Materials Science and NanoEngineering Publications

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High-performance 2D electronic devices enabled by strong and tough two-dimensional polymer with ultra-low dielectric constant
(Springer Nature, 2024) Fang, Qiyi; Yi, Kongyang; Zhai, Tianshu; Luo, Shisong; Lin, Chen-yang; Ai, Qing; Zhu, Yifan; Zhang, Boyu; Alvarez, Gustavo A.; Shao, Yanjie; Zhou, Haolei; Gao, Guanhui; Liu, Yifeng; Xu, Rui; Zhang, Xiang; Wang, Yuzhe; Tian, Xiaoyin; Zhang, Honghu; Han, Yimo; Zhu, Hanyu; Zhao, Yuji; Tian, Zhiting; Zhong, Yu; Liu, Zheng; Lou, Jun; Rice Advanced Materials Institute
As the feature size of microelectronic circuits is scaling down to nanometer order, the increasing interconnect crosstalk, resistance-capacitance (RC) delay and power consumption can limit the chip performance and reliability. To address these challenges, new low-k dielectric (k < 2) materials need to be developed to replace current silicon dioxide (k = 3.9) or SiCOH, etc. However, existing low-k dielectric materials, such as organosilicate glass or polymeric dielectrics, suffer from poor thermal and mechanical properties. Two-dimensional polymers (2DPs) are considered promising low-k dielectric materials because of their good thermal and mechanical properties, high porosity and designability. Here, we report a chemical-vapor-deposition (CVD) method for growing fluoride rich 2DP-F films on arbitrary substrates. We show that the grown 2DP-F thin films exhibit ultra-low dielectric constant (in plane k = 1.85 and out-of-plane k = 1.82) and remarkable mechanical properties (Young’s modulus > 15 GPa). We also demonstrated the improved performance of monolayer MoS2 field-effect-transistors when utilizing 2DP-F thin films as dielectric substrates.
High sound pressure piezoelectric micromachined ultrasonic transducers using sputtered potassium sodium niobate
(Springer Nature, 2024) Xia, Fan; Peng, Yande; Yue, Wei; Luo, Mingze; Teng, Megan; Chen, Chun-Ming; Pala, Sedat; Yu, Xiaoyang; Ma, Yuanzheng; Acharya, Megha; Arakawa, Ryuichi; Martin, Lane W.; Lin, Liwei; Rice Advanced Materials Institute
This work presents air-coupled piezoelectric micromachined ultrasonic transducers (pMUTs) with high sound pressure level (SPL) under low-driving voltages by utilizing sputtered potassium sodium niobate K0.34Na0.66NbO3 (KNN) films. A prototype single KNN pMUT has been tested to show a resonant frequency at 106.3 kHz under 4 Vp-p with outstanding characteristics: (1) a large vibration amplitude of 3.74 μm/V, and (2) a high acoustic root mean square (RMS) sound pressure level of 105.5 dB/V at 10 cm, which is 5–10 times higher than those of AlN-based pMUTs at a similar frequency. There are various potential sensing and actuating applications, such as fingerprint sensing, touch point, and gesture recognition. In this work, we present demonstrations in three fields: haptics, loudspeakers, and rangefinders. For haptics, an array of 15 × 15 KNN pMUTs is used as a non-contact actuator to provide a focal pressure of around 160.3 dB RMS SPL at a distance of 15 mm. This represents the highest output pressure achieved by an airborne pMUT for haptic sensation on human palms. When used as a loudspeaker, a single pMUT element with a resonant frequency close to the audible range at 22.8 kHz is characterized. It is shown to be able to generate a uniform acoustic output with an amplitude modulation scheme. In the rangefinder application, pulse-echo measurements using a single pMUT element demonstrate good transceiving results, capable of detecting objects up to 2.82 m away. As such, this new class of high-SPL and low-driving-voltage pMUTs could be further extended to other applications requiring high acoustic pressure and a small form factor.
Three-chamber electrochemical reactor for selective lithium extraction from brine
(National Academy of Sciences, 2024) Feng, Yuge; Park, Yoon; Hao, Shaoyun; Fang, Zhiwei; Terlier, Tanguy; Zhang, Xiao; Qiu, Chang; Zhang, Shoukun; Chen, Fengyang; Zhu, Peng; Nguyen, Quan; Wang, Haotian; Biswal, Sibani Lisa; Rice Advanced Material Institute
Efficient lithium recovery from geothermal brines is crucial for the battery industry. Current electrochemical separation methods struggle with the simultaneous presence of Na+, K+, Mg2+, and Ca2+ because these cations are similar to Li+, making it challenging to separate effectively. We address these challenges with a three-chamber reactor featuring a polymer porous solid electrolyte in the middle layer. This design improves the transference number of Li+ (tLi+) by 2.1 times compared to the two-chamber reactor and also reduces the chlorine evolution reaction, a common side reaction in electrochemical lithium extraction, to only 6.4% in Faradaic Efficiency. Employing a lithium-ion conductive glass ceramic (LICGC) membrane, the reactor achieved high tLi+ of 97.5% in LiOH production from simulated brine, while the concentrations of Na+ K+, Mg2+, and Ca2+ are below the detection limit. Electrochemical experiments and surface analysis elucidated the cation transport mechanism, highlighting the impact of Na+ on Li+ migration at the LICGC interface.
Supported and Free-Standing Non-Noble Metal Nanoparticles and Their Catalytic Activity in Hydroconversion of Asphaltenes into Light Hydrocarbons
(MDPI, 2024) Kustov, Leonid; Tarasov, Andrei; Kartavova, Kristina; Khabashesku, Valery; Kirichenko, Olga; Kapustin, Gennady; Kustov, Alexander; Abkhalimov, Evgeny; Ershov, Boris
The hydroconversion of asphaltenes into light hydrocarbons catalyzed by supported and free-standing non-noble metal nanoparticles was studied. The activity of Ni or Co immobilized on microspherical oxide carriers and Co nanoparticles dispersed in a hydrocarbon solution of asphaltene was found to be higher than that of a comparative Pt-Pd/Al2O3 catalyst. The yield of light products (C5+) reached up to 91% on cobalt nanoparticles supported onto alumina microspheres.
Laser-induced high-entropy alloys as long-duration bifunctional electrocatalysts for seawater splitting
(Royal Society of Chemistry, 2024) Xie, Yunchao; Xu, Shichen; Meng, Andrew C.; Zheng, Bujingda; Chen, Zhenru; Tour, James M.; Lin, Jian; NanoCarbon Center;Rice Advanced Materials Institute
Electrocatalytic seawater splitting has garnered significant attention as a promising approach for eco-friendly, large-scale green hydrogen production. Development of high-efficiency and cost-effective electrocatalysts remains a frontier in this field. Herein, we report a rapid in situ synthesis of FeNiCoCrRu high-entropy alloy nanoparticles (HEA NPs) by direct CO2 laser induction of metal precursors on carbon paper under ambient conditions. Due to the induced ultrahigh temperature and ultrafast heating/quenching rates, FeNiCoCrRu HEA NPs with sizes ranging from 5 to 40 nm possess uniform phase homogeneity. FeNiCoCrRu HEA NPs exhibit exceptional bifunctional electrocatalytic activities, delivering overpotentials of 0.148 V at 600 mA cm−2 for the hydrogen evolution reaction and 0.353 V at 300 mA cm−2 for the oxygen evolution reaction in alkaline seawater. When assembled FeNiCoCrRu HEA NPs to an electrolyzer, it shows a negligible voltage increase at 250 mA cm−2 even after over 3000-hour operation. This superior performance can be attributed to the high-entropy design, large electrochemical specific area, and excellent chemical and structural stability. An operando Raman spectroscopy study discloses that the Ni and Ru sites serve as active sites for hydrogen evolution, while the Ni site acts as an active site for oxygen evolution. This work demonstrates a laser-induced eco-friendly nanomaterial synthesis. The systematic studies offer an in-depth understanding of HEA design and its correlation with high-efficiency seawater splitting.
SOD1 Is an Integral Yet Insufficient Oxidizer of Hydrogen Sulfide in Trisomy 21 B Lymphocytes and Can Be Augmented by a Pleiotropic Carbon Nanozyme
(MDPI, 2024) Mouli, Karthik; Liopo, Anton V.; Suva, Larry J.; Olson, Kenneth R.; McHugh, Emily A.; Tour, James M.; Derry, Paul J.; Kent, Thomas A.; Smalley-Curl Institute;NanoCarbon Center;Rice Advanced Materials Institute
Down syndrome (DS) is a multisystemic disorder that includes accelerated aging caused by trisomy 21. In particular, overexpression of cystathionine-β-synthase (CBS) is linked to excess intracellular hydrogen sulfide (H2S), a mitochondrial toxin at higher concentrations, which impairs cellular viability. Concurrent overexpression of superoxide dismutase 1 (SOD1) may increase oxidative stress by generating excess hydrogen peroxide (H2O2) while also mitigating the toxic H2S burden via a non-canonical sulfide-oxidizing mechanism. We investigated the phenotypic variability in basal H2S levels in relation to DS B lymphocyte cell health and SOD1 in H2S detoxification. The H2S levels were negatively correlated with the DS B lymphocyte growth rates but not with CBS protein. Pharmacological inhibition of SOD1 using LCS-1 significantly increased the H2S levels to a greater extent in DS cells while also decreasing the polysulfide products of H2S oxidation. However, DS cells exhibited elevated H2O2 and lipid peroxidation, representing potential toxic consequences of SOD1 overexpression. Treatment of DS cells with a pleiotropic carbon nanozyme (pleozymes) decreased the total oxidative stress and reduced the levels of the H2S-generating enzymes CBS and 3-mercaptopyruvate sulfurtransferase (MPST). Our results indicate that pleozymes may bridge the protective and deleterious effects of DS SOD1 overexpression on H2S metabolism and oxidative stress, respectively, with cytoprotective benefits.
Divergent Syntheses of Near-Infrared Light-Activated Molecular Jackhammers for Cancer Cell Eradication
(Wiley, 2024) Li, Bowen; Ayala-Orozco, Ciceron; Si, Tengda; Zhou, Lixin; Wang, Zicheng; Martí, Angel A.; Tour, James M.; Smalley-Curl Institute;NanoCarbon Center;Rice Advanced Materials Institute
Aminocyanines incorporating Cy7 and Cy7.5 moieties function as molecular jackhammers (MJH) through vibronic-driven action (VDA). This mechanism, which couples molecular vibrational and electronic modes, results in picosecond-scale concerted stretching of the entire molecule. When cell-associated and activated by near-infrared light, MJH mechanically disrupts cell membranes, causing rapid necrotic cell death. Unlike photodynamic and photothermal therapies, the ultrafast vibrational action of MJH is unhindered by high concentrations of reactive oxygen species scavengers and induces only a minimal temperature increase. Here, the efficient synthesis of a library of MJH is described using a practical approach to access a key intermediate and facilitating the preparation of various Cy7 and Cy7.5 MJH with diverse side chains in moderate to high yields. Photophysical characterization reveals that structural modifications significantly affect molar extinction coefficients and quantum yields while maintaining desirable absorption and emission wavelengths. The most promising compounds, featuring dimethylaminoethyl and dimethylcarbamoyl substitutions, demonstrate up to sevenfold improvement in phototherapeutic index compared to Cy7.5 amine across multiple cancer cell lines. This synthetic strategy provides a valuable platform for developing potent, light-activated therapeutic agents for cancer treatment, with potentially broad applicability across various cancer types.
Intermolecular Interactions and their Implications in Solid-State Photon Interconversion
(Swiss Chemical Society, 2024) Nienhaus, Lea; Rice Advanced Materials Institute
Photon interconversion promises to alleviate thermalization losses for high energy photons and facilitates utilization of sub-bandgap photons – effectively enabling the optimal use of the entire solar spectrum. However, for solid-state device applications, the impact of intermolecular interactions on the energetic landscape underlying singlet fission and triplet-triplet annihilation upconversion cannot be neglected. In the following, the implications of molecular arrangement, intermolecular coupling strength and molecular orientation on the respective processes of solid-state singlet fission and triplet-triplet annihilation are discussed.
A fast analytical model for predicting battery performance under mixed kinetic control
(Elsevier, 2024) Wang, Hongxuan; Wang, Fan; Tang, Ming
Predicting battery rate performance traditionally relies on computation-intensive numerical simulations. Although faster, simplified analytical models exist, they usually assume a single rate-limiting process such as solid diffusion or electrolyte transport. Here, an improved analytical model, the uniform-reaction-solid-concentration (URCs) model, is developed for battery (dis)charging under mixed control of mass transport in both solid and electrolyte phases. Compared to previous single-particle models extended to incorporate electrolyte kinetics, URCs captures the impact of salt depletion on diminishing the (dis)charge capacity, a critical phenomenon for thick electrodes and/or at high rates. The model demonstrates good agreement with full-order simulations. Importantly, it is compatible with gradient-based optimization algorithms to efficiently search for the optimal battery configurations, while the numerical simulation method struggles to accurately evaluate the derivatives of the objective function and causes optimization to fail. These features allow our model to effectively complement numerical simulations as a useful computational tool for battery design.
Photopatterning of conductive hydrogels which exhibit tissue-like properties
(Royal Society of Chemistry, 2024) Sifringer, Léo; Windt, Lina De; Bernhard, Stéphane; Amos, Giulia; Clément, Blandine; Duru, Jens; Tibbitt, Mark W.; Tringides, Christina M.
Hydrogels are three-dimensional, highly tunable material systems that can match the properties of extracellular matrices. In addition to being widely used to grow and modulate cell behavior, hydrogels can be made conductive to further modulate electrically active cells, such as neurons, and even incorporated into multielectrode arrays to interface with tissues. To enable conductive hydrogels, graphene flakes can be mechanically suspended into a hydrogel precursor. The conductivity of the hydrogel can be increased by increasing the weight percentage of graphene flakes in the precursor while maintaining the mechanical properties of the formed gel similar to the properties of neural tissue. By using a photocrosslinkable hydrogel matrix, such as gelatin methacrylate, with a photoabsorber, the conductive precursor solutions can be crosslinked into predefined complex patterns. Finally, the formulations can be used to support the growth of sensory neurons, derived from human induced pluripotent stem cells, for more than 7 weeks while the neurons remain viable. These scaffolds can be patterned into components of multielectrode arrays, to enable ultrasoft electrodes with tissue-matched properties for further interactions, both in vitro and in vivo, with the nervous systems.
Phase Transformation Driven by Oxygen Vacancy Redistribution as the Mechanism of Ferroelectric Hf0.5Zr0.5O2 Fatigue
(Wiley, 2024) Zhang, Zimeng; Craig, Isaac; Zhou, Tao; Holt, Martin; Flores, Raul; Sheridan, Evan; Inzani, Katherine; Huang, Xiaoxi; Nag, Joyeeta; Prasad, Bhagwati; Griffin, Sinéad M.; Ramesh, Ramamoorthy
As a promising candidate for nonvolatile memory devices, the hafnia-based ferroelectric system has recently been a hot research topic. Although significant progress has been made over the past decade, the endurance problem is still an obstacle to its final application. In perovskite-based ferroelectrics, such as the well-studied Pb[ZrxTi1−x]O3 (PZT) family, polarization fatigue has been discussed within the framework of the interaction of charged defects (such as oxygen vacancies) with the moving domains during the switching process, particularly at the electrode-ferroelectric interface. Armed with this background, a hypothesis is set out to test that a similar mechanism can be in play with the hafnia-based ferroelectrics. The conducting perovskite La-Sr-Mn-O is used as the contact electrode to create La0.67Sr0.33MnO3 / Hf0.5Zr0.5O2 (HZO)/ La0.67Sr0.33MnO3 capacitor structures deposited on SrTiO3-Si substrates. Nanoscale X-ray diffraction is performed on single capacitors, and a structural phase transition from polar o-phase toward non-polar m-phase is demonstrated during the bipolar switching process. The energy landscape of multiphase HZO has been calculated at varying oxygen vacancy concentrations. Based on both theoretical and experimental results, it is found that a polar to non-polar phase transformation caused by oxygen vacancy redistribution during electric cycling is a likely explanation for fatigue in HZO.
Three-dimensional printing of wood
(AAAS, 2024) Thakur, Md Shajedul Hoque; Shi, Chen; Kearney, Logan T.; Saadi, M. A. S. R.; Meyer, Matthew D.; Naskar, Amit K.; Ajayan, Pulickel M.; Rahman, Muhammad M.
Natural wood has served as a foundational material for buildings, furniture, and architectural structures for millennia, typically shaped through subtractive manufacturing techniques. However, this process often generates substantial wood waste, leading to material inefficiency and increased production costs. A potential opportunity arises if complex wood structures can be created through additive processes. Here, we demonstrate an additive-free, water-based ink made of lignin and cellulose, the primary building blocks of natural wood, that can be used to three-dimensional (3D) print architecturally designed wood structures via direct ink writing. The resulting printed structures, after heat treatment, closely resemble the visual, textural, olfactory, and macro-anisotropic properties, including mechanical properties, of natural wood. Our results pave the way for 3D-printed wooden construction with a sustainable pathway to upcycle/recycle natural wood.
Vertical heterostructure of graphite–MoS2 for gas sensing
(Royal Society of Chemistry, 2024) Tripathi, M.; Deokar, G.; Casanova-Chafer, J.; Jin, J.; Sierra-Castillo, A.; Ogilvie, S. P.; Lee, F.; Iyengar, S. A.; Biswas, A.; Haye, E.; Genovese, A.; Llobet, E.; Colomer, J.-F.; Jurewicz, I.; Gadhamshetty, V.; Ajayan, P. M.; Schwingenschlögl, Udo; Costa, Pedro M. F. J.; Dalton, A. B.
2D materials, given their form-factor, high surface-to-volume ratio, and chemical functionality have immense use in sensor design. Engineering 2D heterostructures can result in robust combinations of desirable properties but sensor design methodologies require careful considerations about material properties and orientation to maximize sensor response. This study introduces a sensor approach that combines the excellent electrical transport and transduction properties of graphite film with chemical reactivity derived from the edge sites of semiconducting molybdenum disulfide (MoS2) through a two-step chemical vapour deposition method. The resulting vertical heterostructure shows potential for high-performance hybrid chemiresistors for gas sensing. This architecture offers active sensing edge sites across the MoS2 flakes. We detail the growth of vertically oriented MoS2 over a nanoscale graphite film (NGF) cross-section, enhancing the adsorption of analytes such as NO2, NH3, and water vapor. Raman spectroscopy, density functional theory calculations and scanning probe methods elucidate the influence of chemical doping by distinguishing the role of MoS2 edge sites relative to the basal plane. High-resolution imaging techniques confirm the controlled growth of highly crystalline hybrid structures. The MoS2/NGF hybrid structure exhibits exceptional chemiresistive responses at both room and elevated temperatures compared to bare graphitic layers. Quantitative analysis reveals that the sensitivity of this hybrid sensor surpasses other 2D material hybrids, particularly in parts per billion concentrations.
The rise of borophene
(Elsevier, 2024) Kumar, Prashant; Singh, Gurwinder; Bahadur, Rohan; Li, Zhixuan; Zhang, Xiangwei; Sathish, C. I.; Benzigar, Mercy R.; Kim Anh Tran, Thi; Padmanabhan, Nisha T.; Radhakrishnan, Sithara; Janardhanan, Jith C; Ann Biji, Christy; Jini Mathews, Ann; John, Honey; Tavakkoli, Ehsan; Murugavel, Ramaswamy; Roy, Soumyabrata; Ajayan, Pulickel M.; Vinu, Ajayan
Borophene stands out uniquely among Xenes with its metallic character, Dirac nature, exceptional electron mobility, thermal conductivity, and Young’s moduli—surpassing graphene. Invented in 2015, various methods, including atomic layer deposition, molecular beam epitaxy, and chemical vapor deposition, have successfully been demonstrated to realize substrate-supported crystal growth. Top-down approaches like micromechanical, sonochemical, solvothermal and modified hummer’s techniques have also been employed. Thanks to its high electronic mobility, borophene serves as an active material for ultrafast sensing of light, gases, molecules, and strain. Its metallic behaviour, electrochemical activity, and anti-corrosive nature make it ideal for applications in energy storage and catalysis. It has been proven effective as an electrocatalyst for HER, OER, water splitting, CO2 reduction, and NH3 reduction reactions. Beyond this, borophene has found utility in bioimaging, biosensing, and various biomedical applications. A special emphasis will be given on the borophene nanoarchitectonics i.e. doped borophene and borophene-based hybrids with other 2D materials and nanoparticles and the theoretical understanding of these emerging materials systems to gain more insights on their electronic structure and properties, aiming to manipulate borophene for tailored applications.
Preserving surface strain in nanocatalysts via morphology control
(AAAS, 2024) Shi, Chuqiao; Cheng, Zhihua; Leonardi, Alberto; Yang, Yao; Engel, Michael; Jones, Matthew R.; Han, Yimo
Engineering strain critically affects the properties of materials and has extensive applications in semiconductors and quantum systems. However, the deployment of strain-engineered nanocatalysts faces challenges, in particular in maintaining highly strained nanocrystals under reaction conditions. Here, we introduce a morphology-dependent effect that stabilizes surface strain even under harsh reaction conditions. Using four-dimensional scanning transmission electron microscopy (4D-STEM), we found that cube-shaped core-shell Au@Pd nanoparticles with sharp-edged morphologies sustain coherent heteroepitaxial interfaces with larger critical thicknesses than morphologies with rounded edges. This configuration inhibits dislocation nucleation due to reduced shear stress at corners, as indicated by molecular dynamics simulations. A Suzuki-type cross-coupling reaction shows that our approach achieves a fourfold increase in activity over conventional nanocatalysts, owing to the enhanced stability of surface strain. These findings contribute to advancing the development of advanced nanocatalysts and indicate broader applications for strain engineering in various fields.
Reversible non-volatile electronic switching in a near-room-temperature van der Waals ferromagnet
(Springer Nature, 2024) Wu, Han; Chen, Lei; Malinowski, Paul; Jang, Bo Gyu; Deng, Qinwen; Scott, Kirsty; Huang, Jianwei; Ruff, Jacob P. C.; He, Yu; Chen, Xiang; Hu, Chaowei; Yue, Ziqin; Oh, Ji Seop; Teng, Xiaokun; Guo, Yucheng; Klemm, Mason; Shi, Chuqiao; Shi, Yue; Setty, Chandan; Werner, Tyler; Hashimoto, Makoto; Lu, Donghui; Yilmaz, Turgut; Vescovo, Elio; Mo, Sung-Kwan; Fedorov, Alexei; Denlinger, Jonathan D.; Xie, Yaofeng; Gao, Bin; Kono, Junichiro; Dai, Pengcheng; Han, Yimo; Xu, Xiaodong; Birgeneau, Robert J.; Zhu, Jian-Xin; da Silva Neto, Eduardo H.; Wu, Liang; Chu, Jiun-Haw; Si, Qimiao; Yi, Ming; Rice Center for Quantum Materials
Non-volatile phase-change memory devices utilize local heating to toggle between crystalline and amorphous states with distinct electrical properties. Expanding on this kind of switching to two topologically distinct phases requires controlled non-volatile switching between two crystalline phases with distinct symmetries. Here, we report the observation of reversible and non-volatile switching between two stable and closely related crystal structures, with remarkably distinct electronic structures, in the near-room-temperature van der Waals ferromagnet Fe5−δGeTe2. We show that the switching is enabled by the ordering and disordering of Fe site vacancies that results in distinct crystalline symmetries of the two phases, which can be controlled by a thermal annealing and quenching method. The two phases are distinguished by the presence of topological nodal lines due to the preserved global inversion symmetry in the site-disordered phase, flat bands resulting from quantum destructive interference on a bipartite lattice, and broken inversion symmetry in the site-ordered phase.
Revealing the impact of ammonium ions from different low-dimensional perovskite structures on the film formation and degradation mechanism of FAPbI3 via sequential deposition
(AIP Publishing LLC, 2024) Wang, Yafei; Yuan, Shihao; Feng, Rongsen; Diao, Zecheng; Huang, Jie; Liao, Jiacai; Sidhik, Siraj; Shuai, Xinting; Wang, Meicong; Zou, Tao; Liang, Zhongwei; Zhang, Ting; Mohite, Aditya D.; Li, Shibin
In recent years, the organic–inorganic hybrid perovskite community has been widely employed as the photo-active layer in optical-electronic devices. The black α-phase formamidinium lead iodide (FAPbI3) is the most popular perovskite for realizing high-efficiency solar cells due to its suitable bandgap. However, the issue of stability is also a concern in the research on FAPbI3 solar cells. In this study, different ammonium ions, such as butylamine (BA), guanidine (GA), and butylene diamine (BDA), which are commonly used to construct two-dimensional perovskites, including Ruddlesden–Popper, Dion–Jacobson, and alternating cations in the interlayer space, respectively, were introduced in the fabrication of FAPbI3 using a sequential deposition method. Several structures of PbI2 precursor films were formed by introducing the aforementioned ions, which exhibited different arrangements and connection modes in lead iodides. BA-PbI2 precursor films exhibited higher specific surface areas, which were beneficial to the diffusion, ion exchange, and sequential reaction of FA+. The BDA-PbI2 precursor film slowed down the sequential reaction of FAPbI3 because of reduced van der Waals bonds. The nucleation dynamics and degradation processes of perovskites were deeply investigated in this study. Solar cells based on BA-PbI2, GA-PbI2, and BDA-PbI2 were also fabricated.
Spin disorder control of topological spin texture
(Springer Nature, 2024) Zhang, Hongrui; Shao, Yu-Tsun; Chen, Xiang; Zhang, Binhua; Wang, Tianye; Meng, Fanhao; Xu, Kun; Meisenheimer, Peter; Chen, Xianzhe; Huang, Xiaoxi; Behera, Piush; Husain, Sajid; Zhu, Tiancong; Pan, Hao; Jia, Yanli; Settineri, Nick; Giles-Donovan, Nathan; He, Zehao; Scholl, Andreas; N’Diaye, Alpha; Shafer, Padraic; Raja, Archana; Xu, Changsong; Martin, Lane W.; Crommie, Michael F.; Yao, Jie; Qiu, Ziqiang; Majumdar, Arun; Bellaiche, Laurent; Muller, David A.; Birgeneau, Robert J.; Ramesh, Ramamoorthy; Rice Advanced Materials Institute
Stabilization of topological spin textures in layered magnets has the potential to drive the development of advanced low-dimensional spintronics devices. However, achieving reliable and flexible manipulation of the topological spin textures beyond skyrmion in a two-dimensional magnet system remains challenging. Here, we demonstrate the introduction of magnetic iron atoms between the van der Waals gap of a layered magnet, Fe3GaTe2, to modify local anisotropic magnetic interactions. Consequently, we present direct observations of the order-disorder skyrmion lattices transition. In addition, non-trivial topological solitons, such as skyrmioniums and skyrmion bags, are realized at room temperature. Our work highlights the influence of random spin control of non-trivial topological spin textures.
Strong nonlinear optical processes with extraordinary polarization anisotropy in inversion-symmetry broken two-dimensional PdPSe
(Springer Nature, 2024) Zhu, Song; Duan, Ruihuan; Xu, Xiaodong; Sun, Fangyuan; Chen, Wenduo; Wang, Fakun; Li, Siyuan; Ye, Ming; Zhou, Xin; Cheng, Jinluo; Wu, Yao; Liang, Houkun; Kono, Junichiro; Li, Xingji; Liu, Zheng; Wang, Qi Jie
Nonlinear optical activities, especially second harmonic generation (SHG), are key phenomena in inversion-symmetry-broken two-dimensional (2D) transition metal dichalcogenides (TMDCs). On the other hand, anisotropic nonlinear optical processes are important for unique applications in nano-nonlinear photonic devices with polarization functions, having become one of focused research topics in the field of nonlinear photonics. However, the strong nonlinearity and strong optical anisotropy do not exist simultaneously in common 2D materials. Here, we demonstrate strong second-order and third-order susceptibilities of 64 pm/V and 6.2×10−19 m2/V2, respectively, in the even-layer PdPSe, which has not been discovered in other common TMDCs (e.g., MoS2). Strikingly, it also simultaneously exhibited strong SHG anisotropy with an anisotropic ratio of ~45, which is the largest reported among all 2D materials to date, to the best of our knowledge. In addition, the SHG anisotropy ratio can be harnessed from 0.12 to 45 (375 times) by varying the excitation wavelength due to the dispersion of $${\chi }^{(2)}$$values. As an illustrative example, we further demonstrate polarized SHG imaging for potential applications in crystal orientation identification and polarization-dependent spatial encoding. These findings in 2D PdPSe are promising for nonlinear nanophotonic and optoelectronic applications.
Interplay between Point and Extended Defects and Their Effects on Jerky Domain-Wall Motion in Ferroelectric Thin Films
(American Physical Society, 2024) Bulanadi, Ralph; Cordero-Edwards, Kumara; Tückmantel, Philippe; Saremi, Sahar; Morpurgo, Giacomo; Zhang, Qi; Martin, Lane W.; Nagarajan, Valanoor; Paruch, Patrycja; Rice Advanced Materials Institute
Defects have a significant influence on the polarization and electromechanical properties of ferroelectric materials. Statistically, they can be seen as random pinning centers acting on an elastic manifold, slowing domain-wall propagation and raising the energy required to switch polarization. Here we show that the “dressing” of defects can lead to unprecedented control of domain-wall dynamics. We engineer defects of two different dimensionalities in ferroelectric oxide thin films—point defects externally induced via He2+ bombardment, and extended quasi-one-dimensional 𝑎 domains formed in response to internal strains. The 𝑎 domains act as extended strong pinning sites (as expected) imposing highly localized directional constraints. Surprisingly, the induced point defects in the He2+ bombarded samples orient and align to impose further directional pinning, screening the effect of 𝑎 domains. This defect interplay produces more uniform and predictable domain-wall dynamics. Such engineered interactions between defects are crucial for advancements in ferroelectric devices.

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