Aligned AlN nanowires by self-organized vapor-solid growth

A review on synthesis and applications of gallium oxide materials

Gallium oxide (Ga2O3), as a new kind of ultra-wide band gap semiconductor material, is widely studied in many fields, such as power electronics, UV - blind photodetectors, solar cells and so on. Owing to the advantages of its excellent performance and broad application prospects in semiconductor technology, Ga2O3 materials have attracted extensive academic and technological attention. This review mainly focuses on introducing the main liquid-phase synthesis methods of Ga2O3 nanoparticles, such as direct-precipitation, chemical bath deposition, hydrothermal, solvothermal, and sol-gel method, including the characteristics in process and advantages and disadvantages of these methods. Then, the effects of reaction conditions, such as pH, capping agent, aging and calcination conditions, on the morphologies and sizes of the precursor and the final products were elucidated. Moreover, the applications of Ga2O3 particles in the fields of catalysis, gas sensors, and other devices in current research on Ga2O3 nanomaterials are discussed with the description of the basic working principle and influence factors.

Design and Performance Evaluation of a Deep Ultraviolet LED-Based Ozone Sensor for Semiconductor Industry Applications

Ozone (O3) is a critical gas in various industrial applications, particularly in semiconductor manufacturing, where it is used for wafer cleaning and oxidation processes. Accurate and reliable detection of ozone concentration is essential for process control, ensuring product quality, and safeguarding workplace safety. By studying the UV absorption characteristics of O3 and combining the specific operational needs of semiconductor process gas analysis, a pressure-insensitive ozone gas sensor has been developed. In its optical structure, a straight-through design without corners was adopted, achieving a coupling efficiency of 52% in the gas chamber. This device can operate reliably in a temperature range from 0 °C to 50 °C, with only ±0.3% full-scale error across the entire temperature range. The sensor consists of a deep ultraviolet light-emitting diode in a narrow spectrum centered at 254 nm, a photodetector, and a gas chamber, with dimensions of 85 mm × 25 mm × 35 mm. The performance of the sensor has been meticulously evaluated through simulation and experimental analysis. The sensor's gas detection accuracy is 750 ppb, with a rapid response time (t90) of 7 s, and a limit of detection of 2.26 ppm. It has the potential to be applied in various fields for ozone monitoring, including the semiconductor industry, water treatment facilities, and environmental research.

Crystallography-Derived Young's Modulus and Tensile Strength of AlN Nanowires as Revealed by in Situ Transmission Electron Microscopy

Aluminum nitride (AlN) has a unique combination of properties, such as high chemical and thermal stability, nontoxicity, high melting point, large energy band gap, high thermal conductivity, and intensive light emission. This combination makes AlN nanowires (NWs) a prospective material for optoelectronic and field-emission nanodevices. However, there has been very limited information on mechanical properties of AlN NWs that is essential for their reliable utilization in modern technologies. Herein, we thoroughly study mechanical properties of individual AlN NWs using direct,  in situ bending and tensile tests inside a high-resolution TEM. Overall, 22 individual NWs have been tested, and a strong dependence of their Young's moduli and ultimate tensile strengths (UTS) on their growth axis crystallographic orientation is documented. The Young's modulus of NWs grown along the [101̅1] orientation is found to be in a range 160-260 GPa, whereas for those grown along the [0002] orientation it falls within a range 350-440 GPa. In situ TEM tensile tests demonstrate the UTS values up to 8.2 GPa for the [0002]-oriented NWs, which is more than 20 times larger than that of a bulk AlN compound. Such properties make AlN nanowires a highly promising material for the reinforcing applications in metal matrix and other composites. Finally, experimental results were compared and verified under a density functional theory simulation, which shows the pronounced effect of growth axis on the AlN NW mechanical behavior. The modeling reveals that with an increasing NW width the Young's modulus tends to approach the elastic constants of a bulk material.

Fundamental formulations and recent achievements in piezoelectric nano-structures: a review

Piezoelectric nano-structures have been regarded as the next-generation piezoelectric material due to their inherent nano-sized piezoelectricity. This review summarizes the recent theoretical and experimental findings in piezoelectric nano-structures, including piezoelectric nanowires, nanoplates, nanobeams, nanofilms, nanoparticles, and piezoelectric heterogeneous materials containing piezoelectric nano-inhomogeneities. To begin, the types of piezoelectric nano-structured materials and the wide application of piezoelectric nano-structures in recent years are delineated. Next, the theoretical foundations including the definition of surface stress and electric displacement, the surface constitutive relations, the surface equilibrium equations, and nonlocal piezoelectricity, and their applications, are illustrated. Then, the effective mechanical and piezoelectric properties are depicted. Furthermore, the experimental investigations are classified, and some important observations are discussed. Finally, the perspectives and challenges for the future development of piezoelectric nano-structures are pointed out.

A review of mechanical and electromechanical properties of piezoelectric nanowires

Piezoelectric nanowires are promising building blocks in nanoelectronic, sensing, actuation and nanogenerator systems. In spite of great progress in synthesis methods, quantitative mechanical and electromechanical characterization of these nanostructures is still limited. In this article, the state-of-the art in experimental and computational studies of mechanical and electromechanical properties of piezoelectric nanowires is reviewed with an emphasis on size effects. The review covers existing characterization and analysis methods and summarizes data reported in the literature. It also provides an assessment of research needs and opportunities. Throughout the discussion, the importance of coupling experimental and computational studies is highlighted. This is crucial for obtaining unambiguous size effects of nanowire properties, which truly reflect the effect of scaling rather than a particular synthesis route. We show that such a combined approach is critical to establish synthesis-structure-property relations that will pave the way for optimal usage of piezoelectric nanowires.

Anisotropic optical response of GaN and AlN nanowires

We present a theoretical study of the electronic structure and optical properties of free-standing GaN and AlN nanowires. We have implemented the empirical tight-binding method, with an orbital basis sp(3), that includes the spin-orbit interaction. The passivation of the dangling bonds at the free surfaces is also studied, together with the effects on the electronic structure of the nanowire. For both GaN and AlN nanowires, we have found a remarkable anisotropy of the optical absorption when the light-polarization changes, showing in the case of GaN a dependence on the nanowire size.