ML Thickness Research Articles

(Invited) Optomechanical Nanoprobes in the Quest for Novel Nanoscale Electronic and Photonic Devices

In this talk we will review the efforts from our group in the development of nanoptical, nanomechanical and integrated nano-optomechanical probes that can be utilized for the purpose of developing novel nanoscale electronic and photonic devices, and related materials.[1] For example, there are very few examples of techniques based on atomic force microscopy (AFM) and scanning tumnneling microscopy (STM) capable of acquiring, with nanoscale lateral resolution, quantitative maps of the photocurrent of a thin-film solar cell, or the thermal conductivity, thermal expansivity, and nanomechanical expansivity of nanoscale heat spreaders based on 2D materials and nanostructured thin films, despite huge demand for nanoscale thermal management, for example in designing integrated circuitry for power electronics.Our methods based on scanning near-field optical microscopy (SNOM) and scanning confocal optical microscopy (SCOM) are designed to satisfy such a demand.[1] Near-field optics is a powerful technique capable of achieving nanometer-scale optical resolution beyond the diffraction limit by using evanescent waves, which is uniquely poised to be integrated into AFM and STM probes.We will introduce ω-ω and ω-2ω near-field thermoreflectance imaging as all-optical and contactless approaches to map the thermal conductivity [2] and thermal expansion [3] coefficents at the nanoscale with precision. Testing of our techniques is performed on nanogranular films of gold and multilayer graphene (ML-G) platelets. As a case study, our recently invented ω-ω near-field scanning thermoreflectance imaging (NeSTRI) technique is here applied to multilayer graphene thin films on glass substrates. Thermal conductivity of micrometre-size multilayer graphene platelets is determined and is consistent with previous macroscopic predictions. As far as thermal expansion coefficient (TEC) is concerned, our method demonstrates that the TEC of ML-G is (-5.77±3.79) x10-6 K-1 and is assigned to in-plane vibrational bending modes.[3] A vibrational-thermal transition from graphene to graphite is observed, where the TEC becomes positive as the ML thickness increases. Basically, our nanoscale method demonstrates results in excellent agreement with its macroscopic counterparts, as well as superior capabilities to probe 2D materials and interfaces.As far as novel photonics probes are concerned, we will present [4] a novel method capable of profiling the carrier mobility along the z axis in thin-film photovoltaics. Our setup is based on the integration of photogenerated charge extraction by linearly increasing voltage (p-CELIV) with a scanning confocal optical microscope (SCOM) toward a confocal and cross-sectional p-CELIV (cs-p-CELIV) system. As monomolecular recombination of excess carriers is the most frequent radiative pathway for electrons and holes in solar cells at low power density of illumination, while multimolecular recombination dominates at high power, enhanced multimolecular recombination occurs at the SCOM focal plane. Thus, the cs-p-CELIV signal provides enhanced information on the mobility of all of the cross-sectional layers except the focal plane. By scanning the focal plane along the z axis, the mobility profile can be derived. To demonstrate our technique, we use it to investigate the carrier mobility in hydrogenated amorphous silicon (a-Si:H) solar cells. The mobility profiles obtained by cs-p-CELIV correlate well with well-known depletion layer effects and the H content profile in a-Si:H, which is measured independently.Collectively our methods well represent an excellent demonstration of the possibility to integrate near-field optics and scanning confocal optical microscopy towards the operando investigation of novel nanoscale electronic and photonic devices.[1] P. Bazylewski et al (Fanchini) Appl. Sci. 7, 973 (2017)[2] S. Ezugwu (Fanchini) Nanoscale, 9, 4097 (2017)[3] V. Wong (Fanchini) Adv. Mater. Interfaces 2300806 (2024)[4] N. Stocek (Fanchini) J. Appl. Phys. 135, 043104 (2024)

Contactless Scanning Near‐Field Optical Dilatometry Imaging at the Nanoscale

AbstractTo date, there are very few experimental techniques, if any, that are suitable for the purpose of acquiring quantitative maps of the thermal expansivity of 2D materials and nanostructured thin films with nanoscale lateral resolution in spite of huge demand for nanoscale thermal management, for example in designing integrated circuitry for power electronics. Besides, contactless analytical tools for determining the thermal expansion coefficient (TEC) are highly desirable because probes in contact with the sample significantly perturb any thermal measurements. Here, ω‐2ω near‐field thermoreflectance imaging is presented as a novel, all‐optical, and contactless technique to map the TEC at the nanoscale with precision. Testing of this technique is performed on nanogranular films of gold and multilayer graphene (ML‐G) platelets. With ω‐2ω near‐field thermoreflectance, it is demonstrated that the TEC of Au is higher at the metal‐insulator interface, with an average of (17.12 ± 2.30) ×10−6 K−1 in agreement with macroscopic techniques. For ML‐G, the average TEC is (−5.77 ± 3.79) x10−6 K−1 and is assigned to in‐plane vibrational bending modes. A vibrational‐thermal transition from graphene to graphite is observed, where the TEC becomes positive as the ML thickness increases. The nanoscale method here reported demonstrates results in excellent agreement with its macroscopic counterparts, as well as superior capabilities to probe 2D materials and interfaces.

Nanoscale Quantized Oscillations in Thin‐Film Growth Greatly Enhance Transconductance in Organic Transistors

AbstractA growth mode of pentacene thin films deposited by high vacuum sublimation where the morphology versus thickness h “rings” back and forth between rough 3D films with pyramid islands and smooth 2D films with ziqqurat islands is discovered. The roughness σ versus h exhibits seamless coherent oscillations whose amplitude and wavelength increase as integer multiples of 1.5 ML thickness. The quantized oscillations are reconducted to dynamic wetting/dewetting transitions involving the upper layers of pentacene film. Importantly, the transconductance of organic field effect transistors, either in solid state or electrolyte‐gated, exhibits antiphase oscillations with one‐decade swing. Charge mobilities in the wetting regime reach 0.1 cm2 V−1 s−1, in line with high‐end values reported for thin‐film pentacene transistors. Controlling this growth mode enables the limitations of charge transport imposed by the roughening transition to be overcome, a universal feature of high vacuum growth to date.

Electrochemical Design of Pt-Pd Nanostructures By Surface Limited Redox Replacement Method

The fuel cell technology is a green alternative to fossil fuels [1-2]. Fuel cells are electrochemical systems that use hydrogen and oxygen to create electrical energy with water and heat as biproducts. Besides the main interest of fuel cells applications in the automotive industry, most recent developments of miniature fuel cells that use biomass derived hydrogen have been attracting attention. Such systems require the design of new electrocatalysts with the high CO tolerance better than that of pure Pt. It has been shown that nanoscale Pt such as ultrathin layers and Pt-M nano-alloys, often have improved chemical and physical properties than those of Pt-bulk material due to the combination of electronic and geometric effects. Previous studies have reported that Pt-Pd system is a well-performing catalytic system for future use with the high CO tolerance [3,4]. Surface Limited Redox Replacement (SLRR) is one of the most successful approaches used to produce Pt bimetallic catalysts with high control of atomic structure [5, 6]. This method is based on the replacement of an underpotentially deposited (UPD) layer of a less noble metal by a more noble (such as Pt and Pd) through irreversible surface-controlled redox reaction. Here we will present SLRR based design of Pt-Pd nanoalloys of different composition on Au substrate. The advantages of using the SLRR method to design high quality 2D model Pt alloys will be demonstrated by studies of their electrochemical and catalytic behaviour as a function of structure such as film thickness and alloy composition. In our work, the epitaxial alloy thin films up to 10 ML thickness were grown in one-cell configuration using Cu UPD in sulphate solution as sacrificial layer. The alloys composition and structure were controlled by the concentration ratio of Pt and Pd complex in the solution. The structure of developed alloys was examined by a combination of electrochemical and surface science methods and correlated with their electrocatalytic behaviour during formic acid oxidation reaction.

Spontaneous Folding of CdTe Nanosheets Induced by Ligand Exchange

Two-dimensional (2D) semiconductors exhibit unique electronic and optical properties arising from the atomic-scale thickness and two-dimensional electronic structure. However, it is usually limited by an intrinsically flat morphology of 2D materials. Here, we report an effect of spontaneous folding of quasi-2D CdTe nanosheets stimulated by ligand exchange. We show that initially flat CdTe nanosheets with 100–200 nm lateral size and 5–6 ML thickness are uniformly rolled up when oleic acid is replaced by thiol-containing ligands. Detailed study shows nanosheet folding along the [110] direction forming multiwall scroll-like structures with the diameter being dependent on sheet thickness. A pronounced red shift of the exciton transitions of CdTe nanosheets is found due to thickness increase and strain appearance under thiol attachment. The folding mechanism is likely related to misfit strain at CdTe (001) basal planes as ultrathin CdS layer is formed. Possibility to precisely tune the nanostructure shape simp...

Highly Enhanced Oxygen Reduction Reaction Activity and Electrochemical Stability of Pt/Ir(111) Bimetallic Surfaces

We demonstrate highly enhanced ORR activity and electrochemical stability of Pt/Ir(111) model core-shell catalysts prepared by molecular beam epitaxy (MBE) in ultra-high vacuum (UHV). Reflection high-energy electron diffraction patterns for the surfaces show that Pt grew epitaxially on the clean Ir(111) substrate and the corresponding scanning tunneling microscope images collected in UHV reveal atomically flat terraces with 50–80nm widths at a substrate temperature of 673K. In contrast, the corresponding surfaces prepared at a substrate temperature of 303K show island-like topmost surface structures. The two-monolayer (ML)-thick Pt grown on Ir(111) (Pt2ML/Ir(111)) surfaces, prepared at substrate temperatures of 303K and 673K, show ca. 6 and 24 times higher ORR activities than clean Pt(111), respectively. The anomalous activity enhancement for the latter surface prepared at 673K is probably caused by homogeneous surface strain acting on the Pt shells that is derived from the 2.2% lattice mismatch between the Pt and Ir. The preparation-temperature–dependent ORR activity suggests that the activity can be dominated by the topmost surface and interface structures of the Pt shell–Ir(111) bimetallic system. Furthermore, while the initial ORR activity of pristine surfaces decreases with increasing Pt shell thickness, the stability during room temperature potential cycling between 0.6 and 1.0V in a 0.1M HClO4 solution was greatly enhanced above three ML thickness; the Pt4ML/Ir(111) surface prepared at 673K retained 6.5 times higher ORR activity than Pt(111), even after 5000 potential cycles. The ORR activity and electrochemical stabilities for the Pt/Ir(111) bimetallic surfaces are the highest among the MBE-prepared Pt/M(111) (M=Ir, Pd, Au) systems reported to date. The results obtained in this study show that Pt/Ir core–shell nanostructures are potential candidates for highly active and durable ORR catalysts.

TCNQ Grown on Cu (001): Its Atomic and Electronic Structure Determination

In this paper we have resolved by means of “in situ” X-ray diffraction studies the atomic structure of the TCNQ films from 0.4 to 17 ML thickness grown on Cu(001) substrate. The film grown at low temperature, is a well crystallized and well oriented single phase. The TCNQ film has a (020) orientation. The electronic properties of the film have been studied by means of XPS and UPS spectroscopies. The measured electronic density has been compared to the theoretical ab-inito calculations. In this paper we have studied the structural and electronic properties of relatively thick films of TCNQ on Cu(100). Our results demonstrate that the strong charge transfer between the metallic substrate and the first layer of TCNQ molecules have important consequences for the film electronic and structural properties of films even as thick as 17 ML. From the structural point of view, the films grow with a well-defined (020) orientation that matches the modified molecular structure of the first layer. This first monolayer s...

Growth of epitaxial Pt1-xPbx alloys by surface limited redox replacement and study of their adsorption properties.

The surface limited redox replacement (SLRR) method has been used to design two-dimensional Pt-Pb nanoalloys with controlled thickness, composition, and structure. The electrochemical behavior of these alloys has been systematically studied as a function of alloy composition. A single-cell, two-step SLRR protocol based on the galvanic replacement of underpotentially deposited monolayers of Pb with Pt was used to grow epitaxial Pt1-xPbx (x < 0.1) alloys of up to 10 ML thickness on Au substrates. It is shown that by varying the terminating potential of the galvanic replacement step, the Pb atomic content can be controlled in the films. Electrochemical analysis of the alloys showed that the adsorption of both H and CO exhibits similar, and systematic, decreases with small increases in the Pb content. These measurements, commonly used in electrocatalysis for the determination of active surface areas of Pt, suggested area values much lower than those expected based on the net Pt composition in the alloy as measured by XPS. These results show that Pb has a strong screening effect on the adsorption of both H and CO. Moreover, changes in alloy composition result in a negative shift in the potential of the peaks of CO oxidation that scales with the increase of Pb content. The results suggest electronic and bifunctional effects of incorporated Pb on the electrochemical behavior of Pt. The study illustrates the potential of the SLRR methodology, which could be employed in the design of 2-dimensional bimetallic Pt nanoalloys for fundamental studies of electrocatalytic behavior in fuel cell reactions dependent on the nature of alloying metal and its composition.

Structural and optical properties of ZnSe thin films stacked with PbSe submonolayers

Structural and optical properties of Zinc Selenide (ZnSe) thin films stacked with multiple Lead Selenide (PbSe) submonolayers (ML) were studied. Thermal evaporation was preferred to produce ZnSe–PbSe thin films with the PbSe ML thickness ranges from 2.5 to 10 nm. Polycrystalline nature of the ZnSe was revealed through high resolution X-ray diffractometer measurement. The development of micro strain at the interfaces with increasing PbSe ML thickness was observed. A cross-sectional TEM image shows well-ordered periodicity and reproducibility of the layer thickness. The enhancement of optical absorption of ZnSe was identified upon stacking of PbSe ML. The evidence for quantum confinement in PbSe ML was revealed by the obtained red shift in band gap (2.5–1.8 eV) values as well as photoluminescence emission at 1,071 nm. The presence of tensile strain in the ZnSe layers upon staking of PbSe ML was discussed by the shift in LO phonon modes in Raman spectra.

Electronic states of moiré modulated Cu films

We examined by low-energy electron diffraction and scanning tunneling microscopy the surface of thin Cu films on Pt(111). The Cu/Pt lattice mismatch induces a moiré modulation for films from 3 to about 10 ML thickness. We used angle-resolved photoemission spectroscopy to examine the effects of this structural modulation on the electronic states of the system. A series of hexagonal- and trigonal-like constant energy contours is found in the proximity of the Cu(111) zone boundaries. These electronic patterns are generated by Cu sp-quantum well state replicas, originating from multiple points of the reciprocal lattice associated with the moiré superstructure. Layer-dependent strain relaxation and hybridization with the substrate bands concur to determine the dispersion and energy position of the Cu Shockley surface state.

Temperature stability of ultra-thin mixed BaSr-oxide layers and their transformation

In the context of investigations of physical, chemical and electrical properties of ultra-thin layers of epitaxial and monocrystalline Sr0.3Ba0.7O on Si(100), we also investigated their thermal stability with x-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and low energy electron diffraction (LEED). At temperatures above 400 °C, transformation into silicate layers sets in. The stoichiometry after complete transformation was determined to be close to (Ba0.8Sr0.2)2SiO4 except for layers of only a few monolayers, where the silicate is not stoichiometric. There are strong indications that this silicate is stable until it desorbs at temperatures above 750 °C. Crystallinity, as seen with LEED, is lost during this transformation. Although transformation into silicate is coupled with metal desorption and compactification of the layers, they seem to remain closed. In addition, traces of Ba silicide at the Si interface were detected after layer desorption. This silicide cannot be desorbed thermally. The silicate layer has a bandgap of 5.9 ± 0.2 eV already for 3 ML thickness. Upon exposure to air, carbon and oxygen containing species, but no hydroxide, are formed irreversibly.

Growth and Morphology of Calcium-Oxide Films Grown on Mo(001)

Crystalline calcium-oxide films of various thicknesses have been grown on a Mo(001) support. The growth behavior and resulting film morphology have been characterized with low-energy electron diffraction, Auger spectroscopy, and scanning tunneling microscopy. At low film thickness, a considerable interdiffusion of Mo ions from the support into the ad-layer is revealed, giving rise to the development of a sharp (2 × 2) superstructure with respect to the Mo(001). The Ca/Mo mixed oxide has a similar lattice parameter as the metal substrate and therefore grows pseudomorphically with a very low defect concentration. At 4−5 ML thickness, the supply of Mo from the support is interrupted and pristine CaO patches start to grow on the surface. The reemerging lattice mismatch drives the system into the Stranski-Krastanov mode, as reflected by the formation of three-dimensional oxide islands. Above 15 ML nominal thickness, the islands merge into a closed film with high surface quality and low defect concentration. The bulk character of the oxide is deduced from its band gap and optical properties, which are in good agreement with literature data reported for bulk CaO.

Ultrathin Mn layers on Rh(001): Investigations using scanning tunneling microscopy and density functional calculations

The structural and magnetic properties of ultrathin layers of Mn grown on Rh001 surfaces have been investigated using scanning tunneling microscopy STM and ab initio density-functional calculations. STM shows perfect wetting of the Rh substrate by the first Mn monolayer ML accompanied by a high mobility of the Mn atoms and only little film-substrate intermixing. By way of contrast, the second monolayer is unstable against formation of multilayer islands at 300 K. However, this is only a transient effect and growth approaches a layer-by-layer mode in thicker films. At 170 K growth proceeds layer-by-layer throughout. The structure of the films is face-centered tetragonal fct without any indication of lateral lattice mismatch up to 20 ML thickness. The apparent height differences between terraces of different local thickness are consistent with an average axial ratio close to unity near fcc for 2–3-ML-thick films that decreases continuously to 0.94 in thicker films. Detailed spin-polarized density-functional calculations have been performed for the bulk and the 001 surface of strained fct Mn, as well as for free-standing and supported Mn/Rh001. The results demonstrate that structure and stability of surface and thin films are strongly influenced by antiferromagnetic AFM ordering. In-plane c2 2 AFM is found at the surface while bulk and the deeper layers prefer layered AFM. The calculations reproduce and explain the growth instability of 2 ML films and reproduce qualitatively the thickness-dependent variation in the film structure while the tetragonal distortion imposed by the size mismatch is overestimated because with all known exchange-correlation functionals the size ratio of bulk Rh and Mn crystals is overestimated. The calculations show that interface alloying is slightly exothermic but kinetically hindered because of a high activation energy for exchange processes.

Effect of inserting Ni and Co layers on the quantum well states of a thin Cu film grown on Co/Cu(001)

The effect of Ni and Co inserting layers on the quantum well (QW) states of a Cu film grown on Co/Cu(001) is systematically investigated using angle-resolved photoemission spectroscopy. For electron energy $E\ensuremath{-}{E}_{\text{F}}l\ensuremath{-}0.5\text{ }\text{eV}$, we find that both Ni and Co inserting layers behave similarly to serve as a potential-energy barrier to divide the Cu film into two Cu QWs. For energy near the Fermi energy, the Ni and Co inserting layers have different effects on the Cu QW states while the Co thin layer still perturbs the Cu QW states, the Ni inserting layer behaves as if it were a Cu layer, especially at the Fermi energy, even up to 10 ML thickness. Such different effects of the Ni and Co inserting layers are attributed to their different electronic band matching with the Cu energy band. The first-principles calculation confirms that the electron reflectivity near the Fermi level is indeed very different at the Cu/Ni and Cu/Co interfaces, supporting the experimental results.

Structure and morphology of thin MgO films on Mo(001)

Using a combination of reciprocal and real-space techniques, the structural evolution and its effect on the surface morphology is investigated for MgO films of 1--30 ML thickness epitaxially grown on Mo(001). The strain induced by the mismatch with the substrate is relieved between 1 and 7 ML MgO due to the formation of an ordered network of interfacial misfit dislocations aligned along the MgO $⟨110⟩$ directions, particularly evident after annealing the film at 1070 K. A dislocation periodicity of about $60\text{ }\text{\AA{}}$ has been determined by means of grazing incidence x-ray diffraction. The dislocations induce a tilting of the surface that appears in electron diffraction along the $⟨100⟩$ MgO directions for thin films and changes to $⟨110⟩$ directions when the oxide thickness increases. Scanning tunneling microscopy (STM) shows the presence of a regular pattern on the surface below 7 ML thickness associated to the dislocation network. With increasing thickness, screw dislocations connected by nonpolar steps appear on the oxide surface. Thanks to the combination of different diffraction techniques and STM measurements, a comprehensive picture of the relaxation mechanisms in MgO films on Mo(001) can be drawn.

Fe films grown on GaAs(110) in a two-step process: Improved structural and magnetic properties

Fe films of up to 10 ML thickness were grown on cleaved GaAs(110) in a two-step process that associates low-temperature deposition at 130K with a subsequent annealing to room temperature. Low-energy electron diffraction, scanning tunneling microscopy, and in situ magneto-optical Kerr effect were combined to study these films. The observed magnetic and structural properties are distinctly different from the characteristics of conventionally grown Fe films on GaAs. We found no indication of interface compound formation. The applied two-step growth process is a promising technique to further increase spin-injection and detection efficiencies of Fe∕GaAs hybrid structures.

Resonant two-photon photoemission study of electronically excited states at the lead phthalocyanine/graphite interface

Occupied and unoccupied electronic states of lead phthalocyanine (PbPc) films of 1 ML thickness formed on graphite substrates have been measured by two-photon photoemission (2PPE) spectroscopy. Highly reproducible and well-resolved 2PPE spectra were obtained by selecting sample positions with submicrometer light spot. We have identified the molecule-derived states due to the $\mathrm{HOMO}\ensuremath{-}1$, HOMO, LUMO, $\mathrm{LUMO}+1$, $\mathrm{LUMO}+2$ as well as the first image-potential state (IS). The occupied states are in good agreement with one-photon photoemission results. Resonant excitations between the HOMO and $\mathrm{LUMO}+2$-related levels as well as those between the HOMO level and IS were observed in consistency with energies of relevant levels determined from off-resonant conditions.

Growth Mode and Surface Structure of Cr Ultrathin Film on Fe/Cu(001)

We hereby report a growth mode and surface structure of ultrathin Cr films on fcc Fe/Cu(001). We have found a clear RHEED intensity oscillation during Cr deposition up to four monolayers on 3 and 6 ML Fe/Cu(001), indicating an layer-by-layer growth. Besides, the observed (2×1) LEED pattern at low Cr thickness is similar to that of fcc Fe/Cu(001) in the 5-11 ML thickness range. We have also demonstrated the Cr/Fe multilayer growth with single monolayer of Cr inserted between fcc Fe layers. [DOI: 10.1380/ejssnt.2008.251]

Changes in nutrient concentration induced by hydrological variability and its effect on light absorption by phytoplankton in the Alborán Sea (Western Mediterranean Sea)

The effect of hydrologic variability on the chlorophyll a-specific absorption coefficient [ a ⁎( λ)] was investigated in the NW Alborán Sea during a cruise performed in spring. The study area was characterised by a strong stratification of the water column. The lower limit of the mixed layer coincided with the lower limit of the euphotic layer (EL), which was characterised by very low nitrate (0.23 ± 0.30 μg L − 1 ) and phosphate (0.09 ± 0.04 μg L − 1 ) concentrations. Accordingly, the chlorophyll a (Chl a) concentration in EL was low (0.59 ± 0.40 μg Chl a L − 1 ) indicating that phytoplankton growth was probably limited by nutrient availability. Contrastingly, nitrate concentration increased by 10-folds in the seawater layer located below EL (IL, until 0.1% surface irradiance depth level). In most of the stations, the vertical maximum of Chl a was located in IL (the Chl a concentration mean in the maximum was 2.05 ± 0.89 μg L − 1 ). The optical properties of the phytoplankton communities in EL and IL differed significantly. Thus, a ⁎(440) and a ⁎(675) decreased by about 40% in IL in comparison to EL. The parameter Q ⁎ a (675), which was used as a proxy for pigment packaging magnitude, also decreased in IL (0.62) with respect to EL (0.93), suggesting that the reduction of a ⁎( λ) in IL was due to the pigment packaging effect. In spite of the strong stratification of the water column, inter-station shifts of the ML thickness were produced. Thus, the deepening of ML observed at some stations dealt with higher salinity and nutrient concentration in the surface layer. The horizontal variability of a ⁎( λ) was apparently related to this hydrological variability as a negative correlation between a ⁎(675) and surface salinity was obtained ( r 2 = 0.53) in EL. The correlation between salinity and Q ⁎ a (675) was also negative ( r 2 = 0.31), which indicates that nitrate enrichment in EL dealt with an increase in Chl a packaging effect. These results demonstrate that it is possible to describe variability of a ⁎( λ) from changes in hydrological features of the water column.

Ultrathin Fe layers on Ag (1 0 0) surface

Iron layers (0.15–10 ML thick) deposited on Ag (1 0 0) substrates were investigated by conversion electron Mössbauer spectrometry over a broad temperature range. The layers were characterized by scanning tunneling microscopy. Different forms of the layers, depending on their thickness, were observed. Minimum roughness of the layers were found at 0.15 and 10 ML thickness values. The Mössbauer spectra showed systematic thickness dependence. At low thickness values, broad doublets were observed, while above 6 ML, magnetic split spectra appeared at room temperature. At low temperatures, magnetically split spectra appeared with parameter values characteristic of Fe–Ag and Fe–Fe atomic interactions. The hyperfine split spectra indicated magnetic anisotropy and an enhanced saturation hyperfine magnetic field of ≃40 T. The latter value is the highest ever measured for iron in thin layers.