anti-reflection.pdf

Antireflection properties of graphene layers on planar and textured silicon surfaces

This article has been downloaded from IOPscience. Please scroll down to see the full text article.

2013 Nanotechnology 24 165402

(http://iopscience.iop.org/0957-4484/24/16/165402)

Download details:IP Address: 180.149.52.43The article was downloaded on 28/03/2013 at 05:15

Please note that terms and conditions apply.

View the table of contents for this issue, or go to the journal homepage for more

Home Search Collections Journals About Contact us My IOPscience

IOP PUBLISHING NANOTECHNOLOGY

Nanotechnology 24 (2013) 165402 (8pp) doi:10.1088/0957-4484/24/16/165402

Antireflection properties of graphenelayers on planar and textured siliconsurfacesRakesh Kumar1, A K Sharma1, Mehar Bhatnagar1, B R Mehta1 andShyama Rath2

1 Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, Hauz Khas,New Delhi 110016, India2 Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India

E-mail: [email protected]

Received 29 December 2012, in final form 20 February 2013Published 27 March 2013Online at stacks.iop.org/Nano/24/165402

AbstractIn this study, theoretical and experimental investigations have been carried out to explore thesuitability of graphene layers as an antireflection coating. Microwave plasma enhancedchemical vapor deposition and chemically grown graphene layers deposited on polished andtextured silicon surfaces show that graphene deposition results in a large decrease inreflectance in the wavelength range of 300650 nm, especially in the case of polished silicon.A Si3N4/textured silicon reference antireflection coating and graphene deposited polished andtextured silicon exhibit similar reflectance values, with the graphene/Si surface showing lowerreflectance in the 300400 nm range. Comparison of experimental results with the finitedifference time domain calculations shows that the graphene along with a SiO2 surface layerresults in a decrease in reflectance in the 300650 nm range, with a reflectance value of

Nanotechnology 24 (2013) 165402 R Kumar et al

reviews have highlighted that graphene is likely to benefitphotovoltaics devices as a near transparent electrode andantireflection coating [1217]. This study is a first attemptto examine the suitability of few-layer graphene as anantireflection coating on polished and textured silicon, whichare commonly used in solar cell structures.

An antireflection coating (ARC) is an integral part ofoptoelectronic device fabrication technology. For a fixedwavelength, the phase relationship condition requires theoptical thickness of the layer (the refractive index multipliedby the physical thickness) to be equal to a quarter thewavelength of the incoming wave and the refractive indexto be the geometric mean of the refractive index of thesemiconductor and air. For photovoltaic applications, thereflectance is minimized for a wavelength of 0.6 m whichis close to the maximum power point of the solar spectrum.By increasing the number of layers of different refractiveindex and thickness, the reflectance can be decreased overa wider spectral range. In silicon solar cell technology,texturing of the silicon surface using chemical etchants andsubsequent coating of silicon nitride (Si3N4) is commonlyused to reduce the reflection losses from 4058% for polishedSi to 515% [18]. The monolayer character of a graphenelayer makes it an ideal surface layer which can adhere wellto a planar, textured or corrugated surface.

We report the antireflection properties of graphene filmson polished surface (PS) and chemically textured surface(TS) commonly used in Si solar cell technology. Graphenelayers formed by microwave plasma enhanced chemical vapordeposition (MPCVD) and chemical methods (chemicallyprepared graphene, RGO) are dispersed on silicon surfacesand reflectance was measured in the wavelength range300650 nm. The experimental results are compared withthose for a standard Si3N4 ARC used in silicon solar celltechnology. The optical properties of graphene layers havingdifferent configurations on silicon surfaces were studied usingthe finite difference time domain (FDTD) simulation [19]. Themeasured reflectance for both types of graphene depositedsubstrates was compared with simulated results.

2. Experimental details

Two types of graphene layers (i) prepared using the MPCVDtechnique (designated as G1) and (ii) prepared using achemical route (RGO) procured from ACS Materials USA(designated as G2) were used in this study.

The graphene films were grown on 25 m thick Cu foil(99.98%, Sigma Aldrich, item no. 349208) using the MPCVDtechnique with CH4, H2 and Ar as the precursor forminggases. Before deposition, Cu foil was cleaned in acetic acidfollowed by de-ionized water and isopropyl alcohol to removethe copper oxide present at the surface. Keeping the copperfoil substrate at a temperature of about 750 C, a plasma wascreated by using H2 (400 sccm) and Ar (30 sccm) at a gaspressure of 30 Torr with a microwave (2.45 GHz) power of1.5 kW. After annealing the Cu foil for about 20 min, CH4(10 sccm) was introduced and a graphene layer was depositedfor 5 min. The substrate was allowed to cool down naturally.

Flow of all the gases was stopped as the temperature reachedclose to room temperature.

To study the deposition and optical properties of graphenedeposition of Si, the graphene from the Cu foil was transferredonto a Si substrate. The transfer process involved severalsteps [20]. In the first step, polymethylmethacrylate (PMMA)(Sigma Aldrich, average MW 996 000, item no. 182265,6 wt% in anisole) was spin coated on one side of the Cufoil. The other side of the Cu foil was exposed to O2 plasmato remove graphene from that side since graphene growth isknown to take place on both sides of Cu foil. In a secondstep, Cu foil was etched out using FeCl3 (10%, wt/vol.) for34 h and subsequently PMMA/graphene film was cleanedseveral times in a bath of de-ionized water and carefullytransferred to a quartz and silicon substrate. Thereafter, thesample was allowed to dry for 12 h and then PMMA wasremoved using acetone for 5 h at a temperature of 50 C. Thesample was further treated for 5 h in a H2 (200 sccm) and Ar(30 sccm) environment at a temperature of 450 C to removethe remaining traces of PMMA [20, 21].

Chemically prepared graphene films (containing 92%carbon,


Figure 1. The Raman spectra, AFM micrograph and section profile are shown in (a), (b) and (c) for G1; and (d), (e) and (f) for G2,respectively.

3. Result and discussion

3.1. Elemental and morphological characterization ofgraphene films

Figure 1(a) shows the Raman spectra of graphene depositedon Cu foil using the MPCVD method. As is well known,the three most prominent features of graphene, correspondingto the D peak at 1350 cm1, the G peak at 1580 cm1and the 2D peak at 2680 cm1, are observed [23]. TheD peak is a defect-induced Raman feature observed due todisorder or defects at the edge of the graphene. The G peakis known to be an indication of the sp2 carbon networks inthe sample. In our sample, the intensity of the D peak is quitesmall which indicates defect-free growth of the graphene film.The 2D peak originates from a second-order Raman processand can be used to determine the thickness of graphene. Theintensity ratio (I2D/IG) higher than 1.9 indicates the formationof single-layer graphene in the presented sample [24]. Thethickness of graphene was further confirmed by using sectionprofile analysis of the AFM image. Figure 1(b) shows theAFM image of the graphene layer on the Si substrate. Somewrinkles may be seen in the graphene film. The thicknessof the graphene film calculated from the section profileanalysis, as shown in figure 1(c), has been observed to be0.352 nm, which indicates the presence of a single layer ofgrapheme [25]. This is in good agreement with the resultsobtained from the intensity ratio of the 2D peak to the G peakin Raman spectra.

Figure 1(d) shows the Raman spectra of chemicallyprepared graphene (RGO). The dominance of the D peak inthe Raman spectra indicates the presence of disorder in theRGO film. This may be due to the presence of folding as well

as the residual oxygen and point defects in the RGO film.Figures 1(e) and (f) show the AFM and section profile imagesof RGO film, respectively. Some wrinkles and folding in theRGO film could be clearly seen. The thickness of the RGOfilm calculated from the section profile analysis, as shownin figure 1(f), has been observed to be 1.21 nm. At somepoints, the thickness seems to be higher due to the presenceof the folding and wrinkles in the RGO film. The presenceof functional groups, structural defects and adsorbed watermolecules is known to result in a greater thickness of the RGOmonolayer compared to monolayer graphene prepared by theMPCVD method [2527].

Figure 2 shows a FESEM micrograph of graphene layersdeposited on silicon surfaces of polished samples G1PS(figure 2(a)) and G2PS (figure 2(c)) and textured samplesG1TS (figure 2(b)) and G2TS (figure 2(d)). In sampleG1PS, graphene with some wrinkles is observed to followmost of the specimen surface. In sample G1TS, grapheneappears to be well settled on the pyramids. In sample G2PS,graphene layers are non-uniformly deposited and seem to beagglomerated in comparison to sample G1PS. In sampleG2TS, graphene seems to be unattached to the pyramids at anumber of points.

3.2. Optical characterization of graphene films

Figure 3(a) illustrates the transmittance spectra of graphenefilm G1 on quartz glass (sample G1Q), showing 8897%transmittance in the 300650 nm wavelength range. This isconsidered to fulfil the provision of a transparent coatingin solar cell and other optoelectronic devices [28]. Thereflectance spectra show that the graphene overlayer on thepolished Si surface on sample G1PS results in a drastic

3


Figure 2. FESEM micrograph of MPCVD prepared graphene film G1 transferred on (a) polished Si (G1PS) and (b) textured Si (G1TS)substrate and chemically prepared graphene film G2 spin coated on (c) polished Si (G2PS) and (d) textured Si (G2TS) substrate,respectively.

reduction in the reflectance value from 8843% to 1711% inthe 300650 nm wavelength range. In the case of the graphenelayer on a textured Si surface in sample G1TS, a reductionin reflectance from 1915% to 814% in the 300650 nmwavelength range is observed. It may be noted that althoughthe reflectance of sample G1TS is 8% lower than that ofsample G1PS (17%), reduction in the reflectance value ongraphene deposition is more in G1PS than in G1TS, withrespect to the PS and TS samples without a graphene layer.

Figure 3(b) shows the transmittance spectra of graphenefilm G2 on quartz glass (sample G2Q) and shows 8292%transmittance in the 300650 nm wavelength range. Thetransmittance value of sample G2Q is lower than that ofsample G1Q. This may be due to the difference in thequality and thickness of the RGO monolayer from that ofthe graphene layer prepared by MPCVD [25]. Graphenedeposition on the polished Si surface sample G2PS reducesthe reflectance value from 8843% to 7735%, higher thanthat obtained for sample G1PS in the 300650 nm range. Thereason for such a difference in the reflectance values may beattributed to the different morphology of graphene depositedon samples G1PS and G2PS, particularly noticeable infigures 2(a) and (c) respectively. This observation indicatesthe decisive role of graphene deposition morphology, andthereby of the deposition scheme, to exploit the antireflectioncharacteristics of graphene. In the case of graphene depositionon the textured Si surface sample G2TS the percentage

reflectance decreases from 1915% to 157% almost the sameas that obtained for sample G1TS in the 300650 nm range.

Figure 3(c) illustrates a comparison of the reflectancespectra of MPCVD prepared graphene on a textured Sisubstrate (sample G1TS) and chemically prepared grapheneon a textured Si substrate (sample G2TS) with the referenceantireflection coating of silicon nitride (Si3N4) on a texturedSi substrate (sample SNTS) in the 300650 nm wavelengthrange. It is important to note that the reflectance spectrumof sample SNTS is about 309% in the 300650 nmwavelength range with a peak value of 35% at 330 nm. Thegraphene overlayer on textured Si in sample G1TS showsreflectance values of 813% in the 300430 nm range, wellbelow the reflectance values of SNTS substrate in samerange. In the wavelength range 440650 nm, the reflectancevalue of 14% for the G1TS sample is 4% more than thereflectance values of the SNTS sample. In sample G2TS,the reflectance values of 147% are better than the reflectancevalues for SNTS in the 300650 nm wavelength range.

In summary: (i) G1TS and G2TS respond withvery similar reflectance values


Figure 3. (a) Measured transmittance and reflectance as a function of wavelength of a MPCVD prepared graphene layer (G1) deposited onquartz glass (G1Q) and polished Si (G1PS) textured Si substrate (G1TS), respectively. (b) Measured transmittance and reflectance as afunction of wavelength of a chemically prepared graphene layer (G2) deposited on quartz glass (G2Q) and polished Si (G2PS) textured Sisubstrate (G2TS), respectively. (c) Measured reflectance as a function of wavelength of reference silicon nitride ARC on textured Si(SNTS) MPCVD prepared graphene layer (G1) and chemically prepared graphene layer (G2) deposited on textured Si substrate.

photo-detectors and other UV sensitive photo-electronicdevices [29].

3.3. Reflectance spectra of different model configurationsusing FDTD simulation

The effect of graphene deposition on the reflectance ofpolished and textured Si surfaces was also evaluated usingFDTD simulation via the Lumerical package [19]. A planelight wave was launched normally to the substrate. Perfectlymatched layer (PML) conduction was used for the boundaryof the simulation window, which absorbs the energy withoutinducing any reflection. An override mesh of 0.5 nm was usedto resolve the graphene film. In this simulation, graphene ofthickness 1 nm with optical constants taken from [30, 31]was used in the simulation models. The simulation modelsare as follows: I, polished Si (PS); II, polished Si with twographene layers (PS + G + G); III, polished Si with SiO2(PS + SO); IV, polished Si with SiO2 layer and two graphenelayers (PS + SO + G + G); V, textured Si (TS); VI, texturedSi with two graphene layers (TS + G + G); VII, textured Siwith SiO2 (TS + SO); VIII, textured Si with SiO2 layer andtwo graphene layers (TS + SO + G + G). In this simulation,

graphene is assumed to be a normal bulk material with thethickness of each layer being 1 nm, the thickness of SiO240 nm and the pyramid height of the textured Si surface1 m. As already mentioned in the experimental section, thenative oxide on Si samples (PS and TS) was not etched out.Therefore, the 40 nm thickness of SiO2 assumed in the FDTDsimulation corresponds to the native oxide.

Figure 4(a) shows the reflectance spectra of modelconfiguration (IIV) in the case of a polished Si (PS) surfacein the 300650 nm wavelength range. The reflectance of a barepolished Si substrate without graphene or SiO2 overlayersis calculated as 6034%. On assuming two graphene layerson polished Si the reflectance drops to 4732% in the300650 nm wavelength range. The presence of a SiO2overlayer on polished Si significantly affects the reflectancevalue. With a 40 nm thick SiO2 layer the reflectance valuereduced to 3828% on polished silicon. Subsequently, anaddition of two graphene layers of thickness 1 nm eachreflectance was found to reduce 2024% in the 300650 nmwavelength range.

Figure 4(b) shows the reflectance spectra of modelconfigurations (VVIII) in the case of a textured Si (TS)surface in the 300650 nm wavelength range. Reflectance of a

5


Figure 4. Calculated reflectance as a function of wavelength ofdifferent model configurations: (a) I, polished Si (PS); II, polishedSi with two graphene layers of thickness 1 nm each (PS + G + G);III, polished Si with 40 nm thick SiO2 (PS + SO); IV, polished Siwith 40 nm thick SiO2 and then two graphene layers of thickness1 nm each (PS + SO + G + G); (b) V, textured Si (TS), textured Siwith two graphene layer of 1 nm thickness each (TS + G + G); VI,textured Si with 40 nm thick SiO2 (TS + SO); and VII, textured Siwith 40 nm thick SiO2 and then two graphene layer of thickness1 nm each (TS + SO + G + G).

bare textured Si substrate without graphene or SiO2 overlayersis 3712%. The difference in the reflectance value fromthe experimentally measured 1915% in the 300650 nmwavelength range may be due to difference between pyramidsheight of the experimental textured Si substrate and thetheoretically assumed values. On assuming two graphenelayers on a textured Si surface, no significant change wasobserved in reflectance values. With a SiO2 overlayer ona textured Si surface the reflectance attains 108% in the300650 nm wavelength range. Subsequent addition of twographene layers of thickness 1 nm causes the reflectance todrop to 36% in the 300650 nm wavelength range.

3.4. Electric field intensity distribution of different modelconfigurations using FDTD simulation

In order to see the light trapping effect via the electricfield intensity distribution inside and around the Si materialfor different model configurations of polished Si andtextured Si surfaces at wavelengths of 300 and 600 nm,

two-dimensional FDTD simulation [19] was carried out. Themodel configurations assumed for this are: (i) textured Siwith silicon nitride (TS + SN) as reference antireflectionmodel configuration; (ii) polished Si with SiO2 and then twographene layers (PS+ SO+ G+ G) and (iii) textured Si withSiO2 and then two graphene layers (TS+ SO + G+G). Thesemodel configurations will be referred as M1, M2 and M3,respectively. Here again we assume graphene to be a normalbulk material with the thickness of each layer being 1 nm, thethickness of silicon nitride is 80 nm, the thickness of SiO2 is40 nm and the pyramid height of textured Si surface is 1 m.

From figures 5(a)(c), at 300 nm, the electric fieldintensity distribution for the reference antireflection modelconfiguration M1 shows that the light in not well trappedinside the Si pyramidal structure and the magnitude ofintensity is lower outside Si for model configurations M2and M3. This observation states that the reflectance is lessfor model configurations M2 and M3 in comparison withM1. This is consistent with the experimental results oflower reflectance for sample G1PS and G1TS shown infigure 3(a). At 600 nm, the electric field intensity distributionof the reference antireflection model configuration M1 showsweak intensity outside the Si pyramidal structure, alsofollowed by model configurations M2 and M3, consistentwith its antireflection properties at this wavelength valueshown in figure 3(c). The electric field intensity distributionshown in figure 5(c) implies that the model configuration M3has lower reflectance than the reference antireflection modelconfiguration M1 at 300 nm and almost the same reflectanceat 600 nm.

The comparison of experimental and simulated resultsshows that the presence of SiO2 and a graphene layer, onboth PS and TS substrates, results in a significant reductionin reflectance values throughout the UVvisible spectralrange. Both PS and TS substrates used in the experimentalinvestigation are expected to have 2040 nm of SiO2. Theassumption of a 1 nm thick graphene layer in the calculationwas done keeping in mind the two to three monolayergraphene, especially in case of the chemically preparedsample G2. It is important to note that without the presenceof SiO2 layer, inclusion of two to three graphene layers in themodel configuration did not result in a significant reduction inreflectance. It is worth noting that graphene transferred ontosilicon substrates has some wrinkles and defects. Especiallyin the case of textured Si (as shown in figures 2(b) and (d)),poor adhesion seems to have resulted in locally suspended andloosely adherent graphene. This can significantly affect thetransmittance value.

It is clear that a SiO2 overlayer is essential to realize theantireflection properties of graphene. Similar inferences havebeen drawn in a study on the identification of graphene by thetotal color difference method, which shows that a 72 nm thickAl2O3 film is most suited for this purpose [32]. NormallySiO2 or Si3N4 films are used for graphene identification [33].These results indicate that the dielectric thickness and numberof graphene layers can be the control parameters to reduce thereflectance of the silicon substrate in a particular wavelengthrange. Near field enhancement of plasmonic nanostructures

6


Figure 5. FDTD simulated electric field intensity distribution for different model configurations: (a) M1, silicon nitride referenceantireflection coating on textured Si (TS + SN); (b) M2, polished Si with SiO2 and then two graphene layers (PS + SO + G + G); and(c) M3, textured Si with SiO2 and then two graphene layers (TS + SO + G + G). The vertical scale Y (m) is the silicon to source stackheight and the horizontal scale X (m) is material width.

has been used to explain the spectral selectivity of graphenelayers [34]. A combination of high Fermi velocity in grapheneand the presence of high electric field at the graphenesiliconinterface has been proposed to explain the high quantumefficiency of graphene-layer-based photovoltaic cells [35]. Anincreased degree of field enhancement and interaction strengthhas been proposed in graphene layers having 2D, 1D and 0Dconfinement [36]. In addition to refractive index matching,the above effects may also influence the reflectance and theantireflection properties of graphene layers deposited on asilicon surface. The inert nature of the graphene layer maybe an additional advantage in antireflection applications. Itmay be interesting to explore the passivation properties ofgraphene on silicon surfaces.

4. Conclusion

We have studied the optical reflectance of few-layer MPCVDand chemically grown graphene deposited on polished andtextured silicon surfaces and compared these results withthe Si3N4/textured silicon reference ARC. The results of thepresent study show that the graphene overlayers result ina large decrease in reflectance in the wavelength range of

300650 nm, with an enormous decrease in case of polishedsilicon. Si3N4 reference antireflection coating and graphenedeposited polished and textured silicon is observed to havesimilar reflectance values in the 450650 nm range. In the300400 nm range, graphene/Si surfaces show significantlylower reflectance values (810% in comparison to about 30%in the case of Si3N4). The FDTD calculations show thatthe presence of a SiO2 intermediate layer is an importantrequirement for the observed decrease in reflectance in the300650 nm range. It is conjectured that thickness of SiO2and the number of graphene layers can be varied to achievelow reflectance in a desired wavelength range. Depositionof graphene onto large areas seems to be important forexploiting its antireflection properties for photovoltaic andother optoelectronic applications.

Acknowledgments

The authors thank Ms Pratha Jhawar, Mr S Ravi and Mr SajiSalkalachen from the Semiconductor Device and PhotovoltaicDepartment, BHEL, Bangalore, for discussion related to thiswork.

7


References

[1] Du X, Skachko I, Barker A and Andrei E Y 2008 Approachingballistic transport in suspended graphene NatureNanotechnology 3 4915

[2] Pati S K, Enoki T and Rao C N R (ed) 2011 Graphene and itsFascinating Attributes (Singapore: World Scientific)

[3] Balandin A A 2011 Thermal properties of graphene andnanostructured carbon materials Nature Mater. 10 56981

[4] Wei P, Bao W, Pu Y, Lau C N and Shi J 2009 Anomalousthermoelectric transport of dirac particles in graphene Phys.Rev. Lett. 102 166808

[5] Checkelsky J G and Ong N P 2009 Thermopower and Nernsteffect in graphene in a magnetic field Phys. Rev. B80 081413

[6] Lee C, Wei X, Kysar J W and Hone J 2008 Measurement ofthe elastic properties and intrinsic strength of monolayergraphene Science 321 3858

[7] Nair R R, Blake P, Grigorenko A N, Novoselov K S,Booth T J, Stauber T, Peres N M R and Geim A K 2008Fine structure constant defines visual transparency ofgraphene Science 320 1308

[8] Lee C, Kim J Y, Bae S, Kim K S, Hong B H andChoi E J 2011 Optical response of large scale single layergraphene Appl. Phys. Lett. 98 071905

[9] Li X, Zhu H, Wang K, Cao A, Wei J, Li C, Jia Y, Li Z,Li X and Wu D 2010 Graphene-on-silicon Schottkyjunction solar cells Adv. Mater. 22 27438

[10] Miao X, Tongay S, Petterson M K, Berke K, Rinzler A G,Appleton B R and Hebard A F 2012 High efficiencygraphene solar cells by chemical doping Nano Lett.12 274550

[11] Singh B, Mehta B R, Govind, Feng X and Mullen K 2011Electronic interaction and bipolar resistive switching incopper oxidemultilayer graphene hybrid interface:graphene as an oxygen ion storage and blocking layer Appl.Phys. Lett. 99 222109

[12] Bae S et al 2010 Roll-to-roll production of 30-inch graphenefilms for transparent electrodes Nature Nanotechnology5 5748

[13] Weber C M et al 2010 Graphene-based optically transparentelectrodes for spectroelectrochemistry in the UVvis regionSmall 6 1849

[14] Wu J, Agrawal M, Becerril H A, Bao Z, Liu Z, Chen Y andPeumans P 2009 Organic light-emitting diodes onsolution-processed graphene transparent electrodes ACSNano 4 438

[15] He M, Jung J, Qiu F and Lin Z 2012 Graphene-basedtransparent flexible electrodes for polymer solar cellsJ. Mater. Chem. 22 2425464

[16] Won R 2010 Photovoltaics: graphenesilicon solar cellsNature Photon. 4 411

[17] Cooper D R et al 2012 Experimental review of graphene ISRNCondens. Matter Phys. 2012 56

[18] Singh P K, Kumar R, Lal M, Singh S N and Das B K 2001Effectiveness of anisotropic etching of silicon in aqueousalkaline solutions Sol. Energy Mater. Sol. Cells 70 10313

[19] Lumerical FDTD Solutions. www.lumerical.com[20] van der Zande A M, Barton R A, Alden J S, Ruiz-Vargas C S,

Whitney W S, Pham P H Q, Park J, Parpia J M,Craighead H G and McEuen P L 2010 Large-scale arrays ofsingle-layer graphene resonators Nano Lett. 10 486973

[21] Li X et al 2009 Large-area synthesis of high-quality anduniform graphene films on copper foils Science 324 13124

[22] Paredes J I, Villar-Rodil S, Martnez-Alonso A andTascon J M D 2008 Graphene oxide dispersions in organicsolvents Langmuir 24 105604

[23] Ferrari A C et al 2006 Raman spectrum of graphene andgraphene layers Phys. Rev. Lett. 97 187401

[24] Ferrari A C 2007 Raman spectroscopy of graphene andgraphite: disorder, electronphonon coupling, doping andnonadiabatic effects Solid State Commun. 143 4757

[25] Eda G, Fanchini G and Chhowalla M 2008 Large-areaultrathin films of reduced graphene oxide as a transparentand flexible electronic material Nature Nanotechnology3 2704

[26] McAllister M J et al 2007 Single sheet functionalizedgraphene by oxidation and thermal expansion of graphiteChem. Mater. 19 439604

[27] Stankovich S, Dikin D A, Piner R D, Kohlhaas K A,Kleinhammes A, Jia Y, Wu Y, Nguyen T S andRuoff S R 2007 Synthesis of graphene-based nanosheetsvia chemical reduction of exfoliated graphite oxide Carbon45 155865

[28] Wang S J, Geng Y, Zheng Q and Kim J-K 2010 Fabrication ofhighly conducting and transparent graphene films Carbon48 181523

[29] Chitara B, Krupanidhi S B and Rao C N R 2011 Solutionprocessed reduced graphene oxide ultraviolet detector Appl.Phys. Lett. 99 113114

[30] Weber J W, Calado V E and van de Sanden M C M 2010Optical constants of graphene measured by spectroscopicellipsometry Appl. Phys. Lett. 97 091904

[31] Bruna M and Borini S 2009 Optical constants of graphenelayers in the visible range Appl. Phys. Lett. 94 031901

[32] Gao L, Ren W, Li F and Cheng H-M 2008 Total colordifference for rapid and accurate identification of grapheneACS Nano 2 162533

[33] Jung I, Rhyee J-S, Son J Y, Ruoff R S and Rhee K-Y 2012Colors of graphene and graphene-oxide multilayers onvarious substrates Nanotechnology 23 025708

[34] Liu Y, Cheng R, Liao L, Zhou H, Bai J, Liu G, Liu L,Huang Y and Duan X 2011 Plasmon resonance enhancedmulticolour photodetection by graphene Nature Commun.2 579

[35] Grigorenko A N, Polini M and Novoselov K S 2012 Grapheneplasmonics Nature Photon. 6 74958

[36] Koppens F H L, Chang D E and Garca de Abajo F J 2011Graphene plasmonics: a platform for strong lightmatterinteractions Nano Lett. 11 33707

8

Antireflection properties of graphene layers on planar and textured silicon surfacesIntroductionExperimental detailsResult and discussionElemental and morphological characterization of graphene films Optical characterization of graphene filmsReflectance spectra of different model configurations using FDTD simulationElectric field intensity distribution of different model configurations using FDTD simulation

ConclusionAcknowledgmentsReferences

Documents

anti-reflection.pdf