Browsing by Author "Dole, Nikhil"
Now showing 1 - 4 of 4
- Results Per Page
- Sort Options
Item Control of Metallurgical, Magnetic and Electrical Properties of Electrodeposited CoFeNi Thin Films and Cu Nanostructures(2014-05) Dole, Nikhil; Brankovic, Stanko R.; Bao, Jiming; Ruchhoeft, Paul; Meen, James K.; Majkic, Goran; Garfias, Luis F.The ever increasing quality and reliability demand of microsystems indicate that the electrodeposited magnetic alloys used for their fabrication should have minimum possible magnetic losses at the desired frequency range. In order to meet this challenge, the magnetic industry is facing the task of electrodepositing soft high magnetic moment alloys (SHMM) with high permeability (μr>400) and high resistivity (ρ>100μΩ-cm). The ternary ferromagnetic CoFeNi alloys represent the class of SHMM alloys which inherently have a higher resistivity than their binary (NiFe or CoFe) counterparts, with similar magnetic properties. In the first part of this research, the work exploring the development of solution chemistry for the electrodeposition of CoFeNi magnetic thin films is discussed. The experimental results (FIB, EDS, XRD, 4-point probe and VSM) indicate that a high deposition rate CoFeNi film can be deposited from the developed bath chemistry yielding high saturation magnetization (Ms~2.0 T), high relative permeability (μr~700) and high resistivity (ρ~100μΩ-cm). Additionally, the effect of sulfur containing additives like saccharin on the physical, electrical and metallurgical properties of CoFeNi films is studied. The role played by saccharin in stress reduction is exhibited by performing in-situ stress measurements during thin film growth. The second part of this dissertation focuses on a novel approach towards improving the conductivity of Cu interconnects at nanoscale. The externally applied strain on the Cu interconnects during annealing is used to promote the grain growth via grain boundary densification process. The results indicate that this approach yields positive effect on the resistance of Cu interconnects. The drop in the resistance after annealing at 200°C and 250°C is observed for externally imposed compressive strain along the Cu interconnects with critical dimensions (CD) of 50nm and 64nm. The analysis and results suggest that the compressive strain during annealing induces densification of the grain boundaries with the interface vector parallel to the current path. These results are of great significance for the overall improvement of conductivity of the Cu interconnects as well as reliability and life span of microelectronic devices.Item Electrochemical Synthesis of Functional Films and Surfaces(2020-12) Ahmadi, Kamyar; Brankovic, Stanko R.; Robles Hernandez, Francisco C.; Bao, Jiming; Taylor, E. Jennings; Mayerich, David; Dole, NikhilThis dissertation represents experimental work with significant analytical modeling in areas of electrochemical material science and thin films. It produces several fundamental results with great implications for practitioners in the field and various applications in technological enterprises. The dissertation addresses problems in a broad range of electrochemical synthesis methods, including stress control in the electrochemical deposition of functional films, synthesis of functional surfaces, and monolayer deposits. Thin film residual stress developed during the deposition can adversely affect the film's reliability and functionality. This research describes the origin of the crack formation in Cr and Pd films, two industrially significant coatings, using in situ stress measurement during and after the film deposition as the primary experimental approach. Our finding in chromium electrodeposition from Cr(III) electrolytes relates the origin of cracks to the formation and subsequent decomposition of Cr-H. Employing various experimental methods, data analysis, and modeling, the research describes the design of effective PCD (pulse-currents-deposition) that reduces Cr-H accumulation, the stress generating source, at the deposition stage. The designed PCD with t_on/t_off > 5 where t_on > 0.25 seconds showed drastic crack mitigation in the deposits. Additionally, this work investigates stress development during Pd film deposition and shows that introducing Pb2+ ion in the depositing electrolytes can lead to Pb underpotential co-deposition as Pd-Pb intermetallic, which suppresses the generated stress from hydrogen absorption. This dissertation also demonstrates electrochemical techniques for electroless Pb ML deposition and surface decoration as a practical approach for designing chemical sensors and developing new deposition processes like e-less ALD (atomic-layer-deposition). First, it presents a novel chemi-resistive hydrogen-sulfide sensor, designed and synthesized by atomic-layer surface modification. The modification with AuPd alloy improves chemi-resistivity of Au ultra-thin film and results in fast, reproducible, and linear sensing for hydrogen-sulfide from aqueous environments. Further, this research discusses an analytical study on the electroless Pb ML deposition on various substrates. The analysis shows that the surfaces’ electronic nature and catalytic phenomena are the main factors in electroless ML deposition. These findings have significance for electrochemical deposition on nano features and shed light on a pathway to synthesize core-shell nano-catalysts using a new e-less ALD method.Item Electrochemical Thin Film Growth Assisted by Pb Monolayer(2018-05) Wu, Dongjun; Brankovic, Stanko R.; Bao, Jiming; Yao, Yan; Miljanić, Ognjen Š.; Dole, NikhilThe properties of heteroepitaxial thin films are very much dependent on the method used for their deposition. The electrochemical/electroless deposition represents the ambient temperature growth process for many heteroepitaxial metal overlayers while preserving the integrity of their interface. However, in many substrate-overlayer systems the interfacial free energy of the overlayer/electrolyte is smaller than the sum of the interfacial free energies of the substrate/electrolyte and overlayer/substrate and nucleation and growth of rough 3D films is favored. In epitaxial systems where the thermodynamics predicts Frank-van der Merve or 2D layer-by-layer growth, the difficulties in producing 2D single crystal overlayers by electrodeposition are similar to those encountered during the vacuum deposition at ambient temperature. Owing to strain and kinetic issues, 3D growth occurs often. In recent years, a significant progress has been made in understanding the kinetic aspects controlling the growth modes in vacuum deposition. This development has led to various discoveries in which the growth kinetics during electrochemical growth was manipulated to enhance the evolution of atomically flat epitaxial overlayers. In the first part of this PhD work, electrochemical and electroless Pb UPD phenomena were investigated as a critical step in development of more sophisticated approaches to manipulate growth kinetics during electrochemical/electroless growth of thin films. An electroless atomic layer deposition (eALD) method has been developed using the electroless Pb monolayer as the reducing agent and sacrificial layer in surface limited redox replacement reaction with more noble metal ions (Ptn+). This eALD process is highly selective to metal substrates at which Pb forms the electroless monolayer. Repetition of the eALD cycle leads to formation of a highly compact, smooth and conformal noble metal film. In the second part, electrochemical deposition of 2D Cu thin film on Ru(0001) surface was investigated. In the first case, Cu was co-deposited with periodically deposited and stripped Pb mediator, the Pb mediator serves to increase the density of 2D Cu islands during deposition and promote a layer by layer thin film growth mode. In the second case, a full UPD monolayer of Pb was used as a surfactant during Cu deposition and 2D growth of Cu was obtained on the Ru(0001) surface. In the third part of this work, an electroless approach was investigated for Co deposition on the Cu(h, k, l) polycrystalline substrate. The effect of substrate pre-treatment on the final morphology and structure of deposited Co film was studied; the results suggest that proper annealing of the Cu substrate in the forming gas (75%H2, 24%N2 and 1%CO) is beneficial for the ultimate quality of the deposited Co thin film. Our study shows that with the presence of the electroless Pb monolayer surfactant, the morphology and quality of the deposited Co film is improved in terms of uniformity, continuity and smoothness of the film. The experimental result indicates that the electroless Pb monolayer has efficiently reduced the Schwoebel barrier and enhanced the surface diffusion of atoms during deposition.Item Rational Design of Trimetallic Electrocatalyst for Electrochemical Overall Water Splitting(2018-05) Qin, Fan; Bao, Jiming; Sun, Li; Yao, Yan; Robles Hernandez, Francisco C.; Shan, Xiaonan; Dole, NikhilNoble-metal-free bifunctional electrocatalysts for overall water splitting have attracted increasing attention due to their earth-abundancy and high efficiency. However, current bifunctional electrocatalysts suffer from the disadvantages of the complex synthetic process, low yield, or low energy conversion efficiency. Thus, it is highly desirable and significant to develop efficient electrocatalysts with high energy conversion efficiency through the facile process. The Co-Fe-W multi-metal oxides have been reported as one of the best OER catalysts, but their overall water splitting activity is not reported yet, which might be due to the poor HER activities. In Chapter 3, we develop a trimetallic CoFeW film on Ni foam by hydrothermal deposition and subsequent thermal annealing process. The trimetallic CoFeW exhibits great HER activity (ƞ10=147 mV) due to the improved conductivity and increased electrochemical active surface area after annealing. Benefitting from the enhanced HER and remained OER activities, the trimetallic CoFeW electrodes require a cell voltage of 1.57 V (10 mA∙cm-2) to drive overall water splitting. However, the overall performance is still limited and a more efficient trimetallic system needs to be developed. In Chapter 4, we have developed a trimetallic NiFeMo film on Ni foam via a similar process with different precursors. This electrode successfully integrates the benchmark HER (Ni-Mo) and OER (Ni-Fe) species into a single electrode. As a result of remarkable activities for both HER and OER, the NiFeMo electrode exhibits a low voltage of 1.45 V for overall water splitting, which outperforms the current reported bifunctional electrocatalysts. High-resolution transmission electron microscopy reveals that nanometer-sized single crystal domains of Ni, Fe, and Mo are intimately integrated, which enables a synergistic effect of metallic Ni, Fe, and Mo for efficient HER; while self-formed Ni-Fe-Mo (oxy)hydroxides on the surface of NiFeMo anode become active sites for OER. Such multi-metallic alloy and its (oxy)hydroxides represent a typical HER/OER catalyst couple, and our method provides a new route to develop efficient low-cost metallic alloys for overall water splitting.