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Two material removal modes in chemical mechanical polishing: mechanical plowing vs. chemical bonding
With the rapid development of semiconductors, the number of materials needed to be polished sharply increases. The material properties vary significantly, posing challenges to chemical mechanical polishing (CMP). Accordingly, the study aimed to classify the material removal mechanism. Based on the CMP and atomic force microscopy results, the six representative metals can be preliminarily classified into two groups, presumably due to different material removal modes. From the tribology perspective, the first group of Cu, Co, and Ni may mainly rely on the mechanical plowing effect. After adding H
2
O
2
, corrosion can be first enhanced and then suppressed, affecting the surface mechanical strength. Consequently, the material removal rate (MRR) and the surface roughness increase and decrease. By comparison, the second group of Ta, Ru, and Ti may primarily depend on the chemical bonding effect. Adding H
2
O
2
can promote oxidation, increasing interfacial chemical bonds. Therefore, the MRR increases, and the surface roughness decreases and levels off. In addition, CMP can be regulated by tuning the synergistic effect of oxidation, complexation, and dissolution for mechanical plowing, while tuning the synergistic effect of oxidation and ionic strength for chemical bonding. The findings provide mechanistic insight into the material removal mechanism in CMP.
Journal Article
QUEST FOR QUBITS
How small startups are vying with corporate behemoths for quantum supremacy. Building a quantum computer has gone from a far-off dream of a few university scientists to an immediate goal for some of the world's biggest companies. Tech giants Intel, Microsoft, IBM, and Google are all plowing tens of millions of dollars into quantum computing, which aims to harness quantum mechanics to vastly accelerate computation. Yet the contenders are betting on different technological horses: No one yet knows what type of quantum logic bit, or qubit, will power a practical quantum computer. Google, often considered the field's leader, has signaled its choice: tiny, superconducting circuits. Its group has built a nine-qubit machine and hopes to scale up to 49 within a year—an important threshold. At about 50 qubits, many say a quantum computer could achieve \"quantum supremacy\" and do something beyond the ken of a classical computer, such as simulating molecular structures in chemistry and materials science, or solving problems in cryptography. Small startup company ionQ, a decided underdog, is sticking with its preferred technology: trapped ions.
Journal Article
Grinding force assessment in tangential ultrasonic vibration-assisted grinding gear: Analytical model and experimental verification
Tangential ultrasonic vibration-assisted grinding gear (TUVAGG) is a new promising process combining the ultrasonic vibration with conventional grinding gear (CGG). In this study, an assessment of grinding forces from the point of theoretical and experimental was provided in TUVAGG, revealing its mechanism. Therefore, a prediction model of abrasive grain force was established based on the micro-removal mechanism of materials under ultrasonic vibration. First, the motion characteristics of a single abrasive grain were investigated in TUVAGG. Then, taking into account the two stages of the material removal mechanism, the grinding force model of the plowing stage and cutting stage is determined. Finally, TUVAGG experiments were performed to verify the developed model and to determine that the predicted results coincide with the experimental ones. The grinding force decreases with the increase in spindle speed and ultrasonic amplitude, but increases with the increase in feed speed and radial grinding depth. The prediction and experimental results show that the maximum difference between normal and tangential grinding forces is 12.63 and 14.82%, respectively. The developed model provides a deeper insight into the TUVAGG mechanism and a reference for practical technical applications.
Journal Article
A seven‐year study on the effects of four tillage modes on soil physicochemical properties, microbial biomass, enzymatic activities, and grain yield in a rice–ratoon rice cropping system
Ratoon rice is resource efficient to produce economically sound and environmentally sustainable rice production. However, there is no more information on the relative impact of soil tillage practices on soil physical and chemical properties, microbial biomass, and enzymatic activity, and grain yield in a rice–ratoon rice cropping system remains to be tested. Systematic study of soil under ratooning rice model is a problem to be solved in the development of ratooning rice model. This study primarily investigated the long‐term (from 2014 to 2020) changes in soil bulk density (BD), soil organic carbon (SOC) concentration, total nitrogen (TN) concentration, microbial biomass, β‐glucosidase activity (BG), urease activity (UR), and yield under four treatments: no‐tillage (NT), no plowing tillage + rotatory tillage (RT), plowing tillage in winter + rotatory tillage (PTW), and plowing tillage in spring + rotatory tillage (PTS). NT increased BD by 9.65%–12.97%, and RT increased the 20–40 cm soil layer BD by 8.80% in 2020, compared with the baseline initial value (in 2014). Plowing tillage (PT) time had no significant effect on BD. All tillage methods decreased the SOC concentration in the 0–20 cm soil layer, and only RT increased the TN concentration. PT was the only treatment that increased the SOC and TN concentrations in the 20–40 cm soil layer. Both the main‐season rice yield and the ratoon season rice yield ranked PTW > PTS > NT > RT, in which the main‐season rice yield increased by 28.15% and the ratoon season rice yield increased by 25.19% in PTW. Overall, the PTW treatment had the highest microbial biomass, enzyme activity, and grain yield compared with the other tillage methods. In conclusion, plowing tillage in winter + rotatory tillage is a more suitable tillage method under the mode of ratooning rice. A long‐term study on the effects of tillage on soil traits and yield in a rice–ratoon rice cropping system has been carried out. Plowing tillage in winter + rotatory tillage (PTW) maintains soil permeability at a depth of 0–40 cm. Independent of tillage methods and ratoon rice systems require increased SOM input to maintain C storage. PTW had the highest soil microbial biomass, soil enzyme activity, and grain yield.
Journal Article
Embracing uncertainty in applied ecology
1. Applied ecologists often face uncertainty that hinders effective decision-making. 2. Common traps that may catch the unwary are: ignoring uncertainty, acknowledging uncertainty but ploughing on, focussing on trivial uncertainties, believing your models, and unclear objectives. 3. We integrate research insights and examples from a wide range of applied ecological fields to illustrate advances that are generally underused, but could facilitate ecologists' ability to plan and execute research to support management. 4. Recommended approaches to avoid uncertainty traps are: embracing models, using decision theory, using models more effectively, thinking experimentally, and being realistic about uncertainty. 5. Synthesis and applications. Applied ecologists can become more effective at informing management by using approaches that explicitly take account of uncertainty.
Journal Article
Effect of long-term tillage on soil aggregates and aggregate-associated carbon in black soil of Northeast China
Soil tillage can affect the stability and formation of soil aggregates by disrupting soil structure. Frequent tillage deteriorates soil structure and weakens soil aggregates, causing them to be susceptible to decay. Different types of tillage systems affect soil physical properties and organic matter content, in turn influencing the formation of aggregates. The objective of this study was to evaluate the effect of long-term tillage on soil aggregates and aggregate-associated carbon in a black soil of Northeast China and to identify the optimal conservation tillage in this system. This research was conducted on a long-term tillage experimental field established in 1983 at the Jilin Academy of Agricultural Sciences, Gongzhuling, China. Plots were treated with four tillage systems including no tillage (NT), spacing tillage (ST), moldboard plowing (MP), and conventional tillage (CT). We took samples every 10cm from 0-60cm depth and demonstrated that water-stable soil aggregates >0.25mm in diameter accounted for over 66.0% of total aggregates for all tillage treatments, and the percentage for the ST treatment was 34.5% higher than in the other treatments. The NT treatment had the highest effect at 0-10cm depth, while the effect for the ST treatment was highest at 0-30cm. SOC storage decreased with soil depth, with a significant accumulation at 0-20cm depth. Across treatments, aggregate-associated C at a depth of 0-10cm was higher in the NT and ST treatments than in the MP and CT treatments. The advantage of the NT treatment weakened with soil depth, while the amount of aggregate-associated C remained higher for the ST treatment. There were more macro-aggregates in the ST and NT treatments than in the MP and CT treatments, while the MP and CT treatments had more micro-aggregates. The sum of macro-aggregate contributing rates for soil organic C (SOC) was significantly superior to that of the micro-aggregates. Water-stable aggregates increased by 34.5% in the ST treatment, effectively improving the soil structure. Furthermore, 0.25-1.00 and 1-2mm aggregates had the highest SOC storage and responded rapidly to the various tillage treatments. Hence, they can serve as indicators for the long-term influence of different tillage treatments on the distribution of aggregates and SOC.
Journal Article
Development of a frontal plow for smooth, furless plowing with cutoffs
The existing plows of smooth furless plowing do not provide a full turnover of layers within their own furrow and the incorporation of weeds, they have a high energy consumption. The aim of the study is to substantiate the parameters of the frontal plow cut-off, which ensures a high-quality performance of the technological process according to agrotechnical requirements with the lowest energy consumption during smooth furless plowing. An improved technology of smooth furrowless plowing has been developed, in which at first the seam is given a polygonal shape, then turned 180° within its own furrow. A frontal plow with offsets has been developed to implement the proposed technology. In the research, the laws and rules of theoretical mechanics, mathematical statistics, mathematical planning of experiments and methods of strain gauge were applied. It has been established by theoretical and experimental studies that when the frontal plow is cut off in the form of a triangular wedge, its height is 22 cm, the wing opening angle is 32°, the side edge angle is 36°, the required quality of smooth plowing is provided with the lowest energy consumption. With longitudinal distances between the plowshares of the body and the cut-off of at least 27 cm and between the disc coulter and the cut-off of 16 cm, the required quality of soil cultivation of the front plow is ensured in accordance with the established agro technical requirements.
Journal Article