Strong Compensation Effect Research Articles

Origins of Electrical Compensation in Si‐Doped HVPE GaN

Herein, the results of positron lifetime and X‐ray absorption spectroscopy obtained in Si‐doped GaN crystals, grown by the hydride vapor phase epitaxy (HVPE), are reported. Pushing the Si doping to high concentrations leads to surprisingly strong compensation effects. Positron experiments show that the concentrations of Ga vacancies are not high enough to be efficient compensation centers. Other acceptor‐like impurities are present in concentrations orders of magnitude lower than the Si content in the samples. X‐ray absorption shows that the local environment of Si dopants in compensated samples is different from the fully activated case. Simulated spectra of X‐ray absorption near edge structure strongly suggest that in compensated spectra Si is likely to have more Si atoms in the nearest local environment. Hence, autocompensation of Si dopants appears as a likely compensation mechanism at high Si contents GaN samples grown by HVPE.

Properties and Structure Evolution of CaO–Al2O3–La2O3 Slags with Various Alkali Metal Oxide Contents

To restrain the serious flux–steel reaction, CaO–Al2O3–La2O3‐based mold flux is designed for continuous casting of La‐bearing FeCrAl alloy. The properties and structure of slags with various alkali metal oxide contents are investigated. Results show that with the increase in Na2O or Li2O contents from 0 to 10 wt%, the melting temperature of slags decreased, and the fluxing effect of Li2O is improved. The addition of Na2O within 10 wt% reduces the slag viscosity at the temperature range of 1663–1823 K. While further increasing Na2O content to 15 wt%, the viscous behavior of the slag depends on the balance between the strong charge compensation effect of Na+ and the breaking network effect of O2−. Increasing Li2O contents from 0 to 15 wt% greatly reduces the slag viscosity, which is attributed to the reduction of the fraction of high‐polymerized QAl 4 units from 23.55% to 9.70% and the increase of [AlO6] octahedrons from 0 to 9.02% caused by more O2−. The NBO/Al and NBO fraction is calculated, which is consistent with the viscosity variations. In the melts, the structural roles of Na+, Li+, Ca2+, and La3+ are elucidated. Moreover, the relationship between the variations of crystalline phases and slag structure is discussed.

Defect characterization of heavy-ion irradiated AlInN/GaN on Si high-electron-mobility transistors

The characteristic energies of traps in InAlN/AlN/GaN high-electron mobility transistor structures on Si(111) substrates formed after irradiation with 75 MeV S-ions are studied by means of c-lattice parameter analysis, vertical IV-characteristics, micro-photoluminescence (µ-PL), photocurrent (PC) and thermally stimulated current (TSC) spectroscopy. From the lattice parameter analysis, point defect formation is concluded to be the dominant source of defects upon irradiation. A strong compensation effect manifests itself through enhanced resistivity of the devices as found in vertical IV-measurements. Defect formation is detected optically by an additional PL-band within the green spectral region, while defect states with threshold energies at 2.9 eV and 2.65 eV were observed by PC spectroscopy. The TSC spectra exhibit two defect-related emissions between 300 K and 400 K with thermal activation energies of 0.78–0.82 eV and 0.91–0.98 eV, respectively. The data further supports the formation of Ga vacancies (V Ga) and related complexes acting mainly as acceptors compensating the originally undoped n-type GaN buffer layers after irradiation.

Capturing hidden regulation based on noise change of gene expression level from single cell RNA-seq in yeast

Recent progress in high throughput single cell RNA-seq (scRNA-seq) has activated the development of data-driven inferring methods of gene regulatory networks. Most network estimations assume that perturbations produce downstream effects. However, the effects of gene perturbations are sometimes compensated by a gene with redundant functionality (functional compensation). In order to avoid functional compensation, previous studies constructed double gene deletions, but its vast nature of gene combinations was not suitable for comprehensive network estimation. We hypothesized that functional compensation may emerge as a noise change without mean change (noise-only change) due to varying physical properties and strong compensation effects. Here, we show compensated interactions, which are not detected by mean change, are captured by noise-only change quantified from scRNA-seq. We investigated whether noise-only change genes caused by a single deletion of STP1 and STP2, which have strong functional compensation, are enriched in redundantly regulated genes. As a result, noise-only change genes are enriched in their redundantly regulated genes. Furthermore, novel downstream genes detected from noise change are enriched in “transport”, which is related to known downstream genes. Herein, we suggest the noise difference comparison has the potential to be applied as a new strategy for network estimation that capture even compensated interaction.

Effect of MgO and BaO on viscosity and structure of blast furnace slag

The viscosity was measured by the cylinder method to investigate the effect of MgO and BaO on the viscous behavior of CaO-SiO2-Al2O3-MgO-BaO slags (CaO/SiO2 = 1.05, 7–10 wt%MgO, 0–3.5 wt%BaO). Based on the experimental data, the free running temperature and the activation energy were calculated to analyze the changes of characteristic of viscosity flow. The Fourier transformation infrared (FTIR) and Raman spectra were used to provide the information about the variation of slag structure. The results indicate that the viscosity, free running temperature, as well as activation energy decrease with the increase of MgO content in range of 7 wt%–10 wt%, and increase at BaO content from 0 wt% to 3.5 wt%. MgO provides free oxygen (O2−) to reduce the polymerization degree of slag and decreases the viscosity. However, the addition of BaO tends to form complicated structure and increase the viscosity. When BaO is added into slag, Ba2+ and O2− simultaneously influence the slag structure. O2− can break the Si-O bonds, and thus decrease the polymerization degree of slag. On the other hand, the charge compensation of Ba2+ can form complex aluminate-silicate structure and increase the viscosity of the slag. And the strong charge compensation effect that BaO acted is more dominated in the changes of slag structure.

A single source method to generate Ru-Ni-MgO catalysts for methane dry reforming and the kinetic effect of Ru on carbon deposition and gasification

A single precursor RuxNiyMg1-x-y(OH)(OCH3) derived from solvothermal synthesis was used to generate Ru-Ni-MgO catalysts for methane reforming with CO2. Calcination-reduction pretreatment of precursors could easily cause segregation of Ru and formation of both large and small metallic particles as RuO2 has limited solubility in NiO-MgO solid solution. Uniform small Ru-Ni alloy particles could only be produced within their limited alloying composition range through direct reduction pretreatment of the precursor. Catalysts derived from calcination-reduction exhibited low initial activity that increased with time-on-stream, whereas catalysts derived from direct reduction demonstrated high and steady activity. Over spent catalysts, Ru was found to have changed the type of deposited carbon from a recalcitrant graphitic one that could only be gasified by O2 to a soft type that can be facilely gasified by CO2. Kinetic studies showed that Ru increased the activation barrier for the rate determining CH4 dissociation step and thereby slows down the carbon deposition rate. A first order reaction dependence for CH4 pressure variation and zeroth for CO2 pressure change for pristine Ni- and Ru-catalysts was identified, while a first order and a deviation from zeroth order for CH4 and CO2 pressure variation were observed on bimetallic Ru-Ni catalyst. Such a deviation is associated with the oxyphilic nature of Ru that is enriched in the alloy surface under reforming conditions. The effects of Ru on carbon gasification over spent catalysts were investigated using a modified CO2-TPO measurement based on an extrapolated Wigner–Polanyi equation for carbon gasification. Ru was found to accelerate carbon gasification by increasing the pre-exponential factor for CO2 oxidation of carbon, albeit a disfavored elevated activation barrier was obtained, thus showing a strong compensation effect. Carbon gasification is favored in high concentration of CO2 and at high temperatures for Ru-Ni catalyst.

Effect of alkaline earth metal oxides on the viscosity and structure of the CaO-Al2O3 based mold flux for casting high-al steels

The effect of BaO and MgO content on the viscosity and structure of the CaO-Al2O3 based mold flux system has been studied in this article. The viscosity results suggested that the addition of BaO tends to increase the viscosity of flux system, due to the polymerization of the melts network structure that leads to the increase of the apparent activation energy for viscous flow. However, the addition of MgO tends to decrease the viscosity of the slag melt, in which the free O2– ions depolymerize the network structure leading to the reduction of melt flow resistance and apparent activation energy. The results of FTIR (Fourier transform infrared) and Raman for the molten structures showed that the released O2– ions by BaO and MgO, working as network breaker, can break SiO bonds for the [SiO4]4−-tetrahedral structure units; leading to the reduction of the symmetric Q1([Si2O7]6−) stretching vibrations and the increase of symmetric Q0([SiO4]4−) stretching vibrations. While for [AlO4]5−-tetrahedral structure units, they would be connected and the aluminate-silicate network structure become more complicated due to the strong charge compensation effect that BaO introduced. However, the major role that MgO played is to release O2– ions to depolymerize the complex network structure, due to its weak charge compensation effect.

Hydrogen passivation of vacancies in diamond: Electronic structure and stability from ab initio calculations

ABSTRACTPoint defects in diamond such as vacancies act as a strong donor compensation center; therefore, remarkably reduce electron conductivity of diamond-based devices. Artificial synthesis methods of n-type diamond utilize the hydrogen-containing precursors enabling its diffusion into diamond crystal and subsequent formation of hydrogen-vacancy complexes. Here we employ spin-polarized, hybrid density functional theory calculations, in order to characterize the electronic properties and stability of hydrogen-passivated vacancies in diamond. We found strong thermodynamic preference for hydrogen passivation of four vacancy-related dangling bonds. An analysis of formation energy vs Fermi level diagrams indicate, that strong donor compensation effect associated with vacancies can be entirely neutralized by hydrogen incorporation. Thus, a careful control of hydrogen partial pressure in the growth process might be crucial to improve the electron conductivity of n-type diamond.

Do the smart get smarter? Development of fluid and crystallized intelligence in 3rd grade

There are conflicting theoretical assumptions about the development of general cognitive abilities in childhood: On the one hand, a higher initial level of abilities has been suggested to facilitate ability improvement, for example, prior knowledge fosters the acquisition of new knowledge (Matthew effect). On the other hand, it has been argued that school education with its special focus on promoting less able students results in a compensation effect. A third hypothesis is that the development of cognitive abilities is—as an outcome of the opposing effects—overall independent of the initial state. In this study, 1,102 elementary students in 3rd Grade worked on two versions of the Berlin Test of Fluid and Crystallized Intelligence at two time points with an interval of five months. Beside the question of how initial state and growth are related (Matthew vs. compensation effect), we considered performance gains in fluid intelligence (gf) and crystallized intelligence (gc) as well as cross-lagged effects in a bivariate latent change score model. Both for gf and gc there was a strong compensation effect. Mean change was more pronounced in gf than in gc. We considered student characteristics (interest and self-concept), family background (socio-economic status, parental education) and classroom characteristics (teaching styles) in a series of prediction models to explain these changes in gf and gc. Although several predictors were included, only few had a significant contribution. Several methodological and content-related reasons are discussed to account for the unexpectedly negligible effects found for most of the covariates.

Wurtzite Zn1−y(MgxCd1−x)yO quaternary systems for photodiodes in visible spectral range

We investigated the optical bandgap engineering of ZnO based quaternary alloy films of wurtzite Zn1−y(MgxCd1−x)yO for photodiodes in visible spectral range. Quaternary alloy films were successfully synthesized by remote-plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The wurtzite alloy system has an optical bandgap energy between 2.16eV and 3.25eV, which was controlled by the flow ratio of metalorganic sources. The crystal structure and composition was analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This revealed that carrier compensation effects by alloying with MgO in Zn1−xCdxO system decreases carrier concentration. Strong compensation effects were observed in the bandgap range of Zn1−y(MgxCd1−x)yO between 3.0eV to 3.25eV and the carrier concentration decreased to 1015–1018cm−3. Schottky diodes of PEDOT: PSS/Zn1−y(MgxCd1−y)yO with optical bandgaps in the visible spectral range were fabricated to confirm the viability of photovoltaic applications. The diodes performed photovoltaic characteristics under a Xe–Hg lamp illumination through Schottky junctions. The photoresponse spectra showed a photosensitivity with cutoff energy of 2.23eV and peak energy of 2.90eV at 0V biasing.

Practical observations on the use of Shuffled Complex Evolution (SCE) algorithm for kinetic parameters estimation in pyrolysis modeling

Shuffled Complex Evolution (SCE) algorithm was first used to estimate kinetic parameters of the hypothetical three component charring material decomposing in three parallel steps and consequently applied to real material (beech wood). The study aims to promote the qualified engineering use of the algorithm in the field of pyrolysis modeling by testing the influence of the algorithmic setting, the initial parameter estimate and the search space size on the optimization run effectiveness and efficiency.Three strategies of choosing the search space when having no information about initial parameter values (no qualified guess or estimate of initial parameter values) in case of decomposition patterns that cannot be described by a single effective reaction are discussed. Using the synthetic test problem SCE was highly successful in all three case studies independent of the search space size and overlapping its boundaries. Applied to the real world material, strong compensation effect between parameters was observed. SCE however proved to be capable of providing satisfactory solution for highly challenging blind search.

Thermodynamics of binding of structurally similar ligands to histone deacetylase 8 sheds light on challenges in the rational design of potent and isozyme-selective inhibitors of the enzyme.

Among the different histone deacetylase (HDAC) isozymes, HDAC8 is the most highly malleable enzyme, and it exhibits the potential to accommodate structurally diverse ligands (albeit with moderate binding affinities) in its active site pocket. To probe the molecular basis of this feature, we performed detailed thermodynamic studies of the binding of structurally similar ligands, which differed with respect to the “cap”, “linker”, and “metal-binding” regions of the suberoylanilide hydroxamic acid (SAHA) pharmacophore, to HDAC8. The experimental data revealed that although the enthalpic (ΔH°) and entropic (ΔS°) changes for the binding of individual SAHA analogues to HDAC8 were substantially different, their binding free energies (ΔG°) were markedly similar, conforming to a strong enthalpy–entropy compensation effect. This effect was further observed in the temperature-dependent thermodynamics of binding of all SAHA analogues to the enzyme. Notably, in contrast to other metalloenzymes, our isothermal titration calorimetry experiments (performed in different buffers of varying ionization enthalpies) suggest that depending on the ligand, its zinc-binding group may or may not be deprotonated upon the binding to HDAC8. Furthermore, the heat capacity changes (ΔCp°) associated with the ligand binding to HDAC8 markedly differed from one SAHA analogue to the other, and such features could primarily be rationalized in light of the dynamic flexibility in the enzyme structure in conjunction with the reorganization of the active site resident water molecules. Arguments are presented that although the binding thermodynamic features described above would facilitate identification of weak to moderately tight-binding HDAC8 inhibitors (by a high-throughput and/or virtual screening of libraries of small molecules), they would pose major challenges for the structure-based rational design of highly potent and isozyme-selective inhibitors of human HDAC8.

Carbon sandwich preparation preserves quality of two-dimensional crystals for cryo-electron microscopy

Received 7 June 2013; accepted 21 June 2013Electron crystallography is an important method for determining the structure of membrane proteins. In this paper, we show the impact of a carbon sandwich preparation on the preservation of crystalline sample quality, using characteristic examples of two-dimensional (2D) crystals from gastric H+,K+-ATPase and their analyzed images. Compared with the ordinary single carbon support film preparation, the carbon sandwich preparation dramatically enhanced the resolution of images from flat sheet 2D crystals. As water evaporation is restricted in the carbon-sandwiched specimen, the improvement could be due to the strong protective effect of the retained water against drastic changes in the environment surrounding the specimen, such as dehydration and increased salt concentrations. This protective effect by the carbon sandwich technique helped to maintain the inherent and therefore best crystal conditions for analysis. Together with its strong compensation effect for the image shift due to beam-induced specimen charging, the carbon sandwich technique is a powerful method for preserving crystals of membrane proteins with larger hydrophilic regions, such as H+,K+-ATPase, and thus constitutes an efficient and high-quality method for collecting data for the structural analysis of these types of membrane proteins by electron crystallography.

Probing the Nature of the Co(III) Ion in Corrins: Comparison of Reactions of Aquacyanocobyrinic Acid Heptamethyl Ester and Aquacyano-Stable Yellow Cobyrinic Acid Hexamethyl Ester with Neutral N-Donor Ligands

Equilibrium constants (log K) for substitution of coordinated H(2)O in aquacyanocobyrinic acid heptamethyl ester (aquacyanocobester, ACCbs) and aquacyano-stable yellow cobyrinic acid hexamethyl ester (aquacyano-stable yellow cobester, ACSYCbs), in which oxidation of the C5 carbon of the corrin interrupts the normal delocalized system of corrins, by neutral N-donor ligands (ammonia, ethanolamine, 2-methoxyethylamine, N-methylimidazole, and 4-methylpyridine) have been determined spectrophotometrically as a function of temperature. Log K values increase with the basicity of the ligand, but a strong compensation effect between ΔH and ΔS values causes a leveling effect. The aliphatic amines with a harder donor atom produce ΔH values that are more negative in their reactions with ACSYCbs than with ACCbs, while the softer, aromatic N donors produce more negative ΔH values with ACCbs than with ACSYCbs. Molecular modeling (DFT, M06L/SVP, and a quantum theory of atoms in molecules analysis of the electron density) shows that complexes of the aliphatic amines with SYCbs produce shorter and stronger Co-N bonds with less ionic character than the Co-N bonds of these ligands with the cobester. Conversely, the Co-N bond to the aromatic N donors is shorter, stronger, and somewhat less ionic in the complexes of the cobester than in those of the SYCbs. Therefore, the distinction between the harder Co(III) in ACSYCbs and softer Co(III) in ACCbs, reported previously for anionic ligands, is maintained for neutral N-donor ligands.

Doping compensation for increased robustness of fast recovery silicon diodes

High-power diodes with the radiation enhanced diffusion (RED) of Pd are shown to have much higher ruggedness during the reverse recovery compared to that of the Pt. Anode doping profiles measured by spreading resistance technique after a 10 MeV He implantation with subsequent annealing between 500 and 800 °C reveal different compensation effects between the Pd and Pt. The in-diffusing Pd converts the n-type background doping concentration of N D = 3 × 10 13 cm −3 in the position of radiation defects to that of a p-type with about one order higher concentration. The created low-doped p-layer significantly increases ruggedness of diodes during reverse recovery. In the diodes with the Pt layer, only a modest compensation is observed, a conversion to a p-type layer is missing and robustness is much lower. The DLTS spectra for the Pt and Pd devices show a similar electronic structure and introduction rates of defects at 700 °C, while they differ significantly at 600 and 650 °C both for the majority and minority carriers. It is preliminary suggested that the strong compensation effect after the RED of Pd is caused by a high introduction rate of an acceptor deep level at the lower half of the silicon bandgap.

Deep levels and compensation effects in sulfur-doped GaPN layers grown by organometallic vapor phase epitaxy

Two GaPN epilayers, with different N contents of 0.3% and 0.9%, i.e., at the low-doping level and in the dilute-content range, respectively, have been examined by deep level transient spectroscopy (DLTS) and thermal admittance spectroscopy (TAS). DLTS revealed a main peak below 200K and a low-intensity broad signal above 250K. For the dominant peak, Arrhenius plots revealed an activation energy of 0.4eV below the conduction band and a corresponding trap density above 1017cm−3, in both the samples. The higher N-content sample features for this level a broader line shape and about one-order-of-magnitude larger cross section, as compared with the low N-content epilayer. TAS Arrhenius plots yielded a compressed discrepancy between the signatures of this trap in the two samples, pointing to a common physical origin, likely corresponding to N-split interstitials, and to a possible incidence of Poole–Frenkel effect on this trap behavior. However, the main discrepancy between the results from the two techniques lay in the concentrations as calculated for the signal above 250K. It was found that DLTS underestimates its intensity by at least one order of magnitude. Based on the extension of TAS data at high temperatures, this controversial signal resulted to correspond to Ga interstitials, which can also form complexes and can thus account for the strong compensation effects observed in these epilayers.

Calculation of the Hydration Free Energy Difference between Pyridine and Its Methyl-Substituted Derivatives by Computer Simulation Methods

The difference of the hydration free energy of pyridine and its methyl- and symmetrically dimethyl-substituted derivatives has been calculated by the method of free energy perturbation. To check the precision of the results obtained, we have repeated the calculations using thermodynamic integration over different paths. Besides the hydration free energy, the difference in the energy and entropy of hydration between pyridine and monomethyl- and dimethylpyridines has also been determined. The obtained results clearly show that the hydration free energy of the pyridine derivatives becomes more negative with each additional methyl group. However, the accuracy of the calculation does not allow us to draw any conclusion about the dependence of the hydration free energy on the location of the methyl group. The analysis of the Coulomb and Lennard-Jones contributions to the hydration free energy differences has shown the dominance of the latter term. The comparison of the hydration energy and free energy values has shown that there is a strong compensation effect between the energetic and entropic terms of the free energy. The hydration energy of the solute becomes considerably more negative with each additional methyl group due to the dispersion attraction between the methyl group and the surrounding water molecules. The introduction of a methyl group results in an approximately 30 J/(mol K) decrease of the entropy of hydration, and hence, at 300 K, the entropic contribution to the hydration free energy increases by about 9 kJ/mol. Due to their opposite signs, the entropic and energetic contributions largely cancel each other, resulting in approximately an order of magnitude smaller value for the free energy.

Radiation-induced defects in n-type GaN and InN

The electrical properties of the n-GaN and n-InN, subjected to proton irradiation, are studied. The irradiation of the n-InN results in an increasing concentration of charge carriers, whereas strong compensation effects take place in the proton-irradiated n-GaN. The annealing behavior of the radiation-induced defects in both materials is discussed briefly.

Energetics of two-step binding of a chromophoric reaction product, trans-3-indoleacryloyl-CoA, to medium-chain acyl-coenzyme-A dehydrogenase.

We previously demonstrated that the UV/visible spectrum of a chromophoric ligand, trans-3-indoleacryloyl-coenzyme-A (IACoA), is red-shifted (due to polarization of its carbonyl group) upon binding to pig kidney medium-chain acyl-CoA dehydrogenase (MCAD). The transient kinetic data revealed that the overall binding occurred in two steps. The first (fast) step involved the formation of an MCAD-IACoA collision complex in which the electronic structure of IACoA remained unchanged (the "colorless" complex), followed by a slow isomerization step with a concomitant red-shift in the IACoA spectrum (the "colored" complex) [Johnson, J. K., Wang, Z. X., and Srivastava, D. K. (1992) Biochemistry 31, 10564-10575]. To ascertain the energetics of the above two-step process, we investigated the temperature dependence of the spectral changes, binding constant of the MCAD-IACoA complex, and the rate constants for the conversion between the colorless and colored complexes. The data revealed that as the temperature of the incubation mixture of MCAD and IACoA ([IACoA] >> [MCAD] > Kd) increases from 12 to 35 degrees C, the resultant spectral peak of the MCAD-IACoA complex (lambda max = 417 nm) decreases. However, in this temperature range, the equilibrium constant for the second (isomerization) step remains unaffected. Isothermal titration calorimetric studies for the binding of IACoA to MCAD reveal that the overall binding energy at 25 degrees C (delta G degree = -7.4 kcal/mol) is contributed almost equally by the enthalpic (delta H degree = -3.7 kcal/mol) and entropic (T delta S degree = 3.7 kcal/mol) changes. As the temperature increases, both delta H degree and T delta S degree decrease proportionately, resulting in a strong enthalpy-entropy compensation effect. The temperature dependence of delta H degree yields a delta Cp degree value of -0.24 kcal/mol. The data presented herein throw light on the energetic consequences for the binding of IACoA to MCAD, the apparent similarity between the van't Hoff and calorimetric enthalpies, enthalpic and entropic contributions during the polarization of the carbonyl group of IACoA, and the overall structural-functional features of the enzyme-ligand complex as well as enzyme catalysis.

Defect levels of proton-irradiated silicon with doses ranging from 1 × 10 12 cm −2 to 1 × 10 13 cm −2

Schottky diodes of n-type silicon have been irradiated by 800 keV and 1 MeV protons at doses ranging from 1 × 10 12 cm −2 to 1 × 10 13 cm −2. Thermally Stimulated Capacitance (TSCAP), capacitance-voltage (CV) and Deep Level Transient Spectroscopy (DLTS) have been applied for sample analysis. By TSCAP measurements a strong compensation effect has been observed for irradiation doses up to 5 × 10 12 cm −2. At least five deep levels have been observed in the DLTS spectra, but the E(200) trap, located at E c − 0.36 eV, was only revealed by the fitting procedure. An additional new pure damage level, labelled E(110), with an energy of E c − 0.19 eV and a capture cross section of about 5 × 10 −16 cm 2 has been also observed in the highly damaged region. The variations of the DLTS signal with pulse amplitude of the E c − 0.3 eV level, called E(170), has been found to be different of what is obtained at low dose irradiations: a dip followed by a peak in concentration near the maximum of implanted ions is suggested. A possible explanation of such behavior is discussed. We also report the possibility of an overdoping effect near the proton distribution before thermal annealing.