| It is well known that many physical, chemical and biological evolution progresses are governed the thermal motions of atoms and molecules. In this sense, we can say that the atomic thermal motion is the most noteworthy natural process. In history, the heat-driven nature of chemical reactions was early recognized by human. By the development of modern science, more heat-driven processes were focused by scientists. This is not only because of thermal stability problems in the preparation of various nanoscale devices (quantum dots, nanowires, etc.), but also the requirement of designing new molecules and new materials with unusual physical and chemical characteristics. Although modem physics theory (e.g quantum field theory) has been fully developed, the prediction of thermal reaction rate is still a great trouble. Since in1889the empirical law of chemical reaction rates varying with temperature was proposed by Arrhenius, many chemical reaction rate theories have been developed. Among them transition state theory proposed in1935is the most famous one. However, for decades much practice shows that the transition state theory often biases with the experimental facts, even in orders of magnitude. Until now, the transition state theory has been developed into several complicated models, but eventhough it still cannot effectively change its deviation with actual results. Inheriting the old collision theory, modern molecular reaction dynamics developed in the fifties of last century has gone deep into the details of state-to-state reactions. Besides the above theories, more thermal reaction rate models, such as the RRKM theory, were developed. But due to its complication, modeling rate theoiy cannot be established. In this case, although for a specific thermal process a rate theory may be found to matchthe experimental data, we do not have a unique physical model to couver all the thermal processes, which leads to a lack of theoretical prediction techniques in modern nanomaterials and nanodevices design. We cannot know if a designed nano-system can stably exist at room temperature or under specific conditions, or at what temperature it would collapse.In recent years, many attentions have been focused on the discovery of the two-dimensional graphene. As the first low-dimensional materials in history, graphene is considered a potential new generation of materials with specific physical properties different from general three-dimensional materials. At the same time, we theoretically found the existence of one-dimensional monatomic carbon chains and proposed a tehcnique of preparing monatomic carbon chains from graphene. Thereafter, monatomic carbon chains were found in experiments and that confirmed our theoretical predictions. We hope to design a new generation of nanoscale devices based on one-dimensional and two-dimensional crystals, such as nano-scale rectifiers, to solve the quantum bottleneck of current IC technology. However, we need a theoretical model to predict whether these devices are able to stabilize.In this work, we attempt to solve the above problems, and proposed a statistical mechanical model to cover all the heat-driven processes. Firstly, the Maxwell distribution of kinetic energy of atomic thermal motions was demonstrated for atoms in condensed matter, as well as the gas phase, and established a thermodynamic statistical model based on single atoms but not the entire system to overcome the deficiencies of the transition state theory. This model is simple and easy in operations, and it can be convinently achieved in first-principle calculations. By molecular dynamics simulations and experimental data, we validated the reliability of this model. On this basis, we proposed the fabrications of electrical and optical devices based on monatomic carbon chains and analysis their life. The details are:1. Theoretically proposed a technique to mechanically pull monatomic carbon chains from single-layer graphene, and predicted the lifetime of carbon-chain-graphene structures, showing that a monatomic carbon chains of1cm in length has a lifetime of5×10years at room temperature, i.e. carbon chains are very stable. But metal atomic chains do not have such high stability. The above results have been verified by molecular dynamics simulations and experimental results.2. Theoretically simulated doped techniques to dope one or two kinds of atoms in monatomic carbon chains, and also predicted the stability of the doped carbon chains at room temperature. And a rectifier composed in coherent transport of boron and nitrogen doped carbon chains was designed and its stability was studied. By the results, carbon chains doped with boron and nitrogen atoms are very stable.3. For the large-scale delocalized quantum states existing in one-dimensional crystals, the quantum state instantly changes throughout the system when applying interaction on excite state-to-state transition at one end of the system. Such progress conflicts with relativistic causality, which means that transitions of delocalized states cannot be invoked by localized interactions. In this work, this basic physics question is discussed in the view of interactions between light and carbon chains, and the "contradiction" with relativistic causality is explained. On this basis, a tunable infrared laser based on monatomic carbon chains was designed, and its tuning range covers the lack of current tunable lasers. The pumping method of this tunable laser is very simple. High electro-optical conversion efficiency can be achieved by simple electric pumping.4. The property and structure of nanoclusters has a close relationship. Minor changes of nanocluster structures will significantly change their properties, and current experimental techniques could not accurately measure the structures of nanoclusters. Thus, the theoretical prediction is very important. In this work, the single-atom model was applied on the isomerization process of clusters and a theoretical model was proposed to judg formation probability of clusters isomers. The results show that the widely used free energy criterion is often not applicable in the cluster growth, while the single-atom model can give good predictions of cluster isomerization rate and lifetimes.5. In principle, the single-atom model can be also used for unimolecule chemical reactions which are dominated by internal conversions. In this work, single-atom model was applied to predict unimolecule reaction rates, and the model is extended to bimolecular reactions. To obtain accurate and trustable results, we selected a number of chemical reactions with reliable measured barriers, and their experimental rate data are compared with the single-atom model and traditional transition state theory. The results show that the single-atom model is in good agreement with experimental data, while the transition state theory has large deviation. Molecular dynamics simulations were employed for more strict verification because the reaction barriers can be accurately obtained by the interaction potential, and more importantly, no quantum effects are included. So, molecular dynamics simulations provide more reliable data to verify the single-atom model. By the results, the single-atom model is more accurate and practical than the tranditioncal transition state theory. |
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