Self-assembling materials are the building blocks of bottom-up nanofabrication processes, but they need to be templated to impose long-range order and eliminate defects. In this work, the self-assembly of a thin film of a spherical-morphology block copolymer is templated using an array of nanoscale topographical elements that act as surrogates for the minority domains of the block copolymer. The orientation and periodicity of the resulting array of spherical microdomains are governed by the commensurability between the block copolymer period and the template period and is accurately described by a free-energy model. This method, which forms high-spatial-frequency arrays using a lower-spatial-frequency template, will be useful in nanolithography applications such as the formation of high-density microelectronic structures.

We demonstrate Mach-Zehnder-type interferometry in a superconducting flux qubit. The qubit is a tunable artificial atom, the ground and excited states of which exhibit an avoided crossing. Strongly driving the qubit with harmonic excitation sweeps it through the avoided crossing two times per period. Because the induced Landau-Zener transitions act as coherent beamsplitters, the accumulated phase between transitions, which varies with microwave amplitude, results in quantum interference fringes for n = 1 to 20 photon transitions. The generalization of optical Mach-Zehnder interferometry, performed in qubit phase space, provides an alternative means to manipulate and characterize the qubit in the strongly driven regime.

We investigate the recovery of superconducting NbN-nanowire photon counters after detection of an optical pulse at a wavelength of 1550 nm, and present a model that quantitatively accounts for our observations. The reset time is found to be limited by the large kinetic inductance of these nanowires, which forces a tradeoff between counting rate and either detection efficiency or active area. Devices of usable size and high detection efficiency are found to have reset times orders of magnitude longer than their intrinsic photoresponse time. . Of particular interest would be a detector that combines ultrafast count rates (≥ GHz) with high single-photon detection efficiency at near-infrared wavelengths; however, current near-infrared photon-counting technologies such as avalanche photodiodes [6] and photomultiplier tubes [7] are limited to much lower count rates by long reset times.A promising detector technology was reported recently, in which ultrathin superconducting NbN wires are biased with a DC current I bias slightly below the critical value I C [8]. An incident photon of sufficient energy can produce a resistive "hotspot" which in turn disrupts the superconductivity across the wire, resulting in a voltage pulse. Observations of this photoresponse showed promise for high counting rates, with measured intrinsic response times as low as ∼30 ps [9], and counting rates in the GHz regime [10,11]. In this Letter, we present our own investigation into the counting-rate limitation of these devices, in which we directly observe the recovery of the detection efficiency as the device resets (after a detection event), and develop a quantitative model of this process. We find that detectors having both high detection efficiency and usable active area are limited to much lower count rates than studies of their intrinsic response time had suggested [9].We fabricated our nanowires using a newly developed process [12], on ultrathin (3 − 5 nm) NbN films [13]. We used several geometries, including straight nanowires having widths from 20−400 nm and lengths from 0.5−50 µm, as well as large-area "meander" structures [8,10] (e.g., Fig. 1(b)) having active-area aspect ratios from 1 − 50, fill factors from 25 − 50%, and sizes up to 10-µm square. The devices had critical temperatures T C ∼ 9 − 10 K, and critical current densities J C ∼ 2 − 5 × 10 10

Atomically thin molybdenum disulfide (MoS) is an ideal semiconductor material for field-effect transistors (FETs) with sub-10 nm channel lengths. The high effective mass and large bandgap of MoS minimize direct source-drain tunneling, while its atomically thin body maximizes the gate modulation efficiency in ultrashort-channel transistors. However, no experimental study to date has approached the sub-10 nm scale due to the multiple challenges related to nanofabrication at this length scale and the high contact resistance traditionally observed in MoS transistors. Here, using the semiconducting-to-metallic phase transition of MoS, we demonstrate sub-10 nm channel-length transistor fabrication by directed self-assembly patterning of mono- and trilayer MoS. This is done in a 7.5 nm half-pitch periodic chain of transistors where semiconducting (2H) MoS channel regions are seamlessly connected to metallic-phase (1T') MoS access and contact regions. The resulting 7.5 nm channel-length MoS FET has a low off-current of 10 pA/μm, an on/off current ratio of >10, and a subthreshold swing of 120 mV/dec. The experimental results presented in this work, combined with device transport modeling, reveal the remarkable potential of 2D MoS for future sub-10 nm technology nodes.

We have fabricated and tested superconducting single-photon detectors and demonstrated detection efficiencies of 57% at 1550-nm wavelength and 67% at 1064 nm. In addition to the peak detection efficiency, a median detection efficiency of 47.7% was measured over 132 devices at 1550 nm. These measurements were made at 1.8K, with each device biased to 97.5% of its critical current. The high detection efficiencies resulted from the addition of an optical cavity and anti-reflection coating to a nanowire photodetector, creating an integrated nanoelectrophotonic device with enhanced performance relative to the original device. Here, the testing apparatus and the fabrication process are presented. The detection efficiency of devices before and after the addition of optical elements is also reported.

We investigated electron-beam lithography with an aberration-corrected scanning transmission electron microscope. We achieved 2 nm isolated feature size and 5 nm half-pitch in hydrogen silsesquioxane resist. We also analyzed the resolution limits of this technique by measuring the point-spread function at 200 keV. Furthermore, we measured the energy loss in the resist using electron-energy-loss spectroscopy.

In this paper, we calculate the critical currents in thin superconducting strips with sharp right-angle turns, 180• turnarounds, and more complicated geometries, where all the line widths are much smaller than the Pearl length = 2λ 2 /d. We define the critical current as the current that reduces the Gibbs-free-energy barrier to zero. We show that current crowding, which occurs whenever the current rounds a sharp turn, tends to reduce the critical current, but we also show that when the radius of curvature is less than the coherence length, this effect is partially compensated by a radius-of-curvature effect. We propose several patterns with rounded corners to avoid critical-current reduction due to current crowding. These results are relevant to superconducting nanowire single-photon detectors, where they suggest a means of improving the bias conditions and reducing dark counts. These results also have relevance to normal-metal nanocircuits, as these patterns can reduce the electrical resistance, electromigration, and hot spots caused by nonuniform heating.

Templated self-assembly of block copolymer thin films can generate periodic arrays of microdomains within a sparse template, or complex patterns using 1:1 templates [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . However, arbitrary pattern generation directed by sparse templates remains elusive. Here, we show that an array of carefully spaced and shaped posts, prepared by electron-beam patterning of an inorganic resist, can be used to template complex patterns in a cylindrical-morphology block copolymer. We use two distinct methods: making the post spacing commensurate with the equilibrium periodicity of the polymer, which controls the orientation of the linear features, and making local changes to the shape or distribution of the posts, which direct the formation of bends, junctions and other aperiodic features in specific locations. The first of these methods permits linear patterns to be directed by a sparse template that occupies only a few percent of the area of the final self-assembled pattern, while the second method can be used to selectively and locally template complex linear patterns.Microphase separation of a block copolymer thin film can generate dense arrays of microdomains with periodicity as low as $10 nm (refs 6,16-19). Such arrays have been used as lithographic masks to pattern various functional materials, and to create devices including nanocrystal flash memory, nanowire transistors, gas sensors and patterned magnetic recording media [20][21][22][23][24][25] . Block copolymer thin film self-assembly on an unpatterned substrate leads to close-packed arrays of features such as lines or dots that lack long-range order, thus limiting their utility. As a result, both chemical and topographical substrate features have been used to template or guide block copolymer self-assembly, imposing long-range order and generating microdomain geometries not observed in untemplated films [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . These templates are often defined using electronbeam lithography (EBL) [3][4][5]7,8,11 , because of its ability to pattern small features of arbitrary geometry. However, the serial nature of EBL makes it clearly advantageous to minimize the density of the EBL-written features required to template a given arrangement of block copolymer microdomains. Even in a production context in which EBL is used only to write a master pattern that is to be replicated by some higher-throughput mechanism (such as nanoimprinting), the time required just to write the master can be prohibitively long. The challenge in template design is therefore to find a set of template features of minimum complexity that will deterministically program the block copolymer to form a desired final pattern, such as an interconnect level in an integrated circuit, which may contain both periodic and aperiodic features.We describe an approach to this problem that uses a sparse array of chemically functionalized topographical posts to control the self-assembly of dense linear block copolymer (BCP) stru...