Boron phosphide (BP) nanowires represent a rare 1D semiconductor, combining outstanding chemical stability, ultrahigh hardness, and high thermal conductivity. However, their controlled growth and optical functionality remain largely unexplored due to irregular morphologies, toxic precursors, and complex synthesis routes. Here, we develop a supersaturation-engineered chemical vapor transport (CVT) strategy to synthesize air-stable, single-crystalline cubic BP nanowires with tunable diameters. Strain-engineered Raman spectroscopy reveals pronounced phonon broadening and symmetry-selective frequency shifts, uncovering strong strain-phonon coupling. The inherent noncentrosymmetry and nanoscale confinement further induce highly anisotropic Raman and polarization-resolved SHG responses. The BP nanowires show remarkable environmental stability over 12 months and competitive photodetector performance, with a responsivity of 5.2 × 104 A/W and detectivity exceeding 6.4 × 1011 Jones under 595 nm illumination. The device also shows good ambient-storage stability and flexible-substrate compatibility. Integration with MoS2 amplifies polarization discrimination, achieving an anisotropy ratio of 2.87 at 532 nm, surpassing previously reported low-dimensional systems. This work establishes strain-phonon coupling-mediated polarization control as a new paradigm for BP-based optoelectronic and photonic platforms.

Phononic nanodevices offer a promising route toward quantum technologies, as phonons combine strong confinement within matter with broad coupling capabilities to various quantum systems. In particular, the piezoelectric response of materials such as lithium niobate enables coupling between superconducting qubits and gigahertz-frequency phonons. However, bulk lithium niobate phononic devices typically rely on surface acoustic waves and are therefore inherently subject to leakage from the surface into the bulk substrate. Here, we explore the acoustic behavior of resonator cavities supporting GHz-frequency Lamb waves in a 200 nm-thick suspended lithium niobate layer. We characterize the acoustic response at both room and millikelvin temperatures. We find that our resonator cavities with strong confinement reach intrinsic quality factors of approximately 6000 at the single phonon level. We use the measured parameters of the resonators to model their coupling to a superconducting transmon qubit, allowing us to evaluate their potential as quantum acoustic devices.

Three-dimensional integration is critical for next-generation integrated circuits, yet thermal management remains challenging due to complex interface environment. Owing to its high thermal conductivity, aluminum nitride (AlN) is a promising insulating layer for through-silicon via structures, yet its interfacial thermal behavior with copper (Cu) electrodes remains insufficiently understood. Here, we investigate phonon transport across non-bonded AlN-Cu interfaces governed by van der Waals (vdW) interactions using a machine learning potential (MLP) trained by density functional theory (DFT) data. The MLP accurately reproduces DFT-level phonon dispersion, energy-volume relationships, and interfacial binding energies. Non-equilibrium molecular dynamics simulations reveal total thermal resistance values of 10-14 m2K/GW at room temperature, approximately five times smaller than values obtained with empirical potentials and in excellent agreement with experimental data for similar semiconductor-metal interfaces. Unlike empirical potentials, the MLP predicts increasing thermal resistance with temperature, attributed to phonon softening and vibrational mismatch. Spectral decomposition analyses confirm reduced phonon thermal conductance at elevated temperatures. This work provides fundamental insights into weakly bonded semiconductor-metal interfaces and guidance for thermal management in 3D integrated systems.

The observation of second sound-a propagating wave-like manifestation of hydrodynamic heat transport-in solid crystals has been confined to a handful of materials at cryogenic temperatures, as disorder and Umklapp scattering suppress this phenomenon at room temperature. Here, we report the direct observation of second sound at ambient conditions in isotopically purified graphite. Using transient thermal grating spectroscopy, we measure a distinct damped oscillatory signal that provides unambiguous evidence of second sound, decisively distinguishing it from diffusive and ballistic transport regimes. This collective phonon dynamics enables an enhancement of the effective thermal conductivity, even surpassing the conventional diffusive limit by nearly 10%. Our work establishes the control of phonon-isotope scattering as a powerful strategy to unlock hydrodynamic phonon transport. It demonstrates that phonon hydrodynamics is an accessible and exploitable phenomenon in crystals at room temperature, providing an avenue for the fundamental study and application of wave-like heat transport.

Mathematical order such as the golden ratio, Fibonacci sequences, and other quasiperiodic or aperiodic patterns provide a compact design language for functional matter. This review traces their role from describing non-periodic order in quasicrystals, fractals, and optical systems to actively engineering wave and energy transport, with particular emphasis on phononic and thermal phenomena. We highlight periodic superlattices as phononic crystals that control coherent–incoherent crossover, Golomb ruler-based architectures as paradigms of controlled disorder enabling broadband suppression of transport channels, and quasiperiodic sequences such as Fibonacci, Thue–Morse, and Double–Period designs that generate hierarchical scattering and partial localization. Taken together, these advances show how mathematically encoded order can sculpt phonon and photon landscapes in a highly structured way, suggesting mathematics-guided routes toward cross-scale control of heat, light, and related excitations.

Through-silicon vias (TSVs) are critical vertical interconnects in three-dimensional integrated circuits (3D ICs). The Bosch Deep Reactive Ion Etching (DRIE) process creates periodic scallops on the sidewall, known as line edge roughness (LER), which affects device performance and reliability. However, existing methods can only characterize TSV sidewall qualitatively or require destructive sample preparation, making model-based quantitative LER characterization unavailable for high-aspect-ratio TSVs. This study presents a shadowgraphy-based method to address this gap. Using oblique-angle infrared (IR) illumination, the system projects both top and bottom contours onto a single imaging plane, enabling extraction of critical dimensions (CD) including two diameters and depth. Combined with physical modeling, this approach also proposes a model-based framework for sidewall LER estimation. Monte Carlo Ray Tracing (MCRT) simulations established and verified the correlation between scattering and edge blur. Since inverting this relationship analytically is intractable, Random Forest (RF) and Convolutional Neural Network (CNN) models were employed to estimate roughness from shadow edge profiles. Validation on simulated data achieved root mean square error (RMSE) of approximately 0.03 & micro;m over the 0.01 to 0.20 & micro;m range. Geometric validation demonstrated an RMSE of 0.19 & micro;m for top diameter and 1.04 & micro;m for depth compared to optical microscopy (OM) and scanning electron microscopy (SEM) references. The trained models were applied to experimental shadow images for non-destructive LER estimation as a process monitoring metric. This study shows the potential for TSV and through-glass via (TGV) CD metrology, offering a practical solution for inline metrology in advanced semiconductor packaging.

We demonstrate that the thermal radiation between deep subwavelength membranes of silicon carbide (SiC) exhibits a maximum enhancement over that of infinite SiC surfaces separated by the same vacuum gap. Based on fluctuational electrodynamics, we show that this enhancement occurs at a separation distance of 200 nm and increases for thinner and colder membranes. This peak arises from the dominant contribution of electromagnetic modes localized at the corner and vertical edges of sufficiently thin membranes, which enable a strong coupling of surface phonon-polaritons appearing along their top and bottom surfaces. These resonant corner and edge modes effectively extend the emission cross-sectional area of the membranes over their geometrical one and, therefore, amplify their thermal radiation. For 10-nm-thick membranes of SiC at 300 K, the thermal conductance reaches 54 pWK (- 1), which yields a maximum enhancement of 4.5 over the value for infinite SiC surfaces. Our findings, thus, reveal that the regime of near-field thermal radiation driven by corner and edge modes emerges and is optimized in deep subwavelength membranes separated by intermediate distances.

Phosphorus nanoribbons combine the tunable bandgap and high mobility with the inherent anisotropy of one-dimensional systems, offering promise for functional electronics, but their intrinsic low stability hinders practical applications. Here, we report phosphorus-lithium double-helix nanoribbons with a well-ordered helical architecture and high structural stability under harsh conditions such as in air up to 225°C, water, and even acidic solutions. Comprehensive experimental characterizations and theoretical analyses show that the stability arises from a synergistic combination of Zintl phase formation between phosphorus and lithium atoms, noncovalent interhelical interactions, and geometric protection offered by the distinctive helical architecture. The nanoribbons show tunable optical properties dependent on temperature, thickness, and polarization state. It is demonstrated that these properties enabled nanoribbon-based hydrogels with self-healability and highly efficient photothermal conversion, showing a general approach for stabilizing active low-dimensional materials and paving the way for applying phosphorus-based nanostructures in biomedical engineering and quantum technologies.

We demonstrate the existence of a maximum for the enhancement of the far-field heat transfer between deepsubwavelength membranes of SiC. Using fluctuational electrodynamics, we show that the thermal conductance reaches a peak exceeding the blackbody limit by 460 times for 50-nm-thick membranes of SiC at 200 K. This enhancement is driven by the interplay of two surface polariton modes, whose combined contributions are optimized at this thickness and temperature. Our finding thus reveals that the tradeoff of two polariton resonances limits the ability of subwavelength polar membranes to enhance thermal radiation.

We demonstrate that the thermal radiation between subwavelength membranes of silicon nitride exhibits a minimum enhancement over the blackbody limit, for a given separation distance. Using fluctuational electrodynamics simulations, we show that this minimum appears for membranes' separation distances corresponding to the transition between the far- and near-field regimes. The observed minimum results from the weak contributions of both the evanescent and propagating electromagnetic modes, and its values become lower for higher temperatures and thicker membranes. Outside this transition, the radiative enhancement increases and saturates for sufficiently long separation distances. Notably, the difference between the minimum and saturation values diminishes as the membranes' thickness increases. The far-field plateau of radiative enhancement is primarily governed by the coupling of surface phonon-polaritons propagating along the top and bottom surfaces of sufficiently thin membranes, which expands the effective emission cross-section area beyond the membranes' geometric one. Our findings thus show that while subwavelength polar membranes enable us to significantly enhance the far-field thermal radiation, this enhancement is limited in the far-to-near field transition. This observation highlights the necessity of optimizing both the separation distance and membrane properties to enhance the radiative heat transfer between membranes.

This article presents a comprehensive summary of the through-silicon via (TSV) technology, primarily focused on its metrology and inspection for advanced semiconductor packaging. With the rapid advancement of electronic technology, the size of integrated circuits (ICs) continues to decrease while the functionality of components continually enhances. Three-dimensional ICs (3D ICs) packaging is an essential method for improving both the integration and performance of components. TSVs are one of the key technologies used to achieve 3D ICs, as they enable efficient vertical electrical connections between different layers and significantly increase the device density, being recognized as a vital technology for high performance, miniaturization, and multifunctionality of semiconductor devices. Due to the small and complicated features of TSVs, various types of defects could be observed during manufacturing and operation. These defects affect the performance and reliability of the devices, further leading to potential system failure. Therefore, accurate and effective TSV metrology and inspection technology becomes a key factor in advanced semiconductor packaging, ensuring device performance and functionality. Various metrology technologies have been proposed, including optical inspection, X-ray inspection, scanning electron microscopy (SEM), atomic force microscopy (AFM), etc. Recently, new inspection technologies, such as via metrology based on edge diffraction and through-focus scanning optical microscopy (TSOM), have been continually developing, although those technologies still have potential issues and limitations. As applications of TSVs continue to expand, the need for fast and accurate metrology becomes increasingly important. Future trends include combining current methods with artificial intelligence (AI) to further achieve inspection automation. This article provides a comprehensive review of the main TSV metrology methods, discusses their capabilities, advantages, and limitations, and provides insight into the future TSV technology development trends.

Mathematically inspired structure design has emerged as a powerful approach for tailoring material properties, especially in nanoscale thermal transport, with promising applications both within this field and beyond. By employing mathematical principles, based on number theory, such as periodicity and quasi-periodic organizations, researchers have developed advanced structures with unique thermal behaviours. Although periodic phononic crystals have been extensively explored, various structural design methods based on alternative mathematical sequences have gained attention in recent years. This review provides an in-depth overview of these mathematical frameworks, focusing on nanoscale thermal transport. We examine key mathematical sequences, their foundational principles, and analyze the influence of thermal behavior, highlighting recent advancements in this field. Looking ahead, further exploration of mathematical sequences offers significant potential for the development of next-generation materials with tailored, multi-functional properties suited to diverse technological applications.

Phonons—quantized vibrational modes in crystalline structures—govern phenomena ranging from thermal and mechanical transport to quantum mechanics. In recent years, a new class of artificial materials called phononic crystals has emerged, aiming to control phononic properties. These materials are created by introducing a superlattice structure on top of an already-existing atomic lattice. Typically, phononic crystals are described using a continuous model, in which effective elastic constants approximate potentials between atoms. This approximation, however, assumes the wavelengths of vibrations to be significantly greater than the interatomic distance. In this work, we experimentally investigate the behavior of a honeycomb silicon phononic crystal in the gigahertz range, where the continuum approximation holds, and in the terahertz range, where the phonon wavelengths are comparable to interatomic distances. Using Brillouin light scattering, we investigate the phonon dispersion of the phononic crystal in the gigahertz range, finding a close match with simulations based on the continuous model. Conversely, Raman spectroscopy reveals no difference between the phononic crystal, an unpatterned membrane, and a bulk silicon structure in the terahertz range, showing that the continuous model no longer holds at these higher frequencies.

Energy harvesting is essential for the internet-of-things networks where a tremendous number of sensors require power. Thermoelectric generators (TEGs), especially those based on silicon (Si), are a promising source of clean and sustainable energy for these sensors. Although large thermoelectric figure of merit has been reported for nanostructured Si material, however, nanostructuring has not been effectively used in device applications, and the reported performance of hybrid planar-type Si TEGs never exceeded normalized powers of 0.1 mu Wcm- 2K-2 due to the poor thermoelectric performance of Si and the suboptimal design of the devices. Here, we report a hybrid planar-type Si TEG with a normalized power of 1.3 mu Wcm-2K-2 around room temperature. The increase in thermoelectric performance of Si by nanostructuring based on the phonon-glass electron-crystal concept and optimized three-dimensional heat-guiding structures resulted in a record-high power density. The improvement of power generation by a factor of 10 makes the once-a-day sensing applications realistic in a practical environment for the first time. In-field testing demonstrated that our Si TEG functions as a sufficient energy harvester. This demonstration paves the way for energy harvesting with a low-environmental load and cost-effective material with high throughput, a necessary condition for energy-autonomous sensor nodes for the trillion sensors universe.

We experimentally demonstrate the enhancement of the far-field thermal radiation between two nonabsorbent Si microplates coated with energy-absorbent silicon dioxide (SiO_{2}) nanolayers supporting the propagation of surface phonon polaritons. By measuring the radiative thermal conductance between two coated Si plates, we find that its values are twice those obtained without the SiO_{2} coating. This twofold increase results from the hybridization of polaritons with guided modes inside Si and is well predicted by fluctuational electrodynamics and an analytical model based on a two-dimensional density of polariton states. These findings could be applied to thermal management in microelectronics, silicon photonics, energy conversion, atmospheric sciences, and astrophysics.

Based on fluctuational electrodynamics, we reveal a dimensional crossover in far-field thermal radiation between subwavelength gold membranes. As the membrane thickness decreases from the bulk to the nanoscale, we observe a transition from three-dimensional to two-dimensional heat transfer, which is characterized by a distinct minimum plateau in thermal conductance for intermediate subwavelength thicknesses. This behavior, absent in polar dielectrics, stems from the coupling and decoupling of long-range surface plasmon-polariton modes. The thermal conductance exhibits a T3 dependence for thick membranes at high temperature and transitions to a T2 dependence for ultrathin films at low temperature, reflecting the dimensional shift in the photon density of states. Notably, the minimum plateau falls below the blackbody limit, demonstrating the potential for tailoring far-field thermal radiation in metallic nanostructures through dimensional confinement and plasmonic effects.

The development of emerging technologies, such as quantum computing and semiconductor electronics, emphasizes the growing significance of thermal management at cryogenic temperatures. Herein, by designing isotope interfaces based on the Golomb ruler, we achieved effective suppression of the phonon thermal transport of cryogenic graphene. The pronounced disordering of the Golomb ruler sequence results in the stronger suppression of thermal transport compared to other sequences with the same isotope doping ratio. We demonstrated that the Golomb ruler-based isotope interfaces have strong scattering and confinement effects on phonon transport via extensive molecular dynamics simulations combined with wave packet analysis, with a proper correction for the missing quantum statistics. This work provides a new stream for the design of thermal transport suppression under cryogenic conditions and is expected to expand to other fields.

Efficiently exciting and controlling phonons in diamond nanoresonators represents a fundamental challenge for quantum applications. Here, we theoretically demonstrate the possibility of exciting mechanical modes within a double hybrid cavity (DHC), formed by adjoining to a diamond cavity a second cavity made of aluminum nitride. The latter is piezoelectric and serves as a microwave-to-phonon transducer, activating mechanical modes in the entire DHC. We show the process of matching the cavities' phononic properties, making them work coordinately in the DHC and obtaining a well-confined mode. In the diamond part of the cavity, this mode replicates the fundamental mode of the individual diamond cavity, showing that the piezoelectric transducer does not alter the diamond individual fundamental mode. In the piezoelectric part, the strong confinement of stress and electric field results in a high piezoelectric coupling rate, demonstrating the effectiveness of a phononic cavity as a transducer. The study is contextualized in the framework of a quantum networking application, where the DHC serves as a spin qubit, exploiting the spin-mechanical coupling within diamond color centers.