Solar energy represents one of the most abundant and yet least harvested sources of renewable energy. In recent years, tremendous progress has been made in developing photovoltaics that can be potentially mass deployed. Of particular interest to cost-effective solar cells is to use novel device structures and materials processing for enabling acceptable efficiencies. In this regard, here, we report the direct growth of highly regular, single-crystalline nanopillar arrays of optically active semiconductors on aluminium substrates that are then configured as solar-cell modules. As an example, we demonstrate a photovoltaic structure that incorporates three-dimensional, single-crystalline n-CdS nanopillars, embedded in polycrystalline thin films of p-CdTe, to enable high absorption of light and efficient collection of the carriers. Through experiments and modelling, we demonstrate the potency of this approach for enabling highly versatile solar modules on both rigid and flexible substrates with enhanced carrier collection efficiency arising from the geometric configuration of the nanopillars.

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...

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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.

Three novel isostructural equiatomic gold tetrel pnictides, AuSiAs, AuGeP, and AuGeAs, were synthesized and characterized. These phases crystallize in the noncentrosymmetric (NCS) monoclinic space group Cc (no. 9), featuring square‐planar Au within cis‐[AuTt2Pn2] units (Tt=tetrel, Si, Ge; Pn=pnictogen, P, As). This is in drastic contrast to the structure of previously reported AuSiP, which exhibits typical linear coordination of Au with Si and P. Chemical bonding analysis through the electron localization function suggests covalent two‐center two‐electron Tt−Pn bonds, and three‐center Au−Tt−Au and Au−Pn−Au bonds with 1.6 e− per bond. X‐ray photoelectron spectroscopy studies support the covalent and nonionic nature of Au−Pn and Au−Tt bonds. The title materials were found to be n‐type narrow‐gap semiconductors or semimetals, with nearly temperature‐independent electrical resistivities and low thermal conductivities. A combination of the semimetallic properties with tunable NCS structure provides opportunities for the development of materials based on gold tetrel pnictides.

Droplet control through the use of light-induced thermocapillary effects has recently garnered attention due to its non-intrusive and multifunctional nature. An important issue in droplet control is the estimation of the thermocapillary force. The purpose of the present study is to estimate the thermocapillary force and propose empirical equations between the force and simply measurable key parameters such as droplet diameter and power of heat source. In addition, we aim to shift the droplet trajectory and develop an on-demand droplet routing system based on the estimation of the thermocapillary force. We illuminated a continuous phase with a 532 nm laser beam to minimize possible damage or property changes to target molecules contained within droplets. A mixture of light-absorbing material and oleic acid was used for the continuous phase fluid, while deionized water (DI water) was used for the dispersed phase fluid. We proposed empirical equations to estimate the thermocapillary force, which was then applied to precise droplet shifting and routing. We found that the shifting distance was linearly proportional to the thermocapillary force, and that an on-demand droplet routing system resulted in a success rate greater than 95%.

Complex polymorphic relationships in the LnSiP3 (Ln = La and Ce) family of compounds are reported. An innovative synthetic method was developed to overcome differences in the reactivities of the...

Copper wire bonding is an alternative interconnection technology that serves as a viable, and cost saving alternative to gold wire bonding. Its excellent mechanical and electrical characteristics attract the high-speed, power management devices and fine-pitch applications. Copper wire bonding can be a potentially alternative interconnection technology along with flip chip interconnection. However, the growth of Cu/Al intermetallic compound (IMC) at the copper wire and aluminum interface can induce a mechanical failure and increase a potential contact resistance. In this study, the copper wire bonded chip samples were annealed at the temperature range from 150 C to 300 C for 2 to 250 h, respectively. The formation of Cu/Al IMC was observed and the activation energy of Cu/Al IMC growth was obtained from an Arrhenius plot (ln (growth rate) versus 1/T). The obtained activation energy was 26 Kcal/mol and the behavior of IMC growth was very sensitive to the annealing temperature. To investigate the effects of IMC formation on the copper wire bondability on Al pad, ball shear tests were performed on annealed samples. For as-bonded samples, ball shear strength ranged from 240-260 gf, and ball shear strength changed as a function of annealing times. For annealed samples, fracture mode changed from adhesive failure at Cu/Al interface to IMC layer or Cu wire itself. The IMC growth and the diffusion rate of aluminum and copper were closely related to failure mode changes. Micro-XRD was performed on fractured pads and balls to identify the phases of IMC and their effects on the ball bonding strength. From XRD results, it was confirmed that the major IMC was Cu 9 Al 4 and it provided a strong bondability.