1H Nmr in μc-Si:H Deposited With Different Plasma Excitation Frequencies and Silane Concentrations

1996 ◽  
Vol 420 ◽  
Author(s):  
P. Hari ◽  
P. C. Taylor ◽  
F. Finger
Keyword(s):  
Hydrogen Content ◽  
Excitation Frequency ◽  
Aluminum Foil ◽  
Ir Absorption ◽  
Narrow Component ◽  
Beat Pattern ◽  
Two Samples ◽  
Free Induction ◽  
Plasma Excitation ◽  
Excitation Frequencies

AbstractSix samples of pc-Si:H were prepared by PECVD at 200°C with plasma excitation frequencies ranging from 13 MHz to 95 MHz. Four samples were prepared with gas mixtures of 3% SiH 4 in H2. For these samples the plasma excitation frequencies ranged from 13 MHz to 95 MHz. Two samples at a plasma excitation frequency of 95 MHz were prepared at 5% and 8% SiH4 in H2. All samples were deposited on aluminum foil and etched off using dilute HCI to form powdered samples. These samples were studied by nuclear magnetic resonance (NMR), electron spin resonance (ESR) and infrared (IR) absorption measurements. The broad and narrow components of the free induction decay (FID) in the NMR measurements were compared to the respective components that occur in a-Si:H. The broad components in the various samples of μc-Si:H are similar in width to the broad component in a-Si:H, but the narrow component is narrower by a factor of two as compared to the narrow components in μ-Si:H. The narrow component in pic-Si:H samples exhibits a beat pattern similar to a previously observed Pake doublet. ESR measurements performed between 20 K and 300 K show that the spin densities, which can be attributed to silicon dangling bond states, increase as a function of plasma excitation frequency. The hydrogen content of each μc-Si:H sample was estimated from the NMR measurements, and these estimates are in good arrangement with the hydrogen content estimated from IR measurements.

Role of SiH2 in 1H Nmr of μc-Si:H Deposited with Different Plasma Excitation Frequencies and Silane Concentrations

1996 ◽  
Vol 452 ◽  
Author(s):  
P. Hari ◽  
P. C. Taylor ◽  
F. Finger
Keyword(s):  
Hydrogen Content ◽  
Excitation Frequency ◽  
H Nmr ◽  
Ir Studies ◽  
Wide Range ◽  
Two Samples ◽  
Plasma Excitation ◽  
Excitation Frequencies ◽  
Silane Concentration

AbstractPrevious lH NMR and IR studies of six samples of μc-Si:H prepared under plasma excitation frequencies ranging from 13 MHz to 95 MHz and silane concentrations ranging from 3% to 8% revealed three important results: (1) for a fixed plasma excitation frequency (95 MHz) the hydrogen content increases with silane concentration; (2) for fixed silane concentration the hydrogen content is roughly constant over a wide range of plasma excitation frequencies; and (3) the 1H NMR free induction decay exhibits beat frequencies which correspond to the calculated frequencies due to SiH2 in microcrystalline silicon. In this study we investigate the role of SiH2 in the μc-Si:H structure using 1H NMR measurements. We studied two samples prepared at two different plasma excitation frequencies (13 MHz and 95 MHz). The lU NMR lineshapes of these samples were measured at 300 K and 77 K. The motionally narrowed component of the 1H NMR is not as rapid at room temperature as that observed previously, but the linewidth of this component increases significantly at 77 K. Because of this difference between our results and those reported previously, it is possible that H2 molecules are not responsible for the motional narrowing in our samples. We present plausible arguments for the hindered motion of SiH2 groups in our μc-Si:H samples.

Preparation of Microcrystalline Silicon with the Layer-by-Layer Technique at Various Plasma Excitation Frequencies

1996 ◽  
Vol 452 ◽  
Author(s):  
P. Hapke ◽  
R. Carius ◽  
F. Finger ◽  
A. Lambertz ◽  
O. Vetterl ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Excitation Frequency ◽  
Hydrogen Treatment ◽  
Layer By Layer ◽  
Microcrystalline Silicon ◽  
Nucleation Layer ◽  
Layer Technique ◽  
Plasma Excitation ◽  
Excitation Frequencies ◽  
Layer By Layer Technique

AbstractFor application as nucleation layer in thin film devices, microcrystalline silicon was deposited with the layer-by-layer technique using plasma excitation frequencies between 27 and 95 MHz, various hydrogen treatment times and various film thicknesses per layer. An optimum phase transformation is found at an intermediate plasma excitation frequency, i.e. at this frequency the shortest hydrogen annealing time is necessary for an effective amorphous-to-crystalline phase transformation.

Growth and Structure of Microcrystalline Silicon Prepared with Glow Discharge at Various Plasma Excitation Frequencies

1996 ◽  
Vol 452 ◽  
Author(s):  
F. Finger ◽  
R. Carius ◽  
P. Hapke ◽  
L. Houben ◽  
M. Luysberg ◽  
...  
Keyword(s):  
Glow Discharge ◽  
Excitation Frequency ◽  
Interface Layer ◽  
Silicon Substrates ◽  
Microcrystalline Silicon ◽  
Porous Interface ◽  
Hydrogen Mixtures ◽  
Plasma Excitation ◽  
Excitation Frequencies ◽  
Quartz Substrates

AbstractMicrocrystalline silicon was prepared with glow discharge deposition from silane/hydrogen mixtures at plasma excitation frequencies in the range 13.56 MHz - 116 MHz. The influence of the plasma excitation frequency on the growth and the structural properties of the material is investigated. At high excitation frequencies, higher growth and etching rates, larger grain sizes with less disorder within the grains, higher crystalline volume fractions, a reduced amorphous but more porous interface layer on glass and quartz substrates, and faster nucleation on amorphous silicon substrates are obtained. The results are discussed within a schematical growth model.

Experimental Investigations Into Nonlinear Vibro-Acoustics for Detection of Delaminations in a Composite Laminate

2018 ◽  
Vol 2 (1) ◽  
Author(s):  
Ashish Kumar Singh ◽  
Vincent B. C. Tan ◽  
Tong Earn Tay ◽  
Heow Pueh Lee
Keyword(s):  
Frequency Dependence ◽  
Composite Laminate ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Experimental Investigations ◽  
Frequency Sweep ◽  
Ultrasonic Methods ◽  
Acoustic Methods ◽  
Different Depths ◽  
Excitation Frequencies

In recent years, nonlinear vibro-acoustic methods have shown potential to identify defects which are difficult to detect using linear ultrasonic methods. However, these methods come with their own challenges such as frequency dependence, requirement for a high excitation amplitude, and difficulties in distinguishing nonlinearity from defect with nonlinearity from other sources to name a few. This paper aims to study the dependence of nonlinear vibro-acoustic methods for detection of delaminations inside a composite laminate, on the excitation methods and excitation frequencies. It is shown that nonlinear vibro-acoustic methods are highly frequency dependent and commonly used excitation signals which utilize particular values of excitation frequencies might not always lead to a clear distinction between intact and delaminated regions of the specimen. To overcome the frequency dependence, signals based on frequency sweep are used. Interpretation of output response to sweep signals to identify damage is demonstrated using an earlier available approach, and a simpler approach is proposed. It is demonstrated that the damage detection with sweep signal excitations is relatively less dependent on excitation frequency than the conventional excitation methods. The proposed interpretation technique is then applied to specimens with delamination of varying sizes and with delaminations at different depths inside the laminate to demonstrate its effectiveness.

scholarly journals Maximization of Eigenfrequency Gaps in a Composite Cylindrical Shell Using Genetic Algorithms and Neural Networks

2019 ◽  
Vol 9 (13) ◽  
pp. 2754 ◽  
Author(s):  
Bartosz Miller ◽  
Leonard Ziemiański
Keyword(s):  
Genetic Algorithm ◽  
Neural Networks ◽  
Genetic Algorithms ◽  
Excitation Frequency ◽  
Algorithm Optimization ◽  
External Excitation ◽  
Excitation Frequencies ◽  
Objective Function Values ◽  
Using Data ◽  
Laminated Structures

This paper presents a novel method for the maximization of eigenfrequency gaps around external excitation frequencies by stacking sequence optimization in laminated structures. The proposed procedure enables the creation of an array of suggested lamination angles to avoid resonance for each excitation frequency within the considered range. The proposed optimization algorithm, which involves genetic algorithms, artificial neural networks, and iterative retraining of the networks using data obtained from tentative optimization loops, is accurate, robust, and significantly faster than typical genetic algorithm optimization in which the objective function values are calculated using the finite element method. The combined genetic algorithm–neural network procedure was successfully applied to problems related to the avoidance of vibration resonance, which is a major concern for every structure subjected to periodic external excitations. The presented examples illustrate a combined approach to avoiding resonance through the maximization of a frequency gap around external excitation frequencies complemented by the maximization of the fundamental natural frequency. The necessary changes in natural frequencies are caused only by appropriate changes in the lamination angles. The investigated structures are thin-walled, laminated one- or three-segment shells with different boundary conditions.

Large Grain Size and High Deposition Rate for Microcrystalline Silicon Prepared by VHF-GD

1994 ◽  
Vol 358 ◽  
Author(s):  
P. Hapke ◽  
F. Finger ◽  
M. Luysberg ◽  
R. Carius ◽  
H. Wagner
Keyword(s):  
Grain Size ◽  
Deposition Rate ◽  
High Frequency ◽  
Excitation Frequency ◽  
Chemical Vapour ◽  
High Deposition Rate ◽  
Very High Frequency ◽  
Deposition Parameters ◽  
Plasma Excitation ◽  
Very High

ABSTRACTThe growth mechanism and material properties of -type µc-Si:H prepared with plasma enhanced chemical vapour deposition in the very high frequency range is investigated. By increasing the plasma excitation frequency the grain size, deposition rate and Hall mobility can be simultaneously increased without having to adjust other deposition parameters in particular the temperature. This effect is explained by an enhanced selective etching of amorphous tissue and grain boundary regions together with a sufficient supply of growth species at high frequency plasmas.

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