Efficient model for the elastic load of film-substrate system involving imperfect interface effects

Thin films of GaN and its alloy AlGaN are investigated with respect to their properties of the persistent photoconductivity (PPC). In this work, we show that the film-substrate interface plays an important role for the metastable electrical effect. Strongly absorbed bandgap light causes an increase of photoconductivity which is about one order of magnitude higher when the sample is illuminated from the substrate side near the interface than from the growth side. To access the interface properties at the substrate, we use temperature-dependent Hall effect measurements. The smallest PPC effect was observed for the GaN film with the best interface properties grown on SiC.

Download Full-text

Modified Stoney's Formulas for Small-Scaled Bilayer Systems

Journal of Engineering Materials and Technology ◽

10.1115/1.4006509 ◽

2012 ◽

Vol 134 (3) ◽

Cited By ~ 2

Author(s):

Dongying Liu ◽

Weiqiu Chen

Keyword(s):

Couple Stress ◽

Couple Stress Theory ◽

Modified Couple Stress Theory ◽

Imperfect Interface ◽

Bilayer Film ◽

Type Model ◽

Stress Theory ◽

Modified Couple Stress ◽

Film Substrate ◽

Perfect Interface

The mechanics of a small-scaled bilayer film-substrate system subject to temperature variation is studied. The modified couple stress theory is employed to take account of the size effects that are usually observed in small-scaled structures. In addition, the effect of weak bonding between the film and substrate is examined by using a linear slip-type model. Exact solutions are derived and the closed-form expressions for residual thermal stress and curvature of the system are given. Modified Stoney’s formulas are also presented for the bilayer system with perfect interface or imperfect interface between the film and the substrate.

Download Full-text

Interface Effects on the Persistent Photoconductivity in Thin GaN and AlGaN Films

MRS Proceedings ◽

10.1557/proc-537-g5.5 ◽

1998 ◽

Vol 537 ◽

Cited By ~ 1

Author(s):

O. P. Seifert ◽

O. Kirfel ◽

M. Munzel ◽

M. T. Hirsch ◽

J. Parisi ◽

...

Keyword(s):

Interface Properties ◽

Persistent Photoconductivity ◽

Temperature Dependent ◽

Substrate Side ◽

Electrical Effect ◽

Order Of Magnitude ◽

Hall Effect Measurements ◽

Film Substrate ◽

Gan Film ◽

Interface Effects

AbstractThin films of GaN and its alloy AlGaN are investigated with respect to their properties of the persistent photoconductivity (PPC). In this work, we show that the film-substrate interface plays an important role for the metastable electrical effect. Strongly absorbed bandgap light causes an increase of photoconductivity which is about one order of magnitude higher when the sample is illuminated from the substrate side near the interface than from the growth side. To access the interface properties at the substrate, we use temperature-dependent Hall effect measurements. The smallest PPC effect was observed for the GaN film with the best interface properties grown on SiC.

Download Full-text

Acoustic Vibration of Hexagonal Nanoparticles With Damping and Imperfect Interface Effects

Journal of Vibration and Acoustics ◽

10.1115/1.4048559 ◽

2020 ◽

Vol 143 (3) ◽

Author(s):

Feng Zhu ◽

Ernian Pan ◽

Zhenghua Qian

Keyword(s):

Order Differential Equation ◽

Mass Conservation ◽

Acoustic Vibration ◽

Imperfect Interface ◽

Spherical System ◽

First Order ◽

Present Solution ◽

Constant Coefficients ◽

Propagation Matrix ◽

Interface Effects

Abstract In this paper, acoustic vibration of hexagonal nanoparticles is investigated. In terms of the spherical system of vector functions, the first-order differential equation with constant coefficients for a layered sphere is obtained via variable transformation and mass conservation. The propagation matrix method is then used to obtain the vibration equation in the multilayered system. Further utilizing a new root-searching algorithm, the present solution is first compared to the existing solution for a uniform and isotropic sphere. It is shown that, by increasing the sublayer number, the present solution approaches the exact one. After validating the formulation and program, we investigate the acoustic vibration characteristics in nanoparticles. These include the effects of material anisotropy, damping, and core–shell imperfect interface on the vibration frequency and modal shapes of the displacements and tractions.

Download Full-text

Microtomy of spherical Al2O3 powders

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010007429x ◽

1983 ◽

Vol 41 ◽

pp. 74-75

Author(s):

E.J. Jenkins ◽

D.S. Tucker ◽

J.J. Hren

Keyword(s):

Thin Film ◽

Size Range ◽

Particle Aggregation ◽

Ion Milling ◽

Thin Sections ◽

Α Phase ◽

Convenient Means ◽

Van Der Waals Attraction ◽

Negative Feature ◽

Film Substrate

The size range of mineral and ceramic particles of one to a few microns is awkward to prepare for examination by TEM. Electrons can be transmitted through smaller particles directly and larger particles can be thinned by crushing and dispersion onto a substrate or by embedding in a film followed by ion milling. Attempts at dispersion onto a thin film substrate often result in particle aggregation by van der Waals attraction. In the present work we studied 1-10 μm diameter Al2O3 spheres which were transformed from the amprphous state to the stable α phase.After the appropriate heat treatment, the spherical powders were embedded in as high a density as practicable in a hard EPON, and then microtomed into thin sections. There are several advantages to this method. Obviously, this is a rapid and convenient means to study the microstructure of serial slices. EDS, ELS, and diffraction studies are also considerably more informative. Furthermore, confidence in sampling reliability is considerably enhanced. The major negative feature is some distortion of the microstructure inherent to the microtoming operation; however, this appears to have been surprisingly small. The details of the method and some typical results follow.

Download Full-text

Structural and electronic properties of defects in semiconductors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136398 ◽

1995 ◽

Vol 53 ◽

pp. 4-5

Author(s):

J.L. Batstone

Keyword(s):

Semiconductor Device ◽

Chemical Vapor ◽

Misfit Strain ◽

Organic Chemical ◽

Extended Defects ◽

Transmission Electron ◽

Semiconductor Thin Films ◽

Wide Range ◽

Metal Organic ◽

Film Substrate

The development of growth techniques such as metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy during the last fifteen years has resulted in the growth of high quality epitaxial semiconductor thin films for the semiconductor device industry. The III-V and II-VI semiconductors exhibit a wide range of fundamental band gap energies, enabling the fabrication of sophisticated optoelectronic devices such as lasers and electroluminescent displays. However, the radiative efficiency of such devices is strongly affected by the presence of optically and electrically active defects within the epitaxial layer; thus an understanding of factors influencing the defect densities is required.Extended defects such as dislocations, twins, stacking faults and grain boundaries can occur during epitaxial growth to relieve the misfit strain that builds up. Such defects can nucleate either at surfaces or thin film/substrate interfaces and the growth and nucleation events can be determined by in situ transmission electron microscopy (TEM).

Download Full-text

Microstructural investigation of surface roughness in MBE-grown AlAs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100138646 ◽

1995 ◽

Vol 53 ◽

pp. 454-455

Author(s):

R. Rajesh ◽

R. Droopad ◽

C. H. Kuo ◽

R. W. Carpenter ◽

G. N. Maracas

Keyword(s):

Thin Film ◽

Real Time ◽

Growth Control ◽

Native Oxide ◽

Effusion Cell ◽

Surface Oxide Layer ◽

Microstructural Investigation ◽

Mbe Growth ◽

Film Substrate ◽

And Control

Knowledge of material pseudodielectric functions at MBE growth temperatures is essential for achieving in-situ, real time growth control. This allows us to accurately monitor and control thicknesses of the layers during growth. Undesired effusion cell temperature fluctuations during growth can thus be compensated for in real-time by spectroscopic ellipsometry. The accuracy in determining pseudodielectric functions is increased if one does not require applying a structure model to correct for the presence of an unknown surface layer such as a native oxide. Performing these measurements in an MBE reactor on as-grown material gives us this advantage. Thus, a simple three phase model (vacuum/thin film/substrate) can be used to obtain thin film data without uncertainties arising from a surface oxide layer of unknown composition and temperature dependence.In this study, we obtain the pseudodielectric functions of MBE-grown AlAs from growth temperature (650°C) to room temperature (30°C). The profile of the wavelength-dependent function from the ellipsometry data indicated a rough surface after growth of 0.5 μm of AlAs at a substrate temperature of 600°C, which is typical for MBE-growth of GaAs.

Download Full-text

Microstructure of YBa2Cu3O7-x thin films deposited by dc sputtering

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100152835 ◽

1989 ◽

Vol 47 ◽

pp. 172-173

Author(s):

O. Eibl ◽

G. Gieres ◽

H. Behner

Keyword(s):

Thin Films ◽

Cross Sections ◽

Intermediate Layer ◽

Amorphous State ◽

Critical Currents ◽

Dc Sputtering ◽

State Process ◽

Diffraction Patterns ◽

Film Substrate ◽

Substrate Temperatures

The microstructure of high-Tc YBa2Cu3O7-X thin films deposited by DC-sputtering on SrTiO3 substrates was analysed by TEM. Films were either (i) deposited in the amorphous state at substrate temperatures < 450°C and crystallised by a heat treatment at 900°C (process 1) or (ii) deposited at around 740°C in the crystalline state (process 2). Cross sections were prepared for TEM analyses and are especially useful for studying film substrate interdiffusion (fig.1). Films deposited in process 1 were polycristalline and the grain size was approximately 200 nm. Films were porous and the size of voids was approximately 100 nm. Between the SrTiO3 substrate and the YBa2Cu3Ox film a densly grown crystalline intermediate layer approximately 150 nm thick covered the SrTiO3 substrate. EDX microanalyses showed that the layer consisted of Sr, Ba and Ti, however, did not contain Y and Cu. Crystallites of the layer were carefully tilted in the microscope and diffraction patterns were obtained in five different poles for every crystallite. These patterns were consistent with the phase (Ba1-XSrx)2TiO4. The intermediate layer was most likely formed during the annealing at 900°C. Its formation can be understood as a diffusion of Ba from the amorphously deposited film into the substrate and diffusion of Sr from the substrate into the film. Between the intermediate layer and the surface of the film the film consisted of YBa2Cu3O7-x grains. Films prepared in process 1 had Tc(R=0) close to 90 K, however, critical currents were as low as jc = 104A/cm2 at 77 K.

Download Full-text

Advances in Stem Instrumentation for Biology

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180562 ◽

1990 ◽

Vol 48 (1) ◽

pp. 362-363

Author(s):

J. S. Wall

Keyword(s):

Scanning Transmission Electron Microscope ◽

Carbon Films ◽

Specimen Preparation ◽

Material Deposition ◽

Active User ◽

Percent Improvement ◽

Scanning Transmission ◽

The Moment ◽

Film Substrate ◽

High Level

The forte of the Scanning transmission Electron Microscope (STEM) is high resolution imaging with high contrast on thin specimens, as demonstrated by visualization of single heavy atoms. of equal importance for biology is the efficient utilization of all available signals, permitting low dose imaging of unstained single molecules such as DNA.Our work at Brookhaven has concentrated on: 1) design and construction of instruments optimized for a narrow range of biological applications and 2) use of such instruments in a very active user/collaborator program. Therefore our program is highly interactive with a strong emphasis on producing results which are interpretable with a high level of confidence.The major challenge we face at the moment is specimen preparation. The resolution of the STEM is better than 2.5 A, but measurements of resolution vs. dose level off at a resolution of 20 A at a dose of 10 el/A2 on a well-behaved biological specimen such as TMV (tobacco mosaic virus). To track down this problem we are examining all aspects of specimen preparation: purification of biological material, deposition on the thin film substrate, washing, fast freezing and freeze drying. As we attempt to improve our equipment/technique, we use image analysis of TMV internal controls included in all STEM samples as a monitor sensitive enough to detect even a few percent improvement. For delicate specimens, carbon films can be very harsh-leading to disruption of the sample. Therefore we are developing conducting polymer films as alternative substrates, as described elsewhere in these Proceedings. For specimen preparation studies, we have identified (from our user/collaborator program ) a variety of “canary” specimens, each uniquely sensitive to one particular aspect of sample preparation, so we can attempt to separate the variables involved.

Download Full-text

Parallel Glide: A Fundamentally Different Type of Dislocation Motion in Ultrathin Metal Films

MRS Proceedings ◽

10.1557/proc-779-w4.4 ◽

2003 ◽

Vol 779 ◽

Author(s):

T. John Balk ◽

Gerhard Dehm ◽

Eduard Arzt

Keyword(s):

Thermal Cycling ◽

Grain Boundaries ◽

Film Surface ◽

Metal Films ◽

Geometric Constraints ◽

Film Stress ◽

Diffusional Creep ◽

Creep Model ◽

Substrate Interface ◽

Film Substrate

AbstractWhen confronted by severe geometric constraints, dislocations may respond in unforeseen ways. One example of such unexpected behavior is parallel glide in unpassivated, ultrathin (200 nm and thinner) metal films. This involves the glide of dislocations parallel to and very near the film/substrate interface, following their emission from grain boundaries. In situ transmission electron microscopy reveals that this mechanism dominates the thermomechanical behavior of ultrathin, unpassivated copper films. However, according to Schmid's law, the biaxial film stress that evolves during thermal cycling does not generate a resolved shear stress parallel to the film/substrate interface and therefore should not drive such motion. Instead, it is proposed that the observed dislocations are generated as a result of atomic diffusion into the grain boundaries. This provides experimental support for the constrained diffusional creep model of Gao et al.[1], in which they described the diffusional exchange of atoms between the unpassivated film surface and grain boundaries at high temperatures, a process that can locally relax the film stress near those boundaries. In the grains where it is observed, parallel glide can account for the plastic strain generated within a film during thermal cycling. One feature of this mechanism at the nanoscale is that, as grain size decreases, eventually a single dislocation suffices to mediate plasticity in an entire grain during thermal cycling. Parallel glide is a new example of the interactions between dislocations and the surface/interface, which are likely to increase in importance during the persistent miniaturization of thin film geometries.

Download Full-text