Sebastien Gauthier

• Centre for Materials Elaboration and Structural Studies

Electron standing wave patterns around single hexa-peri-hexabenzocoronene (HBC) molecules adsorbed on the surface of thin KBr(001) films grown on Ag(111) are observed by scanning tunneling microscopy. We suggest that they result from the scattering, by the molecules, of the electrons populating the surface resonance associated with the lowest image...

With a central curved chassis, a four wheels molecule-vehicle was deposited on an Au(111) surface and imaged at low temperature using a scanning tunneling microscope. The curved conformation of the chassis and the consequent moderate interactions of the four wheels with the surface were observed. The dI/dV constant current maps of the tunneling ele...

The adsorption of hexa-peri-hexabenzocoronene (HBC) on NaCl and KBr bilayers deposited on Ag(111) is studied by Scanning Tunneling Microscopy (STM) and spectroscopy at low temperature (5K). HBC tends to move under the influence of the STM tip on NaCl/Ag(111), even in the mildest imaging conditions, preventing the imaging of its molecular electronic...

The formation of highly organized structures based on two ligands with pyridyl functionalities, 4,4'-bipyridine (BPY) and 1,4-di(4,4"-pyridyl) benzene (BPYB)), and Cu adatoms on the Cu(111) surface has been studied with low temperature and variable temperature scanning tunneling microscopy (STM) and first-principle calculations. We are showing that...

Charging of 2D Au nanoplatelets deposited on an insulating SiO2 substrate to or from the tip of a non-contact atomic force microscope (nc-AFM) is demonstrated. Charge transfer is controlled by monitoring the resonance frequency shift Δf(V) during the bias voltage ramp V applied to the tip-back electrode junction. The onset of charge transfer is rev...

Silicon carbide (SiC) is nowadays a major material for applications in high power electronics, quantum optics, or nitride semiconductors growth. Mastering the surface of SiC substrate is crucial to obtain reproducible results. Previous studies on the 6H-SiC(0001) surface have determined several reconstructions, including the (3×3)−R30∘ and the (3×3...

The study revealed that the nature of the AlN (0001) surface could play a fundamental role in the growth mode of metals. In the case of silver (Ag) deposited on the AlN(0001) (2×2)-Nad reconstructed surface, the growth mode was Volmer–Weber. Deposition of indium (In) on a contaminated AlN(0001) surface leads to the formation of a wetting layer, fol...

Noncontact atomic force microscopy images show that gold grows on the (2×2)−Nad reconstructed polar (0001) surface of AlN insulating films, in the form of large monatomic islands. High-resolution images and in situ reflection high-energy electron diffraction spectra reveal two moiré patterns from which an atomic model can be built. Density function...

Combined experimental and theoretical studies permit us to determine new protocols for growing by molecular beam epitaxy the technologically interesting N-rich aluminum nitride (AlN) surfaces. This is achieved by dosing the precursor gases at unusually low rates. With the help of calculated structures by using density functional theory and Boltzman...

Single 1,8-octanedithiol (ODT) molecules adsorbed onto the Cu(100) surface have been characterized by using scanning tunneling microscopy (STM) and studied by semi-empirical calculations. STM images have revealed two types of chiral molecules on the surface upon adsorption and both types of molecules showed two bright spots at the extremities of a...

The adsorption of single hexamethoxyltriphenylene molecules on KBr(001) at low temperature (T<10K) was studied by low temperature (T=5K) non-contact atomic force microscopy in ultra-high vacuum. Images of the frequency shift, measured at constant height, show intramolecular features that are interpreted on the basis of molecular force-field calcula...

Nitride wide-band-gap semiconductors are used to make high power electronic devices or efficient light sources. The performance of GaN-based devices is directly linked to the initial AlN buffer layer. During the last twenty years of research on nitride growth, only few information on the AlN surface quality have been obtained, mainly by ex-situ cha...

The results of the study of the adsorption of 2,3,6,7,10,11-hexacyanopropyloxytriphenylene on KBr(001) by non-contact atomic force microscopy (nc-AFM) coupled to Kelvin probe force microscopy (KPFM) are presented. A particular emphasis is put on the KPFM measurements. In particular, the contrast in the Kelvin potential between a molecular monolayer...

Imaging and Manipulation of Adsorbates using Dynamic Force Microscopy provides an overview of the latest developments in dynamic force microscopy (DFM) of atoms, molecules, and nanoparticles adsorbed on solid surfaces. Significant advances in the capabilities of this technique have been made in the last decade and this book represents a timely snap...

Cantilevers with resonance frequency ranging from 1 MHz to 100 MHz have been developed for dynamic atomic force microscopy. These sensors are fabricated from 3C-SiC epilayers grown on Si(100) substrates by low pressure chemical vapor deposition. They use an on-chip method both for driving and sensing the displacement of the cantilever. A first gold...

Thermally activated rotation of single molecules adsorbed on a silicon-based surface between 77 and 150 K has been successfully achieved. This remarkable phenomenon relies on a nanoporous supramolecular network, which acts as a template to seed periodic molecule rotors on the surface. Thermal activation of rotation has been demonstrated by STM expe...

Artistic representation of thermally activated rotation of pentaphenylbenzene molecules trapped in hexagonal nanopores of a supramolecular network on a SiB(111) surface, suggesting the achievement of molecular machines on semiconducting surfaces, as detailed by F. Palmino et al. on p. 271.

We have developed an energy-filtering device coupled to a quadrupole mass spectrometer to deposit ionized molecules on surfaces with controlled energy in ultra high vacuum environment. Extensive numerical simulations as well as direct measurements show that the ion beam flying out of a quadrupole exhibits a high-energy tail decreasing slowly up to...

We investigated the implementation of a numerical tool able to mimic an experimental noncontact atomic force microscope (nc-AFM). Main parts of an experimental setup are modeled and are implemented inside a computer code. The goal was to build a numerical AFM (n-AFM) as versatile, efficient, and powerful as possible. In particular, the n-AFM can be...

In a combined scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) study, we characterize the reversible switching between two stable states of an organometallic complex, namely, bis-dibenzoylmethanato-copper [Cu(dbm)2] adsorbed on an insulating thin film. The switching is due to the transfer of an electron between th...

Background: Characterization at the atomic scale is becoming an achievable task for FM-AFM users equipped, for example, with a qPlus sensor. Nevertheless, calculations are necessary to fully interpret experimental images in some specific cases. In this context, we developed a numerical AFM (n-AFM) able to be used in different modes and under diffe...

The adsorption on KBr(001) of a specially designed molecule, consisting of a flat aromatic triphenylene core equipped with six flexible propyl chains ending with polar cyano groups, is investigated by using atomic force microscopy in the noncontact mode (NC-AFM) coupled to Kelvin probe force microscopy (KPFM) in ultrahigh vacuum at room temperature...

The scientific and technical challenges involved in the building of the planar electrical connection of an atomic scale circuit to N electrodes (N > 2) on insulating substrates are presented. In the Nanoscience group of Toulouse, the UHV factory has been developed since ten years in order to realize under UHV the five levels of interconnections on...

One way to improve the force sensitivity of Atomic Force Microscopy (AFM) cantilevers is to increase their resonance frequency. SiC is an excellent material for that purpose due to its high Young’s modulus and low mass density. This size reduction makes conventional optical motion detection methods inappropriate. Here, we introduce self-sensing, se...

STM investigations on the adsorption of submonolayers of large organic molecules smaller than 6 nm were carried out on copper surfaces to compare two different deposition methods: the thermal sublimation and the pulse-injection. The blue lander, a member of the lander family, could be deposited intact with the thermal procedure, therefore it was us...

Single decastarphene molecules, adsorbed on Cu(111) and on a bilayer of NaCl/Cu(111) are imaged by a combination of low temperature scanning tunneling microscopy (STM) and dynamic atomic force microscopy in the non-contact mode (nc-AFM). This dual imaging technique provides the intramolecular electron density maps of the frontier molecular orbitals...

The goal of Colchero et al.'s paper [J. Appl. Phys. 109, 024310 (2011)] is to extend the expression of the frequency noise generated by the thermal fluctuation of the cantilever in a non contact (or frequency modulation) force microscope from the low to the large measurement bandwidth regime. We claim that this expression is already valid in the la...

Molecular adsorption studies on atomically clean, well-defined surfaces of bulk insulators are still very scarce and have been restricted to a small number of molecules. In this study, the adsorption of 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP) on KBr(001) was investigated by atomic force microscopy in noncontact mode (NC-AFM) under ultrahigh va...

Scanning tunneling microscopy and dynamic force microscopy in the noncontact mode are used in combination to investigate the reversible switching between two stable states of a copper complex adsorbed on a NaCl bilayer grown on Cu(111). The molecular conformation in these two states is deduced from scanning tunneling microscopy imaging, while their...

The same specimen of Pb/Cu grown under Ultra High Vacuum (UHV) conditions has been investigated by Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). We show that the information obtained by these techniques is consistent when comparable, and complementary. In particular, three different m...

The adsorption of indigo molecules on Cu(111) was investigated by low temperature (5 K) scanning tunneling microscopy from the isolated single molecule regime to one monolayer. Structural optimization and image calculations demonstrate that the molecules are in a physisorbed state. Because of the reduced symmetry at the surface, single molecules ac...

The scientific and technical challenges involved in building the planar electrical connection of an atomic scale circuit to N electrodes (N > 2) are discussed. The practical, laboratory scale approach explored today to assemble a multi-access atomic scale precision interconnection machine is presented. Depending on the surface electronic properties...

An isomer of the methylterrylene molecule was adsorbed both on Cu(111) and on a NaCl bilayer deposited on Cu(111) and imaged by ultra high vacuum scanning tunneling microscopy at low temperature (5 K). On the bare metal surface, the STM images do not reveal any intramolecular resolution and do not depend on the applied tunnel bias. On the contrary,...

Analytical expressions for the noise affecting the different signals of interest in frequency-modulation dynamic force microscopy are derived. Two noise sources are considered, the thermomechanical noise of the cantilever and the noise of the deflection sensor. It is shown that distinguishing between amplitude and phase noise is crucial for a good...

Buckybowls: The adsorption of penta-tert-butylcorannulene, a molecule with fivefold symmetry, on Cu(111), a surface with threefold symmetry, is investigated by scanning tunneling microscopy complemented by structure calculations. The symmetry mismatch is resolved by the formation of threefold-symmetric subunits consisting of three molecules, which...

A dynamic nanostencil system based on a movable atomic force microscopy (AFM) cantilever-borne mask has been developed in ultrahigh vacuum environment. This system is conceived to offer an outstanding nanopatterning capability of nanometer precision as well as in situ AFM characterization with a large scanning range. Evaporation experiments in both...

We present atomic resolution images of monatomic step edges on the KBr(001) surface imaged by dynamic force microscopy operated in the non-contact mode. Under certain experimental conditions, we observe a systematic and reversible change of the atomic contrast when the tip crosses the step. This change is attributed to the reversal of the polarity...

Two isomers of the methylterrylene molecule were adsorbed on a NaCl bilayer deposited on Cu(111) and imaged by ultra high vacuum scanning tunneling microscopy at low temperature (5K). The images acquired for specific bias voltages show a striking similarity with the spatial distribution of the electronic probability density in the highest occupied...

We present the results of the multiscale modeling of the process of lateral manipulation of a Pd adatom adsorbed on the MgO (001) surface using a noncontact atomic force microscope (AFM) at finite temperature and in real time as a tip moves above the surface. We show that the stochastic motion of Pd adatoms can be controlled by localized forces fro...

We present the results of calculations performed to investigate the process of single-atom manipulation with the non-contact atomic force microscope comparing the two most common experimental set-ups: a conventional large amplitude silicon cantilever and a small amplitude quartz tuning fork. The manipulation of a model system—an oxygen vacancy in t...

Analytical expressions giving the noise power spectral densities of the signals of interest in frequency modulation-dynamic force microscopy are derived. They are validated by comparison with numerical simulations performed with a realistic virtual force microscope. Thermal noise as well as detection noise are considered. A tip-substrate interactio...

Stencil lithography is used for patterning and connecting nanostructures with metallic microelectrodes in ultrahigh vacuum. Microelectrodes are fabricated by static stencil deposition through a thin silicon nitride membrane. Arbitrary nanoscale patterns are then deposited at a predefined position relative to the microelectrodes, using as a movable...

Using a virtual dynamic atomic force microscope, that explicitly simulates the operation of a non-contact AFM experiment, we have performed calculations to investigate the formation of atomic-scale contrast in dissipation images. A non-conservative tip–surface interaction was implemented using the theory of dynamical response in scanning probe micr...

Stencil lithography is used for patterning and connecting nanostructures with metallic microelectrodes in ultrahigh vacuum. Microelectrodes are fabricated by static stencil deposition through a thin silicon nitride membrane. Arbitrary nanoscale patterns are then deposited at a predefined position relative to the microelectrodes, using as a movable...

We present the results of calculations performed to model the process of lateral manipulation of an oxygen vacancy in the MgO(001) surface using the non-contact atomic force microscope (NC-AFM). The potential energy surfaces for the manipulation as a function of tip position are determined from atomistic modelling of the MgO(001) surface interactin...

Because of its promising contribution to the bottom-up approach for nanofabrication of complex molecular architectures, self-organization is widely studied nowadays. Numerous studies have tackled supramolecular chirality or low-dimensional molecular nanostructures using in most cases small and rigid molecules adsorbed on metallic substrates. In thi...

Nanometre-size gold clusters supported on MoS(2)(0001) are investigated by means of ultrahigh-vacuum frequency modulation dynamic force microscopy. Topography and frequency shift images are simultaneously obtained using the average tunnelling current to regulate the tip-substrate distance. Two families of clusters are observed, giving different fre...

Because of its tetrahedral structure, spirobifluorene is an innovative molecule for molecular mechanics studies by means of scanning tunneling microscopy. On Cu(100), it was observed only anchored at defects because of its mobility at room temperature. To frustrate its diffusion, it was functionalized with phenyl and thiophene groups. Tetraphenylsp...

Calculations of frequency modulation-atomic force microscopy (FM-AFM) images are presented. A virtual FM-AFM, which realistically simulates the experiment by including the control system of the microscope, is implemented in order to go beyond the usual static approximation. It is shown that the results obtained within the static approach can be rec...

Amplitude resonance curves of a driven dynamic force microscope cantilever interacting with a Cu(100) substrate in ultra high vacuum are derived and analysed, extending a previous study on Al2O3(0001) (Polesel-Maris et al 2003 Nanotechnology 14 1036). It is shown that the charges that are trapped on the oxidized n+-doped silicon tip give rise to lo...

The transport properties of two oligothiophene derivatives, that differ only by the chemical group coupling to gold, are compared. It is shown that the role of the coupling group in the transport properties can be decoupled from that of the conjugated body of the molecules and that Se is a better electronic coupling group than S. These results are...

A precise experimental investigation of the amplitude and phase resonance curves of a driven dynamic force microscope (DFM) cantilever interacting with an Al2O3(0001) surface in ultra-high vacuum is reported. The large amplitude (a few tens of nanometres), high cantilever stiffness (25 N m−1) and high quality factor (a few 104) characterizing these...

Spatial maps of the power spectral density of the high-frequency fluctuations of the tunnelling current have been obtained with a UHV-STM for two different systems: O2/Cu(1 0 0) and large molecules (blue Landers) on Cu(1 0 0). These “noise” images are strongly correlated with simultaneously acquired “topographic” images down to molecular resolution...

The adsorption of a new molecule constituted of a 3.7-nm long conjugated board equipped with eight lateral legs was studied with scanning tunneling microscopy on the Cu(100) and nanostructured Cu(111) surfaces. The conformation of the adsorbed molecules was extracted by comparing experimental images with calculated ones. In particular, we demonstra...

We performed air and ultra-high vacuum scanning tunneling microscopy experiments in order to compare the electronic coupling provided by S and by Se used as alligator clips for bisthiol- and biselenol-terthiophene molecules adsorbed onto gold. The molecules were inserted in a dodecanethiol self-assembled monolayer. Their apparent height above the d...

The room temperature adsorption of a chromium tris-diketonate, i.e., tris-dibenzoylmethanate on Cu(100) was investigated using scanning tunnelling microscopy in ultra high vacuum (UHV-STM). The analysis of the STM images, supported by image calculations demonstrates that the molecule dissociates by loosing one ligand, both products remaining adsorb...

The adsorption on Cu(100) of a long molecular wire constituted of a 2.5 nm conjugated board equipped with four lateral legs is investigated using scanning tunnelling microscopy (STM). The legs are free to rotate when the molecule approaches the surface. Experimental images are analysed and compared to calculated images based on an optimisation of t...

Experiments performed using NC-AFM on a pure graphite surface suggest that the mechanical deformation of the surface under test is able to explain the observed damping signal. A simple analytical model has been built to evaluate the damping signal in terms of the mechanical properties of the surface, the amplitude of the oscillation and the tip-sur...

A short review of recent experimental and theoretical studies of atomic and molecular manipulations of individual adsorbates by scanning tunneling microscopy (STM) is given. The different types of manipulations are detailed, with an analysis of the interactions responsible for the displacement of the adsorbate.

Over the last decade, extensive exploitation of the different kinds of near-fields existing spontaneously or artificially in immediate proximity to the surface of materials has generated a considerable amount of new exciting developments. In this review the main physical properties of these peculiar fields are revisited. In a first stage, following...

The surface structures formed by submonolayer deposition of lead on the (100) face of copper in the 160–220K temperature range are investigated by Low-Energy Electron Diffraction (LEED) and Scanning Tunneling Microscopy (STM). The two ordered structures observed are modelled as checkerboard patterns of c(2×2) antiphase domains, in full agreement wi...

The morphology and structure of Pb deposits on Cu(100) between 150 and 220 K is investigated using low-energy electron diffraction (LEED), auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). It is found that Pb grows along a 〈111〉 axis, with Pb〈110〉 parallel to Cu〈100〉. In the surface plane, this relationship of epitaxy induc...

LEED observations on nitrogen adsorbed on (h11) stepped and (100) copper faces have shown the existence of two surface phases with a first order transition. The first one corresponds, on the (100) face, to the formation of an ordered stepped overlayer composed of alternating square c(2 × 2)N island and bare copper of 〈100〉 atomic rows and on the (h...

We have investigated the thermal instability of Au(111) vicinal surfaces by scanning tunneling microscopy in ultrahigh vacuum. Above an annealing temperature of 700 K, both the Au(11,9,9) and the Au(4,3,3) surfaces undergo a phase separation into (111) facets and portions of (7,5,5). In addition, the faceted surfaces present a long‐range order: the...

The adsorption of Pb on Cu(100) from 0 to 1 ML was investigated by UHV scanning tunneling microscopy. We obtained atomic resolution images of the different superstructures which appear at 300 K with increasing coverage (c(4 × 4), c(2 × 2) and c( √2)R45°). We confirm recent results and propose, partly on the basis of low temperature studies, new arg...

Using scanning tunneling microscopy and low energy electron diffraction, the thermal faceting of two Au(111) vicinal surfaces belonging to the [01] zone is investigated. Above 700 K, a final stable state is found: it consists of a periodic succession of (111) and (755) facets. The superperiod is 70 Å for Au(1199) and 110 Å for Au(433). The quantita...

The Au(4,3,3) surface, vicinal to Au(1,1,1), has been studied by scanning tunneling microscopy in ultra high vacuum. It is thermally unstable towards faceting. For annealing temperatures ranging from 700 K to 1000 K, the stable state of the faceted surface is found to be a periodic succession of (1,1,1) and (7,5,5) facets. The superperiod is about...

We present STM observations of “magic” vicinal areas on a Au(100) sample. The surface displays the well-known quasihexagonal reconstruction on flat (100) as well as on vicinal regions. In these regions, it is observed that the terrace widths are strongly related to the reconstruction period. In addition, the steps present diatomic kinks periodicall...

The influence of the anisotropy of the (5×n) reconstructed (100) face of gold on the generation of vacancy islands by sputtering with 600 eV Ar+ ions has been investigated by scanning tunneling microscopy. The shapes of these islands, bounded by monoatomic steps, are shown to be growth shapes, rather than equilibrium shapes. The growth mechanisms l...

The morphology of the (100) face of copper after sputtering with 600 eV Ar+ ions has been investigated by scanning tunneling microscopy (STM) as a function of ion beam flux and fluence. This process generates vacancy and adatom islands bounded by monatomic steps. These islands exhibit their equilibrium shape, which can be described as a square with...

We present experimental evidence for a dramatic influence on the aspect of tunneling images of the orientation relative to a [110] direction of the steps on vicinal copper surfaces. A model is proposed which relates these observations to the mobility of geometrical kinks of the step edges. This model allows one to deduce from the experimental data...

The main results of Scanning Tunneling Microscopy (STM) studies of the morphology of copper surfaces are presented. It illustrates the ability of this technique to investigate the relationship between surface morphology and the atomic mechanisms which determine it. The first study concerns the equilibrium fluctuations of steps on surfaces vicinal f...

STM images of clean vicinal copper surfaces are presented. The order of magnitude of the diffusion coefficient deduced from these images show that they reflect the structure of the surface in equilibrium at room temperature, on a length-scale of tens of nm. The correlation function along step edges and the terrace-width distribution are evaluated a...

Some of the defects commonly observed by scanning tunnelling microscopy (STM) on graphite can be interpreted as crystal dislocations; we study in this paper the dislocation pattern of different kinds of subboundary (twist boundary and tilt boundary) found on the (0001) cleavage plane of pyrolytic graphite. The origin of the contrast in our STM imag...

We have obtained atomically resolved scanning tunneling microscopy images of sulfur adsorbed on two copper surfaces. These surfaces, the Cu(11,1,1) face and the Cu(8,1,0) face, which are both vicinal from the (100) plane, differ essentially by the atomic structure of their step edges. Two sulfur superstructures are resolved on both surfaces, a p(2×...

Two superstructures of adsorbed sulfur coexisting on the stepped Cu(11 1 1) surface are identified by scanning tunneling microscopy. A p(2×2) and a c(4×2) structures are atomically resolved and their interaction with the steps investigated. The direction taken by a step edge is found to be strongly correlated with the sulfur arrangement on the adja...

The tunneling current between two nonplanar electrodes is treated as a model for scanning tunneling microscopy (STM) in which the tip is nonspherical. One electrode is bounded by a perfect infinite plane with a small protuberence, representing the tip, while the other has a corrugated surface, representing the sample. We calculate the tunneling cur...

Scanning tunneling microscopy (STM) has been established as an important surface sensitive technique both in the domain of atomic imaging [1] and surface electronic spectroscopy [2]. The interpretation of the images relies mostly on the theory of Tersoff and Hamman [3], who have demonstrated that, in the limit of small applied bias and for a spheri...

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The topographic image as given by scanning tunneling microscopy (STM) is deduced in analytic form in a free-electron, or Sommerfeld model. The method is non-numerical and employs perturbed wave functions for an arbitrarily modified plane metal surface to approximate the local density of states (LDOS), at the Fermi level. The curves of constant LDOS...

An insulating layer is produced on aluminum by glow discharge in CF4. This substrate, used as the insulator of metal-insulator-metal diodes is characterized by Inelastic Electron Tunneling Spectroscopy as an aluminum trifluoride AlF3. The adsorption of ammonia, benzylamine. formic and propiolic acid on this substrate is investigated. A comparison b...

This paper is devoted to the study of aluminum-oxide-metal tunneling junctions where the oxide has been grown on aluminum by glow discharge in water vapor. The inelastic electron tunneling spectra obtained from these samples have been investigated and new assignments of the observed bands are proposed. In particular, evidence for the presence of A1...

A study has been made of the optical constants of amorphous H2O ice in the 2.5-80 micron range. The range was selected for its relevance to astrophysics. The results are fit to a model of IR sources in molecular clouds. There is a good fit of the molecular cloud IR signature at 3.1-microns, assuming the grains are made of an intimate mixture of ice...

This paper is devoted to an experimental study of relative intensities in inelastic electron tunneling spectra of organic molecules. The theoretical framework is given by the first theory of tunneling intensities, the theory of Scalapino and Marcus. We compare the predictions of this theory with our experimental data and find evidence for an import...

Inelastic Electron Tunneling Spectroscopy has been used to study the adsorption of NO on evaporated Rh particles supported on alumina. The molecule adsorbs dissociatively and the nitrogen reacts with hydroxyl groups on the alumina surface to form a RhNHx species, as shown by studies using 15NO and a deuteroxyled alumina surface.

The modes of simple carboxylic acids, when adsorbed on alumina are not all undisputably identified. The spectra of marked acetic acid CH3C18O18OH and CD3COOD adsorbed on alumina allow us to clarify the assignments.