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Point defects in two-dimensional materials are of key interest for quantum information science. However, the parameter space of possible defects is immense, making the identification of high-performance quantum defects very challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS2, which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur ( Co S 0 ) and fabricate it with scanning tunneling microscopy (STM). The Co S 0 electronic structure measured by STM agrees with first principles and showcases an attractive quantum defect. Our work shows how HT computational screening and nanoscale synthesis routes can be combined to design promising quantum defects. Point defects in 2D semiconductors have potential for quantum computing applications, but their controlled design and synthesis remains challenging. Here, the authors identify and fabricate a promising quantum defect in 2D WS2 via high-throughput computational screening and scanning tunnelling microscopy. [ABSTRACT FROM AUTHOR]

New photoresists are needed to advance extreme ultraviolet (EUV) lithography. The tailored design of efficient photoresists is enabled by a fundamental understanding of EUV induced chemistry. Processes that occur in the resist film after absorption of an EUV photon are discussed, and a new approach to study these processes on a fundamental level is described. The processes of photoabsorption, electron emission, and molecular fragmentation were studied experimentally in the gas-phase on analogs of the monomer units employed in chemically amplified EUV resists. To demonstrate the dependence of the EUV absorption cross section on selective light harvesting substituents, halogenated methylphenols were characterized employing the following techniques. Photoelectron spectroscopy was utilized to investigate kinetic energies and yield of electrons emitted by a molecule. The emission of Auger electrons was detected following photoionization in the case of iodo-methylphenol. Mass-spectrometry was used to deduce the molecular fragmentation pathways following electron emission and atomic relaxation. To gain insight on the interaction of emitted electrons with neutral molecules in a condensed film, the fragmentation pattern of neutral gas-phase molecules, interacting with an electron beam, was studied and observed to be similar to EUV photon fragmentation. Below the ionization threshold, electrons were confirmed to dissociate iodo-methylphenol by resonant electron attachment. [ABSTRACT FROM AUTHOR]

As superconducting quantum processors increase in complexity, techniques to overcome constraints on frequency crowding are needed. The recently developed method of laser-annealing provides an effective post-fabrication method to adjust the frequency of superconducting qubits. Here, we present an automated laser-annealing apparatus based on conventional microscopy components and demonstrate preservation of highly coherent transmons. In addition, we perform noise spectroscopy to investigate the change in defect features, in particular, two-level system defects, after laser-annealing. Finally, we present a local heating model as well as demonstrate aging stability for laser-annealing on the wafer scale. Our work constitutes an important step toward both understanding the underlying physical mechanism and scaling up laser-annealing of superconducting qubits. [ABSTRACT FROM AUTHOR]

In order to increase computation power and efficiency, the semiconductor industry continually strives to reduce the size of features written using lithographic techniques. The planned switch to a shorter wavelength extreme ultraviolet (EUV) source presents a challenge for the associated photoresists, which in their current manifestation show much poorer photoabsorption cross sections for the same dose. Here we consider the critical role that an inner-shell electronic structure might play in enhancing photoabsorption cross sections, which one can control by the choice of substituent elements in the photoresist. In order to increase the EUV sensitivity of current photoresists, it is critical to consider the inner-shell atomic structure of the elements that compose the materials. We validate this hypothesis using a series of halogenated organic molecules, which all have similar valence structures, but differ in the character of their semi-core and deep valence levels. Using various implementations of timedependent density functional theory, the absorption cross sections are computed for the model systems of CH3X, X = H, OH, F, Cl, Br, I, as well as a representative polymer fragment: 2-methyl-phenol and its halogenated analogues. Iodine has a particularly high cross section in the EUV range, which is due to delayed absorption by its 4d electrons. The computational results are compared to standard database values and experimental data when available. Generally we find that the states that dominate the EUV oscillator strength are generated by excitations of deep valence or semi-core electrons, which are primarily atomic-like and relatively insensitive to the specific molecular structure. [ABSTRACT FROM AUTHOR]

Individual atomic defects in 2D materials impact their macroscopic functionality. Correlating the interplay is challenging, however, intelligent hyperspectral scanning tunneling spectroscopy (STS) mapping provides a feasible solution to this technically difficult and time consuming problem. Here, dense spectroscopic volume is collected autonomously via Gaussian process regression, where convolutional neural networks are used in tandem for spectral identification. Acquired data enable defect segmentation, and a workflow is provided for machine-driven decision making during experimentation with capability for user customization. We provide a means towards autonomous experimentation for the benefit of both enhanced reproducibility and user-accessibility. Hyperspectral investigations on WS2 sulfur vacancy sites are explored, which is combined with local density of states confirmation on the Au{111} herringbone reconstruction. Chalcogen vacancies, pristine WS2, Au face-centered cubic, and Au hexagonal close-packed regions are examined and detected by machine learning methods to demonstrate the potential of artificial intelligence for hyperspectral STS mapping. [ABSTRACT FROM AUTHOR]

Qubits made from superconducting materials are a mature platform for quantum information science application, such as quantum computing. However, material-based losses are now a limiting factor in reaching the coherence times needed for applications. In particular, knowledge of the atomistic structure and properties of the circuit materials is needed to identify, understand, and mitigate material-based decoherence channels. In this work, we characterize the atomic structure of the native oxide film formed on Nb resonators by comparing fluctuation electron microscopy experiments to density functional theory calculations, finding that an amorphous layer is consistent with an Nb2O5 stoichiometry. Comparing x-ray absorption measurements at the Oxygen K edge with first-principles calculations, we find evidence of d-type magnetic impurities in our sample, known to cause impedance in proximal superconductors. This work identifies the structural and chemical composition of the oxide layer grown on Nb superconductors and shows that soft x-ray absorption can fingerprint magnetic impurities in these superconducting systems. [ABSTRACT FROM AUTHOR]

Scanning polarization force microscopy was used to study the topography, polarizability, and contact potential of cleaved NaCl(100) as a function of the relative humidity (RH) between <5% and 40%. In this humidity range there are reversible changes in surface potential and polarizability, while large scale modifications in step topography and irreversible ion redistribution occur above 40% RH. In dry conditions the surface contact potential was more negative near atomic steps than over flat terraces. As humidity was increased, changes were observed in the local polarizability of the steps due to ionic solvation, and the contact potential of the terraces became more negative. At 40% RH surface-potential differences between steps and terraces could no longer be detected. These results are interpreted in terms of preferential anion solvation, initially localized near steps, and later spreading over the entire surface. [ABSTRACT FROM AUTHOR]

Scanning tunneling microscopy is used for examining the initial stages of water adsorption on the Pd(111) and Ru(0001) surface. The studies have shown that the water-Ru interaction is stronger than the water-Pd interaction, which is consistent with the hydrogen-bonded network formation and reduced water-metal bonding seen on Pd relative Ru.

The Pd-O phase diagram and the kinetic parameters of phase transformations in Pd(III) are determined using a photoemission spectroscometer. It is observed that on the Pd(III) surface, oxidation proceeds by formation of stable and metastable structures and bulk oxidation is a two-step process that starts with the metastable growth of the surface oxide upto the bulk, followed by a first-order transformation to PdO, explaining the oxidation/reduction hysteresis.

In this letter, we demonstrate that improved low energy electron absorption is achieved by suppressing the crystallinity of chromium thin-films grown on W[110], which points to a promising route for achieving highly efficient thermionic energy converters. Using low energy electron microscopy (LEEM) and in situ film growth, we show that substrate temperature control permits well-controlled fabrication of either epitaxial Cr[110] films or nanocrystalline Cr layers. We show that the work function of cesium saturated nanocrystalline Cr thin-films is ∼0.20 eV lower than that of epitaxial Cr[110] films. Our LEEM measurements of absorbed and reflected currents as a function of electron energy demonstrate that nanocrystallinity of cesiated chromium films results in 96% electron absorption in the range up to 1 eV above the work function, compared to just 79% absorption in cesiated crystalline Cr[110] films. These results point to metal films with suppressed crystallinity as an economical and scalable means to synthesize nanoengineered surfaces with optimized properties for next generation anode materials in high performance thermionic energy converters. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) and grazing incidence x-ray diffraction (GIXD) have been used to study the structure of self-assembled monolayers of CF3(CF2)n(CH2)2SH (n=11, 7, and 5) on the Au(111) surface. Surprisingly, although the nearest-neighbor fluorinated alkane thiol distance is very close to the lattice constant of a commensurate p(2×2) structure, the close-packed rows of molecules are rotated ∼30° with respect to the underlying gold lattice. That packing is incommensurate or at most only close to the high-order commensurate c(7×7) structure. The relative orientation of the organic monolayer and the Au(111) substrate has been determined unambiguously both with GIXD, and by AFM, taking advantage of an earlier finding (Ref. ) that AFM tips can reversibly displace the thiol molecules under high loads. In addition, we demonstrate that the two techniques provide complementary information on the order and the domain structures of these monolayers. [ABSTRACT FROM AUTHOR]

We have developed an open‐source, Python‐based software platform called ScopeFoundry for performing complex, multidimensional microscopy experiments that integrate diverse types of experimental hardware. ScopeFoundry streamlines experiment development by providing a modular environment where hardware controls and measurement schemes can be arranged and customized. Important software tasks such as data management and user interface generation are automated. Using this platform, we have implemented scanning Auger spectromicroscopy on a modified commercial surface analysis system. Spectromicroscopy produces multidimensional datasets with complete spectra at each image pixel, allowing for detailed analysis of material phases where Auger peaks may change in shape and position. Analysis of the surface phases of an advanced electron emission dispenser cathode is presented as an example. We describe the general ScopeFoundry platform, its application to Auger spectromicroscopy, and ways it can be applied to advance surface analysis and microscopy. [ABSTRACT FROM AUTHOR]

Near-field optical microscopies and spectroscopies seek to investigate materials by combining the best aspects of optical characterization and scan-probe microscopy techniques. In principle, this provides access to chemical, morphological, physical and dynamical information at nanometer length scales that is impossible to access by other means. But a number of challenges, particularly on the scan-probe front, have limited the widespread application of near-field investigations. This work describes how recent probe engineering and technique innovation have addressed many of these challenges. This Feature Article begins with a short overview of the field, providing perspective and motivation for these developments and highlighting some key improvements. This is followed by a more in-depth description of the near-field advances developed at the Molecular Foundry, a national nanoscience User Facility-advances that provide groundwork for generally-applicable nano-optical studies. Finally, a discussion is provided of what progress is still needed in order to realize the ultimate objective of translating all optical measurements to the nanoscale. [ABSTRACT FROM AUTHOR]

A high pressure photoemission system is described that combines differential pumping with an electrostatic lens system. This approach allows optimized differential pumping without loss of signal, thereby increasing the high-pressure performance by at least 2 orders of magnitude compared to passive differential pumping systems. A general analysis of aperture-based high-pressure photoemission is presented, followed by a description of the prototype system which has operated at pressures up to 7 mbar on a synchrotron beamline. Using this approach, photoemission experiments should be possible up to 100 mbar. Example data are presented for dielectric samples in gas atmospheres, for a copper catalyst under reaction conditions, and for liquid water in equilibrium with its vapor. [ABSTRACT FROM AUTHOR]

A new low-energy electron diffraction (LEED) system has been constructed with a pulse counting position sensitive detector using channel plates and a wedge and strip anode. The detector accepts diffracted electrons over a 120° angle and the LEED pattern is recorded as a 256 × 256 pixel image. Individual LEED spot intensities can be measured up to a maximum linear count rate of ∼ 5 kHz while the dark count rate is ∼0.02 Hz, yielding a dynamic range greater than 10[sup 5]. Incident beam currents for LEED measurements are ∼ 1 pA. Diffuse LEED intensities from disordered systems can be measured using the large dynamic range of this instrument. Examples of diffuse LEED measurements are presented. The low incident beam currents also allow for LEED intensity-voltage measurements on surfaces sensitive to electron beam damage and on nonconducting surfaces. [ABSTRACT FROM AUTHOR]

Describes a method for analyzing the external vibrations and intrinsic mechanical resonances affecting scanning probe microscopes by using the microscope as an accelerometer. Resonance modes of the beetle type scanning tunneling microscope (STM) head; Tunnel current noise measurements; Accelerometer measurements.

The Surface Forces Apparatus was used to study the compression and drainage of perfluoropolyethers (PFPEs) between two flat parallel mica surfaces. In the case of Zdols and Demnum-SA, the PFPEs can be squeezed out during slow compression to a final residual film one gyration diameter in thickness. This thickness remained constant up to the highest applied pressure of ∼10 MPa. The residual thickness for Demnum-SA, with one active end group, was found to be approximately 40% larger than that for Zdol of the same molecular weight, with two active end groups. In contrast, Z03, with no active end groups, could be displaced completely from the contact. The dynamics of expulsion were studied by monitoring the variation of the gap width as a function of time after fast (a few milliseconds) step increase in the compressive load. It was found that Zdol behaves as the bulk liquid down to gap widths of four equivalent gyration diameters. A viscosity increase of more than ten times was observed when the gap width was between four and two gyration diameters. Finally, slow compression to the maximum achievable pressure (∼10 MPa) led to a residual layer one gyration diameter in thickness trapped between the mica surfaces. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The de-wetting process of Zdol-type lubricants on hard disks has been studied at the molecular scale with scanning polarization force microscopy (SPFM) and ellipsometry. It was found that de-wetting occurred over hours to days when the initial lubricant layer was thicker than one monolayer (∼20 Å thick). De-wetting was found to take place in a layered fashion for Zdol-TX and Z-Tetraol, with weakly bound second layers accreting into droplets, however, no layering was seen for Zdol during de-wetting, only droplets. The droplets eventually grew to the point where they could be observed by optical microscopy. In all cases, the first monolayer remained bound to the surface. Although the atomic force microscopy (AFM) tip could easily penetrate this first layer, it did not remove it. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]