Fabrication and Characterization of Aluminum Nitride Nanoparticles by RF Magnetron Sputtering and Inert Gas Condensation Technique

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Article Fabrication and Characterization of Aluminum Nitride Nanoparticles by RF Magnetron Sputtering and Inert Gas Condensation Technique

Ishaq Musa 1,* , Naser Qamhieh 2,* , Khadija Said 2, Saleh T. Mahmoud 2 and Hussain Alawadhi 3 1 Department of Physics, Palestine Technical University-Kadoorie, P. O. Box 7, Tulkarem 300, Palestine 2 Department of Physics, UAE University, Al-Ain 15551, UAE; [email protected] (K.S.); [email protected] (S.T.M.) 3 Center for Advanced Materials Research, University of Sharjah, Sharjah 27272, UAE; [email protected] * Correspondence: [email protected] (I.M.); [email protected] (N.Q.)

Received: 3 March 2020; Accepted: 30 March 2020; Published: 21 April 2020

Abstract: Aluminum nitride nanoparticles (AlN-NPs) were fabricated by a RF magnetron sputtering and inert gas condensation technique. By keeping the source parameters and sputtering time of 4 h ﬁxed, it was possible to produce AlN-NPs with a size in the range of 2–3 nm. Atomic force microscopy (AFM), Raman spectroscopy, X-ray diﬀraction (XRD), and UV-visible absorption were used to characterize the obtained AlN-NPs. AFM topography images showed quazi-sphere nanoparticles with a size ranging from 2 to 3 nm. The XRD measurements confirmed the hexagonal wurtzite structure of AlN nanoparticles. Furthermore, the optical band gap was determined by the UV-visible absorption spectroscopy. The Raman spectroscopy results showed vibration transverse-optical modes A1(TO), E1(TO), as well as longitudinal-optical modes E1(LO), A1(LO).

Keywords: AlN nanoparticles; RF magnetron sputtering; atomic force microscopy; Raman spectroscopy; UV-visible absorption

1. Introduction Aluminum nitride (AlN) is a large and direct band-gap semiconductor material (Eg = 6.2 eV). It has a hexagonal wurtzite structure similar to zinc oxide (ZnO) and lattice constants of a = 0.311 nm and c = 0.498 nm. It is characterized by high thermal conductivity and chemical stability, a high melting point, low coefficient of thermal expansion, high electrical resistivity,low dielectric loss, high mechanical stiffness, and high acoustic wave velocity [1–3]. Hence, it has attracted considerable attention of researchers due to its unique property applications in surface acoustic wave (SAW) devices, sensors, thin-film resonators, metal-oxide-semiconductors (MOS) [4], and microelectronic devices [5]. Other versatile applications are used in optoelectronic devices, for example, deep-ultraviolet light-emitting diodes and laser diodes [6], which can be used for a living environment [7]. Many regions of the world are suffering from the pollution of water; therefore, it is necessary to use sterilization systems to clean the water. According to the World Health Organization (WHO), every hour more than 100 children die from water-borne bacteria [8]. Currently, deep ultraviolet light sources such as mercury lamps or excimer lasers are capable of killing these bacteria. Nonetheless, these UV-light sources are not reliable due to their large size, low efficiency, and their toxic substances that cause serious environmental problems [9]. Among wide bandgap semiconductor materials, such as GaN, AlN, and AlGaN, only aluminum nitride-based UV-light-emitting diodes (LEDs) have potential applications for killing water-borne bacteria. In the past decade, various techniques were employed to produce aluminum nitride (AlN)

Coatings 2020, 10, 411; doi:10.3390/coatings10040411 www.mdpi.com/journal/coatings Coatings 2020, 10, x FOR PEER REVIEW 2 of 8 Coatings 2020, 10, 411 2 of 8 laser deposition [13], molecular beam epitaxy [14], and the common deposition process DC reactive thinmagnetron films and sputtering nanostructures [15]. [10–12], such as pulsed laser deposition [13], molecular beam epitaxy [14], and theNanomaterials common deposition offer different process advantages, DC reactive such magnetron as flexible sputtering space [for15]. simplicity reconstruction, enhancedNanomaterials mechanical off stability,er different large advantages, surface area, such and as flexiblesuitable spacecoating, for which simplicity may reconstruction,lead to unique enhancedapplications mechanical in different stability, nanoelectronic-scale large surface area,devices and [16]. suitable The selection coating, whichin fabrication may lead techniques to unique of applicationsnanostructures in diprovidesfferent nanoelectronic-scale the freedom to modify devices the [16physical]. The selectionproperties in of fabrication materials. techniques Synthesis ofof nanostructuresnanoparticles by provides magnetron the freedomsputtering to modifyand inert-gas the physical condensation properties may of open materials. the door Synthesis for basic of nanoparticlesresearch to study by magnetronthese properties sputtering such as and in inert-gashybrid structures condensation composites may openby depositing the door or for coating basic researchAlN nanoparticles to study these on propertiesmulti-wall such carbon as in nanotubes hybrid structures (MWCNTs). composites The transfer by depositing of the or energetic coating AlNelectrons nanoparticles excited by on surface multi-wall plasmon carbon from nanotubes metal (M (MWCNTs).WCNTs) to The the transfer conduction of the band energetic of the electrons emitting excitedmaterial by is surface expected plasmon to enhance from metalthe UV (MWCNTs) emission. toPrevious the conduction studies, bandsuch as of theZnO-coated emitting materialMWCNTs, is expectedshow that to the enhance UV bandgap the UV emission.emission greatly Previous enhanc studies,ed while such as the ZnO-coated green emission MWCNTs, arising show from that defects the UVwas bandgap reduced emission [17]. greatly enhanced while the green emission arising from defects was reduced [17]. InIn thisthis research,research, aluminumaluminum nitridenitride (AlN)(AlN) nanoparticlesnanoparticles areare producedproduced forfor thethe firstfirst timetime usingusing thethe RFRF magnetronmagnetron sputteringsputtering andand inert inert gas gas condensation condensation technique. technique.

2.2. MaterialsMaterials andand MethodsMethods AluminumAluminum nitridenitride nanoparticlesnanoparticles werewere fabricatedfabricated byby RFRF magnetronmagnetron sputteringsputtering withwith inertinert gasgas condensationcondensation inin thethe suitablesuitable system.system. WeWe purchasedpurchased thethe nanoparticlesnanoparticles sourcesource fromfrom MantisMantis DepositionDeposition Ltd.Ltd. (Oxfordshire,(Oxfordshire, UK).UK). AA schematicschematic diagramdiagram ofof thethe experimentalexperimental researchresearch set-upset-up inin ourour lablab forfor thethe fabricationfabrication ofof AlN nanoparticles is is illustrated illustrated in in Figure Figure 1.1 .The The main main parts parts of ofthe the system system shown shown in this in thisfigure figure consist consist of a ofnanoparticle a nanoparticle source source that includ that includeses an RF an magnetron RF magnetron sputtering sputtering unit, a unit, turbo a turbopump pump(TP), a (TP), quadrupolar a quadrupolar mass mass filter filter (QMF), (QMF), and and the the deposition deposition chamber. chamber. The The two two turbo turbo pumps werewere 8−8 utilizedutilized to to evacuate evacuate the the main main and and source source chambers chambers to to a a base base pressure pressure of of 10 10− mbar.mbar. TheThe RFRF magnetronmagnetron typetype dischargedischarge waswas usedused toto generategenerate nanoparticlesnanoparticles fromfrom thethe AlNAlN targettarget purchasedpurchased fromfrom thethe KurtKurt J.J. LeskerLesker CompanyCompany (Je(Jeffersonfferson Hills, PA, PA, USA) USA) with with a a pu purityrity of of 99.8%. 99.8%. Argon Argon ga gass was was used used to create to create the theplasma, plasma, sputter sputter material material from from its its target, target, establis establishh nanoparticle nanoparticle condensati condensation,on, and create pressurepressure gradientgradient betweenbetween thethe sourcesource andand depositiondeposition chamberschambersthat thatallowed allowednanoparticles nanoparticlesto topass pass throughthroughthe the massmass filter.filter. InIn thisthis research,research, thethe massmass filterfilter waswas usedused isis aa quadrupolequadrupole massmass filterfilter locatedlocated betweenbetween thethe nanoparticle’snanoparticle's sourcesource andand thethe depositiondeposition chamber.chamber.

Figure 1. Schematic diagram of the deposition system, including the nanoparticle source and deposition Figure 1. Schematic diagram of the deposition system, including the nanoparticle source and chamber [18]. deposition chamber [18]. The principle of QMF is based on applying alternating current AC and direct current DC voltages [ (U +TheVcos principleωt)] to fourof QMF straight is based metal rods.on applying The two alternating rods were connectedcurrent AC to aand positive direct voltage current while DC ± thevoltages other two[±(U rods + V tocos the ωt negative)] to four voltage. straight Here, metalU isrods. the DCThe voltage, two rodsV is were the amplitude connected of to AC a voltage,positive ωvoltageis frequency, while the and othert is two time. rods Herein, to the a negative grid was voltage. placed Here, at the U outer is the part DC ofvoltage, the mass V is ﬁlter the amplitude that was of AC voltage, ω is frequency, and t is time. Herein, a grid was placed at the outer part of the mass

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usedCoatings to measure 2020, 10, thex FOR ion PEER flux REVIEW of the selected mass/size, and the resulting current was measured3 of 8 by a pico-ampere-meter [18–20]. The Ar flow rate was fixed at 60 sccm which was controlled by a mass flow controllerfilter that instrument was used MKS to measure (Andover, the ion MA, flux USA). of the Another selected partmass/size, in the and system the resulting was the magnetroncurrent was gun placedmeasured in the sourceby a pico-ampere-mete chamber whichr was [18–20]. mounted The Ar on flow a motorized rate was linear fixed translatorat 60 sccm that which enables was the aggregationcontrolled length by a (massL) to beflow varied controller up to instrument 100 mm. In MKS this experimental(Andover, MA, research, USA). Another the aggregation part in the length (L) wassystem fixed was at 30the mm magnetron and defined gun placed as the in distance the sour fromce chamber the sputtering which was target mounted surface on to a themotorized source exit linear translator that enables the aggregation length (L) to be varied up to 100 mm. In this nozzle. The argon gas flow condensates the sputtered atoms to create the nanoparticles and sweeps experimental research, the aggregation length (L) was fixed at 30 mm and defined as the distance the nanoparticles outside the source through the two nozzles into the main chamber. At this stage, from the sputtering target surface to the source exit nozzle. The argon gas flow condensates the the growth of nanoparticles stopped and they flowed through a quadrupole mass filter to measure sputtered atoms to create the nanoparticles and sweeps the nanoparticles outside the source through the nanoparticlethe two nozzles size into distribution. the main chamber. The pressure At this stage, gradient the growth between of nanoparticles the source andstopped main and chambers they allowedflowed the through nanoparticles a quadrupole to flow mass and filter reach to ameasure substrate the fixed nanoparticle where the size nanoparticles distribution. The were pressure deposited on glass,gradient mica, between and silicon the source substrates. and main The sizechambers and shape allowed of AlNthe nanoparticles nanoparticles to were flow characterized and reach a by an atomicsubstrate force fixed microscope where the (AFM) nanoparticles provided were by Dulcineadeposited from on glass, Nanotec mica, S.L. and (Madrid, silicon substrates. Spain). The The X-ray diffractionsize and analysis shape of was AlN obtained nanoparticles by using were Shimadzu characterized (Kyoto, byJapan) an atomic 6100 force XRD microscope with CuKα (AFM)radiation (λ =provided0.15406 by nm). Dulcinea The energyfrom Nanotec dispersive S.L. (Madrid, spectroscopy Spain). The (EDS, X-ray Jeol, diffracti Peabody,on analysis MA, USA)was obtained was used to measureby using the Shimadzu chemical (Kyoto, composition. Japan) 6100 The XRD optical with absorptionCuΚα radiation spectra (λ = were 0.15406 performed nm). The using energy Jasco UV-visibledispersive spectrophotometer spectroscopy (EDS, (Tokyo, Jeol, Japan).Peabody, The MA, Raman USA) spectra was used were to obtained measure using the chemical a Renishaw (Gloucestershire,composition. UK)The inoptical Via Raman absorption microscope spectr witha awere laser excitationperformed source using working Jasco atUV-visible wavelengths spectrophotometer (Tokyo, Japan). The Raman spectra were obtained using a Renishaw of 514 nm. (Gloucestershire, UK) in Via Raman microscope with a laser excitation source working at 3. Resultswavelengths and Discussion of 514 nm.

3.1. AFM,3. Results EDS, and and Discussion XRD

3.1.The AFM, morphology,density,and EDS, and XRD height of AlN nanoparticles were determined by atomic force microscope topographyThe imagesmorphology, in a noncontact density, and dynamic height mode.of AlN Topographynanoparticles results were determined possess high by sensitivity atomic force due to the piezoelectricmicroscope topography and tip characteristics. images in a noncontact The AFM tipdynamic used was mode. AR10-NCHR Topography (Nano results word) possess with high a force constantsensitivity of 42 Ndue/m, to resonance the piezoelectric frequency and tip of 320char kHz,acteristics. and a The tip AFM radius tip of used<15 was nm. AR10-NCHR Figure2a,b shows (Nano the AFMword) topographic with a force image constant of AlN of nanoparticles42 N/m, resonance onthe frequency mica substrate of 320 kHz,. It and is clear a tip fromradius the of <15 ﬁgure nm. that the nanoparticlesFigure 2a,b shows are the spherical. AFM topographic The nanoparticles image of AlN are presentednanoparticles as aon three-dimensional the mica substrate. projectionIt is clear in Figurefrom2c. the The figure height that analysis the nanoparticles of these nanoparticles are spherical. presented The nanoparticles in Figure 2ared shows presented that as the a apparentthree- heightdimensional ranged between projection 1.6 in and Figure 3 nm. 2c. The height analysis of these nanoparticles presented in Figure 2d shows that the apparent height ranged between 1.6 and 3 nm.

FigureFigure 2. Atomic 2. Atomic force microscopyforce microscopy (AFM) (AFM) topography topograp imageshy ofimages aluminum of aluminum nitride (AlN) nitride nanoparticles (AlN) on ananoparticles mica substrate. on a Scan mica sizessubstrate. of (a )Scan 2.5 µsizesm of2.5 (a)µ 2.5m andμm × ( b2.5) 1.5μmµ andm (b1.5) 1.5µ m.μm (×c )1.5 Three-dimensional μm. (c) Three- × × projectiondimensional of nanoparticles projection of and nanoparticles (d) line profiles and (d) for line the profiles 2 separate for the nanoparticles 2 separate nanoparticles identified identified in the image (b). Thein the deposition image (b). timeThe deposition while using time quadrupol while using mass quadrupol filter (QMF) mass filter is 4 h.(QMF) is 4 h.

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The Gaussian distribution presented by the solid line in Figure 33 isis aa fitfit for for the the sizes sizes measured measured using thethe quadrupole quadrupole mass mass filter filter of the of nanoparticle’s the nanoparticle’s production production system. Thesystem. Gaussian The fitGaussian determines fit thedetermines size distribution the size distribution of AlN nanoparticles, of AlN nanoparticle which weres, which fabricated were fabricated using a discharge using a discharge power of power 50 W, −3 Argonof 50 W, flow Argon rate (flowf = 60 rate sccm), (f =chamber 60 sccm), pressure chamberP =pressure1.17 10 P 3= mbar,1.17 ×U 10/V−3= mbar,0.09, andU/V aggregation= 0.09, and × − lengthaggregation (L = 30 length mm). ( TheL = 30 figure mm). shows The thatfigure the shows peak diameterthat the peak was aboutdiameter 2.5 nm.wasThis about result 2.5 nm. confirms This theresult size confirms distribution the size determined distribution by thedet AFMermined shown by the in FigureAFM shown2d. in Figure 2d.

Figure 3.3.The The Gaussian Gaussian ﬁt datafit data solid solid line isline the sizeis the distribution size distribution of AlN nanoparticles of AlN nanoparticles using a quadrupole using a massquadrupole ﬁlter. mass filter.

Figure4 4 shows shows thethe elementelement analysisanalysis ofof AlNAlN nanoparticlesnanoparticles determineddetermined byby thethe electronelectron dispersivedispersive spectroscopy EDS. TheThe elementalelemental atomicatomic percentagepercentage inin AlNAlN nanoparticlesnanoparticles waswas foundfound toto bebe AlAl == 0.62 and N == 0.67 which has Al/N Al/N ratio close to 1. Other elements indicated in Figure 44,, suchsuch asas oxygen,oxygen, sodium, silicon, and carbon, arise from the glass substrate used for depositing the nanoparticles. Moreover, TableTable1 1 shows shows element element analysis analysis determined determined byby thethe EDSEDS forfor the the AlN AlN nanoparticles nanoparticles onon aa glass substrate.

Figure 4. EDS spectrum of AlN nanoparticles deposited on the glass substrate. Figure 4. EDS spectrum of AlN nanoparticles deposited on the glass substrate. Table 1. Element analysis determined by the EDS for the AlN nanoparticles on the glass substrate. Table 1. Element analysis determined by the EDS for the AlN nanoparticles on the glass substrate. Formula Mass% Atom% Sigma Net K Ratio Line Formula Mass% Atom% Sigma Net K Ratio Line N 0.51 0.67 0.13 109 0.0004177 K N 0.51 0.67 0.13 109 0.0004177 K Al 0.92 0.62 0.08 913 0.0013102 K Al 0.92 0.62 0.08 913 0.0013102 K

Figure 5 shows the XRD pattern of AlN nanoparticles deposited on the glass substrate. The diffraction peaks (002), (200), (103), and (311) are corresponding to the hexagonal phase structure reported in the literature [21–24].

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Figure5 shows the XRD pattern of AlN nanoparticles deposited on the glass substrate. The diﬀraction peaks (002), (200), (103), and (311) are corresponding to the hexagonal phase structure reportedCoatings in 2020 the, 10 literature, x FOR PEER [21 REVIEW–24]. 5 of 8 Coatings 2020, 10, x FOR PEER REVIEW 5 of 8

FigureFigure 5. XRD 5. XRD spectrum spectrum of of the the AlN AlN nanoparticles nanoparticles deposited on on the the glass glass substrate. substrate. Figure 5. XRD spectrum of the AlN nanoparticles deposited on the glass substrate. 3.2. Raman Spectroscopy 3.2. Raman Spectroscopy 3.2. Raman Spectroscopy To confirmTo confirm the the formation formation of of the the wurtzite wurtzite structures structures ofof AlN nanoparticles, nanoparticles, Raman Raman spectroscopy spectroscopy 4 was used.To Theconfirm space the group formation of AlN of the is Cwurtzite(P63mc) structures and the of AlN six Raman-active nanoparticles, modesRaman spectroscopy in AlN possibly was used. The space group of AlN is 6𝐶v (P63mc) and the six Raman-active modes in AlN possibly was used. The (space) +group (of AlN) + is 𝐶( (P63mc)) + and( the) + six Raman-active modes in AlN possibly determinedetermine as 1 Aas1 1ATOTO1+1AA1 LOLO +1E1E1TOTO +1E1E1LOLO + 2E2E [25].2 [25 ].Figure Figure 6 6illustrates illustrates the the Raman Raman spectradeterminespectra for AlN for as AlN nanoparticles 1A nanoparticlesTO +1A depositedLO deposited +1E on TO aon silicon a+1E silico substrate.nLO substrate. + 2E The [25]. The Raman RamanFigure spectrum 6spectrum illustrates present present the inRaman in sold sold line wasspectra fittedline was by for fitted deconvolution AlN bynanoparticles deconvolution of the depositedLorentzian of the Lorentzianon a linesilico shapen linesubstrate. shape signal Thesignal performed Raman performed spectrum through through present a standard a standard in sold fitting procedure.linefitting was procedure. Suitablefitted by fitsdeconvolution Suitable are established fits are of establishedthewith Lorentzian Lorentzian with line Lorentzian shape curves, signal curves, whose performed whose centers centers through are identified are a identifiedstandard by the vibrationalfittingby the procedure. modesvibrational in theSuitable modes Raman fitsin spectrum. theare Ramanestablished All spectrum. the wi Ramanth Lorentzian All modesthe Raman curves, were modes labeled whose were withcenters labeled their are corresponding identifiedwith their by the vibrational modes in the Raman spectrum. All the Raman modes were labeled with their values.corresponding The observed values. active The Raman observed modes active for Raman AlN were modes found for toAlN be were consistent found withto be theconsistent wurtzite with phase correspondingthe wurtzite phase values. reported The observed in the literatureactive Raman [26–28]. mo desIn thisfor AlNfigure, were the found observed to be1 peak consistent at 619 with cm− 1 reported in the literature [26–28]. In this figure, the observed peak at 619 cm− corresponds to−1 the thecorresponds wurtzite phaseto the transverse-opticalreported in the literature A1(TO) mode,[26–28]. the In broad this figure, beak centered the1 observed at 670 peakcm−1 correspondsat 619 cm transverse-optical A1(TO) mode, the broad beak centered at 670 cm− corresponds− to1 E1(TO), and to corresponds to the transverse-optical A1(TO) mode, the broad beak centered at 670 cm corresponds− 1 to E1(TO), and to the left of the maximum there is a hump with a lower intensity centered1 at 653 cm the left of the maximum there is a hump with a lower intensity centered at 653 cm corresponding−1 to to E1(TO), and to the left of the maximum there is a hump with a lower−1 intensity centered− at 653 cm corresponding to E2(high). In addition, the peaks 1at 826 and 905 cm were assigned to longitudinal- E2(high). In addition,2 the peaks at 826 and 905 cm− were assigned− to1 longitudinal-optical E1(LO) and correspondingoptical E1(LO) toand E (high).A1(LO), In respectively. addition, the The peaks Raman at 826 frequency and 905 shiftcm peakswere assigned of AlN nanoparticles to longitudinal- can A1(LO),opticalslightly respectively. E differ1(LO) andfrom TheA their1(LO), Raman bulk respectively. that frequency can be The attributed shift Raman peaks tofrequency their of AlN crystallite shift nanoparticles peaks sizes of [29]. AlN can nanoparticles slightly diff ercan from theirslightly bulk that differ can from be attributedtheir bulk that to their can be crystallite attributed sizes to their [29 ].crystallite sizes [29].

Figure 6. Raman spectra of AlN nanoparticles deposited on the silicon substrate. FigureFigure 6. Raman6. Raman spectra spectra of of AlN AlN nanoparticlesnanoparticles deposited deposited on on the the silicon silicon substrate. substrate.

Coatings 2020, 10, 411 6 of 8 Coatings 2020, 10, x FOR PEER REVIEW 6 of 8 3.3. Optical Absorption 3.3. Optical Absorption Optical information of AlN nanoparticles deposited on the glass substrate was determined by Optical information of AlN nanoparticles deposited on the glass substrate was determined by UV-visible spectroscopy. Figure7 illustrates the Tauc plot [ 30], which is a graph for (αhν)2 versus the UV-visible spectroscopy. Figure 7 illustrates the Tauc plot [30], which is a graph for (αhν)2 versus the photon energy hν, where α is the optical absorption coefficient obtained from inset Figure7. The optical photon energy hν, where α is the optical absorption coefficient obtained from inset Figure 7. The energy gap (Eg) was determined by extrapolating the straight line that fit the linear portion of the Tauc optical energy gap (Eg) was determined by extrapolating the straight line that fit the linear portion of plot the intercept the (hν)-axis at (αhν)2 = 0. The value obtained from this figure for AlN nanoparticles the Tauc plot the intercept the (hν)-axis at (αhν)2 = 0. The value obtained from this figure for AlN is equal to 5.1 eV. This value is in good agreement with the theoretical and experimental estimation nanoparticles is equal to 5.1 eV. This value is in good agreement with the theoretical and experimental reported in the literature [2,31,32]. estimation reported in the literature [2,31,32].

Figure 7. 7. (a(a)Tauc) Tauc plot plot ofof bandgap bandgap energy energy for for AlN AlN nanopart nanoparticlesicles deposited deposited on the on theglass glass substrate. substrate. (b) Absorption(b) Absorption of AlN of AlN nanoparticles nanoparticles deposited deposited on glass on glass substrate. substrate. 4. Conclusions 4. Conclusions Aluminum nitride nanoparticles were produced by a RF magnetron sputtering inert gas condensation Aluminum nitride nanoparticles were produced by a RF magnetron sputtering inert gas technique inside an ultra-high vacuum system. The AFM images and quadrupole mass filter (QMF) condensation technique inside an ultra-high vacuum system. The AFM images and quadrupole mass indicated that the sizes of the nanoparticles were of the order of 3 nm. The X-ray diffraction studies filter (QMF) indicated that the sizes of the nanoparticles were of the order of 3 nm. The X-ray confirmed the wurtzite phase of AlN nanoparticles. Furthermore, Raman spectroscopy measurements diffraction studies confirmed the wurtzite phase of AlN nanoparticles. Furthermore, Raman showed vibration transverse-optical modes and longitudinal-optical modes. The broadening peaks of spectroscopy measurements showed vibration transverse-optical modes and longitudinal-optical the Raman vibrational modes were due to the nano-size effects. Moreover, the optical bandgap energy modes. The broadening peaks of the Raman vibrational modes were due to the nano-size effects. obtained for AlN nanoparticles was 5.1 eV. It is worth noting that the production of AlN nanostructures Moreover, the optical bandgap energy obtained for AlN nanoparticles was 5.1 eV. It is worth noting has a potential to be used in fabrication nanoscale devices. that the production of AlN nanostructures has a potential to be used in fabrication nanoscale devices.

Author Contributions: Conceptualization,I.M. I.M. and and N.Q.; N.Q.; methodology, methodology, I.M., I.M., N.Q., N.Q., K.S. K.S. and and H.A.; H.A.; validation, validation, I.M., N.Q. and S.T.M.; data curation, I.M., N.Q. and S.T.M.; writing—original draft preparation, I.M.; writing—review I.M., N.Q. and S.T.M.; data curation, I.M., N.Q. and S.T.M.; writing—original draft preparation, I.M.; writing— and editing, I.M. and N.Q. All authors have read and agreed to the published version of the manuscript. review and editing, I.M. and N.Q. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by United Arab Emirates University under UPAR grants number 31S207 Funding:and 31S313. This research was funded by United Arab Emirates University under UPAR grants number 31S207 and 31S313 Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest. References References 1. Litimein, F.; Bouhafs, B.; Dridi, Z.; Ruterana, P. The electronic structure of wurtzite and zincblende AlN: 1. Litimein,An ab initio F.; comparativeBouhafs, B.; Dridi, study. Z.;New Ruterana, J. Phys. 2002 P. The, 4, 64.electronic [CrossRef structure] of wurtzite and zincblende AlN: 2. AnChoudhary, ab initio comparative R.K.; Mishra, study. P.; Biswas, New A.;J. Phys. Bidaye, 2002 A.C., 4, 64. Structural and optical properties of aluminum nitride 2. Choudhary,thin films deposited R.K.; Mishra, by pulsed P.; Biswas, DC magnetron A.; Bidaye, sputtering. A.C. StructuralInt. Sch. and Res. optical Not. properties2013, 2013 ,of e759462. aluminum [CrossRef nitride] 3. thinYong, films K.-T.; deposited Yu, S.F. by AlN pulsed nanowires: DC magnetron Synthesis, sputtering. physical Int. properties, Sch. Res. Not. and 2013 nanoelectronics, 2013, e759462. applications. 3. Yong,J. Mater. K.-T.; Sci. 2012Yu, S.F., 47 ,AlN 5341–5360. nanowires: [CrossRef Synthesis,] physical properties, and nanoelectronics applications. J. 4. Mater.Kumari, Sci. N.; 2012 Singh,, 47, A.K.;5341–5360. Barhai, P.K. Study of properties of AlN thin films deposited by reactive magnetron 4. Kumari,sputtering. N.; Int.Singh, J. Thin A.K.; Film. Barhai, Sci. P.K. Technol. Study2014 of properties, 3, 43–49. [ofCrossRef AlN thin] films deposited by reactive magnetron sputtering. Int. J. Thin Film. Sci. Technol. 2014, 3, 43–49. 5. Dutheil, P.; Orlianges, J.-C.; Crunteanu, A.; Catherinot, A.; Champeaux, C. AlN, ZnO thin films and AlN/ZnO or ZnO/AlN multilayer structures deposited by PLD for surface acoustic wave applications:

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