More Like this

1. Periodic Poling of X-Cut Thin-Film Lithium Niobate: The Route to Submicrometer Periods

   https://doi.org/10.1109/IFCS-ISAF41089.2020.9234870  

   Rusing, M.; Roeper, M.; Amber, Z.; Kirbus, B.; Eng, L.M.; Zhao, J.; Mookherjea, S. (July 2020, 2020 Joint Conference of the IEEE International Frequency Control Symposium and International Symposium on Applications of Ferroelectrics (IFCS-ISAF))

   null (Ed.)

   Ultra-short poling periods of 1 μm and below in lithium niobate will allow nonlinear optical devices with operation to the UV regime or narrow-band counter-propagating single-photon generation. However, fabrication of such periods in bulk Lithium Niobate penetrating the complete modal areas of waveguides has been challenging. In this work, we demonstrate the fabrication of periodic domain grids with submicrometer periodicity in 300 nm x-cut thin-film lithium niobate. The poling was achieved through application of a single, shaped electrical pulse and electrodes fabricated with a combination of electron-and direct laser-writing lithography. The poling results were investigated with piezo-response force microscopy and second-harmonic microcopy and indicate the poled domains to penetrate fully across the complete film thickness. This will enable the fabrication of novel nonlinear optical devices combining the high efficiency of thin films with ultra-short domain periods. 

   more » « less
2. Wafer-scale waveguide sidewall roughness scattering loss characterization by image processing

   https://doi.org/10.1364/OE.558186  

   Khurana, Mohit; Delfan, Sahar; Yi, Zhenhuan (May 2025, Optics Express)

   Photonic integrated circuits (PICs) are vital for developing affordable, high-performance optoelectronic devices that can be manufactured at an industrial scale, driving innovation and efficiency in various applications. Optical loss of modes in thin film waveguides and devices is a critical measure of their performance. Thin film growth, lithography, masking, and etching processes are imperfect processes that introduce significant sidewall and top-surface roughness and cause dominating optical losses in waveguides and photonic structures. This roughness, as perturbations couple light from guided to far-field radiation modes, leads to scattering losses that can be estimated from theoretical models. Typically, with UV-based lithography, sidewall roughness is significantly larger than wafer-top surface roughness. Atomic force microscopy (AFM) imaging measurement gives a 3D and high-resolution roughness profile, but the measurement is inconvenient, costly, and unscalable for large-scale PICs and at wafer-scale. Here, we evaluate the sidewall roughness profile based on 2D high-resolution scanning electron microscope (SEM) imaging. We characterized the loss on two homemade nitride and oxide films on 3-inch silicon wafers with 12 waveguide devices on each and correlated the scattering loss estimated from a 2D image-based sidewall profile and theoretical Payne model. The lowest loss of guided fundamental transverse electric (TE₀) mode is found at 0.075 dB/cm at 633 nm across 24 devices, a record at visible wavelength. Our work shows 100% success (edge continuity span exceeding 95% of image width/height) in edge detection in image processing of all images to estimate autocorrelation function and optical mode loss. These demonstrations offer valuable insights into waveguide sidewall roughness and a comparison of experimental and 2D SEM image processing based loss estimations with applications in loss characterization at wafer-scale PICs. 

   more » « less
3. Autonomous alignment and healing in multilayer soft electronics using immiscible dynamic polymers

   https://doi.org/10.1126/science.adh0619  

   Cooper, Christopher B.; Root, Samuel E.; Michalek, Lukas; Wu, Shuai; Lai, Jian-Cheng; Khatib, Muhammad; Oyakhire, Solomon T.; Zhao, Renee; Qin, Jian; Bao, Zhenan (June 2023, Science)

   Self-healing soft electronic and robotic devices can, like human skin, recover autonomously from damage. While current devices use a single type of dynamic polymer for all functional layers to ensure strong interlayer adhesion, this approach requires manual layer alignment. In this study, we used two dynamic polymers, which have immiscible backbones but identical dynamic bonds, to maintain interlayer adhesion while enabling autonomous realignment during healing. These dynamic polymers exhibit a weakly interpenetrating and adhesive interface, whose width is tunable. When multilayered polymer films are misaligned after damage, these structures autonomously realign during healing to minimize interfacial free energy. We fabricated devices with conductive, dielectric, and magnetic particles that functionally heal after damage, enabling thin-film pressure sensors, magnetically assembled soft robots, and underwater circuit assembly. 

   more » « less
4. Kirigami enhances film adhesion

   https://doi.org/10.1039/c7sm02338c  

   Zhao, Ruike; Lin, Shaoting; Yuk, Hyunwoo; Zhao, Xuanhe (January 2018, Soft Matter)

   Structures of thin films bonded on substrates have been used in technologies as diverse as flexible electronics, soft robotics, bio-inspired adhesives, thermal-barrier coatings, medical bandages, wearable devices and living devices. The current paradigm for maintaining adhesion of films on substrates is to make the films thinner, and more compliant and adhesive, but these requirements can compromise the function or fabrication of film–substrate structures. For example, there are limits on how thin, compliant and adhesive epidermal electronic devices can be fabricated and still function reliably. Here we report a new paradigm that enhances adhesion of films on substrates via designing rational kirigami cuts in the films without changing the thickness, rigidity or adhesiveness of the films. We find that the effective enhancement of adhesion by kirigami is due to (i) the shear-lag effect of the film segments; (ii) partial debonding at the film segments’ edges; and (iii) compatibility of kirigami films with inhomogeneous deformation of substrates. While kirigami has been widely used to program thin sheets with desirable shapes and mechanical properties, fabricate electronics with enhanced stretchability and design the assembly of three-dimensional microstructures, this paper gives the first systematic study on kirigami enhancing film adhesion. We further demonstrate novel applications including a kirigami bandage, a kirigami heat pad and printed kirigami electronics. 

   more » « less
5. High-temperature insulating ferromagnetic state in charge-disproportionated and spin-state-disproportionated strained SrCoO2.5 thin film

   https://doi.org/10.1063/5.0188767  

   Chowdhury, Sourav; Jana, Anupam; Rawat, Ritu; Yadav, Priyanka; Islam, Rajibul; Xue, Fei; Mandal, A K; Sarkar, Sumit; Mishra, Rajan; Venkatesh, R; et al (May 2024, APL Materials)

   Ferromagnetic insulators (FMIs) have widespread applications in microwave devices, magnetic tunneling junctions, and dissipationless electronic and quantum-spintronic devices. However, the sparsity of the available high-temperature FMIs has led to the quest for a robust and controllable insulating ferromagnetic state. Here, we present compelling evidence of modulation of the magnetic ground state in a SrCoO2.5 (SCO) thin film via strain engineering. The SCO system is an antiferromagnetic insulator with a Neel temperature, TN, of ∼550 K. Applying in-plane compressive strain, the SCO thin film reveals an insulating ferromagnetic state with an extraordinarily high Curie temperature, TC, of ∼750 K. The emerged ferromagnetic state is associated with charge-disproportionation (CD) and spin-state-disproportionation (SSD), involving high-spin Co2+ and low-spin Co4+ ions. The density functional theory calculation also produces an insulating ferromagnetic state in the strained SCO system, consistent with the CD and SSD, which is associated with the structural ordering in the system. Transpiring the insulating ferromagnetic state through modulating the electronic correlation parameters via strain engineering in the SCO thin film will have a significant impact in large areas of modern electronic and spintronic applications. 

   more » « less