Browse Articles

Super elastic and negative triboelectric polymer matrix for high performance mechanoluminescent platforms

Point defect diffusion in III-nitrides: A key mechanism for thermal degradation and non-radiative recombination in GaInN/GaN quantum well structures

Various forms of thermal degradation of light emitters based on III-nitrides have been observed, with no clear conclusion about the mechanism. We investigate the non-radiative carrier lifetime in GaInN/GaN single quantum wells (SQWs) with various emission wavelengths and its relation to the growth conditions. We observe that the non-radiative lifetime in SQWs increases exponentially with decreasing buffer and cladding layer growth temperature. As a first conclusion, diffusion of point defects leading to non-radiative recombination is a universal mechanism present during III-nitride growth. Second, this is likely a predominant mechanism for thermal degradation observed while growing layers on top of the quantum well, e.g., a p-layer, and after post-growth annealing. Performance and reliability of devices can be improved by properly controlling point defect diffusion.

Sun-simulated-driven production of high-purity methanol from carbon dioxide

Efficient spintronic THz emitters without external magnetic field

We investigate the performance of state-of-the-art spintronic THz emitters (W or Ta)/CoFeB/Pt with non-magnetic underlayer deposited using oblique angle deposition. The THz emission amplitude in the presence or absence of an external magnetic field remains the same and remarkably stable over time. This stability is attributed to the enhanced uniaxial magnetic anisotropy in the ferromagnetic layer, achieved by the oblique angle deposition of the underlying non-magnetic layer. Our findings could be used for the development of practical field-free emitters of linearly polarized THz radiation, potentially enabling applications in future THz technologies.

Reconstructing skeletal homeostasis through allogeneic hematopoietic stem cell transplantation in myelofibrosis

Abstract Myeloproliferative neoplasm-associated myelofibrosis is a clonal stem cell process characterized by pronounced bone marrow fibrosis associated with extramedullary hematopoiesis and splenomegaly. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents the only curative treatment leading to bone marrow fibrosis regression. Here we provide an in-depth skeletal characterization of myelofibrosis patients before and after allo-HSCT utilizing clinical high-resolution imaging, laboratory analyses, and bone biopsy studies. Despite unimpaired bone microarchitecture at peripheral skeletal sites, we observe a marked increase in bone mineral density at the lumbar spine and proximal femur, which is histologically related to severe bone marrow fibrosis and osteosclerosis, fully normalizing after allo-HSCT. Importantly, the regression of fibrosis is accompanied by vanishing osteosclerosis along with restored osteoclastic resorption activity and whole-body calcium homeostasis. Together, our results provide evidence for an extensive reconstruction of skeletal homeostasis by allo-HSCT in MF, leading to rapid resolution of osteosclerosis.

Investigating spin-orbit interaction of light in micro- and nanophotonic systems using polarization Mueller matrix

Coupling between the spin and orbital angular momentum of light has led to a variety of exotic spin–orbit photonic effects, establishing a paradigm of nanophotonic meta-devices to control and manipulate light at the nanometer length scale. For the advancement of spin–orbit photonic technologies, quantitative characterization and unambiguous physical interpretation of the various spin–orbit interaction (SOI) effects exhibited in complex nanophotonic systems are of utmost importance. This Perspective addresses some of these outstanding challenges in the domain of spin–orbit photonics, focusing on the simultaneous manifestation of multiple SOI effects in hybridized nanophotonic systems and the role of polarization-based techniques in their characterization and quantification. After introducing the fundamentals and physical origins of SOI effects, we present a polarization Mueller matrix technique as a powerful tool to probe, decouple, and independently quantify these effects in a unified experimental framework, demonstrated with hybridized waveguided plasmonic crystals. We further discuss the potential of structured light and tailored polarization to enable unconventional SOI phenomena in simple nanostructured metamaterials and metasurfaces. These advancements not only enhance our fundamental understanding of SOI phenomena across micro- and nanoscale optical systems but also pave the way for the development of multifunctional and tunable spin–orbit photonic devices.

Thermalization of a flexible microwave stripline measured by a superconducting qubit

With the demand for scalable cryogenic microwave circuitry continuously rising, recently developed flexible microwave striplines offer the tantalizing perspective of increasing the cabling density by an order of magnitude without thermally overloading the cryostat. We use a superconducting quantum circuit to test the thermalization of input flex cables with integrated 60 dB of attenuation distributed at various temperature stages. From the measured decoherence rate of a superconducting fluxonium qubit, we estimate a residual population of the readout resonator of (2.2±0.9)×10−3 photons and we measure a 0.28 ms thermalization time for the flexible stripline attenuators. Furthermore, we confirm that the qubit reaches an effective temperature of 26.4 mK, close to the base temperature of the cryostat, practically the same as when using a conventional semi-rigid coaxial cable setup.

Chiral correlated-plasmons enhanced Raman optical activity from spin-polarized, correlated <i>s</i> band in highly oriented single-crystalline gold quantum-dots

Interactions of chiral light with chiral matter, such as Raman optical activity (ROA) and, independently, spin-polarized materials have attracted a lot of interest for both fundamental science and applications. The ROA, on the one hand, provides information on chiral phonons of molecules. However, the short-lifetime ROA signal in general is extremely weak and requires long exposure times, making it not accessible for many important systems with short lifetime. Materials exhibiting high spin polarization in d or f band, on the other hand, remain very limited even at very low temperature. There has been no report on materials exhibiting spin polarization in s band. Herewith, we report a room temperature, full spin polarization in unconventional, correlated s band of highly oriented single-crystalline gold quantum-dots (HOSG-QDs). Intriguingly, the HOSG-QDs produce a chiral correlated-plasmons enhanced Raman optical activity (CP-ROA) with anomalous ROA enhancement and strong spin-dependent chiral coupling. We then address a fundamental problem in crystal violet. Using spin-polarized HOSG-QDs chips, we observe strong CP-ROA signal, revealing chiral properties. The chiral correlated-plasmons of HOSG-QDs interact with the spin, electronic, and lattice structures of crystal violet, revealing chiral phonons and chiral electronic Raman excitations of crystal violet. Such a strong CP-ROA spectrum is obtained within a minute of measurement and a simple preparation without patterning. Our result shows that the CP-ROA based on a spin-polarized HOSG-QDs is extremely sensitive to the chiral property of phonon and spin and electronic structures and a fast, label-free chiral spectroscopic-based detection.

Ultrahigh field-effect mobility of 147.5 cm2/Vs in ultrathin In2O3 transistors via passivating the surface of polycrystalline HfO2 gate dielectrics

This study presents considerable improvements in the electrical characteristics of atomic-layer-deposited 3-nm-thick In2O3 thin-film transistors (TFTs), which were achieved by introducing a 2-nm-thick amorphous Al2O3 interfacial layer to passivate the surface of a polycrystalline HfO2 gate dielectric. The resulting devices exhibited exceptional electrical characteristics, including an ultrahigh field-effect mobility (μFE) of approximately 147.5 ± 16.6 cm2/V s, subthreshold swing of 103.7 ± 9.1 mV/dec, and threshold voltage (VTH) of 0.5 ± 0.1 V. These enhancement-mode devices represent increases of more than threefold in μFE compared to devices without an amorphous passivation layer. This is despite all the fabrication processes being identical, except for the introduction of the Al2O3 interfacial layer. This improvement can be primarily attributed to the reduced electron scattering through suppressed remote Coulomb interactions. Furthermore, the In2O3 TFTs exhibited enhanced operational stability, showing minimal VTH shifts of 0.15 and −0.01 V under positive and negative bias-stress conditions, respectively. The findings of this study emphasize the critical role of the surface passivation of polycrystalline HfO2 dielectrics in improving the electrical performance of ultrathin In2O3 TFTs.

Mechanism of selective SiO2/photoresist reactive ion etching in an inductively coupled plasma operated in a C4F8/H2 gas mixture

A reactive ion etch process that achieves high selectivity between SiO2 and photoresist (PR) and based on C4F8/H2 chemistry in an inductively coupled radio frequency plasma is developed. The process is accompanied by the formation of a fluorocarbon film, which defines key process characteristics. The SiO2 etching is described as a sum of two competing mechanisms: (i) an inhibition mechanism related to fluorocarbon film deposition and (ii) a defluorination mechanism, describing the diffusion of etching species to the CxFy/SiO2 interface. However, the photoresist etch rate is primarily determined by the inhibition mechanism. In order to achieve high SiO2/PR selectivity, both mechanisms are studied as functions of hydrogen admixture, pressure, gas residence time, and substrate temperature. This study reveals that depending on the superposition of the process parameters, one of the mechanisms can prevail over the other one, which significantly affects etch rates and selectivity. By adjusting the process parameters, a maximum selectivity between SiO2 and PR of 8 is achieved corresponding to a SiO2 etch rate of 200 nm/min.

Single mode, distributed feedback interband cascade lasers grown on Si for gas sensing

A single mode distributed feedback (DFB) interband cascade laser (ICL) grown on a (001) Si substrate has been developed. The designed DFB ICL with a grating on top of the ridge emits at a wavelength near 3.4 μm, suited for methane gas sensing, and operates in continuous wave up to 35 °C, with a maximum output power of 4 mW/facet at 15 °C and a side mode suppression ratio of 20 dB in the whole operating range. Methane detection has been demonstrated by integrating the DFB ICL on Si with a quartz-enhanced photoacoustic spectroscopy setup, a step forward in the development of integrated photonic gas sensors on silicon platforms.

Enhanced electronic property of wafer-scale monolayer MoS2 through S/Mo ratio optimization

Monolayer molybdenum disulfide (MoS2), an emergent two-dimensional (2D) semiconductor, represents the ultimate thickness for scaling down channel materials beyond silicon to overcome the limit of semiconductor technology nodes in the sub-1 nm range. However, despite extensive efforts in the growth of monolayer single-crystal MoS2, growth optimization for higher electronic property and reproducible fabrication for satisfying industrial stability still need to be reported. Here, we report an approach to synthesize wafer-scale monolayer single-crystal MoS2 with high carrier mobility and on/off ratio on sapphire by controlled release of S/Mo precursors ratio during the chemical vapor deposition process. We infer that the main cause of the mismatch in the stoichiometric S/Mo ratio is the oxygen doping. It is found that the MoSx film (x = 1.94) has rather high optimization, as confirmed by the relatively high electronic performances of related devices. Specifically, a fabricated field-effect transistor (FET) array based on the single-crystal monolayer MoS1.94 channels demonstrates significant enhancement in room-temperature mobility (up to 122 cm2 V−1 s−1) and an exceptional on/off ratio (over 1010). This work provides an efficient and reliable approach to produce single-crystal monolayer MoS2 for high-performance microelectronics in the future.

Non-hexagonal symmetry-induced QH-graphene as a promising anode material for sodium-ion batteries: Effects of solvent, vacancy defect, and interlayer coupling

Developing two-dimensional (2D) carbon electrode materials with high performance has become an increasingly fascinating pursuit. However, the most popular carbon allotrope, graphene, possesses chemical inertness arising from its delocalized π-electron network. Breaking of the hexagonal symmetry in graphene can disrupt its π-conjugated system, thus increasing the surface reactivity. Here, by employing first-principles calculations, we predict a 2D carbon allotrope (called QH-graphene), which exhibits remarkable stability across the dynamic, thermal, and mechanical aspects. It has several advantages as an anode material for sodium-ion batteries (SIBs), including a high theoretical capacity (1116.7 mA h g−1), a moderate Na migration barrier (0.35–0.60 eV), a suitable average open-circuit voltage (0.55 V), and a small change in lattice parameters (∼3%). When contacted with electrolyte solvents, the Na adsorption and diffusion capabilities are enhanced. Moreover, introducing a monovacancy defect in QH-graphene improves the adsorption strength of Na but reduces its mobility. Compared with single-layer QH-graphene, QH-graphene bilayer has a stronger binding affinity for Na while maintaining rapid ion diffusion on its exterior surface.

Enhancing radiation hardness of microelectronics through stress-relief milling

Single event effects (SEE) in microelectronic devices are predominantly studied from the perspective of electrical charge generation and collection. This study introduces a multi-physics concept by investigating the impact of highly localized mechanical stress in electrically sensitive regions, such as the gate in a transistor. Our hypothesis is that reducing mechanical stress beneath the gate will decrease voltage transients caused by SEE by limiting charge generation and diffusion. To explore this electro-mechanical coupling in relation to SEE, we milled a microscale trench in the substrate beneath a transistor of the LM124 operational amplifier using a focused ion beam, thereby alleviating mechanical stress in the vicinity of the trench. We then perform pulsed laser SEE testing on the stress-relieved transistor and a control specimen without a micro-trench modification. Our experimental results demonstrate a significant decrease in single event transient peak amplitude and collected charge in the stress-relieved device compared to its pristine counterpart under identical pulsed laser conditions. These findings support our hypothesis and suggest that mitigating mechanical stress localizations could inform the design and fabrication of radiation-hardened electronics.

Band structure engineering in 2D BA2PbI4/InSe perovskite heterostructures and superlattices

Periodic stacking of two van der Waals materials enables the realization of superlattice structures with artificial design of band structure. Two-dimensional perovskites offer structural flexibility for engineering of band structure that can result in superlattice structures. Here, InSe/BA2PbI4 perovskite heterostructure and superlattice are explored by first principles calculation. Both the heterostructure and superlattice show a similar direct bandgap structure. As the concentration of VBA defects increases, the bandgap of the heterostructure and superlattices generally increase in different manners due to different interfacial interaction. The introduction of VI defects leads to the formation of a type-I band alignment, contrasting with the type-II band alignment resulting from VBA defects. These findings offer valuable insights into the defect-driven modulation of electronic properties in semiconductor superlattices and heterostructures, providing opportunities to tailor them for various optoelectronic applications.

Charge-to-spin conversion at argon ion milled SrTiO3/NiFe hetero-interfaces

Two-dimensional electron gases (2DEGs) at perovskite oxide interfaces, such as strontium titanate (STO), have garnered significant attention due to their induced ferromagnetic (FM), spin–orbit coupling, and superconducting properties. The 2DEG, formed at the interface between STO and either insulating oxides or reactive metals, exhibits efficient charge-to-spin interconversion in STO/NM(non-magnetic)/FM structures. The insulating oxide layer at the STO interface attenuates the spin currents injected into the ferromagnet. In contrast, the metallic layers facilitate efficient spin current injection but suffer from spin current diffusion. Here, we present an approach to overcome these challenges by directly creating a 2DEG at the STO surface through Ar+ ion bombardment. This method enables efficient spin-to-charge conversion without an intermediate NM layer. Our experimental and simulation results demonstrate the generation of unconventional spin currents at the STO(Ar+)/NiFe (Permalloy) interface. Our findings may enable applications of complex oxide and ferromagnet interfaces for efficient charge-to-spin conversion, paving the way for low-power, room-temperature oxide-based spintronic devices.

Analysis of inversion-domain boundaries in four-layer polarity-inverted AlN structure

We have fabricated a four-layer polarity-inverted aluminum nitride (AlN) structure using a combination of sputtering and face-to-face annealing. We investigated the impurity concentrations and structure of the polarity inversion-domain boundaries (IDBs) of the four-layer polarity-inverted AlN structure. Atomic-scale observations revealed that the interface of the IDBs from Al-polar AlN to N-polar AlN consists of three monolayers (MLs) of O-Al-O, while the IDBs from N-polar AlN to Al-polar AlN consist of 8–10 ML of AlxOyNz. Additionally, the positions of the IDBs from N-polar AlN to Al-polar AlN shifted by 20–30 nm from the interface of sputtered AlN toward the surface, whereas those from Al-polar AlN to N-polar AlN remained at the same position as the interface of sputtered AlN. The interface energies of these IDBs were investigated using first-principles calculations, which support the O-Al-O structure for the IDB from Al-polar AlN to N-polar AlN and the AlxOyNz structure for the IDBs from N-polar AlN to Al-polar AlN.

Optical force modulated by the charge transfer plasmons

We have investigated the modulation of the trapping potential and trapping force provided by the graphene charge transfer plasmon (CTP) structure that supports two resonance modes. Both the screened bonding dipolar plasmon mode and the charge transfer plasmon mode greatly provide a strong trapping potential and trapping force. The position of the trapping potential well can be dynamically regulated by modulating the Fermi energy or the geometry of the charge transfer bridge, allowing for the dynamic trapping of the nanoparticles. The restricted Brownian motion trajectory of the nanoparticles near the structure indicates that both modes can achieve stable nanoparticles trapping. These two peculiar resonance modes could potentially open up additional possibilities for optical manipulation and particle sorting.

Stoichiometry effect on the structure and phase of antiperovskite Sr3SnO thin films prepared using combinatorial co-sputtering

The observation of superconductivity in antiperovskite Sr3SnO crystals has sparked significant interest in understanding its underlying mechanism and fabricating them in thin film forms. To date, molecular beam epitaxy has been used to prepare Sr3SnO thin films, but superconductivity has not been observed. Sr deficiency and subsequent hole doping have been suggested as crucial for the emergent superconductivity, but difficulty in sample preparation due to high chemical instability of this material system has posed challenges for systematic and extensive studies. In this study, we report the fabrication of Sr3SnO thin films through co-sputtering of Sr and SnO2 and investigate the stoichiometry effect on the structural properties of Sr3SnO thin films using a combinatorial approach. A single Sr3SnO phase is observed over a wide range of off-stoichiometric Sr/Sn ratio regions, with preferred orientation changing depending on the Sr/Sn ratio. The formation of intermetallic Sr–Sn compounds in highly Sr-deficient regions suggests the need for careful consideration in elucidating the origin of superconductivity. The single orientation along the [002] direction and lattice parameter change due to biaxial strain applied by using a LAO substrate are indicative of the possible epitaxial growth of antiperovskite oxides using sputtering. Our experimental approach and findings pave the way for high-throughput preparation and characterization of antiperovskite oxides, thus encouraging research on antiperovskite oxides as well as other exotic materials involving highly reactive elements.

High linearity and low hysteresis LMPs/MXene/AgNWs strain sensor for human motion detection

Resistive strain sensors show great potential in motion detection, medicine and healthcare, and human–machine interaction owing to their ease of fabrication, simple structure, and adjustable electrical performance. However, developing high-performance flexible resistive strain sensors with high sensitivity, high linearity, and low hysteresis remains a challenge. In this work, we report an LMPs (liquid metal particles)/MXene/AgNWs strain sensor (LMA strain sensor) with high sensitivity (GF = 6.339), high linearity (R2 = 0.982 24), and low hysteresis (0.452%). In this process, AgNWs act as a bridge between the MXene nanosheets, and the change in contact area of the MXene nanosheets under stretching endows the sensor with high sensitivity. The aggregated LMPs function as a structural framework, capitalizing on their intrinsic fluidic characteristics to serve as an adhesive between silver nanowires (AgNWs) and MXene nanosheets. This approach effectively minimizes the interstitial spaces between AgNWs and MXene. The formation of Ti-O → Ga3+ coordination bonds between MXene nanosheets and LMPs has strengthened the interfacial interactions. Consequently, the sensor demonstrates superior linearity and low hysteresis. In addition, a sensitive layer with a buckled structure is obtained by stretch-release. The buckled structure inhibits inhomogeneous and irreversible connection losses of the sensitive material, further improving the sensor's mechanical durability. LMA strain sensors can accurately detect various human activities such as breathing detection, motion detection, and expression detection. This work will provide an avenue for developing high-performance strain sensors.