Effect of carrier gas on the surface morphology of V-doped GaN layers

Beta–SiC thin films have been epitaxially grown on 6H–SiC {0001} substrates via chemical vapor deposition (CVD). The growth rate increased linearly with the source/carrier gas flow rate ratio. The activation energy for the growth of β–SiC grown on the Si face of the 6H–SiC substrate was 12 Kcal/mole. These observations are consistent with a surface reaction-controlled process. The as-grown surface morphology is dependent on the terminal layer of the substrate, the growth temperature, and the source/carrier gas flow rate ratio. The C face of a 6H–SiC {0001} substrate caused a higher growth rate and thus poorer surface morphology than the Si face under the same growth conditions. The optimum temperature range for growth of a flat, mirror-like β–SiC surface was determined to be 1773–1823 K in the present CVD system. The microstructure and nucleation of double positioning boundaries were investigated via transmission and scanning electron microscopies. Triangular defects and their modifications were also observed, and their origins have been discussed.

Download Full-text

Effect of Carrier Gas on the Surface Morphology and Mosaic Dispersion for GaN Films by Low-Pressure MOCVD

MRS Proceedings ◽

10.1557/proc-395-261 ◽

1995 ◽

Vol 395 ◽

Cited By ~ 5

Author(s):

T. J. Kistenmacher ◽

D. K. Wickenden ◽

M. E. Hawley ◽

R. P. Leavitt

Keyword(s):

Thin Films ◽

Surface Morphology ◽

Low Pressure ◽

Real Space ◽

The Self ◽

Organic Chemical ◽

Island Growth ◽

Space Images ◽

Carrier Gas ◽

Sapphire Substrates

ABSTRACTLow-pressure metal-organic chemical vapor deposition (MOCVD) has been used to deposit unnucleated and self-nucleated GaN thin films on (00.1) sapphire substrates. For the self-nucleated films, initial layers were grown at 540°C using trimethylgallium and ammonia as elemental sources and either nitrogen or hydrogen as the carrier gas. Using these same gas phase conditions, overlayers on native (00.1) sapphire substrates or the GaN-nucleated (00.1) sapphire substrates were deposited at 1025°C. The surface morphology and mosaic dispersion of these unnucleated and self-nucleated GaN thin films have been surveyed by a combination of real space images from atomic force microscopy and reciprocal space intensity data from X-ray scattering measurements. As expected, the unnucleated GaN films show a large-grained hexagonal relief, typical of three-dimensional island growth. However, the self-nucleated films are shown to be dense mosaics of highly oriented islands, emblematic of a more two-dimensional growth.

Download Full-text

An Established Epithelial Cell Line (NPC/HK1) from a Nasopharyngeal Carcinoma - II. A Sem Study

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100053784 ◽

1982 ◽

Vol 40 ◽

pp. 224-225

Author(s):

Li C.L. ◽

Chew E.C. ◽

Huang D.P. ◽

Ho H.C. ◽

Mak L.S. ◽

...

Keyword(s):

Nasopharyngeal Carcinoma ◽

Epithelial Cell ◽

Surface Morphology ◽

Cell Line ◽

Epithelial Cell Line ◽

Present Communication ◽

Cells In Culture ◽

Sem Study ◽

Well Differentiated

An epithelial cell line, NPC/HK1, has recently been successfully established from a nasopharyngeal carcinoma of the moderately to well differentiated squamous type. The present communication reports on the surface morphology of the NPC/HK1 cells in culture.

Download Full-text

Specimen Collection Effect in Scanning Electron Microscopy Images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095492 ◽

1972 ◽

Vol 30 ◽

pp. 448-449

Author(s):

J. Temple Black ◽

Jose Guerrero

Keyword(s):

Surface Morphology ◽

Secondary Electron Emission ◽

Secondary Electrons ◽

Charge Effects ◽

Material Density ◽

Specimen Collection ◽

The Subject ◽

Curved Paths ◽

Subject Material ◽

Microscopy Images

In the SEM, contrast in the image is the result of variations in the volume secondary electron emission and backscatter emission which reaches the detector and serves to intensity modulate the signal for the CRT's. This emission is a function of the accelerating potential, material density, chemistry, crystallography, local charge effects, surface morphology and especially the angle of the incident electron beam with the particular surface site. Aside from the influence of object inclination, the surface morphology is the most important feature In producing contrast. “Specimen collection“ is the name given the shielding of the collector by adjacent parts of the specimen, producing much image contrast. This type of contrast can occur for both secondary and backscatter electrons even though the secondary electrons take curved paths to the detector-collector.Figure 1 demonstrates, in a unique and striking fashion, the specimen collection effect. The subject material here is Armco Iron, 99.85% purity, which was spark machined.

Download Full-text

The Effect of Benzene on Bluegill Olfactory Lamellae

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010011965x ◽

1985 ◽

Vol 43 ◽

pp. 574-575

Author(s):

D.R. Mattie ◽

J.W. Fisher

Keyword(s):

Surface Morphology ◽

Soluble Fraction ◽

Lepomis Macrochirus ◽

Sublethal Concentration ◽

Water Soluble ◽

Major Constituent ◽

Jet Fuels ◽

Aquatic Biota ◽

Normal Surface ◽

Cacodylate Buffer

Jet fuels such as JP-4 can be introduced into the environment and come in contact with aquatic biota in several ways. Studies in this laboratory have demonstrated JP-4 toxicity to fish. Benzene is the major constituent of the water soluble fraction of JP-4. The normal surface morphology of bluegill olfactory lamellae was examined in conjunction with electrophysiology experiments. There was no information regarding the ultrastructural and physiological responses of the olfactory epithelium of bluegills to acute benzene exposure.The purpose of this investigation was to determine the effects of benzene on the surface morphology of the nasal rosettes of the bluegill sunfish (Lepomis macrochirus). Bluegills were exposed to a sublethal concentration of 7.7±0.2ppm (+S.E.M.) benzene for five, ten or fourteen days. Nasal rosettes were fixed in 2.5% glutaraldehyde and 2.0% paraformaldehyde in 0.1M cacodylate buffer (pH 7.4) containing 1.25mM calcium chloride. Specimens were processed for scanning electron microscopy.

Download Full-text