Cliff C. Hayman

Diamond Growth at Low Pressures

Diamond synthesis has attracted attention ever since it was established in 1797 that diamond is a crystalline form of carbon. Initially, synthesis was attempted at high pressures because diamond is the densest carbon phase. As understanding of chemical thermodynamics developed through the 19th and 20th centuries, the pressure-temperature range of diamond stability was explored. These efforts culminated in the announcement in 1955 of a process for diamond synthesis with a molten transition metal solvent-catalyst at pressures where diamond is thermo-dynamically stable. Worldwide sales of synthetic diamond now approach 330 million carats (73 tons) with a market price of between

Low pressure synthesis of bulk, polycrystalline gallium nitride

500 million to

Synthesis of bulk polycrystalline indium nitride at subatmospheric pressures.

1 billion. Over the past 40 years a parallel effort has been directed toward the growth of diamond at low pressures, where it is metastable. Although diamond was successfully produced, low-pressure synthesis was plagued by extremely low growth rates. Recent developments have led to much higher growth rates, creating great interest in the field. Polycrystalline diamond films can now be produced on a variety of substrates at linear growth rates of tens to hundreds of micrometers per hour. In addition, the recognition of an entirely new class of solids, the so-called “diamondlike” carbons and hydrocarbons has arisen from this work. This article will discuss both crystalline diamond grown at low pressure and the diamondlike phases. The interest in diamond is driven by its extreme properties, summarized in Table I. Diamond stands alone as the densest (number density), strongest (elastic modulus), and hardest known material.

Characterization Of Bulk, Polycrystalline Indium Nitride Grown At Sub-Atmospheric Pressures

Thick films of polycrystalline GaN were grown at low pressures by direct reaction of atomic nitrogen with liquid Ga without the presence of a substrate. The crystals were confirmed to be wurtzitic GaN by x-ray diffraction, transmission electron microscopy, Raman spectroscopy, and elemental analysis. Photoluminescence spectra showed near band edge peaks and broad yellow band emission at both 298 and 10 K. The results show that atomic nitrogen is an attractive alternative to high pressure N2 for the saturation of liquid gallium with nitrogen for the synthesis of bulk GaN.

Synthesis of bulk, polycrystalline gallium nitride at low pressures

Polycrystalline, wurtzitic indium nitride was synthesized by saturating indium with nitrogen from microwave plasma sources. The structure was confirmed by x-ray diffraction, electron diffraction, and elemental analysis. Two types of growth were observed: (i) dendritic crystals on the original melt surface, and (ii) hexagonal platelets adjacent to the In metal source on the upper edge of the crucible. The method does not involve a foreign substrate to initiate growth and is a potential alternative to the high-pressure techniques normally associated with bulk growth of indium nitride. The lattice parameters were a = 3.5366 ± 0.0005 A and c = 5.7009 ± 0.0005 A, with c / a = 1.612 ± 0.0005.

Low-Pressure, Metastable Growth of Diamond and "Diamondlike" Phases

Polycrystalline, wurtzitic indium nitride was synthesized by saturating indium metal with atomic nitrogen from a microwave plasma source. Plasma synthesis avoids the high equilibrium pressures required when molecular nitrogen is used as the nitrogen source. Two types of growth were observed: 1) small amounts of indium nitride crystallized from the melt during cooling and 2) hexagonal platelets formed adjacent to the In metal source on the crucible sides. The mechanism of this latter growth is not established, but may involve transport of indium as a liquid film. The crystals were characterized by electron diffraction, X-ray diffraction, elemental analysis, scanning electron microscopy, and Raman spectroscopy. Lattice parameter and Raman active phonon modes are reported and compared with calculations based on the full-potential linear muffin-tin orbital method (FP-LMTO).

Nucleation of diamond crystals

Bulk, polycrystalline gallium nitride was crystallized from gallium saturated with nitrogen obtained from a microwave electron cyclotron resonance source. The polycrystalline samples are wurtzitic and n-type. Well-faceted crystals give near-band-edge and yellow band photoluminescence at both 10 K and 300 K. The results show that atomic nitrogen is an attractive alternative to high pressure molecular nitrogen for saturation of gallium with nitrogen for synthesis of bulk gallium nitride.