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Atomically precise hydrogen desorption lithography using scanning tunnelling microscopy (STM) has enabled the development of single-atom, quantum-electronic devices on a laboratory scale. Scaling up this technology to mass-produce these devices requires bridging the gap between the precision of STM and the processes used in next-generation semiconductor manufacturing. Here, we demonstrate the ability to remove hydrogen from a monohydride Si(001):H surface using extreme ultraviolet (EUV) light. We quantify the desorption characteristics using various techniques, including STM, X-ray photoelectron spectroscopy (XPS), and photoemission electron microscopy (XPEEM). Our results show that desorption is induced by secondary electrons from valence band excitations, consistent with an exactly solvable non-linear differential equation and compatible with the current 13.5 nm (~92 eV) EUV standard for photolithography; the data imply useful exposure times of order minutes for the 300 W sources characteristic of EUV infrastructure. This is an important step towards the EUV patterning of silicon surfaces without traditional resists, by offering the possibility for parallel processing in the fabrication of classical and quantum devices through deterministic doping. Scanning tunnelling microscopy-based H desorption lithography is used for atomic-scale patterning of quantum devices in Si, but its time-consuming nature hinders scalability. Here the authors report H desorption from Si(001):H surface using extreme-UV light and explore implications for patterning. [ABSTRACT FROM AUTHOR]

Two‐dimensional dopant layers (δ‐layers) in semiconductors provide the high‐mobility electron liquids (2DELs) needed for nanoscale quantum‐electronic devices. Key parameters such as carrier densities, effective masses, and confinement thicknesses for 2DELs have traditionally been extracted from quantum magnetotransport. In principle, the parameters are immediately readable from the one‐electron spectral function that can be measured by angle‐resolved photoemission spectroscopy (ARPES). Here, buried 2DEL δ‐layers in silicon are measured with soft X‐ray (SX) ARPES to obtain detailed information about their filled conduction bands and extract device‐relevant properties. This study takes advantage of the larger probing depth and photon energy range of SX‐ARPES relative to vacuum ultraviolet (VUV) ARPES to accurately measure the δ‐layer electronic confinement. The measurements are made on ambient‐exposed samples and yield extremely thin (< 1 nm) and dense (≈1014 cm−2) 2DELs. Critically, this method is used to show that δ‐layers of arsenic exhibit better electronic confinement than δ‐layers of phosphorus fabricated under identical conditions. [ABSTRACT FROM AUTHOR]

The progress of miniaturization in integrated electronics has led to atomic and nanometer‐sized dopant devices in silicon. Such structures can be fabricated routinely by hydrogen resist lithography, using various dopants such as P and As. However, the ability to non‐destructively obtain atomic‐species‐specific images of the final structure, which would be an indispensable tool for building more complex nano‐scale devices, such as quantum co‐processors, remains an unresolved challenge. Here, X‐ray fluorescence is exploited to create an element‐specific image of As dopants in Si, with dopant densities in absolute units and a resolution limited by the beam focal size (here ≈1 µm), without affecting the device's low temperature electronic properties. The As densities provided by the X‐ray data are compared to those derived from Hall effect measurements as well as the standard non‐repeatable, scanning tunneling microscopy and secondary ion mass spectroscopy, techniques. Before and after the X‐ray experiments, we also measured the magneto‐conductance, which is dominated by weak localization, a quantum interference effect extremely sensitive to sample dimensions and disorder. Notwithstanding the 1.5 × 1010 Sv (1.5 × 1016 Rad cm−2) exposure of the device to X‐rays, all transport data are unchanged to within experimental errors, corresponding to upper bounds of 0.2 Angstroms for the radiation‐induced motion of the typical As atom and 3% for the loss of activated, carrier‐contributing dopants. With next generation synchrotron radiation sources and more advanced optics, the authors foresee that it will be possible to obtain X‐ray images of single dopant atoms within resolved radii of 5 nm. [ABSTRACT FROM AUTHOR]

Dopant impurity species can be incorporated into the silicon (001) surface via the adsorption and dissociation of simple precursor molecules. Examples include phosphine (PH3), arsine (AsH3), and diborane (B2H6) for the incorporation of phosphorus, arsenic, and boron, respectively. Through exploitation of precursor surface chemistry, the spatial locations of these incorporated dopants can be controlled at the atomic scale via the patterning of a hydrogen lithographic resist layer using scanning tunneling microscopy (STM). There is strong interest in the spatial control of bismuth atoms incorporated into silicon for quantum technological applications; however, there is currently no known precursor for the incorporation of bismuth that is compatible with this STM-based lithographic method. Here, we explore the precursor chemistry (adsorption, diffusion, and dissociation) of bismuth trichloride (BiCl3) on Si(001). We show atomic-resolution STM images of BiCl3 exposed Si(001) surfaces at low coverage and combine this with density functional theory calculations to produce a model of the surface processes and the observed features. Our results show that, at room temperature, BiCl3 completely dissociates to produce bismuth ad-atoms, ad-dimers, and surface-bound chlorine, and we explain how BiCl3 is a strong candidate for a bismuth precursor compound compatible with lithographic patterning at the sub-nanometer scale. [ABSTRACT FROM AUTHOR]

Germanium has emerged as an exceptionally promising material for spintronics and quantum information applications, with significant fundamental advantages over silicon. However, efforts to create atomic‐scale devices using donor atoms as qubits have largely focused on phosphorus in silicon. Positioning phosphorus in silicon with atomic‐scale precision requires a thermal incorporation anneal, but the low success rate for this step has been shown to be a fundamental limitation prohibiting the scale‐up to large‐scale devices. Here, we present a comprehensive study of arsine (AsH3) on the germanium (001) surface. We show that, unlike any previously studied dopant precursor on silicon or germanium, arsenic atoms fully incorporate into substitutional surface lattice sites at room temperature. Our results pave the way for the next generation of atomic‐scale donor devices combining the superior electronic properties of germanium with the enhanced properties of arsine/germanium chemistry that promises scale‐up to large numbers of deterministically placed qubits. [ABSTRACT FROM AUTHOR]

Germanium has emerged as an exceptionally promising material for spintronics and quantum information applications, with significant fundamental advantages over silicon. However, efforts to create atomic‐scale devices using donor atoms as qubits have largely focused on phosphorus in silicon. Positioning phosphorus in silicon with atomic‐scale precision requires a thermal incorporation anneal, but the low success rate for this step has been shown to be a fundamental limitation prohibiting the scale‐up to large‐scale devices. Here, we present a comprehensive study of arsine (AsH3) on the germanium (001) surface. We show that, unlike any previously studied dopant precursor on silicon or germanium, arsenic atoms fully incorporate into substitutional surface lattice sites at room temperature. Our results pave the way for the next generation of atomic‐scale donor devices combining the superior electronic properties of germanium with the enhanced properties of arsine/germanium chemistry that promises scale‐up to large numbers of deterministically placed qubits. [ABSTRACT FROM AUTHOR]

It has been observed in scanning tunneling microscopy (STM) that the adsorption of molecules on the (001) surface of a Group IV semiconductor can lead to an asymmetric ordering of the dimers immediately adjacent to the adsorbate. This so-called pinning may occur along the dimer row on only one, or both sides of the adsorbate. Here we present a straightforward methodology for predicting such pinning and illustrate this approach for several different adsorbate structures on the Si(001) surface. This approach extends earlier work by including the effects of coupling across the adsorbate as well as the nearest-neighbor interactions between the chemisorbed dimer and its adjacent dimers. The results are shown to be in excellent agreement with the room temperature experimental STM data. The examples also show how this approach can serve as a powerful tool for discriminating between alternative possible adsorbate structures on a dimerized semiconductor (001) surface, especially in cases of molecular adsorption where the STM measurements provide insufficient details of the underlying atomic structure. [ABSTRACT FROM AUTHOR]

A detailed understanding of the chemical reactions of organic molecules with semiconductor surfaces will greatly aid schemes for the incorporation of organic functionality into existing technologies. In this paper we report on the reaction of acetaldehyde (CH3CHO) with silicon (001) as revealed by a combination of temperature-dependent scanning tunneling microscopy (STM) experiments and density functional theory (DFT). We observe that low-coverage exposures at room temperature result almost exclusively in the formation of a single adsorbate species. Conversion of this structure into thermodynamically favored bridge-bonded structures is achieved through temperature anneals between 150–250 °C. We determine the chemical identity of each of the experimentally observed species by comparison with DFT total energy calculations and simulated STM images. Calculations of transition states are used to formulate a full reaction pathway explaining the formation of the observed species. Excellent agreement is found between our experimental measurements and theoretical calculations. The results also present a picture consistent with our previous work on acetone and reveal a general reaction pattern for molecules containing the acetyl COCH3 functional group, where the initial attachment to the surface is mediated by a carbonyl C=O group. This suggests that modification of the residue R will facilitate in binding other electronically active molecules to the surface in a controlled fashion. [ABSTRACT FROM AUTHOR]

We demonstrate the locating and imaging of single phosphorus atoms and phosphorus dopant nanostructures, buried beneath the Si(001) surface using scanning tunneling microscopy. The buried dopant nanostructures have been fabricated in a bottom-up approach using scanning tunneling microscope lithography on Si(001). We find that current imaging tunneling spectroscopy is suited to locate and image buried nanostructures at room temperature and with residual surface roughness present. From these studies, we can place an upper limit on the lateral diffusion during encapsulation with low-temperature Si molecular beam epitaxy. [ABSTRACT FROM AUTHOR]

We present three important results relating to the fabrication of a quantum computer in silicon: (i) the interaction of the dopant gas phosphine with Si(001), (ii) a comparison of the morphology of epitaxial Si layers grown on clean and on monohydride-terminated Si(001), and (iii) a direct measure of the segregation/diffusion of incorporated P atoms during Si epitaxial growth and annealing. After low phosphine (PH[sub 3]) dosing of a Si(001) surface dual bias scanning tunneling microscopy was used to identify the PH[sub x](x = 2, 3) species on the surface. Subsequent annealing to 350°C resulted in the P atom from the PH[sub x] molecule being incorporated into the surface to form Si–P heterodimers. The threefold coordination that results from incorporation is expected to be advantageous for phosphorus quantum bit fabrication since it will reduce P segregation and diffusion during Si epitaxial overgrowth. One question to be addressed in the encapsulation process for quantum bits is whether the H resist layer needs to be removed or whether we can grow through the hydrogen layer. We demonstrate that five-monolayer-thick epitaxial Si layers deposited at low temperature (250°C) using molecular beam epitaxy have a significantly lower roughness and defect density when grown on a clean Si(001) surface compared to a H-terminated surface. Attempts to encapsulate phosphorus quantum bits at 260°C and to recover the surface quality of the epitaxial layer resulted in P atoms segregating and diffusing to the surface. These results suggest that the hydrogen layer is desorbed first before the P atoms are encapsulated in epitaxial silicon grown at very low temperature (below 250°C) to minimise phosphorus segregation. [ABSTRACT FROM AUTHOR]

The atomic scale structural and electronic characteristics of a silicon sample implanted with bismuth atoms are investigated using cross-sectional scanning tunneling microscopy (XSTM) and scanning tunneling spectroscopy (STS). We demonstrate that cleaving ion implanted samples provides an effective room temperature route for the preparation of atomically flat silicon surfaces with low defect density, preventing the diffusion of volatile impurities such as dopants. This enables atomic resolution STM studies of solitary implanted impurity atoms in their intrinsic silicon crystal sites and further allows us to map out a depth profile of the band-structure of the implanted area using STS. [ABSTRACT FROM AUTHOR]