Electrocrystallization of the organic superconductor bis(ethylenedithio)tetrathiafulvalene triiodide, (ET)2I3, on a highly ordered pyrolytic graphite (HOPG) substrate has been visualized using in situ atomic force microscopy (AFM). Previous studies have revealed the formation of a coincident epitaxial monolayer with a structure identical to that of a (001) layer of the superconducting beta phase of this material prior to bulk crystal growth. However, the symmetry of the HOPG substrate leads to domain boundary defects during self assembly of the separately growing domains. The number of defects is significantly reduced after an electrochemical annealing process in which the potential is cycled about the monolayer deposition potential. Annealing of these films is important if they are to be used in electronic devices as the defects may serve as barriers to electron transport in the two-dimensional layers.

In addition to (ET)2I3, monolayer growth also has been visualized during electrocrystallization of (ET)2ReO4 on HOPG. The role of coincident epitaxy with HOPG in the monolayer formation and molecular orientation will be discussed.

Structurally modified substrates have also been investigated. Studies of the electrocrystallization of (ET)2I3 on HOPG, thermally treated to produce well-defined monolayer depth pit structures, have demonstrated that (ET)2I3 monolayer growth can occur inside the pit structures. The presence of monolayer domain boundaries within large pits indicates that multiple, independent nucleation events can occur in the pits, providing an opportunity to determine critical nucleation sizes by varying the pit dimensions. Recently we have discovered that MoS2 substrates can be electrochemically etched, giving rise to monolayer deep triangular pits.

Ultrathin film growth of vanadyl phthalocyanine was attempted on vicinal surfaces of hydrogen-terminated Si(111) in order to see the effect of regularly spaced steps to the growth feature. It has been observed that molecular arrangement was substantially affected when the terrace width was narrower than 2∼4 times of the molecular lattice constants. This result is probably due to the weakness of molecular interaction in the material and it accounts for the reason why ordinary graphoepitaxy has not been successful for the organic thin films.

We have assembled a scanning tunneling microscope with an inverted sample that allows the sample surface to be contacted by fluid electrolytes in a controlled atmosphere. A hanging meniscus is formed between the sample and a small cup surrounding the tunneling tip. In-situ imaging of the electrode/electrolyte interface is conveniently achieved with clean samples under potentiostatic control. The functioning of the microscope is illustrated by the imaging of the electrodeposition of copper on gold. This microscope has been used to image hydrogen-terminated silicon surfaces and to demonstrate that islands, tentatively assigned as silicon oxide, are formed on rinsing in water but can be avoided if the surface is not rinsed on withdrawal from the ammonium fluoride etching solution. Finally, STM shows that the convenient, gas-phase photochlorination of H-Si(111) produces the simple Cl-Si(111)(1×1) structure with little or no etching of the silicon surface.

This works addresses the question of the direct attachment of organic molecules on Si(111) by an electrochemical method. Anodic grafting of -OR group is demonstrated by in-situ STM and the LDOS characterized. The grafting of aryl groups, by reduction of aryl diazonium salts in aqueous solution, is also described. This approach leads to well ordered and close-packed thin molecular films with various functionality. Different chemical and structural characterizations conclude to a Si-C binding, between the Si surface and aryl groups. The stability of films is also investigated.

Etching of silicon in aqueous fluoride solutions can lead to almost atomically flat surfaces with a low density of surface states and recombination centers. The final quality of the surface, however, is strongly dependent on the solution composition and pH. We have performed electrochemical impedance spectroscopy in combination with potential modulated microwave reflectance spectroscopy (PMMRS) to elucidate the processes occurring at the surface during etching. PMMRS is a novel technique that only probes the free carriers in the conduction and valence bands and is, under certain conditions, not affected by processes involving electrically active surface states or charge transfer. This unique feature allows us to separate the energetics of the semiconductor from surface processes. Microwave reflectivity (δR) versus potential curves in HF solutions demonstrate the variation of the flatband potential as a function of pH. The AR response in the narrow potential region around the flatband potential and at more negative potentials is also discussed.

The photoluminescence (PL) of c-Si is probed stroboscopically with single pulses of a N2 laser during electrochemical treatments (hydrogenation and anodic oxidation). The PL intensity of indirect semiconductors such as Si is controlled by the non-radiative surface and bulk recombination. By this reason the density of surface states can be estimated for unknown surfaces by using a calibrated standard. The surface state density of a hydrogenated Si surface increases by exchanging the electrolyte by gaseous N2 or water.

An electrolyte electroreflectance study has been performed on boron phosphide thin films epitaxially grown on silicon (100) substrates. To our knowledge, this paper is the first report on the electrolyte electroreflectance spectrum of BP. All our boron phosphide of 1.5 μm thick films show a pronounced peak at the energy 4.25 eV, indicating a critical point in the valence or conduction band of the semiconductor. Photoreflectance measurements confirm these results. The 4.25 eV energy level is much lower than previously reported direct bandgap values of BP. The electrolyte electroreflectance spectrum of much thinner layers shows, besides the 4.25 eV peak, some other features at still lower incident photon energies caused by interference effects.

We applied electrochemical oxidation as a low thermal budget process for the passivation of thin SiGe epilayers on Si substrate and compared the results with those obtained on thermally oxidized layers. The use of a thin silicon cap on the SiGe layer reduces the electrochemical corrosion with dissolution of Ge during oxidation and leads to a higher amount of GeO2 in the oxidized SiGe layer than anodic oxidation without a Si cap. The protected SiGe layer shows a slight Ge enrichment at the interface which is different from the behavior of the non-protected SiGe layer. The highest Ge pile-up is achieved by the thermally oxidized samples where the oxide layer is formed by nearly pure SiO2. Using photoluminescence spectroscopy we showed that the passivation and quality of the interface is best if no Ge enrichment occurs. The results suggest that electrochemical oxidation of SiGe layers is preferable to high temperature processing.

Chalcogenide semiconductors have been deposited epitaxially from aqueous solutions either chemically or electrochemically at growth rates of up to 0.7 μmhr−1. After recalling the basic principles of these deposition processes, results are presented concerning chemically deposited CdS on InP, GaP and CuInSe2 substrates, electrodeposited CdTe on InP, and CdSAnP heterostructures. Characterisation of these structures by RHEED, TEM, HRTEM, and glazing angle X ray diffraction allows to analyse the effects of substrate orientation, polarity, lattice match plus the influence of temperature on epitaxial growth. These results are discussed in terms of self organisation and a site selective growth mechanisms due to the free enegy of formation of each compound.

Thin-layer electrochemical studies of the underpotential deposition (UPD) of Zn, Te, Se, and S on polycrystalline Au substrates have been performed. These studies were initiated to investigate the electrodeposition of ZnTe, ZnSe, and ZnS by electrochemical ALE (ECALE). Zn UPD on Au begins at -0.5 V and results in a coverage of 0.47 monolayer (ML). Te and Se atomic layers were formed using a two step process where bulk chalcogenide was removed by reduction, leaving the atomic layer. The reduction of the last atomic layer of Te or Se was not observed, regardless of how negative the potential was scanned. Sulfur atomic layers were spontaneously deposited below -0.6 V from a sulfide solution. Thermodynamic effects are clearly evident during the first monolayer of deposition. Zinc deposition onto Te, Se, and S coated electrodes occurs at progressively more positive potentials as the stability of the zinc compounds increase.

This initial information was used to develop ECALE cycles for the compounds, and thin-films were formed by repeated application of the cycles. The dependence of the deposit coverage on the deposition potentials was examined and found to display the characteristic “S” curve of a surface limited process. In addition, the dependence of the coverage on the number of ECALE cycles performed was found to be near the ideal 0.5 ML per cycle for ZnSe and ZnS. The ZnTe coverage per cycle was less than expected indicating that further optimization of deposition conditions is needed.

To investigate the initial steps of GaAs etching Br2 and H2O were (co)adsorbed onto the (110) cleavage plane at 100 K and the interaction investigated by SXPS and LEED. H2O is dissociatively adsorbed at low temperatures and leads to Fermi level pinning close to midgap. Br2 leads, depending on coverage, to the formation of bromides of different stoichiometries. During annealing to 290 K the bromides mostly evaporate from the surface (etching). Br2 and H2O coadsorption leads to Ga-oxide remaining on the surface. For the reactive interfaces band bending is not observed. The results of the adsorption experiments are compared to electrochemically prepared surfaces.

We present differential oxidation rate effects in cleaved heterostructures containing GaAs, AlGaAs, InGaP and InGaAs measured by atomic force microscopy (AFM). AFM images of the cleaved structures are presented, along with step height measurements at the different material interfaces. These height differences are the result of differences in oxidation rates of the heterostructure layers. The method used to extract the small step-height information from the images is also presented. Typical step heights range from about one to twenty angstroms for the structures measured. We have also observed steps which mimic the oxidation steps, but which are not related to the epitaxially grown material structure. However, in these cases images of both sides of the cleaved pieces show inverse (rather than similar) topographies. We also present results of digital etching techniques used to enhance the step heights based on the same differential oxidation mechanism.

The general concepts governing the electrochemical deposition of metal films on semiconductors are discussed, and recent results on the fabrication of Schottky junctions consisting of silicon electrodeposited with platinum, copper and gold are presented. In order to obtain good adherent metal films, the density of nuclei should be high and the films should be grown at low current densities where the charge transfer process is rate limiting. This situation can be realized using potential controlled electrochemical deposition. For metal deposition on silicon, the surface should be pretreated in HF to dissolve the oxide layer. Furthermore, the surface should be stable during deposition which can be achieved by tailoring the deposition solutions and by using electrochemical deposition at negative potentials. It is shown that by using this approach, n-type silicon / Pt, Au, and Cu Schottky junctions can be fabricated of a quality comparable to that of junctions prepared by sputter and vapor deposition techniques.

The presence of ultra-trace (as low as 1010 – 1013 atoms/cm2) quantities of metal contaminants on silicon substrates is well known to adversely affect the electrical properties of the silicon based microelectronic devices. In this paper, we report our most recent experimental findings on the trace metal deposition mechanisms and its interplays with silicon substrate surface properties at specific chemical environments. The emphases were on the deposition kinetics and morphology, especially at the early stage of metal out-plating process. For instance, our atomic force microscopy results revealed that the Cu deposition on H-Si(100) surface was dominated by nucleation of nanometer-sized Cu nuclei at the initial stage (less than 60 seconds). The growth of the existing Cu nuclei was suppressed for the initial nucleation period until all the nucleation sites were consumed. The number of nucleation sites were found to closely relate to wafer intrinsic properties and solution compositions. A novel sensor which provides direct detection of part-per-trillion level of metal ion impurities in wet cleaning solutions will also be presented.

Platinum electroless deposition on Si(lOO) from HF solutions is hindered on n+ substrates as compared to p-substrates defining an induction period and displaying a more local behavior. The results are discussed in terms of a global electrochemical process. Platinum reduces injecting holes to the silicon valence band and silicon atoms oxidizes. The final morphological situation is a porous silicon layer which contains platinum nuclei formed by filling pits originated in the first stages of the deposition process.

Nanocomposite films of copper metal and cuprous oxide were electrodeposited at room temperature from an alkaline copper(11) lactate solution. The electrode potential oscillated spontaneously during constant-current deposition of the composites. The oscillations were periodic in a stirred solution, but became chaotic in unstirred solution. For a given current density the phase composition was a strong function of solution pH. As the pH was increased, the cuprous oxide content increased. At pH 12, no oscillations were observed, and pure cuprous oxide was deposited. At pH 9, the phase composition varied from pure cuprous oxide at current densities below 0.1 mA/cm2 to 96 mole percent copper at 2.5 mA/cm2.

Different new micro-methods such as anisotropy micro-ellipsometry (AME), photoresist micro-electrochemistry, micro-photocurrent spectroscopy, and UV-laser scanning were performed simultaneously to characterize and modify heterogeneous semiconducter surfaces. All measurements were carried out on single grains with the Ti/TiO2 system as an example. The crystallographic orientations of the substrate grains were determined in-situ by AME. It is shown that both the electronic and the optical properties of the semiconducting TiO2 films sensitively depend on the substrate texture. Film properties such as layer thickness and defect state concentration vary with the substrate orientation in a systematic manner.

The TiO2 films were modified at high local resolution by means of focused UV-laser illumination. Both a thickening (writing) or thinning (erasing) of the films could be realized depending on the potential applied during the illumination. Therefore, the anodic potential could be used to control the layer thickness and to generate semiconducting structures with thickness gradients.

The results of an in situ investigation of the structural changes that occur during the operation of working battery electrodes using synchrotron radiation are presented. Two types of electrodes were investigated: an AB2-type Laves phase alloy anode with the composition ZrxTi1-xM2 and a proprietary cell based on a LixMn2O4 spinel compound cathode made by Gould electronics. For the Laves phase alloy compositions with x=0.25 and 0.5 and M=V0.5N1.1Mn0.2Fe0.2 were examined. Cells made from two different batches of LixMn2O4 material were investigated. The relationships between battery performance and structural changes will be discussed. In the later case, we also discuss the role of over-discharging on the LixMn2O4 structure and on battery operation.

In this report, a monolayer of N-(3-aminopropyl) pyrrole is used as a template layer for the controlled growth of polypyrrole on polycrystalline and oriented films of the high temperature superconductor, YBa2Cu3O7. Large increases in the growth rate and smoothness of the polymer layer are obtained with the use of the monolayer template as compared with the bare superconductor electrodes. Observation of the electrochemical growth characteristics as well as polymer morphological properties allows for an evaluation of the local surface conductive properties of superconductor-based ceramic and thin film samples. The use of the amine substituted pyrrole self-assembled monolayer serves to drastically alter the polymer growth characteristics and the surface adhesion properties.

Using electrochemical oxidation as a probe technique for the mechanisms by which oxidation occurs in c-axis La2CuO4 films, the vital role played by specific through-film microstructural defects has been observed using transmission electron microscopy. These defects are namely the large through-film precipitates sometimes found in these films and {111} planar faults. Two high-oxygen-content phases are formed; one locally and with a superstructure, the other of reduced orthor-hombicity and larger c-axis than as-grown material. Some films were found not to oxidize, and the defects in these films were compared with those in the oxidizable films.