Pulsed lasers are used in tandem with one-dimensional nanostructures in a wide range of contemporary physical chemistry experiments, including four-dimensional transmission electron microscopy, scanning probe microscopy, and laser-assisted atom-probe tomography (APT). In this work, closed-form solutions for the pulsed photothermal heating of one-dimensional nanomaterials are compared with experimental time-of-flight APT ion spectra from both amorphous and crystalline silicon targets. Analytical results are given for targets with either a uniform cylindrical morphology or an arbitrary degree of conical tapering. Counterintuitively, increasing a conical specimen’s taper-angle is shown to lead to increases in the maximum temperature reached at the tip of the specimen. In particular, the heat source for tapered targets is affected by internal morphology-dependent cavity resonances that increase the maximum tip temperature relative to an untapered cylindrical structure. Experimental time-of-flight ion spectra for both crystalline- and amorphous-silicon specimens are observed to agree with pulsed photothermal heating calculations. The results presented here will be of general use for quantifying photothermal heating in a wide range of experiments including tip-enhanced near-field scanning-probe microscopy, time-resolved electron microscopy, and also laser-assisted atom probe tomography.

Graphene aerogels derived from graphene-oxide (GO) starting materials recently have been shown to exhibit a combination of high electrical conductivity, chemical stability, and low cost that has enabled a range of electrochemical applications. Standard synthesis protocols for manufacturing graphene aerogels require the use of sol–gel chemical reactions that are maintained at high temperatures for long periods of time ranging from 12 h to several days. Here we report an ultrafast, acid-catalyzed sol–gel formation process in acetonitrile in which wet GO-loaded gels are realized within 2 h at temperatures below 45 °C. Spectroscopic and electrochemical analysis following supercritical drying and pyrolysis confirms the reduction of the GO in the aerogels to sp2 carbon crystallites with no residual carbon–nitrogen bonds from the acetonitrile or its derivatives. This rapid synthesis enhances the prospects for large-scale manufacturing of graphene aerogels for use in numerous applications including sorbents for environmental toxins, support materials for electrocatalysis, and high-performance electrodes for electrochemical capacitors and solar cells.

The ability to rationally engineer the growth and nanomanufacturing of one-dimensional nanowires in high volumes has the potential to enable applications of nanoscale materials in a diverse range of fields including energy conversion and storage, catalysis, sensing, medicine, and information technology. This review provides a roadmap for the development of large-scale nanowire processing. While myriad techniques exist for bench-scale nanowire synthesis, these growth strategies typically fall within two major categories: 1) anisotropically-catalyzed growth and 2) confined, template-based growth. However, comparisons between growth methods with different mass transport pathways have led to confusion in interpreting observations, in particular Gibbs–Thomson effects. We review mass transport in nanowire synthesis techniques to unify growth models and to allow for direct comparison of observations across different methods. In addition, we discuss the applicability of nanoscale, Gibbs–Thomson effects on mass transport and provide guidelines for the development of new growth models. We explore the scalability of these complex processes with dimensionless numbers and consider the effects of pressure, temperature, and precursor material on nanowire growth.

Coherent laser radiation has enabled many scientific and technological breakthroughs including Bose–Einstein condensates, ultrafast spectroscopy, superresolution optical microscopy, photothermal therapy, and long-distance telecommunications. However, it has remained a challenge to refrigerate liquid media (including physiological buffers) during laser illumination due to significant background solvent absorption and the rapid (∼ps) nonradiative vibrational relaxation of molecular electronic excited states. Here we demonstrate that single-beam laser trapping can be used to induce and quantify the local refrigeration of physiological media by >10 °C following the emission of photoluminescence from upconverting yttrium lithium fluoride (YLF) nanocrystals. A simple, low-cost hydrothermal approach is used to synthesize polycrystalline particles with sizes ranging from <200 nm to >1 μm. A tunable, near-infrared continuous-wave laser is used to optically trap individual YLF crystals with an irradiance on the order of 1 MW/cm2. Heat is transported out of the crystal lattice (across the solid–liquid interface) by anti-Stokes (blue-shifted) photons following upconversion of Yb3+ electronic excited states mediated by the absorption of optical phonons. Temperatures are quantified through analysis of the cold Brownian dynamics of individual nanocrystals in an inhomogeneous temperature field via forward light scattering in the back focal plane. The cold Brownian motion (CBM) analysis of individual YLF crystals indicates local cooling by >21 °C below ambient conditions in D2O, suggesting a range of potential future applications including single-molecule biophysics and integrated photonic, electronic, and microfluidic devices.

Photodynamic therapy has been used for several decades in the treatment of solid tumors through the optical generation of chemically reactive singlet-oxygen molecules (1O2). Recently, nanoscale metallic and semiconducting materials have been reported to act as photosensitizing agents with additional diagnostic and therapeutic functionality. To date there have been no reports of observing the generation of singlet-oxygen at the level of single nanostructures, particularly at near-infrared (NIR) wavelengths. Here we demonstrate that NIR laser tweezers can be used to observe the formation of singlet oxygen produced from individual silicon and gold nanowires via use of a commercially available reporting dye. The laser trap also induces two-photon photoexcitation of the dye following a chemical reaction with singlet oxygen. Corresponding two-photon emission spectra confirms the generation of singlet oxygen from individual silicon nanowires at room temperature (30 °C), suggesting a range of applications for investigating semiconducting and metallic nanoscale materials for solid tumor photoablation.

A theoretical model is developed here in tandem with single-beam laser trapping experiments to elucidate the effects of the numerous thermal, optical, and geometric parameters that affect internal temperature distributions within finite nanowires (NWs) during laser irradiation. Analytical solutions to the heat-transfer equation are presented to predict internal temperature distributions within individual nanowires based on numerical calculations of the internal electromagnetic heat source. Single-beam laser-trapping experiments are performed to measure photothermal heating of silicon NWs. Silicon has not been considered to date for photothermal heating applications due to its indirect band gap and low absorption coefficient in the near-infrared tissue-transparency window. We also show here that ion implantation may be used to increase the optical absorption of silicon nanowires (SiNWs), leading to significant heating to temperatures greater than 42 °C in an aqueous environment at an irradiance of 3 MW/cm2. Experimental observations of photothermal heating agree well with theoretical predictions. Calculations for comparison with amorphous carbon NWs reveal significantly greater heating effects, as well as internal radial gradients not observed for SiNWs.

The dissipative absorption of electromagnetic energy by 1D nanoscale structures at optical frequencies is applicable to several important phenomena, including biomedical photothermal theranostics, nanoscale photovoltaic materials, atmospheric aerosols, and integrated photonic devices. Closed-form analytical calculations are presented for the temperature rise within infinite circular cylinders with nanometer-scale diameters (nanowires) that are irradiated at right angles by a continuous-wave laser source polarized along the nanowire’s axis. Solutions for the heat source are compared to both numerical finite-difference time domain (FDTD) simulations and well-known Mie scattering cross sections for infinite cylinders. The analysis predicts that the maximum temperature increase is affected not only by the cylinder’s composition and porosity but also by morphology-dependent resonances (MDRs) that lead to significant spikes in the local temperature at particular diameters. Furthermore, silicon nanowires with high thermal conductivities are observed to exhibit extremely uniform internal temperatures during electromagnetic heating to 1 part in 106, including cases where there are substantial fluctuations of the internal electric-field source term that generates the Joule heating. For a highly absorbing material such as carbon, much higher temperatures are predicted, the internal temperature distribution is nonuniform, and MDRs are not encountered.

Aerogel materials have myriad scientific and technological applications due to their large intrinsic surface areas and ultralow densities. However, creating a nanodiamond aerogel matrix has remained an outstanding and intriguing challenge. Here we report the high-pressure, high-temperature synthesis of a diamond aerogel from an amorphous carbon aerogel precursor using a laser-heated diamond anvil cell. Neon is used as a chemically inert, near-hydrostatic pressure medium that prevents collapse of the aerogel under pressure by conformally filling the aerogel’s void volume. Electron and X-ray spectromicroscopy confirm the aerogel morphology and composition of the nanodiamond matrix. Time-resolved photoluminescence measurements of recovered material reveal the formation of both nitrogen- and silicon- vacancy point-defects, suggesting a broad range of applications for this nanocrystalline diamond aerogel.