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Layered tin monoxide (SnO) offers an exciting two-dimensional (2D) semiconducting system with great technological potential for next-generation electronics and photocatalytic applications. Using a combination of first-principles simulations and strain field analysis, this study investigates the structural dynamics of oxygen (O) vacancies in monolayer SnO and their functionalization by complementary lightweight dopants, namely C, Si, N, P, S, F, Cl, H and H₂. Our results show that O vacancies are the dominant native defect under Sn-rich growth conditions with active diffusion characteristics that are comparable to that of graphene vacancies. Depending on the choice of substitutional species and its concentration within the material, significant opportunities are revealed in the doped-SnO system for facilitating n/p-type tendencies, work function reduction, and metallization of the monolayer. N and F dopants are found to demonstrate superior mechanical compatibility with the host lattice, with F being especially likely to take part in substitution and lead to degenerately doped phases with high open-air stability. The findings reported here suggest that post-growth filling of O vacancies in Sn-rich conditions presents a viable channel for doping 2D tin monoxide, opening up new avenues in harnessing defect-engineered SnO nanostructures for emergent technologies. Economic Development Board (EDB) Ministry of Education (MOE) Nanyang Technological University This research article was supported by the Economic Development Board, Singapore and Infineon Technologies Asia Pacific Pte Ltd through the Industrial Postgraduate Programme with Nanyang Technological University, Singapore, and the Ministry of Education, Singapore (Academic Research Fund TIER 1-RG174/15).

In the recent years, the mechanical robustness and reliability of three-dimensional (3D) integrated circuit (IC) packaging have become tremendously challenging due to its continuous reduction in size and increase in vertical integration. Thermal problems such as the silicon (Si) substrate cracking and interfacial delamination are increasingly dominant due to the presence of high heat density in the small multilayer IC packaging. Furthermore, as the manufacturing and processing steps of the 3D ICs are significantly different from that of the conventional ICs, new defect and failure mechanisms that are unique to 3D ICs are not well-investigated. The reduction in size has also increased the sensitivity of the 3D ICs to microdefects that had not previously threatened their reliability and integrity. The increased complexity and miniaturization of 3D IC packaging and its consequential problems demand for new failure analysis methods. Therefore, this PhD research is proposed to study the physical failure modes and mechanisms associated with 3D ICs via molecular dynamics (MD) simulation and finite element method (FEM), and to develop new failure analysis methods for packaging characterization, thereby improving the packaging techniques and processes. Si is commonly used as a substrate material in the IC packaging but yet its fracture behavior theoretical framework is still not well-developed. Thus, studies are first carried out on Si to understand its fracture mechanism through MD simulation and experiment. As the mechanical properties of Si are strongly influenced by the crystallographic orientation, defects, grain boundary (GB) and temperature, their effects on the tensile properties and failure mechanisms of Si are investigated. The results show that when Si is subjected to tensile loading, it undergoes brittle fracture and its (111) plane is the most favorable cleavage plane due to its high atomic packing density, thus resulting in the highest stiffness and lowest fracture strength. The presence of structural defects generally weakens the integrity of Si, particularly for the (100) oriented Si subjected to tensile loading in the [010] direction, its integrity is much more sensitive to these structural defects. The three-point bend test is also performed to investigate the crystallographic orientation and defects effects and the experimental results are found to be consistent with the MD results. The investigation of ∑25(710) tilt and ∑25(001)twist GBs in bicrystal Si nanofilms show that their fracture strengths are lower than that of single-crystal Si, which is caused by the change in crystallographic orientation of the grains. It is observed that these nanofilms generally fail through sliding dislocation mechanism. The reduction in size results in the increase of surface effect, and thus less energy is required for dislocation sliding to occur at the surface. The strength is further weakened by the addition of notch at the free edge of the GB. The increase in temperature (up to 600 K) has insignificant influence on the failure mechanism but generally lowers the fracture strength as expected. These combined simulation and experimental findings are then used to substantiate and explain the fracture behavior of bulk Si subjected at the macroscale, thereby improving the accuracy of root cause analysis. Furthermore, understanding and predicting interfacial delamination failure in the multilayered IC packaging are essential for their performance and reliability. The MD study is first performed to investigate the effect of voids and temperature on the interfacial fracture behavior in a-Si3N4/Si bilayer systems. When the bilayer system is subjected to tensile loading, its fracture behavior is found to be temperature-dependent. At 300 K, the interfacial strength of the bilayer system is ~22.5 GPa and it undergoes brittle fracture at the interface. However, failure occurs in the a-Si3N4 layer in a ductile mode when temperature is increased to 600K. With the existence of void in the Si layer in the a-Si3N4/Si system, crack initiates at the void and propagates towards the interface at 300 K. As the temperature increases to 600 K, the same bilayer system undergoes brittle fracture at the interface at a significantly lowered interfacial strength. With the inclusion of an interfacial void, the bilayer system fractures at the interface with a deteriorated strength regardless of the temperature. The simulation results also show that the presence of an interfacial void has a more adverse impact on the interfacial strength than having a void in the Si layer. Under the shear loading, the bilayer system deforms in three stages: elastic deformation, plastic flow in the a-Si3N4 layer and interfacial sliding. The presence of voids and the increase in temperature lower the stress required for interfacial sliding but they do not have significant effect on the shear deformation process. Subsequently, a combined approach based on MD-FEM simulations is adopted to characterize and predict delamination in a-Si3N4/Si bilayer system. The material parameters that are required to be input into the cohesive constitutive relation in FEM are derived from MD simulation. The work of interfacial fracture obtained by the FEM simulation is about 0.11 J/m2 which is in good agreement with the experimentally obtained value of about 0.085 J/m2. The above approach is also extended to characterize the interfacial energies and predict interfacial delamination in the Cu/Ti/SiO2/Si multilayered system. The thermodynamic work of adhesion W derived from MD simulation is used as the failure criterion for the FEM simulation as it is independent of the system geometry and applied strain rate. The interfacial fracture energy of 8.23 and 9.79 J/ m2 obtained from the MD-FEM simulations and the indentation damage experiment respectively, are also in good agreement. Hence, the combined approach is accurate and effective in characterizing and predicting the interfacial delamination in the multilayered IC packaging. This PhD dissertation has investigated the fracture behaviour of bulk Si, bilayer systems and multilayered systems to understand their failure mechanisms and help in the failure analysis process. This study is able to provide useful information for 3D ICs design and applications and helpful in improving their stability and reliability. Doctor of Philosophy (MAE)

It is challenging to understand and predict interfacial delamination in multi-layered integrated circuit (IC) packaging due to the difficulties in experimentally quantifying the critical fracture energy of interfacial adhesion. This study takes a combined approach based on molecular dynamics (MD) simulation and finite element method (FEM) to characterize the interfacial fracture energy and predict delamination in the Cu/Ti/SiO 2 /Si multilayer systems. MD simulation is first conducted on each interface of the multiple layers at the atomistic level to obtain the material parameters such as the critical interfacial fracture energy that are required for the interfacial cohesive constitutive relation. Then, FEM is used to model and predict the interfacial delamination of the multi-layered system under indentation loading at the macroscale with the cohesive zone being considered around the delamination or crack tips. Finally, the indentation damage test is performed to validate the modeling results. The proposed combined modeling approach will have the potential to provide guidance in design and applications of IC packaging for improved stability and reliability.

Background Treatment of retinopathy of prematurity (ROP) to prevent blindness depends on timely eye exams of at-risk infants. Purpose To examine the effectiveness of a user-friendly pamphlet in improving parents' perceived importance of and ultimate adherence to ROP screening guidelines. Methods A pamphlet on ROP was provided to parents of at-risk infants. Before and after reading the pamphlet, the parents were evaluated on their knowledge of ROP and their perception of the importance of timely follow-up screening. Results Before and after pamphlet exposure, the knowledge of ROP essentially stayed the same for all parents. Before pamphlet exposure, a couple of parents chose lower than "Extremely Important" for perceived importance of follow-up eye exams. After pamphlet exposure, all parents chose "Extremely Important" for importance of follow-up. Conclusion Providing a user-friendly pamphlet on ROP to parents of preterm infants could increase the perceived importance of timely follow-up eye exams, thus reducing the rate of potentially preventable blindness.

This work studies the effects of temperature, voids at or near the interface on the interfacial fracture behavior, and mechanisms of the Si/a-Si3N4 bilayer systems via molecular dynamics simulations. Under mode I loading, at 300 K, the interfacial strength of the bilayer system without voids is ∼22.5 GPa and it undergoes brittle fracture at the interface. However, at 600 K, failure occurs in the a-Si3N4 layer in a ductile mode. With the existence of void in the Si layer, crack initiates at the void and propagates toward the interface when the temperature is 300 K. However, as temperature increases to 600 K, the defected bilayer system undergoes brittle fracture at the interface at a significantly lowered interfacial strength. With the presence of void at the interface, the bilayer system fractures at the interface with a deteriorated strength regardless of temperature. Under mode II loading, the Si/a-Si3N4 system undergoes three deformation processes: elastic deformation, followed by plastic deformation in the a-Si3N4 layer, and subsequently, interfacial sliding. The presence of voids at different locations and the increase in temperature lower the stresses required for interfacial sliding but do not have significant effect on the shear deformation processes. This study provides an insight to fracture behavior of Si/a-Si3N4 system at certain operating conditions.

This present work studies the effects of grain boundaries (GBs), notches and temperature on the mechanical properties of silicon (Si) nanofilms via molecular dynamics simulations. Both ∑25 (7 1 0)〈0 1 0〉 tilt and ∑25(0 0 1)〈0 0 1〉 twist GBs are considered. It is found that the single-crystalline Si nanofilm has relatively low fracture strength of ∼11.6 GPa at room temperature, and fracture occurs through the dislocation sliding mechanism regardless of the existence of notches. At the same temperature, the bi-crystalline Si generally has lower fracture strength than that of the single-crystalline due to the presence of GBs, which changes the crystallographic orientation of the Si nanofilms. Moreover, strength of the bi-crystalline Si depends on the type of the GBs, and it fractures through either the dislocation sliding or cleavage mechanism, depending on the presence of notches. The temperature reduces the fracture strength of the nanofilms but does not change the failure mechanism.

Previous studies have demonstrated that Pseudomonas putida strains are not only capable of growth on a wide range of organic substrates, but also chemotactic towards many of these compounds. However, in most cases the specific chemoreceptors that are involved have not been identified. The complete genome sequences of P. putida strains F1 and KT2440 revealed that each strain is predicted to encode 27 methyl-accepting chemotaxis proteins (MCPs) or MCP-like proteins, 25 of which are shared by both strains. It was expected that orthologous MCPs in closely related strains of the same species would be functionally equivalent. However, deletion of the gene encoding the P. putida F1 orthologue (locus tag Pput_4520, designated mcfS) of McpS, a known receptor for organic acids in P. putida KT2440, did not result in an obvious chemotaxis phenotype. Therefore, we constructed individual markerless MCP gene deletion mutants in P. putida F1 and screened for defective sensory responses to succinate, malate, fumarate and citrate. This screen resulted in the identification of a receptor, McfQ (locus tag Pput_4894), which responds to citrate and fumarate. An additional receptor, McfR (locus tag Pput_0339), which detects succinate, malate and fumarate, was found by individually expressing each of the 18 genes encoding canonical MCPs from strain F1 in a KT2440 mcpS-deletion mutant. Expression of mcfS in the same mcpS deletion mutant demonstrated that, like McfR, McfS responds to succinate, malate, citrate and fumarate. Therefore, at least three receptors, McfR, McfS, and McfQ, work in concert to detect organic acids in P. putida F1.

A new approach for fracture characterization of a particular case study on silicon die crack is presented. It consists of four phases — visual inspection, molecular dynamics, finite element method and experiment. This work aims to use these techniques to investigate and provide a theoretical explanation and analysis of the physical failure modes and mechanisms involved, from the molecular to package level.

Biofilm formation in wounds is a serious problem which inhibits proper wound healing. One possible contributor to biofilm formation in a wound is the bacteria growing within the overlying bandage. To test this mechanism, we used bandages that contained a coating of organo-selenium that was covalently attached to the bandage. We tested the ability of this coating to kill bacteria on the bandage and in the underlying tissue. The bandage material was tested with both lab strains and clinical isolates of Staphylococcus aureus, Pseudomonas aeruginosa and Staphylococcus epidermidis. It was found that the organo-selenium coated bandage showed inhibition, of biofilm formation on the bandage in vitro (7–8 logs), with all the different bacteria tested, at selenium concentrations in the coating of less than 1.0%. These coatings were found to remain stable for over one month in aqueous solution, 15 min in boiling water, and over 6 years at room temperature. The bandages were also tested on a mouse wound model where the bacteria were injected between the bandage and the wound. Not only did the selenium bandage inhibit biofilm formation in the bandage, but it also inhibited biofilm formation in the wound tissue. Since selenium does not leave the bandage, this would appear to support the idea that a major player in wound biofilm formation is bacteria which grows in the overlying bandage.

The prediction of interfacial delamination in multi-layered IC packaging has been a rather complex process as it is challenging to quantify the critical energies of interfacial adhesion experimentally. In this study, a combined approach based on molecular dynamics (MD) and finite element method (FEM) simulations is adopted to characterize and predict delamination in an a-Si3N4/Si bilayer system. The necessary material parameters that are required for the interfacial cohesive constitutive relation in FEM simulation are derived by MD simulation rather than experiment. The work of interfacial fracture obtained by the FEM simulation is about 0.11 J m−2. To validate the presented approach, an experimental nanoindentation test is also conducted to measure the work of interfacial fracture which is obtained to be about 0.085 J m−2. The results obtained by the MD-FEM simulations and the experiment show very good agreement. Therefore, the combined approach can also be applied to investigate other bi-materials or even multi-layered systems, thus facilitating the prediction of interfacial delamination and helping to improve the stability and reliability of the 3D multi-layered IC packaging.