Home > Article > Near Field Opto Chemical Sensors

Near Field Opto Chemical Sensors

Optical Fibre, New Developmentsincludes intelligstems that are seltoring, self-correcting and repairing, and selfOn this-field effects to enhance the overall performance of the final deviceare related to an enhancement effect of the optical near-fieldductive structures of tin dioxide(SnO2)length()e main objective is tose localizedbyns of metal oxideano sizedcrease light matter interaction and provide innovative and valuable sensing mechanismsr next generation of fiber optic chemical and biological nan2006: Buosciolo et al, 2006ue to the strongtegration techniques and transducer developmenthave bebeen simultaneously add optimizednd of the near-field optical properties in relation to suitable processing and post-processingcorrelation of the surface layer morphology and the emerging near-fieldtensity distribution with the sensing performance [Consales et al, 2006b; C006)

We found that sensitive layers with very roughperturbation of the optical near-field, exhibited surprisingly sensing perforfor bothwater chemicals monitoring and against chemical pollutants in air environment, attemperature( Cusano et al, 2006; Buosciolo et al, 2008b)ilar effects of light maniion have been observed, in recent yolocalized surface plasmons and in subwavelengtn both metal films anda recentodel (Lezec Thio, 2004)relative to the last case, the transmission of light is modulatedot bpling to surface plasmons, but by interfeof diffractedenerated by subwavelength periodic features at the surface, leading to transmissionsized structures opensfrontiers not onlyy In sensingng applicaave also vast potential to be applied in many fields ranging from high perfoanometer-scale photonic devices up to in-fiber micro systemsHere, we review the technological steps carried out by our group for the demonstration of amechanism arising from near-field effectsth size approaching the optical wavelengstructured thechapter as follows: sections 2 and 3 are focused on thproperties and characteristics of tinI transdwithparticular emphasis on the state of the art on chemicalbasedopto-chemical sensodeposit particle layersdioxide on optical fiber substrates at wavelength scale Section

describe how, by acting on the deposition paraIn particular, we will show that: the near-field collected in presence of Snoz layers with ath topographyGaussian shape of the fundamental mode propagating through the single-modesence of layers characterized by several Sn(dimensions greater than about 500 nm, the near-field profile results to be significantmodified in correspondence of them; finally, layers characterized by the presence of isolatedicrostructures, with dimensions comparable to radiation wavelength, reveal higpability of near-field enhancement combined with a strong increasingroscopyAtomic foicroscopy (SNOM)employing them in sensinglications: as we will see in the folloany damage was producedperform this kind of analysisThe invention of scanning tunneling microscopy in 1981 began a revolution in microscopywhich has led to a whole nas scanning probe microscopy (SPM), among them AFM and SNOM SPMs do not usto produce the magnified image; instead, a locabe is scanned over the surface ofpropertyth the surface this localobe is fabricated from a material appropriate for the measurement of the particulaurface property The scanning process ismechanical but withrecision and without producing any damage of the specimen

Moreover, SPM is capable ofaging all kind of specimen (including soft materials and biomolecular systems) at sub-g or coating, in a rangecopyFig 3 it is reported the AFM-SNOM system employed for the surface morphology andharacterization; in fact, it isle of simultaneous snom and normalrce AFM imaging using the same probe(Buosciolo et al, 2006)he super-resolution of SNOM is achieved via a sub-wavelength aperture placed in theMeasurements were carried out in collection modea Cr/Al-coated fiber with 200 nmilluminating the fiber under investigaith a superluminescentiode(central wavelength Ar=1310 nm, X2=1550 nm) The tip was maintained in the neaple surface using optically detected normal force feedback Thiscomplished by oscillating the tip and detecting the scattered light from a laser focusedfeedback circuitused to maintain a constant tip-sample distance while scanning thethe probe collects the lightmple exactly at the end face In thisthe fibeped into a SNOM image and an independent AFM nororded simultaneously by the feedback signal that produces a three-dimensional image of

Lock-InCCDDiode tDisplayPiezo scanner50nm)Sample FiberFig 3 Scanning probe system: simultaneous atomic force(AFM) and scanning near-fieldThetion of SNOM images is limited by the aperture size of the probe(200 nm)thhe resolunsion ofplmetallization layer), while in the z direction is only limited by external vibrationsProv: ges were obtained in air using tapping mode operation and in a regiond 40 min for images with pixel resolprocessedbyWsxmfreesoftwaredownloadableathttprticular, topographic imagesattened, off-line, using zero-or-first order polynomialfits to account for z offsets and sample tilttion on the surfacestructures of the sensitive coatings and the knowledge of the remorphology and the opticalfield collected in the closeprobes( Consales et al 2006mple, in Fig 4(a)is reported the typical bi-dimensional (2D)solution volume of 5 ml of ethanol solution of SnCl45HO withEsp ge on asus layerof001ol/l

The image refers to a(12x12)um area, approximately centered on the optical fiberre, indicated with the green circleThe most important measurement of surface roughnesmooth with a RMS roughness of about 2798 nm In addition, Fig 4(b) shows that the

Near-Field Opto-Chemicashape of the electromagnetic field collected in the close proximity of the film surface is notnfluenced by the presence of such SnO2 layer, as demonstrated by the fact that it assumesthe typical Gaussian profile of the field emerging from the cleaved end of a single modeal fib24681012(a)lected by the SNOMthe same region(12x12)Hm2(b)of the SnO particles layerd by changing tharameters of the ESP deposition process, such as the concentration and thume of theethanol solution of SnCl4 5H:O, the alignment of the optical fiber end under the needle frome precursor solution is sprayed or the substrate temperauringAs matter of the fact, Fig 5 (a) shows the 2D imageof SnCl-5H2O with a concentration of 001 mol/haas differentlyunder the syringe needt can be observed that a very different morphology and, as a consequence, optical near-fieldfile, have been obtained In this case, in fact, the sensitive layer exhibits an highly roughncrease of the RMS roughness up to 1m

By an analysis of the heights and sizef approximately 400 nm and mean lateral(x, y)dimensionpproximately 46Fig 5(b) reveals that, in thisthe optical profilefield isinfluenced by such overlay morphology Ascorrespondence of the SnO2 gth dimensions comparable with the light wavelengthregion only, the biggest grains able to produce a perturbation ofthe field hatean height of about 700 nm and a mdth of about 550 n

Optical Fibre, New DevelopmentsFig 5 Topographic image of the sample B(a) and optical near-field simultaneouslycollected by the SNOM probe in thet was demonstrated that this effect can be attributed to the high refractive index of the sneguide the light but, the lateralallow a correct light localization due to the significantlap of thefield Thisterpretationonfirmed btestigation of theparticle layer effects in the case of larger and isolated grains( Cusano et al, 200filed enhancement effect was observed for the first time by the authors inet al, 2007) in the case of SnO2 grains whose spatial dimensions approach theHere, we report theof Sn Cla-5H2O equal to1 As it is possible to note from the 2Ded microstructure has approximately the shape of an halfand z a 1

0 um, on a flat Sno, subsdent from Fig 6(b) that the optical near-field is strongly enhanced in correspondence ofe such grain The local intensity enhancement, calculated as the ratio between theeasured intensity and the corresponding intensity of the unperturbed fioout 18(Cusano et al, 2007)onstrate that the field enhancement is observInge, the emergent field at a constant sample-probe distance of approximately 2 um, waspletely maintain information about the filistortion of the benape is still clearly observable in Fig 7(a)tip distance, up to few times the wavelength the collected optical field profile assshape, as expected in far field imagingover, it was possible to construct a map of the radiation intensity coupled into thestandard optical fiber coated with the SnOz overlay simply by coupling the cantilevered

Near-Field Opto-Chemical Sensorsoptical probe to the superluminescent diode and the fiber sample to the In GaAs detectorIt was found that the profile of the radiation intensity coupled to the sample fiber using thethe optical fiber coating and collected in the forward configuration(Fig 6(b)) In this casintensity enhancement is about 1

5 calculated using the same procedure reportedabove in the textm2347Xun6 Topografieldcollected by the SNOM probe in the same region(9x9)um2(b)52V118v7field collected from thele c at constant sample-tip distance of about 2upled into the standardilluminated by the SNOM probe(b)ts, the authors were able to give an effecof the observed phenomenon: the radiation impinging at the base of the grain, coming fromhe layer of the same material, continues to propagate inside of it(confined by the high

Optical Fibre, New Developmentsrefractive index contrast between the oxide and the air and by the geometry of the grainthe grain surfacsince the structure dimensionsleength (anot due to truly evanescent field In fact, the reverse profile is very similar to thattained in forward configuration indicating a strong recipestructure able to convert at its ends (due to diffraction limit)all the propagating contributen the evanescent counterpartIn other words, the particular microstrforesee the possibility to develop a new concept of SnO2-transducer based on a surfacelocalized interaction of the opticalfield with chemicals, named by the authorld opto-chemicalhis frameworkdemonstrated the capability of the ded near-field opto-nsors to detect very low concentrations of toand also of ammonia moleculesparticular, a comparison between the sensing performance of SnO2-based sensnaracterized by almost flat (unable to influence the near-field) and peculiar rough surfacesbleield)will be reported to demonstrate that sensitive layers able togly enhance the opf sensitivity and responses dynamics( Cusano et al 2006; Consales et al, 2007a; B2008b)53 Effect of the processing parametersned in the section 43, ithown in literature that the concentration of theprayed solution playportant role in the film surface morphology Since the overlayerlay morphology weted by theors the obtained resultsConsales et al

2006b; Buosciolo et al, 200%a: Buosciolo et al 2008bTo this aim, two groups of samples were fabricated by using different solutionto only twothe mentioned groups is reported The full description of the two groups of samples can beIn Fig 8(a)and(c)the typical 2D height images of two SnO layers(sample Dprepared by using a solution volume of 5 ml of ethanol solution of SnCl4-5HzO with antration of o ool mFigures 8(b)and (d) demonstrate that the most pronounced modification of the typicalGaussian profile, emerging from standard single mode optical fibers, occurs indence of the sample D In fact, the structures dimensapproach the opticnm)and the structures spacing is large enough to make possible anfective light localization in the high refractive index Sno grains( Cusano et al, 2007)prepared by using a solution volume of 5 ml of ethanol solution of SnCl4-5HzO with atration of 001

2383xum(b)g 8

AFM topoimages (a),( c)and near-fieldsimultaneously collected byhe NSOM probeD and E respectively, prepared using a solutionconcentration of/l, before annealing processd a mean height of the order of 150 nm, while few othersdimensions ofhe order of 1 um ancrostructure whoseharacteristic dimensions are a 1430 nm be1900 nm and h450 npography (see Fig 9(c) presents several structures of rectangular shape whosand b vary in the following range:a∈(23÷34)mb∈(34448)umFigures 9(b)and() demonstrate that the most pronounced modification of the near-fieldThe conclusion is that increasing the metal chloridetration it is possible to obtain aore structuredce morphology able to significantly influence the optical near-field

Near-Field Opto-Chemical Sensorsreports the morphological and optical characterization of the so produced superstratesarried out by atomic force and scanning near-field opticalopy, very useful toclearly outline the effecessing parameters on particles size and distribution as wellsng performances of fiber optic chemo-sensors incorporating tin dioxide particle layersth air and liquidnts discussing the dependence of the sensing properties onwidely used as sensitive materials for electricalvironmental, security and industrial applications The idea of using semiconductors as952 when Brattain and bardeen first reportedensitive effects on germanium(Brattain &z Bardeen, 1952) Later, Seiyama et al foundet al 196The principle of operation of such class of sensors relies upon a change of electricanductivity of the semiconductor material as a consequence of the gas adsorptiond energy diffusion,Ived in the operatf the semiconductby the variation of the electronic properties of wide-band-gap semiconductorsuch as SnO2 and Zno due to the gases adsorption that modifies the intrinsic electronidefect formation (Szklarski, 1989) The gas sensitivity of semiconderain by reversible effects resulting from chemisorption of molecules, formation ofspace charge areas, and variation of the concentration of the charge carriers in theAlthough the general principle of the detection mechanism is appreciated, the size of thethe semiconductor, the nature and concentration of surface reactive centers, and the reatructure of the material: the size, structure, and degree of agglomeration of crystallites,In principle, any semiconductingbe exploitedring changesf its resistance during interaction with the detected gas molecules at an operatingture typically above 200C Because tin oxide(SnO2)offers hiently Iperating temperatures, attention has been coflammable, i

e CHa and H, and toxic i e co, H,s and Nan be referred to as the best-understood prototype of oxide based gas sensevertheless, highly specific and sensitive SnOznown that sensor selectivity can be fine-tuned over a wide range by varying the Sn(of operation, etc The electric conductivityde semiconductors is extremelnsitive to thesurface reactiving chemisorbed oxygen (O2, O2-, O-) and the gas mixturemponents, proceeding at 100-500C Rumyantsevaa et al, 2008; Barsan, et al, 1999)

Optical Fibre, New DevelopmentsMoreover, tin oxide is sensitive to both oxidizing gaschand NO,, andeducing species, such as CO and CHa(Becker, 2001) In particular, in the case of oxidizinggases the raising in conductivity upon gas-sduced by the surface reaction between the gas and thechemically active specieof tin oxide, as an example CO+ Oads+ CO2+er; while, in thereducing gases, theme the con

duction electronsoxide resistivity, as an example NO→NO+In conclusions, the advantages offered by wide-band-gaductor oxides as sensingclass of sensors materials: the relatively high operative temperature, the poor selectivity dueunspecificity of the contribution made by the gas phase molecules to the total electricresponse and the long term drift (berveglie3 State of the art on snO based sensorsgreat pf tin dioxide based gas seompleted in the years 1968-69 when he establishedarted selling theaderrs production The first TGS was ahick fillmof the to wder as sensitive element The rapid success and the grown in theproduction of the TGSs in the years following the first TGS realization is attributed not onlerformances but also to the large diffusion in that yearsgas and theent numerous accidental gas explosions (Hokura Watson, 1994)

leading to the need of security gas sensfter almost fifty vears since the first TGS realizatichnologicalents in the sensing field stronglvailablebothunity Many of them are still based on tin dioxide asThe first generation of sensors based on tin dioxide as sensitive matbythick film technology Inthick filmors, the tin dioxide is mo1981) In operation, thbstrate is heated bergized filament and the resistance of the activefreshfallsthe concentration ofcontaminant gaspend on percclular regions, by varying small details in the preparation procecharacteristics, Therefore the materials fabrication processes have beenproved towards thin film technology, that offers higher reproducibility and long termto enhance the performances and the selectivity of these sensors severalapproaches have been pursuedn approach consists in the careful choice of the working temperature of the sensor that isable to enhance the sensitivity to certain gasesparison with others( Fort et al 2002)Since the optimum oxidation temperatures are different from gas to gas, operating the

Near-Field Opto-Chemical Sensorstransducer at two different temperatures leads to the enhancement of thr selectivityA large number of additives in SnOz, such as In, Cd, BizO3 and noble metals (ie palladiumthe selectivity and to enhance the response of the tin-dioxide gas sensors (Y1983)nsitivity to other gases and to reduce temperature of operation Palladium inclusionsxample, leads to a lowering of the sensor resistance, a speeding up of transient behaarticular the optimum operating temperature for sensing CO gas On the other hand, theoping of SnO2 with trivalent additive favors the detection of oxidant gases By suitablylecting the dopant the temperature of device operation can be tailored for a specifion(Erann et al, 2004; Ivanov et al, 2004) Other additives such as gold, rhodiunium and indium have more significant effects on selectivity, as dal metalides including those of lanthanum and coppeloyed approach to enhance the sensor selectivity concerns exploiting differentechniprocessing alurse,these approachesnot limited to tin-oxide basedTsNonetheless, interesting results have beenmeasuring the transducer conductivity variations duringconcentration In factin thisthe reaction kineticsexploited to differentimong differenr Berberich et al 2000: Llobet et al 1997: Ngo et al 2006generally, the realization ofy of sensors with different features andmployment of pattern recognition techniques demonstrated to be a suitable strategy todiscriminate among different target molecules(Gardner et al, 1992; Hong et al, 2000; Lee elal

, 2001; Delpha et al, 2004)991, when yshowed that reduction of crystallite size causedhuge improvement in conductometric sensor performance In fact, in a low grainide almost all the carriers are trapped in surface states and only a few thermal activatedavailable for conduction In this configuration the transition from activated toconductance The challenge thus became to prepare stable materials with smaThishas been assisted by the recent progress in nanotechnolank to which fine control over the crystallinity, morphologevel of these sensing materials could be obtainedAn important step forward has been achiby the successful preparation of stable singlees or nanoribbons)(Pan et al, 2001; Comini et al, 2002ollowed by the publication of some fundamental demonstrations(Cui et al, 2001:Law et al 2002; Arnold et al, 2003; Li et al, 2003)of detecting a variety of chemicals andusing sedes since then thissentencinggnificant growth in the past six years and it is not yet clear whether it will reach saturationon(Comini, 2008; Chen et al, 2008)

Optical Fibre, New DevelopmentsIn particular, Snd nanobelts have been wideductometriesensors, both in normal resistor or in field effectTransitor(FET) configurations(Maffeis et al, 2002; Panchapakesa2006: Helwig et aldetection of CO, NO,, and ethanol (Comini et al, 2002) It relied on simple DC-resistiments and was made by dispersing SnOz nanobelts atop platinum interdigitatedectrodes, prefabricated on an alumina substrate In 2005, the possibility to integrate tiride nanobelts with micro-machined substrate has been proved by Yu et al (Yu et005), that reported on a single-SnO2-nanobelt sensor integrated with microheater to sensal, 2008)prophigh-performance ethanol sensor based on branched SnO/Sb-dopedhemical sensors based on metal oxide 1-D structure configured in FET devices have alsoeen extensively studied For example, Law et al (Law et al

, 2002 published a contribcrystalline tin oxideire They made use of UV light, that has proven to be effecso with thin films( Comini et al, 2001)Zhang et al(Zhang et al, 2004)also presented some experiments on SnOz single nanowirein pure nitrogen, nitrogen-oxygen and nitrogen-oxygen-COanostructure-based conductometric sensors with Pd(Kolmakov et al, 2005), Ag( Chen2006)and Au (Qian et al, 2006disadvantage of conductometric sensors is their need for atemperature, which leads to power wastage Recently, some contribution on new(and yetnot well explored)optical detection methods have also been proposed for the realization ofbased materialsnental changes, instead of the electricaltributionsbeen reported on the quenching in the visible photoluminescence(PL) ofn oxide nanostructures due to the introduction of NO,, NH, and Co in dry and humidsynthetic air and normal ambient pressure conditions(Faglia et al, 2005: Baratso, in the last few years, SnO2 was exploited as sensitive wavelength-scale particle layfor the realization of anear-field fiber optic chemicalrs aborket al 2006: buoso2008b) The electrostatic spray pyrolysis was exploited to transfer SnO2 thin films composength dimensions atop the termination of standardal sensing becauseable to significantly modify the optical near-field profilerging from the film surface As matterenhancements of the evanescenttrong sensitivity to surface effects induced asnce of analyte molecule interactio

4 Tin dioxide opto-chemicalFor the realization of the proposed near-field opto-chemical sensors, the reflectofiguration has been exploited(Pisco et al, 2006) It is essentially based ontrinsic Fabry-Perot(FP) interferometer which, as schematically represented in Figa microstructured tin dioxidefilm deposited at the distal end of a properly cut andrepared optical fibertical fibStructured sensitive layerT Refected radiationFig 1 Schematiof the reflectometric configurationIn line of principle, the key point of this configuration is the dependence of the reflectance atthe fiber/sensitive layer interface on the optical and geometric properties of the sensitivein fact, contrarily to what happen for the standard FP configurations(Pisco et al, 2006),theteraction of the field with the chemicals present within the athere occurs not in theume of the layer but mainly on its surface by means of the evanescent part of the fieldpromoting a significant improvement of the fiber optic sensor performance

The chemo-ptic variations induced by the surface-chemicals interaction lead to changes in the filmflectance and thus in the intensity of the optical signal reflected at the fiber/ film interfaceAs we will see in the section 61, this optical intensity modulation is simply detectable bsingle-wavelength reflectance42 Integration of sensing layers with standard optical fibersMany sensitive materials and transducing techniques are today available to develop optbut it's necessary to find the suitable deposition technique, depending onthe nature of the material and the transducing substrate, in order tool theorphological and geometrical features of the sensitive layer This governance is, in fact,tial to fully benefit of the materials properties and to be able to mathematicallhematine tof its performances Hence, the challenge inlis field is not jusg to the chemical tailoring of the material properties, but also thesensing platform At thetimeabrication procedure and equipment are mandatory for a fast and cost-effectivhe following, a brief introduction to the Electrostatic Spray Pyrolysis(EsP) technique andoptimization and customization for the deposition of the selectedsensitive material onto the fiber substrates are presented

Optical Fibre, New DevelopmentsMoreover, the possibility to obtain thin films at nano and micro scale and to tailor thetures by properly changing the esP deposition parameters will also be43 Electrostatic Spray Pyrolysis(ESP)deposition techniquering the last three decades, one ofchniques to deposit a wide variety of materials in thin film form(Perednis Gauckl2005) Unlike many other film deposition techniques, spray pyrolysis represents a veryosts)

It offers an extremely easy technique for preparing films of any compositiequality substratesd focals the method hasen multfilms can be easily prepared using this versatile techniqhin metal oxide and chalcogenide film deposited by spray pyrolysis and differentESPechnique in which thee electrosprayedtes from the end of a highly biased metal capillary(typically 5-25lectrolyte(usually ethanol orwater solutions of metal chlorides)larged dropletectrostatic fieldsolarized droplets separafrom each other by means of repulsive forces and they arearried by electrostatic field aledropletsa cone in the space, called Tailor's cone, The substrate coverage by droplets isthe heated substrate(the substrate temperature is usually in the range 300-450oC), chemicalreaction of metal chloride with solution water vapor, stimulated by the temperature, takesfilm(Matsui et al, 2003hereby, metal oxide layer grows due to the thermal transformation of metal chnsequence of the interaction with water vapoIt's evident from this brief description that ESP involves many processes occurring eithermultaneously or sequentially The most important of theseansport, solvent evaporation, droplet impact with consecutive spreading, and precursortion thtionlved in all mentionedthe substrate surfacturalerties like crystallined surfFor instance, for SnOz samples deposited at higher temperatures, low resistivity and higherroughness were observed, whereas for films deposited at temperatures less than 340C highesistivity, lower crystalline size and less ratio of polycrystalline phase were found(Patil ete recent work of ghimbeu et alreport on theinfluences of deposition temperatthe surface morphology of Std Cu-dopedO, thin films, Dense filmsmooth surface characterized by several cracksdeposited at low temperature such as 150C; denser films comprised of large particle ofbout 1 um, whiches of small particles, were obtained at 250C; while films

Near-Field Opto-Chemicarepared at 350 and 400 C showed a porous structure and a surface roughness that increaseincreasing temperaturehe precursor solution is the second important process variable Solvent, type of saltnfluence the physical and chemicalperties of the precursor solution Therefore, structure and properties of a deposited filmForSntd SnO z-MnzO3 fild using the espchnique and employed in Taguchi type hydrogenal, 1999) The grain size of the porous films ranged from 1 to 10 um It was observemethin SnOz films for gas sensors were also prepared by spray pyrolysisInorganic asr solution (pink et al 1980) Smooth but not very uniform filmere obtained using a solution of(NH4)2 Sn Cls in water On the other hand, very uniformbut relatively rough films were deposited using a solution of(CH3 COO) SnClz ind for films obtained from the organiclution The sensitivity and rise time were found to depend on the deposition temperatured the type of prsolution used The best results were achieved by sprayrganic prsolution onto a substrate at about 300%che first attempts to prepare SnO2 layers using the ESP were carried out by Gourari et al(Zaouk et al

, 2000) Although conductive substratnventionally used in ESP, Zaouk et al(Zaouk et al, 2000) revealed the availabilityESP for the insulator substrate They investigated the electrical and optical properties of theped SnO2 lay7059 substrates44 Customization and optimization of EsP deposition techniqThe esp technie distal end of standard silica optical fibers(SOFs) by the authors in the 2005(Pisco etd For the SnO particle layers deposition, single mode optical fibers were prepared byting a few centimeters from the fiber-end The bare fiber werewashed in chloroform in order to remove any coating residuals, Then the fiber-end wereroperly cut, by using a precision cleaver, in order to obtain a planar cross-section, wheredeposited A schematic view of the experimental set-up used for thefabrication is shown in Figrce(fuG 0-30kv) twoonnectedflexiblmmeectric field between thenecessaryconstituted by two stainless steel plates of a few sqtimeters and by a nichrome wirconnected with a 300w voltThe heater was supplied with a chromium-nickeermocouple connected with a multimeter for the temperature monitoring The distancebetween the needle and the optical fiber-end was about 30

Optical Fibre, New DevelopmentsSprayedMutichematic view of the experimental set-up used for the deposition of the sensitivelayer onto the optical fiberregulated by means of an air pump connected with the first syringe Tin dioxide films ansition was performed at a constant temperature of 320*5C Liquid flow has beeThe SnO, layperformed by means of a constant volume, 5 ml, ofhanol solution of SnCl 5H-O at two different concentrations: 001 and 0

001 mol/lDuring the deposition, it is also possible the formation of amorphous Sno phase Thermeatment is one of the ways to transform SnO, to SnOz and clean the films surface from thether dopants like water or alcohol present in the initial solution( Ramamoorthy et al, 2003)after the deposition procedure, the prepared samples were annealed afeased from room temperaturnstant rate of 5C/min and, after the annealing procedure, the temperature was decreasedtemperature5 Characterization of the surface morphology and of the transmitted opticalas described in thesection 41, the principle of operation of the proposed sensorsthe reflected power at the fiberlay leads to changes in its complex dielectric funddmdsothis reason a strong effort was devoted to investigate the properties of the deposited SneIms in terms of the surfaceIn the presentn, we first introduce something about the above mentionedharacterization technique and the employed experimental apparatus; then we report on thenfluence of surface features on the transmitted optical field in near proximity of the