Low Energy Cluster Beam Deposition Research Articles

Cobalt cluster-assembled thin films deposited by low energy cluster beam deposition: Structural and magnetic investigations of deposited layers

Cobalt cluster-assembled thin films were deposited on amorphous-carbon-coated copper grids and on silicon substrates at room temperature by low energy cluster beam deposition. Characterizations using high-resolution transmission electronic microscopy and atomic force microscopy reveal randomly stacked agglomerates of 9–11nm diameter, which are themselves composed of small 3.6nm diameter fcc cobalt clusters. The films are ferromagnetic up to room temperature and above, which implies that the clusters are exchange coupled. The approach to saturation is analyzed within the random anisotropy model. The values of the exchange coefficient A and the anisotropy constant K then derived are discussed. The temperature dependence of the coercivity below 100K is discussed in terms of thermal activation effects. All results indicate that the fundamental entity governing the magnetic behaviors is constituted by the 9–11nm diameter agglomerates rather than by the clusters themselves.

SELF-ASSEMBLY OF ORDERED SILVER NANOPARTICLE CHAINS ON TRIBLOCK COPOLYMER TEMPLATES

Poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer templates which present an in-plane cylinder pattern have been prepared by controlling the solvent evaporation rate. Then silver clusters have been deposited onto the SBS copolymer templates by low energy clusters beam deposition (LECBD) apparatus. The morphology of the sample has been characterized by AFM with tapping-mode. It is shown that silver clusters aggregate into nanoparticle chains onto the template at about 100% coverage. Optical absorption spectra reveal that the surface plasmon resonance (SPR) of silver nanoparticle chains occurs at 550 nm, being a red shift of -85 nm compared to silver nanoclusters deposited on the fused quartz substrate, and the width of SPR peak broadens.

Hierarchical Self-assembly of Silver Nanocluster Arrays on Triblock Copolymer Templates

Poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer templates which present in-plane cylinders of polystyrene (PS) aligned parallel to the plane of the substrate have been prepared by a solvent-induced order-disorder phase transition method. Silver nanoclusters have been obliquely deposited onto the SBS copolymer templates at low coverage, utilizing the directed low-energy cluster beam deposition (LECBD) method. The morphology of the samples has been characterized by a tapping-mode AFM. It is shown that the silver nanoclusters form ordered linear arrays and the intercluster distance within each individual linear array is comparable to the cluster size. Optical absorption spectra indicate that the surface plasmon resonance (SPR) of the silver nanocluster linear arrays occurs at about 444.5 nm, manifesting a red shift of approximately 21.4 nm compared to the SPR absorption of silver nanoclusters deposited on a fused quartz substrate. This is attributed mainly to the near-field electrodynamic interactions between the silver nanoclusters. This hierarchical approach to create ordered nanostructures transcends the spatial limits of lithography and provides a promising route to achieve well-ordered cluster-based nanostructures.

Synthesis and characterization of Sb 2O 3 cluster assembled nanostructured thin films

Cluster assembled Sb 2O 3 nanocrystals having sizes ranging from 3 nm to 17 nm have been prepared by the Low Energy Cluster Beam Deposition technique. The purity of the sample has been ascertained by the Particle Induced X-rays Emission study. Transmission electron microscopic study reveals the presence of irregular shape, randomly distributed Sb 2O 3 nanocrystals in the deposit. Micro-Raman study establishes the homogeneity of the Sb 2O 3 cluster generated nanostructured thin film.

Observation of semiconductor to insulator transition in Sb/Sb 2O 3 clusters synthesized by low-energy cluster beam deposition with different conditions

Nanostructured thin films of Sb 2O 3 clusters having sizes in the range of 3–17 nm were synthesized by the low-energy cluster beam deposition technique. The crystallite size was found to decrease with increase in rate of flow of the carrier gas. The high-resolution transmission electron microscope image and the selected-area diffraction pattern show the formation of a core shell structure with Sb core and Sb 2O 3 shell at moderate oxygen flow pressure. Optical absorption spectra exhibit semiconductor characteristics for the samples prepared at intermediate oxygen flow pressure, and insulating features were observed in case of samples prepared at higher oxygen flow pressure. Room-temperature Raman spectra consist of a pair of broad peaks, red shifted with respect to the corresponding peaks of the bulk Sb 2O 3.

Formation, evolution, and degradation of nanostructured covalent thin films deposited by low-energy cluster beam deposition

Low-energy cluster beam deposition (LECBD) is considered an intriguing technique for obtaining thin layers with well-defined structures at the nano- and mesoscale levels, allowing novel optical, electronic, and magnetic properties. The produced layers are highly porous and extremely reactive due to the high surface to volume ratio and must be characterized with in situ techniques to study their original composition and their evolution once exposed to reactive gases. In this work, we present a general overview and some results on the formation, evolution, and deposition of silicon and carbon cluster beams produced using a laser vaporization source.

Synthesis of LECBD grown cluster assembled SeO2 thin films

Cluster assembled selenium oxide (SeO2) thin films, as a function of oxygen flow pressure (OFP) have been synthesized by a low energy cluster beam deposition (LECBD) technique. The OFP dependent surface morphology leading to well separated nanoclusters (size ranging from 50 to 200nm) and fractal features are confirmed from transmission electron microscopic (TEM) measurements. A diffusion limited aggregation (DLA) mediated fractal growth with dimension as 1.71±0.01 has been observed for high OFP (60mbar). Structural analysis by glancing angle X-ray diffraction (GXRD) and selected area diffraction (SAD) studies identify the presence of tetragonal phase SeO2 in the deposit. Micro-Raman studies indicate the shifts in bending and stretching vibrational phonon modes in cluster assembled SeO2 as compared to their bulk counter part due to the phonon confinement effect.

Atomic-scale modification of hybrid FePt cluster-assembled films

We present a study on the production of iron-platinum bimetallic clusters with a laser vaporization cluster source, and subsequent low-energy cluster beam deposition in ultrahigh-vacuum conditions. Time-of-flight mass spectrometry investigations of the clusters in the gas phase show that FePt is a stable alloy at the nanoscale. Magnetic and structural properties of the deposited $2.25\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ cluster-assembled films with different Fe:Pt ratios are investigated with vibrating sample and superconducting quantum interference device magnetometry, Rutherford backscattering spectrometry, transmission electron microscopy, and x-ray diffraction. The as-deposited cluster films are highly porous and magnetically soft. A systematic study of the influence of annealing on the sample properties revealed that the chemically disordered-ordered phase transition only occurs in the cluster films with Fe:Pt ratio close to 1:1, and at temperatures higher than $500\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Combining magnetization and structural investigations we distinguish between the phase transition inside a single cluster and the coalescence of clusters, which starts to dominate at temperatures above $550\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, leading to complete cluster intermixing on the atomic level.

Rare-earth-based nanoclusters embedded in sol–gel waveguiding thin films

We present a new structural method for clusters analysis based on sol–gel planar waveguides and luminescent nanoparticles of Gd 2O 3:Eu 3+. Clusters are deposited onto a TiO 2 sol–gel layer then covered by a second TiO 2 film. The resulting structure exhibits waveguiding properties. High-quality and large surface titanium oxide films are dip coated onto Pyrex substrates. The Gd 2O 3:Eu 3+ nanoparticles are produced by the low-energy cluster beam deposition technique. This method allows the synthesis of cubic-phase Gd 2O 3:Eu 3+ clusters exhibiting a diameter with a range between 2 and 4 nm. Waveguiding properties of the sol–gel films are used to excite the Gd 2O 3:Eu 3+ nanoparticles by optical launching of a laser beam using (transverse electric mode TE 0 mode: mode order=0). This TE 0 mode energy propagates into the middle of the waveguide and provides a high excitation of Gd 2O 3:Eu 3+. The first advantage of this method is to excite only few clusters in the matrix along the propagation line and due to the energy confinement to provide the Eu 3+ luminescence emission with a high signal-to-noise ratio. The second advantage is to prevent the migration of the clusters during annealing and to follow the influence of this treatment on the Gd 2O 3:Eu 3+ clusters behaviour.

Structural and “in situ” vibrational study of luminescent cluster assembled silicon thin films

A Low Energy Cluster Beam Deposition apparatus is employed to produce cluster assembled silicon thin films (1–500 nm thick) by using a laser vaporization source. The generated clusters are studied since their formation through time of flight mass spectra and the calculated size in the gas phase are compared with those of the deposited aggregates obtained through Dynamic Scanning Force Microscopy. The deposited material is also studied “in situ” by Raman and infrared spectroscopy. The spectra reveal that the as deposited clusters are hydrogenated with negligible amount of oxide. A comparison of the film properties before and after their air exposure shows that the exposition induces a consistent oxidation, leading to a near-infrared luminescent silicon nanoparticles surrounded by SiO x shells.

SELF-ASSEMBLY OF SILVER NANOCLUSTERS ON TRIBLOCK COPOLYMER TEMPLATES

Poly (styrene-b-butadiene-b-styrene) (SBS) triblock copolymer templates have been prepared by solvent-induced order-disorder phase transition method. Silver nanoclusters have been deposited onto the SBS copolymer templates by low energy clusters beam deposition (LECBD) method. The microstructures of the template and cluster deposits have been characterized by AFM with tapping-mode. It is shown that the triblock copolymers are self-assembled to form an in-plane cylinder ordered microstructure. In the case of low coverage (<50%), silver nanaoclusters deposited on the template tend to aggregate along with the pattern of the template and coalesce into larger nanoparticles. Optical absorption spectra reveal that the surface plasmon resonance (SPR) of silver nanoclusters deposited on the template occurs at 545nm, being a red shift of ~75nm compared to that silver nanoclusters deposited on the fused quartz substrate.

Low energy cluster beam deposited BN films as the cascade for field emission

The atomic deposited BN films with the thickness of nanometers (ABN) were prepared by radio frequency magnetron sputtering method and the nanostructured BN films (CBN) were prepared by Low Energy Cluster Beam Deposition. UV-Vis Absorption measurement proves the band gap of 4.27eV and field emission of the BN films were carried out. F-N plots of all the samples give a good fitting and demonstrate the F-N tunneling of the emission process. The emission of ABN begins at the electric field of 14.6 V/{\mu}m while that of CBN starts at 5.10V/{\mu}m. Emission current density of 1mA/cm2 for ABN needs the field of 20V/{\mu}m while that of CBN needs only 12.1V/{\mu}m. The cluster-deposited BN on n-type Silicon substrate proves a good performance in terms of the lower gauge voltage, more emission sites and higher electron intensity and seems a promising substitute for the cascade of Field Emission.

Functionalized Cluster-Assembled Magnetic Nanostructures for Applications to high Integration-Density Devices

This paper presents recent results on the preparation and characterization of original magnetic nanostructures from nanoclusters preformed in the gas phase. Magnetic binary-clusters (i.e. Co-Sm, Co-Pt, Co-Ag) with rather well controlled sizes, structures and compositions, are prepared in the gas phase using a combined laser vaporization-rare gas condensation source and subsequently deposited at low energy (LECBD : Low Energy Cluster Beam Deposition) on various functionalized substrates to grow cluster-assembled magnetic nanostructures exhibiting specific magnetic properties. Especially a high magnetic anisotropy and consequently a high magnetic blocking temperature compatible with future applications to high density memory devices and spin electronics are expected. In this context of applications, 2D-organized arrays of functionalized binary-cluster assembled dots are prepared by LECBD on FIB-functionalized substrates (FIB: Focussed Ion Beam) with the ultimate objective to reach areal densities in the range of the Tbits/in2.

Formation, evolution and degradation of nanostructured covalent thin films deposited by Low Energy Cluster Beam Deposition

ABSTRACTLow Energy Cluster Beam Deposition (LECBD) is considered an intriguing technique to obtain thin layers with well defined structures at the nano- and meso-scale levels, allowing novel optical, electronic and magnetic properties. The produced layers are highly porous and extremely reactive due to the high surface to volume ratio and must be characterized with “in situ” techniques in order to study their original composition and their evolution once exposed to reactive gases. In this work we present a general overview and some results on the formation evolution and deposition of silicon and carbon cluster beams produced using a laser vaporization source.

Ag-Co clusters deposition on Ag(100): an atomic scale study

The slowing down of Co10Ag191 and Co285Ag301 nanoclusters on a Ag (100) surface is studied at the atomic scale by means of classical Molecular Dynamics simulations. The slowing down energy, 0.25 to 1.5 eV/atom, is characteristic of low energy cluster beam deposition and aerosol focused beam techniques. The two clusters differentiate by their size, stoechiometry and structure. While Co forms one or several groups just beneath the cluster surface in Co10Ag191, Co285Ag301 displays a core-shell structure where Ag forms one complete monolayer around the Co core. As a consequence of the impact, the smallest cluster undergoes deep reorganization and becomes fully epitaxial with the substrate. The larger one only undergoes partial accommodation and partially retains the memory of its initial morphology. For both, after impact, the Co forms one group covered by Ag. The substrate damage is significant and depends on the slowing down energy. It results in a Ag step surrounding the cluster which may be more than one atomic layers high and isolated add-atoms or small monolayer islands apart from the step. The latter originate from the cluster and the former from the substrate. Further details in the consequences of the impact are given, concerning the cluster penetration, its deformation and lattice distortions, with emphasis on the cluster size and stoechiometry.

Magnetic assembled nanostructures from pure and mixed Co-based clusters

The low energy cluster beam deposition (LECBD) technique is used to prepareoriginal magnetic nanostructures from Co-based clusters preformed in thegas phase and subsequently embedded in non-magnetic matrices in ultrahighvacuum. Nanostructured films of pure cobalt and mixed CoM clusters (withM = Ag or Pt) with controlled sizes and compositions have been investigated. We study thecorrelations between the specific structure, morphology and the resulting magneticproperties obtained for individual nanoclusters by the highly sensitive microSQUIDmagnetometry technique and on assemblies of non-interacting clusters by conventionaltechniques. From the role of various contributions, we will underline at the nanometre scalethe dominant role of the surface/interface effects on the magnetic anisotropy.

Nanometric copper and cobalt clusters deposited using pulsed laser ablation; AFM and MFM investigations

A laser ablation cluster generator, using low energy clusters beam deposition (LECBD), has been developed for synthesis of Cu and Co clusters. These materials have been chosen in order to compare the self-assembling mechanisms of diamagnetic and ferromagnetic clusters on a surface. Aggregates are deposited on silicon substrates under high vacuum. The distributions in size of the Cu and Co clusters have been investigated, in both cases, using atomic force microscopy (AFM) pointing out circular shapes of approximately 8 nm in diameter. Then, magnetic force microscopy (MFM) images are achieved on Co cluster layers and compared with images given by a Co continuous film deposited using conventional pulsed laser deposition.

Extraordinary Hall effect and X-ray photoemission studies of two dimensional films of magnetic nanoclusters

The low energy cluster beam deposition technique (LECBD) is used to prepare nanostructured thin films from clusters (Co, Ag, and mixed Co–Ag) preformed in the gas phase. Two dimensional (2D)-films of isolated supported clusters randomly distributed on the substrate, as well as isolated clusters embedded in various matrices by a co-deposition technique are prepared. Magnetic properties of Co-clusters films with equivalent Co-thickness as low as 0.01nm are investigated using the extraordinary hall effect (EHE) measurements. The results emphasize the very high sensitivity of the EHE-technique to study the magnetic behaviour of very thin cluster films. Complementary transmission electron microscopy observations and X-ray photoemission spectroscopy measurements (XPS) on mixed Co–Ag clusters are also performed to investigate on the cluster morphology (homogeneous CoAg-alloy or core-shell structure due to the surface segregation of Ag-atoms) which could influence the corresponding magnetic properties.

Numerical study of the collective magnetic behavior of nanoparticle assembled films

The magnetic hysteresis and the temperature-dependent magnetization of interacting nanoparticle assemblies are studied by Monte Carlo simulations. By comparison of the simulation results with measurements in Fe/Ag samples grown by low energy cluster beam deposition demonstrate that interparticle exchange interactions dominate over the dipolar interactions and are responsible for the collective magnetic behavior in this system. The simulation of the magnetic properties of quasi-two-dimensional ordered arrays of Co nanoparticles, prepared by self-assembly from a colloidal dispersion, demonstrates that dipolar interactions are responsible for an increase of the blocking temperature relative to the isolated particles. The collective behavior is manifest by oscillations in the magnetization with increasing layer coverage.

Thermal properties of thin and thick Ni3Al cluster assembled layers: an atomic scale simulation study

Diffusion properties at inner surfaces and interfaces of Ni3Al nanostructured materials are investigated by means of classical molecular dynamics with a second moment tight-binding potential. Model samples as prepared by low energy cluster beam deposition (LECBD) on a metal substrate are used. The first consists in a cluster layer interacting with the substrate. The second is a fragment of the first, to which periodic boundary conditions are applied in order to approximate an infinitely thick layer. Half of the atoms are either located at pore surfaces or at cluster interfaces. As a consequence of temperature, the model thick film undergoes strong compaction, which is identified as the result of coalescence. The effect is less pronounced for the cluster film on a substrate, suggesting the latter to contribute to the nanostructured layer stability. The comparison of the diffusion properties of these samples is made. For both samples, atomic diffusion at surfaces and interfaces is found particularly fast and the diffusion coefficient obeys an Arrhenius law with an activation energy of 0.3eV, similar to that found in liquid Ni3Al.