Selected publications

@article{D6DD00177G,

title = {AI-designed and AI-implemented control systems for bespoke scientific instrumentation: application to scanning microscopy},

author = {Ke Wang and David J. Ward and Matthew Ord and Boyao Liu and Andrew P. Jardine},

url = {http://dx.doi.org/10.1039/D6DD00177G},

doi = {10.1039/D6DD00177G},

year  = {2026},

date = {2026-05-08},

urldate = {2026-01-01},

journal = {Digital Discovery},

volume = {5},

issue = {6},

pages = {2448-2457},

publisher = {RSC},

abstract = {The pace of innovation in custom scientific instrumentation is frequently bottlenecked by the complexity of software engineering. While hardware designs evolve rapidly, developing robust and integrated control systems remains resource-intensive and often exceeds the software expertise available in experimental laboratories. Here, we present an AI-assisted workflow for constructing and validating an integrated control system for a bespoke scientific instrument, demonstrated on the Scanning Helium Microscope (SHeM). We emphasise that this work does not develop or train new AI models; instead, we use publicly accessible, general-purpose Large Language Models (LLMs) as practical engineering tools. Using these models, we co-develop a modular software stack spanning hardware interfaces, communication middleware, scan control, and user interfaces. To reduce the risk of deploying AI-generated code to fragile hardware, we introduced a digital sandbox that emulates instrument behaviour and supports pre-deployment verification, together with cross-validation using a second LLM and mandatory human review. We demonstrate successful deployment on a physical SHeM for 2D imaging and diffraction measurements, with behaviour consistent with a manually developed control system. This work provides a reproducible and safety-oriented template for AI-assisted software engineering in bespoke scientific instrumentation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{rys7-5t69,

title = {Determining adsorbate diffusion coefficients on surfaces from helium-3 spin-echo measurements of atomistic dynamics},

author = {Min Lin and Sam M. Lambrick and Andrew P. Jardine},

url = {https://link.aps.org/doi/10.1103/rys7-5t69},

doi = {10.1103/rys7-5t69},

year  = {2026},

date = {2026-02-12},

urldate = {2026-02-01},

journal = {Physical Review B},

volume = {113},

issue = {8},

pages = {085418},

publisher = {American Physical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{10.1063/5.0319099,

title = {Diffraction contrast imaging of hydrogen passivation of silicon using helium microscopy},

author = {Ke Wang and Abbie Lowe and Chenyang Zhao and Boyao Liu and David J. Ward and Holly Hedgeland and William Allison and Andrew P. Jardine and Paul C. Dastoor},

url = {https://doi.org/10.1063/5.0319099},

doi = {10.1063/5.0319099},

issn = {0003-6951},

year  = {2026},

date = {2026-01-01},

journal = {Applied Physics Letters},

volume = {128},

number = {11},

pages = {111604},

abstract = {Hydrogen is a key element in the transition to a sustainable energy future, playing a vital role in clean fuel technologies, energy storage, and semiconductor engineering. Yet despite its significance, hydrogen remains challenging to image directly, due to its low mass and weak interaction with conventional microscopy probes. In this study, we present the first direct spatially resolved image of hydrogen-passivated surfaces across large (mm) lateral length scales, obtained using scanning helium microscopy (SHeM), an emerging and exclusively surface-sensitive imaging technology based on neutral and extremely low-energy helium atom beams. Using HF:NH4F-treated Si(111) surfaces as a model system, we directly observe a strong contrast between hydrogen-passivated and non-passivated surfaces as well as localized heterogeneities within the nominally homogeneous hydrogen layer. These spatial features are further probed using temperature programmed desorption and helium diffraction measurements, confirming surface diffraction from the hydrogen-stabilized surface lattice, rather than topography or absorption, as the origin of the observed contrast. Our work establishes SHeM as a powerful tool for light-element surface imaging, with broad implications for hydrogen-related behaviors in many fields.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1002/adfm.75366b,

title = {Tracing Sub-Monolayer Contamination on Wafer-Scale 2D Materials},

author = {Chenyang Zhao and Sam M. Lambrick and Ke Wang and Shaoliang Guan and Aleksandar Radić and David J. Ward and Andrew P. Jardine and Boyao Liu},

url = {https://advanced.onlinelibrary.wiley.com/doi/abs/10.1002/adfm.75366},

doi = {https://doi.org/10.1002/adfm.75366},

year  = {2026},

date = {2026-01-01},

journal = {Advanced Functional Materials},

volume = {36},

number = {46},

pages = {e75366},

abstract = {ABSTRACT Trace amounts of sub-monolayer contamination impact the performance and reproducibility of 2D materials-based devices. Conventional characterization techniques have limited capability in detecting lightly-bound sub-monolayer contamination on wafer-scale. Scanning helium microscopy (SHeM), a non-destructive ultra-sensitive neutral-atom imaging and diffraction approach, is used to investigate surface cleanliness of monolayer and bulk MoS2. This study maps the growth and removal of adventitious carbon, a ubiquitous contaminant, which is found to grow on MoS2 even in ultra-high vacuum (UHV). This contamination can be removed by heating to $sim! 80^circ mathrmC$, though it reappears after cooling to room temperature for a few hours. By quantifying the rate of the contamination process across different regions with micrometer lateral resolution, it is found that flat regions are more susceptible to adventitious carbon contamination than delaminated regions. Furthermore, thermally activated desorption measurements reveal an activation energy of $sim!! 1 ,rm eV$ for adventitious carbon on MoS2. These findings highlight that surface cleanliness of 2D materials cannot be guaranteed even under UHV, and establish SHeM as a powerful tool for microscopic 2D material cleanliness characterization. The approach offers a new route to wafer-scale imaging of 2D material quality, with implications for improving device reproducibility and enabling clean industrial fabrication.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{10.1039/d6cp00967k,

title = {Quantum simulations of the ballistic motion of a surface adsorbate},

author = {Matthew Ord and Ziyou Lu and William Allison and Boyao Liu},

url = {https://doi.org/10.1039/d6cp00967k},

doi = {10.1039/d6cp00967k},

issn = {1463-9076},

year  = {2026},

date = {2026-01-01},

journal = {Physical Chemistry Chemical Physics},

volume = {28},

number = {28},

pages = {17708-17716},

abstract = {In thermal equilibrium, a surface adsorbate moves ballistically for short timescales and diffusively over longer timescales. The distinction between these regimes depends on the rate of energy transfer between the adsorbate and substrate, which is conventionally described in terms of friction. Motion in the ballistic regime is determined by the local adiabatic potential, independent of the friction, and measurements of ballistic motion should therefore reveal information about those local interactions. Here, we present a method for simulating ballistic motion by calculating the intermediate scattering function (ISF), which is directly accessible through experiment. We show, using a simple tight-binding argument, that the motion can be treated as that of an adsorbate with an effective mass, distinct from its actual mass. Furthermore, the effective mass is expected to be energy, and hence temperature, dependent. A more detailed quantum simulation demonstrates that the experimental ISF also depends on the initial state before scattering, a result that suggests it should be possible to identify the degree of localisation within the adsorbate site. These results establish a direct link between the quantum nature of the system and experiment, opening the door to future measurements.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1111/jmi.70038,

title = {Surface visualisation of bacterial biofilms using neutral atom microscopy},

author = {Nick A. Jeinsen and David J. Ward and Matthew Bergin and Sam M. Lambrick and David M. Williamson and Richard M Langford and Lisa F. Dawson and Vibhuti Rana and Sushma Shivaswamy and Xuening Zhou and Michelle Mikesh and Vernita D. Gordon and Brendan W. Wren and Katherine A. Brown and Paul C. Dastoor},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/jmi.70038},

doi = {https://doi.org/10.1111/jmi.70038},

year  = {2025},

date = {2025-10-03},

journal = {Journal of Microscopy},

abstract = {Abstract The scanning helium microscope (SHeM) is a new technology that uses a beam of neutral helium atoms to image surfaces non-destructively and with extreme surface sensitivity. Here, we present the application of the SHeM to image bacterial biofilms. We demonstrate that the SHeM uniquely and natively visualises the surface of the extracellular polymeric substance matrix in the absence of contrast agents and dyes and without inducing radiative damage.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{10.1063/5.0260104,

title = {Heliometric stereo: A new frontier in surface profilometry},

author = {Aleksandar Radić and Sam M. Lambrick and Chenyang Zhao and Nick A. Jeinsen and Andrew P. Jardine and David J. Ward and Paul C. Dastoor},

url = {https://doi.org/10.1063/5.0260104},

doi = {10.1063/5.0260104},

issn = {0021-8979},

year  = {2025},

date = {2025-01-01},

journal = {Journal of Applied Physics},

volume = {138},

number = {4},

pages = {044902},

abstract = {Accurate and reliable measurements of three-dimensional surface structures are important for a broad range of technological and research applications, including materials science, nanotechnology, and biomedical research. Scanning helium microscopy (SHeM) uses low-energy ( ∼ 64 meV) neutral helium atoms as the imaging probe particles, providing a highly sensitive and delicate approach to measuring surface topography. To date, topographic SHeM measurements have been largely qualitative, but with the advent of the heliometric stereo method—a technique that combines multiple images to create a 3D representation of a surface—quantitative maps of surface topography may now be acquired with SHeM. Here, we present and discuss two different implementations of heliometric stereo on two separate instruments, a single-detector SHeM and a multiple-detector SHeM. Both implementations show good accuracy (5% and 10%, respectively) for recovering the shape of a surface. Additionally, we discuss where heliometric stereo is most applicable, identify contrast features that can limit its accuracy, and discuss how to mitigate these limitations with careful design and sample choices that be readily implemented on current instruments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{10.1063/5.0247870,

title = {Minimizing interference in low-pressure supersonic beam sources},

author = {Jack Kelsall and Aleksandar Radić and John Ellis and David J. Ward and Andrew P. Jardine},

url = {https://doi.org/10.1063/5.0247870},

doi = {10.1063/5.0247870},

issn = {0021-9606},

year  = {2025},

date = {2025-01-01},

journal = {The Journal of Chemical Physics},

volume = {162},

number = {9},

pages = {094304},

abstract = {Free-jet atomic, cluster, and molecular sources are typically used to produce beams of low-energy, neutral particles and find application in a wide array of technologies, from neutral atom microscopes to instruments for surface processing. We present a simple analytical theory that is applicable to many of these sources, when (i) the nozzle-skimmer distance is such that free molecular flow is achieved and (ii) there is negligible interference within the skimmer itself. The utility of the model is demonstrated by comparing experimental data with calculations performed using the theory. In particular, we show that skimmer interference is negligible compared to attenuation by “background” gas for room-temperature beams. Our treatment does not depend on any free parameters and obviates the complexity of previous theories. As a result, we are able to devise a number of design recommendations to minimize interference in sources operating with cryogenic-temperature beams.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{RADIC2025113809,

title = {On the application of components manufactured with stereolithographic 3D printing in high vacuum systems},

author = {Aleksandar Radić and Sam Morgan Lambrick and Sam Rhodes and David James Ward},

url = {https://www.sciencedirect.com/science/article/pii/S0042207X24008558},

doi = {https://doi.org/10.1016/j.vacuum.2024.113809},

issn = {0042-207X},

year  = {2025},

date = {2025-01-01},

journal = {Vacuum},

volume = {232},

pages = {113809},

abstract = {We explore the ultrahigh-vacuum (UHV) compatibility of Formlabs ‘Clear Resin’ via vat photopolymerisation (VPP). We report on a method for using VPP additive manufacturing, specifically Formlabs’ widely available stereolithographic (SLA) printing using their ‘Clear Resin’ material, to rapidly and cheaply prototype components for use in high-vacuum (HV) environments. We present pump down curves and residual gas analysis to demonstrate the primary vacuum contaminant from freshly printed SLA plastics is water with no evidence of polymers outgassing from the material and thus the vacuum performance can be controlled with simple treatments which do not involve surface sealing. An unbaked vacuum system containing SLA printed components achieved 1.9 × 10-8mbar base pressure whilst retaining structural integrity and manufacturing accuracy. Outgassing rates in the HV test chamber and preliminary results in a UHV chamber indicate that our method can be extended to achieve ultrahigh-vacuum compatibility. We further report on the effect of atmospheric exposure to components and present evidence to suggest that water re-ad/absorption occurs exclusively on the surface, by showing that the bulk mass changes of the material is irreversible on the timescale investigated (<2weeks).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ZHAO2025114006,

title = {A multi-detector neutral helium atom microscope},

author = {C. Zhao and S. M. Lambrick and N. A. von Jeinsen and Y. Yuan and X. Zhang and A. Radić and D. J. Ward and J. Ellis and A. P. Jardine},

url = {https://www.sciencedirect.com/science/article/pii/S0042207X24010522},

doi = {https://doi.org/10.1016/j.vacuum.2024.114006},

issn = {0042-207X},

year  = {2025},

date = {2025-01-01},

urldate = {2025-01-01},

journal = {Vacuum},

volume = {234},

pages = {114006},

abstract = {Scanning helium microscopy (SHeM) is an emerging technique that uses a beam of neutral atoms to image and analyse surfaces. The low energies (∼64 meV) and completely non-destructive nature of the probe particles provide exceptional sensitivity for studying delicate samples and thin devices, including 2D materials. To date, around five such instruments have been constructed and are described in the literature. All represent the first attempts at SHeM construction in different laboratories, and use a single detection device. Here, we describe our second generation microscope, which is the first to offer multi-detector capabilities. The new instrument builds on recent research into SHeM optimisation and incorporates many improved design features over our previous instrument. We present measurements that highlight some of the unique capabilities the instrument provides, including 3D surface profiling, alternative imaging modes, and simultaneous acquisition of images from a mixed species beam.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Liu_2024b,

title = {Low-cost bidirectional coil driver with microamp precision},

author = {Boyao Liu and William Allison},

url = {https://doi.org/10.1088/1361-6501/ad4dce},

doi = {10.1088/1361-6501/ad4dce},

year  = {2024},

date = {2024-05-01},

journal = {Measurement Science and Technology},

volume = {35},

number = {8},

pages = {087001},

publisher = {IOP Publishing},

abstract = {We describe a compact constant current power supply with µA precision designed to drive coils. The unit generates currents from −125 mA to 125 mA with a load up to 10 Ω using a precision 16-bit digital to analogue converter, driven from a microcontroller (e.g. Raspberry Pi Pico). All power for the unit is derived from the 5 V of the microcontroller. As a demonstration of the capability of the power supply, it was applied to spin manipulation in a helium spin echo system.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{PhysRevLett.132.176202,

title = {Distinguishing Quasiparticle-Phonon Interactions by Ultrahigh-Resolution Lifetime Measurements},

author = {Boyao Liu and William Allison and Bo Peng and Nadav Avidor and Bartomeu Monserrat and Andrew P. Jardine},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.132.176202},

doi = {10.1103/PhysRevLett.132.176202},

year  = {2024},

date = {2024-04-01},

journal = {Physical Review Letters},

volume = {132},

issue = {17},

pages = {176202},

publisher = {American Physical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{PhysRevLett.132.056202,

title = {Experimental Characterization of Defect-Induced Phonon Lifetime Shortening},

author = {Boyao Liu and Jack Kelsall and David J. Ward and Andrew P. Jardine},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.132.056202},

doi = {10.1103/PhysRevLett.132.056202},

year  = {2024},

date = {2024-01-01},

journal = {Physical Review Letters},

volume = {132},

issue = {5},

pages = {056202},

publisher = {American Physical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{10.1063/5.0206374,

title = {3D surface profilometry using neutral helium atoms},

author = {Aleksandar Radić and Sam M. Lambrick and Nick A. Jeinsen and Andrew P. Jardine and David J. Ward},

url = {https://doi.org/10.1063/5.0206374},

doi = {10.1063/5.0206374},

issn = {0003-6951},

year  = {2024},

date = {2024-01-01},

journal = {Applied Physics Letters},

volume = {124},

number = {20},

pages = {204101},

abstract = {Three-dimensional mapping of surface structures is important in a wide range of biological, technological, healthcare, and research applications. Neutral helium atom beams have been established as a sensitive probe of topography and have already enabled structural information to be obtained from delicate samples where conventional probes would cause damage. Here, we empirically demonstrate, for the first time, a reconstruction of a complete surface profile using measurements from a modified scanning helium microscope using the heliometric stereo method and a single detector instrument geometry. Results for the surface profile of tetrahedral aluminum potassium sulfate crystals demonstrate that the areas of surfaces and facet orientations can be recovered to within 5% of the expected values.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Staszewski2023,

title = {Blue shifts in helium-surface bound-state resonances and quantum effects in cosine-law scattering},

author = {Luke Staszewski and Nadav Avidor},

doi = {10.1039/d3cp02291a},

issn = {1463-9084},

year  = {2023},

date = {2023-12-06},

urldate = {2023-12-06},

journal = {Physical Chemistry Chemical Physics},

volume = {25},

number = {47},

pages = {32632--32636},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {The scattering of gas from surfaces underpins technologies in fields such as gas permeation, heterogeneous catalysis and chemical vapour deposition. The effect of surface defects on the scattering is key in such technologies, but is still poorly understood. It is known empirically that unordered surfaces result-in random-angle scattering, with the effect thought to be classical. We here demonstrate the transition from quantum mechanical diffraction to cosine-scattering, and show that quantum bound-state resonances can greatly affect this transition. Further, we find that randomly distributed defects induce a blue-shift in the bound-state energies. We explore this phenomena, which can lay the basis for helium based quantum metrology of defects in 2D materials and material surfaces.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{PhysRevLett.131.236202,

title = {2D Helium Atom Diffraction from a Microscopic Spot},

author = {Nick A. Jeinsen and Sam M. Lambrick and Matthew Bergin and Aleksandar Radić and Boyao Liu and Dan Seremet and Andrew P. Jardine and David J. Ward},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.131.236202},

doi = {10.1103/PhysRevLett.131.236202},

year  = {2023},

date = {2023-12-01},

urldate = {2023-12-01},

journal = {Physical Review Letters},

volume = {131},

issue = {23},

pages = {236202},

publisher = {American Physical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lambrick2022,

title = {Observation of diffuse scattering in scanning helium microscopy},

author = {S. M. Lambrick and M. Bergin and D. J. Ward and M. Barr and A. Fahy and T. Myles and A. Radić and P. C. Dastoor and J. Ellis and A. P. Jardine},

doi = {10.1039/d2cp01951e},

issn = {1463-9084},

year  = {2022},

date = {2022-10-28},

urldate = {2022-10-28},

journal = {Physical Chemistry Chemical Physics},

volume = {24},

number = {43},

pages = {26539--26546},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {In understanding the nature of contrast in the emerging field of neutral helium microscopy, it is important to identify if there is an atom–surface scattering distribution that can be expected to apply broadly across a range of sample surfaces. Here we present results acquired in a scanning helium microscope (SHeM) under typical operating conditions, from a range of surfaces in their native state, i.e. without any specialist sample preparation. We observe diffuse scattering, with an approximately cosine distribution centred about the surface normal. The ‘cosine-like’ distribution is markedly different from those distributions observed from the well-prepared, atomically pristine, surfaces typically studied in helium atom scattering experiments. Knowledge of the typical scattering distribution in SHeM experiments provides a starting basis for interpretation of topographic contrast in images, as well as a reference against which more exotic contrast mechanisms can be compared.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ruckhofer2022,

title = {Evolution of ordered nanoporous phases during h-BN growth: controlling the route from gas-phase precursor to 2D material by in situ monitoring},

author = {Adrian Ruckhofer and Marco Sacchi and Anthony Payne and Andrew P. Jardine and Wolfgang E. Ernst and Nadav Avidor and Anton Tamtögl},

doi = {10.1039/d2nh00353h},

issn = {2055-6764},

year  = {2022},

date = {2022-10-24},

urldate = {2022-10-24},

journal = {Nanoscale Horizon},

volume = {7},

number = {11},

pages = {1388--1396},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {Large-area single-crystal monolayers of two-dimensional (2D) materials such as graphene and hexagonal boron nitride (h-BN) can be grown by chemical vapour deposition (CVD). However, the high temperatures and fast timescales at which the conversion from a gas-phase precursor to the 2D material appears, make it extremely challenging to simultaneously follow the atomic arrangements. We utilise helium atom scattering to discover and control the growth of novel 2D h-BN nanoporous phases during the CVD process. We find that prior to the formation of h-BN from the gas-phase precursor, a metastable (3 × 3) structure is formed, and that excess deposition on the resulting 2D h-BN leads to the emergence of a (3 × 4) structure. We illustrate that these nanoporous structures are produced by partial dehydrogenation and polymerisation of the borazine precursor upon adsorption. These steps are largely unexplored during the synthesis of 2D materials and we unveil the rich phases during CVD growth. Our results provide significant foundations for 2D materials engineering in CVD, by adjusting or carefully controlling the growth conditions and thus exploiting these intermediate structures for the synthesis of covalent self-assembled 2D networks.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Avidor2021,

title = {Probing surface motion above ambient temperature with helium spin-echo spectroscopy},

author = {Nadav Avidor},

doi = {10.1038/s42254-021-00387-2},

issn = {2522-5820},

year  = {2021},

date = {2021-10-12},

urldate = {2021-12-00},

journal = {Nature Reviews Physics},

volume = {3},

number = {12},

pages = {769--769},

publisher = {Springer Science and Business Media LLC},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bergin2021,

title = {Low-energy electron ionization mass spectrometer for efficient detection of low mass species},

author = {M. Bergin and D. J. Ward and S. M. Lambrick and N. A. von Jeinsen and B. Holst and J. Ellis and A. P. Jardine and W. Allison},

doi = {10.1063/5.0050292},

issn = {1089-7623},

year  = {2021},

date = {2021-07-01},

urldate = {2021-07-01},

journal = {Review of Scientific Instruments},

volume = {92},

number = {7},

publisher = {AIP Publishing},

abstract = {The design of a high-efficiency mass spectrometer is described, aimed at residual gas detection of low mass species using low-energy electron impact, with particular applications in helium atom microscopy and atomic or molecular scattering. The instrument consists of an extended ionization volume, where electrons emitted from a hot filament are confined using a solenoidal magnetic field to give a high ionization probability. Electron space charge is used to confine and extract the gas ions formed, which are then passed through a magnetic sector mass filter before reaching an ion counter. The design and implementation of each of the major components are described in turn, followed by the overall performance of the detector in terms of mass separation, detection efficiency, time response, and background count rates. The linearity of response with emission current and magnetic field is discussed. The detection efficiency for helium is very high, reaching as much as 0.5%, with a time constant of (198 ± 6) ms and a background signal equivalent to an incoming helium flux of (8.7 ± 0.2) × 106 s−1.</jats:p>},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lambrick2021,

title = {True-to-size surface mapping with neutral helium atoms},

author = {Sam M. Lambrick and Adrià Salvador Palau and Poul Erik Hansen and Gianangelo Bracco and John Ellis and Andrew P. Jardine and Bodil Holst},

doi = {10.1103/physreva.103.053315},

issn = {2469-9934},

year  = {2021},

date = {2021-05-00},

urldate = {2021-05-00},

journal = {Physical Review A},

volume = {103},

number = {5},

publisher = {American Physical Society (APS)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ward2021,

title = {Inter-adsorbate forces and coherent scattering in helium spin-echo experiments},

author = {David J. Ward and Arjun Raghavan and Anton Tamtögl and Andrew P. Jardine and Emanuel Bahn and John Ellis and Salvador Miret-Artès and William Allison},

doi = {10.1039/d0cp04539j},

issn = {1463-9084},

year  = {2021},

date = {2021-04-08},

urldate = {2021-04-08},

journal = {Physical Chemistry Chemical Physics},

volume = {23},

number = {13},

pages = {7799--7805},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {<p>Using helium atom scattering to identify adsorbate interactions and separate the effects of long and short range forces.</p>},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{PhysRevLett.126.155901,

title = {Ultrafast Diffusion at the Onset of Growth: O/Ru(0001)},

author = {Jack Kelsall and Peter S. M. Townsend and John Ellis and Andrew P. Jardine and Nadav Avidor},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.126.155901},

doi = {10.1103/PhysRevLett.126.155901},

year  = {2021},

date = {2021-04-01},

urldate = {2021-04-01},

journal = {Physical Review Letters},

volume = {126},

issue = {15},

pages = {155901},

publisher = {American Physical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bergin2020,

title = {Observation of diffraction contrast in scanning helium microscopy},

author = {M. Bergin and S. M. Lambrick and H. Sleath and D. J. Ward and J. Ellis and A. P. Jardine},

doi = {10.1038/s41598-020-58704-1},

issn = {2045-2322},

year  = {2020},

date = {2020-12-00},

urldate = {2020-12-00},

journal = {Scientific Reports},

volume = {10},

number = {1},

publisher = {Springer Science and Business Media LLC},

abstract = {Scanning helium microscopy is an emerging form of microscopy using thermal energy neutral helium atoms as the probe particle. The very low energy combined with lack of charge gives the technique great potential for studying delicate systems, and the possibility of several new forms of contrast. To date, neutral helium images have been dominated by topographic contrast, relating to the height and angle of the surface. Here we present data showing contrast resulting from specular reflection and diffraction of helium atoms from an atomic lattice of lithium fluoride. The signature for diffraction is evident by varying the scattering angle and observing sharp features in the scattered distribution. The data indicates the viability of the approach for imaging with diffraction contrast and suggests application to a wide variety of other locally crystalline materials.</jats:p>},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Raghavan2021,

title = {Alkali metal adsorption on metal surfaces: new insights from new tools},

author = {Arjun Raghavan and Louie Slocombe and Alexander Spreinat and David J. Ward and William Allison and John Ellis and Andrew P. Jardine and Marco Sacchi and Nadav Avidor},

doi = {10.1039/d0cp05365a},

issn = {1463-9084},

year  = {2020},

date = {2020-11-05},

urldate = {2021-04-08},

journal = {Physical Chemistry Chemical Physics},

volume = {23},

number = {13},

pages = {7822--7829},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {The adsorption of sodium on Ru(0001) is studied using 3He spin-echo spectroscopy (HeSE), molecular dynamics simulations (MD) and density functional theory (DFT). In the multi-layer regime, an analysis of helium reflectivity, gives an electron–phonon coupling constant of λ = 0.64 ± 0.06. At sub-monolayer coverage, DFT calculations show that the preferred adsorption site changes from hollow site to top site as the supercell increases and the effective coverage, θ, is reduced from 0.25 to 0.0625 adsorbates per substrate atom. Energy barriers and adsorption geometries taken from DFT are used in molecular dynamics calculations to generate simulated data sets for comparison with measurements. We introduce a new Bayesian method of analysis that compares measurement and model directly, without assuming analytic lineshapes. The value of adsorbate–substrate energy exchange rate (friction) in the MD simulation is the sole variable parameter. Experimental data at a coverage θ = 0.028 compares well with the low-coverage DFT result, giving an effective activation barrier Eeff = 46 ± 4 meV with a friction γ = 0.3 ps−1. Better fits to the data can be achieved by including additional variable parameters, but in all cases, the mechanism of diffusion is predominantly on a Bravais lattice, suggesting a single adsorption site in the unit cell, despite the close packed geometry.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lambrick2020,

title = {Multiple scattering in scanning helium microscopy},

author = {S. M. Lambrick and L. Vozdecký and M. Bergin and J. E. Halpin and D. A. MacLaren and P. C. Dastoor and S. A. Przyborski and A. P. Jardine and D. J. Ward},

doi = {10.1063/1.5143950},

issn = {1077-3118},

year  = {2020},

date = {2020-02-10},

urldate = {2020-02-10},

journal = {Applied Physics Letters},

volume = {116},

number = {6},

publisher = {AIP Publishing},

abstract = {<jats:p>Using atom beams to image the surface of samples in real space is an emerging technique that delivers unique contrast from delicate samples. Here, we explore the contrast that arises from multiple scattering of helium atoms, a specific process that plays an important role in forming topographic contrast in scanning helium microscopy (SHeM) images. A test sample consisting of a series of trenches of varying depths was prepared by ion beam milling. SHeM images of shallow trenches (depth/width < 1) exhibited the established contrast associated with masking of the illuminating atom beam. The size of the masks was used to estimate the trench depths and showed good agreement with the known values. In contrast, deep trenches (depth/width > 1) exhibited an enhanced intensity. The scattered helium signal was modeled analytically and simulated numerically using Monte Carlo ray tracing. Both approaches gave excellent agreement with the experimental data and confirmed that the enhancement was due to localization of scattered helium atoms due to multiple scattering. The results were used to interpret SHeM images of a bio-technologically relevant sample with a deep porous structure, highlighting the relevance of multiple scattering in SHeM image interpretation.</jats:p>},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tamtögl2020,

title = {Nanoscopic diffusion of water on a topological insulator},

author = {Anton Tamtögl and Marco Sacchi and Nadav Avidor and Irene Calvo-Almazán and Peter S. M. Townsend and Martin Bremholm and Philip Hofmann and John Ellis and William Allison},

doi = {10.1038/s41467-019-14064-7},

issn = {2041-1723},

year  = {2020},

date = {2020-01-14},

urldate = {2020-12-00},

journal = {Nature Communications},

volume = {11},

number = {1},

publisher = {Springer Science and Business Media LLC},

abstract = {The microscopic motion of water is a central question, but gaining experimental information about the interfacial dynamics of water in fields such as catalysis, biophysics and nanotribology is challenging due to its ultrafast motion, and the complex interplay of inter-molecular and molecule-surface interactions. Here we present an experimental and computational study of the nanoscale-nanosecond motion of water at the surface of a topological insulator (TI), BiTe. Understanding the chemistry and motion of molecules on TI surfaces, while considered a key to design and manufacturing for future applications, has hitherto been hardly addressed experimentally. By combining helium spin-echo spectroscopy and density functional theory calculations, we are able to obtain a general insight into the diffusion of water on BiTe. Instead of Brownian motion, we find an activated jump diffusion mechanism. Signatures of correlated motion suggest unusual repulsive interactions between the water molecules. From the lineshape broadening we determine the diffusion coefficient, the diffusion energy and the pre-exponential factor.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Avidor2019,

title = {PIGLE — Particles Interacting in Generalized Langevin Equation simulator},

author = {N. Avidor and P.S.M. Townsend and D.J. Ward and A.P. Jardine and J. Ellis and W. Allison},

doi = {10.1016/j.cpc.2019.04.013},

issn = {0010-4655},

year  = {2019},

date = {2019-09-00},

urldate = {2019-09-00},

journal = {Computer Physics Communications},

volume = {242},

pages = {145-152},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Townsend2019,

title = {Signatures of multiple jumps in surface diffusion on honeycomb surfaces},

author = {Peter S. M. Townsend and Nadav Avidor},

doi = {10.1103/physrevb.99.115419},

issn = {2469-9969},

year  = {2019},

date = {2019-03-13},

urldate = {2019-03-00},

journal = {Physical Review B},

volume = {99},

issue = {11},

pages = {115419},

publisher = {American Physical Society (APS)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lambrick2018,

title = {A ray tracing method for predicting contrast in neutral atom beam imaging},

author = {S.M. Lambrick and M. Bergin and A.P. Jardine and D.J. Ward},

doi = {10.1016/j.micron.2018.06.014},

issn = {0968-4328},

year  = {2018},

date = {2018-10-00},

journal = {Micron},

volume = {113},

pages = {61--68},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rittmeyer2016,

title = {Energy Dissipation during Diffusion at Metal Surfaces: Disentangling the Role of Phonons versus Electron-Hole Pairs},

author = {Simon P. Rittmeyer and David J. Ward and Patrick Gütlein and John Ellis and William Allison and Karsten Reuter},

doi = {10.1103/physrevlett.117.196001},

issn = {1079-7114},

year  = {2016},

date = {2016-11-03},

urldate = {2016-11-00},

journal = {Physical Review Letters},

volume = {117},

issue = {19},

pages = {196001},

publisher = {American Physical Society (APS)},

abstract = {Helium spin echo experiments combined with ab initio based Langevin molecular dynamics simulations are used to quantify the adsorbate-substrate coupling during the thermal diffusion of Na atoms on Cu(111). An analysis of trajectories within the local density friction approximation allows the contribution from electron-hole pair excitations to be separated from the total energy dissipation. Despite the minimal electronic friction coefficient of Na and the relatively small mass mismatch to Cu promoting efficient phononic dissipation, about (20 ±5)% of the total energy loss is attributable to electronic friction. The results suggest a significant role of electronic nonadiabaticity in the rapid thermalization generally relied upon in adiabatic diffusion theories.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Barr2016,

title = {Unlocking new contrast in a scanning helium microscope},

author = {M. Barr and A. Fahy and J. Martens and A. P. Jardine and D. J. Ward and J. Ellis and W. Allison and P. C. Dastoor},

doi = {10.1038/ncomms10189},

issn = {2041-1723},

year  = {2016},

date = {2016-04-22},

urldate = {2016-04-22},

journal = {Nature Communications},

volume = {7},

number = {10189},

publisher = {Springer Science and Business Media LLC},

abstract = {Delicate structures (such as biological samples, organic films for polymer electronics and adsorbate layers) suffer degradation under the energetic probes of traditional microscopies. Furthermore, the charged nature of these probes presents difficulties when imaging with electric or magnetic fields, or for insulating materials where the addition of a conductive coating is not desirable. Scanning helium microscopy is able to image such structures completely non-destructively by taking advantage of a neutral helium beam as a chemically, electrically and magnetically inert probe of the sample surface. Here we present scanning helium micrographs demonstrating image contrast arising from a range of mechanisms including, for the first time, chemical contrast observed from a series of metal–semiconductor interfaces. The ability of scanning helium microscopy to distinguish between materials without the risk of damage makes it ideal for investigating a wide range of systems.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rotter2016,

title = {Coupling between diffusion and orientation of pentacene molecules on an organic surface},

author = {Paul Rotter and Barbara A. J. Lechner and Antonia Morherr and David M. Chisnall and David J. Ward and Andrew P. Jardine and John Ellis and William Allison and Bruno Eckhardt and Gregor Witte},

doi = {10.1038/nmat4575},

issn = {1476-4660},

year  = {2016},

date = {2016-02-22},

urldate = {2016-04-00},

journal = {Nature Materials},

volume = {15},

number = {4},

pages = {397--400},

publisher = {Springer Science and Business Media LLC},

abstract = {The realization of efficient organic electronic devices requires the controlled preparation of molecular thin films and heterostructures. As top-down structuring methods such as lithography cannot be applied to van der Waals bound materials1, surface diffusion becomes a structure-determining factor that requires microscopic understanding. Scanning probe techniques provide atomic resolution, but are limited to observations of slow movements, and therefore constrained to low temperatures. In contrast, the helium-3 spin-echo (HeSE) technique achieves spatial and time resolution on the nm and ps scale, respectively, thus enabling measurements at elevated temperatures2. Here we use HeSE to unveil the intricate motion of pentacene admolecules diffusing on a chemisorbed monolayer of pentacene on Cu(110) that serves as a stable, well-ordered organic model surface3. We find that pentacene moves along rails parallel and perpendicular to the surface molecules. The experimental data are explained by admolecule rotation that enables a switching between diffusion directions, which extends our molecular level understanding of diffusion in complex organic systems.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lechner2013b,

title = {Quantum Influences in the Diffusive Motion of Pyrrole on Cu(111)},

author = {Barbara A. J. Lechner and Holly Hedgeland and John Ellis and William Allison and Marco Sacchi and Stephen J. Jenkins and B. J. Hinch},

doi = {10.1002/anie.201208868},

issn = {1521-3773},

year  = {2013},

date = {2013-03-26},

urldate = {2013-05-03},

journal = {Angewandte Chemie International Edition},

volume = {52},

number = {19},

pages = {5085--5088},

publisher = {Wiley},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{PhysRevLett.110.086103,

title = {Measurement of the Phason Dispersion of Misfit Dislocations on the Au(111) Surface},

author = {E. M. McIntosh and P. R. Kole and M. El-Batanouny and D. M. Chisnall and J. Ellis and W. Allison},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.110.086103},

doi = {10.1103/PhysRevLett.110.086103},

year  = {2013},

date = {2013-02-01},

journal = {Physical Review Letters},

volume = {110},

issue = {8},

pages = {086103},

publisher = {American Physical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jardine2010,

title = {Determination of the Quantum Contribution to the Activated Motion of Hydrogen on a Metal Surface: H/Pt(111)},

author = {A. P. Jardine and E. Y. M. Lee and D. J. Ward and G. Alexandrowicz and H. Hedgeland and W. Allison and J. Ellis and E. Pollak},

doi = {10.1103/physrevlett.105.136101},

issn = {1079-7114},

year  = {2010},

date = {2010-09-00},

urldate = {2010-09-00},

journal = {Physical Review Letters},

volume = {105},

number = {13},

publisher = {American Physical Society (APS)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hedgeland2009b,

title = {Measurement of single-molecule frictional dissipation in a prototypical nanoscale system},

author = {H. Hedgeland and P. Fouquet and A. P. Jardine and G. Alexandrowicz and W. Allison and J. Ellis},

doi = {10.1038/nphys1335},

issn = {1745-2481},

year  = {2009},

date = {2009-08-00},

urldate = {2009-08-00},

journal = {Nature Physics},

volume = {5},

number = {8},

pages = {561--564},

publisher = {Springer Science and Business Media LLC},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{JARDINE2009323,

title = {Helium-3 spin-echo: Principles and application to dynamics at surfaces},

author = {A. P. Jardine and H. Hedgeland and G. Alexandrowicz and W. Allison and J. Ellis},

url = {https://www.sciencedirect.com/science/article/pii/S0079681609000495},

doi = {https://doi.org/10.1016/j.progsurf.2009.07.001},

issn = {0079-6816},

year  = {2009},

date = {2009-01-01},

journal = {Progress in Surface Science},

volume = {84},

number = {11},

pages = {323-379},

abstract = {In this review we give a detailed description of the recently developed helium-3 spin-echo technique and its application to several classes of surface dynamic measurements. We review existing surface dynamical probes briefly and illustrate the need for new experimental tools that measure on nanoscale distances and over picosecond timescales. We then describe the helium-3 spin-echo method, which is one such tool, together with the approaches used to describe such measurements and the instrumentation developed to realise its application. The main application of helium-3 spin-echo is the study of surface dynamics, hence we review the approaches which have been established to interpret dynamical data and the signatures for various forms of motion, before going on to summarise the experimental studies to date. We also describe Fourier transform atom spectroscopy, a new method for measuring elastic and resonant scattering that is facilitated by the availability of spin-echo instruments. Finally, we look towards future scientific challenges for the technique.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Alexandrowicz2006,

title = {Onset of 3D Collective Surface Diffusion in the Presence of Lateral Interactions: Na/Cu⁡(001)},

author = {G. Alexandrowicz and A. P. Jardine and H. Hedgeland and W. Allison and J. Ellis},

doi = {10.1103/physrevlett.97.156103},

issn = {1079-7114},

year  = {2006},

date = {2006-10-00},

urldate = {2006-10-00},

journal = {Physical Review Letters},

volume = {97},

number = {15},

publisher = {American Physical Society (APS)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Fouquet2005,

title = {Thermal energy He3 spin-echo spectrometer for ultrahigh resolution surface dynamics measurements},

author = {P. Fouquet and A. P. Jardine and S. Dworski and G. Alexandrowicz and W. Allison and J. Ellis},

doi = {10.1063/1.1896945},

issn = {1089-7623},

year  = {2005},

date = {2005-05-01},

urldate = {2005-05-01},

journal = {Review of Scientific Instruments},

volume = {76},

number = {5},

publisher = {AIP Publishing},

abstract = {We present details of a He3 spin-echo spectrometer, designed to make possible a wide range of new surface dynamics measurements. The apparatus operates at beam energy of 8meV, sufficiently high to enable processes such as surface Bragg diffraction and permit inelastic and quasielastic scattering measurements at up to momentum transfers of about 4Å−1. We describe the requirements for the machine, details of the major components used to fulfil these requirements, and the performance of the overall spectrometer. The machine can access a Fourier time range of 0.01ps–1ns, and yields a resolution of 3μeV for inelastic spectrum reconstruction, although under favorable circumstances quasielastic broadenings as narrow as 20neV can be resolved, allowing correspondingly slower processes to be studied.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jardine2004,

title = {Ultrahigh-Resolution Spin-Echo Measurement of Surface Potential Energy Landscapes},

author = {Andrew P. Jardine and Shechar Dworski and Peter Fouquet and Gil Alexandrowicz and David J. Riley and Gabriel Y. H. Lee and John Ellis and William Allison},

doi = {10.1126/science.1098490},

issn = {1095-9203},

year  = {2004},

date = {2004-06-18},

journal = {Science},

volume = {304},

number = {5678},

pages = {1790--1793},

publisher = {American Association for the Advancement of Science (AAAS)},

abstract = {We demonstrate two approaches that use the recently developed helium spin-echo technique to measure surface potential energy landscapes. For helium–lithium fluoride (100), we use the selective adsorption phenomenon to obtain the complete experimental band structure of atoms in a corrugated surface potential. For carbon monoxide–copper (001), we measure the diffusion-induced energy broadening in the scattered helium beam and extract properties of the adsorbate-substrate potential. The measurements are made possible by the resolution of our new spectrometer, which improves on existing resolution by three orders of magnitude. We show that it is possible to produce benchmark energy landscapes to assist evaluation and development of first-principles theory in the problematic van der Waals/weak chemisorption regime.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Holst1997,

title = {An atom-focusing mirror},

author = {Bodil Holst and William Allison},

doi = {10.1038/36769},

issn = {1476-4687},

year  = {1997},

date = {1997-11-20},

journal = {Nature},

volume = {390},

number = {6657},

pages = {244--244},

publisher = {Springer Science and Business Media LLC},

keywords = {},

pubstate = {published},

tppubtype = {article}

}