Solid-state Dewetting Research Articles

In Situ Solid-State Dewetting of Ag-Au-Pd Alloy: From Macro- to Nanoscale.

Metal alloy nanostructures represent a promising platform for next-generation nanophotonic devices, surpassing the limitations of pure metals by offering additional "buttons" for tailoring their optical properties by compositional variations. While alloyed nanoparticles hold great potential, their scalability and underexplored optical behavior still limit their application. Here, we establish a systematic approach to quantifying the unique optical behavior of the AgAuPd ternary system while providing a direct comparison with its pure constituent metals. Computationally, we analyze their electronic structure and uncover the transition of Pd d states to Pd/Ag hybridized s states in the bulk form, explaining the similar optical properties observed between Pd and AgAuPd. Experimentally, we fabricate pure metal and fully alloyed nanoparticles through solid-state dewetting, a scalable method. During the process, we trace the optical transition in the systems from the initial thin film stage to the final nanoparticle stage with in situ ellipsometry. We reveal the interplay between optical properties influenced by chemical interdiffusion and localized surface plasmon resonance arising from morphological changes with ex situ surface characterizations. Additionally, we analytically implement a metallic layer derived from the ternary system in a trilayer device, resulting in a single-time and irreversible color filter, to demonstrate an application encompassing a lithography-free and cost-effective route for nanophotonic devices.

As-deposited and dewetted Cu layers on plasma treated glass: Adhesion study and its effect on biological response

Improving the adhesion of nanosized copper films to a glass substrate is vital for their application in electronics and medicine, as it enhances their overall reliability. For this purpose, we employed Ar plasma etching (240 s) and magnetron sputtering to create copper layers on a glass substrate. Furthermore, we investigated the effect of subsequent solid state dewetting (at 300 °C) of Cu nanolayers on the interface stability. Increasing the sputtering time resulted in elevated copper concentration, UV-Vis absorption, conductivity, and surface roughness. The as-deposited and dewetted samples exhibited very good wettability with water contact angles below 60°. Importantly, plasma treatment improved the adhesion of the Cu layers to the glass. Subsequent dewetting accelerated surface diffusion and the oxidation of Cu atoms, causing structural and morphological changes. The presence of CuO after dewetting caused loss of the surface plasmon resonance (SPR) band in the UV-Vis spectrum and a decrease in sample conductivity due to the transformation of the copper layer from a metal to an oxide. Biological testing revealed a more pronounced bactericidal effect for the as-deposited Cu layer against E. coli and S. epidermidis on contrary to dewetted samples. The similar cytotoxic trend was observed for human dermal fibroblasts and hepatocytes. Nonetheless, biological testing confirmed better cell adhesion on dewetted Cu layers compared to the as-deposited ones. Therefore, our copper nanostructured samples could find application as antibacterial coatings of biomedical devices.

A level-set method for simulating solid-state dewetting in systems with strong crystalline anisotropy

Accurately modeling solid-state dewetting in materials with strong crystalline anisotropy is an open problem in materials science with importance for both the manufacturing and reliability of nano-scale devices. In this work, we propose and demonstrate a level-set method framework for simulating solid-state dewetting which is capable of modeling systems with strongly anisotropic surface energies and diffusivities. Surface energy anisotropy is handled through the use of the Cahn-Hoffman vector construction, and surface self-diffusivity anisotropy is handled through the use of a diffusivity tensor. We benchmark our method against isotropic phenomena with analytical descriptions and go on to demonstrate that our method is capable of reproducing a host of experimentally observed behaviors in strongly anisotropic single-crystal materials.

Recrystallization of deformed metal nanoparticles

Despite great advances in the fabrication methods of metal nanoparticles with various sizes and shapes, the available tools for manipulating their microstructure and morphology still remain limited. In the present work we introduce the age-old metallurgical technique of recrystallization to the synthesis of metallic nanoparticles. We uniaxially compressed a large number of single crystalline and defect free Pt nanoparticles obtained by solid-state dewetting and annealed them at the temperature of 1000 °C. Our findings reveal that, while the as-dewetted particles exhibited similar shapes and crystallographic orientations, the plastic deformation and annealing led to a diverse range of shapes, microstructures, and orientations among the particles. We categorized the particles into four distinct types based on their appearance: slanted, terraced, “Danish pastry”, and broken particles. Finally, we propose a differentiation mechanism responsible for this diversification, which relies on a combination of recrystallization, surface step formation, and solid-state dewetting processes.

A study of multiple solid-state dewetting of sputtered Au ultra-thin films for chip-based LSPR sensor applications

This article proposes a lithography-free technique to fabricate Au NPs on glass substrates using multiple solid-state dewetting (SSD) of sputtered Au ultra-thin films for LSPR sensor chip applications. We studied the influence of initial film thickness and the number of repeated process cycles on the morphology and LSPR sensing performance. This fabrication process allowed control over particle size, gap spacing, and density of the Au NPs, which influenced the LSPR peak position as observed using field emission scanning electron microscopy (FE-SEM) and UV–Vis–NIR spectrophotometry. To demonstrate LSPR sensing performance, the refractive index (RI) sensitivity was evaluated by measuring the wavelength shift of the LSPR peak in a series of glycerol/phosphate-buffered saline (PBS) mixtures, varying the refractive index from 1.33909 to 1.37409. The results showed that RI sensitivity and the figure of merit (FOM) for all prepared samples ranged from 37.191 ± 12.26–73.592 ± 9.70 and 0.35 ± 0.12–0.75 ± 0.02, respectively. An increase in repeated process cycles tended to decrease RI sensitivity and FOM. The best LSPR performance was achieved with an 8 nm initial film thickness after the first cycle, with an RI sensitivity of 70.937 ± 2.60 and an FOM of 0.75 ± 0.02, attributed to optimal Au size and density. Additionally, the binding efficiency response to human IgG with high regeneration cycles was demonstrated, highlighting the potential for biosensor applications.

Tunable Nanoislands Decorated Tapered Optical Fibers Reveal Concurrent Contributions in Through-Fiber SERS Detection.

Creating plasmonic nanoparticles on a tapered optical fiber (TF) tip enables a remote surface-enhanced Raman scattering (SERS) sensing probe, ideal for challenging sampling scenarios like biological tissues, site-specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Ultimately, this limits the design of the best-performance remote SERS sensing probe. Here we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands with varied geometric parameters in direct contact with the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark molecule, rhodamine 6G (R6G), and serotonin, a highly relevant neurotransmitter for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, we observed a different behavior for serotonin linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10-7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provides new clues to discover and understand intricate plasmonic-driven chemical reactions.

High temperature evolution of a confined silicon layer

The temperature-induced phase and morphology changes of a thin layer sandwiched between two substrates which it partially wets are investigated using transmission electron microscopy, scanning electron microscopy, and x-ray scattering techniques. For this, SiC wafers were bonded with Si layers of various thicknesses and annealed at temperatures below and above the Si melting point. Below the melting point of Si, solid-state dewetting occurs. It starts with the heterogeneous nucleation of pits at the Si/SiC interfaces and progresses to their partial transformation into voids crossing the whole film. The further growth of voids is accompanied with an increase in the Si film thickness. Final equilibrium is shown to be impacted by Si crystallographic state evolution. Above the Si melting temperature, liquid Si drives SiC interfaces step bunching. When high steps and large terraces are formed over the two SiC surfaces, Si is shown to be trapped within quasi-closed pockets. Eventually, the interface locally closes around these Si inclusions with the creation of SiC/SiC direct contacts. The influence of both annealing temperatures and Si film thickness on all these processes is discussed.

A $$\theta $$-L Approach for the Simulation of Solid-State Dewetting Problems with Strongly Anisotropic Surface Energies

A $$\theta $$-L Approach for the Simulation of Solid-State Dewetting Problems with Strongly Anisotropic Surface Energies

Deformed graphene FET biosensor on textured glass coupled with dielectrophoretic trapping for ultrasensitive detection of GFAP

Numerous efforts have been undertaken to mitigate the Debye screening effect of FET biosensors for achieving higher sensitivity. There are few reports that show sub-femtomolar detection of biomolecules by FET mechanisms but they either suffer from significant background noise or lack robust control. In this aspect, deformed/crumpled graphene has been recently deployed by other researchers for various biomolecule detection like DNA, COVID-19 spike proteins and immunity markers like IL-6 at sub-femtomolar levels. However, the chemical vapor deposition (CVD) approach for graphene fabrication suffers from various surface contamination while the transfer process induces structural defects. In this paper, an alternative fabrication methodology has been proposed where glass substrate has been initially texturized by wet chemical etching through the sacrificial layer of synthesized silver nanoparticles, obtained by annealing of thin silver films leading to solid state dewetting. Graphene has been subsequently deposited by thermal reduction technique from graphene oxide solution. The resulting deformed graphene structure exhibits higher sensor response towards glial fibrillary acidic protein (GFAP) detection with respect to flat graphene owing to the combined effect of reduced Debye screening and higher surface area for receptor immobilization. Additionally, another interesting aspect of the reported work lies in the biomolecule capture by dielectrophoretic (DEP) transport on the crests of the convex surfaces of graphene in a coplanar gated topology structure which has resulted in 10 aM and 28 aM detection limits of GFAP in buffer and undiluted plasma respectively, within 15 min of application of analyte. The detection limit in buffer is almost four decades lower than that documented for GFAP using biosensors which is is expected to pave way for advancing graphene FET based sensors towards ultrasensitive point-of-care diagnosis of GFAP, a biomarker for traumatic brain injury.

In-situ construction of bioactive nanostructures on Ti alloy surfaces through ultra-low concentration alkali treatment and low-temperature annealing

Osseointegration is crucial for the long-term stability of orthopedic implants. Nanosurfacing can impart osteoinductivity to the implant. However, the application potential of most available nanotechnologies in surface modification of implants is limited, and there is an urgent need to develop new effective nanosurfacing techniques with greater practicality. In this study, we for the first time, utilized an ultra-low concentration NaOH solution (0.55 mM) combined with low-temperature annealing to achieve solid-state dewetting (SSD) on Ti alloy surfaces, resulting in well-defined TiO2 nanoisland-like crystals. In vitro cell experiments demonstrated that the constructed nanostructures significantly affected the adhesion, proliferation, and osteogenic differentiation capability of MC3T3-E1 cells. The nanostructures formed at 550 °C exhibited the most pronounced enhancement of cell osteogenic differentiation capability. This method is simple, easy to operate, and scalable, holding significant application potential in the surface modification of Ti alloys.

Transport and dielectric properties of MIS structure with embedded Si QDs (AuPd/SiO2:Si QDs/n-Si) grown by MBE

This study focuses on the growth of silicon quantum dots (Si QDs) on insulator substrates via solid-state dewetting of ultrathin silicon films deposited by molecular beam epitaxy (MBE). The resulting Si QDs exhibit well-defined spherical shapes, low size dispersion with an average diameter of 6 nm, and a high density (1012/cm2), making them ideal for microelectronic applications. Current-voltage spectroscopy and impedance spectroscopy were employed to investigate the electrical transport and dielectric properties of Si QDs integrated into a metal-insulator-semiconductor (MIS) structure (AuPd/SiO2: Si QDs/n-Si). Current-voltage measurements reveal that the insertion of Si QDs into the MIS structure improves the electrical transport by introducing new conduction mechanisms. Impedance measurements demonstrate the influence of Si QDs on the frequency dependence of the real part of the dielectric constant (ε′) and the loss tangent (tan δ). Furthermore, Si QDs impact both the real (M′) and imaginary (M″) parts of the electric modulus. Despite slight deviations in dielectric properties, the MIS structure retains its fundamental nature. These investigations affirm the high electrical quality of Si QDs grown via solid-state dewetting and offer valuable insights for researchers engaged in the development of Si QD-based devices, such as non-volatile memories and MIS photodetectors.

Electrical and dielectric properties of ferromagnetic GeMn nanocrystals embedded in metal-oxide-semiconductor Schottky diodes (Al/SiO2:GeMn NCs/n-Si) grown by MBE

This study examines the electrical and dielectric characteristics of magnetic GeMn nanocrystals integrated into a metal-insulator-semiconductor (MOS) configuration for optoelectronic applications. The nanocrystals were produced by solid-state dewetting of an amorphous GeMn layer deposited by MBE on SiO2/Si. The nanocrystals exhibit a well-defined hemispheric shape, high homogeneity, and with a Curie temperature higher than that of the ambient temperature. Characterizations by transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) revealed the crystallinity of the nanocrystals and optimal incorporation of manganese in the nanocrystals, eliminating the usual diffusion or segregation anomalies observed during growth of GeMn alloy on silicon or germanium. Electrical and dielectric tests conducted via current-voltage and impedance spectroscopies on these structures confirmed the integrity of the oxide layer surrounding the GeMn nanocrystals from defects associated with the manganese. In addition, these measurements validated the proper functioning of the MOS structure as a MOS-type Schottky diode. The in-depth analysis of dielectric parameters, such as permittivity (ε), tangent δ, and electric modulus (M) as a function of frequency and bias voltage, revealed no anomalies, thus reinforcing the high quality of the MOS structure enclosing the GeMn nanocrystals.These results mark a significant advance in the growth and integration of magnetic semiconductor nanostructures for optoelectronic applications, paving the way for promising technological developments.

Decomposition and dewetting of super-saturated Cu-15 at. % Co solid solution film

Nano-structured copper thin films present numerous applications for miniaturization of electronic devices. Their long term stability is key for reliable functionality. This work explores the thermal stability and solid state dewetting of a Cu-Co solid solution thin film and compares it to pure Cu. As according to the phase diagram Co is practically immiscible in Cu at room temperature, a metastable solid solution of Cu-15 at. % Co was deposited as thin film on a sapphire wafer. The microstructural evolution of the Co super-saturated film at temperatures ranging from 673 to 1073 K was evaluated using X-ray diffraction and high resolution microscopy techniques such as scanning electron and transmission electron microscopy. Interestingly, there is a competition between grain growth and phase separation. Co precipitates at grain boundaries acting as pinning sites preventing rapid grain growth during heat treatment at intermediate annealing temperature. However, grain growth occurs very quickly at higher temperatures, once the elemental phases of Cu and Co are formed. The competition between grain growth and phase separation and their consequence for dewetting are discussed.

Enhanced control over size, areal density, and shape of substrate-supported Au and Ag nanoparticles by solid-state dewetting and alloying

The ability to manipulate the dimensions, areal density, and form of substrate-supported Au and Ag nanoparticles (NPs) is highly desirable for utilizing their plasmonic properties in biosensing, photovoltaics, and nanophotonic applications. The transformation of thin films into the substrate-supported nanostructures by solid-state dewetting (SSD), provides an avenue to manipulate the dimensional aspects of nanostructures simply and cost-effectively on a large scale. However, spontaneous agglomeration of the film produces randomly distributed and non-uniform nanostructures that must be controlled. Here, we have systematically studied the effect of annealing temperature, between 200 °C and 750 °C, on the dewetting morphology evolution of Au, Ag, and Au–Ag bilayer ultrathin films sputter deposited on the c-plane (0001) sapphire substrates. Regardless of the film thickness, Ag films dewet faster than Au films and produce spherical NPs, compared to faceted Au NPs, with broader size distribution. Whereas, by the SSD of Au–Ag bilayer ultrathin films, highly spherical and monodisperse AuAg bimetallic NPs can be fabricated. Furthermore, we have shown the possibility of fabricating the AuAg bimetallic NPs of varying compositions by adjusting the thickness of individual layers, thus enabling us to smoothly tune the spectral location of plasmonic resonance within the visible range.

Lithography-free tailoring of thin-film nanomorphology for enhanced real-time refractive-index sensing with tunable resonance peaks in the visible spectrum

The precise detection of target substances through refractive-index sensing is essential in various fields such as environmental monitoring, food assessment, and optical applications. This study demonstrates a real-time refractive index sensor based on a liquid-infiltrated metal-insulator-metal island (MIMi) structure in a lithography-free manner. In the MIMi structure, the top layer of the metal islands is formed through solid-state dewetting, which serves as an etching mask to form nanopillars in the insulator layer. This allows for the infiltration of external substances, resulting in different structural colors depending on the refractive index. This design results in a redshift of the resonance peak as the infiltrated refractive index increases. Furthermore, by adjusting the area fraction of the metal-island layer and etching depth of the insulator layer, the resonance-peak position can be controlled within the visible range according to the target refractive index. The advantages of our design are the use of cost-effective materials and the ability to implement scalable fabrication. Our proposed method offers a convenient method to sense the target refractive index in real time.

Dewetting upside-down: two-sided solid state dewetting of thin gold film on soft KBr substrate

Abstract We deposited a 30 nm-thick Au film on single crystalline KBr substrate and studied the solid state dewetting behavior of the film at a temperature of 350 °C. At this temperature, the ions of the KBr compound exhibit significant mobility along the Au–KBr interface, which affects the morphology and kinetics of the solid state dewetting. We performed statistical morphology analysis of the Au–KBr interface by selectively dissolving the KBr substrate after the dewetting heat treatments and subsequent atomic force microscopy imaging of the “upside-down” oriented Au film. We demonstrated that atomic mobility at the interface leads to embedding of the partially dewetted Au film into the KBr substrate. We proposed a quantitative model of the shape evolution of a disc-shaped Au particle on the KBr substrate under the condition of finite interface mobility of the substrate species. The model predictions were consistent with the experimentally observed sinking rates of Au nanostructures.

Rim nucleation and step-train orientation effects in SOI(111) dewetting

We demonstrate that the step-train orientation of a vicinal surface plays an important role in solid-state dewetting. Focusing on SOI(111), we observe the formation of hexagonal voids in the silicon film due to dewetting. These voids are surrounded by an asymmetric rim, which is wider on the higher-terrace side compared to the lower-terrace side. Our findings also reveal a layer-by-layer growth of the rim around the dewetting voids during the early stages, before the formation of branched structures. Dewetting fingers develop faster and are thinner in the step-down direction compared to the step-up direction. Kinetic Monte Carlo (KMC) simulations confirm our experimental observations and provide insights into the atomic details underlying rim and finger formation. During the initial stages of dewetting, the nucleation of a new rim layer is not required: Atoms leaving the dewetting void are captured by the adjacent upper step, leading to the growth of the upper terrace that thus surrounds the dewetting void. The nucleation of a new rim layer only becomes necessary when the distance between the edge of the void and the upper terrace increases. The energetics involved in the dewetting kinetics of SOI(111) are consistent with those of SOI(100).

Self-Confined Dewetting Mechanism in Wafer-Scale Patterning of Gold Nanoparticle Arrays with Strong Surface Lattice Resonance for Plasmonic Sensing.

A self-confined solid-state dewetting mechanism is reported that can fundamentally reduce the use of sophisticated nanofabrication techniques, enabling efficient wafer-scale patterning of non-closely packed (ncp) gold nanoparticle arrays. When combined with a soft lithography process, this approach can address the reproducibility challenges associated with colloidal crystal self-assembly, allowing for the batch fabrication of ncp gold arrays with consistent ordering and even optical properties. The resulting dewetted ncp gold nanoparticle arrays exhibit strong surface lattice resonance properties when excited in inhomogeneous environments under normal white-light incidence. With these SLR properties, the sensitive plasmonic sensing of molecular interactions is achieved using a simple transmission setup. This study will advance the development of miniaturized and portable devices.

The effect of composition and long-range order on the strength of defect-free faceted Cu-Au nanoparticles

Solid solution and long-range atomic order hardening represent two well-known strategies for increasing strength of bulk metallic materials. Here, we observed the opposite trends in mechanical behavior of defect-lean nanoparticles of Cu-Au alloys fabricated by solid state dewetting of Cu-Au bilayers deposited on sapphire substrate. In the fully disordered state, the nanoparticles of Cu3Au alloy exhibited the highest compressive strength reaching staggering 41 GPa for the smallest studied particles, followed by nanoparticles of pure Cu, and of CuAu alloy. Thus, taking pure Cu and Au nanoparticles as a reference, both solid solution hardening (Cu3Au) and solid solution softening (CuAu) were observed in nanoscale plasticity of the Cu-Au system. Additional annealings at the temperature of 350 °C, 40 °C below the critical point of A1-L12 transformation, were performed to induce different degrees of the long-range order in the Cu3Au nanoparticles. It was shown that the strength of fully ordered Cu3Au nanoparticles is very similar to that of their fully disordered counterparts, whereas the partially ordered Cu3Au nanoparticles larger than 500 nm in size exhibited a significant drop in strength. No effect of long-range order on compressive strength of smaller nanoparticles was observed. These findings were discussed in terms of plasticity mechanisms controlled by nucleation of new dislocations. Specifically, it was proposed that the presence of oxidation-induced Au-rich subsurface layer in the Cu3Au nanoparticles is responsible for their ultrahigh strength.

Control of Self-Assembly and Elemental Mixing of AuNi Bimetallic Nanoparticles via Solid-State and Liquid-State Dewetting of Metal Thin Films

Immiscible Au-Ni alloy thin films undergo phase separation and dewetting because of thermodynamic and morphological instability at elevated temperatures below the miscibility gap. We report the formation and assembly of bimetallic nanoparticles (BNPs) on topographic Si templates. An ordered array of inverted pyramidal pits were produced via solid-state and liquid-state dewetting of a 12-nm-thick Au-Ni thin film by respectively using thermal annealing and laser irradiation. Upon direct thermal annealing at 600 and 800 <sup>o</sup>C, the thin film on the templates self-assembled into an ordered array of BNPs composed of Au-rich and Ni-rich sub-clusters in pits. But the relative proportions of the two sub-clusters varied with annealing temperature due to the additional formation of smaller Ni-rich NPs that were scattered around the BNPs. Laser irradiation of the film, in contrast, formed an ordered array of fully mixed alloy NPs on the template and left no other residues on the surface. Subsequent thermal annealing induced the elements within the NPs to segregate, resulting in Au-rich and Ni-rich sub-clusters. In brief, the combination of solid-state and liquidstate dewetting processes on a topographic template not only enabled the 2-dimesional self-assembly of BNPs but also allowed control of the mixing of alloying elements within the BNPs. These results offer insights into the tailored fabrication of BNPs, which have potential applications in bio-functional catalysts, and plasmonic and chemical sensors.