Germanium nanowires: from synthesis, surface chemistry, assembly to devices

In order to continue the ever impressive and successful scaling pace of MOSFETs, tremendous research efforts have been spent to seek new materials to complement or replace Si as the Si-based ones are predicted to reach theoretical limits soon. Ge has low band gaps and high carrier mobilities, thus offering appealing potentials as a candidate of choice for future electronics. For the same purpose of discovering new materials, another area of interest is low dimensional nanostructures such as nanowires (NWs), owing to the facile synthesis, high structure perfection and superior properties. In this context, Ge NW has combined advantages and is particularly promising. I focus on this subject and have advanced in a wide range, from understanding and controlling synthesis and surface chemistry, to highly ordered assembly and devices with excellent performance

Complementary Symmetry Nanowire Logic Circuits: Experimental Demonstrations and in Silico Optimizations

Complementary symmetry (CS) Boolean logic utilizes both p- and n-type field-effect transistors (FETs) so that an input logic voltage signal will turn one or more p- or n-type FETs on, while turning an equal number of n- or p-type FETs off. The voltage powering the circuit is prevented from having a direct pathway to ground, making the circuit energy efficient. CS circuits are thus attractive for nanowire logic, although they are challenging to implement. CS logic requires a relatively large number of FETs per logic gate, the output logic levels must be fully restored to the input logic voltage level, and the logic gates must exhibit high gain and robust noise margins. We report on CS logic circuits constructed from arrays of 16 nm wide silicon nanowires. Gates up to a complexity of an XOR gate (6 p-FETs and 6 n-FETs) containing multiple nanowires per transistor exhibit signal restoration and can drive other logic gates, implying that large scale logic can be implemented using nanowires. In silico modeling of CS inverters, using experimentally derived look-up tables of individual FET properties, is utilized to provide feedback for optimizing the device fabrication process. Based upon this feedback, CS inverters with a gain approaching 50 and robust noise margins are demonstrated. Single nanowire-based logic gates are also demonstrated, but are found to exhibit significant device-to-device fluctuations

Silicon p-FETs from Ultrahigh Density Nanowire Arrays

Statistical numbers of field-effect transistors (FETs) were fabricated from a circuit of 17-nm-wide, 34-nm-pitch Si nanowires boron doped at a level of 10^(18) cm^(-3). Top-gated 4-μm-wide Si nanowire p-FETs yielded low off-currents (∼10^(-12) A), high on/off ratios (10^5−10^6), good on current values (30 μA/μm), high mobilities (∼100 cm^2/V−s), and low subthreshold swing values (∼80 mV/decade between 10^(-12) and 10^(-10) A increasing to 200 mV/decade between 10^(-10)−10^(-8) A)

Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors

The development of a robust method for integrating high-performance semiconductors on flexible plastics could enable exciting avenues in fundamental research and novel applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios. Here, we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO_2, a hazardous pollutant. We also use SiO_2 surface chemistries to construct a 'nano-electronic nose' library, which can distinguish acetone and hexane vapours via distributed responses. The excellent sensing performance coupled with bendable plastic could open up opportunities in portable, wearable or even implantable sensors

Process Knowledge-guided Autonomous Evolutionary Optimization for Constrained Multiobjective Problems

Various real-world problems can be attributed to constrained multi-objective optimization problems. Although there are various solution methods, it is still very challenging to automatically select efficient solving strategies for constrained multi-objective optimization problems. Given this, a process knowledge-guided constrained multi-objective autonomous evolutionary optimization method is proposed. Firstly, the effects of different solving strategies on population states are evaluated in the early evolutionary stage. Then, the mapping model of population states and solving strategies is established. Finally, the model recommends subsequent solving strategies based on the current population state. This method can be embedded into existing evolutionary algorithms, which can improve their performances to different degrees. The proposed method is applied to 41 benchmarks and 30 dispatch optimization problems of the integrated coal mine energy system. Experimental results verify the effectiveness and superiority of the proposed method in solving constrained multi-objective optimization problems.The National Key R&D Program of China, the National Natural Science Foundation of China, Shandong Provincial Natural Science Foundation, Fundamental Research Funds for the Central Universities and the Open Research Project of The Hubei Key Laboratory of Intelligent Geo-Information Processing.http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=4235hj2023Electrical, Electronic and Computer Engineerin

Tuning redox potentials of CO_2 reduction catalysts for carbon photofixation by Si nanowires

Si nanowires (SiNWs) are shown to absorb visible light to reduce Ni catalysts into Ni^0 compounds, enabling alkyne carboxylation reactions with CO_2 as a carbon feedstock. The reduced Ni catalysts are effective in CO_2 fixation through a 4-octyne carboxylation reaction. The reduction potentials of the Ni catalysts can be tuned from -1.35 to -0.51 V (vs. saturated calomel electrode) by altering the binding ligands. The results shed light on the nature of charge transfer from SiNWs to the catalyst for this new class of photocatalytic reactions. By controlling the CO_2 reduction potential of the catalysts with carefully ligand designs, it will bring more opportunities and options to realize the highly selective, effective and sustainable CO_2 reduction in the future