Diamond may be grown at low pressures where it is the metastable form of carbon. Recent advances in a wide variety of plasma and electrical discharge methods have led to dramatic increases in growth rates. All of these methods have certain aspects in common, namely, the presence of atomic hydrogen and the production of energetic carbon-containing fragments under conditions that support high mobilities on the diamond surface. Some understanding of the processes taking place during nucleation and growth of diamond has been achieved, but detailed molecular mechanisms are not yet known. Related research has led to the discovery of a new class of materials, the "diamondlike" phases. Vapor-grown diamond and diamondlike materials may have eventual applications in abrasives, tool coatings, bearing surfaces, electronics, optics, tribological surfaces, and corrosion protection.

https://science.sciencemag.org/content/sci/241/4868/913.full.pdf

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

On etudie le depot chimique en phase vapeur et la croissance cristalline de revetement de diamant

/pdf/diamond-ceramic-coating-of-the-future-31m184yw0t.pdf

Diamond—Ceramic Coating of the Future

Surface science aspects of etching reactions

Diamond cold cathodes have been formed by fabricating mesa-etched diodes using carbon ion implantation into p-type diamond substrates. When these diodes are forward biased, current is emitted into vacuum. The cathode efficiency (emitted current divided by diode current) varies from 2*10/sup -4/ to 1*10/sup -10/ and increases with the addition of 10/sup -2/-torr partial pressure of O/sub 2/ into the vacuum system. Current densities of 0.1 to 1 A-cm/sup -2/ are estimated for a diode current of 10 mA. This compares favorably with Si cold cathodes (not coated with Cs), which have efficiencies of approximately 2*10/sup -5/ and current densities of approximately 2*10/sup -2/ A-cm/sup -2/. It is believed that higher current densities and efficiencies can be obtained with more efficient cathode designs and an ultrahigh-vacuum environment. >

Diamond cold cathode

An electron-emission mechanism for cold cathodes is described based on the enhancement of electric fields at metal–diamond–vacuum triple junctions. Unlike conventional mechanisms, in which electrons tunnel from a metal or semiconductor directly into vacuum, the electrons here tunnel from a metal into diamond surface states, where they are accelerated to energies sufficient to be ejected into vacuum. Diamond cathodes designed to optimize this mechanism exhibit some of the lowest operational voltages achieved so far.

A new surface electron-emission mechanism in diamond cathodes

The high thermal conductivity, low rf loss, and inertness of diamond make it useful in traveling wave tubes operating in excess of 500 GHz. Such use requires the controlled etching of type IIA diamond to produce grating like structures tens of micrometers deep. Previous work on reactive ion etching with O2 gave etching rates on the order of 20 nm/min and poor etch selectivity between the masking material (Ni or Cr) and the diamond. We report on an alternative approach which uses a Xe+ beam and a reactive gas flux of NO2 in an ion‐beam‐assisted etching system. An etching rate of 200 nm/min was obtained with an etching rate ratio of 20 between the diamond and an aluminum mask.

Ion‐beam‐assisted etching of diamond

A new Al etching technique is described that uses an ion beam from a Kaufman ion source and a directed Cl2 flux. The ion beam is used primarily to remove the native oxide and to allow the Cl2 to spontaneously react with the Al film forming volatile Al2Cl6. By controlling both the flux equivalent pressure of Cl2 and the ion beam current, this etching technique makes possible the anisotropic etching of Al with etch rates from 100 nm/min to nearly 10 microns/min with a high degree of selectivity.

Anisotropic etching of Al by a directed Cl2 flux

Transmission electron microscopy has been employed to characterize GaAs permeable base transistor structures. Submicrometer‐period tungsten base gratings fabricated on GaAs substrates by using either liftoff or etching techniques have been studied. Fabrication‐related problems such as electrically isolated tungsten debris and poor tungsten adhesion to GaAs have been identified. The crystal quality of GaAs layers grown by vapor phase epitaxy over the tungsten base gratings has also been investigated. Both stacking faults and voids have been found in these layers. The concentration of voids, which have an elongated‐bubble shape, depends on the orientation of the base grating on the GaAs surface. The effect of these structural imperfections on device performance is discussed.

N. P. Economou

Papers

Ion‐beam‐assisted etching of diamond

Anisotropic etching of Al by a directed Cl2 flux

Transmission electron microscopy of GaAs permeable base transistor structures grown by vapor phase epitaxy

VIB-5 millimeter-wavelength GaAs permeable base transistors