Effect of temperature on metastable phases induced in silicon during nanoindentation
- PDF / 334,872 Bytes
- 5 Pages / 585 x 783 pts Page_size
- 92 Downloads / 187 Views
Indentations were performed on silicon using a Berkovich indenter at loads up to 12 mN, at temperatures from 20 to 135 °C. Transmission electron microscopy revealed crystalline silicon phases in the residual indentation imprint at and above 35 °C. Also, the first reconfirmation of the occurrence of Si-VIII during unloading was observed at temperatures of 100 and 125 °C. Interestingly, at 125 °C a cavity was also observed, and an unidentifiable phase was observed at 135 °C. The observations show the strong effect of temperature on pressure-induced phase transformation in silicon.
I. INTRODUCTION
Pressure-induced phase transformation of silicon is well known, and numerous studies have been undertaken in the past decade.1–12 High-pressure diamond anvil cell (DAC) and indentation experiments have shown that the cubic diamond structure of silicon (Si-I) undergoes an irreversible phase transformation to a metallic -Sn (Si-II) phase at a pressure of ∼11–12 GPa using both spherical and Berkovich indenters.1,2 This phase is unstable below 2 GPa and undergoes further transformation to crystalline SI-III and Si-XII phases or amorphous silicon (a-Si), depending on the maximum load applied and the unloading rate.3,4 Most of the above observations have been performed at higher loads (>20 mN) and at room temperature. A recent study of the thermal stability of residual indentation imprints has reported that the transformation of crystalline phases to other phases starts at or above 170 °C.5 Studies of high-temperature indentation on silicon at elevated temperatures (150–250 °C) and at higher loads (>20 mN) have suggested the formation of a new phase, Si-XIII.4 The aim of this article was to elucidate the effects of moderate temperature (25–135 °C) on the phase transformations induced in silicon during low-load nanoindentation. II. EXPERIMENTAL PROCEDURES
An array of multiple nanoindentations was performed on the silicon (100) [cleaved from a Czochralski-grown Si (100)] with a spacing of at least 50 m using a Triboa)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0023 J. Mater. Res., Vol. 23, No. 1, Jan 2008
http://journals.cambridge.org
Downloaded: 14 Mar 2015
Indenter (Hysitron, Inc., Minneapolis, MN) fitted with an in situ heating facility. This uses a Peltier cell to heat the sample stage from −20 to 150 °C without using ohmic resistance heating. Twenty indentations were performed at each of three loads (12, 10, and 8 mN) with a Berkovich indenter having a tip radius of 100 nm at room temperature (∼20 °C), 35, 50, 75, 100, 125, and 135 °C. The sample was heated at a rate of ∼8 °C/min and was subsequently cooled down to room temperature after the experiment. Before the start of the experiment, a 15-min delay was given to equilibrate the sample at test temperature, while keeping the unloaded indenter tip in contact with the sample surface. A typical time for an entire experiment was about 3 h for 10 indents at each of the three loads. A loading rate as slow at 200 N/s wa
Data Loading...
