# Presentation: 334327

## Actual Crack Size and Shape of Electro-deposited Chromium Layers

- 2007. 10. 26
- Y. Choi* and Y. S. Hahn
- *Sunmoon University, Korea
- Korea Atomic Energy Research Institute

## Backgrounds

**Microstructure of coating layers such as chromium deposit for automobile industry and copper thin film for electronic industry is very important because it significantly influences its performance. Sometimes, we need dense or porous structure for various applications. **
**Cracks are inevitably formed during electroplating because hydrogen evolution on cathode surface and abnormal growth of columnar grains. **
**Hence, quantitative analysis of crack size and distribution is so important, however, it is difficult to find a consistency in previous research data.**

## Previous Cracks Observation 

**Fig. 1 Trivalent chromium layers observed by (L) optical microscopy and (M) scanning electron microscopy (R) transmission electron microscopy and corresponding selected area diffraction pattern.**
** ****It is difficult to observe any real size of inner cracks by using destructive sample preparation methods. So we should use non-destructive observation methods.**

**Previous Cracks Observation **

## Objective

**Find a reliable observation method to collect quantitative data of the crack size and distribution of thin films.**

## Why small angle neutron scattering ?

**Neutrons reveal structure and dynamics because neutron show where atoms are and what atoms do.**
**Neutrons ****see more than X-rays because X-rays are scattered by electron whereas, neutron by atomic nuclei.**
**Neutrons reveal inner stress because neutron diffraction can show how much the distance between the atoms has changed.**
**Neutron shows what atoms remember of their earlier position when they are move randomly  in relation to each other in liquid and melt.**

** ****ref : Shull and Brockhouse got Nobel Prize in physics 1994  for their  pioneering contributions to the development of neutron scattering techniques for studies of condensed matter.**

## 1. Crack Size and Distribution by SANS

** ****SANS shows that most of inner crack are about 40 nm in size.    **
**    ****: recall Bragg’s law, d=2********/Q**

## Actual Crack Morphology

## Slide 8

## Slide 9

## Slide 10

## Micro-size Cracks 

** ****: Micro-size cracks seem to be “calabash” shape defects**

## 3. How to evaluate “Calabash Shape” crack ?

**Porod  Law : applicable for the relatively large crack size **

**Scattering intensity expressed by following equation.**
** **
**where K****p**** is expressed by scattering length density (********) and specific surface area (Sv).**
**Defect size can be estimated by using that specific surface area is equal to 3/R with the assumption of spherical shape.**

## 7. Defect Analysis by SANS

**Fig. 4. Calabash crack size of eco-friendly trivalent chromium layers with poor NSF life  : average size of crack are 4.9 ********m for D.C plating, 3.3-7.9 ********m for the pulse plating**** **

## Summary

**Most of nano-size crack of trivalent chromium layer has about 40 nm in size, whereas, micro-size cracks are 4.9 ********m for direct current plating, 3.3-7.9 ********m for various pulse plating conditions. The crack size was decreased with decreasing plating current density and voltage.**
**The micro-size crack seems to be “Calabash shape” which is formed by the interconnection of several nano-size cracks.**
**Small angle neutron scattering (SANS) is one of useful methods for evaluating of cracks in eco-friendly trivalent chromium layer and other thin films.**** **

## Slide 15