We have developed a pump-probe microscope capable of exciting single semiconductor nanostructure in one location and probing it another with both high spatial temporal resolution. Experiments performed on Si nanowires enable direct visualization the charge cloud produced by photoexcitation at localized spot as spreads along nanowire axis. The time-resolved images show clear evidence rapid diffusional spreading recombination free carriers, which is consistent ambipolar diffusion surface...

Semiconductor nanowires (NWs) are a developing platform for electronic and photonic technologies, many demonstrated devices utilize p-type/n-type (p–n) junction encoded along either the axial or radial directions of wires. These miniaturized junctions enable diverse range functions, from sensors to solar cells, yet physics has not been thoroughly evaluated. Here, we present finite-element modeling Si NW p–n with total diameters ∼240 nm donor/acceptor doping levels ranging 1016 1020 cm–3. We...

Si nanowires (NWs) have been widely explored as a platform for photonic and electronic technologies. Here, we report bottom-up method to break the conventional "wire" symmetry synthetically encode high-resolution array of arbitrary shapes, including nanorods, sinusoids, bowties, tapers, nanogaps, gratings, along NW growth axis. Rapid modulation phosphorus doping combined with selective wet-chemical etching enabled morphological features small 10 nm be patterned over wires more than 50 μm in...

Ultrafast charge carrier dynamics in silicon nanowires (NWs) grown by a vapor–liquid–solid mechanism were interrogated with optical pump–probe microscopy. The high time and spatial resolutions achieved the experiments provide insight into of single nanostructures. Individual NWs excited femtosecond pump pulse focused to diffraction-limited spot, producing photogenerated carriers (electrons holes) localized region structure. Photoexcited undergo both electron–hole recombination diffusional...

Silicon nanowires incorporating p-type/n-type (p-n) junctions have been introduced as basic building blocks for future nanoscale electronic components. Controlling charge flow through these doped nanostructures is central to their function, yet our understanding of this process inferred from measurements that average over entire structures or integrate long times. Here, we used femtosecond pump-probe microscopy directly image the dynamics photogenerated carriers in silicon encoded with p-n...

Vertically aligned semiconductor nanowires (NWs) have many potential applications for NW-based technologies, ranging from solar cells to intracellular sensors. Aligned NWs can be fabricated by top-down etching of planar wafers or synthesized the bottom up using vapor–liquid–solid (VLS) mechanism induce epitaxial growth on lattice-matched substrates. The VLS process permits modulation dopants along NW axis, which if combined with dopant-dependent wet-chemical etching, used encode precise...

Semiconductor nanowires (NWs) are often synthesized by the vapor–liquid–solid (VLS) mechanism, a process in which liquid droplet—supplied with precursors vapor phase—catalyzes growth of solid, crystalline NW. By changing supply precursors, NW composition can be altered as it grows to create axial heterostructures, applicable range technologies. The abruptness heterojunction is mediated catalyst, act reservoir material and impose lower limit on junction width. Here, we demonstrate that this...

The vapor–liquid–solid (VLS) mechanism is widely used for the synthesis of semiconductor nanowires (NWs), yet several aspects are not fully understood. Here, we present comprehensive experimental measurements on growth rate Au-catalyzed Si NWs over a range temperatures (365–480 °C), diameters (30–200 nm), and pressures (0.1–1.6 Torr SiH4). We develop kinetic model VLS that includes (1) incorporation into liquid Au–Si catalyst, (2) evaporation from catalyst surface, (3) crystallization at...

Semiconductor nanowires (NWs) have been demonstrated as a potential platform for wide-range of technologies, yet method to interconnect functionally encoded NWs has remained challenge. Here, we report simple capillarity-driven and self-limited welding process that forms mechanically robust Ohmic inter-NW connections. The occurs at the point-of-contact between two temperatures 400-600 °C below bulk melting point semiconductor. It can be explained by surface diffusion, inducing localized...

The silicon p-n junction is the most successful solar energy technology to date, yet it accounts for a marginal percentage of worldwide production. To change status quo, disruptive technological breakthrough needed. In this Perspective, we discuss potential complex nanowires serve as platform next-generation photovoltaic devices. We review synthesis, electrical characteristics, and optical properties core/shell that are subwavelength in diameter contain radial junctions. highlight unique...

The patterning of semiconductors with nanometer-scale precision is a cornerstone modern technology. Top-down methods, ranging from photolithography to focused-ion beam milling, are typically used fabricate complex nanostructures. In this Perspective, we discuss an alternative bottom-up method encode similar high-resolution morphology in semiconductor nanowires (NWs). This process, termed ENGRAVE for "Encoded Nanowire GRowth and Appearance through VLS Etching", combines fast modulation...

Bottom-up, chemical methods to control the morphology of semiconductor nanostructures are a promising complement top-down fabrication techniques that currently dominate industry.

Ratcheting effects play an important role in systems ranging from mechanical socket wrenches to biological motor proteins. The underlying principle is convert a fluctuating, unbiased force into unidirectional motion. Here, we report the ratcheting of electrons at room temperature using semiconductor nanowire with precisely engineered asymmetry. Modulation diameter creates cylindrical sawtooth geometry broken inversion symmetry on nanometer-length scale. In two-terminal device, this structure...

Dark-field microscopy (DFM) is widely used to optically image and spectroscopically analyze nanoscale objects. In a typical DFM configuration, sample illuminated at oblique angles an objective lens collects light scattered by the range of lower angles. Here, we develop waveguide scattering (WSM) as alternative technique photonic nanostructures. WSM uses incoherent white-light source coupled dielectric slab generate evanescent field that illuminates objects located within several hundred...

Ultrafast carrier dynamics in silicon nanowires with average diameters of 40, 50, 60, and 100 nm were studied transient absorption spectroscopy. After 388 photoexcitation near the direct band gap silicon, broadband spectra from 400 to 800 collected between 200 fs 1.3 ns. The exhibited both absorptive bleach features that evolved on multiple time scales, reflecting contributions thermalization recombination as well shifts ground-state spectrum. initially formed "hot" carriers relaxed edge...

Although silicon (Si) nanowires (NWs) grown by a vapor-liquid-solid (VLS) mechanism have been demonstrated for range of photonic, electronic, and solar-energy applications, continued progress with these NW-based technologies requires increasingly precise compositional morphological control the growth process. However, VLS typically encounters problems such as nonselective deposition on sidewalls, inadvertent kinking, unintentional or inhomogeneous doping, catalyst-induced gradients. Here, we...

Surface trap density in silicon nanowires (NWs) plays a key role the performance of many semiconductor NW-based devices. We use pump–probe microscopy to characterize surface recombination dynamics on point-by-point basis 301 NWs grown using vapor–liquid–solid (VLS) method. The velocity (S), metric quality that is directly proportional density, determined by relationship S = d/4τ from measurements lifetime (τ) and NW diameter (d) at distinct spatial locations individual NWs. find varies as...

Although Rydberg-atom-based electric field sensing provides key advantages over traditional antenna-based detection, it remains limited by the need for a local oscillator (LO) low-field and phase-resolved detection. In this work, we demonstrate that closed-loop quantum interferometric schemes can be used to generate system-internal reference directly replace an external LO Rydberg sensing. We reveal interferometrically defined internal phase frequency analogously atom-based down-mixing...

Knowledge of nucleation and growth mechanisms is essential for the synthesis nanomaterials, such as semiconductor nanowires, with shapes compositions precisely engineered technological applications. Nanowires are conventionally grown by seemingly well-understood vapor-liquid-solid mechanism, which uses a liquid alloy catalyst growth. However, we show that it possible to instantaneously reversibly switch phase between superheated solid state under isothermal conditions above eutectic...

Although Rydberg atom-based electric field sensing provides key advantages over traditional antenna-based detection, it remains limited by the need for a local oscillator (LO) low-field and phase resolved detection. In this work, we demonstrate that closed-loop quantum interferometric schemes can be used to generate system-internal reference directly replace an external LO sensing. We reveal quantum-interferometrically defined internal frequency analogously down-mixing intermediate lock-in...