Band Gap Of Zn Research Articles

Mössbauer and magnetic studies of Fe-doped ZnO nanoparticles prepared by solution co-precipitation method

A series of Zn[Formula: see text]FexO ([Formula: see text], 0.015, 0.045, 0.075) nanoparticles were synthesized using the solution co-precipitation method, and their structural and property characteristics were investigated. X-ray diffraction (XRD) analysis revealed that all Zn[Formula: see text]FexO samples exhibited a hexagonal wurtzite crystal structure with the P63mc space group. The introduction of Fe doping led to a slight lattice distortion in the samples. The morphology of the nanoparticles, including polydispersion and agglomeration, as well as the presence of the second phase ZnFe2O4, was examined by scanning electron microscope (SEM) and transmission electron microscope (TEM). UV–Vis diffuse reflectance spectroscopy demonstrated that the band gap of Zn[Formula: see text]FexO lies between 3.152 and 3.163[Formula: see text]eV. With the increase in Fe ion doping, the band gap shows a slight decreasing trend. Mössbauer spectroscopy revealed that iron ions in the nanoparticles existed in a trivalent state and exhibited two different configurations: One involved iron replacing zinc without creating a vacancy, while the other involved iron substituting zinc with a vacancy. The ferromagnetic nature of the Fe-doped samples can be attributed to the exchange interaction between two Fe[Formula: see text] ions mediated by the F-center mechanism.

Effects of short-range order on phase equilibria and opto-electronic properties of ternary alloy ZnxCd1-xTe

We employ first principles methods based on density functional theory and beyond to study ZnxCd1-xTe, 0≤x≤1, alloys in the zinc blende (B3) crystal structure. Cluster Expansion and Monte Carlo formalisms were deployed to provide a phase diagram determining consolute temperature of 387 K at 40% Zn concentration. Opto-electronic properties are computed with the hybrid HSE06 functional for disordered ZnxCd1-xTe alloys, which were simulated using special quasi-random structures. Bowing effects in the bandgap and effective carrier masses were observed in alloying which can be attributed to local geometrical distortions as portrayed by bond length distributions. Downward bowing in the electronic bandgap will be beneficial in photovoltaic applications through increased net photocurrent. Absorption coefficients show robust absorption in ZnxCd1-xTe as indicated by substantial optical absorption throughout all Zn concentrations, aided by low reflectivity that ensures a high absorption. Presence of short-range order in Zn0.25Cd0.75Te was observed through clustering and anti-clustering among different cationic species of Zn and Cd. It has a value of 0.11 at 1000 K compared to −0.79 at 400 K. The bandgap of Zn0.25Cd0.75Te at 1000 K was found to be slightly higher, 0.05 eV, than at 400 K, consistent with the value of short-range order. Thus, short-range order and possibly composition can be used in the design and synthesis of the appropriate solar cell, thereby improving the performance in this system.

Enhanced stability and tunable bandgap of Zn- and Cu-doped cobalt aluminate

Pristine and metal-doped cobalt aluminate samples were well synthesized using the sol–gel auto-combustion method. The physical properties of the synthesized samples were investigated employing X-ray diffraction and Raman spectroscopy. To validate structure stability, the influence of lattice strain was carried out by comparing Debye–Scherrer’s and Williamson-Hall plot method. Furthermore, Rietveld analysis was performed for precise structural parameters. Four Raman active modes (T2g(2) + T2g(3) + Eg + A1g) were examined within the range of 400 to 900 cm−1, confirming the formation of spinel structure. Here, an anomaly of the quadruple splitting of A1g mode in pristine and Zn2+-doped cobalt aluminate was observed. The FTIR spectroscopy shows metallic bonds confirming the absence of other functional groups. In UV–Vis spectroscopy, doping of Cu2+ (0.72 A) and Zn2+ (0.74 A) with nearly comparable ionic radii as Co2+ (0.72 A), optical bandgap increases ranging from 3.1 to 4.29 eV. Further, Urbach’s energy was plotted for all samples. Results show that doping of Cu2+ and Zn2+ supports reducing local lattice distortion. These features improved stability and wide optical bandgap ensure a vital role in state-of-the-art applications.

Efficient photocatalytic hydrogen production by Zn(1−2x)CuxIn2S(4−1.5x) co-doped with Cu and excess in under visible light irradiation

Herein, in order to achieve visible light responsive ability and efficient photogenerated electron–hole pairs separation Zn(1−2x)CuxIn2S(4−1.5x) photocatalysts were fabricated through a simple one-step solvothermal method. The effects of the Cu/Zn molar ratios on the crystal structure, morphology, optical property, as well as photocatalytic activity have been investigated in detail. In addition, the stability of the photocatalysts and apparent quantum yield were measured. The band gap became wider due to the decrease in Cu doping and Zn. The band gap of Zn(1−2x)CuxIn2S(4−1.5x) (x = 0 ~ 0.20) decreased from 2.67 to 1.76 eV with the increase in x value. When Pt was used as a co-catalyst, H2 evolution rates up to 2400 μmol g−1 h−1 were achieved over Zn0.74Cu0.13In2S3.805. Furthermore, when PdS was used as a co-catalyst, the hydrogen generation rates were improved with up to 3600 μmol g−1 h−1 by optimizing the Zn(1−2x)CuxIn2S(4−1.5x). The apparent quantum yield achieved 16% at 420 nm, 9.4% at 500 nm and 9.1% at 600 nm when x = 0.20. The improved visible light photocatalytic performance is considered to be due to the manipulation of the band structure and efficient photogenerated charge separation due to the effects of Cu doping and composition ratio.

Origin of Energy States in the Bandgap of Zn1 –xMnxO

We report on the results of analysis of optical absorption, EPR signals under optical excitation and magnetic susceptibility of hydrothermal Zn1 –xMnxO single crystals. In the absorption spectra of polarized light at temperatures of 4.2 and 77.3 K, narrow intense a, b, c, and d lines are observed in the energy range 1.877–1.936 eV of light quanta. The spectrum of these lines differs significantly from the spectra of donor and acceptor excitons for ZnO:Co and ZnO:Ni. The intensity of allowed and forbidden EPR signals of the Mn2+(d5) ions does not change under the action of light in the impurity absorption band, while the EPR signals of uncontrollable Fe3+ (d5) ions under illumination practically disappear. New experimental results for Zn1 –xMnxO lead to the conclusion that the d5/d4 donor level of the Mn2+ ion falls into the valence band, while the bandgap of Zn1 –xMnxO contains several dangling bond hybrid (DBH) states due to hybridization of 3d orbitals of the Mn2+ ion with the p-bonds of the nearest O2– oxygen ions. Electron transitions from the DBH states to the conduction band form a broad impurity absorption band of Zn1 –xMnxO, below the edge of which the a, b, c, and d lines referred to as donor excitons [(hloc + d5)e] and emerging as a result of Coulomb interaction of a free s-electron and a hole localized on DBH states (p + d5) are observed. The detection of donor excitons [(hloc + d5)e] makes it possible to study in detail the DBH states in the bandgap, which is important for photocatalysis in the visible light range.

Improvement of Photocatalytic H2-Generation under Visible Light Irradiation by Controlling the Band Gap of ZnIn2S4 with Cu and In

The band gap controlled photocatalyst (Zn0.74Cu0.13In2S3.805) was prepared via a simple one-step solvothermal method. The effects of doping of Cu+ and excess In on the photocatalytic activity of ZnIn2S4 photocatalyst were investigated. In addition, optical properties, surface morphology and crystal structure were evaluated. The maximum H2 evolution rate (2370 µmol h−1 g−1) was achieved with Zn0.74Cu0.13In2S3.805, which was about five times higher than that of untreated ZnIn2S4 under visible light (λ ≥ 420 nm). The band gap of Zn0.74Cu0.13In2S3.805 decreased to 1.98 eV by raising the maximum position of the valence band, compared to ZnIn2S4. Furthermore, the recombination of electron hole pairs was effectively reduced. This research contributes to the development of highly active photocatalysts under visible light.

Synthesis and Photocatalytic Properties of Co-Doped Zn1-xCoxMn2O Hollow Nanospheres

A series of Co-doped Zn1-xCoxMn2O nanocrystals with a spinel structure were successfully prepared by hydrothermal method, and the influence of Co doping concentration on the microstructure, morphology, elemental composition, and optical and photocatalytic properties of the samples was characterized. The experimental results show that all samples exhibit a tetragonal structure, Co2+ ions are successfully substituted for the lattice site of Zn2+ to generate ZnMn2O4 nanocrystals, and the crystalline size decreases as Co-doped concentration increase. The morphologies are loose hollow microsphere structures. The band gap of Zn1−xCoxMn2O samples is smaller than that of pure ZnMn2O4 and has been red shifted. The photocatalytic activity of doped Zn1−xCoxMn2O4 samples is obviously higher than that of pure ZnMn2O4 samples for the photodegradation of MO under visible light irradiation. All these results demonstrate that Co-doped spinel ZnMn2O4 nanocrystals are a meaningful choice for photocatalytic degradation of the pollutants.

Influence of Mn2+ ions on optical and magnetic property of wurtzite Zn0.98−xFe0.01Cu0.01MnxS nanowires

We reported the synthesis of wurtzite-type Zn0.98−xFe0.01Cu0.01MnxS nanowires (NWs) via a simple hydrothermal method, and discussed their structure, optical and magnetic properties depending on the ratio of Mn2+ ions. Both Fe2+, Cu2+ and Mn2+ ions substituted for the Zn2+ sites in ZnS lattice without changing its original wurtzite structure. The maximum solid solubility of the Mn2+ ions in Zn0.98Fe0.01Cu0.01S NWs can reach to 3.57 atom%. The band gap of Zn0.98−xCu0.01Fe0.01MnxS NWs was calculated to be 3.84 eV (x = 0.01) and 3.71 eV (x = 0.1), respectively. The photoluminescence (PL) spectra exhibited six Gaussian peaks covering from blue emission to red emission in visible region. The quenching of PL intensity can be observed at higher Mn2+ doping concentration. The magnetic measurement revealed the room temperature ferromagnetism property, and the saturation magnetization was increased as the Mn2+ doping ratio increased.

Room-temperature ferromagnetic Zn1−xNi x S nanoparticles

Nickel-doped zinc sulfide nanoparticles (Zn1−xNi x S) at x = 0.00, 0.02, 0.05, 0.08 and 0.10 were synthesized by solid-state reaction. The (nickel sulfide) NiS and (zinc sulfide) ZnS nanoparticles in desired ratios were taken, mixed and ground for 6 h at a speed rate of 300 rpm using a planetary ball mill. The milled nanoparticles were sintered at 600 °C for 8 h using a high-temperature vacuum furnace. The structural, optical, luminescence and magnetic properties of the Zn1−xNi x S nanoparticles were characterized by powder X-ray diffraction (XRD), UV–Vis–NIR diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy and vibrating sample magnetometer (VSM). No change in crystal structure was observed from XRD by substitution of Ni into ZnS lattice. The mean crystallite size was found to be 37 nm. The band gap of Zn1−xNi x S nanoparticles decreased from 3.57 to 3.37 eV on increasing the dopant concentration. The room-temperature photoluminescence (PL) spectra of Zn1−xNi x S nanoparticles showed two broad and intense emission peaks at 420 and 438 nm with excitation wavelength of 330 nm. The Zn1−xNi x S nanoparticles showed ferromagnetism at 100 K and at room temperature (300 K) and also the strength of magnetization increased with Ni concentration. The maximum magnetization value of 0.18 emu/g was observed for x = 0.10 at 100 K. The strength of the magnetization observed at 100 K was higher than that of magnetization observed at 300 K.

Synthesis, structural, optical and dielectric properties of transition metal doped ZnMnO nanoparticles by sol-gel combustion technique

Nanocrystalline samples of Zn0.94Mn0.06O and transition metal (TM) doped Zn0.94Mn0.01TM0.05O (TM = Co, Ni, and Cu) were prepared by sol-gel auto combustion method. X-ray diffraction (XRD) pattern infers that all synthesized samples except Zn0.94Mn0.01Ni0.05O and Zn0.94Mn0.01Cu0.05O with secondary phases of NiO and CuO are in single phase with hexagonal wurtzite structure (P63mc space group). Raman spectroscopy reveals four vibrational phonon modes are centered at 331, 380, 410, and 438 cm−1, assigned as E2 (H)-E2(L), A1(TO), E1(TO), and E1(LO) modes, respectively. A Raman spectrum of Zn0.94Mn0.01TM0.05O is entirely different from undoped Zn0.94Mn0.06O sample. Also, the infrared spectrum of transition metal doped samples is completely different from undoped Zn0.94Mn0.06O. Similar spectra are observed for Zn0.94Mn0.01Co0.05O, Zn0.94Mn0.01NiO, Zn0.94Mn0.01Cu0.05O and Zn0.94Mn0.01Zn0.05O samples. It was found that the band gap of Zn0.94Mn0.06O increased from 3.19 to 3.25eV by doping 5% transition metal oxide. Improved dielectric constant and reduced dielectric loss is measured for Zn0.94Mn0.01Ni/Cu0.05O as compared to Zn0.94Mn0.06O.

Room temperature synthesis and multiferroic response of Li co-doped (Zn, Co)O nanocrystallites

We have chemically synthesized Li-doped ZnO and Li co-doped (Zn, Co)O nano-crystallites following a wet chemical sol-gel route. In the structural characterization, we have performed X-ray diffraction (XRD) analysis, which reveals the presence of an impurity free phase. The particle sizes have been calculated utilizing the Scherrer formula which turns out to be lying in the range of 20–24 nm and 30–34 nm for Li-doped ZnO and Li co-doped (Zn, Co)O nanoparticles, respectively which is also confirmed by TEM (Transmission Electron Microscope) micrographs. In the temperature dependent dielectric measurements (which is the main novelty of this work), no phase transitions are observed for un-doped ZnO and also with Li doping up to 2% concentration, but at higher doping concentrations a typical ferroelectric phase transition is observed around 310 K. The frequency dependent dielectric properties show that irrespective of Li concentration, real and imaginary parts of dielectric constant as well as tangent losses show a decreasing trend. In Zn0.96−yCo0.04LiyO samples, we observed that the values of dielectric constant are greatly decreased by the Co-doping. The magnetic characterization displays a diamagnetic behavior of pure ZnO as well as ZnLiO doped samples, while in the Li-doped (Zn, Co)O samples a ferromagnetic trend is observed, achieving a multiferroic response in our samples. In the UV–Vis spectral studies, we observe that the Li-doping (up to 10%) doesn't affect the direct energy band gap of ZnO considerably. Whereas, the band gap of Zn0.95−yCo0.05LiyO display a declining tendency with increasing Li concentrations.

Synthesis and photocatalytic activity of ZnxCd1-xS/TiO2 heterostructures nanofibre prepared by combining electrospinning and hydrothermal method

The Zn x Cd 1–x S/TiO 2 hierarchical heterostructures were successfully fabricated by combining electrospinning technology and hydrothermal methods. The morphology, crystallinity, composition and band gap of Zn x Cd 1–x S/TiO 2 were characterized by SEM, XRD, EDS, and UV-vis diffuse reflectance spectroscopy. The results indicated the sulphur concentration had a significant influence on the composition and morphology of the products. The values of the band gap energy for Zn x Cd 1–x S/TiO 2 varied from 2.33 to 2.66 eV with the change of sulphur concentration.Whenthe molar ratio of S/Ti was 0.96, the Zn x Cd 1–x S/TiO 2 hierarchical heterostructures exhibited enhanced visible light photocatalytic behaviour for the decomposition of Rhodamine B (RhB) under visible light irradiation. The photocatalytic degradation of RhB followed first-order reaction kinetics. KEYWORDS Electrospinning, heterostructures, photocatalysis, dye degradition.

Fabrication of high-quality ZnCdO epilayers and ZnO/ZnCdO heterojunction on sapphire substrates by pulsed laser deposition

ZnCdO is a promising partner of ZnO to form ZnO/ZnCdO heterojunction and quantum wells. High-quality Zn1−xCdxO (0≤x≤9.60 at.%) films have been grown on c-plane sapphire substrates by pulsed laser deposition. XRD pattern confirmed all the ZnCdO films are of single hexagonal phase oriented along c-axis. A band gap of 2.949eV at room temperature has been achieved. The relation between band gap of Zn1−xCdxO system and Cd content x was expressed by Eg(x)=1.023×10−4x2−0.034x+3.253 (0at.%≤x≤100at.%) according to the corrected first principles calculations. Furthermore, band offsets of ZnO/Zn1−xCdxO (x=9.60at.%) heterojunction were characterized by X-ray photoelectron spectroscopy and valence-band offset of 0.203eV was measured. A conduction-band offset of approximately 0.110eV could be inferred from the measured valence-band offset. It is found that a type-I alignment takes place at the interface. The accurate determination of the band alignment of ZnO/Zn1−xCdxO heterojunction facilitates the design of optical and electronic devices based on ZnO/Zn1−xCdxO.

Photoinduced charge redistribution and its influence on excitonic states in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well heterostructures

The photoinduced charge redistribution in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well heterostructures under different conditions of optical excitation has been investigated using scanning probe microscopy and optical spectroscopy in the temperature range from 5 to 300 K. Excitation of the samples by radiation with a photon energy greater than the band gap of Zn(Cd)Se leads to the accumulation of electrons in quantum wells, which is detected using scanning spreading resistance microscopy. For moderate excitation densities (up to 25 W/cm2) and at temperatures ranging from 80 to 100 K, the density of a quasi-two-dimensional electron gas formed in quantum wells is several orders of magnitude higher than the density of electron-hole pairs generated by the excitation radiation. The excess electron concentration in the quantum well leads to a broadening of the exciton resonances and to an increase in the relative intensity of the donor-bound exciton emission line and also determines the increase in the luminescence quantum yield with increasing excitation intensity. An additional illumination with a photon energy less than the band gap of Zn(Cd)Se decreases the concentration of excess electrons in quantum wells. The influence of the additional illumination is observed at a temperature of approximately 100 K and almost completely suppressed at 5 K. The obtained results are explained in terms of the formation of a potential barrier for electrons at the ZnMgSSe/GaAs interface and by the specific features of recombination processes in the electron-hole system containing impurity centers with different charge states.

Zn0.94Cd0.06O nanoparticles with various structures, morphologies and optical properties toward MB optodecolorization

ZnO and Zn0.94Cd0.06O nanoparticles were synthesized by a sol–gel method at different calcination temperatures of 600, 700 and 800°C. Effect of calcination temperature on structural, morphological and optical properties of Zn0.94Cd0.06O nanoparticles was investigated by FT-IR, SEM, EDAX, XRD techniques, UV–vis absorption and photoluminescence (PL) spectroscopy. SEM micrographs showed that increase in the calcination temperature cause to change in the morphplogy of Zn0.94Cd0.06O nanoparticles from spherical at 600°C to rod-shaped particles at 800°C. XRD analysis data revealed that ZnO and Zn0.94Cd0.06O nanoparticles were crystallized in wurtzite phase. The average diameter of the synthesized nanoparticles calculated by Debbye–Scherrer formula was 29nm for ZnO and 24, 130 and 210nm for Zn0.94Cd0.06O nanoparticles calcined at 600, 700 and 800°C, respectively. UV–vis absorption and PL spectra indicated that there is a red-shift in the band-gap of Zn0.94Cd0.06O nanoparticles from 3.28eV to 3.08eV in comparison with that of pure ZnO nanoparticles and the red-shift value decreases with increase in the calcination temperature. All synthesized materials were also examined for their photocatalytic activity in decolorization of methylene blue (MB). The comparative results suggested high efficiency of Zn0.94Cd0.06O nanoparticles calcined at 600°C toward MB decolorization.

Oxygen pressure-dependent band gap modification in Cu-doped and -undoped ZnO films

abstractA study of the effect of oxygen flow rate on the energy band gap of the c-axis-oriented ZnO and Zn0.95Cu0.05O films, deposited on glass substrates by RF magnetron sputtering, is reported. An increase of the oxygen flow rate (partial pressure) during deposition results in an increase in the band gap (Eg) of Zn0.95Cu0.05O films from 2.80 to 3.10 eV. The maximum observed enhancement is 10.5%. For the same oxygen flow rate (partial pressure), the band gap of a Zn0.95Cu0.05O film is found to be lower than that of ZnO as predicted by Ferhat et al (2009 Appl. Phys. Lett.94 142502). A correlation has been observed between the residual strain and the band gap of doped and undoped ZnO films.

Comparisons of In/Al doped ZnO on the density of states based on first-principles

In order to obtain excellent optical and electrical properties of ZnO semiconductor light-emitting materials, some work has been done about the influence of doping. Models of pure ZnO, 12.5% Al-doped Zn0.875Al0.125O and 12.5% In-doped Zn0.875In0.125O are built respectively, and the electronic properties are calculated by first-principles method based on density functional theory (DFT). The results reveal that the lattice constants (a, c) of Zn0.875In0.125O are both larger than that of pure ZnO, which is in line with the changing of volume. The lattice constant a of Zn0.875Al0.125O is decreased while the c is amplified, and the volume of Zn0.875Al0.125O is reduced at the same time. The band gap of Zn0.875In0.125O is narrowed, while the band gap of Zn0.875Al0.125O is broadened. Moreover, through the analysis of density of states (DOS), we can know that the Al doping has a larger contribution to the electrical properties of ZnO than In doping. Al-3s and In-5s all have contributions to the total DOS at the CBM and Al-3p has an influence on the total DOS at the VBM, but In almost has no contribution to the total DOS. Based on the analysis above, it can be known that Al doping provides better electrical properties than In doping in getting promising n-type ZnO.

Zn1−x Mg x O (0≤x≤0.05) nanowalls grown on catalyst-free sapphire substrates by high-pressure PLD and their photoluminescence properties

We report the growth of Zn1−xMgxO (x=0, 0.02, 0.05 at.%) nanowalls on sapphire substrates without any metal catalysts by a high-pressure pulsed laser deposition (PLD). The influences of the experimental parameters like growth pressure, temperature, and target-substrate distance on the growth of Zn1−xMgxO nanowalls were systemically studied and the growth mechanism was discussed. It was found that large area and uniform Zn1−xMgxO nanowalls with c-orientation can be grown on sapphire substrates when the growth temperature and pressure were 950 °C and 400 Torr at a target-substrate distance of 2 cm. A thin layer assisted vapor-solid (VS) process was proposed for Zn1−xMgxO nanowalls growth. The photoluminescence spectrum shows the bandgap of Zn1−xMgxO nanowall was effectively expanded together with defect-related levels formation in a forbidden gap, which also induced enhancement of visible emission.

First-principles calculations of Cd-doped ZnO thin films deposited by pulse laser deposition

Zn1−xCdxO thin films are deposited on quartz substrate by pulse laser deposition. Their band structure and optical properties are experimentally and theoretically investigated. By varying Cd concentration, the band gap of Zn1−xCdxO films can be adjusted in a wide range from 3.219 eV for ZnO to 2.197 eV for Zn0.5Cd0.5O, which produces different emissions from ultraviolet to Kelly light in their photoluminescence spectra. Simultaneity, the electronic structure and band gap of Zn1−xCdxO are investigated by the density functional theory (DFT) with a combined generalized gradient approximation (GGA) plus Hubbard U approach, which precisely predicts the band-gaps of ZnO and Zn1−xCdxO alloys. Both the experimental results and theoretical simulation reveal that with increasing Cd concentration in Zn1−xCdxO alloys, their absorption coefficients in visible light range are evidently enhanced. The adjustable photoluminescence emission and enhanced visible light absorption endow Zn1−xCdxO alloys potential applications in optoelectronic and photocatalytic fields.

Optical properties of Zn 3(OH) 2V 2O 7· nH 2O nanosheets

Strong green photoluminescence (PL) was observed for hydrothermal synthesized Zn 3(OH) 2V 2O 7· nH 2O nanosheets. The energy band structure of the material was theoretically computed using first principle method and experimentally obtained by linear extrapolating from UV–vis reflection spectrum. It is shown that the material is an indirect bandgap semiconductor with a direct bandgap of 3.03 eV at Γ and an indirect gap of 2.8 eV from R to Γ. UV–vis reflection spectrum changes regularly along with doping of cobalt, showing clearly reflection peaks of Co 2+. The bandgap of Zn 3(OH) 2V 2O 7· nH 2O decreases significantly along with doping of cobalt, indicating the substitution of Co 2+ with Zn 2+. The intensity of the PL spectrum of Zn 3(OH) 2V 2O 7· nH 2O that annealed in vacuum remains almost unchanged, whereas it distinctly decreases with doping of cobalt. The results indicate that it is zinc vacancies that cause the green emitting, which is in accordance with Zn deficiency that deduced from energy dispersion spectroscopy characterization.