Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step.

We demonstrated that ${\mathrm{Sc}}_2{\mathrm{O}}_3$ thin films deposited by plasma-assisted molecular-beam epitaxy can be used simultaneously as a gate oxide and as a surface passivation layer on AlGaN/GaN high electron mobility transistors (HEMTs). The maximum drain source current, $I_{\mathrm{DS}},$ reaches a value of over 0.8 A/mm and is $\text{∼40\%}$ higher on ${\mathrm{Sc}}_2{\mathrm{O}}_3/\mathrm{AlGaN}/\mathrm{GaN}$ transistors relative to conventional HEMTs fabricated on the same wafer. The metal–oxide–semiconductor HEMTs (MOS–HEMTs) threshold voltage is in good agreement with the theoretical value, indicating that ${\mathrm{Sc}}_2{\mathrm{O}}_3$ retains a low surface state density on the AlGaN/GaN structures and effectively eliminates the collapse in drain current seen in unpassivated devices. The MOS-HEMTs can be modulated to $\text{+6\hspace{0.17em}}\mathrm{V}$ of gate voltage. In particular, ${\mathrm{Sc}}_2{\mathrm{O}}_3$ is a very promising candidate as a gate dielectric and surface passivant because it is more stable on GaN than is MgO.

A study of V/Al/Pt/Au and Ti/Al/Pt/Au contacts to n-Al0.3Ga0.7N/GaN heterostructures is presented. Vanadium was chosen as a potential replacement for Ti because V is expected to form a thermally stable nitride with a low work function. Low-resistance Ohmic contacts are achieved with V/Al/Pt/Au layers after annealing at 650 °C, which represents a decrease of 150 °C compared to the Ti/Al/Pt/Au counterpart. This contact exhibits two orders of magnitude lower specific contact resistance compared to the Ti/Al/Pt/Au contacts studied in this work when annealed at temperatures less than 800 °C, although the specific contact resistance of the Ti/Al/Pt/Au contacts is lower when annealed at higher temperatures. A contact resistance and specific contact resistance of 0.8±0.1 Ω mm and (1.4±0.3)×10−5 Ω cm2, respectively, are obtained after annealing at 650 °C for 45 s.

Intra- and interlayer atom-atom correlations in molecular beam epitaxially grown dilute InGaAs alloys were studied using cross-sectional scanning tunneling microscopy. By imaging individual chemical constituents we construct a large ensemble of “atom maps” from which two-dimensional In-In pair correlation functions were deduced. We found a total absence of interlayer pair correlation along $\left[001\right]$ and a strong negative correlation for the nearest neighbor (nn) pair along $\left[110\right]$, corresponding to a repulsive interaction energy of 0.1 eV for the nn In pairs along $\left[110\right]$. In addition, a weak long-range oscillation in the correlation function along $\left[110\right]$ is observed.

A comparison was made of specific contact resistivity and morphology of Ti/Al/Pt/WSi/Ti/Au and Ti/Al/Pt/W/Ti/Au ohmic contacts to AlGaN/GaN heterostructures relative to the standard Ti/Al/Pt/Au metallization. The W- and WSi-based contacts show comparable specific resistivities to that of the standard contact on similar layer structures, reaching minimum values of ${\text{∼10}}^{\text{−5}}\mathrm{\hspace{0.17em}\Omega }{\mathrm{cm}}^2$ after annealing in the range $\text{850–900\hspace{0.05em}°}\mathrm{C}.$ However, the W- and WSi-based contacts exhibit much smoother surface morphologies, even after $\text{950\hspace{0.05em}°}\mathrm{C}$ annealing. For example, the root-mean-square roughness of the Ti/Al/Pt/WSi/Ti/Au contact annealed at $\text{950\hspace{0.05em}°}\mathrm{C}$ was unchanged from the as-deposited values whereas the Ti/Al/Pt/Au contact shows significant deterioration of the morphology under these conditions. The improved thermal stability of the W- and ${\mathrm{WSi}}_x$ -based contacts is important for maintaining edge acuity during high-temperature operation.