Cross-sectional micro-Raman Spectroscopy Research Articles

Recrystallization effects in GeV Bi ion implanted 4H-SiC Schottky barrier diode investigated by cross-sectional Micro-Raman spectroscopy

It is especially important to study on the change of 4H-SiC physical properties by swift heavy ion irradiation (SHI) for the future application of SiC devices in extreme irradiation environment. Herein, 4H-SiC Schottky barrier diodes (SBDs) are irradiated by 1.9 GeV 209Bi ion beams without intentional heating. The cross-sectional Micro-Raman Spectroscopy (MRS) results clearly indicated that there are new vibration bands at low fluence. This is attributed to the formation of homonuclear bonds Si–Si and C–C within the SiC network to break down the Raman selection rules. At high fluence, there are only typical Raman data for 4H-SiC crystal and the disappearance of Si–Si and C–C bonds. In addition, it is observed that the interfacial structure is modified due to the silicon and carbon atomic migration during SHI process at the metal-semiconductor interface, and then reacting at high temperature annealing treatment. Furthermore, these results suggest that the evolution of recrystallization effect is varied with irradiation fluence by the cross-sectional MRS.

Observation of the electron-accumulation layer at the surface of InN by cross-sectional micro-Raman spectroscopy

We study plasmon-related excitations in InN by micro-Raman spectroscopy. The surface sensitivity of Raman scattering is found to be strongly enhanced for backscattering from cleaved edges of thick films. This fact enables us to observe the electron accumulation layer at the surface of InN and to deduce the associated volume charge density.

Material Aspects of Icons. A Review on Physicochemical Studies of Greek Icons

Holy icons created in the Byzantine era are a vital entity in Orthodox Christianity, a living tradition unbroken over more than 1500 years. The importance of these symbolic representations has inspired interdisciplinary studies to better understand the materials and process of their construction. Researchers from a variety of fields are working together to place icons in their proper historical and cultural framework, as well as to develop long-term conservation strategies. In this Account, we review very recent analytical results of the materials and painting methods used in the production of Byzantine iconography. The care of icons requires particular attention because of their function; icons are objects of veneration and, for the most part, still stand in today's churches to serve ritual practices. Accordingly, they are affected by random, fluctuating environmental conditions aggravated by public access. Because of the holiness of the icons, the typical tradition of the church is to periodically restore the depicted scenes, either by retouching any defects or by partial or complete overpainting. These interventions greatly increase the complexity of the paint stratigraphy. To reveal the extent and quality of the original painting under several historical overpaintings or dirt overlays on the icon, researchers usually pursue a manifold approach, combining complementary multispectral imaging and spectroscopic techniques nondestructively. Unfortunately, a visual and exhaustive spectroscopic examination of a minimum number of cross-sectional microsamples is almost always necessary to clarify the structure of the paint layers and map the constituent materials identified therein. A full understanding of these details is critical for assessing the painting methods, stylistic conventions, and compositional concepts that render the different iconographic details. Cross-sectional micro-Raman spectroscopy, although time-consuming, now affords the direct identification of the distinct grains of almost all of the inorganic pigments and inert components included in the paint layers. Micro-Raman studies are complemented and cross-checked by micro-FTIR and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) studies. This approach is essential in documenting the evolution of the materials and techniques used in creating icons over the centuries. Analytical data on Greek icons are now available for comparison with similar results from other important schools of iconography, such as in the eastern Mediterranean, the Balkans, or Russia, or, further, with Western schools of painting. The research constitutes a reference base for identifying and solving analytical problems, such as those related to the organic materials found in icons that have not yet been systematically studied. Moreover, the results on icons are also generally applicable to important analytical issues encountered in studying any multilayered paint stratigraphies.

Controlled in situ boron doping of diamond thin films using solution phase

Controlled boron doping of diamond film using nontoxic reagents is a challenge in itself. During the present study, attempts have been made to dope diamond films in situ with boron from a solution of boric acid (H3BO3) in methanol (CH3OH) using a specially designed bubbler that ensured continuous and controlled flow of vapors of boron precursors during deposition. The samples are thoroughly characterized using a host of techniques comprising of x-ray photoelectron spectroscopy, Raman, x-ray diffraction, and current-voltage measurements (I-V). Cross-sectional micro-Raman spectroscopy has been used to obtain depth profile of boron in diamond films. Boron concentration ([B]) in the films is found to vary linearly on a semilog scale with molarity (M) of H3BO3 in CH3OH. Lattice constant of our samples is smaller than the reported American society for testing and materials (ASTM) values due to oxygen incorporation and it increases with [B] in the diamond samples. Heavily boron doped samples exhibit Fano deformation of the Raman line shape and negative and/zero activation barrier in temperature dependent I-V measurements that indicate the formation of metallic phase in the samples. The present study illustrates the feasibility of safe and controlled boron doping of diamond films using a solution of H3BO3 in CH3OH over a significant range of [B] from semiconductor to metallic regime but with a little adverse effect due to unintentional but unavoidable incorporation of oxygen.

Elimination of nonuniformities in thick GaN films using metalorganic chemical vapor deposited GaN templates

Thick hydride vapor phase epitaxial GaN layers are grown on metalorganic chemical vapor deposited GaN template layers as well as directly on sapphire, with the aim of investigating the effect of the template on the strain relaxation and spatial distribution of free carriers in the overgrown GaN films. Spatially resolved cross-sectional micro-Raman spectroscopy, cathodoluminescence, and transmission electron microscopy show improved crystalline quality for growth on metalorganic chemical vapor deposited GaN templates. The highly doped and highly defective near-substrate layer composed of columnar domains, typically present in hydride vapor phase epitaxial GaN films grown directly on sapphire, is absent in the layers grown on templates. Consequently, this results in elimination of the nonuniformities of free electron distribution, a lower residual free carrier concentration (<1017 cm−3), and improved strain relaxation.

Cross-Sectional Micro-Raman Spectroscopy: A Tool for Structural Investigations of Thin Polytypic SiC Layers

Cross-Sectional Micro-Raman Spectroscopy: A Tool for Structural Investigations of Thin Polytypic SiC Layers

Lift-off technique of homoepitaxial CVD diamond films by deep implantation and selective etching

We report on the replication of diamond substrates and the production of thin free-standing monocrystalline diamond films by applying a “lift-off” technique as suggested by Parikh et al. A diamond substrate is first deeply implanted in order to create a damaged subsurface layer that is selectively etched after overgrowth. In this process incomplete delamination and chipping appeared to be a problem. In order to optimize the preparation conditions for a successful lifting, we implanted diamond substrates with O + ions of 4.5 MeV at various doses. The films were subsequently overgrown with microwave plasma-assisted CVD and etched in air at elevated temperatures. With implantation doses between 1 × 10 17 and 5 × 10 17 cm −2 the CVD layers could be completely removed. Using optimized conditions a multiple replication with consecutive application of the lift-off technique has been demonstrated. The films were characterized by optical microscopy, X-ray diffraction and Raman spectroscopy. For the best samples, which were successfully separated, the Raman spectra show a sharp diamond phonon line of 2.5 cm −1 half-width for both the substrate and the lifted layer. To get depth-resolved structural information, cross-sectional micro-Raman spectroscopy was applied on samples that were partially implanted and overgrown with 13 C. Polished side faces gave access to both the predamaged region and the undamaged reference area. The data indicate that the implantation damage is restricted to a thin subsurface layer with only a small influence on the structural quality of the overgrown film.

Epitaxial overgrowth of 13C diamond films on diamond substrates predamaged by ion implantation

Homoepitaxial chemical vapor deposited (CVD) 13C diamond films were grown on 〈100〉 diamond substrates predamaged by implantation with 620 keV Xe ions. The structural quality of the overgrown films was analyzed by plain-view and cross-sectional micro-Raman spectroscopy. Implantation doses below 2×1014 cm−2, for which no damage detectable by Raman spectroscopy was observed in the substrate, had no effect on the quality of the overgrown films. For doses around 4×1014 cm−2, a pronounced predamage of the diamond substrate was found which had a strong degrading effect on the quality of the overgrown layer resulting in a drastic increase of the width of the optic zone-center phonon and in the appearance of Raman scattering from sp2-bonded carbon. Higher implantation doses up to 1×1015 cm−2 resulted in a complete etch removal of the predamaged graphitic surface layer during the initial phase of CVD growth, which thus had no effect on the quality of the film produced by the subsequent overgrowth.