Carrier Distribution and Dynamics of Nanocrystal Solids Doped with Artificial Atoms

Single component and multicomponent nanocrystal (NC) solids represent an exciting new form of condensed matter, as they can potentially capture not only the quantum features of the individual building blocks but also novel collective properties through coupling of NC components. Unlike bulk semiconductors, however, there is no current theory for how introduction of dopants will impact the electronic structure and transport properties of NC solids. Empirically, it is known that in semiconductor NC systems, mixing two different materials of NCs electronically dopes the film. However, it has been challenging to connect the macroscopic measurements of doping effects on transport behavior to a microscopic understanding of how the identity, placement, and abundance of dopants impact these measurements. In this Letter, we report the first temperature-dependent thermopower measurements in doped and undoped NC solids. In combination with temperature-dependent electrical conductivity measurements, how the doping affects the carrier concentration as well as mobility is explored exclusively. These complementary measurements serve as a unique electronic spectroscopy tool to quantitatively reveal the energetics of carriers and electronic states in NC solids

Mapping Li⁺ Concentration and Transport via In Situ Confocal Raman Microscopy

We demonstrate confocal Raman microscopy as a general, nonperturbative tool to measure spatially resolved lithium ion concentrations in liquid electrolytes. By combining this high-spatial-resolution technique with a simple microfluidic device, we are able to measure the diffusion coefficient of lithium ions in dimethyl carbonate in two different concentration regimes. Because lithium ion transport plays a key role in the function of a variety of electrochemical devices, quantifying and visualizing this process is crucial for understanding device performance. This method for detecting lithium ions should be immediately useful in the study of lithium-ion-based devices, ion transport in porous media, and at electrode–electrolyte interfaces, and the analytical framework is useful for any system exhibiting a concentration-dependent Raman spectrum

Evolution of Vibrational Properties in Lanthanum Hexaboride Nanocrystals

Lanthanum hexaboride (LaB₆) is known for its hardness, mechanical strength, thermionic emission, and strong plasmonic properties. However, given the lack of colloidal synthetic methods to access this material, very little is understood about its physical properties on the nanoscale. Recently, a new moderate-temperature synthetic technique was developed to directly synthesize LaB₆ nanoparticles [Mattox et al. Chem. Mater. 2015, 27, 6620]. We report the influence of nanoparticle size on the structural and vibrational properties of LaB₆ using a combination of Raman and Fourier transform infrared spectroscopies. Our studies indicate that the size of the lanthanum salt anion has a larger influence on LaB₆ vibrational energies than particle size. Surprisingly, our work finds that the LaB₆ lattice readily expands to accommodate larger ions and contracts with their removal, while ligand incorporation significantly amplifies and shifts the Raman stretching modes

Enhancing Separation and Mechanical Performance of Hybrid Membranes through Nanoparticle Surface Modification

Membranes with selective gas transport properties and good mechanical integrity are increasingly desired to replace current energy intensive approaches to gas separation. Here, we report on the dual enhancement of transport and mechanical properties of hybrid cross-linked poly­(ethylene glycol) membranes with aminopropyl-modified silica nanoparticles. CO₂ permeability in hybrid membranes exceeds what can be predicted by Maxwell’s equation and surpasses values of the pure polymer. Furthermore, dynamic mechanical and thermogravimetric analyses reveal increases in both the storage modulus and thermal stability in hybrid membranes, with respect to silica nanoparticle loading

Size-Dependent Permeability Deviations from Maxwell’s Model in Hybrid Cross-Linked Poly(ethylene glycol)/Silica Nanoparticle Membranes

Currently, separation of gaseous mixtures largely relies on energy intensive and expensive processes, like chemical looping of amines. This has driven research into less energy-intensive, passive methods of performing separations such as the use of polymer membranes. Although pure polymer membranes have demonstrated appealing separation performance, they suffer from an inherent trade-off between permeability and selectivity, which limits overall performance. Recent research efforts have shown that the introduction of a secondary phase, often an inorganic species, is added to selectively boost permeability or selectivity. However, these hybrid organic/inorganic systems have not seen widespread adoption because synthetic control over the size, shape, and dispersion of the inorganic species is poor and understanding of transport in these membranes is largely empirical. Thus, understanding and optimizing hybrid membranes requires development of well-controlled model systems in which size, shape, and surface chemistry of the inorganic species are precisely controlled, leading to homogeneous membranes amenable to careful study. Here, we report on the synthesis, characterization, and gas transport properties of tailored hybrid membranes composed of cross-linked poly­(ethylene glycol) and silica nanoparticles. We show excellent control of nanoparticle size, loading, and dispersibility. We find that permeability deviations from Maxwell’s model increases as the size of silica nanoparticle decreases and loading increases. These size-dependent deviations from Maxwell’s model are attributed to interfacial interactions, which scale with surface area and act to decrease segmental chain mobility

Synthesis of Single-Crystalline La₁_-<i>_x</i>Ba<i>_x</i>MnO₃ Nanocubes with Adjustable Doping Levels

We report a hydrothermal synthesis of single-crystalline nanocubes composed of lanthanum barium manganite (La1-xBaxMnO3) with three different doping levels (x = 0.3, 0.5, and 0.6). The synthesis yields clearly faceted nanocubes with a pseudo-cubic perovskite structure. Typical nanocubes have sizes ranging between 50 and 100 nm irrespective of doping level. Magnetic measurements performed on nanocube ensembles show that the magnetic properties depend on the doping level. The ability to synthesize nanoscale manganites of a desired doping level should enable detailed investigations of the size-dependent evolution of magnetism, colossal magnetoresistance, and nanoscale phase separation

Experimental and characterization data supporting the study from Inkjet-printed SnO_x as an effective electron transport layer for planar perovskite solar cells and the effect of Cu doping

Inkjet printing is a more sustainable and scalable fabrication method than spin coating for producing perovskite solar cells (PSCs). Although spin-coated SnO2 has been intensively studied as an effective electron transport layer (ETL) for PSCs, inkjet-printed SnO2 ETLs have not been widely reported. Here, we fabricated inkjet-printed, solution-processed SnOx ETLs for planar PSCs. A champion efficiency of 17.55% was achieved for the cell using a low-temperature processed SnOx ETL. The low-temperature SnOx exhibited an amorphous structure and outperformed the high-temperature crystalline SnO2. The improved performance was attributed to enhanced charge extraction and transport and suppressed charge recombination at ETL/perovskite interfaces, which originated from enhanced electrical and optical properties of SnOx, improved perovskite film quality, and well-matched energy level alignment between the SnOx ETL and the perovskite layer. Furthermore, SnOx was doped with Cu. Cu doping increased surface oxygen defects and upshifted energy levels of SnOx, leading to reduced device performance. A tunable hysteresis was observed for PSCs with Cu-doped SnOx ETLs, decreasing at first and turning into inverted hysteresis afterwards with increasing Cu doping level. This tunable hysteresis was related to the interplay between charge/ion accumulation and recombination at ETL/perovskite interfaces in the case of electron extraction barriers

Adapting the Electron Beam from SEM as a Quantitative Heating Source for Nanoscale Thermal Metrology

The electron beam (e-beam) in the scanning electron microscopy (SEM) provides an appealing mobile heating source for thermal metrology with spatial resolution of ∼1 nm, but the lack of systematic quantification of the e-beam heating power limits such application development. Here, we systemically study e-beam heating in LPCVD silicon nitride (SiNx) thin-films with thickness ranging from 200 to 500 nm from both experiments and complementary Monte Carlo simulations using the CASINO software package. There is good agreement about the thickness-dependent e-beam energy absorption of thin-film between modeling predictions and experiments. Using the absorption results, we then demonstrate adapting the e-beam as a quantitative heating source by measuring the thickness-dependent thermal conductivity of SiNx thin-films, with the results validated to within 7% by a separate Joule heating experiment. The results described here will open a new avenue for using SEM e-beams as a mobile heating source for advanced nanoscale thermal metrology development