Strain Effects in GaN on Sapphire: Towards a Quantitative Comprehension

1995 ◽  
Vol 395 ◽  
Author(s):  
O. Briot ◽  
J.P. Alexis ◽  
B. Gil ◽  
R.L. Aulombard
Keyword(s):  
Residual Stress ◽  
Structural Characteristics ◽  
Reflectance Spectroscopy ◽  
Strongly Correlated ◽  
Deformation Potential ◽  
Quantitative Investigation ◽  
Growth Ratio ◽  
Sapphire Substrates ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

ABSTRACTWe present here a detailed investigation of the optical properties of GaN epilayers grown by low pressure MOVPE on sapphire substrates, using 2K photoluminescence as well as 2K reflectance spectroscopy. A large series of samples has been grown under eclectic conditions (V/III ratio, growth temperature, nitridation steps,...) which allows us to propose the first semi-quantitative investigation of the sample-dependent band gap energies. This dependence of the bandgap is analyzed in terms of i) residual stress, ii) exciton parameters and iii) deformation potential characteristics of the A, B, C excitons. the residual stress cannot be simply explained in terms of the differences between the thermal expansion coefficients of the various compounds, but are strongly correlated to the V/III growth ratio imposed during the growth, and subsequently to the influence of this parameter at the scale of electronic and structural characteristics of the deposited layers.

scholarly journals Evolution of the microstructure, residual stresses, and mechanical properties of W–Si–N coatings after thermal annealing

2005 ◽  
Vol 20 (5) ◽  
pp. 1356-1368 ◽  
Author(s):  
A. Cavaleiro ◽  
A.P. Marques ◽  
J.V. Fernandes ◽  
N.J.M. Carvalho ◽  
J.Th. De Hosson
Keyword(s):  
Residual Stress ◽  
Thermal Annealing ◽  
Amorphous Film ◽  
Amorphous Coating ◽  
X Ray Diffraction ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Composition Structure ◽  
The One ◽  
Deposited Film

W–Si–N films were deposited by reactive sputtering in a Ar + N2 atmosphere from a W target encrusted with different number of Si pieces and followed by a thermal annealing at increasing temperatures up to 900 °C. Three iron-based substrates with different thermal expansion coefficients, in the range of 1.5 × 10−6 to 18 × 10−6 K−1 were used. The chemical composition, structure, residual stress, hardness (H), and Young’s modulus (E) were evaluated after all the annealing steps. The as-deposited film with low N and Si contents was crystalline whereas the one with higher contents was amorphous. After thermal annealing at 900 °C the amorphous film crystallized as body-centered cubic α–W. The crystalline as-deposited film presented the same phase even after annealing. There were no significant changes in the properties of both films up to 800 °C annealing. However, at 900 °C, a strong decrease and increase in the hardness were observed for the crystalline and amorphous films, respectively. It was possible to find a good correlation between the residual stress and the hardness of the films. In several cases, particularly for the amorphous coating, H/E higher than 0.1 was reached, which envisages good tribological behavior. The two methods (curvature and x-ray diffraction) used for calculation of the residual stress of the coatings showed fairly good agreement in the results.

Residual Stress in Two Dental Alloys During Porcelain Application

1987 ◽  
Vol 31 ◽  
pp. 255-260
Author(s):  
M. Bagby ◽  
SJ Marshall ◽  
GW Marshall
Keyword(s):  
Residual Stress ◽  
Thermal Expansion ◽  
Residual Stresses ◽  
Casting Process ◽  
Dental Alloys ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thermal Expansion Coefficients ◽  
Dental Restorations ◽  
Expansion Coefficients

Residual stresses in dental castings are widely held to be the cause of distortion and change of fit in ceramic bonded to metal dental restorations. Residual stresses are thought to result from the casting process and from ceramic/metal mismatch of thermal expansion coefficients. Such stresses have not been confirmed experimentally. The purpose of this study was to measure residual stress with x-ray diffraction at the various porcelain application steps for two noble dental alloys with two dental opaque porcelains.

scholarly journals Effects of interfacial residual stress on mechanical behavior of SiCf/SiC composites

2021 ◽  
Author(s):  
Xiaowu Chen ◽  
Guofeng Cheng ◽  
Jinshan Yang ◽  
Jianbao Hu ◽  
Chunjin Liao ◽  
...  
Keyword(s):  
Residual Stress ◽  
Mechanical Behavior ◽  
Ceramic Composites ◽  
Fiber Reinforced ◽  
Thermal Expansion Coefficients ◽  
Sic Fiber ◽  
Ceramics Matrix ◽  
Expansion Coefficients ◽  
Sic Composites ◽  
Reinforcing Fiber

AbstractLayer-structured interphase, existing between reinforcing fiber and ceramics matrix, is an indispensable constituent for fiber-reinforced ceramic composites due to its determinant role in the mechanical behavior of the composites. However, the interphase may suffer high residual stress because of the mismatch of thermal expansion coefficients in the constituents, and this can exert significant influence on the mechanical behavior of the composites. Here, the residual stress in the boron nitride (BN) interphase of continuous SiC fiber-reinforced SiC composites was measured using a micro-Raman spectrometer. The effects of the residual stress on the mechanical behavior of the composites were investigated by correlating the residual stress with the mechanical properties of the composites. The results indicate that the residual stress increases from 26.5 to 82.6 MPa in tension as the fabrication temperature of the composites rises from 1500 to 1650 °C. Moreover, the increasing tensile residual stress leads to significant variation of tensile strain, tensile strength, and fiber/matrix debonding mode of the composites. The sublayer slipping of the interphase caused by the residual stress should be responsible for the transformation of the mechanical behavior. This work can offer important guidance for residual stress adjustment in fiber-reinforced ceramic composites.

scholarly journals Effects of Residual Stress Distribution on Interfacial Adhesion of Magnetron Sputtered AlN and AlN/Al Nanostructured Coatings on a (100) Silicon Substrate

Nanomaterials ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 896 ◽  
Author(s):  
Rashid Ali ◽  
Marco Renzelli ◽  
M. Khan ◽  
Marco Sebastiani ◽  
Edoardo Bemporad
Keyword(s):  
Residual Stress ◽  
Silicon Substrate ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Adhesion Energy ◽  
Thermal Expansion Coefficients ◽  
Bond Layer ◽  
Expansion Coefficients ◽  
Depth Gradients ◽  
Multilayer Stacks

The present study investigated the influence of nanoscale residual stress depth gradients on the nano-mechanical behavior and adhesion energy of aluminium nitride (AlN) and Al/AlN sputtered thin films on a (100) silicon substrate. By using a focused ion beam (FIB) incremental ring-core method, the residual stress depth gradient was assessed in the films in comparison with standard curvature residual stress measurements. The adhesion energy was then quantified by using a nanoindentation-based model. Results showed that the addition of an aluminum layer gave rise to additional tensile stress at the coating/substrate interface, which can be explained in terms of the differences of thermal expansion coefficients with the silicon substrate. Therefore, the coatings without the Al layer showed better adhesion because of a more homogeneous compressive residual stress in comparison with the coating having the Al layer, even though both groups of coatings were produced under the same bias voltage. Results are discussed, and some general suggestions are made on the correlation between coating/substrate property combinations and the adhesion energy of multilayer stacks. The results suggested that the Al bond layer and inhomogeneous residual stresses negatively affected the adhesion of AlN to a substrate such as silicon.

Modeling and Simulation of a Bio-Mimetic MEMS Actuator With Self-Sensing for Thrombus Retrieving

2008 ◽  
Author(s):  
Xi Chen ◽  
Yong Shi ◽  
Sundeep Mangla ◽  
Ming Zhang
Keyword(s):  
Residual Stress ◽  
External Force ◽  
Mathematic Model ◽  
Feedback Control System ◽  
Micro Fabrication ◽  
Thermal Expansion Coefficients ◽  
Closed Position ◽  
Expansion Coefficients ◽  
And Control ◽  
And Diffusion

A new bio-mimetic MEMS actuator device with self-sensing used for thrombus retrieving is presented. The device contains four laterally apposed triangular teeth forming a square which is inspired by the jaws of an earthworm that has radial teeth around a circular mouth. Each tooth is fixed only at the perimeter of the square and consists of several layers including piezoelectric material (PZT) layers, electrode layers (Ti/Pt) and diffusion barrier layers. Due to mismatch of thermal expansion coefficients of different layers, each of the four triangular teeth would initially curve up after the micro fabrication opening the “jaws” of the device. The teeth can then be driven to a closed position by applying an electric field to the PZT layers. The self-sensing method of the piezoelectric device is used for detecting the external force exerted by the teeth and feedback control system in this bio-mimetic MEMS actuator device. The mathematic model which can be used to calculate and control the residual stress causing the curvature of these teeth is discussed. Additionally, residual stress coupled with the piezoelectric stress and external force is also considered. The materials and thickness are optimized by using the linear model developed in this paper. Moreover, with this mathematic model and geometry of these teeth, the motion tracks driven by two different modes are simulated.

Strained Linbo3/Sapphire Heterostructures Grown by Pulsed Laser Deposition

1995 ◽  
Vol 397 ◽  
Author(s):  
Yoshihiko Shibata ◽  
Naohiro Kuze ◽  
Masahiro Matsui ◽  
Masaki Kanai ◽  
Tomoji Kawai
Keyword(s):  
Diffraction Analysis ◽  
Pulsed Laser ◽  
X Ray Diffraction ◽  
X Ray ◽  
Sapphire Substrates ◽  
Thermal Expansion Coefficients ◽  
Transmission Electron ◽  
Expansion Coefficients ◽  
The Difference ◽  
Deposited Films

ABSTRACTThin LiNbO3 films are deposited on (001) sapphire substrates by Ar F pulsed laser ablation. The films are evaluated by X-ray diffraction analysis at various temperatures, as well as high-resolution transmission electron microscopy (TEM). The deposited films are highly epitaxial but that are strained, that is, the a-axis is longer and the c-axis is shorter than those of LiNbO3 single crystals. X-ray diffraction analysis at deposition temperature, as well as TEM show that the strain is caused by the difference in thermal expansion coefficients between LiNbO3 and sapphire substrates.

Effects of Microcracks in CVD Coating Layers on Cemented Carbide and Cermet Substrates on Residual Stress and Transverse Rupture Strength

1997 ◽  
Vol 119 (1) ◽  
pp. 50-54 ◽  
Author(s):  
Sakae Katayama ◽  
Masayuki Hashimura
Keyword(s):  
Residual Stress ◽  
Coating Layer ◽  
Rupture Strength ◽  
Cemented Carbide ◽  
Tensile Residual Stress ◽  
Transverse Rupture Strength ◽  
Beneficial Effects ◽  
Thermal Expansion Coefficients ◽  
Coating Layers ◽  
Expansion Coefficients

Microcracks were mechanically induced in the CVD coating layers on two types of cemented carbides with different thermal expansion coefficients, and one type of cermet. The microcracks were found to have beneficial effects on residual stress, transverse rupture strength, and chipping resistance during interrupted cutting. Residual stress in the coating on cemented carbide is tensile. Tensile residual stress decreases with increasing microcrack width and decreasing microcrack distance. Induction of 20 μm-distant and 0.025 μm-wide cracks relieves tensile residual stress by about 0.5 GPa, increases transverse rupture strength by about 0.70 GPa, and almost doubles the chipping resistance. Residual stress in the coating on cermet is compressive. Microcracks in the coating layer do not change residual stress or transverse rupture strength.

Defects in β-SiC thin films grown on α-SiC substrates

1988 ◽  
Vol 46 ◽  
pp. 568-569
Author(s):  
Karren L. More
Keyword(s):  
Thin Films ◽  
Semiconductor Device ◽  
Lattice Mismatch ◽  
Chemical Vapor ◽  
Substrate Material ◽  
Growth Interface ◽  
Si Substrates ◽  
Thermal Expansion Coefficients ◽  
Device Applications ◽  
Expansion Coefficients

Beta-SiC is an ideal candidate material for use in semiconductor device applications. Currently, monocrystalline β-SiC thin films are epitaxially grown on {100} Si substrates by chemical vapor deposition (CVD). These films, however, contain a high density of defects such as stacking faults, microtwins, and antiphase boundaries (APBs) as a result of the 20% lattice mismatch across the growth interface and an 8% difference in thermal expansion coefficients between Si and SiC. An ideal substrate material for the growth of β-SiC is α-SiC. Unfortunately, high purity, bulk α-SiC single crystals are very difficult to grow. The major source of SiC suitable for use as a substrate material is the random growth of {0001} 6H α-SiC crystals in an Acheson furnace used to make SiC grit for abrasive applications. To prepare clean, atomically smooth surfaces, the substrates are oxidized at 1473 K in flowing 02 for 1.5 h which removes ∽50 nm of the as-grown surface. The natural {0001} surface can terminate as either a Si (0001) layer or as a C (0001) layer.

Influence of Magnetoelastic Anisotropy on Properties of Nanostructured Microwires

2013 ◽  
Vol 646 ◽  
pp. 59-66 ◽  
Author(s):  
Arcady Zhukov ◽  
Margarita Churyukanova ◽  
Lorena Gonzalez-Legarreta ◽  
Ahmed Talaat ◽  
Valentina Zhukova ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Hysteresis Loops ◽  
Magnetic Behaviour ◽  
Soft Magnetic ◽  
Magnetoelastic Anisotropy ◽  
Thermal Expansion Coefficients ◽  
Magnetoelastic Energy ◽  
Expansion Coefficients ◽  
The Difference ◽  
Magneto Resistance

We studied the effect ofthe magnetoelastic ansitropy on properties of nanostructured glass-coated microwires with soft magnetic behaviour (Finemet-type microwires of Fe70.8Cu1Nb3.1Si14.5B10.6, Fe71.8Cu1Nb3.1Si15B9.1 and Fe73.8Cu1Nb3.1Si13B9.1 compositions) and with granular structure (Cu based Co-Cu microwires). The magnetoelastic energy originated from the difference in thermal expansion coefficients of the glass and metallic alloy during the microwires fabrication, affected the hysteresis loops, coercivity and heat capacity of Finemet-type microwires. Hysteresis loops of all as-prepared microwires showed rectangular shape, typical for Fe-rich microwires. As expected, coercivity, HC, of as-prepared microwires increases with decreasing of the ratio ρ defined as the ratio between the metallic nucleus diameter, d to total microwire diameter, D. On the other hand we observed change of heat capacity in microwires with different ratio ρ. In the case of Co-Cu microwires ρ- ratio affected the structure and the giant magneto-resistance of obtained microwires.

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