Thermal rectification is a phenomenon in which thermal transport along a specific axis is dependent upon the sign of the temperature gradient or heat current. This phenomenon offers improved thermal management of electronics as size scales continue to decrease and new technologies emerge by having directions of preferred thermal transport. For most applications where thermally rectifying materials could be of use they would need to exhibit one direction with high thermal conductivity to allow for efficient transport of heat from heat generating components to a sink and one direction with low conductivity to insulate the temperature and heat flux sensitive components. In the process of understanding and developing these materials multiple mechanisms have been found which produce thermally rectifying behavior and much work has been and is being done to improve our understanding of the mechanisms and how these mechanisms can be used with our improved ability to fabricate at the nanoscale to produce efficient materials which have high levels of thermal rectification.

Nanoscale copper rings of different radii, thicknesses, and widths were synthesized on silicon dioxide thin films and were subsequently liquefied via a nanosecond pulse laser treatment. During the nanoscale liquid lifetimes, the rings experience competing retraction dynamics and thin film and/or Rayleigh-Plateau types of instabilities, which lead to arrays of ordered nanodroplets. Surprisingly, the results are significantly different from those of similar experiments carried out on a Si surface. We use hydrodynamic simulations to elucidate how the different liquid/solid interactions control the different instability mechanisms in the present problem.

We introduce a laser assisted electron beam induced deposition (LAEBID) process which is a nanoscale direct write synthesis method that integrates an electron beam induced deposition process with a synchronized pulsed laser step to induce thermal desorption of reaction by-products. Localized, spatially overlapping electron and photon pulses enable the thermal desorption of the reaction by-product while mitigating issues associated with bulk substrate heating, which can shorten the precursor residence time and distort pattern fidelity due to thermal drift. Current results demonstrate purification of platinum deposits (reduced carbon content by ~50%) with the addition of synchronized laser pulses as well as a significant reduction in deposit resistivity. Measured resistivities from platinum LAEBID structures (4 × 10(3)μΩ cm) are nearly 4 orders of magnitude lower than standard EBID platinum structures (2.2 × 10(7)μΩ cm) from the same precursor and are lower than the lowest reported EBID platinum resistivity with post-deposition annealing (1.4 × 10(4)μΩ cm). Finally the LAEBID process demonstrates improved deposit resolution by ~25% compared to EBID structures under the conditions investigated in this work.

Platinum-carbon deposits made via electron-beam-induced deposition were purified via a pulsed laser-induced oxidation reaction and erosion of the amorphous carbon to form pure platinum. Purification proceeds from the top down and is likely catalytically facilitated via the evolving platinum layer. Thermal simulations suggest a temperature threshold of ∼485 K, and the purification rate is a function of the PtC5 thickness (80-360 nm) and laser pulse width (1-100 μs) in the ranges studied. The thickness dependence is attributed to the ∼235 nm penetration depth of the PtC5 composite at the laser wavelength, and the pulse-width dependence is attributed to the increased temperatures achieved at longer pulse widths. Remarkably fast purification is realized at cumulative laser exposure times of less than 1 s.

A liquid metal filament supported on a dielectric substrate was directed to fragment into an ordered, mesoscale particle ensemble. Imposing an undulated surface perturbation on the filament forced the development of a single unstable mode from the otherwise disperse, multimodal Rayleigh− Plateau instability. The imposed mode paved the way for a hierarchical spatial fragmentation of the filament into particles, previously seen only at much larger scales. Ultimately, nanoparticle radius control is demonstrated using a micrometer scale switch.

We have performed time-resolved photoluminescence measurements on suspensions of silicon nanoparticles using near infrared two-photon femtosecond excitation. Our results for 1 nm particles show wide bandwidth but indicate full conversion to direct-like behavior, with a few nanosecond time characteristic, corresponding to oscillator strength comparable to those in direct semiconductors. In addition to fast nanosecond decay, the photoluminescence from 2.85 nm nanoparticle suspension exhibit considerably slower decay, consistent with a transition regime to direct-like behavior. The quantum yield is measured to be ~ 0.48, 0.55, 0.3 for excitation at 254, 310, and 365 nm respectively for the blue 1 nm particles, and ~ 0.16, 0.28, and 0.3 for the red 2.85 nm particles. The direct-like characteristics are discussed in terms of localization on radiative deep molecular-like Si-Si traps with size-dependent depth.

The directed assembly of arrayed nanoparticles is demonstrated by dictating the flow of a liquid phase filament on the nanosecond time scale. Results for the assembly of Ni nanoparticles on SiO2 are presented. Previously, we have implemented a sinusoidal perturbation on the edge of a solid phase Ni, thin film strip to tailor nanoparticle assembly. Here, a nonlinear square waveform is explored. This waveform made it possible to expand the range of nanoparticle spacing-radius combinations attainable, which is otherwise limited by the underlying Rayleigh-Plateau type of instability. Simulations of full Navier-Stokes equations based on volume of fluid method were implemented to gain further insight regarding the nature of instability mechanism leading to particle formation in experiments.

Using the dynamic transmission electron microscope (DTEM), the dewetting of thin nickel films was monitored at nanometer spatial and nanosecond timescales to provide insight into the liquidphase assembly dynamics. Correlated time and length scales indicate that a spinodal instability drives the assembly process. Measured lifetimes of the liquid metal agree with finite-element simulations of the laser-irradiated film. These results can be used to design improved synthesis and assembly routes toward achieving advanced functional nanomaterials and devices. Keywords assembly dynamics, dynamic transmission electron microscopy, pulsed-laser heating, thin-film dewetting LetterThe synthesis and organization of functional nanomaterials via bottom-up self-and directed assembly represents a critical challenge for the future of nanoscience. Generating arrays of nanoparticles with controlled size and spatial distributions is key to this challenge, and processes that exploit morphological instabilities offer the potential to attain these fine-scale spatially correlated structures. There has been long-standing interest in the capillarity and surface tension effects on morphological evolution in various materials systems, dating back to the work of Plateau 1 and Rayleigh 2 . Recently, pulsed-laser-induced dewetting of two-dimensional films 3-9 , one-dimensional lines and rings [10][11][12][13] , and lithographically patterned nanostructures 14,15 has demonstrated that understanding and controlling thin-film and Rayleigh-Plateau instabilities improves the ability to create organized metallic nanoparticle ensembles. Assembled particles have also been shown to "jump" or eject from one substrate and transfer to another depending on the energetics and dynamics of various laser-melted nanostructures [16][17][18] . Heretofore, the as described in the Methods section, the laser spot has a Gaussian profile and thus the radial profile of each image also contains thermal and temporal information. Figure 2d) shows an image taken long after a laser pulse to show the resultant nanoparticle structure in the same field of view. The images in Figure 2 were filtered to remove noise and irrelevant intensity variations using a 3x3 median filter followed by a local brightness and contrast equalization filter using a Gaussian kernel with an rms width of 33 pixels in the x-and y-directions. The raw images are provided in the Supporting Information.Dynamic selected-area diffraction (SAD) patterns were recorded as a function of time to complement the dynamic imaging and estimate the nickel liquid lifetime. Figure 3a) shows a series of SAD patterns taken at various times relative to the specimen pump laser's interaction with the specimen (including as-deposited and post-laser-pulse diffraction patterns using a long exposure time). The simulated diffraction pattern for polycrystalline nickel is included in the long-exposure as-deposited diffraction pattern. The conventional diffraction pattern from the asdeposited film shows broad diffraction ri...