Home Page | CollectionWelcome to TKD CO., LTD

TKD CO., LTD

Home > News > Technical Knowledge > Polycrystalline Diamond Characterisations for High End Technologies (4)

News

Company News
EDM Cuttable Polycrystall…
Polycrystalline Diamond P…
Polycrystalline Diamond (…
TKD CO., LTD attend shang…
Industry News
It is estimated that the …
The era of "one forev…
The world's four diam…
PCD grinding characterist…
Super hard materials ente…
Technical Knowledge
Polycrystalline diamond s…
Polycrystalline Diamond (…
Comparison of advantages …
Basic knowledge of woodwo…
Knowledge of polycrystall…
Polycrystalline Diamond C…
Polycrystalline Diamond C…
Polycrystalline Diamond C…
Polycrystalline Diamond C…
PCD Cutting Tool Blanks

Polycrystalline Diamond Characterisations for High End Technologies (4)

2022/1/11 16:06:32 TKD CO., LTD Reading 0 Times

(a) DND-DMSO seeding suspension particle size distribution; (b) cross-sectional SEM image of freestanding PCD; and (c) corresponding XRD signals from as-grown and nucleation side (NS).

The as-grown surfaces of the PCD coatings are very rough in nature which is labelled in Figure 1b. Cross-sectional microscopy image reveals columnar growth of diamond crystals from the substrate side. The interface between the Si wafer and diamond columns consists of a very thin layer of diamond micro-crystals which were initially coalesced with each other to form a continuous coating before diamond could grow vertically on top of them. Such thin crust layer on the nucleation side gives very poor XRD signals (top of Figure 1c) corresponding to diamond reflection planes, whereas, the peak intensities from the opposite as-grown surface (bottom one of Figure 1c) is very strong and characteristics of diamond cubic crystals. DND seeds initially formed islands which grow in a single layer until touching upon each other to form a continuous film. The diamond columns also do not grow exactly at 90° in the z direction. The adatoms from the plasma may add in a random way to produce some misorientation between the adjacent diamond columns. Moreover the top surface of diamond PCDs are very rough and sometimes appear porous. Such, (i) random coalescence of thin crust layer on the nucleation side, (ii) misorientation in between diamond columns and (iii) uneven as-grown surface of the diamond films, suggest that the CVD grown diamond may have some pores present in the freestanding coating. It is also true that in practice we assume that the CVD grown films are having 100% theoretical density but it is understood that that is not actually the case. So in order to know the pores that might present, BET surface area was calculated for the PCDs. Gas molecules are dosed into the sample chamber after cooling the solid down to a constant temperature in order to partially accumulate the gas molecules onto the solid surface which can be applied for the characterisation of surfaces as well as for the pore characterisation. The nitrogen adsorption at the temperature of liquid nitrogen (77 K) is standard method for such surface characterisation . It is assumed that the nitrogen condenses onto the surface in a monolayer and so once the size of the gas atoms/molecules are known, the surface area can be estimated from the amount of adsorbed gas.

 

It was found that white PCD is having less surface area compare to the black PCD (Table 1). Nitrogen adsorption and desorption isotherms measured at 77 K allow the determination of pore volume and sizes. It was similarly observed that both the values are higher for black colour PCD. So it is inferred that black PCDs are having more CVD growth defects which is giving bigger pores and higher amount of porosity—i.e. addition of carbon atoms into the diamond sp3 lattice is more incoherent.

2.png


Table 1.

Freestanding PCD surface area and pore analysis.

 

PCDs grown using 3% CH4 in H2 resulted in black colour (Figure 2a), whereas, the coatings were white translucent in nature when 1% CH4 was used. Colour of the freestanding diamond coatings vary due to the presence of defects inside the diamond lattice. For example when boron or nitrogen is substituting the carbon atoms, it results in blue or yellow colour of the diamond crystals. The PCD could become completely opaque or black in colour due to the presence growth defects like dislocations, twining, grain boundaries, stacking faults etc. On the other hand when 1% CH4 was used to deposit diamond, the crystals were less defective and could synthesise white transparent freestanding coatings as shown in Figure 2.


3.png

(a) Black grade PCDs, (b) white grade PCD, (c) bright-field TEM image of a black PCD grain with some dislocations pinned at the grain boundary. (d) Corresponding wide beam dark field (WBDF) image showing clearly discernible dislocations. Inset shows the two-beam condition used for imaging the dislocations, (e) bright-field TEM image of defect free White PCD grain with some twins and grain—boundaries.



Pre: Polycrystalline Diamond Characterisations for High End Technologies (3)…
2010-2022 all right reserved © TKD CO., LTD Home | About US | Contact | Facebook | Face Book | SiteMap | 豫ICP备18018494号