmenting their stiffness, traction stress and fluidic velocity fields in retaliation to bulk substrate rigidity. Importantly, Agrin overhauls cytoskeletal architecture via enhancing actomyosin cables upon sensing geometric stress and force following an injury. Moreover, we identify Matrix Metalloproteinase-12 (MMP12) as a downstream effector of Agrin’s mechanoperception. We also reveal a promising potential of a recombinant Agrin fragment as a bio-additive material that assimilates optimal mechanobiological and pro-angiogenic parameters by engaging MMP12 in accelerated wound healing. Together, we propose that Agrin-MMP12 pathway integrates a broad range of mechanical stimuli to coordinate a competent skin wound healing niche.

(Invited) Impact of Processing Factors on the Low-Frequency Noise of Gate-All-Around Silicon Vertical Nanowire FETs

Future CMOS technology nodes will rely on Gate-All-Around (GAA) FETs with ultimate control over the short-channel effects. In this class of devices, GAA Vertical Nanowires (VNWs) offer some clear integration advantages over horizontal architectures. In addition, some operational parameters are also favourable, like, the low-frequency (LF) noise, as shown recently [1]-[3]. In this work, an overview will be given of the impact of certain processing factors on the noise spectrum and magnitude of silicon GAA VNW FETs.Silicon NWs with a diameter of ~45 (50) nm have been epitaxially grown on either bulk or Silicon-On-Insulator (SOI) substrates. They are either undoped (intrinsic) or in-situ B/P-doped (p/nMOS), resulting in the latter case in a Junctionless (JL) structure. For the “bulk” devices an in-situ B-doped (or P-doped) silicon back contact has been deposited as source electrode, while an in-situ B-doped SiGe source was grown on SOI (pFETs). In both cases, a highly B-doped SiGe (or P-doped silicon) drain was deposited on the 90 nm long NWs to reduce the series resistance. LF noise measurements have been performed as described elsewhere [1],[2], in linear operation (|VDS|=0.05 mV), for a current range from about 10 nA to a few mA. Spectra have been recorded in Forward (F) mode or in Reverse (R) mode, with source and drain switched.The impact of the width of the RMG cap, shown in Fig. 1 on the F noise of GAA VNW nFETs has been reported before [1], showing that the use of a wide cap results in a lower input-referred voltage noise PSD (SVG) (Fig. 2). The asymmetry in SVG at f=10 Hz in F and R operation of GAA VNW pFETs is represented in Fig. 3 (bulk source) and Fig. 4 (SOI). While significantly lower noise is observed in R operation for “bulk”, insignificant differences are seen for the SOI pFETs. At the same time, the PSD is generally lower for the bottom source (bulk) compared with a SiGe source on SOI (Fig. 5). More detailed analysis reveals that the 1/f noise is dominated by mobility fluctuations (Dm) for VNW pFETs on bulk substrates [2]. The situation is more complicated for SOI pFETs a shown in Fig. 6 and depends on the channel doping density. In weak inversion (low ID), either Dn or Dm fluctuations can prevail. At higher ID, access resistance (RS) starts to dominate the 1/f noise behaviour. Finally, also the in-situ B doping density plays a significant role in the LF noise mechanism of the JL channels (Fig. 6), offering several technology knobs to optimize the 1/f noise performance.[1] E. Simoen, A. Chasin, P. Matagne, E. Rosseel, A. Hikavyy, R. Loo, P. Favia, H. Bender, E. Vancoille and A. Veloso, ECS Trans., 97 (5), pp. 59-64 (2020).[2] E. Simoen et al., submitted to Solid-State Electron.[3] T. Imamoto, Y. Ma, M. Muraguchi and T. Endoh, Jpn. J. Appl. Phys., 54, p. 04DC11 (2015). Figure 1

(Invited) Recent Progress on Selective Area Regrowth and Doping for Vertical GaN Power Transistors

Wide bandgap semiconductor GaN is a very promising candidate for efficient power conversion applications due to its large bandgap energy and high critical electric field. Vertical GaN power devices grown on bulk substrates are enabling the next-generation power electronics with higher efficiency, higher power density and smaller form factor. However, selective area doping in GaN is far from mature, which is limiting the realization of many advanced GaN power devices such as vertical junction effect transistors (VJFETs), junction barrier Schottky (JBS), superjunction, and junction termination extension (JTE). Epitaxial regrowth or selective area regrowth has been regarded as one of the most promising routes to selective area doping.Currently, the regrown p-n junctions suffer from large leakage currents and premature breakdown. To understand this phenomena, the regrowth experiments were carried out by metalorganic chemical vapor deposition via an etching-then-regrowth process. The etching was performed by inductively coupled plasma (ICP) etching. The regrowth dynamics with different trench widths and depths was revealed, where basal plane and lateral growth modes were identified. It was also found that shallow trenches for selective area regrowth was beneficial for reducing the reverse leakage currents of regrown p-n junctions.The regrowth interface plays a critical role in understating the leakage mechanism of regrown p-n junctions. With developed material characterization techniques, the regrown structures and interface were analyzed in detail. Cathodoluminescence (CL) and secondary electrons (SEs) were used to realize both lateral and vertical dopant profiling at a sub-micron scale [1]. The regrowth interface by dry etching accumulated lots of impurities and charges, contributing to the formation of a p+-n+ tunneling junction. This was further confirmed by the electrostatic potential profile at the regrowth interface using electron holography [2]. This tunneling junction is likely to be the major contributor to the large reverse leakage currents and low breakdown voltages in regrown junctions. To improve the regrowth interface, novel etching technologies were demonstrated. It was found that low-power dry etching significantly reduced the interfacial charges and the reverse leakage currents of regrown p-n junctions [3]. Atomic layer etching (ALE) was also successfully developed for GaN, which uses self-limiting chemical processes, thus removing the damaged layers without inducing further etching damage. The tertiarybutylchloride (TBCl) based in situ etching may serve as an alternative etching method to dry etching with reduced etching damage [4]. In terms of devices, regrown p-n junctions with low leakage currents [3] and the first normally-off VJFETs were demonstrated. Further improvements in selective area regrowth and associated devices can be expected via regrowth optimization and regrowth interface engineering via surface treatments and low-damage etching. These results represent an important step towards realizing selective area doping for GaN power transistors. H. Liu et al., Appl. Phys. Lett., 114, 082102 (2019)S. Alugubelli, et al., Appl. Phys. Lett., 115, 201602 (2019)K. Fu et al., IEEE Electron Device Lett. 40, 1728 (2019)B. Li et al., Appl. Phys. Lett., 115, 162101 (2019)

Engineering of cis-Element in Saccharomyces cerevisiae for Efficient Accumulation of Value-Added Compound Squalene via Downregulation of the Downstream Metabolic Flux.

Transcriptional downregulation is widely used for metabolic flux control. Here, marO, a cis-element of Escherichia coli mar operator, was explored to engineer promoters of Saccharomyces cerevisiae for downregulation. First, the ADH1 promoter (PADH1) and its enhanced variant PUADH1 were engineered by insertion of marO into different sites, which resulted in decrease in both gfp5 transcription and GFP fluorescence intensity to various degrees. Then, marO was applied to engineer the native ERG1 and ERG11 promoters due to their importance for accumulation of value-added intermediates squalene and lanosterol. Elevated squalene content (4.9-fold) or lanosterol content (4.8-fold) and 91 or 28% decrease in ergosterol content resulted from the marO-engineered promoter PERG1(M5) or PERG11(M3), respectively, indicating the validity of the marO-engineered promoters in metabolic flux control. Furthermore, squalene production of 3.53 g/L from cane molasses, a cheap and bulk substrate, suggested the cost-effective and promising potential for squalene production.

Understanding and exploiting acoustic field-microswimmer interactions in acoustofluidic devices

Acoustic microfluidic devices offer exquisite control for manipulation of objects sized from tens of nanometers to tens of microns. Our work focuses on applying various acoustofluidic solutions to understand microswimmer behavior and the mechanisms underlying the beating of propulsive cilia/flagella. Ultrasonic trapping in bulk acoustic wave (BAW) and substrate acoustic wave (SAW) fields enables observation of swimming without constraining rotational degrees of freedom and without damaging the cells. Here, we summarize recent studies using biciliate C. reinhardtii algae cells, including three-dimensional body motion, synchronization/asynchronization of cis and trans cilia waveforms, and thermal and fluid-property effects. Acoustofluidic approaches provide unprecedented flexibility as a tool to investigate cell motility. Conversely, acoustic field-microswimmer interactions can also be exploited by applying the C. reinhardtii cells as dynamic probes to assess acoustofluidic device performance. We have previously reported use of these cells to identify optimal resonant frequencies of operation and to qualitatively map the strength of the acoustic field in BAW devices. Here, we extend the method to quantify the acoustic energy density of a straight microchannel operating at the first half-wavelength resonance, achieving agreement within 1 % to a standard method based on passive particle tracking. New applications for SAW devices are also presented.

Exceptional Elasticity of Microscale Constrained MoS2 Domes.

The outstanding mechanical performances of two-dimensional (2D) materials make them appealing for the emerging fields of flextronics and straintronics. However, their manufacturing and integration in 2D crystal-based devices rely on a thorough knowledge of their hardness, elasticity, and interface mechanics. Here, we investigate the elasticity of highly strained monolayer-thick MoS2 membranes, in the shape of micrometer-sized domes, by atomic force microscopy (AFM)-based nanoindentation experiments. A dome’s crushing procedure is performed to induce a local re-adhesion of the dome’s membrane to the bulk substrate under the AFM tip’s load. It is worth noting that no breakage, damage, or variation in size and shape are recorded in 95% of the crushed domes upon unloading. Furthermore, such a procedure paves the way to address quantitatively the extent of the van der Waals interlayer interaction and adhesion of MoS2 by studying pull-in instabilities and hysteresis of the loading–unloading cycles. The fundamental role and advantage of using a superimposed dome’s constraint are also discussed.

Hydrogen Bonding Stiffens Peptide Amphiphile Supramolecular Filaments by Aza-Glycine Residues

Peptide amphiphiles (PAs) are a class of molecules comprised of short amino acid sequences conjugated to hydrophobic moieties that may exhibit self-assembly in water into supramolecular structures. We investigate here how mechanical properties of hydrogels formed by PA supramolecular nanofibers are affected by hydrogen bond densities within their internal structure by substituting glycine for aza-glycine (azaG) residues. We found that increasing the number of PA molecules that contain azaG up to 5 mol% in PA supramolecular nanofibers increases their persistence length fivefold and decreases their diffusion coefficients as measured by fluorescence recovery after photobleaching. When these PAs are used to create hydrogels, their bulk storage modulus (G′) was found to increase as azaG PA content in the supramolecular assemblies increases up to a value of 10 mol% and beyond this value a decrease was observed, likely due to diminished levels of nanofiber entanglement in the hydrogels as a direct result of increased supramolecular rigidity. Interestingly, we found that the bioactivity of the scaffolds toward dopaminergic neurons derived from induced pluripotent stem cells can be enhanced directly by persistence length independently of storage modulus. We hypothesize that this is due to interactions between the cells and the extracellular environment across different size scales: from filopodia adhering to individual nanofiber bundles to cell adhesion sites that interact with the hydrogel as a bulk substrate. Fine tuning of hydrogen bond density in self-assembling peptide biomaterials such as PAs provides an approach to control nanoscale stiffness as part of an overall strategy to optimize bioactivity in these supramolecular systems. supramolecular biomaterials. Statement of significanceHydrogen bonding is an important driving force for the self-assembly of peptides in both biological and artificial systems. Here, we increase the amount of hydrogen bonding within self-assembled peptide amphiphile (PA) nanofibers by substituting glycine for an aza-glycine (azaG). We show that increasing the molar concentration of azaG increases the internal order of individual nanofibers and increases their persistence length. We also show that these changes are sufficient to increase survival and tyrosine hydroxylase expression in induced pluripotent stem cell-derived dopaminergic neurons cultured in 3D gels made of these materials. Our strategy of tuning the number of hydrogen bonds in a supramolecular assembly provides mechanical customization for 3D cell culture and tissue engineering.

Cu-based heterostructure photocatalysts derived from Cu sludge and municipal sewage sludge for efficient degradation of 2,4-dichlorophenol

The recycling methods of copper (Cu) from the hazardous waste of Cu sludge including high-temperature melting and extraction often encounter the problems such as the difficulty in getting high-purity Cu, secondary pollution, and the terminal waste treatment. To display the values of Cu sludge more effectively, it is first used as the Cu source to form the Cu0-based (CSS) heterostructure photocatalysts with the reduction property generated from sewage sludge in its carbonization process. In the obtained CSS photocatalysts, the Cu0 particles are in-situ grown on the surface of the sewage sludge active carbon and inorganic materials (Al2O3 or CaSO4) contained bulk substrate particles to provide long-wavelength absorption ability and fully expose the active sites for photocatalysis. The degradation rate of 2,4-dichlorophenol (DCP) upon UV–Vis-NIR irradiation reaches a high value of 95.5% for the optimum CSS sample, which also possesses Vis-NIR and NIR responsive photocatalytic activities. The enhanced photodegradation rates of DCP over the CSS samples compared with those of their individual precursors are attributed to the localized surface plasmon resonance effect of Cu0 and the efficient charge carrier separation between the heterostructures constructed by Cu0 and its surface oxide of CuO, as well as the impurities of Fe2O3, Fe3O4, and Ca2Fe2O5, resulting in the generation of more O2•− radicals and holes for the dechlorination of DCP and the mineralization of the intermediates. The fabrication strategy of the Cu0-based heterostructure photocatalysts with excellent photocatalytic activities exhibits a promising resource utilization method for the high-value application of Cu sludge.

Sensitivity and resistance of amperometric biosensors in substrate inhibition processes

A theoretical model of a sensitivity and resistance of amperometry biosensors with substrate inhibition kinetics is discussed. This model is based on the system of non-stationary diffusion equations containing a non-linear term related to non-Michaelis-Menten kinetics of the enzymatic reaction. This paper presents the approximate analytical expression of sensitivity and resistance of biosensor for small values of reaction diffusion parameters. The effect various parameters such as thickness of enzyme layer, bulk substrate concentration, Michaelis-Menten and saturation constant on sensitivity and resistance of biosensor are discussed.

Gateless and Capacitorless Germanium Biristor with a Vertical Pillar Structure

For the first time, a novel germanium (Ge) bi-stable resistor (biristor) with a vertical pillar structure was implemented on a bulk substrate. The basic structure of the Ge pillar-typed biristor is a p-n-p bipolar junction transistor (BJT) with an open base (floating), which is equivalent to a gateless p-channel metal oxide semiconductor field-effect transistor (MOSFET). In the pillar formation, we adopted an amorphous carbon layer to protect the Ge surface from both physical and chemical damage by subsequent processes. A hysteric current-voltage (I-V) characteristic, which results in a sustainable binary state, i.e., high current and low current at the same voltage, can be utilized for a memory device. A lower operating voltage with high current was achieved, compared to a Si biristor, due to the low energy bandgap of pure Ge.

Quantum photonics in triangular-cross-section nanodevices in silicon carbide

Silicon carbide is evolving as a prominent solid-state platform for the realization of quantum information processing hardware. Angle-etched nanodevices are emerging as a solution to photonic integration in bulk substrates where color centers are best defined. We model triangular cross-section waveguides and photonic crystal cavities using Finite-Difference Time-Domain and Finite-Difference Eigensolver approaches. We analyze optimal color center positioning within the modes of these devices and provide estimates on achievable Purcell enhancement in nanocavities with applications in quantum communications. Using open quantum system modeling, we explore emitter-cavity interactions of multiple non-identical color centers coupled to both a single cavity and a photonic crystal molecule in SiC. We observe polariton and subradiant state formation in the cavity-protected regime of cavity quantum electrodynamics applicable in quantum simulation.

Hybrid Approach for Wood Modification: Characterization and Evaluation of Weathering Resistance of Coatings on Acetylated Wood

Wood, as a biological material, is sensitive to environmental conditions and microorganisms; therefore, wood products require protective measures to extend their service life in outdoor applications. Several modification processes are available for the improvement of wood properties, including commercially available solutions. Among the chemical treatments, acetylation by acetic anhydride is one of the most effective methods to induce chemical changes in the constitutive polymers at the cellular wall level. Acetylation reduces wood shrinkage-swelling, increases its durability against biotic agents, improves UV resistance and reduces surface erosion. However, even if the expected service life for external cladding of acetylated wood is estimated to be 60 years, the aesthetics change rapidly during the first years of exposure. Hybrid, or fusion, modification includes processes where the positive effect of a single treatment can be multiplied by merging with additional follow-up modifications. This report presents results of the performance tests of wood samples that, besides the modification by means of acetylation, were additionally protected with seven commercially available coatings. Natural weathering was conducted in Northern Italy for 15 months. Samples were characterized with numerous instruments by measuring samples collected from the stand every three months. Superior performance was observed on samples that merged both treatments. It is due to the combined effect of the wood acetylation and surface coating. Limited shrinkage/swelling of the bulk substrate due to chemical treatment substantially reduced stresses of the coating film. Hybrid process, compared to sole acetylation of wood, assured superior visual performance of the wood surface by preserving its original appearance.

(Invited) Integration of 2D Materials in Van Der Waals Photonic Heterostructures

Recently, significant attention has been focused at photonic properties of vertical heterostructures of two-dimensional (2D) materials which is driven by large range of their applications in sensing and information technology. In this work, the Van der Waals heterostructures were produced by integration of CVD grown 2D MoS2 with transferred monolayer graphene. Each of 2D layers possesses its own surface electromagnetic (optical) modes. While in the photonic heterostructure these modes are strongly coupled. Scattering-type scanning near-field optical microscopy allows to visualize 2D surface polaritons, as well as their hybridization with the resonances of the bulk substrate polaritons. Using excitation frequencies well below substrate resonances, a signature of charge transfer in van der Waals heterostructures with nanometer resolution was obtained.Acknowledgement: Authors acknowledge the JSNN, a member of the Southeastern Nanotechnology Infrastructure Corridor (SENIC) and National Nanotechnology Coordinated Infrastructure (NNCI), supported by the NSF (ECCS-1542174), The PSU Two-Dimensional Crystal Consortium – Materials Innovation Platform 2DCC-MIP, supported by NSF cooperative agreement (DMR-1539916). S.V.R. acknowledges PSU MRSEC supported by NSF (DMR-2011839). Authors are grateful to Dr. S. Aravamudhan (JSNN) and Dr. J. Redwing (2DCC-MIP).

Xenon Plasma Focused Ion Beam Milling for Obtaining Soft X-ray Transparent Samples

We employ xenon (Xe) plasma focused ion beam (PFIB) milling to obtain soft X-ray transparent windows out of bulk samples. The use of a Xe PFIB allows for the milling of thin windows (several 100 nm thick) with areas of the order of 100 µm × 100 µm into bulk substrates. In addition, we present an approach to empirically determine the transmission level of such windows during fabrication by correlating their electron and soft X-ray transparencies. We perform scanning transmission X-ray microscopy (STXM) imaging on a sample obtained by Xe PFIB milling to demonstrate the conceptual feasibility of the technique. Our thinning approach provides a fast and simplified method for facilitating soft X-ray transmission measurements of epitaxial samples and it can be applied to a variety of different sample systems and substrates that are otherwise not accessible.

Unusual layer-by-layer growth of epitaxial oxide islands during Cu oxidation

Elucidating metal oxide growth mechanisms is essential for precisely designing and fabricating nanostructured oxides with broad applications in energy and electronics. However, current epitaxial oxide growth methods are based on macroscopic empirical knowledge, lacking fundamental guidance at the nanoscale. Using correlated in situ environmental transmission electron microscopy, statistically-validated quantitative analysis, and density functional theory calculations, we show epitaxial Cu2O nano-island growth on Cu is layer-by-layer along Cu2O(110) planes, regardless of substrate orientation, contradicting classical models that predict multi-layer growth parallel to substrate surfaces. Growth kinetics show cubic relationships with time, indicating individual oxide monolayers follow Frank-van der Merwe growth whereas oxide islands follow Stranski-Krastanov growth. Cu sources for island growth transition from step edges to bulk substrates during oxidation, contrasting with classical corrosion theories which assume subsurface sources predominate. Our results resolve alternative epitaxial island growth mechanisms, improving the understanding of oxidation dynamics critical for advanced manufacturing at the nanoscale.