Low Pressure Chemical Vapor Deposition of III/V-Nitrides Using Organometallics and Hydrazoic Acid Precursors

In and Ga nitride films have been deposited on various substrates using organometallics and hydrazoic acid (HN₃) as nitrogen precursor. The film deposition was carried out under low pressure (10^?510 ^?6 Torr) and low V/III ratios (1-10). XPS analysis indicated that the ln(Ga):N atomic ratio of unity can be easily achieved by adjusting the experimental conditions. For the growth of InN on Si(100) substrate, 308-nm photon beam is needed to speed up the film deposition rate. He(II) UPS spectra of InN films are in good agreement with the result of a pseudo-potential calculation for InN valence band, while the spectra of GaN compare favorably with a recent semi-ab-initio calculation and with the UPS results of GaN single crystal films. The bandgap of our GaN films is ～ 3.3 cV as determined by photoluminescence and UV-VIS absorption spectra. Raman spectra taken from GaN Films showed peaks at 66 and 88 meV for TO and LO phonons, respectively, indicating a wurtzite structure of the GaN. In a corresponding X-ray diffraction spectrum, the (002) peak is about 400 times more intense than that of the (101) peak, suggesting that the GaN layers are highly oriented with the c-axis normal or nearly so to the Al₂O₃ substrate.     

Benzene thermal conversion to nanocrystalline indium nitride from sulfide at low temperature

A benzene thermal conversion route has been successfully developed to prepare nanocrystalline indium nitride at 180-200 degrees C by choosing NaNH(2) and In(2)S(3) as novel nitrogen and indium sources. This route has been also extended to the synthesis of other group III nitrides. The product InN was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and infrared spectroscopy (IR). The optical properties of nanocrystalline InN were also recorded by means of UV-vis absorption spectroscopy and photoluminescence (PL) spectroscopy, indicating that the as-prepared sample was within the quantum confinement regime. Finally, the formation mechanism was also investigated.     

Reactions of hydrazoic acid and trimethylindium on TiO2 rutile (110) surface: a computational study on the formation of the first monolayer InN

This article reports the result of a computational study on the reaction of hydrazoic acid and trimethylindium (TMIn), coadsorbed on TiO2 rutile (110) surface. The adsorption geometries and energies of possible adsorbates including HN3-In(CH3)3(a) and its derivatives, HN3-In(CH3)2(a), N3-In(CH3)2(a), N3-In(CH3)(a), and N-In(a), have been predicted by first-principles calculations based on the density functional theory (DFT) and the pseudopotential method. The mechanisms of these surface reactions have also been explicitly elucidated with the computed potential energy surfaces. Starting from the interaction of three stable HN3 adsorbates, HN3-Ob(a), H(N2)N-Ob(a), and Ti-NN(H)N-Ob(a), where Ob is the bridged O site on the surface, with two stable intermediates from the adsorption and dissociative adsorption of TMIn, (H3C)3In-Ob(a) and (H3C)2In-Ob(a)+H3C-Ob(a), InN products can be formed exothermically via four reaction paths following the initial barrierless In-atom association with the N atom directly bonded to H, by CH4 elimination (with approximately 40 kcal/mol barriers), the InN-N bond breaking and the final CH3 elimination or migration (with <20 kcal/mol barriers). These Langmuir-Hinshelwood processes producing the two most stable InN(a) side-on adsorptions confirm that HN3 and TMIn are indeed very efficient precursors for the deposition of InN films on TiO2 nanoparticles. The result of similar calculations for the reactions occurring by the Rideal-Eley mechanism involving HN3(a)+TMIn(g) and HN3(g)+TMIn(a) indicates that they are energetically less favored and produce the less stable InN(a) with end-on configurations.     

Nanometer-scale optical imaging of epitaxially grown GaN and InN islands using apertureless near-field microscopy

Nanometer-scale chemical imaging of epitaxially grown gallium nitride (GaN) and indium nitride (InN) islands is performed using scattering-type apertureless near-field scanning optical microscopy (ANSOM). The scattering of 633 nm laser radiation is modulated by an oscillating metallic probe, and the scattered radiation is detected by homodyne amplification, followed by high-harmonic demodulation, yielding optical near-field scattering maps with a spatial resolution better than 30 nm. The image contrast between InN and GaN, and the tip-sample distance dependence, can be qualitatively explained by a simple dipole-coupling model. The ANSOM images of InN and GaN also show structures that are absent in the topographic counterpart, and these substructures are explained by the variations of the local dielectric environment of InN and GaN.     

Formation of indium nitride nanorods within mesoporous silica SBA-15

We report the first formation of arrays of InN nanorods inside the nanoscale channels of mesoporous silica SBA-15. In(NO3)3 dissolved in methanol was incorporated into SBA-15 powder without prior pore surface functionalization. Formation of InN nanorod arrays was carried out by ammonolysis at 700 degrees C for 8 h. The final products have been characterized by FT-IR spectra, (29)Si MAS NMR spectra, Raman spectra, XRD patterns, TEM images, nitrogen adsorption-desorption isotherm measurements, and optical spectroscopy. The freestanding InN nanorods observed after silica framework removal with HF solution show diameters of 6-7.5 nm and lengths of 25-50 nm. Formation of a trace amount of In2O3 was also verified. The InN nanorods exhibit a broad band centered at around 550-600 nm, and a band gap energy of 1.5 eV was determined. No light absorption in the near-IR region was measured. The nanorods give a weak emission band centered at around 600 nm. These optical properties are believed to be related to the possible incorporation of oxygen during InN nanorod synthesis.     

Formation of arrays of gallium nitride nanorods within mesoporous silica SBA-15

We report the first formation of arrays of GaN nanorods inside the nanoscale channels of mesoporous silica SBA-15. GaCl3 dissolved in toluene was incorporated into the methyl group-functionalized SBA-15 powder. The pore surfaces functionalized with methyl groups should facilitate the impregnation with GaCl3. Formation of GaN nanorod arrays within SBA-15 was carried out by heating the powder to 700 degrees C for 3 h under nitrogen atmosphere, followed by ammonolysis at 900 degrees C for 5 h. epsilon-Ga2O3, an unusual phase for Ga2O3, formed after the first thermal process and was converted into wurtzite GaN during ammonolysis. The final products have been characterized by FT-IR spectra, powder XRD patterns, TEM images and SAED patterns, EDS analysis, and nitrogen adsorption-desorption isotherm measurements to confirm the presence of GaN nanostructures. The nanorods are 6-7.5 nm in diameter, and can be a few hundreds of a nanometer in length to exhibit nanowire structure. Free-standing GaN nanorod arrays were revealed upon removal of the silica framework with HF solution. Optical characterization of the isolated GaN nanorod arrays shows a strong and sharp near band-edge emission at 375 nm, and two phonon-assisted donor-acceptor peaks at 395 and 415 nm. A broad but weak emission in the region of 335-360 nm due to the quantum confinement effect of short nanorods was observed.     

Studies on Growth of N-Polar InN Films by Pulsed Metal-organic Vapor Phase Epitaxy

We reported the growth of N-polar InN films on N-polar GaN/sapphire substrates by pulsed metal-organic vapor phase epitaxy. The crystalline quality, surface morphology, optical and electrical properties of N-polar InN films were investigated in details by varying the breaking time and trimethylindium(TMIn) duration of pulse cycle. It has been found that when the breaking time and the TMIn duration in each cycle remain at 30 and 60 s, respectively, the N-polar InN film obtained exhibits a better crystalline quality and greater optical properties. Meanwhile, the surface morphology and electrical properties of the N-polar InN films also greatly depend on the given growth conditions.     

Computational study of reaction pathways for the formation of indium nitride from trimethylindium with HN3: comparison of the reaction with NH3 and that on TiO2 rutile (110) surface

The reactions of trimethylindium (TMIn) with HN3 and NH3 are relevant to the chemical vapor deposition of indium nitride thin film. The mechanisms and energetics of these reactions in the gas phase have been investigated by density functional theory and ab initio calculations using the CCSD(T)/Lanl2dz//B3LYP/Lanl2dz and CCSD(T)/Lanl2dz//MP2/Lanl2dz methods. The results of both methods are in good agreement for the optimized geometries and relative energies. These results suggest that the reaction with HN3 forms a new stable product, dimethylindiumnitride, CH3-In=N-CH3 via another stable In(CH3)2N3 (dimethylindium azide, DMInA) intermediate. DMInA may undergo unimolecular decomposition to form CH3InNCH3 by two main possible pathways: (1) a stepwise decomposition process through N2 elimination followed by CH3 migration from In to the remaining N atom and (2) a concerted process involving the concurrent CH3 migration and N2 elimination directly giving N2+CH3InNCH3. The reaction of TMIn with NH3 forms a most stable product DMInNH2 following the initial association and CH4-elimination reaction. The required energy barrier for the elimination of the second CH4 molecule from DMInNH2 is 74.2 kcal/mol. Using these reactions, we predict the heats of formation at 0 K for all the products and finally for InN which is 123+/-1 kcal/mol predicted by the two methods. The gas-phase reaction of HN3 with TMIn is compared with that occurring on rutile TiO2 (110). The most noticeable difference is the high endothermicity of the gas-phase reaction for InN production (53 kcal/mol) and the contrasting large exothermicity (195 kcal/mol) released by the low-barrier Langmuir-Hinshelwood type processes following the adsorption of TMIn and HN3 on the surface producing a horizontally adsorbed InN(a), Ti-NIn-O(a), and other products, CH4(g)+N2(g)+2CH3O(a) [J. Phys. Chem. B 2006, 110, 2263].     

Powder‐XRD and 14N magic angle‐spinning solid‐state NMR spectroscopy of some metal nitrides

Some metal nitrides (TiN, ZrN, InN, GaN, Ca₃N₂, Mg₃N₂, and Ge₃N₄) have been studied by powder X‐ray diffraction (XRD) and ¹⁴N magic angle‐spinning (MAS) solid‐state NMR spectroscopy. For Ca₃N₂, Mg₃N₂, and Ge₃N₄, no ¹⁴N NMR signal was observed. Low speed (ν_r = 2 kHz for TiN, ZrN, and GaN; ν_r = 1 kHz for InN) and ‘high speed’ (ν_r = 15 kHz for TiN; ν_r = 5 kHz for ZrN; ν_r = 10 kHz for InN and GaN) MAS NMR experiments were performed. For TiN, ZrN, InN, and GaN, powder‐XRD was used to identify the phases present in each sample. The number of peaks observed for each sample in their ¹⁴N MAS solid‐state NMR spectrum matches perfectly well with the number of nitrogen‐containing phases identified by powder‐XRD. The ¹⁴N MAS solid‐state NMR spectra are symmetric and dominated by the quadrupolar interaction. The envelopes of the spinning sidebands manifold are Lorentzian, and it is concluded that there is a distribution of the quadrupolar coupling constants Q_cc's arising from structural defects in the compounds studied. Copyright © 2015 John Wiley & Sons, Ltd.     

Ag作催化剂制备的GaN的形貌及其性能

用化学气相沉积法(CVD)在Si(100)衬底上以Ag纳米颗粒为催化剂制备了微纳米结构的GaN,原料是熔融态的金属Ga和气态的NH3。采用X射线衍射仪(XRD)、透射电镜(TEM)、X-ray能谱仪(EDS)、场发射扫描电子显微镜(SEM)、光致发光能谱(PL)和霍尔效应测试对样品进行了结构、成分、形貌和发光、电学性能分析。结果表明:生成的自组装GaN为六方纤锌矿的类似小梯子的微纳米单晶结构,且在不同的温度下,GaN的发光性能和电学性能也有所不同,相对于强的紫外发光峰,其它杂质发光峰很微弱,且均呈p型导电。对本实验所得到的GaN微纳米结构的可能形成机理进行了探讨。     

Reactions of hydrazoic acid on TiO2 nanoparticles: an experimental and computational study

This article reports the results of a computational and experimental study on the reaction of hydrazoic acid, HN3, adsorbed on 15-20 nm TiO2 particle films. Experimentally, FTIR spectra of HN3(a) have been measured by varying HN3 dosage, UV irradiation time and surface annealing temperature. Three sharp peaks, related to v(a)(NNN) of HN3(a) and N3(a) with different configurations in the 2000-2200 cm(-1) region, and a broad band absorption, related to associated and isolated HN(a) and HO(a) adsorptions in the 3000-3800 cm(-1) region, have been detected. Computationally, molecular structures, vibrational frequencies and adsorption energies of possible adsorbates including HN3 and its derivatives, N3, N2, NH, and H, have been predicted by first-principles calculations based on the density functional theory (DFT) and the pseudopotential method. On the basis of the experimental and computational results, the peak appeared at 2075 cm(-1), which increases at a faster rate with HN3 exposure time, is attributed to a stable adsorbate, N3-Ti(a), with the predicted adsorption energy, E(ads) = 13 kcal/mol. The peak at 2118 cm(-1), which survives at the highest surface temperature in the heating experiment, is attributable to the most stable adsorbate, Ti-N2N(H)-O(a) with E(ads) = 36 kcal/mol. The peak at 2170 cm(-1), which vanishes most readily in all of the aforementioned experiments, is related to less stable molecular adsorbates, end-on HN3-Ti(a) with E(ads) = 5 kcal/mol and side-on HN(N2)-Ti(a) with E(ads) = 8 kcal/mol. A potential energy diagram for the formation of various absorbates with their transition states has been established for the HN3/TiO2 system. On the basis of the predicted desorption energies, the four most stable products of the HN3 reaction on TiO2 are H-O(a), 118 kcal/mol; HN-O(a), 85 kcal/mol; Ti-N2N(H)-O(a), 36 kcal/mol; and N3-O(a), 19 kcal/mol.     

Photoelectron spectroscopy of electronic surface structure of the Cs/GaN and Cs/InN interfaces

The electronic structure of the epitaxial GaN, InN nanolayers, and the ultrathin Cs/GaN and Cs/InN interfaces was investigated under ultrahigh vacuum at various Cs coverages. The experiment was carried out using synchrotron-based photoelectron spectroscopy. The photoemission spectra of the valence band and the In 4d, N 2s, Ga 3d, and Cs 4d semicore levels were studied as a function of Cs coverages. It was found that the Cs adsorption in the submonolayer coverage region causes substantial changes in the spectra due to charge transfer between the Cs adlayer and surface Ga or In atoms. The strong interaction of the dangling bonds of Ga or In with Cs adatoms effectively increases the Ga or In valency.     

Large-scale cubic InN nanocrystals by a combined solution- and vapor-phase method under silica confinement

Large-scale cubic InN nanocrystals were synthesized by a combined solution- and vapor-phase method under silica confinement. Nearly monodisperse cubic InN nanocrystals with uniform spherical shape were dispersed stably in various organic solvents after removal of the silica shells. The average size of InN nanocrystals is 5.7 ± 0.6 nm. Powder X-ray diffraction results indicate that the InN nanocrystals are of high crystallinity with a cubic phase. X-ray photoelectron spectroscopy and energy-dispersive spectroscopy confirm that the nanocrystals are composed of In and N elements. The InN nanocrystals exhibit infrared photoluminescence at room temperature, with a peak energy of ~0.62 eV, which is smaller than that of high-quality wurtzite InN (~0.65-0.7 eV) and is in agreement with theoretical calculations. The small emission peak energy of InN nanocrystals, as compared to other low-cost solution or vapor methods, reveals the superior crystalline quality of our samples, with low or negligible defect density. This work will significantly promote InN-based applications in IR optoelectronic device and biology.     

Plasma Treatment Enhanced Magnetic Properties in Manganese Doped Titanium Nitride Thin Films

The ferromagnetic manganese doped TiN films were grown by plasma assisted molecular beam epitaxy on MgO(001) substrates. The nitrogen concentration and the ratio of manganese at Ti lattice sites increase after the plasma annealing post treatment. TiN(002) peak shifts toward low angle direction and TiN(111) peak disappears after the post treatment. The lattice expansion and peak shift are mainly ascribed to the reduction of nitrogen vacancies in films. The magnetism was suppressed in as-prepared sample due to the pinning effect of the nitrogen vacancies at defect sites or interface. The magnetism can be activated by the plasma implantation along with nitrogen vacancies reduce. The decrease of nitrogen vacancies leads to the enhancement of ferromagnetism.     

Enhanced ultraviolet emission from ZnS-coated ZnO nanowires fabricated by self-assembling method

A simple chemical route for ZnS-coated ZnO nanowires with preferential (002) orientation is reported. Sodium sulfide and zinc nitrate were employed to supply S and Zn atoms at 60 degrees C to form ZnS-coated ZnO nanowires structures. Electron diffraction measurement shows that the ZnO/ZnS core-shell nanostructure is single crystalline. Interesting features are found in the photoluminescence (PL) spectra of ZnS-coated ZnO nanostructures. After coating, the UV emission of nanorods is dramatically enhanced at the expense of the green emission. The core/shell structure with higher band gap shell material and reduced surface states should be responsible for this PL enhancement.     

Direct observation of defect levels in InN by soft X-ray absorption spectroscopy

We have used synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to study the electronic structure of nitrogen-related defects in InN(0001). Several defect levels within the band gap or the conduction band of InN were clearly resolved in NEXAFS spectra around the nitrogen K-edge. We attribute the level observed at 0.3 eV below the conduction band minimum (CBM) to interstitial nitrogen, the level at 1.7 eV above the CBM to antisite nitrogen, and a sharp resonance at 3.2 eV above the CBM to molecular nitrogen, in full agreement with theoretical simulations.     

Passivation of InP(100) substrates: first stages of nitridation by thin InN surface overlayers studied by electron spectroscopies

This article investigates the nitridation effect of InP(100) semiconductor surfaces performed using a glow discharge cell. Auger electron spectroscopy and XPS were used to understand the different steps of this process. An important point is the initial quantity of metallic indium on the InP(100) surfaces. Indeed the indium droplets, created in well‐known quantity, play the role of precursor. At a relatively low temperature of 523 K the system undergoes surface restructuring, which includes removal of the In droplets and the formation of two InN monolayers. Phosphorus–nitrogen bonds have been detected by the analysis of P LMM Auger peaks, and In? N bonds by analysis of the In 4d XPS peak. However, the presence or not of metallic indium inside this InN overlayer is crucial for passivation of the substrate. Ex situ photoluminescence measurements correlated to the electron spectroscopies results have shown the good passivation effect of the InP(100) surfaces by InN overlayers for 40 min of nitridation. Copyright © 2005 John Wiley & Sons, Ltd.     

New liquid nitrogen cryogenic modulator for comprehensive two-dimensional gas chromatography

A new liquid nitrogen (LN2) jet-based thermal modulator for performing comprehensive two-dimensional (2D) gas chromatographic (GC x GC) separations has been designed and constructed. Temperature measurements of the trapping zone, a segment of uncoated fused silica capillary, show that it can be cooled to -196 degrees C in about 300 ms. A film of liquid nitrogen develops on the outside of the trapping capillary even when the oven temperature is in excess of 200 degrees C. Compounds as volatile as propane can be trapped by the modulator and held for periods of at least 1 min without breakthrough. The peak widths for n-alkanes are on the order of 80 ms at half height after passing through an 80cm second dimension column. Repeated analysis of gasoline demonstrated excellent run-to-run reproducibility of the system.     

Two new structurally related strontium gallium nitrides: Sr4GaN3O and Sr4GaN3(CN2)

The strontium gallium oxynitride Sr(4)GaN(3)O and nitride-carbodiimide Sr(4)GaN(3)(CN(2)) are reported, synthesized as single crystals from molten sodium at 900 degrees C. Red Sr(4)GaN(3)O crystallizes in space group Pbca (No. 61) with a = 7.4002(1) Angstroms, b = 24.3378(5) Angstroms, c = 7.4038(1) Angstroms, and Z = 8, as determined from single-crystal X-ray diffraction measurements at 150 K. The structure may be viewed as consisting of slabs [Sr(4)GaN(3)](2+) containing double layers of isolated [GaN(3)](6-) triangular anions arranged in a "herringbone" fashion, and these slabs are separated by O(2-) anions. Brown Sr(4)GaN(3)(CN(2)) has a closely related structure in which the oxide anions in the Sr(4)GaN(3)O structure are replaced by almost linear carbodiimide [CN(2)](2-) anions [Sr(4)GaN(3)(CN(2)): space group P2(1)/c (No. 14), a = 13.4778(2) Angstroms, b = 7.4140(1) Angstroms, c = 7.4440(1) Angstroms, beta = 98.233(1) degrees, and Z = 4].     

Optical and field emission properties of thin single-crystalline GaN nanowires

Thin high-quality gallium nitride (GaN) nanowires were synthesized by a catalytic chemical vapor deposition method. The synthesized GaN nanowires with hexagonal single-crystalline structure had thin diameters of 10-50 nm and lengths of tens of micrometers. The thin GaN nanowires revealed UV bands at 3.481 and 3.285 eV in low-temperature PL measurements due to the recombination of donor-bound excitons and donor-acceptor pairs, respectively. The blue shifts of UV bands in the low-temperature PL measurement were observed, indicating quantum confinement effects in the thin GaN nanowires which have smaller diameters than the exciton Bohr radius, 11 nm. For field emission properties of GaN nanowires, the turn-on field of GaN nanowires was 8.5 V/microm and the current density was about 0.2 mA/cm(2) at 17.5 V/microm, which is sufficient for the applications of field emission displays and vacuum microelectronic devices. Moreover, the GaN nanowires indicated stronger emission stability compared with carbon nanotubes.