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ZnO-based nanostructures by PLD: growth mechanism, doping and geometry
The present work covers investigation of the growth mechanism and growth
kinetics of the ZnO nanowires and nanoneedles fabricated by using high-pressure
pulsed laser deposition. The growth model based on the combination of four different flows of the interfacial particles is introduced. A variation of the free energy is given as a major reason of the change of the growth mechanism which appears by using different doped seed layers, growth temperature and the doping of the deposited material. A fabrication of the ultrathin nanowires with a diameter of d < 10 nm at CMOS compatible growth temperature of T = 400°C is demonstrated.
The diameter of these nanowires is comparable with the Bohr radius.
The growth of the Al and Ga doped and undoped ZnO nanoneedles with a sharp
tip was shown. The doping of the nanowires and nanoneedles can be promising
for their applications. By using a patterned sapphire substrate, an unidirectional
growth of the nanowires and nanoneedles was achieved. These nanostructures
are tilted by 58°ZnO with respect to the surface normal.:Bibliographic Record
Contents
1 Introduction
I Basics and Methods
2 Basic properties and growth concept
2.1 ZnO nanowires and nanoneedles
2.1.1 Applications
2.2 Nanowire and nanoneedle fabrication
2.2.1 Growth mechanisms which require a catalyst
2.2.2 Catalyst-free epitaxial growth mechanism
2.3 Free energy and the growth mechanism
2.4 NW growth techniques
2.5 Aligned tilted growth
3 Growth and characterization
3.1 Preparation of the seed layers by CVD
3.2 Preparation of the seed layers by low pressure PLD
3.3 HP PLD for the NW and NN growth
3.4 Characterization techniques
3.4.1 X-ray Diffraction
3.4.2 Atomic Force Microscopy
3.4.3 Scanning electron microscopy
3.4.4 Energy Dispersive X-ray Spectroscopy
3.4.5 Spectroscopic Ellipsometry
3.4.6 Cathodoluminescence
3.4.7 Angle-varied X-ray photoelectron spectroscopy
3.4.8 Etching of the seed layers
4 Seed layer characterization
4.1 Doping concentration
4.2 Surface morphology
4.3 Crystalline quality
4.4 Surface polarity
4.5 Summary of the Chapter
II NW growth: results
5 NW growth characteristics
5.1 Material free energy and the deposited material parameters
5.2 Growth kinetics
5.3 Summary of the Chapter
6 NW growth on doped seed layers
6.1 Al doped seed layers
6.2 NW growth on Ga doped seed layers
6.3 Optical characteristics of the ZnO NWs
6.4 Summary of the Chapter
7 Growth of ZnO(Al) and ZnO(Ga) NWs
7.1 Al-doped ZnO NWs grown on ZnO(Al) seed layers
7.2 Ga-doped ZnO NWs grown on ZnO(Ga) seed layers
7.3 Summary of the Chapter
8 Growth of tilted ZnO NWs and NNs
8.1 Patterning of the substrates .
8.2 Growth of tilted NNs
8.3 Growth of tilted NWs
8.4 Optical properties of the tilted nanostructures
8.5 Summary of the Chapter
9 Summary and outloock
9.1 Summary
9.2 Outlook
Acknowledgements
Curriculum Vitae
List of own Articles
List of own Conference Talks and Posters
Reference
Electronic, magnetic and optical properties of oxide surfaces, heterostructures and interfaces: role of defects
Ph.DDOCTOR OF PHILOSOPH
Pulsed Laser Deposition of Transition Metal Dichalcogenides-Based Heterostructures for Efficient Photodetection
From the past few decades, photodetectors (PDs) are being regarded as crucial components of many photonic devices which are being used in various important applications. However, the PDs based on the traditional bulk semiconductors still face a lot of challenges as far as the device performance is concerned. To overcome these limitations, a novel class of two-dimensional materials known as transition metal dichalcogenides (TMDCs) has shown great promise. The TMDCs-based PDs have been reported to exhibit competitive figures of merit to the state-of-the-art PDs, however, their production is still limited to laboratory scale due to limitations in the conventional fabrication methods. Compared to these traditional synthesis approaches, the technique of pulsed laser deposition (PLD) offers several merits. PLD is a physical vapor deposition approach, which is performed in an ultrahigh-vacuum environment. Therefore, the products are expected to be clean and free from contaminants. Most importantly, PLD enables actualization of large-area thin films, which can have a significant potential in the modern semiconductor industry. In the current chapter, the growth of TMDCs by PLD for applications in photodetection has been discussed, with a detailed analysis on the recent advancements in this area. The chapter will be concluded by providing an outlook and perspective on the strategies to overcome the shortcomings associated with the current devices
Progress in pulsed laser deposited two-dimensional layered materials for device applications
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2D semiconductor nanomaterials and heterostructures : controlled synthesis and functional applications
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