In this work, we present a method for targeted and maskless fabrication of single silicon vacancy (V Si ) defect arrays in silicon carbide (SiC) using focused ion beam. Firstly, we studied the photoluminescence (PL) spectrum and optically detected magnetic resonance (ODMR) of the generated defect spin ensemble, confirming that the synthesized centers were in the desired defect state. Then we investigated the fluorescence properties of single V Si defects and our measurements indicate the presence of a photostable single photon source. Finally, we find that the Si ++ ion to V Si defect conversion yield increases as the implanted dose decreases. The reliable production of V Si defects in silicon carbide could pave the way for its applications in quantum photonics and quantum information processing. The resolution of implanted V Si defects is limited to a few tens of nanometers, defined by the diameter of the ion beam.Silicon carbide (SiC) is a technologically mature semiconductor material, which can be grown as inch-scale high-quality single crystal wafers and has been widely used in microelectronics systems and high-power electronics, etc. In recent years, some defects in SiC have been successfully implemented as solid state quantum bit 1-8 and quantum photonics 9-11 . They meet essential requirements for spin-based quantum information processing such as optical initialization, readout and microwave control of the spin state, which are similar as the nitrogen vacancy (NV) centers in diamond. 12 In particular, silicon vacancy (V Si ) defect in 4H-SiC has increasingly attracted attention owing to its excellent features, such as non-blinking single photon emission and long spin coherence times which persist up to room temperature (about 160 µs). 3,5,13 These remarkable properties have been exploited in many applications in quantum photonics, 9,10 and quantum metrological studies such as high sensitivity magnetic sensing 14,15 and temperature sensing. 16 The V Si defect consists of a vacancy on a silicon site which exhibits a C 3v symmetry in 4H-SiC. 3,5 In order to extend its applications in quantum information science, it is essential to develop the technique of scalable efficient generation of single V Si defect arays in 4H-SiC. Since the collected fluorescence rate of a single V Si defect is modest with only about 10 kcps, 3,5,17 it is required to couple with some photonic devices to improve the counts towards the construction of photonics networks. 3,9,10,17,20 However, in order to realize the mode-maximum of photonic devices, it is necessary to place the V Si defects relative to the optimal position with sub-wavelength-scale precision. Previously there are three methods to generate V Si defect: the electron irradiation, neutron irradiation, and carbon implantation, however, these methods either can't control the position of the V Si defect, or need a electron beam lithography (EBL) pre-fabricated photoresist patterned mask, 3,5,9,17 which is not convenient for coupling to pre-fabricated photonic devices...

Partially or fully disordered proteins are instrumental for signal-transduction pathways; however, many mechanistic aspects of these proteins are not well-understood. For example, the number and nature of intermediate states along the binding pathway is still a topic of intense debate. To shed light on the conformational heterogeneity of disordered protein domains and their complexes, we performed single-molecule experiments by translocating disordered proteins through a nanopore embedded within a thin dielectric membrane. This platform allows for single-molecule statistics to be generated without the need of fluorescent labels or other modification groups. These studies were performed on two different intrinsically disordered protein domains, a binding domain from activator of thyroid hormone and retinoid receptors (ACTR) and the nuclear coactivator binding domain of CREB-binding protein (NCBD), along with their bimolecular complex. Our results demonstrate that both ACTR and NCBD populate distinct conformations upon translocation through the nanopore. The folded complex of the two disordered domains, on the other hand, translocated as one conformation. Somewhat surprisingly, we found that NCBD undergoes a charge reversal under high salt concentrations. This was verified by both translocation statistics as well as by measuring the ζ-potential. Electrostatic interactions have been previously suggested to play a key role in the association of intrinsically disordered proteins, and the observed behavior adds further complexity to their binding reactions.

Abstract:The Helium Ion Microscope (HIM) has the capability to image small features with a resolution down to 0.35 nm due to its highly focused gas field ionization source and its small beam-sample interaction volume. In this work, the focused helium ion beam of a HIM is utilized to create nanopores with diameters down to 1.3 nm. It will be demonstrated that nanopores can be milled into silicon nitride, carbon nanomembranes (CNMs) and graphene with well-defined aspect ratio. To image and characterize the produced nanopores, helium ion microscopy and high resolution scanning transmission electron microscopy were used. The analysis of the nanopores' growth behavior, allows inferring on the profile of the helium ion beam.Nanopores in atomically thin membranes can be used for biomolecule analysis, 1 electrochemical storage, 2 as well as for the separation of gases and liquids. 3 All of these applications require a precise control of the size and shape of the nanopores. It was shown that the focused beam of a transmission electron microscope (TEM) is able to create nanopores in membranes of silicon nitride and graphene with diameters down to 2 nm. 4,5 Pores can be further shrunk in a TEM by areal electron impact. 6 However, the preparation of such nanopores in a TEM is time-consuming and is limited to small samples (~3 mm diameter) that fit into the microscope. Focused ion beam tools (FIB) offer more flexibility concerning the sample size and a higher milling speed. Among these FIB tools gallium liquid metal ion sources (LMIS) are widely used, allowing minimum sizes of 3 nm diameter for nanopores. 7 The development of a reliable gas field ionization source (GFIS) type allowed the construction of the helium ion microscope which surpasses the imaging and milling resolution of 9 First studies about milling with helium ions reported sample damage by amorphization and helium implantation during milling on bulk substrates. 10 The latter effect is absent on membranes, where nanopores with diameters of 2.6 nm were milled by HIM. 11 In all these reports, pores were created by single spot exposures. Here we present a different route to create small nanopores in membranes by milling circular patterns. Furthermore we are able to connect the growth of nanopores to the ion beam profile.

Patterning with a focused ion beam (FIB) is an extremely versatile fabrication process that can be used to create microscale and nanoscale designs on the surface of practically any solid sample material. Based on the type of ion-sample interaction utilized, FIB-based manufacturing can be both subtractive and additive, even in the same processing step. Indeed, the capability of easily creating three-dimensional patterns and shaping objects by milling and deposition is probably the most recognized feature of ion beam lithography (IBL) and micromachining. However, there exist several other techniques, such as ion implantation- and ion damage-based patterning and surface functionalization types of processes that have emerged as valuable additions to the nanofabrication toolkit and that are less widely known. While fabrication throughput, in general, is arguably low due to the serial nature of the direct-writing process, speed is not necessarily a problem in these IBL applications that work with small ion doses. Here we provide a comprehensive review of ion beam lithography in general and a practical guide to the individual IBL techniques developed to date. Special attention is given to applications in nanofabrication.

Color centers in diamond are promising solid-state qubits for scalable quantum photonics applications. Amongst many defects, those with inversion symmetry are of an interest due to their promising optical properties. In this work, we demonstrate a maskless implantation of an array of bright, single germanium vacancy (GeV) centers in diamond. Employing the direct focused ion beam technique, single GeV emitters are engineered with the spatial accuracy of tens of nanometers. The single GeV creation ratio reaches as high as 53% with the dose of 200 Ge + ions per spot. The presented fabrication method is promising for future nanofabrication of integrated photonic structures with GeV emitters as a leading platform for spin-spin interactions.