Browsing by Author "Peng, Qing"
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Item Achieving Excellence in Graduate Research: A Guide for New Graduate Students(Wiley-Blackwell, 2015) Parker, Charles B.; Amsden, Jason J.; Peng, Qing; Stoner, Brian R.; Glass, Jeffrey T.; Duke University; University of Alabama Tuscaloosa; Research Triangle InstituteItem Atomic Layer Deposition for Surface Modifications and Solid Film Fabrication(University of Alabama Libraries, 2021) Yan, Haoming; Peng, Qing; University of Alabama TuscaloosaAlong with the unceasing development of the surface and material science, modification of substrates surfaces in nanoscale, to fabricate the functional materials with precisely controlled dimensions, refined composition and desired properties becomes crucial. In this report, atomic layer deposition (ALD), a vapor phase, sequential and self-limiting deposition process, has been used as an alternative strategy to modify the surface of materials and fabricates nanometer or micrometer level of functional materials with precise control. In the first part of this dissertation, ALD was used to modify the surface of the shape-engineered nanocrystals (SENCs), which enhanced the thermal stability of the SENCs from 300˚C to 700˚C and enhanced the catalytic activities of the nanocrystals as well. We also proposed a new reaction mechanism of metal-organic precursor with oxide surface, in which the conventional layered ALD growth does not happen but the oxide surface was modified via controlled metal doping. In the second part of this dissertation, ALD precursors were used to reacting with liquid substrates to fabricate freestanding solid thin films. Benefits from the unique reaction mechanism of the ALD metal-organic precursors, the thickness and the compositions of the fabricated films can be controlled. The fundamental of gas-liquid reaction has been discussed in this study. In the third part of this dissertation, area-selective ALD (AS-ALD) has been reported using carboxylic acid self-assembled monolayer as a growth inhibitor. Excellent selectivity of AS-ALD has been achieved by using this method, which could potentially be used in microfabrication as a substitution step for photolithography.Item Electrodeposition of Cobalt for Advanced Interconnect Applications(University of Alabama Libraries, 2021) Hu, Yang; Huang, Qiang; University of Alabama TuscaloosaCopper (Cu) damascene processes have been used to produce back end of line (BEOL) interconnect structures in integrated circuits (IC). As the critical dimension of BEOL structures approaches the electron mean free path of Cu or below, the Cu resistivity exponentially increases, posing significant challenges on further scaling. Metals with shorter electron mean free path, for example cobalt (Co), have been explored as the alternative material to replace Cu in the finest metal levels.The Co electrodeposition process for interconnect applications must produce Co films that can reproducibly fill deep vias or trenches without any defects. It is can be achieved by adding small amounts of organic additives to the plating bath, which lead to the Co electrodeposition preferentially at the bottom of trench, known as bottom-up filling, or super conformal filling, or simply “super-filling”. As the size of interconnect continues to shrink, additives are becoming the key to the successful application of Co electrodeposition in IC manufacture. In this dissertation, a new class of organic additives, dioximes (dimethylglyoxime, cyclohexane dioxime, and furil dioxime), have been investigated for their effects on the electrochemical deposition process of cobalt. In Chapter 2, the nucleation and growth behavior of Co deposition with the addition of dimethylglyoxime and cyclohexane dioxime are studied. Double-peak nucleation curves are observed during Co deposition for the first time. In Chapter 3, a descriptive model is established for the Co nucleation process using furil dioxime, where the suppression effect on Co deposition and the catalytic effect on hydrogen evolution are both more pronounced among the dioxime molecules. Mercaptopropanesulfonate, or MPS, a well-known accelerator used in Cu damascene process, is investigated during the Co deposition in Chapter 4. A potential oscillation is observed during galvanostatic deposition for the first time and a kinetically controlled mechanism is proposed. In Chapter 5, Co films are electrodeposited with different additives including dimethylglyoxime, sodium chloride, and 3-mercapto-1-propanesulfonate. It is found that the addition of 3-mercapto-1-propanesulfonate into the electrolyte significantly increases the S incorporation level and decreases the grain size, both contributing to a higher sheet resistance of film.Item Electrodeposition of materials from novel solvents(University of Alabama Libraries, 2019) Sides, William Donald; Huang, Qiang; University of Alabama TuscaloosaThe electrodeposition of metals and alloys is explored with a focus on solvents and additives capable of reducing or eliminating hydrogen evolution while operating at highly cathodic potentials. The nucleation and growth behavior of binary codepositing systems are modelled in Chapter 2. Deep eutectic solvents based on choline chloride and urea are demonstrated to be capable of electrodepositing metallic manganese for the first time in Chapter 3. Chapter 4 describes the first time manganese has been incorporated into an electrodeposited magnetic iron-group alloy. Water-in-salt electrolytes are applied to the electrodeposition of metals in Chapters 5 and 6. These electrolytes are shown to suppress the proton reduction reaction and subsequent hydrogen evolution in aqueous systems. The tetrabutylammonium ion is also shown to be capable of suppression of proton reduction. The origins of this suppression are examined in Chapter 6, and it is determined that the additive adsorbs onto the electrode surface, blocking proton access. The suppressing behaviors of tetrabutylammonium and water-in-salt electrolytes are combined to achieve significant suppression of proton reduction and the ability to electrodeposit metals at highly negative cathodic potentials. Chapter 6 describes the use of these solvents to electrodeposit ruthenium for interconnect applications. The origin of enhanced superconductivity in rhenium electrodeposited from water-in-salt electrolytes is explored in Chapter 5. A disordered atomic structure is found to be highly correlated with enhanced superconductivity.Item Improve the stability of organic-inorganic hybrid perovskite by vapor-solid reaction(University of Alabama Libraries, 2019) Yu, Xiaozhou; Peng, Qing; University of Alabama TuscaloosaAbstract Organic-inorganic hybrid perovskites, such as CH3NH3PbI3 and NH2CH=NH2PbI3, emerge as a new class of low-cost semiconductors that have the potential applications in high-efficiency photovoltaic cells, light emitting diodes, lasers, and sensors. However, hybrid perovskites can be easily degraded by H2O, O2, and light in ambient conditions. To improve the stability of hybrid perovskites, we carried out a comprehensive study including the degradation kinetics and surface modification by vapor-solid reactions for encapsulation. The degradation kinetics of perovskites were studied by using in situ methods. We found CH3NH3PbI3 perovskite degrades slowly at 85°C. This result indicates hybrid perovskites alone is not stable in the working conditions. We enhanced the stability of perovskites by surface modification through studying the surface reaction mechanism on perovskites. We found that by increasing the partial pressure of vapor reactants such as pyridine, the vapor-perovskite reactions will change from surface terminated reaction to bulk transformation reactions. A thin pin-hole free oxide barrier layer cannot only block H2O and O2 from meeting perovskites but also encapsulate the gas byproducts from the degradation reactions to stop the reversible degradation reaction. Atomic layer deposition (ALD) is a promising method to deposit a pinhole-free metal oxide barrier film onto perovskites. Although there are numerous reports in applying ALD on hybrid perovskites, the nucleation mechanism of ALD on these perovskites are poorly understood. Herein, we will present our findings about the atomic level surface reaction mechanism during ALD on perovskite-related substrates. Collectively, we are able to create a couple of new pathways to improve the stability of perovskite materials.Item The spin Seebeck effect in magnetic insulating oxides(University of Alabama Libraries, 2019) Li, Zhong; Gupta, Arunava; Mankey, Gary J.; University of Alabama TuscaloosaThe spin Seebeck effect (SSE), the generation of a spin current from a thermal gradient, is a novel effect which involves the interaction between charge, spin and heat. Insulating magnetic materials, like yttrium iron garnet (YIG, Y₃Fe₅O₁₂) and nickel ferrite (NFO, NiFe₂O₄), are ideal for the study of this new effect due to avoiding other magnetic effects. Thin films of Y₃Fe₅O₁₂, Ce₀.₇₅Y₂.₂₅Fe₅O₁₂ and NiFe₂O₄ have been grown and optimized on different substrates (MgAl₂O₄, MgGa₂O₄, CoGa₂O₄) using the pulsed laser deposition (PLD) technique, and their crystal structures were investigated using X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). For the magnetocrystalline anisotropy in the thin films, vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) measurements are done. We further did spin Seebeck effect measurements on optimized samples. First, for thin films of Ce₀.₇₅Y₂.₂₅Fe₅O₁₂, homogeneous substitution of Ce in YIG results in the enhancement of the signal in magneto-optic Kerr effect (MOKE) without forming CeO₂ when at lower O₂ atmosphere. The spin Seebeck effect measurements on Ce:YIG films show similar trends and comparable results with pure YIG films suggesting potential applications for thermoelectric generation. Second, an increase in the spin Seebeck voltage is observed with decreasing lattice mismatch between NFO thin films and substrates, which also correlates well with the decrease in the Gilbert damping parameter from FMR measurements. Furthermore, we have developed a vector measurement of the spin Seebeck effect in epitaxial NiFe₂O₄ thin films, which were grown by pulsed laser deposition on (011)- or (001)-oriented MgGa₂O₄ and CoGa₂O₄ substrates with varying lattice mismatches. This new method for SSE measurement shows the existence of a magnetic strain anisotropy in NiFe₂O₄ thin films significantly impacts the shape and magnitude of the SSE voltage hysteresis loops, which demonstrates that voltage signals from bidirectional SSE measurements can be utilized as a new vectorial magnetometry technique to reveal the complete magnetization reversal process.Item Study of structure-property-performance relationships for organic thin-film transistors and polymeric solar cells(University of Alabama Libraries, 2016) Bi, Sheng; Li, Dawen; University of Alabama TuscaloosaOrganic electronics has great potential for fabricating low cost, flexible and large-area devices. Despite the rapid development, several main challenges of the field need to be addressed in both organic conjugated polymer and small molecules based devices, including organic thin-film transistors (OTFTs) and polymer solar cells (PSCs). This dissertation first explores two approaches to align small molecule crystals and improve surface coverage. The controlled evaporative self-assembly (CESA) method is combined with binary solvent system using small molecule SMDPPEH to control the crystal growth. By optimizing the two solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. Also, polymer additives can be added into small molecule to control crystal alignment. As a result, mobilities are at least 10 times higher than that from spin-coated film. The SMDPPEH based OTFTs exhibit a mobility of 1.6×10-2 cm2/Vs, which is the highest mobility from SMDPPEH ever reported. The donor-acceptor vertical composition profile on the performance of the P3HT/PCBM based organic bulk heterojunction solar cells was studied. In this simulation study, variety of donor-acceptor vertical configurations was investigated for both regular and inverted PSC structures. The physical mechanisms behind the diversification of open circuit voltage, short circuit current, and fill factor, and thus power conversion efficiency from various vertical configurations are explained. The effect of vertical composition profile from the study could serve as guidance for experimental optimization of organic bulk heterojunction solar cells. Also, morphology variation of ZnO electron transport layer from atomic layer deposition and sol-gel methods on the performance of organic inverted solar cells were investigated. AFM and SEM were utilized to characterize the morphology of ZnO thin films and nanorods so as to explain the efficiency difference. The final part of the work demonstrates one-step multi-layer pattern transfer to make organic solar cells on rigid and flexible substrates. A multi-layer inking and stamping, a cost-efficient, purely additive pattern transfer technique, was developed to fabricate PSCs. GLYMO is added into PEDOT:PSS hole transport layer and its effect on PSC performance and pattern transfer yield was investigated to reach overall PSC efficiency and high yield pattern transfer.