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Publisher Summary A systemic approach to maintain, control, and prevent the oxygen doping of CNT-based IR detectors is presented in this chapter. It includes two different processes—oxygen removal by the vacuum thermal annealing and oxygen prevention by parylene C packaging. The photonic behavior of the oxygen-doped and the de-doped CNT-based IR detector are studied. The oxygen molecules removal by thermal annealing process provides significant improvement in the performance of the CNT-based devices and the contact resistances at the CNT–metal interfaces. The fabrication, thermal annealing process, and packaging process of CNT-based IR detectors are also presented. Furthermore, the CNT-based IR detectors, successfully fabricated and their IR responses and I-V characteristics are investigated. Experimental results indicated that the IR sensing ability of the packaged device. Moreover, the packaged CNT-based device was able to sustain and exhibit repeatable photoresponses for a long period of time, which could not be observed from the results of CNT-based devices without parylene C coating. It indicated that parylene C acted as an excellent packaging material, which not only protected CNT-based devices from oxygen contamination, but also improved the stability of the CNT device. Based on the current results, the thermal annealing process and packaging process may potentially become efficient methods to fabricate a CNT-based IR detector array with reliable performance.

Publisher Summary Carbon nanotubes (CNTs) are known to be a very unique material for various kinds of practical nanodevices. Due to large variations in electronic properties of CNTs and their extremely small size, a systemic approach for large-scale production of CNT-based nanodevices with consistent properties is still lacking. Manipulation and classification of CNTs is challenging and is not easily implemented by using the traditional robotic system. This chapter presents a new approach to classify and deposit nanotubes that provides an effective and reliable means to manufacture CNT-based devices. Homogeneous nanotubes can be precisely selected by using a microfluidic system and applying electrokinetic force to grade the nanotubes based on their electronic properties. Results indicated that directions of dielectrophoretic forces on different types of CNTs could be controlled by varying the frequency of the applied electric field. Repeatable and consistent experimental results of multiple CNT-based devices have been obtained by using the separation and deposition processes. Hence, the system provides a batch manipulation of CNTs for device manufacturing. As a result, this enhances the manufacturing and assembly of CNT-based nanodevices, which is important for the development of future nano-optoelectronic sensors and devices.

Publisher Summary This chapter demonstrates a new approach to manipulate and classify the graphene flake by choosing an optimal frequency of the applied electric field. In recent years, graphene has been the subject of increasing attention because it has a great potential for use in nano optoelectronics. Graphene is another novel nanomaterial and researchers have found a strong photoresponse near the graphene–metal interfaces. In addition graphene-based photodetectors can potentially be used for high-speed optical communications. The most common fabrication technique used for graphene-based nanostructures can be divided into two steps—first, electron beam lithography (EBL) is employed to pattern metal electrodes on a graphene. Then the resulting structures are etched by an oxygen plasma. However, plasma etching induces localization of charge carriers in graphene and changes its electronic properties. The disadvantages of EBL include its high cost and its low throughput. EBL machines are expensive and they also require substantial maintenance. Moreover, the patterning process takes a long time to complete because the electron beam is required to scan samples pixel by pixel. Discussion correlated the conductivity of the graphene flake with the frequency of the applied electric field. The theoretical prediction agrees well with the experimental results. With the ability to select high-conductivity graphene, the experimental result shows that graphene is a promising candidate for IR detection. The present study provides a systematic and reproducible method of selecting and separating high-conductivity graphene, which can also be used to manufacture novel IR nano sensors.

Publisher Summary This chapter discusses the five types of CNT field-effect transistors CNTFETs to investigate and improve the performance of CNT-based IR detectors. In the Au–CNT–Au CNTFET back-gate, the detector performance is improved by applying voltages to the back-gate, resulting in smaller dark current and higher Iphoto. Back-gate is capacitative-coupled to the CNT, and thus, application of Vg can electrostatically modulate the Fermi energy of CNT so as to control the Schottky barriers that are responsible for Iphoto generation. The Ag–CNT–Ag CNTFET back-gate produces higher Voc under IR illumination, since the built-in potential between Ag and CNT is higher than that of Au and CNT, showing the significance of metal workfunction. The two CNTFETs have symmetric metal structures, that constrain the performance of the detectors, because separated electrons and holes from one Schottky barrier need to tunnel through another barrier. In the Au–CNT–Ag CNTFET back-gate, an asymmetric metal structure is used, and both Iphoto and Voc are highly improved. The reason is that the electrons and holes from the Ag-CNT interface only needed to pass through a small barrier between Au and CNT before being collected. CNTFET with back-gate structure is easy to fabricate and provide valuable information for improving detector performance. However, the back-gate structure is not suitable for larger scale detector arrays, because the back-gate will modulate all detectors simultaneously. A middle-gate CNTFET was fabricated in order to control each detector independently. But a CNT detector with middle-gate structure and symmetric metal structure cannot deliver optimal performance. In order to find the optimal detector design, an asymmetric multigate CNTFET is introduced, with asymmetric metal structure and multiple gates, including back-gate, gates for source and drain, and middle gates.

In addition to using single-pixel photodetectors, infrared (IR) imaging plays an important role in industrial, medical, and military applications, but traditional IR imaging still has limited functions. Advances in IR cameras using nanomaterials has become an interesting topic. We will introduced an IR imaging system using carbon nanotube (CNT). Instead of a large-scale CNT detector array, the system requires only one pixel because of the use of compressive sensing. Initially, compressive sensing had fewer measurements than Nyquist—Shannon sampling rate but kept the main data on the observed signal. Nyquist—Shannon sampling theorem demands the sampling device must have higher bandwidth to catch the original signal. However, the problem is that there is increasing demand on faster data sampling technology for the current deluge data sensing and processing. Compressive sensing solved this problem. It provides a better solution for using fewer measurement but still can get the same measurement results of signals. Moreover, if the sensor itself has some limitations on power or sensing cell amounts which can only afford fewer measurement, compressive sensing has good performance to deal with this problem. As compressive sensing is involved, it realized the dream for using only one optical detector to sample the data and finally reconstruct the observed images. In addition, the theoretical analysis shows this CNT-based single-pixel IR camera can sense the data and reconstruct the observed IR image. In this chapter, couples of experiments have been set up, and the results perfectly support the compressive sensing theory.

Publisher Summary In this chapter, an electrical breakdown system for multiwalled CNTs (MWCNTs) is discussed to control the band gap of the MWCNT. The system plays an important role in the nanomanufacturing of CNT-based devices, and can be used as a reliable post treatment after the CNTs are deposited on the metal electrodes. The development of the system includes research into a real-time CNT electrical breakdown controller and an extended Kalman filter (EKF) for fault detection, which determines the breakdown status. By controlling the diameter of a MWCNT, a specific band gap material can be generated. The MWCNT consists of multilayer of carbon shells and can be either semiconducting or metallic. Theoretical and experimental studies have shown that the outermost layer of the MWCNT dominates the electrical conductivity of the MWCNT. To precisely adjust the band gap, one starts with a MWCNT with a relatively large diameter and small band gap. The electrical breakdown process is then used to remove the outermost layer of the MWCNT.

Publisher Summary In this chapter, a photodetector using a single indium antimonide (InSb) nanowire is shown to effectively detect infrared (IR) signals at room temperature. Indium antimonide nanowires with diameters of 10–35 nm and tens of microns long were grown by the vapor-liquid-solid approach using an InSb powder source and Au catalyst. The quantum confinement can modify the band gap energy when the diameter of the nanowires is smaller than the Bohr radius, making the fabrication of InSb photodetectors covering both near infra red and mid infra red in feasible. Both symmetric and asymmetric InSb nanowire photodetectors were fabricated and investigated under NIR and MIR irradiation. High quantum efficiency was observed for a 10-nm InSb nanowire photodetector at room temperature. The dark current of the nanowire detector was significantly reduced due to the nanoscale diameter of the wire and suppression of phonon scattering.

Publisher Summary This chapter deals with the fabrication and investigation of carbon nanotubes-based Schottky photodiodes using different metals and structures. It is found that the work functions of metals play an important role in determining the properties of the photodiodes. Symmetric Schottky photodiodes using different metals have varied dark current and photocurrent of several orders of magnitude. Low built-in potentials resulted in large dark current and photocurrent, while high built-in potentials caused smaller dark current and photocurrent. Two Schottky barriers reversely connecting with each other in the symmetric metal structure, which was verified by position-dependent photocurrent measurements, can explain this. In order to improve the performance of CNT-based Schottky photodiodes, asymmetric structure photodiodes using metals with high/low work functions at two contacts were fabricated. Compared to the symmetric photodiodes, asymmetric photodiodes had lower dark current and higher photocurrent.

Publisher Summary This chapter demonstrates photon confinement by photonic crystal for carbonnanotubes (CNT)-based infrared sensors (IR). The solution of light transmission in photonic crystal is an eigenvalue problem of electromagnetism. The photonic band gap of photonic crystal is related to the dielectric constant of two different dielectric media, lattice geometry and their sizes, and the transverse electrical field–and transverse magnetic field–like modes of an incident source. The quantum resonant nanocavity of photonic crystal enables the control of localization of an infrared source in the nanoscale area for performance enhancement of optical sensors. While designing photonic crystal with defective cavity, one should consider—the dielectric constant contrast and size of point defect to match with the resonant state of infrared light, and the lattice size arrangement to obtain max light energy in the point defect. These factors determine the performance of CNT-based IR sensors with photonic crystal.