## 4 Diamond-Based 1D Metal Oxide Heterojunction Classes
### 1 D N-TiO\({}_{2}\)/p-Diamond Related Optoelectronic Devices  
1D TiO\({}_{2}\) nanostructures with a wide bandgap (3.2 eV) and a large surface area [88] were selected as a promising material for application in electronics [89; 90; 91]. Common functional TiO\({}_{2}\) nanomaterials have attracted widespread attention due to superior perfor \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Heterojunction Morphology** & **Synthesis Route** & **Applications (Properties)** & **Ref.** \\ \hline ZnO film/diamond & Magnetron sputtering & Surface acoustic wave & [65] \\ ZnO film/diamond & Magnetron sputtering & Films’ quality & [66] \\ ZnO film/diamond & MOCVD & Electrical properties & [67] \\ ZnO film/diamond & Atomic Layer Chemical Vapour Deposition & Electrical properties & [72] \\ ZnO film/diamond & Magnetron Sputtering & Heterojunction diode & [68] \\ ZnO NRs/diamond & Low-temperature solution & Tyrosine biosensor & [69] \\ ZnO NRs/diamond & Hydrothermal method & Photocatalytic activities & [33] \\ ZnO NRs/diamond & Hydrothermal method & Photocatalytic activities & [81] \\ ZnO NRs/diamond & Low-temperature solution & Electrical properties & [82] \\ ZnO NRs/diamond & Hydrothermal method & Photoelectric anodes & [83] \\ ZnO NRs/diamond & Hydrothermal method & UV photodetector & [84] \\ ZnO NRs/diamond & Sol-gel method & Hydrogen gas sensors & [85] \\ ZnO NRs/diamond & Hydrothermal method & UV detection and field emission & [86] \\ ZnO NWs/diamond & Hydrothermal method & Electrical transport properties & [30] \\ ZnO NRs/diamond & Thermal evaporation method & NDR properties & [31] \\ ZnO NRs/diamond & Thermal evaporation method & UV photoelectrical properties & [22] \\ ZnO NRs/diamond & Thermal evaporation method & Electrical transport behavior & [24] \\ ZnO NRs/diamond & Thermal evaporation method & NDR properties & [23] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Heterojunction applications and properties of 1D n-ZnO/p-diamond. Figure 16: (**a**) _I-V_ plots of the n-ZnO NR/p-BDD heterojunction fabricated with p-degenerated-diamond, displaying the NDR phenomenon. The inset shows a thermal equilibrium energy band diagram heterojunction. (**b**) The _I-V_ curve of the n-ZnO NRs/p-degenerated diamond at 20–120 \({}^{\circ}\)C. The inset presents a linear relationship of _I-V_ plots for ohmic contacts of Ag/p-degenerated diamond and Ag/ITO [23; 31]. mance derived from their inherent 1D architecture [92; 93; 94]. 1D nanostructures offer more possibilities for better optical and electrical properties, such as faster carrier generation, better charge separation, and longer charge carrier life [95; 96; 97]. TiO\({}_{2}\) is an intrinsic n-type semiconductor and may form a p-n heterojunction combined with the p-type semiconductor [98; 99; 100; 101; 102]. N-type TiO\({}_{2}\) and p-type BDD have excellent and unique properties, which make them ideal semiconductors for forming heterojunction structures. In their previous study, [PERSON] et al. [103] deposited 1D TiO\({}_{2}\) NRs with different morphology grown on BDD film with ZnO layer using the hydrothermal method. TiO\({}_{2}\) NRs/ZnO/BDD heterojunction may enhance the photocatalytic activity of TiO\({}_{2}\) NRs/ZnO and TiO\({}_{2}\) NRs/BDD heterojunctions, respectively. In addition, TiO\({}_{2}\) NTs arrays were fabricated on the p-type BDD substrate by means of liquid phase deposition using ZnO NRs template. Compared with the case of a single TiO\({}_{2}\) NTs, n-TiO\({}_{2}\) NTs/p-diamond heterostructure shows significantly enhanced photocatalytic activity and good recyclability (Figure 17) [38; 39]. Afterward, TiO\({}_{2}\) NTs were deposited by the same method on hemispherical CVD diamond films. The degradation of reactive yellow 15 (RY15) solution showed that the product exhibits high photocatalytic performance (Figure 18) [104].