Diamond, as one of the hardest natural materials on Earth, has captured the immense interest of scientists and engineers since its discovery. Its exceptional physical properties bestow diamond with remarkable value. Its dazzling luster and high corrosion resistance have made it a symbol of preciousness for thousands of years. Its extreme hardness renders diamond an essential tool in industrial applications like cutting, grinding, and drilling. Furthermore, diamond exhibits outstanding thermal conductivity, making it an ideal choice for high-performance heat dissipation materials. However, the unique crystal structure of diamond is a double-edged sword. While it brings about numerous exceptional physical properties, it also raises the bar for its fabrication and processing. The stable crystal structure makes modifying or doping diamond challenging, greatly limiting its applications in the field of electronics. The smooth and stable interface of diamond also complicates its compatibility with other materials in composite systems. These challenges have long constrained the utilization and development of diamond as a functional material. With the rapid advancement of electronic information technology and quantum science, the development and application of diamond have become increasingly urgent. Its potential as an exceptionally high-performance semiconductor material calls for immediate exploration.

Based on this, we have developed a dual-phase diamond that introduces a second phase dominated by sp² hybridization within the sp3 hybridized diamond crystal. Through this dual-phase design, diamond's inherent properties are preserved while enhancing its conductivity, thermal stability, and various other performance aspects. This expansion of diamond's capabilities broadens its potential industrial applications. Here, we focused on the manufacturing and investigation of dual-phase structures in diamonds of different scales. We conducted an in-depth study on the structure and properties of dual-phase diamond, proposing specific strategies and practices for its applications, all of which yielded promising results.

In Chapter Three, we firstly succeeded in synthesizing micro sized dual-phase diamond (MDPD) through a simple method. We conducted an in-depth analysis of the distribution and formation mechanism of the dual-phase structure. Experimental results demonstrated that MDPD demonstrated a notable electrical conductivity of 1.2 S‧cm^-1 and displayed the characteristics of a negative temperature coefficient semiconductor. Furthermore, in comparison to original diamond, MDPD exhibited an improved thermal stability of over 200 K. Based on these unique features, we employed MDPD as a material for ultra-low temperature sensing. It exhibited the capability to detect temperatures as low as 1 mK while maintaining excellent stability.

In Chapter Four, we further developed nano sized dual-phase diamond (NDPD) building upon MDPD, and applied it as a negative electrode material in aqueous Zn-metal batteries (AZMBs), protecting zinc anodes. The dual-phase structure within NDPD also exhibits an amorphous-crystalline heterostructure. This amorphous-crystalline heterostructure possesses a high Zn²⁺ adsorption capacity, effectively reducing the deposition barrier of Zn²⁺ during charge-discharge processes. Addressing the issue of dendrite growth, which is a primary cause of short-circuit failure in AZMBs, NDPD plays a synergistic role in chemically isolating and mechanically suppressing dendrite growth. Its elevated intrinsic hardness effectively inhibits the formation of dendrites. Furthermore, the hydrophobic nature of NDPD effectively prevents side reactions and accelerates zinc nucleation kinetics by faster desolvation of hydrated zinc ions. Utilizing these attributes, Zn@NDPD symmetric cells demonstrate a remarkably prolonged operational duration exceeding 3200 hours under a current density of 5 mA‧cm^-2. These cells display low nucleation and growth overpotentials, high CE, and an outstanding cumulative deposition capacity of 8000 mAh‧cm^-2.

In Chapter Five, we successfully fabricated larger-sized (5×5 mm²) bulk dual-phase diamond (BDPD), presenting a more challenging task, and distinguished it from conventional graphitized diamond both in macroscopic morphology and structure. The hardness of BDPD remains comparable to that of original diamond and remains unaffected by heat treatment. Additionally, BDPD demonstrates respectable conductivity, exceeding 0.5 mS·cm^-1. The conductivity of BDPD increases with prolonged heat treatment time, reaching its peak after 50 hours. Through Hall effect characterization, we observed that BDPD is a temperature-sensitive semiconductor with variable carrier types. This phenomenon is referred to as temperature-induced Lifshitz transition. Above 250 K, it behaves as a P-type semiconductor, while below 250 K, it behaves as an N-type semiconductor.