Quantum Beam Sci., Volume 6, Issue 1 (March 2022) – 13 articles

Short-pulse ion beams have been developed in recent years and now enable applications in materials science. A tunable flux of selected ions delivered in pulses of a few nanoseconds can affect the balance of defect formation and dynamic annealing in materials. We report results from color center formation in silicon with pulses of 900 keV protons. G-centers in silicon are near-infrared photon emitters with emerging applications as single-photon sources and for spin-photon qubit integration. G-centers consist of a pair of substitutional carbon atoms and one silicon interstitial atom and are often formed by carbon ion implantation and thermal annealing. Here, we report on G-center formation with proton pulses in silicon samples that already contained carbon, without carbon ion implantation or thermal annealing. The number of G-centers formed per proton increased when we increased the pulse intensity from 6.9 × 10⁹ to 7.9 × 10¹⁰ protons/cm²/pulse, demonstrating a flux effect on G-center formation efficiency. We observe a G-center ensemble linewidth of 0.1 nm (full width half maximum), narrower than previously reported. Pulsed ion beams can extend the parameter range available for fundamental studies of radiation-induced defects and the formation of color centers for spin-photon qubit applications. Full article

Sputtering yields of Si have been measured for C₆₀ ions in the energy range from 10 to 540 keV, where the nuclear stopping is dominant, by measuring thickness change of a pre-amorphized layer with conventional Rutherford-backscattering spectroscopy. The measured sputtering yield shows the maximum, which is approximately 600 Si/C₆₀, around 100 keV. Comparing with the sputtering yields for a monatomic ion calculated both based on the linear-collision-cascade theory of Sigmund and using the SRIM2008 code, nonlinear effect on the sputtering yield has been observed. The nonlinear effect depends on the energy of C₆₀ ions: it is very large around the energies where the sputtering yield has the maximum and hardly observed at 10 keV. Full article

Three-dimensional laser scanning is a novel measurement technique that is frequently used for the documentation of cultural heritage (CH) objects. In the process of 3D scanning, one can obtain computing 3D models of artworks to be documented. It allows one to produce detailed digitized archives of important CH objects. Moreover, the use of 3D scanning enables the digital reconstruction of architectural fragments, sculptures, and other artworks. One more important application of this technique relates to the creation of molds and replicas for replacements of outdoor CH objects in case their preservation requirements do not allow them to remain in their original place due to the influence of environmental factors. One of the most effective ways of creating replicas is the use of laser additive technologies. Therefore, the combination of 3D scanning and additive technologies is a very promising way of preservation of CH. This paper describes several case studies concerned with the combined usage of 3D laser scanning and additive technologies for digital reconstruction and replication and of outdoor sculptures in St. Petersburg city. One of them is the reconstruction of the zinc sculpture “Eva at the fountain” (XIX century, England), which was destroyed during WWII. Its replica was created by means of laser stereolithography. Eventually, one more project is related to the reconstruction of the fragment of the sufficiently damaged cast-iron XIX century monument. This object was reconstructed using two laser technologies: direct metal laser sintering (DMLS), and laser cladding (LC). Full article

Laser–plasma proton sources and their applications to preclinical research has become a very active field of research in recent years. In addition to their small dimensions as compared to classical ion accelerators, they offer the possibility to study the biological effects of ultra-short particle bunches and the correspondingly high dose rates. We report on the design of an experimental setup for the irradiation of cell cultures at the L2A2 laboratory at the University of Santiago de Compostela, making use of a 1.2 J Ti: Sapphire laser with a 10 Hz repetition rate. Our setup comprises a proton energy separator consisting of two antiparallel magnetic fields realized by a set of permanent magnets. It allows for selecting a narrow energy window around an adaptable design value of 5 MeV out of the initially broad spectrum typical for Target Normal Sheath Acceleration (TNSA). At the same time, unwanted electrons and X-rays are segregated from the protons. This part of the setup is located inside the target vessel of the L2A2 laser. A subsequent vacuum flange sealed with a thin kapton window allows for particle passage to external sample irradiation. A combination of passive detector materials and real-time monitors is applied for measurement of the deposited radiation dose. A critical point of this interdisciplinary project is the manipulation of biological samples under well-controlled, sterile conditions. Cell cultures are prepared in sealed flasks with an ultra-thin entrance window and analysed at the nearby Fundación Pública Galega Medicina Xenómica and IDIS. The first trials will be centred at the quantification of DNA double-strand breaks as a function of radiation dose. Full article

This article is devoted to the study of the possibility of the passivation of iron-based metallic materials. The experimental results obtained for the laser treatment of carbon steel model samples by the radiation of repetitively pulsed and continuous-wave 1.064 µm Nd:YAG lasers are described. It is shown that the laser treatment allows the formation of dense protection films, 62–77 microns thick, on the steel surface. The films enhance the anticorrosion properties of the metal. Exposure to laser radiation reduces the surface roughness (from R_a = 0.53 µm to R_a = 0.38 µm). Laser radiation power densities of 10.2 × 10⁵ W/cm² and 10.7 × 10⁵ W/cm² for these two laser generating modes, respectively, correspond to the optimum (in terms of the degree of corrosion resistance) modes of steel treatment. The conducted studies show that the application of Nd: YAG lasers is a promising method for the surface passivation of artworks created from steel and cast iron. One of the most promising applications of the proposed method for the anticorrosion protection of iron is the passivation of the surface of iron-based historical monuments. Full article

In this review work, the passage of charged and neutral beams through dielectric capillary guides is described from a uniform point of view of beams channeling in capillaries. The motion of beams into the hollow channels formed by the inner walls of capillaries is mainly determined by multiple small-angle scattering (reflection) and can be described in the approximation of surface channeling. It is shown that the surface interaction potential in the case of micro- and nano-capillaries is actually conditioned by the curvature of the reflecting surface. After presenting the analysis of previously performed studies on X-rays propagation into capillaries, which is valid for thermal neutrons, too, the surface channeling formalism is also developed for charged particle beams, in particular, moving in curved cylindrical capillaries. Alternative theories explaining experimental results on the beams passage through capillaries are based on simple thermodynamic estimates, on various diffusion models, and on the results of direct numerical simulations as well. Our work is the first attempt to explain the effective guiding of a charged beam by a capillary from the general standpoint of quantum mechanics, which made it possible to analytically explore the interaction potential for surface channeling. It is established that, depending on the characteristics of a projectile and a dielectric forming the channel, the interaction potential can be either repulsive or attractive; the limiting values of the potential function for the corresponding cases are determined. It has been demonstrated that the surface channeling behaviour can help in explaining the efficient capillary guiding for radiations and beams. Full article

This paper treats the characteristic topics of MeV/atom cluster ion beams produced using tandem accelerators both in the production stage and in the penetration stage from the viewpoint of fundamental processes. The former is related to atomic collisions in that production and decay of a cluster ion $C_n{}^{+} (n=1-4)$ colliding with a charge-changing rare gas underlined through the electron-loss process. Regarding the latter, relatively small carbon clusters $C_n{}^{+} (n=2-10)$ are treated. The reduction effect of the average charge of cluster ions in a material is first presented. Next, the electronic stopping power and the energy loss, the polarization force, and the coulomb explosion under cluster-ion impact are described in the dielectric function form. Alignment and structure effects are stressed. As a large and highly symmetric cluster, the electronic stopping power and the average charge are shown for a C₆₀ cluster ion moving inside a solid. Throughout the paper, it is emphasized that the vicinage effect originating from correlation on spatial structure and orientation of constituent ions plays the key role. Moreover, results obtained in cluster production and penetration phenomena are mostly different from multiplication of those under single-ion impact. Full article

The ever-growing interest in additive manufacturing (AM) is evidenced by its extensive utilisation to manufacture a broad spectrum of products across a range of industries such as defence, medical, aerospace, automotive, and electronics. Today, most laser-based AM is carried out by employing continuous-wave (CW) and long-pulsed lasers. The CW and long-pulsed lasers have the downside in that the thermal energy imparted by the laser diffuses around the irradiated spot and often leads to the creation of heat-affected zones (HAZs). Heat-affected zones may degrade the material strength by producing micro-cracks, porous structures and residual stresses. To address these issues, currently, attempts are being made to employ ultrafast laser sources, such as femtosecond (fs) lasers, in AM processes. Femtosecond lasers with pulse durations in the order of ${10}^{-15}$s limit the destructive laser–material interaction and, thus, minimise the probability of the HAZs. This review summarises the current advancements in the field of femtosecond laser-based AM of metals and alloys. It also reports on the comparison of CW laser, nanosecond (ns)/picosecond (ps) lasers with fs laser-based AM in the context of heat-affected zones, substrate damage, microstructural changes and thermomechanical properties. To shed light on the principal mechanisms ruling the manufacturing processes, numerical predictions are discussed and compared with the experimental results. To the best of the authors’ knowledge, this review is the first of its kind to encompass the current status, challenges and opportunities of employing fs lasers in additive manufacturing. Full article

Quartz (SiO₂) crystals possess intrinsic columnar pores perpendicular to (0001) surfaces, consisting of three- and six-membered ring (3MR and 6MR) structures of Si and O atoms. The diameters of the larger pores, i.e., 6 MRs, are ~0.49 nm, while the diameters of fullerene (C₆₀) ions are 0.7 nm, i.e., larger than either type of the pores. Transmission electron microscopy observation evidenced approximately two times longer ion tracks in the channeling condition, i.e., 0° incidence to (0001) surface, than an off-channeling condition, i.e., 7° incidence in this case, under 6 MeV C₆₀ ion injection. The track length at the 0° incidence decreases more steeply than that at the 7° incidence with decreasing the energy from 6 MeV to 1 MeV. Finally, the track lengths at the 0° and 7° incidences become comparable, i.e., the channeling-like effect disappears at 1 MeV irradiation. This study experimentally indicates that the channeling-like effect of C₆₀ ions is induced in quartz crystals, while the sizes of the channels are smaller than the C₆₀ ions. Full article

To boost the science case of MIRACLES, the time-of-flight backscattering spectrometer at the European Spallation Source (ESS), an optimized neutron guide system, is proposed. This systematic study resulted in an enhancement in the transport of cold neutrons, compared with the previous conceptual design, with wavelengths ranging from λ = 2 Å to 20 Å along the 162.5-m distance from source to sample. This maintained the undisturbed main focus of the instrument, viz, to carry out quasielastic and inelastic neutron scattering (QENS and INS) experiments on a large dynamic range and for both energy-gain and energy-loss sides. To improve the collection of cold neutrons from the source and direct them to the sample position, the vertical geometry was adjusted to an adapted version of a ballistic elliptical profile. Its horizontal geometry was conceived to: (i) keep the high-resolution performance of the instrument, and (ii) minimize the background originating from fast and thermal neutrons. To comply with the first requirement, a narrow guide section at the pulse shaping chopper position has been implemented. To fulfil the second, a curved guide segment has been chosen to suppress neutrons with wavelengths λ < 2 Å. Subsequent tailoring of the phase space provided an efficient transport of cold neutrons along the beamline to reach a 3 × 3 cm² sample. Finally, additional calculations were performed to present a potential upgrade, with the exchange of the final segment, to focus on samples of approximately 1 × 1 cm²; the proposal anticipates a flux increase of 70% in this 1 cm² sample area. Full article

Electron beam irradiation into type-Ib diamond is known as a good method for the creation of high concentration negatively-charged nitrogen-vacancy (NV⁻) centers by which highly sensitive quantum sensors can be fabricated. In order to understand the creation mechanism of NV⁻ centers, we study the behavior of substitutional isolated nitrogen (P1 centers) and NV⁻ centers in type-Ib diamond, with an initial P1 concentration of 40–80 ppm by electron beam irradiation up to 8.0 × 10¹⁸ electrons/cm². P1 concentration and NV⁻ concentration were measured using electron spin resonance and photoluminescence measurements. P1 center count decreases with increasing irradiation fluence up to 8.0 × 10¹⁸ electrons/cm². The rate of decrease in P1 is slightly lower at irradiation fluence above 4.0 × 10¹⁸ electrons/cm² especially for samples of low initial P1 concentration. Comparing concentration of P1 centers with that of NV⁻ centers, it suggests that a part of P1 centers plays a role in the formation of other defects. The usefulness of electron beam irradiation to type-Ib diamonds was confirmed by the resultant conversion efficiency from P1 to NV⁻ center around 12–19%. Full article