Archaeological sites of the Mediterranean region are widely colonized by weed species causing various problems both to the monuments and the functionality of the sites. Due to recent regulatory restrictions for herbicide use at archaeological sites, flame weeding was studied as an alternative weed management method. The objective of the study was to test two propane doses (99 kg ha−1 and 129 kg ha−1) applied two, three, or four times at three archaeological sites of Greece (Kolona, Ancient Messene and Early Christian Amfipolis). Percent weed control and weed heights were significantly affected by flaming treatments. Visual evaluation of percent weed control suggested that the propane dose of 129 kg ha−1 applied four times provided excellent weed control (>90%) for over 2 months. Annual broadleaf weeds were controlled better with flaming than grasses and perennial broadleaf species. The high propane dose applied four times reduced average vegetation height to about 10 cm, which was the desirable vegetation height wanted by the managers of the archeological sites suggesting that flame weeding has the potential to be used effectively for weed management in archaeological sites of the Mediterranean region.

We present a new concept applicable to the epitaxial growth of dislocation-free semiconductor structures on a mismatched substrate with a thickness far exceeding the conventional critical thickness for plastic strain relaxation. This innovative concept is based on the out-of-equilibrium growth of compositionally graded alloys on deeply patterned substrates. We obtain space-filling arrays of individual crystals several micrometers wide in which the mechanism of strain relaxation is fundamentally changed from plastic to elastic. The complete absence of dislocations at and near the heterointerface may pave the way to realize CMOS integrated SiGe X-ray detectors.

We report on the maskless integration of micron-sized GaAs crystals on patterned Si substrates by metal organic vapor phase epitaxy. In order to adapt the mismatch between the lattice parameter and thermal expansion coefficient of GaAs and Si, 2 μm tall Ge crystals were first grown as virtual substrate by low energy plasma enhanced chemical vapor deposition. We investigate the morphological evolution of the GaAs structures grown on top of the Ge crystals at the transition towards full pyramids with energetically stable {111} facets. A substantial release of strain is shown in GaAs crystals with a height of 2 μm and lateral sizes up to 15×15 μm2 by both X-ray diffraction and photoluminescence.

Transmittance, reflectance and Raman measurements have been performed from 50 to 700 cm−1 on different thin films of β-FeSi2 epitaxially grown by MBE on Si substrates. Vibrational spectra show much more structures than the five phonons usually observed in this material; the dependence on the crystalline orientation, the thickness, the growth and the annealing temperature has been studied.

We discuss the properties of semiconducting iron silicides, grown epitaxially on Si(001) and Si(111) by molecular beam epitaxy. The growth on Si (111) involves phase transitions from epitaxially stabilized metallic phases, leading to larger epitaxial β-FeSi2 grains than most other deposition procedures. The structural and electric properties of β-FeSi2/Si(001) are improved considerably for growth temperatures above 650 °C. Hall mobilities of p—conducting films reach values up to 600 cm2/Vsec at 100 K, at carrier densities below 1017 cm−3. Despite of the high majority carrier mobility and low carrier density, the photoelectric response of p-β-FeSi2/n-Si(001) diodes does not yield any significant contribution from the silicide, however, in accordance with the expected band structure diagram.

Self assembled quantum dots of Ge were obtained by magnetron sputter epitaxy of seven monolayers of Ge on a 33nm thick undoped Si buffer grown on top of a p-doped (100) Si substrate. The samples obtained in this manner were then capped with an increasing number of silicon layers in order to study the effect of Si deposition on the strain and the morphology of the dots. They were characterized “ex situ” by spectroscopic ellipsometry and Raman spectroscopy. The optical experiments revealed well defined differences between the capped and uncapped samples and among samples with different cap thicknesses.

By monitoring the energy and the splitting of the E0', E1 and E2 interband optical transitions of Ge and the Ge-Si vibrational mode, the optical measurements evidence strain effects as well as the formation of SiGe alloy, in agreement with the “in situ” STM measurements.

Coherently strained Ge islands were grown at a substrate temperature of 550°C by magnetron sputter epitaxy on Si (001) and studied by scanning tunnelling microscopy (STM). The shape changes induced by exposure to a Si-flux at 450°C were investigated as a function of the Si-coverage. During Si-capping, multifaceted domes were found to flatten and to transform into {105}-faceted pyramids and subsequently into stepped mounds through intermediate shapes. The observed sequence of morphological changes is induced by Si-Ge intermixing and is shown to be the inverse of that occurring during Ge or Si1-xGex growth on Si (001). The results are interpreted with a model in which the stable shape of an island mainly depends on its volume and composition.

Coherently strained Ge islands were grown at a substrate temperature of 550°C by magnetron sputter epitaxy on Si (001) and studied by scanning tunnelling microscopy (STM). The shape changes induced by exposure to a Si-flux at 450°C were investigated as a function of the Sicoverage. During Si-capping, multifaceted domes were found to flatten and to transform into {105}-faceted pyramids and subsequently into stepped mounds through intermediate shapes. The observed sequence of morphological changes is induced by Si-Ge intermixing and is shown to be the inverse of that occurring during Ge or Si1-xGex growth on Si (001). The results are interpreted with a model in which the stable shape of an island mainly depends on its volume and composition.

Low temperature growth of thin crystalline Si films on amorphous glass substrates by Molecular Beam Epitaxy (MBE) as well as by two different plasma enhanced chemical vapour deposition (PECVD) systems both using a DC plasma was carried out and the mictrostructural properties were analysed. In particular, the control over the texture along [220] orientation and the resulting columnar nature of the films were studied. The TEM cross section of Si films grown by MBE shows grains with an average width of 750 nm and a length of 3 microns. Using the low energy PECVD (LEPECVD) technique microcrystalline Si films were obtained with a growth rate of up to 35Å/sec. For high quality Si films with larger grains one may grow Si films by MBE whereas for Si films with passivated grain boundaries and for increased deposition rate, it is preferred to grow Si films by the newly developed methods of DC-PECVD.

Low energy plasma enhanced chemical vapour deposition (LEPECVD) is a deposition technique developed for the epitaxy of Si and SiGe at ultra-high deposition rates. Due to a high current plasma discharge composed of low energy particles, a high plasma enhancement can be obtained without any accompanying plasma induced damage of the wafer surface. The most important application of LEPECVD so far is for compositionally graded relaxed SiGe buffer layers. Such relaxed buffer layers are demonstrated with end composition up to pure Ge and with a growth time below 1 hour. A p-type hetero-MOSFET formed in a SiGe channel compressively strained to a Si0.5Ge0.5 relaxed buffer layer, is demonstrated as one example where the high growth rates of LEPECVD allows the synthesis of devices which cannot be produced with an acceptable throughput with conventional deposition methods. The room temperature effective hole mobility of 760 cm2/Vs obtained on such devices demonstrates a high structural and electrical quality of the LEPECVD material.

Self assembled quantum dots of Ge were obtained by magnetron sputter epitaxy of seven monolayers of Ge on a 33nm thick undoped Si buffer grown on top of a p-doped (100) Si substrate. The samples obtained in this manner were then capped with an increasing number of silicon layers in order to study the effect of Si deposition on the strain and the morphology of the dots. They were characterized “ex situ” by spectroscopic ellipsometry and Raman spectroscopy. The optical experiments revealed well defined differences between the capped and uncapped samples and among samples with different cap thicknesses.

By monitoring the energy and the splitting of the E0', E1 and E2 interband optical transitions of Ge and the Ge-Si vibrational mode, the optical measurements evidence strain effects as well as the formation of SiGe alloy, in agreement with the ``in situ'' STM measurements.

Sil−xGex alloy layers and ultra-short period SimGen superlattices on alloy buffer layers of the same concentration have been grown by MBE. The superlattices as a whole have been shown to have the lattice constant of the underlying alloy buffer layer, the individual Si and Ge layers being fully strained. Samples with a graded Ge content have been used to study the relaxation as a function of Ge content by means of X-ray diffraction and RBS and channeling.

Transmission electron spectroscopy reveals that interface roughness is not simply statistical in these superlattices. Rather, electron diffraction shows additional features from a period doubling in the (111) directions, indicating that a corresponding interfacial ordering occurs. These features show 2- or 3-dimensional behavior depending on the thickness of the Si and Ge layers in the superlattices. Annealing studies show these features to persist even for annealing temperatures where the superlattices disintegrate into alloys.

Pseudomorphic Fe1-x Si films have been grown on Si(111) by molecular beam epitaxy (MBE) at room temperature (RT). Structural investigations revealed that the phase crystallizes in the cubic CsCl structure with a lattice constant close to half that of Si. Upon annealing, films thicker than 15Å undergo a phase transition to the stable bulk ε-FeSi, either in epitaxial or in polycrystalline form at temperatures around 300°C. Thinner films do not transform to the ε-FeSi phase. Instead they exhibit a continuous increase of the Si content up to the stoichiometry of FeSi2 The CsCl symmetry persists, exept for prolonged annealing close to the transition to βFeSi2, where γ-FeSi2 (CaF2 ) forms as an intermediate phase.

Epitaxial single-domain CoSi2(100) layers were grown on Si(100) by use of a template technique. In-situ scanning tunneling microscopy (STM) and reflection high energy electron diffraction (RHEED) were used for a detailed surface study. The (√2×√2)R45 reconstruction of the Co-rich “C-surface” and the (3√2×√2)R45 as well as a newly discovered (√2×√2)R45 of the Si-rich “S-surface” were resolved in real space and are discussed in detail. The transition from the C- to the S-surface above 500 °C is related to a (2×2) reconstruction.

Spectroscopic ellipsometry was used to characterize several short-period SimGen strained superlattices grown on Si(100) substrates or on graded SixGel-x alloy buffers (strainsymmetrization) by magnetron sputter epitaxy, a novel technique with potential application to industry-scale production of epitaxial Si/Ge heterostructures. Ellipsometric spectra were analyzed within a multilayer model, which included an oxide overlayer, in order to derive the effective dielectric fimctions of the SLs. spectra cannot be simulated by a sequence of Ge+Si slabs and compared to those of the compositionally equivalent alloys showed noticeable differences which can be ascribed to a combination of strain and confinement effects. The results agree with experimental findings and theoretical predictions on analogous SLs grown by MBE, thus confirming the reliability of the used technique to produce good quality SLs.

Thin (CsCl)CoSi films of thicknesses from 44 to 105 Å were grown by MBE at room temperature onto ultrathin annealed CoSi2 templates. Also two CoSi2 films of about 100 Å with the CaF2 structure and with the defected CsCl structure were obtained epitaxially.

Far infrared reflectance and transmittance measured on such samples show optical structures between 240 and 370 cm-1. In the range 1.4–5 eV spectroscopic ellipsometry was performed, too. A change in the optical response was revealed among the different samples, which can be ascribed to strain, roughness and/or disorder at the interfaces.