A facile room-temperature method for assembling colloidal copper sulfide (Cu2-xS) nanoparticles into highly electrically conducting films is presented. Ammonium sulfide is utilized for connecting the nanoparticles via ligand removal, which transforms the as-deposited insulating films into highly conducting films. Electronic properties of the treated films are characterized with a combination of Hall effect measurements, field-effect transistor measurements, temperature-dependent conductivity measurements, and capacitance-voltage measurements, revealing their highly doped p-type semiconducting nature. The spin-cast nanoparticle films have carrier concentration of ∼ 10(19) cm(-3), Hall mobilities of ∼ 3 to 4 cm(2) V(-1) s(-1), and electrical conductivities of ∼ 5 to 6 S · cm(-1). Our films have hole mobilities that are 1-4 orders of magnitude higher than hole mobilities previously reported for heat-treated nanoparticle films of HgTe, InSb, PbS, PbTe, and PbSe. We show that electrophoretic deposition (EPD) as a method for nanoparticle film assembly leads to an order of magnitude enhancement in film conductivity (∼ 75 S · cm(-1)) over conventional spin-casting, creating copper sulfide nanoparticle films with conductivities comparable to bulk films formed through physical deposition methods. The X-ray diffraction patterns of the Cu2-xS films, with and without ligand removal, match the Djurleite phase (Cu(1.94)S) of copper sulfide and show that the nanoparticles maintain finite size after the ammonium sulfide processing. The high conductivities reported are attributed to better interparticle coupling through the ammonium sulfide treatment. This approach presents a scalable room-temperature route for fabricating highly conducting nanoparticle assemblies for large-area electronic and optoelectronic applications.

In this work, we demonstrate a general lithium-ion battery electrode fabrication method for colloidal nanoparticles (NPs) using electrophoretic deposition (EPD). Our process is capable of forming robust electrodes from copper sulfide, manganese sulfide, and germanium NPs without the use of additives such as polymeric binders and conductive agents. After EPD, we show two postprocessing treatments ((NH4)2S and inert atmosphere heating) to effectively remove surfactant ligands and create a linked network of particles. The NP films fabricated by this simple process exhibit excellent electrochemical performance as lithium-ion battery electrodes. Additive-free Cu(2-x)S and MnS NP films show well-defined plateaus at ∼1.7 V, demonstrating potential for use as cathode electrodes. Because of the absence of additives in the NP film, this additive-free NP film is an ideal template for ex situ analyses of the particles to track particle morphology changes and deterioration as a result of Li ion cycling. To this end, we perform a size-dependent investigation of Cu(2-x)S NPs and demonstrate that there is no significant relationship between size and capacity when comparing small (3.8 nm), medium (22 nm), and large (75 nm) diameter Cu(2-x)S NPs up to 50 cycles; however, the 75 nm NPs show higher Coulombic efficiency. Ex situ TEM analysis suggests that Cu(2-x)S NPs eventually break into smaller particles (<10 nm), explaining a weak correlation between size and performance. We also report for the first time on additive-free Ge NP films, which show stable capacities for up to 50 cycles at 750 mAh/g.

A general mathematical kinetic growth model is proposed on the basis of observed growth regimes of hydrothermally synthesized KTaO nanoparticles from electron microscopy studies on the surface morphology and surface chemistry. Secondary electron imaging demonstrated that there are two dominant growth mechanisms: terrace nucleation, where the surfaces are rough, and terrace growth, where surfaces are smooth. In the proposed model based upon standard step-flow growth, the rates of both mechanisms are established to be dependent on the chemical potential change of the growth environment-terrace nucleation dominates with larger negative chemical potential, and terrace growth dominates with smaller negative chemical potential. This analysis illustrates the importance of ending a synthesis in a regime of low negative chemical potential in order to achieve smooth well-faceted nanoparticles.

Gadolinium scandate (GdScO) has been synthesized at 300 °C through the decomposition of a mixed cation hydroxide hydrogel in a humid environment. Increasing the reaction temperature produced larger particles that better adopted the Wulff shape. A lack of water vapor during the synthesis caused the solid network of the hydrogel to collapse upon heating so an amorphous xerogel was produced. Water vapor in the system imbibed the hydrogel and allowed for greater diffusion of the atomic species to allow for crystallization into the perovskite phase at temperatures lower than typical sol-gel processes. Temperatures less than 300 °C, or an excess of water vapor, promoted the formation of Gd(OH) and ScOOH in addition to or in lieu of GdScO.

A general approach to the formation of well-faceted nanoparticles is discussed and successfully applied to the production of several rare-earth scandates. Two steps were used, with higher temperatures first to nucleate the perovskite phase, followed by lower temperatures to smooth the particle surfaces. Exploiting these two different regimes led to smaller nanoparticles with more faceting. This general approach may be tailored to other material systems as a step towards producing shape-controlled nanoparticles for a desired application.