Due to the development of high-frequency electronic devices, electromagnetic pollution has attracted global attention. Electromagnetic interference (EMI) shielding materials with low thickness, improved EMI shielding performance and lightweight are highly required for protecting the devices. Metal foams (MFs) and carbon-related materials have been successfully applied in EMI shielding. Herein, by utilizing the plasma-enhanced chemical vapor deposition (PECVD) method, high-quality vertical graphene nanowalls (VGNs) were prepared on Cu foam (CF) and Ni foam (NF) substrates. The combination of porous VGNs and MFs significantly improved their electrical conductivity, thus their EMI shielding performance was enhanced. The electrical conductivity of the VGNs/CF films could reach 4.81 × 106 S·m-1, increased by 15.3 % compared with the pristine CF films. At a frequency range of 8.2–12.4 GHz, the EMI shielding effectiveness values of VGNs/CF films with a thickness of ∼ 120 µm could reach 81.7 dB, increased by 25.9% compared with the pristine CF films. The VGNs/MF composite films with preferable EMI shielding effectiveness provide a new possibility for developing high-performance EMI shielding materials. 

Synthesis of high-quality vertical graphene nanowalls on metal foams and their applications in EMI shielding

Synthesis of High-Quality Vertical Graphene Nanowalls on Metal Foams and Their Applications in Emi Shielding

This work presents experimental results on the synthesis of carbon nanowalls (CNWs) with predefined morphology on the surface of nanoporous alumina membrane using method of radio-frequency plasma-enhanced chemical vapor deposition. Obtained samples were characterized by the methods of scanning electron microscopy and Raman spectroscopy. From the microstructure analyses of CNWs, it has been observed that there is a time dependence of the reproducibility of membrane morphology by CNWs. At the early stage of CNWs growth, CNWs grow preferably around the edges of nanopores and continue to grow vertically with time. Nanopores size begin to shrink drastically and pores are completely covered by secondary flake-like CNWs after 25 minutes of growth.

Obtaining of Carbon Nanowalls with A Specified Morphology

Flexible Pressure Sensors with a Sandwich Structure Based on Vertical Graphene Nanowalls by HFCVD

This work presents experimental results on the synthesis of carbon nanowalls (CNWs) with predefined morphology on the surface of nanoporous alumina membrane using method of radio-frequency plasma-enhanced chemical vapor deposition. Obtained samples were characterized by the methods of scanning electron microscopy and Raman spectroscopy. From the microstructure analyses of CNWs, it has been observed that there is a time dependence of the reproducibility of membrane morphology by CNWs. At the early stage of CNWs growth, CNWs grow preferably around the edges of nanopores and continue to grow vertically with time. Nanopores size begin to shrink drastically and pores are completely covered by secondary flake-like CNWs after 25 minutes of growth. 

Vertical graphene nanowalls (VGNs) with excellent heat-transfer properties are promising to be applied in the thermal management of electronic devices. However, high growth temperature makes VGNs unable to be directly prepared on semiconductors and polymers, which limits the practical application of VGNs. In this work, the near room-temperature growth of VGNs was realized by utilizing the hot filament chemical vapor deposition method. Catalytic tantalum (Ta) filaments promote the decomposition of acetylene at ∼1600 °C. Density functional theory calculations proved that C2H* was the main active carbon cluster during VGN growth. The restricted diffusion of C2H* clusters induced the vertical growth of graphene nanoflakes on various substrates below 150 °C. The direct growth of VGNs successfully realized the excellent interfacial contact, and the thermal contact resistance could reach 3.39 × 10-9 m2·K·W-1. The temperature of electronic chips had a 6.7 °C reduction by utilizing directly prepared VGNs instead of thermal conductive tape as thermal-interface materials, indicating the great potential of VGNs to be directly prepared on electronic devices for thermal management.

Near Room-Temperature Synthesis of Vertical Graphene Nanowalls on Dielectrics.

Hot Universe Baryon Surveyor (HUBS) is a proposed Chinese space mission to search for the so-called “missing baryons”. HUBS will focus on soft X-ray detection. The central part of the HUBS telescope is a soft X-ray spectrometer that uses a large transition-edge sensors array to detect the photon emission from a warm-hot intergalactic medium. The detector array comprises more than 3600 pixels. To read such a large number of pixels, a multiplexed readout technique is obligatory. We aim to develop a time-division multiplexed (TDM) readout system for HUBS. We choose TDM because it is the most mature and common one among various multiplexed readout techniques. We started by developing a proto-type TDM system that uses a single-stage SQUID readout. The basic multiplexing unit is composed of a SQUID series array (SSA) in parallel with a SQUID-based superconducting/normal conducting switch (SN switch). The SSA is composed of 16 individual SQUID cell that adopts a 1st order serial gradiometer design. The switch is also made of SQUID cells connected in series. The SQUID cell for a switch can comprise two Josephson junctions (JJs) like a usual DC-SQUID. It can also take the form of a Zappe interferometer that consists of four JJs. We will present the design and the simulation results of the sensor SQUID array and the SN switches.

Development of sensor SQUID and Zappe interferometer switch for HUBS


 The proximity effect to reduce the transition temperature of a superconducting film is frequently used in transition-edge sensors. Here, we developed these transition-edge sensors using Mo/Au/Au tri-layer films to detect soft X-rays. They were equipped with an overhanging photon absorber. We reduced the fabrication complexity by integrating the sensor patterning with the tri-layer film formation. We determined the electro-thermal parameters of the sensors through a series of resistance vs. temperature and current vs. voltage measurements. We also demonstrated their energy-resolving capability by using a 55Fe radioactive X-ray source. The best energy resolution was approximately 6.66 eV at 5.9 keV, with a theoretical count rate of 500 Hz.

Transition-Edge Sensors using Mo/Au/Au Tri-layer Films


 Superconducting quantum interference devices (SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors (TESs). The linear flux range is an important parameter for SQUID amplifiers, especially those controlled by high-bandwidth digital flux-locked-loop circuits. A large linear flux range helps to accurately measure the input signal and also allows increasing the multiplexing factor in the time-division multiplexed (TDM) readout scheme of the TES array. We report an improvement of the linear flux range of a SQUID using self-feedback effect. When an asymmetric SQUID loop is designed, a voltage-biased SQUID shows an asymmetric current-flux (I-Φ) response curve. The linear flux range is improved alongside the I-Φ curve with a shallow slope. The experimental results agree well with the numerical simulations. The asymmetric SQUID will sever as a building block in the development of the TDM readout systems for large TES arrays.

Bo Gao

Papers

Near Room-Temperature Synthesis of Vertical Graphene Nanowalls on Dielectrics.

Development of sensor SQUID and Zappe interferometer switch for HUBS

Transition-Edge Sensors using Mo/Au/Au Tri-layer Films

Increasing the linear flux range of SQUID amplifier using self-feedback effect

Characterizations of the electrothermal parameters of a transition edge sensor microcalorimeter and its energy resolution