The principal theme of this thesis is to see the planetary processes underlying observable variations. Various planetary processes in atmosphere, surface and interior exert long-term or short-timescale influence on the superficial properties that can be easily observed. This thesis combines observations with theoretical modelling to mine out the essential information of the Venus atmosphere and Enceladus’s ice shell and promote the understanding of variations and evolution of our Solar System.

The Venus atmosphere is essential for understanding why Earth and Venus have evolved so differently even though they are similar in mass and radius. However, the complicated coupling among atmospheric dynamics, chemistry and clouds on Venus is still not well investigated. Using chemical-transport models (CTMs), I aimed to disentangle the effects from various atmospheric processes and guide observations of future Venus missions (DAVINCI+, VERITAS and EnVision).

Recent ground observations from TEXES/IRTF have for the first time revealed the co-evolution of SO2 and H2O at the cloud top of Venus. The two species exhibit a temporal anti-correlation. I used a one-dimensional CTM to investigate the mechanism of this anti-correlation. I found that the anti-correlation can originate from the sulfur photochemistry in the middle atmosphere, while the variations can be caused by the lower-atmosphere perturbations. Eddy diffusion alone cannot explain the observations. This study emphasizes the urgent need of detecting the cloud layer and the deep atmosphere of Venus.

The instrumentation TEXES/IRTF also found a two-peak feature in the local-time distribution of SO2 at the cloud top, consistent with SPICAV/VEx observations. I developed a two-dimensional CTM and connected it to a Venus GCM to investigate this feature. My work revealed that the two peaks can be explained by the combination of the semi-diurnal tides and the retrograde superrotating zonal (RSZ) flow. SOIR/VEx also observed a statistical difference between terminators for CO in the upper atmosphere. From my simulations, this difference can be explained by the transition from the RSZ flow to the sub-solar to anti-solar (SS-AS) circulation. My work also discussed mechanisms underlying the local-time distributions of other species and implied a complex coupling of photochemistry and dynamics in the Venus mesosphere.

The Cassini flyby observed that Enceladus currently experiences a high surface heat flow. This leads to the question whether its ice shell is in steady state or its sub-surface ocean is freezing with time. To support the steady state of the ice shell, amounts of endogenic heat are required, which are currently thought coming from tidal dissipation. However, the exact process that produces sufficient tidal dissipation to match the observations remains elusive. I used a libration model to investigate the heating effect of the diurnal forced libration. I found that although the forced libration enhances the tidal dissipation in the ice shell, the total heating in the shell is still insufficient to match the observed surface heat loss. If Enceladus is in steady state, there should exist a large heat source beneath the shell, either in the ocean or in the core. If in steady state, Enceladus is likely to be in a stable thermal equilibrium, which resists small perturbations on the ice shell. This implies that thermal runaway or episodic heating is unlikely to originate from the librations of the ice shell.

Until 2003, the semiconductor industry followed Dennard scaling rules to improve complementary metal-oxide-semiconductor (CMOS) transistor performance. However, performance gains with further reductions in transistor gate length are limited by physical effects that do not scale commensurately with device dimensions: short-channel effects (SCE) due to gate-leakage-limited gate-oxide thickness scaling, channel mobility degradation due to enhanced vertical electric fields, increased parasitic resistances due to reductions in source/drain (S/D) contact area, and increased variability in transistor performance due to random dopant fluctuation (RDF) effects and gate work function variations (WFV). These emerging scaling issues, together with increased process complexity and cost, pose severe challenges to maintaining the exponential scaling of transistor dimensions. This dissertation discusses the benefits of oxygen-insertion (OI) technology, a CMOS performance booster, for overcoming these challenges.

The benefit of OI technology to mitigate the increase in sheet resistance ($R_{sh}$) with decreasing junction depth ($X_J$) for ultra-shallow-junctions (USJs) relevant for deep-sub-micron planar CMOS transistors is assessed through the fabrication of $R_{sh}$ test structures, electrical characterization, and technology computer-aided design (TCAD) simulations. Experimental and secondary ion mass spectroscopy (SIMS) analyses indicate that OI technology can facilitate low-resistivity USJ formation by reducing $R_{sh}$ and $X_J$ due to retarded transient-enhanced-diffusion (TED) effects and enhanced dopant retention during post-implantation thermal annealing. It is also shown that a low-temperature-oxide (LTO) capping can increase $R_{sh}$ unfavorably due to lower dopant activation levels, which can be alleviated by OI technology.

This dissertation extends the evaluation of OI technology to advanced FinFET technology, targeting 7/8-nm low power technology node. A bulk-Si FinFET design comprising a super-steep retrograde (SSR) fin channel doping profile achievable with OI technology is studied by three-dimensional (3-D) TCAD simulations. As compared with the conventional bulk-Si (control) FinFET design with a heavily-doped fin channel doping profile, SSR FinFETs can achieve higher $I_{on}/I_{off}$ ratios and reduce the sensitivity of device performance to variations due to the lightly doped fin channel. As compared with the SOI FinFET design, SSR FinFETs can achieve similarly low $V_{DD,min}$ for 6T-SRAM cell yield estimation. Both SSR and SOI design can provide for as much as 100 mV reduction in $V_{DD,min}$ compared with the control FinFET design. Overall, the SSR FinFET design that can be achieved with OI technology is demonstrated to be a cheaper alternative to the SOI FinFET technology for extending CMOS scaling beyond the 10-nm node.

Finally, this dissertation investigates the benefits of OI technology for reducing the Schottky barrier height ($\Phi_{Bp}$) of a Pt/Ti/p-type Si metal-semiconductor (M/S) contact, which can be expected to help reduce the specific contact resistivity for a p-type silicon contact. Electrical measurements of back-to-back Schottky diodes, SIMS, and X-ray photoelectron spectroscopy (XPS) show that the reduction in $\Phi_{Bp}$ is associated with enhanced Ti 2p and Si 2p core energy level shifts. OI technology is shown to favor low-$\Phi_{Bp}$ Pt monosilicide formation during forming gas anneal (FGA) by suppressing the grain boundary diffusion of Pt atoms into the crystalline Si substrate.

This thesis is composed of two distinct themes. The first concerns the chemical structure of Venus's atmosphere. Venus's atmosphere can be roughly separated into lower and middle regions separated by a thick cloud deck. When modeling the chemistry of Venus' atmosphere past researchers have focused on these regions separately. In doing so they have made conflicting assumptions about the cloud region that connects them. In Chapter 2 I present the first detailed chemical model of Venus' atmosphere that includes both the lower and middle atmosphere. This model is used to characterize the chemical recycling pathways of observed trace species. In this study I find that there also exists a yet unidentified sink of sulfur-dioxide in the Venusian clouds.

The second theme of this thesis concerns understanding the interior structure and history of Kuiper Belt objects. In July 2015, NASA's New Horizons spacecraft made its close flyby of Pluto. This opened a new era for understanding not only of Pluto, but also the nature of Kuiper Belt objects generally. To this end I developed a model of how the bulk density of Kuiper Belt objects would evolve through time due to changes in porosity and the melting and refreezing of a subsurface ocean. In Chapter 3 I apply this model to Pluto and its largest moon Charon. I found that the density contrast between Pluto and Charon is large enough that it can only be reasonably explained by a difference in bulk composition (eg. rock to ice ratio).

In Chapter 4 I apply this model to bulk density measurements of Kuiper Belt objects (KBOs) generally. It has previously been observed that small KBOs have a much lower bulk density than their larger counterparts. I have found that this can naturally be explained by smaller KBOs being more porous. This difference in porosity is due to the longer cooling timescale of large KBOs causing them to warm more from the heat of radioactive decay. This in turn causes the ice to viscously relax away porosity. Small KBOs in contrast can efficiently conduct out this heat while staying cold and rigid. Because this depends on the abundance and heat production of radioactive elements, I have used this density information to place a constraint on when these objects formed.

In Chapter 5 I revisit Pluto examining what the observed tectonics imply about the history of Pluto's subsurface ocean. Namely I consider whether these observations are more consistent with Pluto having that ocean shortly after formation or developing it over a longer timescale through radioactive decay of long lived radioisotopes. If Pluto did form its ocean slowly, this would have caused global compression for which we find no tectonic evidence. If, however, Pluto started with an ocean we predict two stages of extension which is far more consistent with the observed geology.

Solar system giant planets are known for their opaque and colorful aerosols. Their weather layers harbor dynamic and fascinating cloud activities, convective plumes, and banded circulations. Observations also suggest remote giant planets, such as brown dwarfs, exhibit large-scale circulations. Weather layers also serve as the boundary condition of giant planets that control their evolution. It has been debated for several decades that moist convection is important to heat transport in the atmosphere and the formation of large-scale dynamics on giant planets. However, it is still unclear how moist convection operates the visible weather events, atmospheric circulations, and evolution of giant planets. In this thesis, I seek to combine state-of-the-art numerical simulations, analytical analysis, and telescope observations to shed light on the impact of moist convection on the atmospheric dynamics and cloud formation of giant planets and support ongoing and future space missions to enhance their future scientific return.

Convection- and cloud-resolving simulations are computationally expensive due to the issue of atmospheric aspect ratio, in which the vertical resolution limits the numerical timestep and computational efficiency. Chapter~\ref{chap:1-VIC} presents a solution to this problem. We introduce a state-of-the-art vertically-implicit-correction scheme that can improve the computational efficiency by a factor of 10-to-1000 and correctly capture the small-scale turbulence and large-scale dynamics. The implementation of this scheme in the nonhydrostatic model, SNAP, greatly facilitates studies in later chapters, which require numerical simulations.

The temperature structure of giant planet weather layers, which serve as the boundary of the planet and control the evolution of the planet, is poorly constrained. The molecular weight difference between the dominant hydrogen-helium mixture and the heavy cloud-forming species may inhibit thermal convection and alter the temperature structure of giant planets from adiabats to superadiabats. Chapter~\ref{chap:2-convective-inhibition} shows a new picture of convective inhibition with a significantly reduced inhibition threshold by consistently considering both downdrafts and updrafts in the weather layer. I argue that convective inhibition may have a broader impact on thermal convection in various planets with a reduced inhibition threshold than previously expected.

The latent heat cycle, which is associated with the condensation of cloud-forming species and evaporation of their condensates, transports a significant amount of energy across the weather layer. Analytical and 2D numerical solutions in Chapter~\ref{chap:3-self-regulated-moist-convection} show that the cloud column density and mixing efficiency (i.e., eddy diffusivity) of cloud-forming species are significantly regulated by the latent heat flux, which is limited by internal heat fluxes of giant planets. The predicted cloud density, cloud opacity, and mixing efficiency with the self-regulated moist convection are several orders of magnitude smaller than traditional studies suggested. The simulated temperature structure and relative humidity profiles also support the conclusion from Chapter~\ref{chap:2-convective-inhibition} that convection inhibition and superadiabatic weather layer may occur with less abundant moisture.

Chapter~\ref{chap:4-Jupiter-Superadiabat} carefully studies the heat transport and thermal structure at Jupiter's water weather layer in a localized 3D regime. Latent heat dominates heat transport in Jupiter's weather layer since thermal convection is turned off by the mass-loading effect. The mass-loading effect leads to a persistent and subsaturated stable layer that disjoints the weather layer into two convective zones. As a result, Jupiter's weather layer is superadiabatic. The simulated mixing efficiency and temperature structure support conclusions in Chapters~\ref{chap:2-convective-inhibition} and \ref{chap:3-self-regulated-moist-convection}. This research has important implications for interior and evolution studies. It also suggests that the ammonia depletion observed by Juno's microwave radiometer and ground-based telescopes may be caused by a warmer deep atmosphere.

Brown dwarfs and direct-imaging planets exhibit rotational modulations in different wavelengths, leading to the observed rotational light curves. It is proposed that such variation is induced by patchy cloud patterns on these substellar objects. Chapter~\ref{chap:5-jupiter-light-curve} studies the rotational modulation of Jupiter from visible to mid-infrared and suggests that the wave-beating patterns such as 5 $\rm \mu$m hot spots and vortices like the great red spot have a significant contribution to emission light curves.

These studies bridge theories and observations of moist convection and cloud activities on giant planets by analytical analysis and numerical simulations. Enriching implications from these studies can greatly benefit the understanding of giant planets' weather layers and support the ongoing Juno mission and the future flagship Uranus Orbiter and Probe.