| Self-assembly crystalline silicon nanowires(c-SiNWs),with unique geometric and photoelectric characteristics,are becoming the very fundamental and promising building blocks to develop a new generation of large area thin film electronics,such as thin film transistors,sensors,memory and logic devices.However,one of the major technical hundles to their large scale device applications is the huge challenge in handling,positioning and integrating these tiny c-SiNWs into precise locations,as required for batch-manufacturing of electronics based on the self-assembly SiNWs.On the other hand,the emerging of soft electronics,such as wearable or portable bio and chemical sensors and smart communications demands flexibility or stretchability that are hard to meet for bulk crystalline silicon(c-Si),which is known to be rigjd and brittle.Even in the form of quasi-one-dimensional c-SiNWs,c-Si can only become bendable but still hardly stretchable.Therefore,new geometry control strategies are urgently needed to shape the c-SiNWs into elastic forms of springs or fractal 2D patterns,so as to extend the legend of modern Si technology to enable high performance stretchable electronic applications.This thesis work is based on a new in-plane solid-liquid-solid(IPSLS)growth mechanism,which is mediated by low-melting metal catalyst droplets of indium or tin that absorb hydrogenated amorphous silicon(a-S:H)matrix and produce in-plane c-SiNWs behind.Compared to the well-known vapor-liquid-solid(VLS)growth mechanism,this in-plane growth mode has a unique strong growth interface interaction and a rich set of growth kinetics that can be explored to engineer the geometry of SiNWs.This thesis first focuses on the growth dynamics and control principles of the IPSLS SiNWs,to demonstrate a self-automated growth of diameter-modulated island-chain SiNWs and self-turning zigzag SiNW springs;Then,a large area assembly of self-positioned SiNW array is achieved and exploited to fabricate high performance thin-film transistors(TFTs);Finally,we will stage a programmable line-shape design and batch-manufacturing of in-plane c-SiNW springs that can be easily stretched to>270%with yet stable electric conductance.These results pave a way for exploring c-Si based high performance flexible/stretchable electronics.Specifically,this thesis will consist of the following 4 sectors:1)In-plane self-assembly growth and geometry engineering of a new island-chain SiNWs via a liquid droplet mediated Plateau-Rayleigh transformation,which has been accomplished via low temperature(<350 ?)thin film deposition and can be easily guided into precise locations and directions.This new strategy provides a powerful new technique to modulate the transport of electron,photon,and phonon in the quasi-1D SiNW channels.2)A novel cyclic turning-twining growth mechanism of stretchable mono-like zigzag SiNWs.Direct in situ SEM observation of the SiNW growth and HR-TEM characterization reveal a rich set of growth dynamics,which feature a series of regular growth direction turning and twinning behavior.A growth kinetics model is proposed to explain the regular turning-twin dynamics as a result of seeking a growth balance that requires a periodic orientation switching among major crystallographic Si orientations.Indeed,a largely enhanced elastic "stress-strain" response of the high quality zigzag SiNW channels is witnessed,with a stretchability of 12%under tensile strain.3)A new strategy to achieve batch-manufacturing of large area in-plane SiNW array,and to fabricate high performance fin-TFTs with a high hole mobility of>100 cm2 V-1 s-1 and an excellent subthreshold swing of 163 mV dec-1.More excitingly,the precise arrangement of the poly-SiNW channels,along with the selective etching of the remnant a-Si:H thin film,makes them transparent to visible light and thus ideal for implementing the transparent TFT circuitry.These results could promise a new technology of large area high-performance poly-Si TFTs,and has a great application in replacing the traditional a-Si technology in the field of the large area flat panel display.4)A deterministic and programmable line-shape engineering of ultra-long SiNWs,produced by a reliable indium droplet mediated in-plane solid-liquid-solid growth mechanism.This unique capability has been explored to batch-manufacture an orderly array of highly stretchable SiNW springs and arbitrary singly connected 2D patterns.HR-TEM analysis reveals a mono-like high crystalline quality in the SiNW spring over continuous turning tracks,thanks to a gentle nanocrystal-pulling growth from the running catalyst droplet.Strikingly,the SiNW springs are found to be extremely stretchable>270%and elastic,while carrying a robust electric current,as testified by in situ SEM probe manipulation and I-V testing.This programmable line-shape-engineering strategy holds a great promise could eventually extend the legend of modern Si technology into the emerging stretchable electronic applications,and develop a new generation of stretchable devices with high mobility and stability. |
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