Synthetic methods used to produce metal nanoparticles typically lead to a distribution of particle sizes. In addition, creation of the smallest clusters, with sizes of a few to tens of atoms, remains very challenging. Nanoporous metal-organic frameworks (MOFs) are a promising solution to these problems, since their long-range crystalline order creates completely uniform pore sizes with the potential for both steric and chemical stabilization. We report a systematic investigation of silver nanocluster formation within MOFs using three representative MOF templates. The as-synthesized clusters are spectroscopically consistent with dimensions < or =1 nm, with a significant fraction existing as Ag(3) clusters, as shown by electron paramagnetic resonance. Importantly, we show conclusively that very rapid TEM-induced MOF degradation leads to agglomeration and stable, easily imaged particles, explaining prior reports of particles larger than MOF pores. These results solve an important riddle concerning MOF-based templates and suggest that heterostructures composed of highly uniform arrays of nanoparticles within MOFs are feasible.

We analyze the optical, chemical, and electrical properties of chemical vapor deposition (CVD) grown hexagonal boron nitride (h-BN) using the precursor ammonia-borane (H3N-BH3) as a function of Ar/H2 background pressure (PTOT). Films grown at PTOT ≤ 2.0 Torr are uniform in thickness, highly crystalline, and consist solely of h-BN. At larger PTOT, with constant precursor flow, the growth rate increases, but the resulting h-BN is more amorphous, disordered, and sp 3 bonded. We attribute these changes in h-BN grown at high pressure to incomplete thermolysis of the H3N-BH3 precursor from a passivated Cu catalyst. A similar increase in h-BN growth rate and amorphization is observed even at low PTOT if the H3N-BH3 partial pressure is initially greater than the background pressure PTOT at the beginning of growth. h-BN growth using the H3N-BH3 precursor reproducibly can give large-area, crystalline h-BN thin films, provided that the total pressure is under 2.0 Torr and the precursor flux is well-controlled.* Correspondence should be addressed to lyding@illinois.edu, jkoepkeuiuc@gmail.com, and joshua.wood@northwestern.edu. Films of h-BN have been used as insulating spacers, 1 encapsulants, 2 substrates for electronic devices, 3, 4 corrosion and oxidation-resistant coatings, 5, 6 and surfaces for growth of other 2D nanomaterials such as graphene 7 and WS2. 8 Most of these studies employed small-area (~100 µm 2 ) h-BN pieces exfoliated from sintered h-BN crystals, 9 limiting technological use of h-BN films. Additionally, unlike graphene, h-BN is difficult to prepare in monolayer form by exfoliation. The electronegativity difference between B and N and the reduced resonance stabilization relative to graphene results in electrostatic attractions between layers and in-plane. Consequently, it is more challenging to control h-BN grain size and layer number. Furthermore, partially ionic B-N bonds can form between neighboring BN layers, serving to "spot weld" such layers together. 10 Several groups have sought to overcome these limitations by using chemical vapor deposition (CVD) to grow large-area, monolayer h-BN films. [11][12][13][14][15][16][17][18][19][20][21][22] CVD growth of h-BN has been accomplished using various precursors (e.g., ammonia borane, borazine, and diborane) on transition metal substrates (e.g., Cu, Ni, 23 Fe, 24 Ru, 25, 26 etc.). Of these h-BN growth substrates, we focus on Cu, as Cu has a high catalytic activity, 27 is inexpensive, and is the typical growth substrate 28 for conventional graphene CVD.Regarding h-BN growth precursors, volatile borazine-B3N3H6, isoelectronic with benzene-is far from an ideal choice, as borazine is hazardous and decomposes quickly even at room temperature. While borazine can pyrolyze and dehydrogenate 23, 25,29,30 to generate h-BN films, 13,17,19,20,22,31 partial dehydrogenation is common, [30] resulting in oligomeric BN compounds and aperiodic h-BN grain boundaries. 13,17 Finally, thin films of h-BN can also be grown from mixtures of diborane (B2H6) and ammonia (NH3...

The performance of carbon nanotube network (CNN) devices is usually limited by the high resistance of individual nanotube junctions (NJs). We present a novel method to reduce this resistance through a nanoscale chemical vapor deposition (CVD) process. By passing current through the devices in the presence of a gaseous CVD precursor, localized nanoscale Joule heating induced at the NJs stimulates the selective and self-limiting deposition of metallic nanosolder. The effectiveness of this nanosoldering process depends on the work function of the deposited metal (here Pd or HfB2), and it can improve the on/off current ratio of a CNN device by nearly an order of magnitude. This nanosoldering technique could also be applied to other device types where nanoscale resistance components limit overall device performance.

Pure, dense, and stoichiometric MgO thin films have been deposited at temperatures as low as 225 °C by chemical vapor deposition using a recently reported magnesium precursor, magnesium N,N-dimethylaminodiboranate, which has the highest room-temperature vapor pressure among known Mg-containing compounds, with water as a co-reactant. The films are characterized by x-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and spectroscopic ellipsometry. Conformal coating on a trench with 35:1 aspect ratio is achieved at a film growth rate of 2 nm/min. The growth rate can be tuned between 2–20 nm/min according to the requirement of the structure to be coated.

In this paper, we present an efficient yet accurate inductance extraction methodology and also apply it to clocktree RLC extraction. We first show that without loss of accuracy, the inductance extraction problem of n traces with or without ground planes can be reduced to a number of one-trace and two-trace subproblems. We then solve one-trace and two-trace subproblems via a table-based approach. We finally validate the linear cascading assumption that enables us to apply our inductance extraction approach to clocktree RLC extraction and optimization.