T.J. Davis

Use of different excitation wavelengths for the analysis of CVD diamond by Laser Raman Spectroscopy

Abstract Raman spectroscopy has been shown to be an accurate technique for the qualitative characterisation of chemical vapour deposited (CVD) diamond films. The intensities of the diamond and non-diamond components in the spectrum vary with the wavelength of the laser excitation. This shows that laser Raman at different wavelengths can be used as a selective probe for the different constituents of the deposited film. In the present work, this selectivity has been used to examine the effect of methane concentration during growth on the Raman spectra of CVD diamond. Diamond films were deposited on single crystal Si(100) wafer substrates by microwave plasma enhanced, and hot filament assisted CVD. Methane concentrations of 0.36–2.16% in hydrogen were used as the feedstock. Laser wavelengths ranging from the ultraviolet (244 nm) to the infra-red (780 nm) were used to perform Raman spectroscopy on the deposited diamond films. Scanning electron microscopy (SEM) was used to determine the morphology of the films and related to the Raman spectra.

Field emission from chemical vapor deposited diamond and diamond-like carbon films: Investigations of surface damage and conduction mechanisms

Field emission properties of undoped chemical vapor deposited diamond and diamond-like carbon films have been measured for a variety of different deposition conditions. The nature and appearance of the damage site after testing has been investigated with scanning electron microscopy and laser Raman mapping. These observations, together with the mathematical form of the observed current–voltage relations, are correlated with the conductivity of the film. The results are consistent with a model for the overall emission current that combines conduction mechanisms through the bulk of the film with Fowler–Nordheim tunneling.

Field emission properties of diamond films of different qualities

Field emission properties of diamond films were studied by macroscopic I–V measurement. A lower turn-on field and a higher emission current were observed for diamond films produced by higher methane concentration, or with higher density of defects, introduced by ion implantation. However, diamond films of poorer quality experience a severe reliability problem. Cold implantation followed by rapid thermal or laser annealing produced diamond emitters with a turn-on field as low as 5 V/μm and the desired reliability.

Mapping crystalline quality in diamond films by micro-Raman spectroscopy

Abstract It is known that different growth sectors within diamond films grown by chemical vapor deposition can contain different concentrations of defects. The defects in the diamond can be in the form of inclusions of non-diamond carbon. The quality of the diamond can be observed by the change in the ratios of diamond and non-diamond components in the Raman spectrum and in the widths of the Diamond Raman Line. In (001) textured growth, the (001) sectors are observed to be made up of good quality diamond, whereas the neighboring (111) growth sectors have high concentrations of defects and inclusions. Because of the transparency of diamond, it is possible to map the Raman signal with a confocal microscope to depths of hundreds of microns. In this way, it has been possible to show that the regions of relatively defect-free diamond lie within inverted pyramids. The bases of these pyramids correspond to the observed square (001) facets, whereas the sides of the pyramid correspond to (111) planes. This feature of textured diamond films has been observed by transmission electron microscopy of cross-sections of such films, but this is the first time that it has been shown in-situ. The “Blue-Cross” of defect related luminescence [N.C. Burton, J.E. Butler, A.R. Lang, J.W. Steeds, Proc. R. Soc. Lond. A 449 (1995) 555–566] is observed by PL and correlates well with a mapping of the FWHM. The result demonstrates the ability of confocal micro-Raman spectroscopy to map the crystalline quality in diamond films on a micron scale. It is demonstrated for the first time that the pattern of defect densities previously observed by TEM can be observed in particular growth features of diamond films by confocal Raman spectroscopy.

Field-emission studies of boron-doped CVD diamond films following surface treatments

Abstract The electron emission from highly twinned, undoped Chemical Vapour Deposited (CVD) diamond thin films has been found to exhibit a stable voltage threshold of 15 V μ −1 . In this study the same material has been boron-doped by ion-implantation at two different energy profiles. A number of surface treatments including, Excimer laser annealing, hydrogen passivation, argon/oxygen plasma etching and also coating with gold, were employed in an attempt to enhance the electron emission properties of the highly twinned surface. It has been found that these treatments tend to degrade the electron emission performance, promoting more surface damage and instability in the electron emission current. These results are compared against the emission performance of samples of high quality boron-doped material exhibiting both similar and dissimilar surface textures.

Growth and field emission properties of multiply twinned diamond films with quintuplet wedges

A unique microwave plasma chemical vapor deposition (MPCVD) technique was employed to produce multiply twinned diamond films with quintuplet wedges. Biased nucleation, nonbiased growth, and high methane/hydrogen ratio (≳5%) were used to prepare the multiply twinned diamond films. The growth parameter α was carefully controlled to be close but larger than 3/2 to allow the multiply twinned particles with quintuplets to outgrow the parent face to form the secondary crystals with uniformly distributed particle sizes and smooth surface. Since there is no need to suppress the natural growth of twins in vapor‐grown diamond, higher growth rate was achieved. Excellent field emission properties of such films compared to the normal MPCVD diamond films were also obtained.

Calculation of the stress in large square facets of MPCVD grown diamond from cathodoluminescence and raman spectroscopy measurements and comparison to stress predicted from finite element models

Abstract Thin films of diamond grown by microwave plasma assisted chemical vapour deposition on silicon substrates have been observed to be under stress. Large (100) oriented square facets were observed in the films examined. The size of these crystallites allowed large numbers of readings to be taken by the different techniques illustrated at different points within a single crystallite. Stress in diamond crystals has been shown to affect the peak position and splitting of the 575 nm luminescence peak system in diamond. By the application of different accelerating voltages in a SEM at different positions on the square facet, the stress distribution in the crystallite could be mapped. Stresses in diamond are known to affect the triply degenerate first order phonon line observed by Raman spectroscopy. Using backscattered Raman on a confocal Raman spectrometer a map of the variation of biaxial stress within a volume could be built up. The stresses observed by these techniques and those predicted by finite element modelling of the diamond crystals were compared and the results were found to be in general agreement.