Laser cooling and trapping of atoms have revolutionized atomic physics with the realization to cool and trap atoms into the ultra-cold regime. This has led the precision of spectroscopy on atoms to an unprecedented level, which make cold atoms not only platforms to search for new physics and test fundamental laws of nature, but also ultra-precise tools to measure fundamental physical quantities such as time and magnetic fields. Cooling and trapping molecules into the cold and ultra-cold regime foresees similar revolutions. The rich internal energy structure and large permanent electric dipole moments of molecules enable a variety of applications beyond the realm of cold atoms, including searches for the electron electric dipole moment, studies of ultra-cold chemistry, and realizations of strongly interacting quan- tum many-body systems. However, the complex energy structure of molecules also render them difficult to laser cool and trap, especially at high densities. In this thesis, we present our progress on pursuing laser cooling and trapping of a new species, aluminum monochlo- ride(AlCl). The highly diagonal Franck-Condon factors(FCFs) and high scattering rate with large single photon recoil velocities owning to a cycling transition at DUV wavelength range make it a favorable candidate. We present our absorption spectroscopy on the A1Π ← X1Σ+ transition to extrapolate the molecular constants and estimate the Frank-Condon factors, and our effort to study the various targets for laser ablation production of AlCl to optimize its initial production. We also present our in-beam fluorescence spectroscopy to resolve the relevant hyperfine structure in the A1Π state in order to understand and construct optical cycling schemes.

My Ph.D research interest is applying standard micro/nano synthesis, fabrication, and processing equipment to creatively develop next-generation nanoelectronics and nanophotonics devices by employing two-dimensional (2D) semiconducting materials and novel device concepts.

In details, TMDs, such as WS2, WSe2, MoS2, MoSe2, represent a large family of layered materials, many of which exhibit tunable band gaps that can transition from an indirect band gap in bulk crystals to direct a band gap in monolayer nanosheets. Besides, the black phosphorus and monolayer phosphorene attracted considerable recent interest as an alternative layered semiconductor expected to exhibit high carrier mobility and layer-number tunable electronic properties. An important feature of these layered materials is the van der Waals interactions between neighboring layers that may allow much more flexible integration of distinct materials without the limitation of lattice mismatch, the similar lattice structure but with distinct properties that enable lateral epitaxial heterogeneous integration, thus opening up vast possibilities to nearly arbitrarily combine and control different properties at the atomic scale.

My first research project focused on the FETs performance optimization using WSe2, a new 2D transition metal dichalcogenides (TMDs) (Nano Lett 15, 709-713 (2015)). By tuning the substrate temperature gradient, carrier gas flow, and relative position of the targeted substrate in a home-made CVD system, I succeeded in producing high quality and large scale WSe2 flake with controllable layer number, single crystal size, and even stacking mode, which in turn achieved exceptional transistors performance with record hole mobility of over 350 cm2V-1s-1 and on/off ratio of above 108. This experience gave me a unique perspective on the optimization of CVD parameters and device contact engineering.

Driven by this pioneering study of WSe2, I further developed an in situ source-switch CVD system to synthesize the first atomically thin WSe2/WS2 heterostructure with 1D interface. Based on this specially designed heterostructure, I made the first WSe2/WS2 heterojunction featuring the photovoltaic effect. (Nat. Nanotechnol. 9, 1024 (2014)). My research with this promising material is an important advance in the development of layered semiconductor heterostructures and an essential step towards achieving functional 2D electronics. I also did deep research on the synthesis and electronic properties of the WS2xSe2-2x alloy nanosheets, which realized the full optical response and electronic properties tuning of the two-dimensional material. Additionally, our pioneering method realized the controllable doping of TMDs by the modulation of atomic ratio (Nano Lett. 16, 264 (2016)).

Fascinated by 2D materials, I extended this research by developing a novel intercalation method to obtain the monolayer phosphorene molecular superlattice (MPMS), based on black phosphorus (BP), an emerging 2D materials with great electronics application potential. With this creative method, I can now control BP from few-layer down to monolayer without properties degradation, and achieve exceptionally high performance with the MPMS transistors to 107 on/off ratio and a lifetime of 15X than that of BP. I also developed a novel device concept, BP-MPMS heterojunction with typical p+/p++ junction properties.

Carbon is both abundant and functionally versatile due to the variability of orbital hybridization of carbon atoms forming linear, planar, and tetrahedral bonds leading to many allotropes. Different allotropes exhibit different physical properties such as electrical conductivity, surface area, and surface chemistry. The work presented here focuses on aromatic carbon materials and examines the tunability of physical properties, molecular to macroscopic structural formation, and importance in environmental applications, specifically soot pollution mitigation and next-generation single atom catalysis.

First, scanning tunneling microscopy (STM) experiments explore the intermolecular interactions of coronene (C12H24), a polycyclic aromatic hydrocarbon hypothesized to play a key role in incipient soot formation. The hazardous impacts of incipient soot – including lengthy suspension in the earth’s atmosphere and deep penetration into human respiratory systems – may be circumvented through an improved understanding of soot formation. Observations of coronene clusters reveal structures strikingly similar to recent models of clusters hypothesized to initiate soot formation. In contrast to mature soot, cluster surfaces are composed primarily of molecular edges. These findings have important implications for how additional molecules attach and become incorporated into growing soot particles.

Second, a first principles approach is used to identify how the local molecular environment on a graphene support can be used to stabilize a single platinum atom catalyst. Inspired by visions of achieving ultimate cost-effectiveness and performance, a single atom catalyst represents the most efficient use of precious metals while concurrently offering the potential for high chemical activity. Density functional theory results indicate that pyridinic nitrogen-doped graphene is a promising candidate to support a single Pt atom acting as a catalyst that is resistant to poisoning and enhances carbon monoxide oxidation efficiency. Experimental efforts demonstrate a pathway towards developing these supports, using bicontinuous interfacially jammed emulsion gels as templates for the growth of three-dimensional, porous graphene. STM, X-ray photoelectron spectroscopy, and Raman spectroscopy characterize the resultant architectures, relating nanoscale observations to macroscale properties such as specific surface area and mechanical strength.

This work – examining aromatic carbon materials – demonstrates how surface science techniques can unravel self-assembly and the physics that shape our macroscale environment.

Crowdfunding is a rapidly growing means of raising capital from a largecrowd of people via the internet. In the U.S., Title III of the JOBS Act exempts offerings using crowdfunding from registering with SEC. To implement the statutory exemption, SEC issued Regulation Crowdfunding (Reg CF). Reg CF imposes certain obligations on issuers, investors, and funding portals. Now in the U.S., offerings using crowdfunding proliferate. Among all these offerings, common stock, debt, and Simple Agreement for Future Equity (SAFE) are the most-issued types of securities. Revenue sharing note becomes a marked type of debt securities. The SAFE is a convertible security that can convert into equity security, in most cases, preferred stock. It is widely used in crowdfunding offerings and has two variants. Meanwhile, it also gives rise to suspicion over its safety, and even SEC’s failed attempt to ban its use in crowdfunding offerings. However, its popularity shows no sign of decline. In contrast, in China, crowdfunding industry used to prosper but now is dying due to regulatory clampdown. To resurrect the industry, two legal loopholes in China Securities Law (CSL) should be corrected. The first is only a modicum of securities are governed by CSL. Notes and SAFEs are outside of CSL’s reach. The second is CSL’s numeric benchmark for a public offering is neither scientific nor reasonable. But overall, the priority is to provide a statutory exemption for crowdfunding offerings in China. Reg CF and a rich body of relevant cases in the U.S. could be useful for China’s rulemaking undertakings in crowdfunding.

The present dissertation deals with how a specific kind of modern political discourse and practice, which was associated with an American style approach to public administration, was introduced, experienced, and then adapted during the 1930s and 1940s in China. The research focuses on local officials who graduated from the Central Politics School, an institution established by the Nationalist Party to train professional public administrators. These individuals were supposed to modernize the entire system of Chinese local governance, making it more rational by bringing it inline with the precepts of scientific knowledge and the scientific method. The actions of the school’s graduates in various counties expose the failure of orthodox public administration methods to deal effectively with Chinese political reality, due to a tendency to underestimate the importance of variable human factors. It was, ironically, only when some of the school’s best former students broke with the precepts of their training and use innovative strategies, which took local realities into account and made use of ideas derived from China’s own statecraft traditions, that they achieved success. This dissertation thus suggests that researchers need to pay more attention in future to Chinese statecraft and its assumptions regarding the importance of sensitivity to human nature and variability, as well as imported ideas concerning rationality and scientific methods, when trying to understand trends in Chinese politics and governance. Moreover, the historical meaning of the rise and deviation of public administration is by no means a story only of frustrated modernization or periodic revivals of “tradition.” Rather, it represents an important case study of how non-scientific indigenous resources are deployed in the face of drives in settings outside the West to impose a form of political modernity, which has the potential to overcome the problems insurmountable in the current political conceptual framework.