Electron Stimulated Desorption Process Research Articles

Десорбция атомов лития c поверхности Li/Li-=SUB=-x-=/SUB=-Au-=SUB=-y-=/SUB=-, стимулированная электронным облучением

The processes of electron-stimulated desorption (ESD) of Li atoms in the Li/LixAuy Au/W system have been investigated for the first time. The formation of a semiconductor 2D LixAuy layer is revealed. It is shown that ESD processes occur at the interface of the Li monolayer - 2D LixAuy layer.

Электронно-стимулированная десорбция атомов лития из слоев лития на поверхности Li-=SUB=-x-=/SUB=-Au-=SUB=-y-=/SUB=-

For the first time, semiconductor 2D layers LixAuy have been created on the surface of gold deposited on a tungsten substrate. The processes of electron-stimulated desorption (ESD) of Li atoms in the Li / LixAuy / Au / W system are studied. It is shown that ESD processes occur in the Li monolayer and the LixAuy layer closest to it. A model of ESD of Li atoms in the Li / LixAuy / Au / W system is proposed.

Electron-Stimulated Desorption of K Atoms from Potassium Adlayers on a KxAuy Surface

Electron-stimulated desorption (ESD) of K atoms from the surface of K/KxAuy/Au/W system has been studied. It is established that the ESD process occurs in the K adlayer and adjacent KxAuy subsurface layer. A model of the ESD of K atoms from the K/KxAuy/Au/W system is proposed. Semiconductor nature of KxAuy compounds is confirmed.

Электронно-стимулированная десорбция атомов калия из слоев калия на поверхности K-=SUB=-x-=/SUB=-Au-=SUB=-y-=/SUB=-

The K atom electron-stimulated desorption (ESD) processes in K/KxAuy/Au/W system have been studied. There have been shown that ESD processes have been occurred in the K adlayer and in the nearest KxAuy layer. The K atom ESD model in K/KxAuy/Au/W system have been suggested. Semiconductor nature of KxAuy compounds have been corroborated.

The electron-stimulated desorption yield and penetration range of exciting electrons

We have studied the concentration dependences of the yield of electron-stimulated desorption (ESD) of Cs and Na atoms adsorbed on nonmetallic coatings grown on W substrates. It is established that ESD processes occur at the interface between the adlayer and underlying nonmetallic coating. The decay in the concentration dependence of the ESD yield of alkali-metal atoms observed after reaching their monolayer coverage is related to a decrease in the amount of exciting electrons attaining this interface.

Electron Induced Surface Reactions of cis-Pt(CO)2Cl2: A Route to Focused Electron Beam Induced Deposition of Pure Pt Nanostructures.

Using mechanistic data from surface science studies on electron-induced reactions of organometallic precursors, cis-Pt(CO)2Cl2 (1) was designed specifically for use in focused electron beam induced deposition (FEBID) of Pt nanostructures. Electron induced decomposition of adsorbed 1 under ultrahigh vacuum (UHV) conditions proceeds through initial CO loss as determined by in situ X-ray photoelectron spectroscopy and mass spectrometry. Although the Pt-Cl bonds remain intact during the initial decomposition step, larger electron doses induce removal of the residual chloride through an electron-stimulated desorption process. FEBID structures created from cis-Pt(CO)2Cl2 under steady state deposition conditions in an Auger spectrometer were determined to be PtCl2, free of carbon and oxygen. Coupled with the electron stimulated removal of chlorine demonstrated in the UHV experiments, the Auger deposition data establish a route to FEBID of pure Pt. Results from this study demonstrate that structure-activity relationships can be used to design new precursors specifically for FEBID.

Electron-stimulated desorption of cesium atoms from adlayers on a gold surface

We have studied the process of electron-stimulated desorption (ESD) of Cs atoms from a Cs/CsAu/Au/W system. It is established that ESD takes place from a Cs adlayer and the adjacent CsAu layer of this system. A model of Cs atom desorption from the Cs/CsAu/Au/W system is proposed. The results confirm the semiconductor nature of CsAu compounds.

Electron-Induced Surface Reactions of η3-Allyl Ruthenium Tricarbonyl Bromide [(η3-C3H5)Ru(CO)3Br]: Contrasting the Behavior of Different Ligands

Toward the goal of better understanding the elementary steps involved in the electron beam-induced deposition (EBID) of organometallic precursors, the present study is aimed at understanding the sequence of electron-stimulated reactions of surface-bound η3-allyl ruthenium tricarbonyl bromide [(η3-C3H5)Ru(CO)3Br], an organometallic complex with three different ligands: carbonyl (CO), halide (Br), and η3-allyl (η3-C3H5). X-ray photoelectron spectroscopy and mass spectrometry were used in situ to probe the effects of 500 eV electrons on nanometer scale films of [(η3-C3H5)Ru(CO)3Br]. Initially, electron irradiation decomposes the precursor, reducing the central Ru atom and causing the ejection of CO ligands into the gas phase. Experimental evidence points to the inability of electron irradiation to remove the carbon atoms of the η3-allyl (η3-C3H5) ligand from the resulting EBID deposits. Although the Br atoms are not labile in the initial molecular decomposition step, they are removed from the film after exposure to higher electron doses as a result of a slower, electron-stimulated desorption process. Comparative studies with [(η3-C3H5)Ru(CO)3Cl] reveal that the identity of the halogen does not influence the elementary reaction steps involved in the decomposition process. Collectively, results from these studies suggest that sufficiently volatile organometallic precursors with a small number of carbonyl and halide ligands could be used to generate deposits in EBID with significantly higher metal concentrations (and correspondingly lower levels of organic contamination) compared to existing EBID precursors.

Atomic precision lithography on Si

Lithographic precision is as or more important than resolution. For decades, the semiconductor industry has been able to work with ±5% precision. However, for other applications such as micronanoelectromechanical systems, optical elements, and biointerface applications, higher precision is desirable. Lyding et al. [Appl. Phys. Lett. 64, 11 (1999)] have demonstrated that a scanning tunneling microscope can be used to remove hydrogen (H) atoms from a silicon (100) 2 × 1 H-passivated surface through an electron stimulated desorption process. This can be considered e-beam lithography with a thin, self-developing resist. Patterned hydrogen layers do not make a robust etch mask, but the depassivated areas are highly reactive since they are unsatisfied covalent bonds and have been used for selective deposition of metals, oxides, semiconductors, and dopants. The depassivation lithography has shown the ability to remove single H atoms, suggesting the possibility of precise atomic patterning. This patterning process is being developed as part of a project to develop atomically precise patterned atomic layer epitaxy of silicon. However, significant challenges in sample preparation, tip technology, subnanometer pattern placement, and patterning throughput must be overcome before an automated atomic precision lithographic technology evolves.

Electron irradiation effect on depth profiling of a SiO 2/Si(1 0 0) surface by Auger electron spectroscopy

Electron irradiation effect on depth profiling of a SiO 2/Si(1 0 0) surface has been studied. A theoretical model for electron stimulated desorption (ESD) and gas adsorption on the solid surface has been proposed. The ESD process on the solid surface has been evaluated by Auger electron spectroscopy (AES) combined with a depth profiling technique. Our model can explain the observed ESD effect in low electron current densities less than 30 A/m 2. In higher current densities, the deviation from the model appears because dynamic diffusion process becomes dominant. Furthermore the dependencies of the ion sputtering rate and the depth resolution on the current density of the electron radiation have been observed quantitatively, whose origin has been discussed based on a model.

Mechanism of low-energy electron stimulated desorption of O− from hydrogenated and hydrogen-free diamond surfaces exposed to activated oxygen

In this work we report on a study of the mechanism of O− electron stimulated desorption (ESD) from hydrogenated and hydrogen-free polycrystalline diamond films exposed to thermally activated oxygen for incident electron energies in the 4–22 eV range. Two types of experiments were carried out in order to assess the nature of the ESD processes: (i) total O− and H− yields as a function of incident electron energy and (ii) kinetic-energy distribution (KED) of O− desorbed from the hydrogen-free diamond surface. The discussed ESD mechanism is referred to the information obtained from x-ray photoelectron spectroscopy, near-edge x-ray absorption fine structure, and core level H+ photodesorption measurements which reveal formation of C=O and C–O–C bonds on the hydrogen-free diamond surface, and C=O and C–O–H bonds on the hydrogenated one. Based on the maximum kinetic-energy value of O− and the ESD threshold measured for hydrogen-free surface, all low-energy (5–10 eV) O− ions are attributed to desorption by the dissociative electron attachment (DEA) to C–O–C, while DEA to C=O occurs at the incident electron energy higher than ∼10 eV. O− ESD from the hydrogenated diamond surface exposed to thermally activated oxygen is a more complicated process. Its threshold is substantially higher than for hydrogen-free diamond, and the line shape of the ESD yield curve is very similar to that of chemisorbed CO molecules. Several reaction pathways leading to production of O− by DEA are discussed for this sample. At incident electron energies higher than ∼15 eV, O− ESD proceeds also via dipolar dissociation processes for both hydrogenated and hydrogen-free diamond surfaces.

Observation of triangular terraces and triangular craters of CaF 2 film on Si(1 1 1) substrate

We have investigated the growth mode and surface morphology of CaF 2 film on Si(1 1 1)7×7 substrate by reflection high-energy electron diffraction (RHEED) using very weak electron beam and atomic force microscopy (AFM). It was found by RHEED intensity oscillation measurements and AFM observations that three-dimensional (3D) islands grow at RT; however, rather flat surface appears with two-dimensional (2D) islands around 300 °C. Especially, at high temperature of 700 °C, characteristic equilateral triangular terraces (or islands) with flat and wide shape grow with the tops directed toward [1 1 −2] of substrate Si(1 1 1). On the other hand, the desorption process of the CaF 2 film due to electron stimulated desorption (ESD) was also examined. It was found that the ESD process at 300 °C forms characteristic equilateral triangular craters on the film surface with the tops (or corners) directed toward [−1 −1 2] of substrate Si(1 1 1), provided that the film was grown at 700 °C.

Dissociative electron attachment and dipolar dissociation ofH−electron stimulated desorption from hydrogenated diamond films

In this work we report, a study of the mechanism of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ electron stimulated desorption (ESD) from hydrogenated diamond films for incident electron energies in the 2\char21{}45 eV range. Two types of experiments were carried out in order to assess the nature of the ESD processes leading to desorption as a function of incident electron energy: (i) kinetic energy distribution (KED) of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ and (ii) ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ anions yield at fixed ion energy (FIE) measurements. The KED measurements show that for incident electrons of up to \ensuremath{\sim}11 eV the most probable kinetic energy of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ions monotonically increases from about 1.7 to 3.3 eV. For higher incident electron energies, the ion energy distribution peaks at about 1.5 eV and is nearly constant. From these measurements it is derived that the ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ESD cross section has a resonance behavior displaying two well-defined peaks at 9 and 22 eV and a monotonic increase with a threshold at \ensuremath{\sim}14 eV as a function of incident electron energy. From the KED and FIE spectra the 9- and 22-eV peaks are interpreted as due to dissociative electron attachment via a single Feshbach anion resonance state, albeit accessed directly and indirectly, respectively. A possible intermediate process involving a well-known electronic excitation of the hydrogenated diamond at 13 eV is suggested. For incident electron energies higher than \ensuremath{\sim}14 eV, ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ESD proceeds also via dipolar dissociation processes.

Associative electron stimulated desorption of neutral CO molecules

The Electron Stimulated Desorption (ESD) of neutral CO molecules was studied on polycrystalline Ni surface. Combined ESD and temperature programmed desorption (TPD) measurements were used to observe the variations of neutral ESD yield in dependence on CO coverage, containing direct information about the cross section for ESD of neutral CO molecules in relation to various CO adsorption states. The results show evidence of ESD of neutral CO molecules from dissociative adsorption states. The cross section for this associative ESD process is relatively high in comparison with the CO ESD cross section for molecular CO adsorption.

AFM studies of electron-stimulated desorption process of KBr(001) surface

Electron stimulated desorption of the KBr(001) surface due to 1 keV electron bombardment was investigated in an ultra-high vacuum by means of non-contact atomic force microscopy. Characteristic structures like rectangular holes of monolayer depth and small agglomerations of atoms were observed. The dependence of the structure size and density was measured as a function of the electron dose. Analysis of the experimental data indicates that the process of desorption occurs in a layer-by-layer mode and that the efficiency of the process was influenced by the surface topography.

Electron beam-assisted formation of silicon oxynitride layers (3.5 nm) on silicon at moderate temperatures using NO gas: growth kinetics and mechanisms

Exposure to low pressures, P NO, of pure nitric oxide gas (1 × 10 −6 mbar ⩽ P NO ⩽ 1 × 10 −4 mbar) on a clean Si(1 0 0) surface at moderate temperatures T (room temperature (RT) to 600°C) leads to the formation of a 0.5 nm thick oxynitride passivating layer. Under low-energy electron beam irradiation (primary energy=250 eV, electron current density=1.25 mA cm −2) film growth occurs, independent of the temperature in the investigated range. A maximum thickness of about 3.5 nm can be obtained at 600°C and at RT. We show that the oxynitride films formed are, in fact, oxide films with an SiO x N y interfacial layer with the silicon substrate. The higher the temperature the larger the nitrogen content in the interfacial region without, practically, any increase in film thickness. A model for growth kinetics of these films in a nitric oxide environment is proposed. The reacting species are assumed to be O − and NO − ions which move in an electric field, acting as a driving force. The model assumes that the oxide growth is limited by time-dependent interface reaction of nitrogen at oxidation growth sites and by a thermally activated electron-stimulated desorption process of oxygen.

Effects of Electron Irradiation on Methylthiolate Monolayer on Au(111): Electron-Stimulated Desorption

Effects of electron irradiation on a methylthiolate (CH3S) self-assembled monolayer on Au(111) have been studied by using scanning tunneling microscope (STM), Auger electron spectroscopy (AES), low-energy electron diffraction, and thermal-desorption spectroscopy (TDS). AES results indicated that irradiation of the CH3S/Au(111) surface by an electron beam induces electron-stimulated desorption (ESD), in which mainly the methyl moiety desorbs via S−C bond cleavage, leaving a sulfur atom on the surface. From a quantitative analysis of TD spectra, the cross section of the ESD is estimated to be 2.8 × 10-17 cm2 for 100-eV electrons. Two-dimensional arrangements of the methylthiolate and the sulfur species under the ESD process have been investigated with STM. The STM observations indicated that the sulfur adatoms form 2D islands that grow in size with the progress of the ESD process, while unaffected methylthiolates are distributed between the sulfur islands. After the completion of the ESD, the Au(111) surfac...

A review of electron stimulated desorption processes influencing the measurement of pressure or gas composition in ultra high vacuum systems

A review of the Electron Stimulated Desorption, ESD, processes as responsible for producing modification of the gas composition or erroneous readings in those measuring devices using electron beams is presented. After reviewing the basic ESD mechanisms of Menzel-Gomer and Redhead, Feibelman-Knotek and the Auger electron stimulated desorption, some examples of these effects on readings of hot cathode ionization gauges and mass spectrometers are presented. Then, the ESD of H 2 W , H 2O Nb(110) systems and the ion desorption from a typical transition metal oxide such us the TiO 2 (110) are discussed.

Transmission of low-energy O+ ions through ultrathin films of Ar, Kr, and Xe.

We present a systematic study of the transmission of low-energy (10 eV) ${\mathrm{O}}^{+}$ ions through ultrathin films of Ar, Kr, and Xe. The ions are produced by electron-stimulated desorption from an oxidized W(100) crystal; they desorb from the surface in directions close to the surface normal with a peak kinetic energy of \ensuremath{\sim}7 eV and their yield, mass/energy, and angle are measured with a digital electron-stimulated desorption ion angular distribution (ESDIAD) detector. Rare gases are condensed at \ensuremath{\sim}25 K onto the oxidized W(100) crystal and their film thickness is determined by means of thermal-desorption spectroscopy. The ${\mathrm{O}}^{+}$ ions desorbed in the presence of a rare-gas film have to pass through the film before reaching the detector. We find that 10% of ${\mathrm{O}}^{+}$ can be transmitted through 1.6 atomic layers of Ar, 2.9 ML of Kr, and 4.0 ML of Xe. From the ${\mathrm{O}}^{+}$ signal attenuation by films thicker than 2 ML we derive attenuation cross sections of 6.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{cm}}^{2}$ for Ar, 2.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{cm}}^{2}$ for Kr, and 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{cm}}^{2}$ for Xe. For Xe, we observe indications that the angular distribution of the ions changes due to large-angle scattering, and for Kr (and previously for Xe) we measure a shift in the energy distribution towards lower energies; we interpret this to be due to elastic forward scattering of the oxygen ions by the Xe atoms.We attribute the attenuation of the ${\mathrm{O}}^{+}$ in the films mainly to elastic backscattering; we suggest that either a high neutralization probability of ${\mathrm{O}}^{+}$ in the Ar film (charge transfer) or an Ar structure different from fcc (such as blocking of ${\mathrm{O}}^{+}$ by Ar) is the reason for the strong attenuation of ${\mathrm{O}}^{+}$ in Ar. We find greater attenuation per monolayer for thicker films than for the first monolayer; we correlate this with the fcc structure of the rare-gas films. We discuss the energy loss of the primary electrons in the rare-gas film, the effect of the adsorption of rare gases on the electron-stimulated desorption process, and the possibility of preferential ${\mathrm{O}}^{+}$ desorption through channels in the rare-gas film. We draw conclusions from our results concerning the depth of origin of secondary ions desorbed under the influence of electron, photon, or ion radiation.

Isotope effect in electron stimulated desorption: The role of internal degrees of freedom in CO desorption from Pt(111)

Electron stimulated desorption (ESD) of CO+, O+, metastable neutral CO*, and ground state neutral CO from the CO/Pt(111) was studied, using isotopic substitution of CO. Four isotopic versions of CO were compared in their desorption behavior. Contrary to the prediction of theoretical models that suggest a decrease of the ESD yield with increasing mass of a given desorption product, the CO+ and CO* ESD yields were found to be larger from the (heavier) 12C18O than from the (lighter) 13C16O adsorbate. The O+ ESD yields followed the expected trend Y(16O+)≳Y(18O+). No isotope effect was observed for ground state neutral CO desorption. Qualitative arguments explaining the anomalous isotope effect, and emphasizing the importance of internal dynamics, in particular, the rotation of diatomic desorption products in the ESD process, are presented. Here it is shown that the velocity of departure of the carbon end of the rotating CO molecule may control neutralization or quenching effects for CO+ or CO* produced by electron stimulated desorption. Thus, neutralization or quenching of the excited CO species occurs via carbon-centered orbitals of the departing species.