Farnaz Niroui

We report an anti-stiction coating that avoids use of per/polyfluoroalkyl substances (PFAS). This is achieved through covalent grafting of polydimethylsiloxane (PDMS) to silicon surfaces, realizing nanometer-thin polymer layers. The resulting coatings display hydrophobicity and surface adhesion comparable to a PFAS-based counterpart. We demonstrate the prospects of these PDMS coatings for reducing in-use stiction, showing enhanced device performance compared to non-treated structures. We further show that fluorine-free cross-linking of the polymer layer enhances the robustness of the coatings, showing a 26% increase in device stability. This is achieved using precursors that are available at industrial scale, with established safety profiles, enabling immediate deployment.

The relative instability of high-efficiency blue phosphorescent organic light-emitting devices (OLEDs) is an important and longstanding challenge. Conventional models of degradation emphasize the dynamics of emissive triplet excitons on phosphorescent molecules, neglecting the potential role of nonemissive, “dark,” triplet excitons on host and charge blocking molecules. Bright and dark triplet dynamics are probed using surface plasmon polariton-coupled modulation and magnetic exciton annihilation modulation, respectively. It is observed that dark triplet excitons dominate both the instability and efficiency roll-off of a high-performance blue phosphorescent OLED. Dissociating dark triplets both improves device stability and reduces efficiency losses at high brightness by a factor of 2. The combined benefit to stability of Purcell engineering and dark triplet management is a factor of 3.5. The results demonstrate that dark triplet excitons reduce the potential benefit of Purcell engineering, emphasizing the importance of characterization and control of dark triplets to realize the goal of stable blue phosphorescent OLEDs.

A large mechanical sensitivity can be achieved by a mechanically tunable quantum tunneling barrier. The tunneling resistance across the nanometer-sized gap can be changed by several orders of magnitude through a sub-angstrom-scale displacement. Here, we demonstrate the performance of a strain sensor formed from pre-stretched Platinum (Pt) on PDMS, where perturbation of the thickness of the nanogap cracks due to strain change the resistance of the device. A gauge factor >500 is realized in a device that is mechanically stabilized by self-assembled monolayer (SAM). Then, we extend the application of the nanogap based strain sensor to temperature and infrared detection. Fabricated proof-of-concept metal/SAM/metal suspended bolometers yield a temperature coefficient of resistance (TCR) between -0.006 K-1 and - 0.085 K-1, and theoretical predictions show that with further optimization the TCRs could be improve to as much as -2.7 K-1, which is more than one order of magnitude better than the state-of-the-art VOx bolometers. Furthermore, this work quantifies the 50 Hz to 10 kHz noise performance of suspended metal/nanogap/metal bolometers and compares the noise spectrum of devices with and without SAM, as well as 10 nm Pt channel vs. 30 nm Pt channel devices. Finally, early stage 830 nm optical measurements show that the device sensitivity of a 10nm Pt / air nanogap / 10 nm Pt peaks at low bias (< 1V, <20 pA) and that the 3dB point of the sensor extends past 10 kHz. The experimental results of this work suggest that nanogap-based sensor architectures exhibit a high sensitivity and may also enable fast response time detectors.

We present a platform for direct van der Waals integration of two-dimensional (2D) materials into high-performance chemical sensors.In our approach, the fabrication of device layers and their integration with 2D materials are separated.Prefabricated device layers are engineered to have sufficient surface interactions to directly pick up the 2D layer upon contact.This enables a singlestep 2D material-to-sensor integration that preserves pristine interfaces, while uniquely keeping the surfaces fully exposed to the environment, allowing for high-sensitivity detection.Using this platform, we fabricated and characterized MoS2 devices for NO2 gas sensing, demonstrating high sensitivity compared to conventionally fabricated devices.Our versatile one-step integration platform can be extended to other materials and analytes, and allow for rapid screening of emerging 2D materials for new sensing functionalities.

We present a platform for localized and conformal strain engineering of two-dimensional (2D) materials with nanoscale control and compatible with wafer-scale processing.Unlike conventional approaches where strain is induced by 2D material transfer onto pre-fabricated topographical structures, our approach enables post-transfer, spontaneous formation of non-planar features to strain the 2D layer.As a result, straining can be achieved without the common formation of bubbles, wrinkles, or tears in the material.We show that such uniform straining can be used to engineer the 2D material band structure post-synthesis, tuning its optical and electronic characteristics.This platform opens up new device opportunities in sensors, transistors, and quantum light sources.

Abstract Despite remarkable progress in the development of halide perovskite materials and devices, their integration into nanoscale optoelectronics has been hindered by a lack of control over nanoscale patterning. Owing to their tendency to degrade rapidly, perovskites suffer from chemical incompatibility with conventional lithographic processes. Here, we present an alternative, bottom-up approach for precise and scalable formation of perovskite nanocrystal arrays with deterministic control over size, number, and position. In our approach, localized growth and positioning is guided using topographical templates of controlled surface wettability through which nanoscale forces are engineered to achieve sub-lithographic resolutions. With this technique, we demonstrate deterministic arrays of CsPbBr 3 nanocrystals with tunable dimensions down to &lt;50 nm and positional accuracy &lt;50 nm. Versatile, scalable, and compatible with device integration processes, we then use our technique to demonstrate arrays of nanoscale light-emitting diodes, highlighting the new opportunities that this platform offers for perovskites’ integration into on-chip nanodevices.

Progress in understanding brain-viscera interoceptive signaling is hindered by a dearth of implantable devices suitable for probing both brain and peripheral organ neurophysiology during behavior. Here we describe multifunctional neural interfaces that combine the scalability and mechanical versatility of thermally drawn polymer-based fibers with the sophistication of microelectronic chips for organs as diverse as the brain and the gut. Our approach uses meters-long continuous fibers that can integrate light sources, electrodes, thermal sensors and microfluidic channels in a miniature footprint. Paired with custom-fabricated control modules, the fibers wirelessly deliver light for optogenetics and transfer data for physiological recording. We validate this technology by modulating the mesolimbic reward pathway in the mouse brain. We then apply the fibers in the anatomically challenging intestinal lumen and demonstrate wireless control of sensory epithelial cells that guide feeding behaviors. Finally, we show that optogenetic stimulation of vagal afferents from the intestinal lumen is sufficient to evoke a reward phenotype in untethered mice.

Insects maintain remarkable agility after incurring severe injuries or wounds. Although robots driven by rigid actuators have demonstrated agile locomotion and manipulation, most of them lack animal-like robustness against unexpected damage. Dielectric elastomer actuators (DEAs) are a class of muscle-like soft transducers that have enabled nimble aerial, terrestrial, and aquatic robotic locomotion comparable to that of rigid actuators. However, unlike muscles, DEAs suffer local dielectric breakdowns that often cause global device failure. These local defects severely limit DEA performance, lifetime, and size scalability. We developed DEAs that can endure more than 100 punctures while maintaining high bandwidth (>400 hertz) and power density (>700 watt per kilogram)-sufficient for supporting energetically expensive locomotion such as flight. We fabricated electroluminescent DEAs for visualizing electrode connectivity under actuator damage. When the DEA suffered severe dielectric breakdowns that caused device failure, we demonstrated a laser-assisted repair method for isolating the critical defects and recovering performance. These results culminate in an aerial robot that can endure critical actuator and wing damage while maintaining similar accuracy in hovering flight. Our work highlights that soft robotic systems can embody animal-like agility and resilience-a critical biomimetic capability for future robots to interact with challenging environments.

Pristine van der Waals (vdW) interfaces between two-dimensional (2D) and other materials are core to emerging optical and electronic devices. Their direct fabrication is, however, challenged as the vdW forces are weak and cannot be tuned to accommodate integration of arbitrary layers without solvents, sacrificial-layers or high-temperatures, steps that can introduce damage. To address these limitations, we introduce a single-step 2D material-to-device integration approach in which forces promoting transfer are decoupled from the vdW forces at the interface of interest. We use this adhesive matrix transfer to demonstrate conventionally-forbidden direct integration of diverse 2D materials (MoS2, WSe2, PtS2, GaS) with dielectrics (SiO2, Al2O3), and scalable, aligned heterostructure formation, both foundational to device development. We then demonstrate a single-step integration of monolayer-MoS2 into arrays of transistors. With no exposure to polymers or solvents, clean interfaces and pristine surfaces are preserved, which can be further engineered to demonstrate both n- and p-type behavior. Beyond serving as a platform to probe the intrinsic properties of sensitive nanomaterials without the influence of processing steps, our technique allows efficient formation of unconventional device form-factors, with an example of flexible transistors demonstrated.

We report an approach for scalable fabrication of suspended, ultrathin, nonplanar nanostructures without the use of sacrificial layers. We achieve this by engineering interfacial forces through a patterned self-assembled molecular monolayer to enable controlled delamination of a deposited oxide thin-film in predetermined locations. This allows formation of nonplanar structures with thicknesses < 10 nm and nanogaps reaching < 10 nm – features hard to achieve with conventional fabrication. This approach is versatile as it extends conventional, wafer-scale planar fabrication techniques to nonplanar designs. The resulting features are tunable in structure and compatible with various materials, enabling applications in miniaturized nanoelectromechanical devices including ultrathin mechanical resonators.