Applications of three-dimensional carbon nanotube networks

• Manuela Scarselli,
• Paola Castrucci,
• Francesco De Nicola,
• Ilaria Cacciotti,
• Francesca Nanni,
• Emanuela Gatto,
• Mariano Venanzi and
• Maurizio De Crescenzi

Beilstein J. Nanotechnol. 2015, 6, 792–798, doi:10.3762/bjnano.6.82

• respond to incident light in the visible and near-ultraviolet region and to generate a photocurrent. Keywords: carbon nanotube sponge; electrochemical; hydrophobicity; lipophilicity; Introduction In the last years, there has been growing interest in developing natural and synthetic three-dimensional

• incident light and generate a photocurrent, we cut a piece of the CNT-sponge, which has a self-sustainable structure, and used it as the working electrode in a standard electrochemical cell. In this manner, it was possible to register a good photo-response of the CNT-network in the visible and near

• deposited. By measuring the ratio between the mass of the dry CNT bulk material and the mass after oil adsorption, the oil-adsorption capacity was evaluated. The adsorbed oil in the material was then removed burning it in air and then was used to repeat the above process for many cycles. Photocurrent

Graphene quantum interference photodetector

• Mahbub Alam and
• Paul L. Voss

Beilstein J. Nanotechnol. 2015, 6, 726–735, doi:10.3762/bjnano.6.74

• ][17][18][19]. The primary distinguishing features of graphene photodetectors are: photodetection over a wide spectral range from infrared to ultraviolet wavelengths, a transit-time-limited bandwidth of approximately 1.5 THz and a high internal quantum efficiency of 15–30% [2][3][19]. The photocurrent

• electrons and holes. Photocurrent generation without a p–n junction and bias has also been demonstrated by utilizing the built-in electric field at the metal–graphene interface [20]. In this paper, we present the simulation results of two different approaches for an all-graphene (leads and device

• time of the electron through the device. Since we are assuming that the device length is less than the mean free path of the electron, we are neglecting all phonon interactions here. The photocurrent flows through the leads because one of the leads (drain) cannot supply the electrons to fill up the

Observation of a photoinduced, resonant tunneling effect in a carbon nanotube–silicon heterojunction

• Carla Aramo,
• Antonio Ambrosio,
• Michelangelo Ambrosio,
• Maurizio Boscardin,
• Paola Castrucci,
• Michele Crivellari,
• Marco Cilmo,
• Maurizio De Crescenzi,
• Francesco De Nicola,
• Emanuele Fiandrini,
• Valentina Grossi,
• Pasqualino Maddalena,
• Maurizio Passacantando,
• Sandro Santucci,
• Manuela Scarselli and
• Antonio Valentini

Beilstein J. Nanotechnol. 2015, 6, 704–710, doi:10.3762/bjnano.6.71

• characteristics were intensively studied on different substrates, resulting in high photoresponsivity with a large reverse photocurrent plateau. In this paper, we report on the photoresponsivity characteristics of the device, the heterojunction threshold and the tunnel-like effect observed as a function of

• 378 to 980 nm. Figure 5a reports the photocurrent measured in the configuration shown in Figure 2b. When the drain voltage exceeds the threshold voltage shown in Figure 3, the reverse photocurrent begins to grow linearly until reaching a plateau, which is constant over a large voltage range. The

• photocurrent depends quite linearly on the intensity of the illumination, as shown in Figure 5b. No saturation effects were observed up to tens of mW. The photodetector is sensitive to light radiation over a wide range of wavelengths. Figure 5c shows the measured photoresponsivity (photocurrent generated by 1

Carrier multiplication in silicon nanocrystals: ab initio results

• Ivan Marri,
• Marco Govoni and
• Stefano Ossicini

Beilstein J. Nanotechnol. 2015, 6, 343–352, doi:10.3762/bjnano.6.33

• . Consequently, at the nanoscale CM can be as fast as (or faster than) phonon scattering processes and Auger cooling mechanisms [11]. Therefore, CM represents an effective way to minimize energy loss factors and constitutes a possible route for increasing solar cell photocurrent, and hence, to increase solar

• approaches [21][24][25][26][27][28][29][30] although only recently was a full ab initio interpretation of CM proposed [31]. Recently, a relevant photocurrent enhancement arising from CM was observed in a PbSe-based, quantum dot (QD) solar cell [32], which proves the possibility of exploiting CM effects to

Low-cost plasmonic solar cells prepared by chemical spray pyrolysis

• Erki Kärber,
• Atanas Katerski,
• Ilona Oja Acik,
• Valdek Mikli,
• Arvo Mere,
• Ilmo Sildos and
• Malle Krunks

Beilstein J. Nanotechnol. 2014, 5, 2398–2402, doi:10.3762/bjnano.5.249

• photocurrent due to the plasmonic effects of NPs have been demonstrated, for example, for thin film Si solar cells [3], polymer cells [10][11], dye-sensitized cells [12][13] and for solar cells that use ultrathin inorganic absorber layers [14]. However, the use of an in-line spray method for the deposition of

• order to increase the photocurrent in the sprayed solar cell. Experimental Using commercially available, ITO-covered glass as a substrate, Au-NPs were deposited onto the ITO layer (ITO/Au-NP/ZnO/In2S3/CuInS2) or on top of the absorber layer (ITO/ZnO/In2S3/CuInS2/Au-NP). Details regarding the ITO/ZnO

Inorganic Janus particles for biomedical applications

• Isabel Schick,
• Steffen Lorenz,
• Dominik Gehrig,
• Stefan Tenzer,
• Wiebke Storck,
• Karl Fischer,
• Dennis Strand,
• Frédéric Laquai and
• Wolfgang Tremel

Beilstein J. Nanotechnol. 2014, 5, 2346–2362, doi:10.3762/bjnano.5.244

• efficiencies. This influence was mainly ascribed to the enhanced dye absorption by the magnified near-field of Au nanoparticles and the plasmon-enhanced photocurrent generation (Figure 6c) [51]. Synthesis of inorganic Janus particles The synthesis of hetero-nanoparticles requires an even higher degree of

• (DSSCs) with tailor-designed Au–TiO2 nanostructures integrated into the photoanode representing the increased photocurrent by LSPR and scattering effects [51]. (a, b) Adapted with permission from [50]. Copyright 2012 WILEY-VCH. (c, d) Reproduced with permission from [51]. Copyright 2014 The Royal Society

Photodetectors based on carbon nanotubes deposited by using a spray technique on semi-insulating gallium arsenide

• Domenico Melisi,
• Maria Angela Nitti,
• Marco Valentini,
• Antonio Valentini,
• Teresa Ligonzo,
• Giuseppe De Pascali and
• Marianna Ambrico

Beilstein J. Nanotechnol. 2014, 5, 1999–2006, doi:10.3762/bjnano.5.208

• , electron microscopy, in scanning (SEM) and transmission (TEM) modes, was used. Current–voltage (I–V) characterizations under dark and illuminated conditions, from NIR to UV region, were performed with two different device configurations. The resulting QE and the photocurrent spectral measurements are

• . The voltage supply was connected to the top ITO contact whereas the sample was grounded at the rear through the aluminium support. For the calculation of QE, a typical configuration for spectral photocurrent measurements with a light source, wavelength selector and reference diode has been used

• Detectors, serial no. 97-527) was used for the QE calculation. An Agilent source/monitor unit was used to record the current–voltage characteristics. To obtain more detailed information of the photodetector in the range of vis–NIR, photocurrent spectra of the SFS and of the ITO/GaAs/Ti/Au control sample

Donor–acceptor graphene-based hybrid materials facilitating photo-induced electron-transfer reactions

• Anastasios Stergiou,
• Georgia Pagona and
• Nikos Tagmatarchis

Beilstein J. Nanotechnol. 2014, 5, 1580–1589, doi:10.3762/bjnano.5.170

• . This configuration allows for photocurrent measurements under electrochemical bias. Electrophoretic deposition is applied to fabricate films of the graphene-based hybrid material onto an optically transparent electrode (OTE) covered with nanostructured SnO2. Typically, a suspension of the graphene

• /SnO2/graphene-based hybrid material) is deposited within a short period of time. The photocurrent action spectrum of the OTE/SnO2/graphene-based hybrid material electrode is evaluated by examining the wavelength dependence of the incident-photon-to-current conversion efficiency (IPCE). The IPCE values

• are calculated by normalizing the photocurrent densities by energy and intensity of the incident light according to the following equation: where i is the photocurrent density (A·cm−2), Win is the incident light intensity (W·cm−2), and λ is the excitation wavelength (nm). Donor–acceptor hybrids based

Growth evolution and phase transition from chalcocite to digenite in nanocrystalline copper sulfide: Morphological, optical and electrical properties

• Priscilla Vasthi Quintana-Ramirez,
• Ma. Concepción Arenas-Arrocena,
• José Santos-Cruz,
• Marina Vega-González,
• Omar Martínez-Alvarez,
• Víctor Manuel Castaño-Meneses,
• Laura Susana Acosta-Torres and
• Javier de la Fuente-Hernández

Beilstein J. Nanotechnol. 2014, 5, 1542–1552, doi:10.3762/bjnano.5.166

• structure. All CuxS products could be promising for optoelectronic applications. Keywords: abundant materials in the crust of Earth; electrical resistance; nanocrystals; nanodisks; non-toxic semiconductors; optical band gap; phase transition; photocurrent; Introduction Metallic chalcogenides based on

An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals

• Parul Chawla,
• Son Singh and
• Shailesh Narain Sharma

Beilstein J. Nanotechnol. 2014, 5, 1235–1244, doi:10.3762/bjnano.5.137

• polymer and acceptor chalcopyrite has to be sufficiently fast to their respective electrodes in order to avoid non-radiative recombination, which can occur at the interface between the two materials and can therefore alter the device photocurrent [24]. However, after successful exciton dissociation across

Enhanced photocatalytic hydrogen evolution by combining water soluble graphene with cobalt salts

• Jing Wang,
• Ke Feng,
• Hui-Hui Zhang,
• Bin Chen,
• Zhi-Jun Li,
• Qing-Yuan Meng,
• Li-Ping Zhang,
• Chen-Ho Tung and
• Li-Zhu Wu

Beilstein J. Nanotechnol. 2014, 5, 1167–1174, doi:10.3762/bjnano.5.128

• oxide; EY: eosin Y). Graphene enhances the catalytic efficiency of hydrogen evolution remarkably. By using transient photovoltage and photocurrent techniques [48][49][50], the function of graphene was examined. More recently, our group has demonstrated the efficient forward electron-transfer mediated by

Optical modeling-assisted characterization of dye-sensitized solar cells using TiO₂ nanotube arrays as photoanodes

• Jung-Ho Yun,
• Il Ku Kim,
• Yun Hau Ng,
• Lianzhou Wang and
• Rose Amal

Beilstein J. Nanotechnol. 2014, 5, 895–902, doi:10.3762/bjnano.5.102

• , 78.6, and 98.7 nm, respectively. The longest TNT array of 20.6 μm in length showed enhanced photovoltaic performances of 3.87% with significantly increased photocurrent density of 8.26 mA·cm−2. This improvement is attributed to the increased amount of the adsorbed dyes and the improved electron

• light illuminated from a back side passing through Pt-deposited FTO glass, and subsequently the penetrated light is absorbed by dye-sensitized well-ordered TNT arrays. In Figure 2, the photocurrent density–voltage curves for the TNT-based N719 DSSCs are shown depending on 3.3, 11.5, and 20.6 μm long TNT

• illumination (Inset SEM image indicates well-ordered TNT arrays prepared by anodization). Photocurrent–voltage characteristics of N719-DSSCs fabricated by using 3.3 μm, 11.5 μm, and 20.6 μm TNT arrays under an AM 1.5 solar simulator (100 mW·cm−2). IPCE spectrum of the N719-DSSCs fabricated by using 3.3 μm

Biomolecule-assisted synthesis of carbon nitride and sulfur-doped carbon nitride heterojunction nanosheets: An efficient heterojunction photocatalyst for photoelectrochemical applications

• Hua Bing Tao,
• Hong Bin Yang,
• Jiazang Chen,
• Jianwei Miao and
• Bin Liu

Beilstein J. Nanotechnol. 2014, 5, 770–777, doi:10.3762/bjnano.5.89

• performances of CN, CNS and the CN/CNS heterostructure. As shown in Figure 6b, photocurrent densities of the samples increase with forward bias voltage, indicating a typical n-type semiconductor behavior. Among all samples, the CN/CNS heterostructure demonstrates the highest photocurrent as compared with the

• photoelectrode, which can be attributed to the large contact area between the CN/CNS photoelectrode and the electrolyte as well as an appropriate band alignment of the CN/CNS interface. It has been well-established that photocurrent is generated because of the diffusion of photogenerated electrons to the back

• contact and the simultaneous consumption of photogenerated holes by the hole acceptor in the electrolyte. As such, the superior photocurrent of CN/CNS heterostructure indicates the more efficient charge carrier separation and longer lifetime of the free charge carriers. A control experiment using

Nanostructure sensitization of transition metal oxides for visible-light photocatalysis

• Hongjun Chen and
• Lianzhou Wang

Beilstein J. Nanotechnol. 2014, 5, 696–710, doi:10.3762/bjnano.5.82

• photogenerated electrons from CdS to TiO2 nanotubes, and exhibited a much enhanced photocurrent generation and photocatalytic efficiency under visible-light irradiation. Kamat et al. compared the performances of CdS photosensitized ordered arrays of tubular TiO2 architectures with a CdS photosensitized

• photosensitization of nanoporous titanium dioxide, zinc oxide, tin dioxide, niobium oxide, and tantalum oxide by quantum-sized cadmium sulfide, lead sulfide, silver sulfide, antimony sulfide, and bismuth sulfide. They found that the photocurrent quantum yields of these photosensitized transition metal oxides can be

• irradiation [65]. Ingram et al. employed plasmonic Ag nanocubes as building blocks to fabricate silver nanocube-N doped TiO2 photoelectrocatalysts for PEC water splitting [67]. An investigation of the relationship between the photocurrent and light intensity by Ingram et al. revealed that N-doped TiO2

A visible-light-driven composite photocatalyst of TiO₂ nanotube arrays and graphene quantum dots

• Donald K. L. Chan,
• Po Ling Cheung and
• Jimmy C. Yu

Beilstein J. Nanotechnol. 2014, 5, 689–695, doi:10.3762/bjnano.5.81

• ), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and UV–vis absorption spectroscopy. The product exhibited high photocatalytic performance in the photodegradation of methylene blue and enhanced photocurrent under visible

• comparison, the activity of pure TiO2 (P25) was tested under the same conditions and it was found to be low. TNAs were stably grown on a conducting Ti substrate, so the entire foil can be directly used for photoelectrochemical applications. Photocurrent responses of the catalysts were measured under visible

• light irradiation. Figure 6 clearly shows a significant enhancement of photocurrent after the loading of GQDs, indicating the charge separation efficiency of TNAs is greatly enhanced. The stable current reveals that GQDs are covalently bonded to TNAs instead of adsorbed onto the surface of TNAs. The

Photovoltaic properties of ZnO nanorods/p-type Si heterojunction structures

• Rafal Pietruszka,
• Bartlomiej S. Witkowski,
• Grzegorz Luka,
• Lukasz Wachnicki,
• Sylwia Gieraltowska,
• Krzysztof Kopalko,
• Eunika Zielony,
• Piotr Bieganski,
• Ewa Placzek-Popko and
• Marek Godlewski

Beilstein J. Nanotechnol. 2014, 5, 173–179, doi:10.3762/bjnano.5.17

• highest value of generated photocurrent flows through the junction with an illumination in the range of 900 nm to 1000 nm, i.e., when carriers are generated in a Si substrate. Samples with a similar value of the shunt resistance (A, B) have a similar photoresponse curves. Quantum efficiency values

Optimization of solution-processed oligothiophene:fullerene based organic solar cells by using solvent additives

• Gisela L. Schulz,
• Marta Urdanpilleta,
• Roland Fitzner,
• Eduard Brier,
• Elena Mena-Osteritz,
• Egon Reinold and
• Peter Bäuerle

Beilstein J. Nanotechnol. 2013, 4, 680–689, doi:10.3762/bjnano.4.77

• (vide infra) demonstrate that the DCV5T-Bu4:PC61BM devices generate a photocurrent in the range of 400 to 700 nm and display maximum conversion at 580 nm. The EQE at 580 nm was measured to 40% and 36% for solar cells made with and without solvent additives, respectively. Further information regarding

• ), similar Voc, and FFs resulting in a lower PCE of 2.5% compared to the best DCV5T-Bu4:PC61BM device (3.0%). The stronger absorption of DCV5T-Bu4:PC71BM blends in the region from 400 to 500 nm is apparent in the normalized thin film absorption spectra shown in Figure 5a and in the photocurrent generated in

• , and improve charge transport to the electrodes. The better photocurrent saturation values for the vacuum-deposited cells, 1.17 versus 1.28 for the solution-processed devices, indicate reduced recombination, resulting in increased charge collection. The relatively modest difference in solar cell

Kelvin probe force microscopy of nanocrystalline TiO₂ photoelectrodes

• Alex Henning,
• Gino Günzburger,
• Res Jöhr,
• Yossi Rosenwaks,
• Biljana Bozic-Weber,
• Catherine E. Housecroft,
• Edwin C. Constable,
• Ernst Meyer and
• Thilo Glatzel

Beilstein J. Nanotechnol. 2013, 4, 418–428, doi:10.3762/bjnano.4.49

• . The observed logarithmic dependence demonstrates a photodiode behavior according to Equation 5 and is an indication for a built-in (Schottky barrier) potential at the interface. It should be noted that the photocurrent, Jph, in Equation 5 is approximately proportional to the light intensity, I. When

• the open-circuit voltage (Equation 5), it is the reverse saturation current density, J0, and the conduction band minimum, Ecb, that are influenced by the surface dipole and finally affect Voc: wherein A is the correction factor and Jph the photocurrent density. A performance comparison of DSCs

Photoelectrochemical and Raman characterization of In₂O₃ mesoporous films sensitized by CdS nanoparticles

• Mikalai V. Malashchonak,
• Sergey K. Poznyak,
• Eugene A. Streltsov,
• Anatoly I. Kulak,
• Olga V. Korolik and
• Alexander V. Mazanik

Beilstein J. Nanotechnol. 2013, 4, 255–261, doi:10.3762/bjnano.4.27

• the SILAR deposition. The surface modification of In2O3 with CdS nanoparticles leads to the spectral sensitization of photoelectrochemical processes that manifests itself in a red shift of the long-wavelength edge in the photocurrent spectrum by 100–150 nm. Quantum-confinement effects lead to an

• Ag|AgCl|KCl (sat.) electrode as the reference electrode (+0.201 V versus SHE). The cell was controlled by a conventional programmable potentiostat. Photocurrent spectra were obtained by using a setup equipped with a high-intensity grating monochromator, a 1 kW xenon lamp and a slowly rotating light

• chopper (0.3 Hz). Spectral dependencies of the photocurrent were corrected for the spectral intensity distribution of the monochromator output. UV–vis absorption spectra of the films deposited onto quartz substrates were recorded on a Shimadzu UV-2550 spectrophotometer. Raman spectra were taken at room

Photoresponse from single upright-standing ZnO nanorods explored by photoconductive AFM

• Igor Beinik,
• Markus Kratzer,
• Astrid Wachauer,
• Lin Wang,
• Yuri P. Piryatinski,
• Gerhard Brauer,
• Xin Yi Chen,
• Yuk Fan Hsu,
• Aleksandra B. Djurišić and
• Christian Teichert

Beilstein J. Nanotechnol. 2013, 4, 208–217, doi:10.3762/bjnano.4.21

• properties. Here, photoconductive atomic force microscopy (PC-AFM) has been applied to investigate transient photoconductivity and photocurrent spectra of upright-standing ZnO nanorods (NRs). With a view to evaluate the electronic properties of the NRs and to get information on recombination kinetics, we

• have also performed time-resolved photoluminescence measurements macroscopically. Results: Persistent photoconductivity from single ZnO NRs was observed for about 1800 s and was studied with the help of photocurrent spectroscopy, which was recorded locally. The photocurrent spectra recorded from single

• ZnO NRs revealed that the minimum photon energy sufficient for photocurrent excitation is 3.1 eV. This value is at least 100 meV lower than the band-gap energy determined from the photoluminescence experiments. Conclusion: The obtained results suggest that the photoresponse in ZnO NRs under ambient

Functionalization of vertically aligned carbon nanotubes

• Eloise Van Hooijdonk,
• Carla Bittencourt,
• Rony Snyders and
• Jean-François Colomer

Beilstein J. Nanotechnol. 2013, 4, 129–152, doi:10.3762/bjnano.4.14

• et al. [120] carried electrophoretic coating of VA-CNTs with TiO2 NPs in order to create coaxial nanowires. In parallel, they synthesized aligned TiO2 nanotubes and nanomembranes, using the VA-CNT film as a template. All these products have novel photocurrent and photoinduced properties. More

Reduced electron recombination of dye-sensitized solar cells based on TiO₂ spheres consisting of ultrathin nanosheets with [001] facet exposed

• Hongxia Wang,
• Meinan Liu,
• Cheng Yan and
• John Bell

Beilstein J. Nanotechnol. 2012, 3, 378–387, doi:10.3762/bjnano.3.44

• ), respectively. Transmission electron microscopy (TEM, Philips CM 200) was used to monitor the detailed structure of the TiO2 powder. The thickness of the TiO2 films for the DSCs was determined by a profilometer (Dektak 150). The photocurrent density–voltage (J–V) characteristics of the DSCs were obtained by

• -transfer and charge-transport process in DSCs can be measured by small-perturbation-based transient methods, such as electrochemical impedance spectroscopy (EIS) or intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) [13][15]. Compared to IMPS and

Structural, electronic and photovoltaic characterization of multiwalled carbon nanotubes grown directly on stainless steel

• Luca Camilli,
• Manuela Scarselli,
• Silvano Del Gobbo,
• Paola Castrucci,
• Eric Gautron and
• Maurizio De Crescenzi

Beilstein J. Nanotechnol. 2012, 3, 360–367, doi:10.3762/bjnano.3.42

• highly oriented pyrolytic graphite (HOPG). Notably, a broadening of the π-plasmon peak in the case of MWCNTs is evident. In addition, a photocurrent was measured when MWCNTs were airbrushed onto a silicon substrate. External quantum efficiency (EQE) and photocurrent values were reported both in planar

• and in top-down geometry of the device. Marked differences in the line shapes and intensities were found for the two configurations, suggesting that two different mechanisms of photocurrent generation and charge collection are in operation. From this comparison, we are able to conclude that the

• geometry gives a photocurrent intensity and an external quantum efficiency (EQE) value much higher than those measured in the in-plane configuration. Results and Discussion In Figure 1 the chemical vapour deposition chamber used to grow the CNTs is displayed. The stainless-steel substrate is mounted on a

Ultraviolet photodetection of flexible ZnO nanowire sheets in polydimethylsiloxane polymer

• Jinzhang Liu,
• Nunzio Motta and
• Soonil Lee

Beilstein J. Nanotechnol. 2012, 3, 353–359, doi:10.3762/bjnano.3.41

• device with Ag electrodes. Previously, we studied the UV photoconduction of ZnO nanowire films with different PL properties, i.e., defect contents. The UV photocurrent of those ZnO nanowire films (2 mm wide and 10 mm long) with vacuum deposited Ag electrodes was in the range of 13–90 μA at 8 V when

• measured in air [10]. In this work, the UV photocurrent of the device with Ag paste electrodes, embedded in PDMS, exceeds 400 μA at 8 V. Even at a reverse bias of −8 V, the current is 160 μA, much higher than that of the device without PDMS. In the dark, the current values of the device in PDMS are 110 nA

• nanowire film can be enhanced by PDMS coating. The responsivity of the device, defined as the photocurrent per unit of incident optical power, is determined by the UV photoconductivity of the ZnO nanowires. From the I–V curves we can deduce that the PDMS coating over ZnO nanowires results in an

Junction formation of Cu₃BiS₃ investigated by Kelvin probe force microscopy and surface photovoltage measurements

• Fredy Mesa,
• William Chamorro,
• William Vallejo,
• Robert Baier,
• Thomas Dittrich,
• Alexander Grimm,
• Martha C. Lux-Steiner and
• Sascha Sadewasser

Beilstein J. Nanotechnol. 2012, 3, 277–284, doi:10.3762/bjnano.3.31

• frequency. For the Cu3BiS3 sample signatures of the three relatively broad, deep defect levels were observed at all frequencies. We remark that dips in the amplitude spectra could appear, for example, when the sign of SPV signals changed. For better interpretation a correlation of SPV with photocurrent