In the fall of 2012 the Stanford University materials science course Solar Cells, Fuel Cells and Batteries: Materials for the Energy Solution was offered as a flipped class and a massively open online course (MOOC). To the best of our knowledge, this was the first materials science MOOC. Here we describe how the course was implemented, and present results on performance, demographics and other observations that were made. Finally, we provide some perspectives for the future of the implementation of these engineering MOOCs.

Acid hydrolysis of cellulose leads to the formation of nanowhiskers, which can self-assemble to form a liquid crystal phase at a concentration determined by their aspect ratio. This work investigates the properties of the un-hydrolysed materials on which the length of the nanowhiskers depend. It was found that the length is determined by the branching pattern of the cellulose microfibrils and the crystallinity of the material.

Sharper nanotips are required for application in nanoprobing systems due to a shrinking contact size with each new transistor technology node. We describe a two-step etching process to fabricate W nanotips with controllable tip dimensions. The first process is an optimized AC electrochemical etching in KOH to fabricate nanotips with a radius of curvature (ROC) down to 90 nm. This was followed by a secondary nanotip sharpening process by laser irradiation in KOH. High aspect ratio nanotips with ROC close to 20 nm were obtained. Finally we demonstrate the application of the fabricated nanotips for nanoprobing on advanced technology SRAM devices.

A study about the achievement of dichromatic white light-emitting diodes (LEDs) was performed. A series of dual wavelength LEDs with different last quantum-well (LQW) structure were fabricated. The bottom seven blue light QWs (close to n-GaN layer) of the four samples were the same. The LQW of sample A was 3 nm, and that of sample B, C and D were 6 nm, a special high In content ultra-thin layer was inserted in the middle of the LQW of sample C and on top of that of sample D. XRD results showed In concentration fluctuation and good interface quality of the four samples. PL measurements showed dual wavelength emitting, the blue light peak position of the four samples were almost the same, sample A with a narrower LQW showed an emission wavelength much shorter than that of sample B, C, D. EL measurement was done at an injection current of 100 mA. Sample A only showed LQW emission due to holes distribution. Because of wider LQW, the emission wavelength of sample B, C and D was longer and peak intensity was weaker. Sample D with insert layer on top of LQW showed strongest yellow light emission with a blue peak. As the injection current increased, sample A showed highest output light power due to narrower LQW. Of the other three samples with wider LQW, sample D showed highest output power. Effective yellow light emission has always been an obstacle to the achievement of dichromatic white LED. Sample D with insert layer close to p-GaN can confine the hole distribution more effectively hence the recombination of holes and electrons was enhanced, the yellow light emission was improved and dichromatic white LED was achieved.

Hydrogen can be used as an environmentally friendly fuel to power vehicles, electric devices, and spacecraft with water vapor as the only emission. One associated challenge is the development of safe hydrogen storage systems. Hydrogen tanks and other hydrogen infrastructure elements will be exposed to both high-pressure hydrogen and cyclic stresses. In our work, 304 stainless steel specimens were precharged with hydrogen and subjected to rotational bending fatigue with a maximum stress amplitude of 90 ksi. A diffusion model was solved to approximate the concentration of hydrogen in the specimen at the time of the test. Contrary to our previous work with simple bending fatigue tests, hydrogen precharging actually increased rotational bending fatigue life from 28,074 (Sx = 7,430, N = 103) cycles to 91,513 (Sx = 40,209, N=32) cycles, a factor of approximately 3.25. This result demonstrates that the effect of hydrogen on fatigue life can be highly situational, and great care should be taken when designing systems that will be exposed to high-pressure hydrogen under fatigue conditions.

The aim of this work is to improve bone-implant bonding. This can, potentially, be achieved through the use of an implant coating composed of fibre networks. It is hypothesised that such an implant can achieve strong peri-prosthetic bone anchorage, when seeded with human mesenchymal stem cells (hMSCs). The materials employed were 444 and 316L stainless steel fibre networks of the same fibre volume fraction. The present work confirms that hMSCs are able to proliferate and differentiate towards the osteogenic lineage when seeded onto the fibre networks. Cellular viability, proliferation and metabolic activity were assessed and the results suggest higher proliferation rates when hMSC are seeded onto the 444 networks as compared to 316L. Cell distribution was found uniform across the seeded surfaces with 444 showing a somewhat higher infiltration depth.

The use of Ga-Au alloys of different compositions as metal catalysts for the growth of abrupt SiGe/Si nanowire axial heterostructures has been investigated. The heterostructures grown in a continuous process by just switching the gas precursors, show uniform nanowire diameters, almost abrupt compositional changes and no defects between the different sections. These features represent significant improvements over the results obtained using pure Au.

We summarize some recent new results probing inter- and intra-chain coupling in aggregated P3HT in isolated nanoparticles and nanofibers. Time-resolved photoluminescence studies show interesting correlations between amplitude and decay constant for different decay components that are tied to both polymer regio-regularity and nanoparticle processing conditions. In the frequency domain, we observe distinct signatures of both H- and J-aggregate type exciton coupling, manifested as different vibronic progressions with different electronic origins, linewidths, and Huang-Rhys factors. We show how the extent of this H/J composite coupling can be tuned to a certain extent by changes in molecular parameters (polymer molecular weight and regioregularity) and by solvent processing conditions. Finally we discuss recent results of near-field optical absorption probes of nanoparticles and nanofibers where optical contrast is afforded by the different absorption cross-section (at 532 nm) for aggregated vs. unaggregated P3HT.

Silicon is a very promising material for anodes of lithium ion batteries. It exhibits a high theoretical capacity of 3579 mAh/g. However, during the lithiation and de-lithiation, silicon materials experience up to a 300% volume change, leading to poor cyclability [1-2]. Research shows that reducing the silicon particle size can mitigate this problem. Carbon nanotubes (CNTs) function well as electrode materials in electrolytic cells because of their high electrical conductivity and surface area. In this work, we combine silicon nanoparticles (Si NPs) and CNTs as anode materials. Si NPs are generated using a plasma-enhanced chemical vapor deposition technique and their surface is modified with a 12-carbon long aliphatic chain to impart solubility in non-polar solvents. They are applied onto a nanotube-based layer using a wet-phase deposition technique. SEM and TEM analysis confirm that they form a conformal coating onto the nanotube surface. The CNTs - Si NPs composite active material is tested in half-cells where lithium foil acts as counter electrode. We have achieved an average of 810 mAh/g discharge capacity for composites with a CNTs to Si NPs weight ratio of 1:1. We expect to be able to increase the discharge capacity by increasing the Si NPs weight content.

Thanks to an original approach based on the carburization of silicon nanowires, silicon carbide-based one dimensional nanostructures – SiC nanotubes, Si-SiC core-shell nanowires and SiC nanowires – have been synthesized. The original process, which relies on controlling the out-diffusion of Si atoms through SiC, can be monitored by the temperature, the pressure and the time of carburization. These SiC-based 1D nanostructures have been characterized by SEM, FIB-SEM and TEM microscopies and also Raman spectroscopy. Bio-nano-sensors, nano-Field-Effect-Transistors (nano-FETs) or gas sensors may be some applications for these nanostructures.

We investigated quantization behavior in conductance of an Ag/Ta2O5/Pt gapless-type atomic switch. Stepwise increases and decreases in the conductance were observed when small positive and negative bias voltages were applied to the Ag electrode, respectively, where each step corresponds to the conductance of a single atomic point contact. The conductance level could also be controlled by applying voltage pulses with varied amplitudes. Furthermore, when the interval time of consecutive input pulses was turned, we also observed long-term potentiation behavior similar to that of biological synapses. These results indicate that the oxide-based, gapless-type atomic switch has potential for use as a building block of neural computing systems.

The structure of nanocrystalline diamond was approximated by spherical nanograins assuming that the grain core with a perfect crystal lattice is surrounded by a sequence of shells with (essentially) identical atomic architecture but with altered density. We call such a model a nanocrystal with density modulated waves. To examine the effect of density modulation present in nanograins, we built atomistic models of nanodiamond grains and compared the average values of inter-atomic distances calculated for the grains with density waves to those calculated for grains with the perfect, diamond crystal lattice. We show that the atomic structure of nanodiamond can be best described by a model where, between the inner core and the surface layer, three density waves with intermittent compressive and tensile strains exist. The sequence of the density waves is preserved in all examined nanodiamond samples without regard to chemical treatment and vacuum annealing (at up to 1200°C).

Herein, we investigated the noncovalent interactions derived from functionalized carbon nanotube matrices grafting metallic alloy PtRu nanoparticle-decorated Vulcan carbon (fMWCNTs-g-PtRu/C) toward the enhancement of alcohol oxidation reactions. The fMWCNTs noncovalently grafted PtRu/C was successfully synthesized and demonstrated significant enhancement of the electro-catalytic activity and stability toward alcohol oxidation reactions as revealed by electrochemical characterizations. The presented results indicate that the grafting matrix specifically enhances ethanol oxidation reaction kinetics much more than methanol and propanol oxidation reactions. Since the same loading of PtRu/C was used for all tests, the differentiation between these reactants revealed the different strength of noncovalent interactions between the functional matrix and corresponding reactants. This result reveals a new strategy for using fMWCNTs matrix as potential catalyst supports due to its facile fabrication and functionalization, cost effectiveness and environmental friendliness, factors in which all of them are necessary for the practical application of direct alcohol fuel cells in near future.

Fabrication of integrated circuits is a multi-step process that involves chemical mechanical polishing (CMP) for planarizing the deposited layers. Although dependent on the consumables and machine operating conditions, most CMP researchers assume that the polishing occurs in the mixedlubrication regime, where the applied load on the wafer is supported by the hydrodynamic slurry pressure and the contact stress generated during the pad-wafer contact. The particle augmented mixed lubrication (PAML) approach has been employed by Terrell and Higgs (2009) as a high-fidelity asperity-scale mixed-lubrication CMP model. The current work introduces a more computationally efficient wafer-scale PAML model, called PAML-lite, which employs a two-dimensional average flow Reynold's Equation incorporating spatial dependence of entrainment velocities to model the hydrodynamic pressure. The contact mechanics are modeled using a Winkler elastic foundation in cylindrical polar coordinates. The resulting slurry hydrodynamic pressure distribution and contact stress are used to determine the equilibrium configuration of the system in the form of a nominal clearance and rolling and pitch angles. Local and wafer scale material removal rate (MRR) is predicted by assuming a uniform distribution of particle sizes. The prediction of PAML-lite were then benchmarked against experimental results. Upon verification, parametric studies were conducted to understand the effect of some unexplored CMP parameters.

The effect of tungsten oxide (WO3) thin film thickness on the surface plasmon resonance (SPR) properties have been investigated. WO3 films of varying the thickness (36 nm, 60 nm, 80 nm, 100 nm, 150 nm and 200nm) have been deposited onto Au coated prism (Au/prism) by radio frequency (RF) magnetron sputtering technique. The SPR responses of bilayer films were fitted with the Fresnel’s equations in order to calculate the dielectric constant of WO3 thin film. The variation of complex dielectric constant and refractive index with the thickness of WO3 thin film was studied.

The temperature dependence of cross-plane lattice thermal conductivity for thin film IV-VI semiconductors grown by molecular beam epitaxy was measured. Samples consisting of PbSe/PbSrSe multiple quantum wells (MQWs) on PbSe/PbSnSe superlattices (SLs) were grown with variations in SL layer thickness and the number of SL pairs. Localized lattice temperatures within the MQW layers were extracted from analysis of continuous wave photoluminescence (PL) emission spectra at heat sink temperatures between 100 K and 250 K. These data, finite element analysis, and electrical characterization were used to determine cross-plane lattice thermal conductivity of two different SL materials. A SL material with three different PbSe/PbSnSe thicknesses (1.2/1.2, 1.8/1.8, and 2.4/2.4 nm) exhibited a fairly constant lattice thermal conductivity from 1.2 to 1.3 W/mK as the sample was cooled from 250 K to 100 K. Another SL material with five different PbSe/PbSnSe thicknesses (0.5/0.5, 1.0/1.0, 1.6/1.6, 2.1/2.1, and 2.6/2.6 nm) exhibited very low lattice thermal conductivities from 0.46 to 0.47 W/mK 250 K to 100 K. These results are consistent with reflection of low energy heat transporting acoustic phonons within the SL material.

Carbon-Li4Ti5O12 (C-LTO) and carbon nanotube-Li4Ti5O12 (CNT-LTO) nanocomposite particles have been synthesized by hydrothermal method and a following high-temperature calcinations using a mixture of micro-size Li-Ti-O precursors and conducting black and carbon nanotubes, respectively. Two different types of coating layers have been characterized and analyzed on two kinds of Li4Ti5O12 particles surface by high resolution transmission electron microscopy images (HR-TEM) and selected area electron diffraction (SAED). Typical HR-TEM images and SAED patterns at nano-scale confirmed and showed that both particles exhibited a well-developed spinel nanocrystal with average sizes around 20-50 nm. The C-LTO particles exhibited the roughly spherical shape with more than 5 nm graphitic coating uniformly on the spherical surfaces; however, the CNT-LTO particles showed uniform square nanocrystal with edge length around 30 nm and a few layers of graphene covering the surface.

Electrochemical studies of galvanostatic discharge/charge cycling capacity testing indicated that both Li4Ti5O12particles showed the superior initial discharge capacity of more than 200 mA·h/g at 0.1C rate, and also the CNT-LTO particles show much improved specific capacity than that of the C-LTO particles during different cycling processing. It has been proposed that, grephene covering layers and the CNT interconnection networks are prove to increase electronic conductivity and improve the kinetics of Li4Ti5O12 toward fast lithium insertion/extraction. The comparative experimental results demonstrated that both nanoscale grephene layer and CNT inter-networks among particles is highly effective in improving the electrochemical properties of the CNT-LTO particles.

Mg@ZnO thin films were prepared by DC/RF magnetron co-sputtering in (N2+O2) ambient conditions using metallic Mg and Zn targets. We present a comprehensive study of the effects of film thickness, variation of O2 content in the working gas and annealing temperature on the structural, optical and magnetic properties. The band gap energy of the films is found to increase from 4.1 to 4.24 eV with the increase of O2 partial pressures from 5 to 20 % in the working gas. The films are found to be ferromagnetic at room temperature and the saturation magnetization increases initially with the film’s thickness reaching a maximum value of 14.6 emu/cm3 and then decreases to finally become diamagnetic beyond 95 nm thickness. Intrinsic strain seems to play an important role in the observed structural and magnetic properties of the Mg@ZnO films. On annealing, the as-obtained ‘mostly amorphous’ films in the temperature range 600 to 800°C become more crystalline and consequently the saturation magnetization values reduce.

Graphyne is a generic name for a family of carbon allotrope two-dimensional structures where sp2 (single and double bonds) and sp (triple bonds) hybridized states coexists. They exhibit very interesting electronic and mechanical properties sharing some of the unique graphene characteristics. Similarly to graphene, the graphyne electronic properties can be modified by chemical functionalization, such as; hydrogenation, fluorination and oxidation. Oxidation is of particular interest since it can produce significant structural damages.

In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics and structural changes of the oxidation of single-layer graphyne membranes at room temperature. We have considered α, β, and γ-graphyne structures. Our results showed that the oxidation reactions are strongly site dependent and that the sp-hybridized carbon atoms are the preferential sites to chemical attacks. Our results also showed that the effectiveness of the oxidation (estimated from the number of oxygen atoms covalently bonded to carbon atoms) follows the α, β, γ-graphyne structure ordering. These differences can be explained by the fact that for α-graphyne structures the oxidation reactions occur in two steps: first, the oxygen atoms are trapped at the center of the large polygonal rings and then they react with the carbon atoms composing of the triple bonds. The small rings of γ-graphyne structures prevent these reactions to occur. The effectiveness of β-graphyne oxidation is between the α- and γ-graphynes.