Direct AFM Observation of Strain Effects on MOCVD-Grown GaN Epilayer Surface Morphology

2004 ◽  
Vol 831 ◽  
Author(s):  
D.I. Florescu ◽  
D.S. Lee ◽  
J.C. Ramer ◽  
V.N. Merai ◽  
A. Parekh ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Surface Morphology ◽  
Strain Relaxation ◽  
Compressive Strain ◽  
Growth Direction ◽  
Excellent Correlation ◽  
Sapphire Substrates ◽  
Afm Observation ◽  
Miscut Angle ◽  
Epilayer Surface

ABSTRACTIn this study, we investigate the dependence of GaN surface morphology on the absolute strain values for thin (<10 μm) epitaxial films grown by MOCVD on c-plane sapphire substrates of various miscut angles towards the m-plane. Results indicate an excellent correlation between the surface roughness observed employing an AFM tool and epilayer strain values. An overall increase of surface roughness (decrease of atomic terrace width) is found with decreasing compressive strain (epilayer vs. bulk value). In addition, sapphire substrates with increasing miscut angle (0.30 deg) appear to relax the inherent, built-in strain differently in the vertical (growth) direction when compared to just (0.00 deg) substrates. Strain relaxation by typical V-shaped, hexagonal pits is directly imaged through the comparison of surface features inside and outside of pits in the thin GaN epilayer films.

Study of SiC Epitaxial Growth Using Tetrafluorosilane and Dichlorosilane in Vertical Hotwall CVD Furnace

2015 ◽  
Vol 821-823 ◽  
pp. 137-140 ◽  
Author(s):  
Anusha Balachandran ◽  
Hai Zheng Song ◽  
T.S. Sudarshan ◽  
Shamaita S. Shetu ◽  
M.V.S. Chandrashekhar
Keyword(s):  
Surface Roughness ◽  
Surface Morphology ◽  
Epitaxial Growth ◽  
Doping Concentration ◽  
Specular Surface ◽  
Growth Regime ◽  
Order Of Magnitude ◽  
Controlled Doping ◽  
Specific Influence ◽  
Epilayer Surface

This paper presents one of the first comparative studies of distinctive results obtained using halogenated silicon precursors, dichlorosilane (SiH2Cl2, DCS) and tetrafluorosilane (SiF4, TFS) for SiC homo epitaxial growth. Both TFS and DCS possess very distinct properties that show specific influence on SiC growth. SiC epitaxial growth using TFS greatly suppresses parasitic deposition in the gas delivery system. Growth using TFS shows carbon mediated growth regime, and exhibits controlled doping concentration of the epilayer by an order of magnitude lower than that in the growth using DCS at the same C/Si ratio. Studies of epilayer surface morphology show that the epilayers from TFS growth have a specular surface in a wide C/Si range whereas in the growth using DCS, the epilayer surface roughness is strongly dependent on the C/Si ratio.

Layer Thickness Dependence of Strain in GaN grown by HVPE

2001 ◽  
Vol 693 ◽  
Author(s):  
Gyu Gwang Sim ◽  
P. W. Yu ◽  
D. C. Reynolds ◽  
D. C. Look ◽  
Sang Soo Kim ◽  
...  
Keyword(s):  
Layer Thickness ◽  
Strain Relaxation ◽  
Compressive Strain ◽  
Energy Shift ◽  
Thickness Dependence ◽  
Hydride Vapor Phase Epitaxy ◽  
Strain Effect ◽  
Transition Energies ◽  
Sapphire Substrates ◽  
Thermal Expansion Coefficients

AbstractWurzite GaN epilayers on sapphire substrates usually suffer from biaxial compressive strain due to the mismatches of the thermal expansion coefficients and the lattice constants between GaN layers and sapphire substrates. We have investigated the layer thickness effects on strain and transition energies by photoluminescence (PL), photoreflectance (PR) and X-ray diffraction (XRD). Samples used in this study are grown by hydride vapor phase epitaxy (HVPE) and have the layer thickness of 0.76, 2.6, 5.3 and 48 m. The PL and PR spectra showed the redshift of the transition energies with increasing layer thickness. This is attributed to strain-induced energy shift. The layer thickness dependence of strains is directly observed by XRD. The strain along the c -axis (εzz) decreased with increasing layer thickness. This indicates the strain is relaxed with layer thickness. From strain variation with layer thickness, we suggest that strain relaxation process is rapid at the initial stage of growth and becomes slower as the layer grows. The full width at half maximum (FWHM) of PL spectra and theta rocking curves decrease with increasing layer thickness. This indicates the crystal quality improves as the strain is reduced. Since the strain effect is very small at the layer thickness of 48 μm, we expect zero strain for thicker layers that can potentially be used as substrates for homoepitaxy.

scholarly journals Ultrasonic dispersion method used in glass polishing experiment

2021 ◽  
Vol 13 (4) ◽  
pp. 168781402110118
Author(s):  
Zenan Chu ◽  
Tao Wang ◽  
Qiang He ◽  
Kai Zhao
Keyword(s):  
Surface Roughness ◽  
Rare Earth ◽  
Surface Morphology ◽  
Ultrasonic Method ◽  
Average Surface Roughness ◽  
Polishing Process ◽  
Ultrasonic Dispersion ◽  
Processing Efficiency ◽  
Average Surface ◽  
Evaluation Indexes

To solve the problems of low processing efficiency and poor glass surface quality when using rare earth polishing powder to grind super-hard K9 glass. The potential, phase structure, surface morphology, and particle size distribution of the nano-rare earth polishing powder were characterized. Compare the evaluation indexes such as polishing efficiency, surface morphology, and contact angle after the polishing process is changed. The results of the comparative study show that the average surface roughness of the glass after heating ultrasonic polishing process is 0.9064 nm, the polishing rate reaches 0.748 μm/min, the average surface roughness of the glass without heating ultrasonic polishing process is 1.3175 nm, and the polishing rate reaches 0.586 μm/min, the ultrasonic assisted polishing process is superior to the conventional polishing process. The heating ultrasonic method provides experimental basis for precise and rapid processing.

Ge-Quantum Dots on SI(001) Tailored by Carbon Predeposition

1998 ◽  
Vol 533 ◽  
Author(s):  
O. Leifeld ◽  
D. Grützmacher ◽  
B. Müller ◽  
K. Kern
Keyword(s):  
Surface Roughness ◽  
Critical Thickness ◽  
Carbon Deposition ◽  
Compressive Strain ◽  
Second Step ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Island Nucleation ◽  
Facet Formation

AbstractThe morphology of Si(001) after carbon deposition of 0.05 to 0.11 monolayers (ML) was investigated in situ by ultrahigh vacuum scanning tunneling microscopy (UHV-STM). The carbon induces a c(4×4)-reconstruction of the surface. In addition, carbon increases the surface roughness compared to clean Si(001) (2×1). In a second step, the influence of the carbon induced restructuring on Ge-island nucleation was investigated. The 3D-growth sets in at considerably lower Ge coverage compared to the clean Si(001) (2×1) surface. This leads to a high density of small though irregularly shaped dots, consisting of stepped terraces, already at 2.5 ML Ge. Increasing the Ge-coverage beyond the critical thickness for facet formation, the dots show { 105 }- facets well known from Ge-clusters on bare Si(001) (2×1). However, they are flat on top with a (001)-facet showing the typical buckled Ge rows and missing dimers. This indicates that the compressive strain is not fully relaxed in these hut clusters.

Surface integrity of quenched steel 1045 machined by CBN grinding wheel and SiC grinding wheel

2017 ◽  
Vol 8 (2) ◽  
pp. 179-187 ◽  
Author(s):  
Kankan Ji ◽  
Xingquan Zhang ◽  
Shubao Yang ◽  
Liping Shi ◽  
Shiyi Wang ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Surface Morphology ◽  
Compressive Stress ◽  
Surface Integrity ◽  
Grinding Wheel ◽  
Micro Hardness ◽  
Content Type ◽  
Quenched Steel ◽  
Cut Depth ◽  
Cbn Grinding Wheel

Purpose The purpose of this paper is to evaluate surface integrity of quenched steel 1045 ground drily by the brazed cubic boron nitride (CBN) grinding wheel and the black SiC wheel, respectively. Surface integrity, including surface roughness, sub-surface hardness, residual stresses and surface morphology, was investigated in detail, and the surface quality of samples ground by two grinding wheels was compared. Design/methodology/approach In the present work, surface integrity of quenched steel 1045 machined by the CBN grinding wheel and the SiC wheel was investigated systematically. All the specimens were machined with a single pass in the down-cutting mode of dry condition. Surface morphology of the ground specimen was observed by using OLYMPUS BX51M optical microscopy. Surface roughness of seven points was measured by using a surface roughness tester at a cut-off length of 1.8 mm and the measurement traces were perpendicular to the grinding direction. Sub-surface micro-hardness was measured by using HVS-1000 digital micro-hardness tester after the cross-section surface was polished. The residual stress was tested by using X-350A X-ray stress analyzer. Findings When the cut depth is increased from 0.01 to 0.07 mm, the steel surface machined by the CBN wheel remains clear grinding mark, lower roughness, higher micro-hardness and higher magnitude of compressive stress and fine microstructure, while the surface machined by the SiC grinding wheel becomes worse with increasing of cut depth. The value of micro-hardness decreases, and the surface roughness increases, and the surface compressive stress turns into tensile stress. Some micro-cracks and voids occur when the sample is processed by the SiC grinding wheel with cut depth 0.07 mm. Originality/value In this paper, the specimens of quenched steel 1045 were machined by the CBN grinding wheel and the SiC wheel with various cutting depths. The processing quality resulted from the CBN grinding wheel is better than that resulted from the SiC grinding wheel.

Investigation on Surface Grinding of Ti-6Al-4V Using Minimum Quantity Lubrication

2012 ◽  
Vol 500 ◽  
pp. 308-313 ◽  
Author(s):  
Guo Qiang Guo ◽  
Zhi Qiang Liu ◽  
Xiao Hu Zheng ◽  
Ming Chen
Keyword(s):  
Surface Roughness ◽  
Plastic Deformation ◽  
Surface Morphology ◽  
Specific Energy ◽  
Minimum Quantity Lubrication ◽  
Grinding Force ◽  
Dry Grinding ◽  
Surface Damages ◽  
Side Flow ◽  
Mql System

This paper investigates the effects of MQL system on the grinding performance of Ti-6Al-4V using SiC abrasive, the evaluation of the performance consisted of analyzing the grinding force, surface roughness and surface morphology. The experiment result indicated that the favorable lubricating effect of MQL oil makes it has the lowest value of grinding force, specific energy and force raito. MQL has better surface finish than dry grinding and fluid grinding has the lowest value of surface roughness under different grinding depth. Surface damages such as: side flow, plastic deformation, redeposition are present in dry and fluid grinding. As grinding depth increased, the damages become much more severe. But in MQL condition, it gives better surface integrity than dry and fluid grinding.

Stress Relaxation in Uniquely Oriented SiGe/Si Epitaxial Layers

1999 ◽  
Vol 594 ◽  
Author(s):  
M. E. Ware ◽  
R. J. Nemanich
Keyword(s):  
Stress Relaxation ◽  
Surface Morphology ◽  
Strain Relaxation ◽  
Epitaxial Layers ◽  
Misfit Dislocations ◽  
Strained Layers ◽  
Force Microscopy ◽  
Si Substrates ◽  
Atomic Force ◽  
Deposited Films

AbstractThis study explores stress relaxation of epitaxial SiGe layers grown on Si substrates with unique orientations. The crystallographic orientations of the Si substrates used were off-axis from the (001) plane towards the (111) plane by angles, θ = 0, 10, and 22 degrees. We have grown 100nm thick Si(1−x) Ge(x) epitaxial layers with x=0.3 on the Si substrates to examine the relaxation process. The as-deposited films are metastable to the formation of strain relaxing misfit dislocations, and thermal annealing is used to obtain highly relaxed films for comparison. Raman spectroscopy has been used to measure the strain relaxation, and atomic force microscopy has been used to explore the development of surface morphology. The Raman scattering indicated that the strain in the as-deposited films is dependent on the substrate orientation with strained layers grown on Si with 0 and 22 degree orientations while highly relaxed films were grown on the 10 degree substrate. The surface morphology also differed for the substrate orientations. The 10 degree surface is relatively smooth with hut shaped structures oriented at predicted angles relative to the step edges.

A Comparative Study of GaN Films Grown on Different Faces of Sapphire by ECR-Assisted MBE

1992 ◽  
Vol 242 ◽  
Author(s):  
T. D. Moustakas ◽  
R. J. Molnar ◽  
T. Lei ◽  
G. Menon ◽  
C. R. Eddy
Keyword(s):  
Surface Morphology ◽  
Low Temperatures ◽  
Smooth Surface ◽  
Growth Process ◽  
X Ray Diffraction ◽  
Epitaxial Relationship ◽  
X Ray ◽  
Sapphire Substrates ◽  
Growth Method ◽  
Step Growth

ABSTRACTGaN films were grown on c-plane (0001), a-plane (1120) and r-plane (1102) sapphire substrates by the ECR-assisted MBE method. The films were grown using a two-step growth process, in which a GaN buffer is grown first at relatively low temperatures and the rest of the film is grown at higher temperatures. RHEED studies indicate that this growth method promotes lateral growth and leads to films with smooth surface morphology. The epitaxial relationship to the substrate, the crystalline quality and the surface morphology were investigated by RHEED, X-ray diffraction and SEM studies.

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