Nowadays, video surveillance and motion detection system are widely used in various environments. With the relatively low-price cameras and highly automated monitoring system, video and image analysis on road, highway and skies becomes realistic. The key process in the analysis is to separate the useful information such as moving foreground objects from the original video sequence where Robust Principal Component Analysis (RPCA) plays an important role in extracting the foreground objects. RPCA have been widely used in data analysis and dimension reduction with applications in image recovery, information clustering and computer vision. But one drawback of RPCA lies in the fact that it does not guarantee the nonnegativity of pixels. It is important to have nonnegative foreground object since negative pixels that are not in the range between 0 and 255 are meaningless and the foreground objects are thus not visible. State-of-the-art methods do not consider the nonnegativity of the foreground object in their algorithms. This thesis focuses on the problem of extracting foreground moving object from background scenes and guarantee the nonnegativity of foreground object. This thesis proposes a method that combines RPCA and Nonnegative Matrix Factorization (NMF). It ensures the pixels that constitute the foreground object is nonnegative by using the basic model of RPCA and nonnegative components that NMF provides. The efficacy of the proposed algorithms is tested on publicly available dataset. Experiment shows in detail how the proposed algorithms achieve in recovering the foreground object with high true positive rate. Together with RPCA algorithm, the performance of recovery is compared and their advantages and disadvantages are discussed. ... Read more

It is demonstrated that moderate oxygen vacancies can greatly improve the photo-responsive performance of Zinc oxide (ZnO) nanoparticles thin film/p-Si heterojunctions. The ZnO nanoparticles thin film/p-Si heterojunctions shows a stable, repeatable photo response at 365 nm or 900 nm. Under 900 nm of 0.1 mWcm ⁻² the sensitivity of device reaches an excellent value of 1.2 × 10 ⁶ cm ² /W, with outstanding detectivity of 3.6 × 10 ¹² cmHz ^1/2 W ⁻¹ and ultrahigh responsivity of 3.5 AW ^-1 at −2 V, and a fast response speed with rising time (∼ms). The comprehensive properties of present device are significantly better than those reported ZnO thick film/Si heterojunctions and even compared with that of some new 2D nanomaterials/Si heterojunctions in all aspects of performance, achieving an optimal balance among all the critical features. The excellent performance of ZnO nanoparticles thin film/p-Si heterojunctions may be attributed to rising Fermi level of ZnO nanoparticles thin film due to moderate oxygen vacancies, the excellent optical absorption characteristics of ZnO nanoparticles thin film and the interface effect between ZnO nanoparticles thin film and Si. This high-performance heterojunctions photodetector should have important prospects for practical applications, and the integration of such metal oxide nanostructures with traditional Si semiconductor would open up great opportunities for next-generation optoelectronic devices. ... Read more

It is demonstrated that hydrogen treatment as a simple, effective strategy can greatly improve the broadband photo-responsive performance of pristine TiO2 nanorod arrays (NRAs)/SiO2/n-Si heterojunctions. The hydrogen-treated TiO2 NRAs/SiO2/n-Si heterojunction shows a stable, repeatable and broadband photo response from 365 nm to 980 nm at 100 μW cm-2. The responsivity (R) of H:TiO2 NRAs/SiO2/n-Si approaches the ultrahigh value of 468 A W-1 and it has an outstanding detectivity (D∗) of 1.96 × 1014 cm Hz1/2 W-1 and an excellent sensitivity (S) of 2.63 × 107 cm2 W-1, in contrast to the values of R (10-6-10-1 A W-1) or S (2 × 103 cm2 W-1) from reported TiO2 nanofilm/TiO2 NRAs/n-Si(111) photodetectors, indicating a huge responsivity enhancement of up to 4-8 orders of magnitude. Additionally, the response and recovery time are extremely short (3.5-3.9 ms). The comprehensive characteristics make the device stand out among the previously reported 1D metal oxide nanostructure/Si based photodetectors. In fact, the R, S and D∗ values of the heterojunction are 2-4 orders of magnitude higher than those of some new 2D nanomaterials/Si based photodetectors. The excellent photo-responsive performance may be attributed to the energy band structure of the TiO2@TiO2-xHx core/shell structure, the interface effect of the TiO2@TiO2-xHx/Si heterojunction, etc. This research provides a new concept for the design of other metal oxide based heterojunction photodetectors. ... Read more