Low Energy Ion Beam Techniques Research Articles

Channeling of low-energy ions on hydrogen-covered single-crystal surfaces

Low-energy ion beam techniques such as direct recoil spectroscopy (DRS) are well-suited for directly detecting adsorbed hydrogen. However, with this approach it has previously only been possible to detect the hydrogen configuration on single-crystal surfaces for a narrow range of conditions (e.g., when the adsorbate atoms reside close to the surface). In this study we investigate the experimental and modeling tools needed to extend DRS to a much wider range of adsorption geometries. At grazing incidence, we show how adsorbed hydrogen affects ion focusing along open surface channels, thereby revealing fine details about the binding geometry even for adsorbates residing high above the substrate. Under such conditions, the scattering process is characterized by ions interacting with many atoms simultaneously. Therefore interpreting these types of measurements properly requires realistic molecular dynamics (MD) simulations with accurate scattering potentials at large distances. As an illustration of the progress that can be made, we consider how hydrogen is recoiled from W(100)$+$H(ads) during exposure to a low-energy (1 keV) Ne${}^{+}$ analysis beam at grazing incidence. The closest approach distance of the ions is $>$1 $\AA{}$, making hydrogen located high above the substrate readily accessible. By mapping the hydrogen recoils over different crystallographic directions using DRS, we identify focusing mechanisms that provide information on the adsorbed hydrogen configuration. When W(100) is continuously dosed with H${}_{2}$(g) to maintain a saturation coverage, we observe enhanced recoil signals along the $\ensuremath{\langle}$100$\ensuremath{\rangle}$ and $\ensuremath{\langle}$110$\ensuremath{\rangle}$ azimuths consistent with hydrogen residing in bridge sites. The reproduction of the complex experimental scattering spectra by our MD modeling techniques offers a pathway to locate hydrogen well within its vibrational envelope.

Shallow junction formation by polyatomic cluster ion implantation

Recent integrated circuits require shallower junctions which are less than 0.1 μm depth. Therefore, there is a strong demand for low energy ion beam techniques. Equivalent low-energy and high-current ion beams can be realized quite easily with cluster, because the kinetic energy of the cluster is shared between the constituent atoms. Additionally, cluster-ion beams avoid damage due to excessive charge. We have used polyatomic clusters, decaborane (B 10H 14), as a kind of B cluster, in order to form a very shallow p + n junction. B SIMS profile of B 10H 14 implanted into Si (100) at 20 keV was quite similar to that of B implanted at 2 keV. These SIMS measurements revealed that the cluster ion beam can realize equivalent low-energy implantation quite easily. The implantation efficiency achieved was about 90%. The damage induced by B 10H 14 implantation was completely removed by a 600°C furnace anneal for 30 min, and implanted B atoms were electrically activated. After rapid thermal annealing (RTA) at 900°C of a sample prepared with a dose of 5 × 10 13 ions/cm 2, the sheet resistance decreased to about 600 Ω/sq. and the activation efficiency was about 50%. These results show that a polyatomic cluster ion beam is useful for shallow junction formation.

Interaction of silicon cluster ions with ammonia: The kinetics

The chemical reactions of Si+n (n=10–50) with ammonia have been studied using injected ion drift tube techniques at thermal energies (296–414 K), and low energy ion beam techniques, at a center of mass collision energy of ∼0.2 eV. Virtually all of the products arise from the adsorption of one or more ammonia molecules on to the parent cluster ion. In the drift tube experiments all clusters (except those with 11, 13, 14, 19, 22, and 23 atoms) were found to react with ammonia at close to the collision rate at room temperature. The reaction rates decrease with increasing temperature. Thermally activated desorption of ammonia from the products contributes to the negative temperature dependence. This observation suggests that unlike bulk silicon surfaces, which are known to adsorb NH3 dissociatively (and desorb H2 at ∼800 K), the silicon clusters may not be able to dissociate ammonia (at least on the time scale of our experiments). For clusters with 30–50 atoms, total cross sections for adduct formation were measured at collision energies of ∼0.2 eV. The cross sections are close to the hard sphere values and increase slowly with cluster size. In contrast to the results of Smalley and co-workers, obtained using Fourier transform ion cyclotron resonance, we do not find Si+33, Si+39, and Si+45 to be particularly unreactive. Several possible explanations for the large differences in the reactivities of these clusters (as measured by the two different experimental techniques) are discussed.

Chemistry of semiconductor clusters. A survey of the reactions of Si25+ using low-energy ion beam techniques

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemistry of semiconductor clusters. A survey of the reactions of Si25+ using low-energy ion beam techniquesMartin F. Jarrold and J. Eric BowerCite this: J. Am. Chem. Soc. 1989, 111, 6, 1979–1986Publication Date (Print):March 1, 1989Publication History Published online1 May 2002Published inissue 1 March 1989https://doi.org/10.1021/ja00188a005RIGHTS & PERMISSIONSArticle Views49Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1015 KB) Get e-Alerts Get e-Alerts

Surface chemistry on metal clusters: Observation of multiple structures for C 2H 4 chemisorbed on aluminum clusters

The chemisorption of C 2H 4 on aluminum cluster ions, Al itn + ( n=24–26), has been studied using low-energy ion beam techniques. Three different types of Al itnC 2H 4 + adduct (labelled A, B and C) were observed over different collision energy ranges. Formation of adduct A proceeds with no activation barrier, but there are activation energies of 0.5–1.0 and 3.0–3.5 eV for adducts B and C, respectively. It is argued that these three distinct adducts are due to different structures of the C 2H 4 species on the cluster surface. Chemisorption of C 2H 4 in adducts A and B is probably non-dissociative, but adduct C arises from dissociative chemisorption.

Activation barriers for chemisorption of deuterium on aluminum cluster ions: Influence of oxygen preadsorption

Activation barriers for chemisorption of deuterium on size-selected aluminum clusters with one or two preadsorbed oxygen atoms (Al n O k +, n=10–27, k=1, 2) are reported. These measurements were made by determining the collision energy threshold for chemisorption using low energy ion beam techniques. Oxygen preadsorption has a dramatic effect on the activation barriers for some of the smaller clusters ( n<18). For example, preadsorption of one oxygen atom on Al 15 + causes the activation barrier to increase by over 0.5 eV from that observed with the bare cluster. The origin of these very size-specific changes caused by oxygen preadsorption may be the result of a global perturbation of the cluster's electronic properties rather than involving a site-specific mechanism.

Studies of Surfaces of Materials Using Low Energy Ion Beams

Characterization of solid surfaces using low energy, i.e. ? 10keV, ion beams has gained increasing popularity during the past decade. The three most commonly used low energy ion beam techniques are: secondary ion mass spectrometry (SIMS), sputter-induced photon spectrometry (SIPS) and ion scattering spectrometry (ISS). As far as detection sensitivity is concerned, SIMS is probably superior to almost all surface analytical techniques. Impurity levels in the parts per million range can be easily determined. SIMS is widely applied to semiconductor problems in which concentration-versus-depth information is usually sought. SIPS is especially suited to compositional analysis of non-conducting materials since, unlike techniques based on detection of charged particles, charging of the sample surface by the primary beam does not affect the collection of optical radiation from sputtered excited atoms. ISS is probably the best available technique for studying the composition of the topmost surface layer of any material. Its monolayer sensitivity due to the properties of low energy scattering is unique among surface analytical techniques. This paper discussed the use of each of these three techniques to solve problems in materials science.