Capabilities for recording neural activity in behaving mammals have greatly expanded our understanding of brain function. Some of the most sophisticated approaches use light delivered by an implanted fiber-optic cable to optically excite genetically encoded calcium indicators and to record the resulting changes in fluorescence. Physical constraints induced by the cables and the bulk, size, and weight of the associated fixtures complicate studies on natural behaviors, including social interactions and movements in environments that include obstacles, housings, and other complex features. Here, we introduce a wireless, injectable fluorescence photometer that integrates a miniaturized light source and a photodetector on a flexible, needle-shaped polymer support, suitable for injection into the deep brain at sites of interest. The ultrathin geometry and compliant mechanics of these probes allow minimally invasive implantation and stable chronic operation. In vivo studies in freely moving animals demonstrate that this technology allows high-fidelity recording of calcium fluorescence in the deep brain, with measurement characteristics that match or exceed those associated with fiber photometry systems. The resulting capabilities in optical recordings of neuronal dynamics in untethered, freely moving animals have potential for widespread applications in neuroscience research.

Bioresorbable electronic materials serve as foundations for implantable devices that provide active diagnostic or therapeutic function over a timeframe matched to a biological process, and then disappear within the body in a way that avoids secondary surgical extraction procedures. Approaches to power supply in these physically transient systems are critically important. This paper describes a fully biodegradable, monocrystalline silicon photovoltaic (PV) platform based on microscale cells (microcells) designed to operate at wavelengths with long penetration depths in biological tissues (red and near infrared wavelengths) such that external illumination can provide realistic levels of power. Systematic characterization and theoretical simulations of operation under porcine skin and fat establish a foundational understanding of these systems and their scalability. In vivo studies of a representative platform capable of generating ~60 W of electrical power with an open circuit voltage (V oc ) of ~4 V under 4 mm of porcine skin and fat illustrate an ability to operate blue light-emitting diodes (LEDs) as subdermal implants in rat models for 3 days. Here, the PV system fully resorbs over a period of 4 months. Histological analysis reveals that the degradation process introduces no inflammatory responses in the surrounding tissues, consistent with excellent biocompatibility of the devices, their constituent materials and degradation by-products. The results suggest the potential for using silicon photovoltaic microcells as bioresorbable power supplies for a range of transient biomedical implants.

LETTER ARTICLEHigh performance semiconductor lasers on silicon are critical elements of next generation photonic integrated circuits. Transfer printing methods provide promising paths to achieve hybrid integration of III-V devices on Si platforms. This paper presents materials and procedures for epitaxially releasing thin-film microscale GaAs based lasers after their full fabrication on GaAs native substrates, and for subsequently transfer printing arrays of them onto Si wafers. An indium-silver based alloy serves as a thermally conductive bonding interface between the lasers and the Si, for enhanced performance. Numerical calculations provide comparative insights into thermal properties for devices with metallic, organic and semiconductor interfaces. Under current injection, the first of these three interfaces provides, by far, the lowest operating temperatures. Such devices exhibit continuous-wave lasing in the near-infrared range under electrical pumping, with performance comparable to unreleased devices on their native substrates.Silicon (Si) based complementary metal-oxide-semiconductor (CMOS) technology serves as the foundation for the entire integrated circuit (IC) industry. As Si CMOS approaches its scaling limits, interest increases in strategies capable of integrating alternative semiconductors and device structures on Si platforms [1]. For example, the potential for Si based photonics to improve performance (density, energy, speed, etc) in future IC chips [2-4] has created strong demand for efficient on-chip lasers [5]. Attempts to realize this goal range from use of Si Raman lasers to epitaxial growth of Ge or III-V compounds on Si [6][7][8][9][10][11][12]. In spite of much progress, such monolithic approaches do not yet provide the levels of performance that can be achieved in conventional III-V lasers. The challenges include low emission efficiencies in Si and Ge, and defects that arise from large lattice and thermal expansion coefficients mismatches between usual III-V materials (GaAs and InP) and Si and from the polar/non polar character of the III-V/Si interface [13]. By comparison, strategies that involve separate growth of III-V materials followed by integration on Si offer significant promise [14,15]. Approaches based on epitaxial liftoff and transfer printing, in particular, have important proven capabilities in this context, with impressive published examples of both edge and surface emitting lasers formed with thin-film, releasable III-V membranes directly bonded to Si [16,17]. In these schemes, selective removal by wet etching of an epitaxially grown sacrificial layer releases active material structures from the III-V substrate. Soft elastomer stamps serve as non-destructive tools to retrieve these materials and then to deliver them to Si wafers, in array formats in a single step or in a step and repeat fashion. This type of process offers high-speed operation and excellent overlay registration, enabled by controlled van der Waals bonding to the surface of the stamp. A disadvantage of prev...

Pulsed laser-induced dewetting (PLiD) of Ag 0.5 Ni 0.5 thin films results in phase-separated bimetallic nanoparticles with size distributions that depend on the initial thin film thickness. Co-sputtering of Ag and Ni is used to generate the as-deposited (AD) nanogranular supersaturated thin films. The magnetic and optical properties of the AD thin films and PLiD nanoparticles are characterized using a vibrating sample magnetometer, optical absorption spectroscopy, and electron energy loss spectroscopy (EELS). Magnetic measurements demonstrate that Ag 0.5 Ni 0.5 nanoparticles are ferromagnetic at room temperature when the nanoparticle diameters are >20 nm and superparamagnetic <20 nm. Optical measurements show that all nanoparticle size distributions possess a local surface plasmon resonance (LSPR) peak that red-shifts with increasing diameter. Following PLiD, a Janus nanoparticle morphology is observed in scanning transmission electron microscopy, and low-loss EELS reveals size-dependent Ag and Ni LSPR dipole modes, while higher order modes appear only in the Ag hemisphere. PLiD of Ag–Ni thin films is shown to be a viable technique to generate bimetallic nanoparticles with both magnetic and plasmonic functionality.

While many plasmonic phenomena have been realized by using standard nanoscale synthesis in a single 2-dimensional plane, enhanced functionality should be possible by extending into the third dimension. Several nanoscale synthesis approaches have been explored to achieve 3-dimensional (3d) geometries; however, a robust strategy for synthesizing complex 3d plasmonic architectures is lacking. In this study, we utilize a hybrid of direct-write 3d nanoprinting and thin film deposition to fabricate 3d plasmonic structures. Focused electron beam induced deposition (FEBID) is used to deposit nonplasmonic 3d scaffolds, which are subsequently isolated with a conformal SiO2 layer and coated with a gold layer to create functional 3d plasmonic nanostructures. A variety of rod antennae, split-ring nanoresonators, and ring resonators are synthesized, and low-loss electron energy loss spectroscopy (EELS) is utilized to characterize their full plasmonic spectra with nanoscale resolution. Complementary EELS simulations are performed to interpret the spectra and elucidate the associated electric and magnetic field distributions of the infrared and near optical modes. This work demonstrates the flexibility that FEBID scaffolds offer for the advancement of 3d plasmonic devices and future advanced optical and magnetic metamaterials.