Material World Network: SWCNT Sensors: Interplay Between Schottky Barrier and Gas Adsorption

这是美国乔治城大学(GU)和莫斯科俄罗斯研究中心(RRC)库尔恰托夫研究所的联合项目，目的是解决一个非常具有挑战性的问题：识别碳纳米管(CNT)设备的传感机制。碳纳米管场效应晶体管(CNT-FET)作为纳米级、高灵敏度的化学传感器具有非凡的潜力。然而，到目前为止，还没有进行系统的研究来了解潜在的反应机制。一个直观且被广泛接受的解释是，分子与纳米管表面结合，纳米管和分子之间发生电荷转移。第二种可能性是纳米管和电触点之间界面处的肖特基势垒发生变化。该项目将通过使用专门设计的实验方法来确定响应机制，对碳纳米管设备与几种化学品的分析物分子之间的相互作用进行深入的实验和理论研究，这些化学物质包括空穴掺杂剂NO2和电子掺杂剂NH3。这项研究将包括孤立的碳纳米管、碳纳米管网络和用金属纳米颗粒装饰的纳米管，以及使用开尔文探针系统来测量形成电极或纳米颗粒的材料暴露在受控浓度的气体中时金属功函数的变化。样品制作、初步测试和金属电极功函数变化的测量将在GU进行，在那里将获得气室开尔文探头系统。作为不同气体浓度和湿度水平函数的样品响应的表征将仅在GU部分执行，并且主要在RRC执行。RRC Kurchat ov研究所的定制气体传感器测试设施可以控制几十ppb的分析物浓度和高达400摄氏度的样品温度变化。通过对一些制造的器件进行随温度变化的测量，该团队将测量肖特基势垒高度和碳纳米管导电通道的掺杂水平。这项研究将影响所有碳纳米管器件的应用，因为难以控制纳米管/电极界面及其对环境的敏感性是实现基于纳米管的集成电路的主要绊脚石之一。此外，如果不同的化学品涉及不同的机制，则可以通过只允许与目标化学品相对应的特定机制来设计选择性传感器。美国研究生将前往俄罗斯，在俄罗斯实验室使用设备对样品进行测试。高级调查人员还将访问俄罗斯，与俄罗斯同行举行年度会议。该奖项由材料研究部和国际科学与工程办公室共同资助。

This is a joint project between Georgetown University (GU), USA, and the Russian Research Centre (RRC) Kurchatov Institute in Moscow, with the goal to tackle a very challenging problem: identifying the sensing mechanism in carbon nanotube (CNT) devices. Carbon nanotube field effect transistors (CNT-FETs) have extraordinary potential as nanoscale, highly-sensitive chemical sensors. However, to date, no systematic study has been done to understand the underlying response mechanism. An intuitive and widely accepted explanation is that molecules bind to the surface of the nanotube and charge transfer occurs between the nanotube and the molecules. A second possibility is a change in the Schottky barrier at the interface between the nanotube and the electrical contacts. This project will conduct a thorough experimental and theoretical investigation of the interaction between carbon nanotube devices and analyte molecules for several chemicals, including hole dopants such as NO2, and electron dopants, such as NH3, by using experimental methods specifically designed to determine the response mechanism. This study will include isolated carbon nanotubes, carbon nanotube networks and nanotubes decorated with metal nanoparticles, as well as the use of a Kelvin Probe system to measure the change in the metal work-function for the materials forming the electrodes or the nanoparticles, upon exposure to a controlled concentration of gases. The sample fabrication, the preliminary testing and the measurements of the change in the work-function of the metal electrodes will be performed at GU, where a Gas-cell Kelvin probe system will be acquired. The characterization of the sample response as a function of concentration and humidity level for different gases will be performed only in part at GU and mainly at RRC. A custom built gas sensor testing facility at the RRC Kurchatov Institute allows control of analyte concentrations from several tens of ppb and variation of the sample temperature up to 400 degrees C. By performing measurements as a function of temperature on some of the fabricated devices the team will measure both the Schottky barrier height and the doping level of the CNT conducting channel. The modeling to analyze the experimental results will be done by the RRC group.This study will impact all carbon nanotube device applications, since the difficulty controlling the nanotube/electrode interface and its sensitivity to the environment is one of the major stumbling blocks for the realization of nanotube-based integrated circuits. Moreover, if different mechanisms are involved for different chemicals, it will be possible to design selective sensors by allowing only a specific mechanism, corresponding to a targeted chemical, to occur. The US graduate students will travel to Russia to participate in testing of the samples with the equipment in the Russian laboratory. The senior investigators will also visit Russia for a yearly meeting with the Russian counterpart.This award is co-funded by the Division of Materials Research and the Office of International Science and Engineering.