Jun Chen

Gated field-emission arrays (FEAs) based on nanowires have significant applications in vacuum microelectronic devices. Controllable integration of nanowires in microstructures is a key issue to be solved in gated FEAs. Structural design is a general strategy for stress redistribution to regulate nanowire growth. As a model system, we identify microstructure-induced stress variation as a critical factor that governs nanowire growth and emission uniformity in gated ZnO nanowire FEAs. To overcome this problem, we propose an inner-gate structure to eliminate the stress release caused by vias for optimizing the growth of ZnO nanowires. The maximum emission current density (5.53 mA/cm2) and transconductance (2606 nS) obtained in this work are higher than those of the previously reported gated ZnO nanowire FEAs. Moreover, an anode probe is employed to measure the field-emission characteristics from a single pixel of inner-gate ZnO nanowire FEAs. The self-limiting current effect of ZnO nanowires is found to improve the pixel uniformity of the device. The addressing characteristics of the fabricated ZnO nanowire FEAs have been studied for flat-panel display applications. This work demonstrates that structure-stress engineering provides a general method for optimizing nanomaterial growth in microstructures.

We demonstrate an on-chip integrated vacuum nanodiode with a CsPbBr₃ sheet-cathode for direct electron detection. Under 5 keV electron irradiation at a beam current of 100 pA, the device achieves an on/off ratio of 248 at a cathode-anode bias of 15 V, enabling high contrast detection due to the low dark current of ~100 pA. At a bias of 23.5 V, the detection efficiency reaches 141%, exceeding the theoretical gain from impact ionization and thus enabling high sensitivity detection. This work extends vacuum nanodiodes to direct electron detection. The high responsivity and on‑chip integrability make the device promising for detector arrays in high-throughput multi-beam scanning electron microscopy.

Cold cathode flat-panel X-ray source (FPXS) holds promising applications in compact imaging, radiation therapy, food disinfection, and so on. Achieving uniform and high brightness emission is essential for realizing these applications. In this work, we demonstrate that uniform emission from a ZnO nanowire cold cathode FPXS operated under high power, larger than 200W. To realize high-power operation, the device uses liquid cooling to mitigate anode heat buildup. Experimental results confirm that this approach successfully achieves a high power of 201W in DC mode and 284.4W in pulsed mode. A maximum surface dose rate of 9.64Gy/min was achieved at DC anode voltage of 50kV. A significant improvement in uniformity was observed when the device operated under higher current, which is attributed to the self-ballasting effect inherent to the semiconductor ZnO nanowire emitters. A theoretical simulation of the self-ballasting effect was carried out, and the results fit well with experimental ones. High emission uniformity of 84.1% was achieved for the FPXS device. Furthermore, the high-power FPXS has successfully demonstrated both static and dynamic projection imaging capabilities. Our results are important for realizing the practical application of FPXS technology.

Finding alternative ways to reduce the field emission energy spread is highly significant for advancing high monochromatic electron sources. This work is proposed to utilize the fractional barrier shape of the metal tip structure, induced by the field concentration effect, to suppress the energy spread. Simulations indicated that the tip radius plays the most important role in the barrier shape among the geometrical parameters of the metal tip field emitter. As the tip radius decreased from 50 nm (where the barrier can be approximated as triangular) to 0.5 nm, the theoretical minimum of full width at half maximum (FWHM) of the energy spread at room temperature was reduced from ∼0.165 to ∼0.153 eV due to the fractional barrier shape. With further consideration of quantum confinement effect, this value could be reduced to ∼0.131 eV. The optimal tip radius for obtaining the minimum FWHM under an applicable emission current ranging from 1 to 100 nA was ∼1 nm. All results present the concept of modulating field emission electron energy spread by tailoring the barrier shape, which is useful for developing high monochromatic electron sources.