Thin film bismuth piezoresistors, defined on oxidized silicon wafers, are investigated as a function of their orientation for their eventual integration on micro-electro-mechanical (MEMS) microsensors. Bismuth’s piezoresistance (or elasto-resistance) is experimentally investigated to accurately determine its longitudinal and transverse strain sensitivities. Whisker-shaped resistive elements defined on different orientations (from 0o, the beam’s main strain axis, to 90o, perpendicular to that axis) undergo changes of resistance (ΔR), associated with the induced strains on silicon cantilevers beam’s surface when these are mechanically loaded under pure bending stress conditions. For Bi-resistors, the traditional gage factor concept, (ΔR/Ro)/εl, is found to be equal to +16 and +33, for elements oriented along 0 and 90o, respectively, considerably larger than those for metals or metal alloys. These high sensitivity values and the “unusual” positive, higher value for the 90o (perpendicular) resistors can be of considerable interest for microsensors applications. The results of this study enable us to precisely determine the bismuth’s longitudinal and transverse strain sensitivities that are calculated to be equal to +26 and +40.5 respectively. This experimental study is extended to explore the Bi-films’ response to bi-axial strain fields.

Laser irradiation of Bismuth thin films through a diffractive mask was investigated. The thin films were composed of nano and microcrystals Bismuth with sizes ranging from 20 to 500 nm. Upon laser irradiation (λ=355 nm) the structured illumination field locally modified the material. In the high intensity regions the surface was transformed whilst low intensity areas were left intact. The modification mechanism was melting followed by coalescence of the nanocrystals giving rise to a more uniform structure. The laser irradiated area was characterized by scanning electron microscopy and atomic force microscopy. The patterns were computed by Fresnel diffraction theory and the agreement between the theory and the experiments was very good.

A comprehensive and rather complete study for the synthesis of Bismuth thin-films using physical vapor deposition (PVD) techniques aimed at identifying key features of their crystallographic structure and morphology/topography, as a function of the synthesis method is presented. These films were deposited on oxidized and non-oxidized polished silicon substrates, glass-plates and polyimide flexible films, by thermal evaporation (resistive boat and e-beam) DC- and RF-magnetron assisted sputtering, and pulsed laser (ablation) deposition (PLD). The synthesis was performed controlling the main deposition parameters of these methods.

XRD-spectra conclusively indicate that the films can be preferentially oriented along the [003] or [012] Bi-structure’s directions, depending on the source-to- substrate (STS)-distance, sputtering power, substrate’s temperature and PLD ion’s kinetic energy. It is also concluded that a relatively short STS-distance results in a rather polycrystalline structure, near independent to the used sputtering power.

The Laser induced oxidation process of bismuth was investigated using Raman spectroscopy. Upon laser irradiation (λ = 532 nm) pure Bismuth was transformed gradually into Bi2O3. Raman spectra of the samples showed the characteristics peaks for pure Bi located at 71 cm-1 and 96 cm-1. The oxidation process was monitored by Raman spectra with four additional bands located at about 127 cm-1, 241 cm-1, 313 cm-1 and 455 cm-1. Maintaining constant the exposure time of irradiation, the intensity of these bands depended on laser irradiation power. The presence of Bi2O3 in the sample was confirmed through by energy dispersion spectroscopy (EDS).

This work studies the performance of sputtered bismuth films as disposable working electrodes for stripping voltammetry. The electrodes were produced by coating a glass substrate with a bismuth film using DC magnetron sputtering under different conditions of power and time. The Bi-based sensors were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. Electrochemical evaluation included linear sweep voltammetry using different buffer solution and pHs to observe the effect of the deposition conditions and thickness on the potential window accessible for stripping analysis. Subsequently, the electrodes were tested for the detection of low concentrations of trace metals (Cd(II) and Pb(II)) by square wave anodic stripping voltammetry (SWASV). Clear and reproducible stripping peaks were observed for trace concentrations in the 50 - 450 ppb range of the target analytes. The detection limit of the Bi electrodes were quantitatively estimated from the analyses of SWASV, demonstrating that even using simple sensor geometry, detection limits in the 14-20 ppb range could be obtained. The reproducibility of the measurements is good (relative standard deviations about 4%) after 10 consecutive measurements which define the maximum number of times that the sensor can be used.

Patterned micro- and nanowires of several compositions in the solution series of BixTey were electrochemically deposited using Electroplate and Lift (E&L) Lithography on Ultrananocrystalline Diamond (UNCD) templates. The composition of the deposited BixTey wires was controlled by mixing saturated solutions of bismuth nitrate and tellurium in various ratios in the electroplating bath. All wires were electroplated via pulsed depositions at -1.4V vs. the saturated calomel electrode (SCE). The morphology and composition of all wires were studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In general, the BixTey wires were fine-grained and brittle, often fracturing during the liftoff process. By contrast, wires containing less than 5% Te are smooth, and strong enough to support their own weight without a supporting medium for a length of over 100 times the wire diameter.

Bismuth ferrite (BiFeO3) is a magnetoelectric, multiferroic material with coexisting ferroelectric and magnetic orderings. It is considered as a candidate for the next generation of ferroelectric random-access memory devices because BiFeO3, in contrast to industrial ferroelectrics used today, does not contain the toxic element lead. Furthermore, its polarization values are higher than those of lead-based ferroelectrics. The magnitude of the polarization of a BiFeO3 film is dependent on its orientation and is related to the domain structure. This contribution presents and discusses the preparation of epitaxial BiFeO3 (BFO) thin films grown on SrRuO3/SrTiO3 substrates by pulsed laser deposition (PLD) and their characterization, especially by piezo force microscopy (PFM) and atomic force acoustic microscopy (AFAM). The thickness of an individual BFO film varies between 100 and 200 nm. The epitaxial nature of films in the crystallographic (100), (110), and (111) directions was confirmed by x-ray diffraction (XRD). Thin SrRuO3 layers, also prepared by PLD, were used as bottom electrode for the ferroelectric hysteresis measurements. Low frequency PFM measurements showed a monodomain structure for the as-grown (110) and (111) oriented samples. In BFO (100) films, different polarization variants were observed by ultrasonic piezo force microscopy (UPFM). The domain structure is reproduced from minimization of the electrostatic and elastic energies. Switching experiments using standard PFM as well as UPFM were carried out on the three samples with the objective of testing the coercive field and domain stability. The AFAM technique was used to map the elastic properties of the BFO thin-films at the micro- and nanoscale.

Bismuth iron oxide BFO films were produced by the pulsed laser deposition technique. These films are a mixture of BiFeO3 ferroelectrical and Bi25FeO40 piezoelectrical phases. The ferroelectrical domain structure of these films was studied via contact resonance piezoresponse force microscopy (CR-PFM) and resonance tracking PFM (RT-PFM). The proportions of area of these BFO phases were derived from the PFM images. The ferroelectrical domain size corresponds to the size of the BiFeO3 crystals. The CR-PFM and RT-PFM techniques allowed us to be able to distinguish between the ferroelectric domains and the piezoelectric regions existing in the polycrystalline films.