Research Index / Materials Science / PLD for c-BN

Pulsed-laser deposition (PLD) uses laser pulses to ablate material from a target and deposit it onto a substrate. PLD has a number of advantages over conventional thin-film deposition techniques. Using ultrafast laser pulses adds some more control to the deposition process which is particularly useful for the deposition of the cubic crystal phase of boron nitride.

General PLD		Ultrafast PLD
Operationally simple High-purity films Clean, Fast Thickness control Good method for cBN		Energy into plume: high-energy ion bombardment Reactive chemistry: energetic ions, ionized nitrogen, high charge states Precisely reproducible plumes: due to avalanche breakdown of dielectric targets

Hofsäss, et al, "Threshold for the Phase Formation of Cubic Boron Nitride Thin Films", Phys. Rev. B, 55 13230 (1997)

Experimentally, researchers have found that at least two parameters are important for the formation of the cubic phase of boron nitride (BN). These are substrate temperature and energy of the depositing ions. The crystal phase of thin films grown by sputtering and aided by a technique known as mass-separated ion beam deposition (MSIBD) is shown at the right (from Hofsäss, et al. - see reference below graph). Using MSIBD, a boron nitride target is sputtered in the presence of a nitrogen ion beam and deposited on a substrate (typically silicon). The nitrogen ion beam is used for two reasons: 1) to compensate for a deficiency of nitrogen ions due to the formation of nitrogen gas, and 2) to assist the formation of cubic-BN with high-energy ions. Depending on the substrate temperature and nitrogen ion beam energy, the thin film crystal phase is unordered or amorphous (a-BN), hexagonal (h-BN), or cubic (c-BN). To form cubic-BN, the substrate temperature must be greater than 150-200 degrees Celsius, and the nitrogen ion beam energy must be greater than 100 electron volts (eV). (An electron volt is the energy an electron receives from being accelerated across 1 volt. Gas molecules vibrating at room temperature have an average energy of about 0.026 electron volts. The common unit of energy, a Joule, is much too large for particle physics: 1 Joule ~ 10¹⁹ eV)

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