Search

Atomic layer deposition (ALD) typically employs metal precursor and co-reactant pulses to deposit thin films in a layer-by-layer fashion. While conventional ABAB-type ALD sequences implement only two functionalities, namely a metal source and ligand exchange agent, additional functionalities have emerged, including etching and reduction agents. Herein, we construct gas phase sequences – coined as ALD+ – with complexities reaching beyond classic ABAB-type ALD by freely combining multiple functionalities within irregular pulse schemes, e.g. ABCADC. The possibilities of such combinations are explored as a smart strategy to tailor bimetallic thin film and nanoparticle (NP) properties. By doing so, we demonstrate that bimetallic thin films can be tailored with target thickness and through the full compositional range, whilst the morphology can be flexibly modulated from thin films to NPs by shuffling the pulse sequence. These complex pulse schemes are expected to be broadely applicable, but are here explored for Pd-Ru bimetallic thin films and NPs.

Atomic layer deposition (ALD) of boron-containing films has been mainly studied for use in two-dimensional materials and for B doping of Si. Furthermore, lithium-containing borates show great promi...

Atomic layer deposition (ALD) of noble metals is an attractive technology potentially applied in nanoelectronics and catalysis. Unlike the combustion-like mechanism shown by other noble metal ALD processes, the main palladium (Pd) ALD process using palladium(ii)hexafluoroacetylacetonate [Pd(hfac)2] as precursor is based on true reducing surface chemistry. In this work, a thorough investigation of plasma-enhanced Pd ALD is carried out by employing this precursor with different plasmas (H2*, NH3*, O2*) and plasma sequences (H2* + O2*, O2* + H2*) as co-reactants at varying temperatures, providing insights in the co-reactant and temperature dependence of the Pd growth per cycle (GPC). At all temperatures, films grown with only reducing co-reactants contain a large amount of carbon, while an additional O2* in the co-reactant sequence helps to obtain Pd films with much lower impurity concentrations. Remarkably, in situ XRD and SEM show an abrupt release of the carbon impurities during annealing at moderate temperatures in different atmospheres. In vacuo XPS measurements reveal the remaining species on the as-deposited surface after every exposure. Links are established between the particular surface termination prior to the precursor pulse and the observed differences in GPC, highlighting hydrogen as the key growth facilitator and carbon and oxygen as growth inhibitors. The increase in GPC with temperature for ALD sequences with H2* or NH3* prior to the precursor pulse is explained by an increase in the amount of hydrogen species that reside on the Pd surface which are available for reaction with the Pd(hfac)2 precursor.

Pt doped semiconducting metal oxides and Pt metal clusters embedded in an oxide matrix are of interest for applications such as catalysis and gas sensing, energy storage and memory devices. Accurate tuning of the dopant level is crucial for adjusting the properties of these materials. Here, a novel atomic layer deposition (ALD) based method for doping Pt into In2O3 in specific, and metals in metal oxides in general, is demonstrated. This approach combines alternating exposures of Pt and In2O3 ALD processes in a single ‘supercycle’, followed by supercycle repetition leading to multilayered nanocomposites. The atomic level control of ALD and its conformal nature make the method suitable for accurate dopant control even on high surface area sup-ports. Oxidation state, local structural environment and crystalline phase of the embedded Pt dopants were obtained by means of X-ray characterization methods and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In addition, this approach allows characterization of the nucleation stages of metal ALD processes, by stacking those states multiple times in an oxide matrix. Regardless of experimental conditions, a few Pt ALD cycles leads to the formation of oxidized Pt species due to their highly dispersed nature, as proven by X-ray absorption spectroscopy (XAS). Grazing-incidence small-angle X-ray scattering (GISAXS) and high-resolution scanning transmission electron microscopy, combined with energy dispersive X-ray spectroscopy (HR-STEM/EDXS) show that Pt is evenly distributed in the In2O3 metal oxide matrix without the formation of clusters. For a larger number of Pt ALD cycles, typ. > 10, the oxidation state gradually evolves towards fully metallic, and metallic Pt clusters are obtained within the In2O3 metal oxide matrix. This work reveals how tuning of the ALD supercycle approach for Pt doping allows controlled engineering of the Pt compositional and structural configuration within a metal oxide matrix.

Surface enhanced Raman spectroscopy (SERS) and stimulated Raman spectroscopy (SRS) are well established techniques capable of boosting the strength of Raman scattering. The combination of both techniques (surface enhanced stimulated Raman spectroscopy, or SE-SRS) has been reported using plasmonic nanoparticles. In parallel, waveguide enhanced Raman spectroscopy has been developed using nanophotonic and nanoplasmonic waveguides. Here, we explore SE-SRS in nanoplasmonic waveguides. We demonstrate that a combined photothermal and thermo-optic effect in the gold material induces a strong background signal that limits the detection limit for the analyte. The experimental results are in line with theoretical estimates. We propose several methods to reduce or counteract this background., SCOPUS: ar.j, info:eu-repo/semantics/published

The increasing interest in atomic layer deposition (ALD) of Pt for the controlled synthesis of supported nanoparticles for catalysis demands an in-depth understanding of the nucleation controlled growth behaviour. We present an in situ investigation of Pt ALD on planar Si substrates, with native SiO2, by means of X-ray fluorescence (XRF) and grazing incidence small-angle X-ray scattering (GISAXS), using a custom-built synchrotron-compatible high-vacuum ALD setup and focusing on the thermal Pt ALD process, comprising (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and O-2 gas at 300 degrees C. The evolution in key scattering features provides insights into the growth kinetics of Pt deposits from small nuclei to isolated islands and coalesced worm-like structures. An analysis approach is introduced to extract dynamic information on the average real space parameters, such as Pt cluster shape, size, and spacing. The results indicate a nucleation stage, followed by a diffusion-mediated particle growth regime that is marked by a decrease in average areal density and the formation of laterally elongated Pt clusters. Growth of the Pt nanoparticles is thus not only governed by the adsorption of Pt precursor molecules from the gas-phase and subsequent combustion of the ligands, but is largely determined by adsorption of migrating Pt species on the surface and diffusion-driven particle coalescence. Moreover, the influence of the Pt precursor dose on the particle nucleation and growth is investigated. It is found that the precursor dose influences the deposition rate (number of Pt atoms per cycle), while the particle morphology for a specific Pt loading is independent of the precursor dose used in the ALD process. Our results prove that combining in situ GISAXS and XRF provides an excellent experimental strategy to obtain new fundamental insights about the role of deposition parameters on the morphology of Pt ALD depositions. This knowledge is vital to improve control over the Pt nucleation stage and enable efficient synthesis of supported nanocatalysts.

Surface enhanced Raman spectroscopy (SERS) is a selective and sensitive technique, which allows for the detection of protease activity by monitoring the cleavage of peptide substrates. Commonly used free-space based SERS substrates, however, require the use of bulky and expensive instrumentation, limiting their use to laboratory environments. An integrated photonics approach aims to implement various free-space optical components to a reliable, mass-reproducible and cheap photonic chip. We here demonstrate integrated SERS detection of trypsin activity using a nanoplasmonic slot waveguide as a waveguide-based SERS substrate. Despite the continuously improving SERS performance of the waveguide-based SERS substrates, they currently still do not reach the SERS enhancements of free-space substrates. To mitigate this, we developed an improved peptide substrate in which we incorporated the non-natural aromatic amino acid 4-cyano-phenylalanine, which provides a high intrinsic SERS signal. The use of non-natural aromatics is expected to extend the possibilities for multiplexing measurements, where the activity of several proteases can be detected simultaneously.

The thermal and plasma-enhanced atomic layer deposition (ALD) growth of titanium oxide using an alkylamine precursor - tetrakis(dimethylamino)titanium (TDMAT) - was investigated. The surface species present during both the precursor and co-reactant pulse were studied with in situ reflection mid-IR spectroscopy (FTIR) and in vacuo X-ray photoelectron spectroscopy (XPS). The thermal process using H2O vapor proceeds through a typical ligand exchange reaction mechanism. The plasma-enhanced ALD processes using H2O-plasma or O2-plasma exhibit an additional decomposition and combustion reaction mechanism. After the plasma exposure, imine (N[double bond, length as m-dash]C) and isocyanate (N[double bond, length as m-dash]C[double bond, length as m-dash]O) surface species were observed by in situ FTIR. In addition, nitrites (NOx) were detected using in vacuo XPS during the O2-plasma process. This study presents the importance of the use of in situ FTIR and in vacuo XPS as complementary techniques to learn more about the ALD reaction mechanism. While in situ FTIR is very sensitive to changes of chemical bonds at the surface, exact identification and quantification could only be done with the aid of in vacuo XPS.

Thermal atomic layer deposition (ALD) and plasma-enhanced ALD (PE-ALD) of Pt, using MeCpPtMe3 as the precursor and O2 gas or O2 plasma as the reactant, are studied with in situ reflection Fourier transform infrared spectroscopy (FTIR) at different substrate temperatures. This is done to identify the functional groups present during Pt ALD and investigate the origin of the temperature dependent growth rate of the thermal process. Evidence is given that CH and C[double bond, length as m-dash]C containing species are present on the surface after precursor exposure at low substrate temperatures (

The reaction mechanism of the recently reported Me3AuPMe3-H-2 plasma gold ALD process was investigated using in situ characterization techniques in a pump-type ALD system. In situ RAIRS and in vacuo XPS measurements confirm that the CH3 and PMe3 ligands remain on the gold surface after chemisorption of the precursor, causing self-limiting adsorption. Remaining surface groups are removed by the H-2 plasma in the form of CH4 and likely as PHxMey groups, allowing chemisorption of new precursor molecules during the next exposure. The decomposition behaviour of the Me3AuPMe3 precursor on a Au surface is also presented and linked to the stability of the precursor ligands that govern the self-limiting growth during ALD. Desorption of the CH3 ligands occurs at all substrate temperatures during evacuation to high vacuum, occurring faster at higher temperatures. The PMe3 ligand is found to be less stable on a gold surface at higher substrate temperatures and is accompanied by an increase in precusor decomposition on a gold surface, indicating that the temperature dependent stability of the precursor ligands is an important factor to ensure self-limiting precursor adsorption during ALD. Remarkably, precursor decomposition does not occur on a SiO2 surface, in situ transmission absorption infrared experiments indicate that nucleation on a SiO2 surface occurs on Si-OH groups. Finally, we comment on the use of different co-reactants during PE-ALD of Au and we report on different PE-ALD growth with the reported O-2 plasma and H2O process in pump-type versus flow-type ALD systems.

We used a nanoplasmonic slot waveguide for the first time demonstration of waveguide-based detection of protease activity using Surface-Enhanced Raman Spectroscopy (SERS), paving the way for an integrated lab-on-a-chip protease activity monitoring.

Downscaling of supported Pt structures to the nanoscale is motivated by the augmentation of the catalytic activity and selectivity, which depend on the particle size, shape and coverage. Harsh thermal and chemical conditions generally required for catalytic applications entail an undesirable particle coarsening, and consequently limit the catalyst lifetime. Herein we report an in situ synchrotron study on the stability of supported Pt nanoparticles and their stabilization using atomic layer deposition (ALD) as the stabilizing methodology against particle coarsening. Pt nanoparticles were thermally annealed up to 850 degrees C in an oxidizing environment while recording in situ synchrotron grazing incidence small angle X-ray scattering (GISAXS) 2D patterns, thereby obtaining continuous information about the particle radius evolution. Al2O3 overcoat as a protective capping layer against coarsening via ALD was investigated. In situ data proved that only 1 cycle of Al2O3 ALD caused an augmentation of the onset temperature for particle coarsening. Moreover, the results showed a dependence of the required overcoat thickness on the initial particle size and distribution, being more efficient (i.e. requiring lower thicknesses) when isolated particles are present on the sample surface. The Pt surface accessibility, which is decisive in catalytic applications, was analyzed using the low energy ion scattering (LEIS) technique, revealing a larger Pt surface accessibility for a sample with Al2O3 overcoat than for a sample without a protective layer after a long-term isothermal annealing.

A plasma-enhanced atomic layer deposition (PE-ALD) process to deposit metallic gold is reported, using the previously reported Me3Au(PMe3) precursor with H-2 plasma as the reactant. The process has a deposition window from 50 to 120 degrees C with a growth rate of 0.030 +/- 0.002 nm per cycle on gold seed layers, and it shows saturating behavior for both the precursor and reactant exposure. X-ray photoelectron spectroscopy measurements show that the gold films deposited at 120 degrees C are of higher purity than the previously reported ones (

The morphology evolution of supported palladium nanoparticles (Pd NPs) during plasma-enhanced atomic layer deposition using palladium hexafluoroacetylacetonate (Pd(hfac)2) as precursor was investigated using in situ and ex situ X-ray fluorescence (XRF) and grazing incidence small angle X-ray scattering (GISAXS), as well as ex situ scanning electron microscopy (SEM). The initial areal density of Pd NPs increases through adding cycles of the three-step process using Pd(hfac)2, H2 plasma and trimethylaluminum (TMA) prior to the standard Pd(hfac)2 + H2 plasma process. The participation of an O2 plasma exposure as additional co-reactant before or after the H2 plasma step also plays a role in the nucleation density and particle coalescence, affecting also the shape of the deposited particles. Based on the gathered knowledge, a synthetic approach that enables precise control of the Pd nanoparticle dimensions and coverage is developed.

Silicon nitride (SiN) is currently the most prominent CMOS-compatible platform for photonics at wavelengths ANDlt;1ANDx2009;ANDx2009;AND, SCOPUS: ar.j, info:eu-repo/semantics/published

Surface-Enhanced Raman Spectroscopy (SERS) allows for the highly specific detection of molecules by enhancing the inherently weak Raman signals near the surface of plasmonic nanostructures. A variety of plasmonic nanostructures have been developed for SERS signal excitation and collection in a conventional free-space microscope, among which the gold nanodomes offer one of the highest SERS enhancements. Nanophotonic waveguides have recently emerged as an alternative to the conventional Raman microscope as they can be used to efficiently excite and collect Raman signals. Integration of plasmonic structures on nanophotonic waveguides enables reproducible waveguide-based excitation and collection of SERS spectra, such as in nanoplasmonic slot waveguides. In this paper, we compare the SERS performance of gold nanodomes, in which the signal is excited and collected in free space, and waveguide-based nanoplasmonic slot waveguide. We evaluate the SERS signal enhancement and the SERS background of the different SERS platforms using a monolayer of nitrothiophenol. We show that the nanoplasmonic slot waveguide approaches the gold nanodomes in terms of the signal-to-background ratio. We additionally demonstrate the first-time detection of a peptide monolayer on a waveguide-based SERS platform, paving the way towards the SERS monitoring of biologically relevant molecules on an integrated lab-on-a-chip platform.

Currently only two Au ALD processes exist, using two different precursors. The first Au ALD process, reported by Griffiths et al. [1], is a three step process using Me3AuPMe3 as the precursor in combination with an oxygen plasma and water vapour as the reactants. The deposition of metallic gold was reported at a deposition temperature of 120°C, with only some carbon and oxygen impurities present in the film (6.65% C and 1.83% O). A growth per cycle of 0.05 nm per cycle was achieved. The other Au ALD process, reported by Mäkelä et al. [2], uses Me2Au(S2CNEt2) as the precursor and ozone as the reactant. Deposition between 120-180°C was reported with self-limiting growth at 180°C and a growth rate of 0.09 nm per cycle. The deposited films had low resistivity values (4-16 µΩ cm) and were chemically pure with few impurities, O (2.9%), H (0.9%), C (0.2%), and N (0.2%). A new plasma enhanced ALD process has been developed using Me3AuPMe3 and H2 plasma as the precursor and reactant, respectively. Saturating behaviour for both precursor and reactant is achieved. The growth per cycle for this process is 0.03 nm per cycle. The process exhibits a broad saturating temperature window, from 50°C to 120°C. This temperature window is limited by decomposition of the precursor above 120°C. X-ray diffraction measurements show that the as-deposited gold films are poly crystalline (face centered cubic). The deposited gold films are very pure, with no phosphorous present in the film and very few carbon impurities (0.3%). Low resistivity values (5.85 µΩ cm), close to the bulk value of gold (2.44 µΩ cm), were achieved. The surface chemistry and growth mechanism are investigated using in-situ RAIRS measurements, optical emission spectroscopy, and mass-spectrometry. Scanning electron microscopy measurements show that the initial growth starts with the nucleation of gold particles on the surface, as is the case for most noble metal ALD processes. The formed gold nanoparticles grow and coalesce during the ALD process. The spacing of the gold particles makes this process interesting for surface enhanced Raman spectroscopy (SERS). Free space Raman measurements were performed on some of the samples and these showed excellent surface enhancement of the Raman signal of a monolayer of 4-nitrothiophenol bound to the ALD gold films. As far as we know is this the first report of an ALD gold film that shows SERS properties. In contrast to other SERS substrate fabrication methods, often involving lithography, this ALD process provides a direct way to fabricate SERS substrates on both planar and complex substrates, without the need for a lot of process steps. [1] M. B. E. Griffiths, P. J. Pallister, D. J. Mandia, and S. T. Barry, Chem. Mater. 28(1) (2016) 44-46 [2] M. Mäkelä, T. Hatanpää, K. Mizohata, J. Räisänen, M. Ritala, and M. Leskelä, Chem. Mater. 29(14) (2017) 6130-6136

A plasma-enhanced atomic layer deposition (ALD) process using the Ag(fod)(PEt3) precursor [(triethylphosphine)(6,6,7,7,8,8,8-heptafluoro-2,2-dimethy1-3,5-octanedionate)silver(I)] in combination with NH3-plasma is reported. The steady growth rate of the reported process (0.24 +/- 0.03 nm/cycle) was found to be 6 times larger than that of the previously reported Ag ALD process based on the same precursor in combination with H-2-plasma (0.04 +/- 0.02 nm/cycle). The ALD characteristics of the H-2-plasma and NH3-plasma processes were verified. The deposited Ag films were polycrystalline face-centered cubic Ag for both processes. The film morphology was investigated by ex situ scanning electron microscopy and grazing-incidence small-angle X-ray scattering, and it was found that films grown with the NH3-plasma process exhibit a much higher particle areal density and smaller particle sizes on oxide substrates compared to those deposited using the H-2-plasma process. This control over morphology of the deposited Ag is important for applications in catalysis and plasmonics. While films grown with the H-2-plasma process had oxygen impurities (similar to 9 atom %) in the bulk, the main impurity for the NH3-plasma process was nitrogen (similar to 7 atom %). In situ Fourier transform infrared spectroscopy experiments suggest that these nitrogen impurities are derived from NH surface groups generated during the NH3-plasma, which interact with the precursor molecules during the precursor pulse. We propose that the reaction of these surface groups with the precursor leads to additional deposition of Ag atoms during the precursor pulse compared to the H-2-plasma process, which explains the enhanced growth rate of the NH3-plasma process.

We report on the atomic layer deposition of ZnO for interfacing with existing Si 3 N 4 photonics which lacks 2nd-order nonlinear functionalities. We measure a χ(2) of 15 pm/V in line with a bulk ZnO crystal.

Surface enhanced Raman spectroscopy (SERS) is a widely known sensing technique that uses a plasmonic enhancement to probe analytes in ultra-small volumes. Recently, the integration of plasmonic structures with photonic integrated waveguides promised the full integration of a SERS system on a chip. Unfortunately, the previously reported sensors provide modest overall SERS enhancement resulting in a limited signal to noise ratio. Here, we report a photonic waveguide interfaced SERS sensor that shows an order of magnitude higher pump to Stokes conversion efficiency and lower background than previous realizations. Moreover, the plasmonic structure is fabricated without the use of e-beam lithography but rather using a combination of atomic layer deposition and deep UV photolithography. We investigate numerically the performance of the sensor in terms of Raman conversion efficiency for various design parameters. The experimental results are presented via the acquisition of SERS spectra that show a conversion efficiency of 10-9 for a monolayer of 4-nitrothiophenol. To explore the broadband characteristic of our sensor in the therapeutic spectral window, two different pump wavelengths, i.e. 632 and 785 nm, are used. To the best of our knowledge, this is the first ever broadband SERS demonstration of an on-chip Raman sensor. We further study the reproducibility of our SERS sensor, reaching a relative standard deviation of the acquired spectra (RSD) < 5%., SCOPUS: ar.j, info:eu-repo/semantics/published