Quantitative Fracture Strength and Plasticity Measurements of Lithiated Silicon Nanowires by <i>In Situ</i> TEM Tensile Experiments

We report <i>in situ</i> tensile strength measurement of fully lithiated Si (Li–Si alloy) nanowires inside a transmission electron microscope. A specially designed dual probe with an atomic force microscopy cantilever and a scanning tunneling microscopy electrode was used to conduct lithiation of Si nanowires and then perform <i>in situ</i> tension of the lithiated nanowires. The axial tensile strength decreased from the initial value of 3.6 GPa for the pristine unlithiated Si nanowires to 0.72 GPa for the lithiated Li–Si alloy. We observed large fracture strain ranging from 8% to 16% for Li–Si alloy, 70% of which remained permanent after fracture. This indicates a certain degree of tensile plasticity in the lithiated silicon before fracture, important for constitutive modeling of the lithium-ion battery cyclability. We also compare the <i>ab initio</i> computed ideal strengths with our measured strengths and attribute the differences to the morphology and flaws in the lithiated nanowires

Quantitative Fracture Strength and Plasticity Measurements of Lithiated Silicon Nanowires by <i>In Situ</i> TEM Tensile Experiments

We report <i>in situ</i> tensile strength measurement of fully lithiated Si (Li–Si alloy) nanowires inside a transmission electron microscope. A specially designed dual probe with an atomic force microscopy cantilever and a scanning tunneling microscopy electrode was used to conduct lithiation of Si nanowires and then perform <i>in situ</i> tension of the lithiated nanowires. The axial tensile strength decreased from the initial value of 3.6 GPa for the pristine unlithiated Si nanowires to 0.72 GPa for the lithiated Li–Si alloy. We observed large fracture strain ranging from 8% to 16% for Li–Si alloy, 70% of which remained permanent after fracture. This indicates a certain degree of tensile plasticity in the lithiated silicon before fracture, important for constitutive modeling of the lithium-ion battery cyclability. We also compare the <i>ab initio</i> computed ideal strengths with our measured strengths and attribute the differences to the morphology and flaws in the lithiated nanowires

Quantitative Fracture Strength and Plasticity Measurements of Lithiated Silicon Nanowires by <i>In Situ</i> TEM Tensile Experiments

We report <i>in situ</i> tensile strength measurement of fully lithiated Si (Li–Si alloy) nanowires inside a transmission electron microscope. A specially designed dual probe with an atomic force microscopy cantilever and a scanning tunneling microscopy electrode was used to conduct lithiation of Si nanowires and then perform <i>in situ</i> tension of the lithiated nanowires. The axial tensile strength decreased from the initial value of 3.6 GPa for the pristine unlithiated Si nanowires to 0.72 GPa for the lithiated Li–Si alloy. We observed large fracture strain ranging from 8% to 16% for Li–Si alloy, 70% of which remained permanent after fracture. This indicates a certain degree of tensile plasticity in the lithiated silicon before fracture, important for constitutive modeling of the lithium-ion battery cyclability. We also compare the <i>ab initio</i> computed ideal strengths with our measured strengths and attribute the differences to the morphology and flaws in the lithiated nanowires

Dynamic Process of Phase Transition from Wurtzite to Zinc Blende Structure in InAs Nanowires

In situ high-resolution transmission electron microscopy revealed the precipitation of the zinc-blende (ZB) structure InAs at the liquid/solid interface or liquid/solid/amorphous carbon triple point at high temperature. Subsequent to its precipitation, detailed analysis demonstrates unique solid to solid wurtzite (WZ) to ZB phase transition through gliding of sharp steps with Shockley partial dislocations. The most intriguing phenomenon was that each step is 6 {111} atomic layers high and the step migrated without any mechanical stress applied. We believe that this is the first direct <i>in situ</i> observation of WZ–ZB transition in semiconductor nanowires. A model was proposed in which three Shockley partial dislocations collectively glide on every two {0001} planes (corresponds to six atomic planes in an unit). The collective glide mechanism does not need any applied shear stress

Microstructural Evolution of Tin Nanoparticles during In Situ Sodium Insertion and Extraction

The microstructural changes and phase transformations of tin nanoparticles during electrochemical sodiation were studied with a nanosized sodium ion battery using in situ transmission electron microscopy. It was found that the first sodiation process occurred in two steps; that is, the crystalline Sn nanoparticles were initially sodiated via a two-phase mechanism with a migrating phase boundary to form a Na-poor, amorphous Na_<i>x</i>Sn alloy (<i>x</i> ∼ 0.5), which was further sodiated to several Na-rich amorphous phases and finally to the crystallized Na₁₅Sn₄ (<i>x</i> = 3.75) via a single-phase mechanism. The volumetric expansion was about 60% in the first step and 420% after the second step. However, despite the huge expansion, cracking or fracture was not observed, which is attributed to the second step of the single-phase sodiation that accommodates large portion of the sodiation-induced stress over the entire particle. Excellent cyclability was also observed during the reversible sodiation/desodiation cycles, showing great potential of Sn nanoparticles as a robust electrode material for rechargeable batteries

Dynamic Process of Phase Transition from Wurtzite to Zinc Blende Structure in InAs Nanowires

In situ high-resolution transmission electron microscopy revealed the precipitation of the zinc-blende (ZB) structure InAs at the liquid/solid interface or liquid/solid/amorphous carbon triple point at high temperature. Subsequent to its precipitation, detailed analysis demonstrates unique solid to solid wurtzite (WZ) to ZB phase transition through gliding of sharp steps with Shockley partial dislocations. The most intriguing phenomenon was that each step is 6 {111} atomic layers high and the step migrated without any mechanical stress applied. We believe that this is the first direct <i>in situ</i> observation of WZ–ZB transition in semiconductor nanowires. A model was proposed in which three Shockley partial dislocations collectively glide on every two {0001} planes (corresponds to six atomic planes in an unit). The collective glide mechanism does not need any applied shear stress

Dynamic Process of Phase Transition from Wurtzite to Zinc Blende Structure in InAs Nanowires

In situ high-resolution transmission electron microscopy revealed the precipitation of the zinc-blende (ZB) structure InAs at the liquid/solid interface or liquid/solid/amorphous carbon triple point at high temperature. Subsequent to its precipitation, detailed analysis demonstrates unique solid to solid wurtzite (WZ) to ZB phase transition through gliding of sharp steps with Shockley partial dislocations. The most intriguing phenomenon was that each step is 6 {111} atomic layers high and the step migrated without any mechanical stress applied. We believe that this is the first direct <i>in situ</i> observation of WZ–ZB transition in semiconductor nanowires. A model was proposed in which three Shockley partial dislocations collectively glide on every two {0001} planes (corresponds to six atomic planes in an unit). The collective glide mechanism does not need any applied shear stress

Dynamic Process of Phase Transition from Wurtzite to Zinc Blende Structure in InAs Nanowires

In situ high-resolution transmission electron microscopy revealed the precipitation of the zinc-blende (ZB) structure InAs at the liquid/solid interface or liquid/solid/amorphous carbon triple point at high temperature. Subsequent to its precipitation, detailed analysis demonstrates unique solid to solid wurtzite (WZ) to ZB phase transition through gliding of sharp steps with Shockley partial dislocations. The most intriguing phenomenon was that each step is 6 {111} atomic layers high and the step migrated without any mechanical stress applied. We believe that this is the first direct <i>in situ</i> observation of WZ–ZB transition in semiconductor nanowires. A model was proposed in which three Shockley partial dislocations collectively glide on every two {0001} planes (corresponds to six atomic planes in an unit). The collective glide mechanism does not need any applied shear stress

Size-Dependent Fracture of Silicon Nanoparticles During Lithiation

Lithiation of individual silicon nanoparticles was studied in real time with <i>in situ</i> transmission electron microscopy. A strong size dependence of fracture was discovered; that is, there exists a critical particle diameter of ∼150 nm, below which the particles neither cracked nor fractured upon first lithiation, and above which the particles initially formed surface cracks and then fractured due to lithiation-induced swelling. The unexpected surface cracking arose owing to the buildup of large tensile hoop stress, which reversed the initial compression, in the surface layer. The stress reversal was attributed to the unique mechanism of lithiation in crystalline Si, taking place by movement of a two-phase boundary between the inner core of pristine Si and the outer shell of amorphous Li–Si alloy. While the resulting hoop tension tended to initiate surface cracks, the small-sized nanoparticles nevertheless averted fracture. This is because the stored strain energy from electrochemical reactions was insufficient to drive crack propagation, as dictated by the interplay between the two length scales, that is, particle diameter and crack size, that control the fracture. These results are diametrically opposite to those obtained previously from single-phase modeling, which predicted only compressive hoop stress in the surface layer and thus crack initiation from the center in lithiated Si particles and wires. Our work provides direct evidence of the mechanical robustness of small Si nanoparticles for applications in lithium ion batteries

Ultrashort Channel Silicon Nanowire Transistors with Nickel Silicide Source/Drain Contacts

We demonstrate the shortest transistor channel length (17 nm) fabricated on a vapor–liquid–solid (VLS) grown silicon nanowire (NW) by a controlled reaction with Ni leads on an in situ transmission electron microscope (TEM) heating stage at a moderate temperature of 400 °C. NiSi₂ is the leading phase, and the silicide–silicon interface is an atomically sharp type-A interface. At such channel lengths, high maximum on-currents of 890 (μA/μm) and a maximum transconductance of 430 (μS/μm) were obtained, which pushes forward the performance of bottom-up Si NW Schottky barrier field-effect transistors (SB-FETs). Through accurate control over the silicidation reaction, we provide a systematic study of channel length dependent carrier transport in a large number of SB-FETs with channel lengths in the range of 17 nm to 3.6 μm. Our device results corroborate with our transport simulations and reveal a characteristic type of short channel effects in SB-FETs, both in on- and off-state, which is different from that in conventional MOSFETs, and that limits transport parameter extraction from SB-FETs using conventional field-effect transconductance measurements