We present the results of a thorough study of wet chemical methods for transferring chemical vapor deposition grown graphene from the metal growth substrate to a device-compatible substrate. On the basis of these results, we have developed a "modified RCA clean" transfer method that has much better control of both contamination and crack formation and does not degrade the quality of the transferred graphene. Using this transfer method, high device yields, up to 97%, with a narrow device performance metrics distribution were achieved. This demonstration addresses an important step toward large-scale graphene-based electronic device applications.

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In this work, a Fourier transform infrared spectroscopy-based method is developed to measure the gas-phase dynamics occurring during atomic layer deposition. This new technique is demonstrated during the deposition of hafnium oxide using tetrakis͑ethylmethylamido͒hafnium and water vapor. The repeatability of the deposition process is utilized to signal average across multiple cycles. This approach required synchronizing the precursor injection pulses with the moving mirror of the spectrometer. The system as implemented in this work achieves spectra with a time resolution of Ϸ150 ms, but better resolution can be easily obtained. Using this technique, the authors are able to optically measure transients in the molecular number densities of the precursors and product that are the effects of mass transport and surface reactions.

Atomic layer deposition of titanium dioxide using tetrakis(dimethylamido)titanium (TDMAT) and water vapor is studied by reflection-absorption infrared spectroscopy (RAIRS) with a time resolution of 120 ms. At 190 °C and 240 °C, a decrease in the absorption from adsorbed TDMAT is observed without any evidence of an adsorbed product. Ex situ measurements indicate that this behavior is not associated with an increase in the impurity concentration or a dramatic change in the growth rate. A desorbing decomposition product is consistent with these observations. RAIRS also indicates that dehydroxylation of the growth surface occurs only among one type of surface hydroxyl groups. Molecular water is observed to remain on the surface and participates in reactions even at a relatively high temperature (110 °C) and with long purge times (30 s).

In situ spectroscopic ellipsometry was used to analyze hafnium diboride thin films deposited by chemical vapor deposition from the single-source precursor Hf͑BH 4 ͒ 4. By modeling the film optical constants with a Drude-Lorentz model, the film thickness, surface roughness, and electrical resistivity were measured in situ. The calculated resistivity for amorphous films deposited at low temperature ranged from 340 to 760 ⍀ cm. These values are within 25% of those measured ex situ with a four-point probe, indicating the validity of the optical model. By modeling the real-time data in terms of film thickness and surface roughness, the film nucleation and growth morphology were determined as a function of substrate type, substrate temperature, and precursor pressure. The data show that at low precursor pressures ͑ϳ10 −6 Torr͒ and at low substrate temperatures ͑Ͻ300°C͒, the onset of growth is delayed on both Si and SiO 2 surfaces due to the difficulty of nucleation. A higher substrate temperature or precursor pressure reduces this delay. At low temperatures the film morphology is a sensitive function of the precursor pressure because site-blocking effects change the reaction probability; the authors show that the morphology of newly grown film can be reversibly transformed from dense smooth to rough columnar by decreasing the precursor pressure.

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Atomic layer deposition (ALD) of Al 2 O 3 using trimethylaluminum and H 2 O is known to proceed through sequential surface reactions that leave the surface alternately terminated with AlCH 3 and OH groups. Using in situ reflection− absorption infrared spectroscopy in a flow reactor, we monitor the consumption of AlCH 3 groups by brief pulses of H 2 O at temperatures between 105 and 300 °C. At low temperatures, the surface reactions occur by what appears to be two stages that can be fit to a biexponential decay. Rate laws based on species of AlCH 3 groups that also predict a biexponential decay are found to depend on unrealistic activation energies for their constituent reactions when applied to the data. However, a model in which the effective activation energy changes linearly with AlCH 3 coverage does adequately fit the data. This model produces the apparent biexponential decay at low temperatures, and it confirms prior suggestions of a coverage dependence in the rate constant. The decrease in the effective activation energy with increasing coverage can be interpreted in terms of a cooperative effect between adjacent AlCH 3 groups. These findings may provide a framework for further studies, and both the kinetic model and parametric fits to the data may be useful in the construction of models of this important ALD process.

Metal-mediated exfoliation has been demonstrated as a promising approach for obtaining largearea flakes of 2D materials to fabricate prototypical nanoelectronics. However, several processing challenges related to organic contamination at the interfaces of the 2D material and the gate oxide must be overcome to realize robust devices with high yield. Here, we demonstrate an optimized process to realize high-performance field-effect transistor (FET) arrays from largearea (» 5000 μm 2 ) monolayer MoS2 with a yield of 85 %. A central element of this process is an exposed material forming gas anneal (EM-FGA) that results in uniform FET performance metrics (i.e., field-effect mobilities, threshold voltages, and contact performance). Complementary analytical measurements show that the EM-FGA process reduces deleterious channel doping effects by decreasing organic contamination, while also reducing the prevalence of insulating molybdenum oxide, effectively improving the MoS2-gate oxide interface. The uniform FET performance metrics and high device yield achieved by applying the EM-FGA technique on large-area 2D material flakes will help advance the fabrication of complex 2D nanoelectronics devices and demonstrates the need for improved engineering of the 2D materialgate oxide interface.