Drying nano particles solution on an oscillating tip at an air liquid interface: what we can learn, what we can do

Evaporation of fluid at micro and nanometer scale may be used to self-assemble nanometre-sized particles in suspension. Evaporating process can be used to gently control flow in micro and nanofluidics, thus providing a potential mean to design a fine pattern onto a surface or to functionalize a nanoprobe tip. In this paper, we present an original experimental approach to explore this open and rather virgin domain. We use an oscillating tip at an air liquid interface with a controlled dipping depth of the tip within the range of the micrometer. Also, very small dipping depths of a few ten nanometers were achieved with multi walls carbon nanotubes glued at the tip apex. The liquid is an aqueous solution of functionalized nanoparticles diluted in water. Evaporation of water is the driving force determining the arrangement of nanoparticles on the tip. The results show various nanoparticles deposition patterns, from which the deposits can be classified in two categories. The type of deposit is shown to be strongly dependent on whether or not the triple line is pinned and of the peptide coating of the gold nanoparticle. In order to assess the classification, companion dynamical studies of nanomeniscus and related dissipation processes involved with thinning effects are presented

Procédures de mesure du « bruit » d'un AFM : un retour d'expérience.

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Electrical and physical topography in energy-filtered photoelectron emission microscopy of two-dimensional silicon pn junctions

International audiencePhotoelectron emission microscopy (PEEM) is a powerful non-destructive tool for spatially resolved, spectroscopic analysis of surfaces with sub-micron chemical heterogeneities. However, in the case of micron scale patterned semiconductors, band line-ups at pn junctions have a built-in lateral electric field which can significantly alter the PEEM image of the structure with respect to its physical dimensions. Furthermore, real surfaces may also have physical topography which can reinforce or counteract the electrically induced distortion at a pn junction. We have measured the experimental PEEM image distortion at such a junction and carried out numerical simulations of the PEEM images. The simulations include energy filtering and the use of a contrast aperture in the back focal plane in order to describe the changes in the PEEM image of the junction with respect to its real physical dimensions. Threshold imaging does not give a reliable measurement of micron sized p and n type patterns. At higher take-off energies, for example using Si 2p electrons, the pattern width is closer to the real physical size. Physical topography must also be quantitatively accounted for. The results can be generalized to PEEM imaging of any structure with a built-in lateral electric field

Aspects of lateral resolution in energy-filtered core level photoelectron emission microscopy

International audienceLateral resolution is a major issue in photoelectron emission microscopy (PEEM) and received much attention in the past; however a reliable practical methodology allowing for inter-laboratory comparisons is still lacking. In modern, energy-filtered instruments, core level or valence electrons give much lower signal levels than secondary electrons used in still most of the present experiments. A quantitative measurement of the practical resolution obtained with core level electrons is needed. Here, we report on critical measurements of the practical lateral resolution measured for certified semiconducting test patterns using core level photoelectrons imaged with synchrotron radiation and an x-ray PEEM instrument with an aberration-corrected energy filter. The resolution is 250 ± 20 nm and the sensitivity, 38 nm. The different contributions to the effective lateral resolution (electron optics, sample surface imperfections, counting statistics) are presented and quantitatively discussed

Core level photoelectron spectromicroscopy with Al Kalpha1 excitation at 500 nm spatial resolution

International audienceCore level photoelectron spectromicroscopy in laboratory conditions (XPS imaging) with standard Al Kalpha1 excitation (1486.6 eV), either in scanning or parallel imaging mode, is currently limited to a spatial resolution of ∼4 um. Using energy-filtered X-ray photoelectron emission microscopy (XPEEM) and a bright monochromated Al Kalpha source (photon flux ∼1012 photons/(s.mm2)), we demonstrate refined results regarding lateral and energy resolutions on cross-sectioned epitaxial Si/SiGe layers imaged with photoelectrons of 266.4 eV energy referred to the Fermi level of the sample (Ge 2p3/2 transition). Despite an elemental contrast of only 50%, XPS imaging performed this way has an edge lateral resolution of 480 nm and an energy resolution of 0.56 eV, the spectroscopic information being available at the decanometric scale. Since the lateral resolution is only limited by the counting statistics due to a modest illumination flux, this method paves the way to laterally resolved XPS and UPS in the 100 nm range

Sub-10 nm spatial resolution for electrical properties measurements using bimodal excitation in electric force microscopy (vol 92, 023703, 2021)

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Sub-10 nm spatial resolution for electrical properties measurements using bimodal excitation in electric force microscopy

International audienceWe demonstrate that under ambient and humidity-controlled conditions, operation of bimodal excitation single-scan electric force microscopy with no electrical feedback loop increases the spatial resolution of surface electrical property measurements down to the 5 nm limit. This technical improvement is featured on epitaxial graphene layers on SiC, which is used as a model sample. The experimental conditions developed to achieve such resolution are discussed and linked to the stable imaging achieved using the proposed method. The application of the herein reported method is achieved without the need to apply DC bias voltages, which benefits specimens that are highly sensitive to polarization. Besides, it allows the simultaneous parallel acquisition of surface electrical properties (such as contact potential difference) at the same scanning rate as in amplitude modulation atomic force microscopy (AFM) topography measurements. This makes it attractive for applications in high scanning speed AFM experiments in various fields for material screening and metrology of semiconductor systems

Correlative TOF-SIMS & XPS for the analysis of dopants for organic light-emitting diodes layers

International audienceOrganic light-emitting diodes (OLEDs) are widely used for display and lighting applications yet improvements need to be made in device lifetime, efficiency and luminance to address new applications. To facilitate these developments, there is a need to study the impact of new molecules and dopants [1]. The use of Ag to replace Cs as a dopant was recently demonstrated [2, 3] in 2019 and should be more air-stable. Here we study Ag doped BPhen (4,7-Diphenyl-1,10-phenanthroline) and Ca doped BPhen in a set of test samples where the BPhen layer is sandwiched between two electrodes. We used a correlative protocol to combine TOF-SIMS and XPS measurements on exactly the same sample area [4]. TOF-SIMS tandem mass spectrometry was performed on the Ag doped BPhen layer to confirm the formation of a Ag-BPhen complex. XPS C 1s and N 1s spectra acquired from the same layers show a 0.6 eV peak shift to higher binding energy that is consistent with an n-type doping for both Ag and Ca doped films in comparison to the undoped BPhen film.To assess the stability in air, both films were depth profiled after different air exposure times. For Ca doped films the silicon interface width increases rapidly. After 30 minutes the film has an RMS roughness of 1.25 nm which is over four times that of the Ag doped film after the same air exposure time. This roughening is attributed to crystallization of the Ca-doped BPhen film. Backscattered Argon clusters was also used to analyze layers as a function of air exposure [5, 6]. These results confirm improved stability of Ag-doped vs Ca doped films

Etude de l'influence de la pointe sur les mesures KFM sur échantillon d'AlGaAs/GaAs

La microscopie à sonde de Kelvin (KFM) est capable de fournir une mesure résolue spatialement et en énergie de la structure de bande en surface d'un matériau. Elle dépend néanmoins fortement des propriétés physiques de la pointe utilisée, propriétés pouvant être la largeur de l'apex, la forme géométrique de la surpointe (nanocristal, nanofil) ou encore la raideur du levier. L'idée de ce travail est de comparer les résultats KFM obtenus sur un échantillon de calibration BAM-L200 [1] pour différentes pointes (Pointes conductrices avec ou sans nanocristaux, avec ou sans surpointe, pointes fines) et selon différentes préparations (Abrasion, chauffage)