High-quality Pt thin films are prepared by atomic layer deposition (ALD) using metal-organic precursors dimethyl-(N,N-dimethyl-3-butene-1-amine-N) platinum (C8H19NPt) and with diluted molecular oxygen (O2) as a reactant. The films are grown at a relatively low temperature of 225 °C on a thermally grown SiO2 substrate, and the process shows all the necessary qualities of an ideal ALD such as self-limiting growth characteristics and a well-defined ALD temperature window between 200 and 250 °C. Noticeably, the current ALD-Pt process shows a very high growth per cycle of 0.167 nm without an incubation period at 225 °C, and perfect conformality is obtained at a dual trench structure (top and bottom width: 40 and 15 nm) with an aspect ratio of around 6.3. The resistivity of the ALD-Pt film at ∼39 nm in thickness deposited at 225 °C is almost the same (∼10.8 μΩ cm) as its bulk resistivity (10.6 μΩ cm), and it is as low as ∼12 μΩ cm at 25 nm in thickness. Comprehensive analyses using x-ray photoelectron spectroscopy, x-ray diffractometry, transmission electron microscopy (TEM), and x-ray reflectance indicate that the extremely low resistivity of ALD-Pt is due to the formation of highly pure and polycrystalline films with high density (∼21.04 g/cm3) and large grain size (∼48 nm for 25 nm thick film). For comparison, ALD-Ru is deposited at the same equipment and deposition temperature, 225 °C, using (ethylbenzene)(1,3-butadiene)Ru(0) (C12H16Ru) and diluted O2 as the reactant. The higher resistivity of ∼20 μΩ cm at a similar thickness (∼23.5 nm) with ALD-Pt is obtained, which is much higher than its bulk value (7.6 μΩ cm). TEM analysis suggests that the formation of relatively smaller-sized grains of ALD-Ru is the main reason for it.
Natural gas hydrates (GHs) filling sand layer pores are the most promising GHs that can be produced via conventional mechanisms in deep-sea environments. However, the seismic tracking of such thin GH-bearing sand layers is subject to certain limitations. For example, because most GH-bearing sand layers are thin and sparsely interbedded with mud layers, conventional seismic data with a maximum resolution of ~10 m are of limited use for describing their spatial distribution. The 2010 Ulleung Basin drilling expedition identified a relatively good GH reservoir at the UBGH2-6 site. However, the individual GH-bearing sand layers at this site are thin and cannot therefore be reliably tracked using conventional seismic techniques. This study presents a new thin layer tracking method using stepwise seismic inversion and 3D seismic datasets with two different resolutions. The high-resolution acoustic impedance volume obtained is then used to trace thin layers that cannot be harnessed with conventional methods. Moreover, we estimate the high-resolution regional GH distribution based on GH saturation derived from acoustic impedance at UBGH2-6. The thin GH layers, previously viewed as a single layer because of limited resolution, are further subdivided, traced, and characterized in terms of lateral variation.
A B S T R A C TWe propose a full-waveform inversion algorithm using the Gauss-Newton inversion method with active constraint balancing that uses the spatially variant damping factor and source normalized wavefield approach for surface seismic data in the frequency domain. The active constraint balancing technique automatically determines the optimum distribution of damping factors that control the stability and resolution in Gauss-Newton inversion by using a parameter resolution matrix and spread function analysis. Through numerical experiments, we present that the active constraint balancing scheme provides stable inversion results without a severe loss of resolution compared with the conventional Gauss-Newton method. The reconstructed image using the active constraint balancing method more closely resembles the true image for the region with low sensitivity. Also, the estimated value converges faster to the smaller RMS error level than those estimated by the conventional Gauss-Newton method. We also implement the normalized wavefield method to overcome the lack of precise knowledge on the source. The source normalized wavefield approach effectively removes the potential inversion errors from source estimation because the source spectrum is eliminated during the normalization procedure. Our inversion algorithm, using the source normalization scheme, provides excellent inversion results even though the data are generated by two slightly different source wavelets. We present that the frequency selection scheme proposed by Sirgue and Pratt, which is based on the average amplitude of the whole received data, provides a useful guideline for selecting the proper frequencies for our inversion. Our novel inversion algorithm successfully reconstructs the velocity model within 10-30 iterations despite its starting from a homogeneous or linearly increasing velocity model. In addition, for testing the performance of our inversion algorithm on a more complicated structure, we apply the algorithm to the SEG/EAGE overthrust model. Successful inversion is achieved as the reconstructed image approaches the true model with the consistently converging RMS error even though insufficient data are used.
A case study on swell correction of Chirp sub-bottom profiler (SBP) data using multi-beam echo sounder (MBES) data
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