Ta3N5 has ideal properties for the efficient water splitting under sunlight illumination, but its formation is only triggered by the incorporation of oxygen in its lattice. As a result, material ...properties may deviate from those of an ideal Ta3N5 crystal, which can promote or impede the water splitting. This paper is to quantify variations in key properties relevant for the photoelectrolysis as a function of oxygen incorporation and to determine an optimum oxygen concentration. Thin films were prepared by direct current magnetron sputtering in an Ar/N2/O2 gas mixture at two different N2 and varying O2 concentrations. The films were characterized by grazing-incidence x-ray diffraction (GI-XRD), total transmission and reflectance spectroscopy (TTRS) from which the band gap is deduced, photocurrent measurements on which the calculation of the efficiency-mobility-lifetime (ημτ) product is based and photoelectrolysis experiments. Finally, the stability of films was determined by x-ray photoelectron spectroscopy (XPS) measured before and after the photoelectrolysis. We show that material properties degrade with oxygen incorporation during the film growth. At the highest oxygen concentrations investigated, the material becomes amorphous and shows strong surface oxidation and a possible reaction with the electrolyte during the photoelectrolysis. Samples deposited at an oxygen concentration below 1%, exhibit the Ta3N5 phase, a band gap below 2.0eV, a high mobility-lifetime product, photoelectrolytic activity and a good relative stability against surface oxidation during the photoelectrolysis.
•Nano-crystalline Ta3N5 thin films were prepared by DC magnetron sputtering in Ar/N2/O2 gas mixture without post-annealing.•The addition of oxygen is necessary to obtain the Ta3N5 phase.•Film properties degrade with increasing oxygen incorporation.•Photocurrent onset is around 0V vs. NHE.
Ta3N5 belongs to the group of transition metal nitrides with the cation in a high oxidation state. These are typically challenging to synthesize owing to the low reactivity of nitrogen. This applies ...similarly to Ta3N5 that crystallizes only in the presence of oxygen during synthesis. Typical preparation methods are ammonolysis of oxidized Ta or magnetron sputtering of a Ta target in an atmosphere of Ar, N2 and O2. However, the material typically obtained by either synthesis method is of varying degrees of crystallinity and the key parameter affecting the crystallinity remains elusive. In this study, we examine the role of oxygen for the crystallinity of Ta3N5 samples by studying. Thin film samples prepared by magnetron sputtering reveal that oxygen is indeed the central driver for Ta3N5 crystallinity. While little oxygen in the films yields the metallic δ-TaN phase, excess oxygen results in low crystallinity Ta3N5 or Ta-O-N films. Ta3N5 samples with a high degree of crystallinity are obtained by limiting the oxygen supply to the sample during the deposition. A comparison with other studies suggests a fundamental oxygen incorporation limit above which the crystallinity of Ta3N5 is compromised. The most crystalline sample from this study contains 4.4 at.% of oxygen. It is grown onto a Si(100) substrate, covered with a 30 nm-thick metallic diffusion layer. For this sample, we observe Ta3N5 grains between 80 and 120 nm in size.
•The degree of crystallinity of Ta3N5 thin films is determined by its oxygen content.•A fundamental limit of oxygen incorporation in Ta3N5 crystalline films is suggested.•Ta interlayer between Si substrate and Ta3N5 promotes crystallization.•Large Ta3N5 grain sizes between 80 and 120 nm are obtained.
Tantalum nitride based thin films have been deposited on
p-Si (100) and SiO
2/Si by thermal Atomic Layer Deposition (ALD) using either the Ta(=
N
t
Bu)(NEt
2)
3 or a derivative, in which one ...dialkylamido ligand is substituted by a η
5-cyclopentadienyl (η
5-Cp), as metal organic precursors with ammonia as reducing agent. TaN
xC
y self-limiting temperature dependent ALD growth was achieved for the TaCp(=
N
t
Bu)(NEt
2)
2/NH
3 process with a growth rate of 0.51–0.91
Å cycle
−1 in the 400–425
°C temperature range while between 240 and 280
°C, the growth of TaN based films from the Ta(=
N
t
Bu)(NEt
2)
3 was accompanied by a partial decomposition of the precursor. The η
5-cyclopentadienyl type compound allows lower nitrogen content in the precursor and thereafter in the deposited film. Although N/Ta ratio is close to one at temperatures of 390 and 400
°C, as analyzed by Rutherford Back Scattering and Nuclear Reaction Analysis, films were amorphous independently of the deposition temperature. Since Ta–C bonds are present in the Cp derivative, the TaCp(=
N
t
Bu)(NEt
2)
2 tends more likely to form tantalum carbide compared to Ta(=
N
t
Bu)(NEt
2)
3, which leads to lower thin film resistivity. For both precursors, employed in their respective ALD window, films were smooth with a root-mean-square roughness close to 1
nm.
•Our paper deals with the understanding of the carbon nanotubes growth parameters following the use of specific thin nitride buffer films.•For a large choice of buffer, we use ultra thin films ...elaborated by the very new method: high power pulsed magnetron sputtering; it allows a larger nitrogen incorporation in the films and lead to out of equilibrium phase formation.•Then by a multiscale investigation, developing a structural, a chemical and a morphology approach, we lead to some conclusion on the correlation between the phase transition for the buffer and morphology transition for the CNTs.•That is a new and deep approach.
We present the role of nitrogen content in tantalum nitride ultra-thin buffers, on the carbon nanotubes (CNTs) growth by chemical vapour deposition at 850°C, assisted by ferrocene as catalyst source. Tantalum nitride (TaNx) films with a very large range of concentration x=0, 1.8 and various nanostructures, from amorphous Ta(N) to Ta3N5, were deposited by Highly Pulsed Plasma Magnetron Sputtering. The buffer films are characterized after heat treatment at 850°C, and after the CNT growth, by wide angle X-ray scattering in grazing incidence and scanning electron microscopy. The CNT diameter explored by transition electron microscopy shows an all-out value for under stoichiometric thin films (Ta1-N1−δ, Ta3-N5−δ) and a minimum value just above the stoichiometric phases (Ta1-N1+δ, Ta3-N5+δ). Firstly one shows that the buffer films under the heat treatment present surface modification highly dependent on their initial state, which influences the catalyst particles diffusion. Secondly at the stoichiometric TaN phase we show that a specific ternary phase FeTa2O6 is formed at the interface CNT/buffer, not present in the other cases, leading to a special CNT growth condition.
Tantalum nitride (TaN
x) films are usually used as barriers to the diffusion of copper in the substrate for electronic devices. In the present work, the TaN
x coating plays an extra role in the iron ...catalyzed chemical vapor deposition production of carbon nanotubes (CNT). The CNTs were grown at 850
°C on TaN
x films prepared by radio frequency magnetron sputtering. The correlation between the CNT morphology and growth rate, and the pristine TaN
x film nature, is investigated by comparing the evolution of the nano-composition, roughness and nano-crystallinity of the TaN
x films both after annealing and CVD at 850
°C.
Ba
0.5Sr
0.5TiO
3 (BST) thin films were deposited by rf magnetron sputtering using a Ba
0.5Sr
0.5TiO
3 target in pure Argon on two electrodes (Pt and RuO
2) at room temperature. The interface ...formation between BST and bottom electrode (Pt or RuO
2) was investigated by XPS for thicknesses in the 1 to 50
nm range. The chemical composition of the BST layers can be modified by the electrode nature over the first five nanometers. A 1
h ex-situ annealing, under flowing oxygen at 600
°C, was necessary to obtain crystallized 150
nm thick BST films, as evidenced by XRD and TEM analysis.
LaAlO
3 and HfAl
x
O
y
thin films have been deposited by magnetron sputtering for replacement of SiO
2 in new Complementary Metal Oxide Semiconductor applications. A three-layer model was found both ...in X-ray reflectivity (XRR) and spectroscopic ellipsometry (SE) analysis to be the best optical model for these two high-κ materials. It was composed of an interfacial layer, covered by a layer of pure LaAlO
3 or HfAl
x
O
y
, and a surface-roughness layer. In the case of LaAlO
3 and HfAl
x
O
y
directly deposited on Si, the interfacial layer is a mixture of high-k material and amorphous-Si inclusions, which thickness is growing after post-deposition annealing (PDA) in O
2 at 600 °C. On the contrary, for films deposited on thermally nitrided Si, the SiON-like interface did not change significantly after a PDA in O
2. XRR analysis showed that the dielectric/Si interface of HfAl
x
O
y
/SiON/Si structure had a significantly smaller roughness than those of HfAl
x
O
y
/Si. When being deposited on SiON/Si substrates, HfAl
x
O
y
, and to a lesser extent LaAlO
3, demonstrate superior diffusion barrier properties pointed out by X-ray photoelectron spectroscopy.
The diameter of carbon nanotubes deposited on TaN coated silicon substrates by catalytic chemical vapor deposition strongly depends on the N/Ta ratio in the coating. The coating characteristics are ...tailored by controlling the deposition parameters in a plasma reactive sputtering process. Photoelectron emission spectroscopy and X-ray diffraction of the coatings show the formation of a composite material. The presence of multi-wall nanotubes is confirmed by transmission electron microscopy. The results show that the structure of the TaN coating modifies the catalyst (Fe) effect changing the kinetics of the nanotube growth.
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