Evaluating metal-organic precursors for focused ion beam-induced deposition through solid-layer decomposition analysis

• Benedykt R. Jany,
• Katarzyna Madajska,
• Aleksandra Butrymowicz-Kubiak,
• Franciszek Krok and
• Iwona B. Szymańska

Beilstein J. Nanotechnol. 2025, 16, 1942–1951, doi:10.3762/bjnano.16.135

• new metal-organic precursors, in the form of supported thick layers, to the ion beam irradiation is studied through analysis of the chemical composition and morphology of the resulting structures. This is done using SEM backscattered electron/energy-dispersive X-ray spectroscopy along with machine

• -dispersive X-ray spectroscopy (EDX); focused ion beam (FIB); focused ion beam-induced deposition (FIBID); machine learning; scanning electron microscopy (SEM); Introduction A variety of nanomanufacturing techniques, such as optical and electron-beam lithography, nanoimprint lithography, atomic layer

• or ion beam-induced deposition (FEBID/FIBID) allows for the precise fabrication of two- and three-dimensional nanostructures with well-defined shapes and dimensions ranging from 5 to 10 nm [1][5][6][7][8][9][10]. This high spatial resolution is achieved by precisely controlling the position and

Electrical, photocatalytic, and sensory properties of graphene oxide and polyimide implanted with low- and medium-energy silver ions

• Josef Novák,
• Eva Štěpanovská,
• Petr Malinský,
• Vlastimil Mazánek,
• Jan Luxa,
• Ulrich Kentsch and
• Zdeněk Sofer

Beilstein J. Nanotechnol. 2025, 16, 1794–1811, doi:10.3762/bjnano.16.123

• Department of Inorganic Chemistry, University of Chemistry and Technology, Prague 6, 166 28, Czech Republic Ion Beam Center, Helmholtz-Zentrum Dresden Rossendorf, 01328 Dresden, Germany 10.3762/bjnano.16.123 Abstract Precise control of electrical conductivity, humidity sensitivity, and photocatalytic

Laser processing in liquids: insights into nanocolloid generation and thin film integration for energy, photonic, and sensing applications

• Akshana Parameswaran Sreekala,
• Pooja Raveendran Nair,
• Jithin Kundalam Kadavath,
• Bindu Krishnan,
• David Avellaneda Avellaneda,
• M. R. Anantharaman and
• Sadasivan Shaji

Beilstein J. Nanotechnol. 2025, 16, 1428–1498, doi:10.3762/bjnano.16.104

Crystalline and amorphous structure selectivity of ignoble high-entropy alloy nanoparticles during laser ablation in organic liquids is set by pulse duration

• Robert Stuckert,
• Felix Pohl,
• Oleg Prymak,
• Ulrich Schürmann,
• Christoph Rehbock,
• Lorenz Kienle and
• Stephan Barcikowski

Beilstein J. Nanotechnol. 2025, 16, 1141–1159, doi:10.3762/bjnano.16.84

• analytical techniques, we can prove that carbon incorporation into HEA NPs via ns-LAL is observable as seen in Figure 6. We prepared a cross-section sample of an amorphous HEA NP from ns-LAL synthesis via focused ion beam (FIB) preparation and compared EELS signals originating from both the core and shell

Influence of ion beam current on the structural, optical, and mechanical properties of TiO₂ coatings: ion beam-assisted vs conventional electron beam evaporation

• Agata Obstarczyk and
• Urszula Wawrzaszek

Beilstein J. Nanotechnol. 2025, 16, 1097–1112, doi:10.3762/bjnano.16.81

• ) coatings deposited using electron beam evaporation (EBE) and ion beam-assisted deposition (IBAD) are presented. Post-process annealing at 800 °C was also conducted to examine its impact on the properties of the prepared coatings. After annealing at 800 °C, a transition from amorphous to the anatase phase

• occurred for all coatings. In particular, an increase in ion beam current led to a reduction in crystallite size by approximately 30% compared to coatings prepared by conventional EBE process. The average anatase crystallite size for annealed films was in the range of 30.8 to 43.5 nm. A detailed SEM

• , adhesive, and durable TiO2 coatings with improved optical and mechanical properties, suitable for applications requiring enhanced wear resistance. Keywords: electron beam evaporation; ion beam-assisted deposition; mechanical properties; nanocrystalline anatase; optical properties; TiO2 coatings

Focused ion beam-induced platinum deposition with a low-temperature cesium ion source

• Thomas Henning Loeber,
• Bert Laegel,
• Meltem Sezen,
• Feray Bakan Misirlioglu,
• Edgar J. D. Vredenbregt and
• Yang Li

Beilstein J. Nanotechnol. 2025, 16, 910–920, doi:10.3762/bjnano.16.69

• surface is a frequently used process of focused ion beam (FIB) systems. Here, we report on the deposition of platinum (Pt) with a new kind of cesium (Cs) FIB, in which the cesium ions are produced by a low-temperature ion source. Platinum was deposited at different acceleration voltages and ion beam

• conditions, but the deposit has lower Pt content for Cs+. The electrical resistivity of the deposit is found to be higher for Cs+ than for Ga+ and decreasing with increasing acceleration voltage. Keywords: cesium ion source; cold atom ion source; focused ion beam (FIB); FIB-induced deposition (FIBID

• ); Introduction The deposition of material at a certain spot on a sample surface is a powerful and useful feature of focused ion beam (FIB) systems. At first, the deposition was used for circuit editing and as a protection layer before milling. Nowadays, the process is more far-reaching, and three-dimensional

Ar⁺ implantation-induced tailoring of RF-sputtered ZnO films: structural, morphological, and optical properties

• Manu Bura,
• Divya Gupta,
• Arun Kumar and
• Sanjeev Aggarwal

Beilstein J. Nanotechnol. 2025, 16, 872–886, doi:10.3762/bjnano.16.66

• phonon symmetry in ZnO films implanted at lower ion beam energies. Zhiguang et al. [16] have observed the appearance of a longitudinal phonon mode in 80 keV nitrogen ion-implanted ZnO films at different fluences. Kennedy et al. [17] have reported enhancement in the disordered phase and an A1 (LO) mode in

• order as the thickness calculated from spectroscopic ellipsometry (Figure 1). After deposition, films are implanted with 30 keV Ar+ ions at different fluences of 1 × 1015, 5 × 1015, 1 × 1016, and 2 × 1016 Ar+ cm−2 using the 200 kV ion accelerator facility at Ion Beam Centre, Kurukshetra University. The

• fluence, which can be attributed to the fact that an enormous amount of energy is transferred to the lattice when the ion beam travels through the sample quickly, which generates dislocations. Raman spectroscopy Figure 4 reveals the Raman spectra of pristine and 30 keV argon-implanted ZnO films at various

Synchrotron X-ray photoelectron spectroscopy study of sodium adsorption on vertically arranged MoS₂ layers coated with pyrolytic carbon

• Alexander V. Okotrub,
• Anastasiya D. Fedorenko,
• Anna A. Makarova,
• Veronica S. Sulyaeva,
• Yuliya V. Fedoseeva and
• Lyubov G. Bulusheva

Beilstein J. Nanotechnol. 2025, 16, 847–859, doi:10.3762/bjnano.16.64

• molybdenum layer sputtered for 90 s. Part of the film surface was covered with a protective Pt layer and a lamella was cut using a focused ion beam (FIB) system (see the Experimental section for details). Figure 1d shows the SEM image of the cross section of the lamella. The bright round spots on the film

High-temperature epitaxial growth of tantalum nitride thin films on MgO: structural evolution and potential for SQUID applications

• Michelle Cedillo Rosillo,
• Oscar Contreras López,
• Jesús Antonio Díaz,
• Agustín Conde Gallardo and
• Harvi A. Castillo Cuero

Beilstein J. Nanotechnol. 2025, 16, 690–699, doi:10.3762/bjnano.16.53

• focused ion beam (FIB) for SEM observation; Au films were evaporated on the TaN samples before the FIB process to protect the samples (Figure 6a). The sample in Figure 6b shows a film thickness of 70 nm, and one can distinguish the Au protective layer used for the FIB process. Figure 6c shows the

Nanoscale capacitance spectroscopy based on multifrequency electrostatic force microscopy

• Pascal N. Rohrbeck,
• Lukas D. Cavar,
• Franjo Weber,
• Peter G. Reichel,
• Mara Niebling and
• Stefan A. L. Weber

Beilstein J. Nanotechnol. 2025, 16, 637–651, doi:10.3762/bjnano.16.49

• nanospectroscopy experiments. The microcapacitors were produced by focused ion beam (FIB) milling on a silicon wafer with a 300 nm layer of SiO2 and a 14 nm sputtered layer of Pt on it (Figure 2). Results and Discussion To investigate whether the C″-sensitive detection leads to an improved spatial resolution of

• Nanolab FIB apparatus with a dual Ga+ ion beam. Multifrequency heterodyne electrostatic force microscopy MFH-EFM was measured on an Oxford Instruments/Asylum Research MFP-3D Infinity AFM in a nitrogen glovebox (level of humidity below 0.3%, level of oxygen below 0.1%). The typical resonance frequency of

• in Figure 8. The electrical connection from the LIA to the cantilever with the two excitation voltages was realized by using a direct cable connection. Focused ion beam milling FIB milling of the cantilever was conducted using a LEO Gemini instrument from Zeiss. It was used with an acceleration

Focused ion and electron beams for synthesis and characterization of nanomaterials

• Aleksandra Szkudlarek

Beilstein J. Nanotechnol. 2025, 16, 613–616, doi:10.3762/bjnano.16.47

• the best of times, it was the worst of times" [2] – onto a 200 × 200 micron square of plastic using an electron beam. This achievement prompts a reflection: is nowadays the best or the worst of times for the development of electron and ion beam technologies? With the hope to contribute addressing this

• ion beam interactions [15]. In addition, the extension of the continuum model has proven useful in predicting the outcomes of ion beam milling processes in multilayered systems, as demonstrated in the case of the Si/SiO2/Pt system [16]. To identify the current state of the technology and routes

• towards its further development, a comprehensive roadmap for focused ion beam technologies has been recently published by an interdisciplinary group of international experts. Although not part of this thematic issue, we encourage the reader to take a look at the original paper [17]. While achieving

N₂⁺-implantation-induced tailoring of structural, morphological, optical, and electrical characteristics of sputtered molybdenum thin films

• Usha Rani,
• Kafi Devi,
• Divya Gupta and
• Sanjeev Aggarwal

Beilstein J. Nanotechnol. 2025, 16, 495–509, doi:10.3762/bjnano.16.38

• Usha Rani Kafi Devi Divya Gupta Sanjeev Aggarwal Ion Beam Centre, Department of Physics, Kurukshetra University, Kurukshetra-136119, India 10.3762/bjnano.16.38 Abstract Molybdenum (Mo) thin films have extensive applications in energy storage devices and photovoltaic solar cells because of their

• generation in Mo thin films with a low-energy argon ion beam (1 keV) across different ion fluences (1016–1018 ions·cm−2). Thornton et al. [16] examined a transition from tensile to compressive stress in argon-ion-implanted Mo thin films as the sputtering gas pressure decreased. Sun et al. [17] also analyzed

• the properties of argon-ion-implanted Mo thin films deposited via ion beam sputtering, varying deposition parameters such as accelerating voltage, incidence angle, and chamber pressure. Films deposited at near-normal incidence exhibited compressive stress and a nearly linear increase with the

Performance optimization of a microwave-coupled plasma-based ultralow-energy ECR ion source for silicon nanostructuring

• Joy Mukherjee,
• Safiul Alam Mollick,
• Tanmoy Basu and
• Tapobrata Som

Beilstein J. Nanotechnol. 2025, 16, 484–494, doi:10.3762/bjnano.16.37

• extraction composed of molybdenum. The study systematically examines the dependence of ion beam current on critical parameters, such as gas pressure, magnetron power, extraction voltage, and ion energies. The Gaussian nature of the beam profile is scrutinized and elucidated within the context of grid

• various parameters is extensively examined and elucidated. Experimental parameters, spanning from plasma generation to ion beam extraction, are systematically optimized for the study of low-energy Ar-ion-induced nanostructures on silicon. The dependence of the extracted ion beam on gas pressure, magnetron

• power, and extraction grid voltage is documented for different ion energies. Additionally, the manuscript establishes the relationship between ion beam current and ion energy. Irradiation of p-type single crystal Si(100) surfaces at off-normal angles (60° and 72.5°) with 450 eV Ar ions results in the

Tailoring of physical properties of RF-sputtered ZnTe films: role of substrate temperature

• Kafi Devi,
• Usha Rani,
• Arun Kumar,
• Divya Gupta and
• Sanjeev Aggarwal

Beilstein J. Nanotechnol. 2025, 16, 333–348, doi:10.3762/bjnano.16.25

• Kafi Devi Usha Rani Arun Kumar Divya Gupta Sanjeev Aggarwal Ion Beam Centre, Department of Physics, Kurukshetra University, Kurukshetra-136119, India 10.3762/bjnano.16.25 Abstract In this study, zinc telluride (ZnTe) films were grown on quartz substrates at room temperature, 300 °C, 400 °C, 500

• ± 0.30 nm for the films deposited at room temperature, 300 °C, 400 °C, 500 °C, and 600 °C, respectively. The structural aspects of the ZnTe/Qz films were analysed using grazing incidence X-ray diffraction (GXRD) on a Bruker AXS D8 Advance with Cu Kα radiation (λ = 1.5406 Å) available at Ion Beam Centre

• -3600 Plus) equipped with Integrating Sphere Assembly (Model-ISR-603) in the wavelength range of 200–2000 nm (accuracy 1 Å) available at Ion Beam Centre, Kurukshetra University. The photoluminescence (PL) emission spectra of ZnTe/Qz films were recorded using a HORIBA Scientific (Fluorescence 3.5

Precursor sticking coefficient determination from indented deposits fabricated by electron beam induced deposition

• Alexander Kuprava and
• Michael Huth

Beilstein J. Nanotechnol. 2025, 16, 35–43, doi:10.3762/bjnano.16.4

• ; Introduction Nanoscale fabrication of free-form structures via methods like focused electron or ion beam induced deposition (FEBID/FIBID) requires precise beam control and sufficient knowledge of key properties of the precursor material used [1]. In addition, a reliable prediction of the expected deposit shape

Orientation-dependent photonic bandgaps in gold-dust weevil scales and their titania bioreplicates

• Norma Salvadores Farran,
• Limin Wang,
• Primoz Pirih and
• Bodo D. Wilts

Beilstein J. Nanotechnol. 2025, 16, 1–10, doi:10.3762/bjnano.16.1

• . The domains in lattice orientation {100} exhibited polarization conversion. The structure inferred from optical measurements was confirmed using conventional and focused ion beam scanning electron microscopy (FIB-SEM). By averaging the reciprocal space images obtained from different lattice

• focused ion beam electron microscope, we exposed the diamond lattice chitinous network underneath the cortex of intact scales (Figure 2b,c). The upper cortex is ≈1 μm thick and has undulations spaced about 5 μm apart (Figure 2b), which were visible in the light microscopy images ( Figure 1b). The lower

• , Watford, UK). The settings were: sputter time 120 s, current 40 mA, and background pressure 0.08 mbar. Cross-sectional images of single scales were recorded using a focused ion beam scanning electron microscope (Scios2, Thermo Fisher Scientific, Waltham, MA, USA) using an Everhart–Thornley detector and an

Ion-induced surface reactions and deposition from Pt(CO)₂Cl₂ and Pt(CO)₂Br₂

• Mohammed K. Abdel-Rahman,
• Patrick M. Eckhert,
• Atul Chaudhary,
• Johnathon M. Johnson,
• Jo-Chi Yu,
• Lisa McElwee-White and
• D. Howard Fairbrother

Beilstein J. Nanotechnol. 2024, 15, 1427–1439, doi:10.3762/bjnano.15.115

• 10.3762/bjnano.15.115 Abstract Ion beam-induced deposition (IBID) using Pt(CO)2Cl2 and Pt(CO)2Br2 as precursors has been studied with ultrahigh-vacuum (UHV) surface science techniques to provide insights into the elementary reaction steps involved in deposition, complemented by analysis of deposits formed

• ability of data acquired from fundamental UHV surface science studies to provide insights that can be used to better understand the interactions between ions and precursors during IBID from inorganic precursors. Keywords: deposition; ion beam; nanostructure; organometallic; precursor; Introduction

• Focused ion beam-induced deposition (FIBID) and focused electron beam-induced deposition (FEBID) are vacuum-based, charged-particle bottom-up nanofabrication techniques that directly fabricate metal containing nanostructures as a consequence of the reactions between ions or electrons and organometallic

New design of operational MEMS bridges for measurements of properties of FEBID-based nanostructures

• Bartosz Pruchnik,
• Krzysztof Kwoka,
• Ewelina Gacka,
• Dominik Badura,
• Piotr Kunicki,
• Andrzej Sierakowski,
• Paweł Janus,
• Tomasz Piasecki and
• Teodor Gotszalk

Beilstein J. Nanotechnol. 2024, 15, 1273–1282, doi:10.3762/bjnano.15.103

• ). However, parasitic strain can cause unforeseen static changes in the geometry of the RoI. This problem is addressed by focused ion beam (FIB) technology, which can be used as a strain engineering tool. We will refer to MEMS with a formed RoI as operational MEMS, or opMEMS for short. In contrast to

• only for the visual assessment of the shape and dimensions of a structure, but also for the observation of movement and deflection of an opMEMS. At the same time, the ion beam allows for local doping of the substrate and anisotropic milling. The NanoLab 600i also provides three gas injection systems

• a whole with schematic electrical connections, and (c) on a SEM image focused on the RoI, with path descriptions and ion beam milling lines marked. Influence of DRIE-milled openings on current leakage across the slit edge. (a) Conducting paths are electrically shorted by leakage along the edge of

A low-kiloelectronvolt focused ion beam strategy for processing low-thermal-conductance materials with nanoampere currents

• Annalena Wolff,
• Nico Klingner,
• William Thompson,
• Yinghong Zhou,
• Jinying Lin and
• Yin Xiao

Beilstein J. Nanotechnol. 2024, 15, 1197–1207, doi:10.3762/bjnano.15.97

• Xiamen Medical College, Fujian, China School of Medicine and Dentistry, Griffith University, Gold Coast QLD 4222, Australia 10.3762/bjnano.15.97 Abstract Ion beam-induced heat damage in thermally low conductive specimens such as biological samples is gaining increased interest within the scientific

• community. This is partly due to the increased use of FIB-SEMs in biology as well as the development of complex materials, such as polymers, which need to be analyzed. The work presented here looks at the physics behind the ion beam–sample interactions and the effect of the incident ion energy (set by the

• acceleration voltage) on inducing increases in sample temperature and potential heat damage in thermally low conductive materials such as polymers and biological samples. The ion beam-induced heat for different ion beam currents at low acceleration voltages is calculated using Fourier’s law of heat transfer

Interface properties of nanostructured carbon-coated biological implants: an overview

• Mattia Bartoli,
• Francesca Cardano,
• Erik Piatti,
• Stefania Lettieri,
• Andrea Fin and
• Alberto Tagliaferro

Beilstein J. Nanotechnol. 2024, 15, 1041–1053, doi:10.3762/bjnano.15.85

• , and they are classified according to the power sources used for the process (i.e., plasma-, direct current-, radiofrequency-, and ion beam-assisted coatings) [85]. All PVD processes are based on a vacuum chamber containing the material to be deposited, known as target, and the chosen substrate onto

• which the deposition occurs. During electron beam evaporation, an electron beam is used to vaporize the target material, while during sputtering, a high-energy ion beam is used to bombard the target. In both cases, atoms are ejected from the target and subsequently condense onto the substrate. The

Level set simulation of focused ion beam sputtering of a multilayer substrate

• Alexander V. Rumyantsev,
• Nikolai I. Borgardt,
• Roman L. Volkov and
• Yuri A. Chaplygin

Beilstein J. Nanotechnol. 2024, 15, 733–742, doi:10.3762/bjnano.15.61

• Alexander V. Rumyantsev Nikolai I. Borgardt Roman L. Volkov Yuri A. Chaplygin National Research University of Electronic Technology - MIET, Bld. 1, Shokin Square, Zelenograd, Moscow, 124498, Russia 10.3762/bjnano.15.61 Abstract The evolution of a multilayer sample surface during focused ion beam

• understanding of the sputtering process, the distribution of oxygen atoms in the redeposited layer derived from the numerical data was compared with the corresponding elemental map acquired by energy-dispersive X-ray microanalysis. Keywords: electron microscopy; focused ion beam; level set simulation

• ; multilayer substrate; silicon; silicon dioxide; sputtering; Introduction The focused ion beam (FIB) technique is an effective method for surface nanostructuring. It is based on the local removal of material by sputtering with a narrow beam of, typically, gallium ions. This feature of the FIB method makes it

Sidewall angle tuning in focused electron beam-induced processing

• Sangeetha Hari,
• Willem F. van Dorp,
• Johannes J. L. Mulders,
• Piet H. F. Trompenaars,
• Pieter Kruit and
• Cornelis W. Hagen

Beilstein J. Nanotechnol. 2024, 15, 447–456, doi:10.3762/bjnano.15.40

• using focused ion beam (FIB) milling and shown as an electron tilt image in Figure 1b, clearly demonstrates the Gaussian shape. For lithography applications, however, both the long tails and the Gaussian cross section are highly undesirable. The tails may form interconnects to neighboring lines, and the

Investigating ripple pattern formation and damage profiles in Si and Ge induced by 100 keV Ar⁺ ion beam: a comparative study

• Indra Sulania,
• Harpreet Sondhi,
• Tanuj Kumar,
• Sunil Ojha,
• G R Umapathy,
• Ambuj Mishra,
• Ambuj Tripathi,
• Richa Krishna,
• Devesh Kumar Avasthi and
• Yogendra Kumar Mishra

Beilstein J. Nanotechnol. 2024, 15, 367–375, doi:10.3762/bjnano.15.33

• fabrication on Si and Ge by 100 keV Ar+ ion beam bombardment is discussed. The irradiation was performed in the ion fluence range of ≈3 × 1017 to 9 × 1017 ions/cm2 and at an incident angle of θ ≈ 60° with respect to the surface normal. The investigation focuses on topographical studies of pattern formation

• clustering of defects leads to a subsequent increase of the damage peak in irradiated samples (for an ion fluence of ≈9 × 1017 ions/cm2) compared to that in unirradiated samples. Keywords: atomic force microscopy; ion beam; nanopatterns; radiation damage; Rutherford backscattering spectrometry; transmission

• structures. Although these structures may not be visible to the naked eye, they certainly have a visible impact on the mentioned applications. Nanopatterning is a very delicate procedure that is only possible with special techniques such as ion beam sputtering (IBS), with which one can achieve nanostructures

Ultrasensitive and ultrastretchable metal crack strain sensor based on helical polydimethylsiloxane

• Shangbi Chen,
• Dewen Liu,
• Weiwei Chen,
• Huajiang Chen,
• Jiawei Li and
• Jinfang Wang

Beilstein J. Nanotechnol. 2024, 15, 270–278, doi:10.3762/bjnano.15.25

• ion beam sputtering was obtained from Fuzhou Yingfei Xun Photoelectric Tech Co., Ltd, China; it possessed a density of 19.3 g·cm−3 and a conductivity of 4.52 × 107 S·m−1. Silver conductive adhesive, which was procured from Shenzhen Ausbond Co., LTD. (Guangdong, China), was employed to affix copper

• structured PDMS was initially cleansed through a 5 min Ar plasma sputtering and, subsequently, coated with a 10 nm thick Ti adhesion layer. After that, ion beam sputtering was utilized to deposit a 50 nm thick Au thin film onto the outer surface of the helically shaped PDMS. Then, a controlled pre-stretch

Ion beam processing of DNA origami nanostructures

• Leo Sala,
• Agnes Zerolová,
• Violaine Vizcaino,
• Alain Mery,
• Alicja Domaracka,
• Hermann Rothard,
• Philippe Boduch,
• Dominik Pinkas and
• Jaroslav Kocišek

Beilstein J. Nanotechnol. 2024, 15, 207–214, doi:10.3762/bjnano.15.20

• unperturbed. Present stability and nature of damages on DNA origami nanostructures enable fusion of DNA origami advantages such as shape and positioning control into novel ion beam nanofabrication approaches. Keywords: DNA nanotechnology; DNA origami; FIB; heavy ions; Introduction Ion beam interaction with

• used in tandem with ion beam therapies against cancer. Another unique application is in long-term data storage [4][5], and ion beams can be used to test the stability of such DNA-origami-based storage under irradiation from natural sources such as cosmic rays or radioisotope decay [6]. More important

• them in procedures based on direct ion beam exposure has so far been avoided because of concerns regarding uncontrollable radiation damage to these soft matter nanostructures. The induction of strand breaks by the direct and indirect effects of ionizing radiation on DNA is a well-known fact [14][15